Risks of Dicofol Use to Federally Threatened 

California Red-legged Frog 

(Rana aurora draytonii) 

Pesticide Effects Determination 

Environmental Fate and Effects Division 

Office of Pesticide Programs 

Washington, D.C. 20460 

June 15, 2009 

1 
Primary Authors: 

Kristina Garber, Biologist 

Charles Peck, Environmental Scientist 

Secondary Reviewers: 

Thomas Steeger, Senior Biologist 

R. David Jones, Senior Agronomist 

Branch Chief, Environmental Risk Assessment Branch 4: 

Elizabeth Behl 

2 
Table of Contents 

1.0 Executive Summary.................................................................................................. 10

2.0 Problem Formulation ............................................................................................... 18

2.1. Purpose................................................................................................................... 18 

2.2. Scope...................................................................................................................... 20 

2.3. Previous Assessments............................................................................................ 21 

2.4. Stressor Source and Distribution ........................................................................... 22 

2.4.1. Environmental Fate Assessment..................................................................... 22 

2.4.2. Environmental Transport Assessment ............................................................ 26 

2.4.3. Mechanism of Action...................................................................................... 28 

2.4.4. Use Characterization....................................................................................... 28 

2.5. Assessed Species.................................................................................................... 32 

2.5.1. Distribution ..................................................................................................... 33 

2.5.2. Reproduction................................................................................................... 35 

2.5.3. Diet.................................................................................................................. 35 

2.5.4. Habitat............................................................................................................. 36 

2.6. Designated Critical Habitat.................................................................................... 37 

2.7. Action Area............................................................................................................ 39 

2.8. Assessment Endpoints and Measures of Ecological Effect ................................... 42 

2.8.1. Assessment Endpoints for the CRLF.............................................................. 42 

2.8.2. Assessment Endpoints for Designated Critical Habitat.................................. 45 

2.9. Conceptual Model.................................................................................................. 47 

2.9.1. Risk Hypotheses.............................................................................................. 47 

2.9.2. Diagram........................................................................................................... 48 

2.10. Analysis Plan ....................................................................................................... 49 

2.10.1. Measures of Exposure................................................................................... 50 

2.10.2. Measures of Effect ........................................................................................ 52 

2.10.3. Integration of Exposure and Effects ............................................................. 53 

2.10.4. Data Gaps...................................................................................................... 53 

3.0 Exposure Assessment................................................................................................ 54

3.1. Label Application Rates and Intervals................................................................... 54 

3.2. Aquatic Exposure Assessment............................................................................... 56 

3.2.1. Modeling Approach ........................................................................................ 56 

3.2.2. PRZM Scenarios ............................................................................................. 58 

3.2.3. Model Inputs ................................................................................................... 61 

3.2.4. Model Results ................................................................................................. 63 

3.2.5. Available Monitoring Data ............................................................................. 65 

3.3. Aquatic Bioaccumulation Assessment................................................................... 66 

3.3.1. Estimated BCF values..................................................................................... 67 

3.3.2. Empirical BCF data......................................................................................... 67 

3.3.3. Bioaccumulation modeling ............................................................................. 68 

3.4. Terrestrial Animal Exposure Assessment.............................................................. 70 

3.4.1. Modeling Approach ........................................................................................ 70 

3.4.1. Field Studies.................................................................................................... 73 

3.5. Accumulation of Dicofol Residues on Soil ........................................................... 74 

3 
3.6. Terrestrial Bioaccumulation Assessment............................................................... 76 

4.0 Effects Assessment .................................................................................................... 77

4.1. Toxicity of dicofol to aquatic organisms ............................................................... 78 

4.1.1. Toxicity of Dicofol to Freshwater Fish........................................................... 79 

4.1.2. Toxicity of Dicofol to Freshwater Invertebrates............................................. 81 

4.1.3. Toxicity of Dicofol to Aquatic Plants............................................................. 81 

4.2. Toxicity of Dicofol’s Degradates to Aquatic Organisms ...................................... 81 

4.2.1. Toxicity of Dicofol’s Degradates to Aquatic Animals ................................... 81 

4.2.2. Toxicity of Dicofol’s Degradates to Aquatic Plants....................................... 82 

4.3. Toxicity of dicofol to terrestrial organisms ........................................................... 83 

4.3.1. Toxicity of Dicofol to Birds............................................................................ 84 

4.3.2. Toxicity of Dicofol to Mammals .................................................................... 87 

4.3.3. Toxicity of Dicofol to Terrestrial Invertebrates.............................................. 87 

4.3.4. Toxicity of Dicofol to Terrestrial Plants......................................................... 87 

4.4. Toxicity of dicofol degradates to terrestrial organisms ......................................... 88 

4.5. Incident Database Review for Dicofol................................................................... 88 

5.0 Risk Characterization............................................................................................... 89

5.1. Risk Estimation...................................................................................................... 89 

5.1.1. Exposures in the Aquatic Habitat ................................................................... 90 

5.1.2. Exposures in the Terrestrial Habitat ............................................................... 96 

5.1.3. Primary Constituent Elements of Designated Critical Habitat ....................... 98 

5.2. Risk Description .................................................................................................. 100 

5.2.1. Direct Effects ................................................................................................ 105 

5.2.2. Indirect Effects (through effects to prey)...................................................... 113 

5.2.3. Indirect Effects (through effects to habitat).................................................. 121 

5.2.4. Primary Constituent Elements of Designated Critical Habitat ..................... 122 

5.2.5. Area of Effects .............................................................................................. 122 

5.2.6. Description of Assumptions, Limitations and Uncertainties ........................ 126 

5.2.7. Addressing the Risk Hypotheses .................................................................. 138 

6.0 Risk Conclusions ..................................................................................................... 139

7.0 References................................................................................................................ 144

Appendices 

Appendix A. Structures of dicofol and its major degradates 

Appendix B. Intersection of Dicofol Use Area and California Red-legged frog Habitat 

Appendix C. The Risk Quotient Method and Levels of Concern 

Appendix D. Treated area estimate for outside building usage 

Appendix E. Example PRZM/EXAMS Input Files and Output File Data 

Appendix F. DDT Characterization 

Appendix G. Outputs from KABAM v.1.0 

Appendix H. Example output from T-REX v.1.4.1 

Appendix I. List of citations accepted and rejected by ECOTOX criteria 

Appendix J. Detailed spreadsheet of available ECOTOX open literature for dicofol 

Appendix K. Summary of human health effects data for dicofol 

Appendix L. Sensitivity distributions for acute exposures of fish and birds to dicofol 

4 
Appendix M. Example output from analysis of likelihood of individual mortality 

Appendix N. Example output from T-HERPS v.1.0 

Appendix O. Use of fugacity approach to estimate exposures to small mammals 

consuming earthworms contaminated with dicofol from soil of treatment sites 

Appendix P. Ultra Low Volume Spray Drift Approach 

Attachments 

Attachment 1: Status and Life History of California Red-legged Frog 

Attachment 2: Baseline Status and Cumulative Effects for the California Red-legged Frog 

List of Tables 

Table 1. Description of evidence supporting effects determination for dicofol use in 

California. Assessment endpoints include survival, growth and reproduction 

of CRLF individuals. ...................................................................................... 14 

Table 2. Summary of effects determination for CRLF critical habitat based on uses of 

dicofol in California........................................................................................ 16 

Table 3. Summary of dicofol environmental fate properties. ........................................... 25 

Table 4. Summary of dicofol degradates observed in submitted environmental fate studies 

for dicofol. Data represent % of total residue detected as specific degradate 

and study day residues were measured. .......................................................... 26 

Table 5. Methods and rates of application of currently registered uses of dicofol in 

California1

....................................................................................................... 28 

Table 6. Summary of California Department of Pesticide Registration (CDPR) Pesticide 

Use Reporting (PUR) data and calculated annual application rates (1999 - 

2006) for currently registered dicofol uses.1

................................................... 32 

Table 7. Assessment endpoints and measures of ecological effects for dicofol............... 44 

Table 8. Summary of dicofol assessment endpoints and measures of ecological effect for 

primary constituent elements of designated critical habitat1

. ......................... 46 

Table 9. Dicofol uses and application information for the CRLF risk assessment1

. ........ 55 

Table 10. Summary of PRZM/EXAMS environmental fate data used for aquatic exposure 

inputs for o,p’-dicofol. 1

.................................................................................. 61 

Table 11. Summary of PRZM/EXAMS environmental fate data used for aquatic exposure 

inputs for p,p'-dicofol. 1 .................................................................................. 62 

Table 12. Aquatic EECs (μg/L) for Dicofol Uses in California, Total o,p’ and p,p’ 

Isomers............................................................................................................ 63 

Table 13. Aquatic EECs (μg/L) for Dicofol, Parent and Degradate Uses in California... 64 

Table 14. Characteristics of model aquatic organisms used to derive BCF values. ......... 67 

5 
Table 15. Estimated BCF values for parent dicofol in aquatic organisms........................ 67 

Table 16. Concentrations of dicofol parent in tissues of aquatic organisms (estimated 

using KABAM)............................................................................................... 68 

Table 17. Estimated Log Kow values of dicofol's residues of concern............................ 69 

Table 18. Concentrations of dicofol total residues of concern in tissues of aquatic 

organisms (μg/kg-ww; estimated using KABAM). Concentrations were 

estimated using Log Kow values representative of the different dicofol 

residues of concern. ........................................................................................ 69 

Table 19. Input parameters to T-REX used to generate dicofol EECs for terrestrial 

animals. ........................................................................................................... 70 

Table 20. Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based 

Exposures of the CRLF and its Prey to Single Applications of dicofol for 

Current Uses in California. ............................................................................. 72 

Table 21. Dicofol EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via 

Effects to Terrestrial Invertebrate Prey Items................................................. 73 

Table 22. Freshwater toxicity profile for dicofol.............................................................. 79 

Table 23. Categories of acute toxicity for aquatic organisms........................................... 79 

Table 24. Acute toxicity data (96-h LC50) for freshwater fish exposed to dicofol. .......... 80 

Table 25. Chronic toxicity data for freshwater fish exposed to dicofol............................ 80 

Table 26. Estimated acute and chronic toxicity values (μg/L) for fish and daphnids 

exposed to dicofol and its degradates (as calculated by ECOSAR). .............. 82 

Table 27. Terrestrial toxicity profile for dicofol............................................................... 83 

Table 28. Categories of acute toxicity for avian and mammalian studies. ....................... 84 

Table 29. Subacute dietary toxicity data (LC50) for birds exposed to dicofol. ................. 84 

Table 30. Chronic toxicity data for birds exposed to dicofol. .......................................... 85 

Table 31. Acute and chronic RQs for aquatic-phase CRLF resulting from AERIAL 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 90 

Table 32. Acute and chronic RQs for aquatic-phase CRLF resulting from GROUND 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 91 

Table 33. Acute and chronic RQs for aquatic-phase CRLF resulting from ULV 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 91 

Table 34. Diet assumptions of small, medium and large aquatic-phase CRLF used in 

KABAM.......................................................................................................... 92 

6 
Table 35. Acute and chronic RQs for aquatic-phase CRLF exposed to dicofol (parent) 

through consumption of aquatic organisms which have accumulated dicofol.

......................................................................................................................... 92 

Table 36. Acute and chronic RQs for aquatic invertebrates resulting from AERIAL 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 93 

Table 37. Acute and chronic RQs for aquatic invertebrates resulting from GROUND 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 94 

Table 38. Acute and chronic RQs for aquatic invertebrates resulting from ULV 

applications of dicofol. EECs are based on parent and degradates of concern.

......................................................................................................................... 94 

Table 39. Acute and chronic, dietary-based RQs and dose-based RQs for direct effects of 

dicofol to the terrestrial-phase CRLF. RQs calculated using T-REX............. 96 

Table 40. RQs for determining indirect effects to the terrestrial-phase CRLF through 

effects to potential prey items, specifically small terrestrial mammals 

consuming short grass..................................................................................... 98 

Table 41. Risk estimation summary for dicofol - direct and indirect effects to the CRLF.

....................................................................................................................... 101 

Table 42. Risk estimation summary for dicofol – PCEs of designated critical habitat for 

the CRLF....................................................................................................... 102 

Table 43. Acute RQs and for aquatic-phase CRLF resulting from applications of dicofol. 

EECs are based on parent and degradates of concern................................... 106 

Table 44. Acute and chronic RQs for aquatic-phase CRLF resulting from AERIAL 

applications of dicofol. EECs are based on parent dicofol only. .................. 107 

Table 45. Acute and chronic RQs for aquatic-phase CRLF resulting from GROUND 

applications of dicofol. EECs are based on dicofol only.............................. 107 

Table 46. Acute and chronic RQs for aquatic-phase CRLF resulting from ULV 

applications of dicofol. EECs are based on parent dicofol only. .................. 108 

Table 47. Refined dose-based RQs7

 for 1.4 g CRLF consuming different food items. 

EECs calculated using T-HERPS. ................................................................ 109 

Table 48. Revised dose-based RQs7

 for 37 g CRLF consuming different food items. 

EECs calculated using T-HERPS. ............................................................. 110 

Table 49. Revised dose-based RQs7

 for 238 g CRLF consuming different food items. 

EECs calculated using T-HERPS. ................................................................ 111 

Table 50. Revised acute dietary-based RQs7 for CRLF consuming different food items. 

EECs calculated using T-HERPS. ................................................................ 112 

Table 51. Revised chronic dietary-based RQs7

 for CRLF consuming different food items. 

EECs calculated using T-HERPS. ................................................................ 113 

7 
Table 52. Acute RQs and associated likelihood of individual effects for aquatic 

invertebrates resulting from applications of dicofol. EECs are based on parent 

and degradates of concern............................................................................. 114 

Table 53. Acute and chronic RQs for aquatic invertebrates resulting from AERIAL 

applications of dicofol. EECs are based on dicofol only.............................. 115 

Table 54. Acute and chronic RQs for aquatic invertebrates resulting from GROUND 

applications of dicofol. EECs are based on dicofol only.............................. 115 

Table 55. Acute and chronic RQs for aquatic invertebrates resulting from ULV 

applications of dicofol. EECs are based on dicofol only.............................. 116 

Table 56. Acute RQs and likelihood of individual mortality for fish and aquatic-phase 

amphibians resulting from applications of dicofol. EECs are based on parent 

and degradates of concern............................................................................. 117 

Table 57. RQs7

 and associated likelihood of individual effects to terrestrial invertebrates 

due to dicofol exposures. .............................................................................. 118 

Table 58. Acute dose-based RQs and associated likelihood of individual effects to small 

terrestrial mammals (consuming short grass) due to dicofol exposures....... 119 

Table 59. Acute dose-based RQs7

 for terrestrial-phase frogs (prey) exposed to dicofol.120 

Table 60. Acute dietary-based RQs for terrestrial-phase frogs (prey) consuming small 

insects and likelihood of individual effects chance resulting from dicofol 

exposures. RQs calculated using T-HERPS. ................................................ 121 

Table 61. Summary of CDPR pesticide use reporting by county for dicofol (annual 

pounds of dicofol applied from 1999 to 2006). ............................................ 124 

Table 62. Single application rate not exceeding acute LOC for dietary- and dose-based 

exposures of the CRLF to dicofol................................................................. 126 

Table 63. Physicochemical and environmental fate properties used as input for estimating 

overall persistence and long-range transport potential using the OECD Tool.

....................................................................................................................... 132 

Table 64. Overall persistence and characteristic travel distances generated using the 

OECD Tool. .................................................................................................. 132 

Table 65. Description of evidence supporting effects determination for dicofol use in 

California. Assessment endpoint is survival, growth and reproduction of 

CRLF individuals.......................................................................................... 140 

Table 66. Summary of effects determination for CRLF critical habitat based on uses of 

dicofol in California...................................................................................... 142 

List of Figures 

Figure 1. Chemical Structures for o,p'- and p,p'-dicofol. ................................................. 11 

Figure 2. Estimated national agricultural use of dicofol for 2002. ................................... 30 

8 
Figure 3. Recovery unit, core area, critical habitat, and occurrence designations for 

CRLF............................................................................................................... 34 

Figure 4. CRLF reproductive events by month. ............................................................... 35 

Figure 5. Initial area of concern for crops described by agricultural landcover which 

corresponds to potential dicofol use sites. This map represents the area 

potentially directly affected by the federal action........................................... 41 

Figure 6. Conceptual model for dicofol effects on aquatic-phase of the CRLF. .............. 48 

Figure 7. Conceptual model for dicofol effects on terrestrial phase of the CRLF............ 49 

Figure 8. Summary of applications of dicofol to cotton in 2004 from CDPR PUR data. 58 

Figure 9. Concentration of total residues of dicofol in soil treated with dicofol for 30 

years. X axis represents time in days. Soil modeled in PRZM using CA 

strawberries and CA fruit scenarios................................................................ 75 

Figure 10. Concentration of total residues of dicofol in pore water of soil treated with 

dicofol for 30 years. X axis represents time in days. Soil modeled in PRZM 

using CA strawberries and CA fruit scenarios................................................ 75 

Figure 11. Intersection between dicofol use areas and CRLF habitat. ........................... 123 

Figure 12. Genus sensitivity distribution for acute (96-h) exposures of fish to dicofol. 135 

Figure 13. Species sensitivity distribution for subacute exposures of birds to dicofol... 136 

9 
1.0 Executive Summary 

The purpose of this assessment is to evaluate potential direct and indirect effects on the 

California red-legged frog (Rana aurora draytonii) (CRLF) arising from Federal 

Insecticide, Fungicide, Rodenticide Act (FIFRA) regulatory actions regarding use of 

dicofol on agricultural and non-agricultural sites. In addition, this assessment evaluates 

whether these actions can be expected to result in effects to the species’ designated 

critical habitat. This assessment was completed in accordance with the U.S. Fish and 

Wildlife Service (U.S. FWS) and National Marine Fisheries Service (NMFS) Endangered 

Species Consultation Handbook (U.S. FWS/NMFS 1998) and procedures outlined in the 

Agency’s Overview Document (U.S. EPA 2004). 

The CRLF was listed as a threatened species by U.S. FWS in 1996. The species is 

endemic to California and Baja California (Mexico) and inhabits both coastal and interior 

mountain ranges. A total of 243 streams or drainages are believed to be currently 

occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and 

Santa Barbara counties (U.S. FWS 1996) in California. 

 

Dicofol is a broad-spectrum acaricide, insecticide, and miticide, initially registered as a 

pesticide in 1957. The current technical formula containing dicofol was reregistered in 

1998. The following uses of dicofol are considered as part of the federal action evaluated 

in this assessment: beans (dry, snap, and lima), citrus (specifically, grapefruit, kumquats, 

lemons, limes, oranges, tangelos, and tangerines), cotton, cucurbits (specifically, 

cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer 

squash), grapes, hops, mint, pecans, peppers, pome fruits (specifically, apples, 

crabapples, pears, and quince), stone fruits (specifically, apricots, sweet and sour 

cherries, nectarines, peaches, plums, and prunes), strawberries, tomatoes, walnuts, 

bermudagrass, turf/ornamental uses (specifically, turf grasses, nursery stock, flowers, 

shade trees, woody shrubs and vines, and sod farms) and outside building surfaces 

(nonagricultural). 

Dicofol is composed of two isomers, p,p'-dicofol and o,p'-dicofol (see Figure 1), that 

occur at a ratio of 4.5: 1 in formulated end-use products. Based on the available 

environmental fate data for dicofol, this chemical and its degradates are expected to 

persist with a half-life of up to 313 days, depending upon the specific environmental 

conditions. Major routes of dissipation are hydrolysis under neutral and alkaline 

conditions and aerobic and anaerobic soil metabolism, with the o,p'-isomer degrading 

more quickly. Dicofol is classified as slightly mobile (Kashuba, et al. 2006). Leaching 

and photodegradation are not expected to be significant routes of dissipation of dicofol in 

the environment. Because of its low vapor pressure (3.9 x 10-7 torr) and Henry’s Law 

Constant (1.4 x 10-7 atm-m3

/mol), low levels of volatilization are possible, but not 

expected. 

10 
Figure 1. Chemical Structures for o,p'- and p,p'-dicofol. 

Major degradates of dicofol are the o,p'- and p,p' isomers of dichlorobenzophenone 

(DCBP); 1, 1-(p-ch1orophenyl-) 2,2-dichloroethanol (FW-152); dichlorobenzhydrol 

(DCBH); hydroxyl-dichlorobenzophenone (OH-DCBP); and chlorobenzoic acid (CBA). 

DCBP was identified in the hydrolysis, photolysis and metabolism studies while the other 

degradates were only present in metabolism studies. There are currently no submitted 

studies addressing the environmental fate and transport of these major degradates. 

However, the studies submitted in support of the aerobic soil metabolism indicate a large 

difference between half lives for dicofol alone (8.5 and 32 days for o,p'- and p,p'-dicofol, 

respectively) and the half lives for dicofol plus its degradates (186 and 313 days for total 

o,p'- and p,p'-dicofol, respectively). 

In order to estimate aquatic exposure concentrations of dicofol and its degradates of 

concern, separate modeling runs were conducted for the o,p'- and p,p'-dicofol parent and 

o,p'- and p,p'-dicofol and degradates. The EECs were then summed to derive an estimate 

for total parent and the total toxic residue. In this risk assessment, degradates of concern 

included: DCBP, FW-152, DCBH and OH-DCBP. It is assumed in this assessment that 

for aquatic animals, the degradates of concern are of equal toxicity compared to the 

parent. Additionally, due to reported DDT contamination (≤0.1%) in dicofol products and 

the established toxicity and ecological risks of DDT, screening-level charaterization of 

DDT was also considered in this assessment (see Appendix F). 

Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey 

and its habitats to dicofol are assessed separately for the two habitats. Tier-II aquatic 

exposure models (PRZM/EXAMS) are used to estimate high-end exposures of dicofol in 

aquatic habitats resulting from runoff and spray drift from different uses. Peak modelestimated environmental concentrations resulting from different dicofol uses range from 

0.15 to 18.0 μg/L for the total parent (o,p'- and p,p'-dicofol, respectively) and 0.38 to 59.6 

μg/L for the total residues of concern (dicofol and degradates). These estimates are 

supplemented with analysis of available California surface water monitoring data from 

the California Department of Pesticide Regulation. The maximum surface water 

concentration of dicofol reported in the California Department of Pesticide Regulation 

surface water database (0.27 μg/L) is roughly 190 times lower than the highest peak 

model-estimated environmental concentration. 

Based on available bioaccumulation data, dicofol and its degradates have the potential to 

accumulate in aquatic organisms. KABAM (KOW (based) Aquatic BioAccumulation 

Model) v.1.0 is used to estimate potential bioaccumulation of dicofol residues in a 

11 
freshwater aquatic food web and subsequent risks these residues pose to aquatic-phase 

CRLF via consumption of contaminated aquatic prey (i.e., aquatic invertebrates and fish). 

In order to characterize the long range transport potential (LRTP) of dicofol, the OECD 

Pov and LRTP Screening Tool was used. Three chemicals known to move via long range 

transport, DDT, aldrin and endrin, were also modeled to provide a context for dicofol 

estimated LRTP. Modeling results indicate that dicofol has comparable or higher LRTP 

estimates than all three chemicals with known potential to move via long range transport. 

The T-REX model is used to estimate dicofol exposures to terrestrial-phase CRLF, its 

potential prey, and its designated critical habitat resulting from uses involving foliar 

applications. T-HERPS is used to further characterize exposures of terrestrial-phase 

CRLF to dietary and dose-based exposures of dicofol resulting from foliar applications. 

AgDRIFT is also used to estimate deposition of dicofol on terrestrial and aquatic habitats 

from spray drift. 

The effects determination assessment endpoints for the CRLF include direct toxic effects 

on the survival, reproduction, and growth of the CRLF itself, as well as indirect effects, 

such as reduction of the prey base or effects to its habitat. Direct effects to the CRLF in 

the aquatic habitat are based on toxicity information for freshwater fish, which are 

generally used as a surrogate for aquatic-phase amphibians. In the terrestrial habitat, 

direct effects are based on toxicity information for birds, which are used as a surrogate 

for terrestrial-phase amphibians. Given that the CRLF’s prey items and designated 

critical habitat requirements in the aquatic habitat are dependant on the availability of 

freshwater aquatic invertebrates, toxicity information for these taxonomic groups is also 

discussed. In the terrestrial habitat, indirect effects due to depletion of prey are assessed 

by considering effects to terrestrial insects, small terrestrial mammals, and frogs. 

Dicofol is very highly toxic to freshwater fish and highly toxic to freshwater invertebrates 

on an acute exposure basis. The no observed adverse effect concentration (NOAEC) for 

chronic effects to the rainbow trout is 4.4 μg/L, with a lowest observed adverse affect 

concentration (LOAEC) of 7.9 μg/L based on reduction in growth. Available chronic 

toxicity data for aquatic invertebrates include a NOAEC of 19 μg/L, with a LOAEC of 33 

μg/L based on reduction in growth. Dicofol is moderately toxic to birds on an acute oral 

and subacute dietary exposure basis, and slightly toxic to mammals on an acute oral 

exposure basis. Dicofol is classified as practically nontoxic to honey bees on an acute 

contact exposure basis. Chronic exposures of the American kestrel to dicofol indicate 

effects to number of eggs laid at concentrations greater than 40 ppm, with a LOAEC of 3 

ppm based on decreased egg shell thickness. Chronic exposures of rats to dicofol 

indicate a NOAEC of 5 ppm, corresponding to a LOAEC of 25 ppm where reproductive 

effects were observed. The EC50 for algae exposed to dicofol is greater than 5,000 but 

less than 10,000 μg/L. No data are available for quantitatively defining an endpoint to 

represent the effects of dicofol exposures to vascular plants. 

Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk. 

Acute and chronic RQs are compared to the Agency’s Levels of Concern (LOCs) for 

12 
13 

Federally-listed threatened (listed) species to identify if dicofol use within the action area 

has any direct or indirect effect on the CRLF and its designated critical habitat. For this 

assessment, RQs were based on EECs representing total residues of concern (dicofol, 

DCBP, FW-152, DCBH and OH-DCBP). Based on estimated environmental 

concentrations in the aquatic and terrestrial habitats resulting from all currently registered 

uses of dicofol, RQ values exceed the Agency’s LOC for direct acute and chronic risk to 

the CRLF; this represents a “may affect” determination. RQs exceed the LOC for risks to 

aquatic invertebrates, fish, aquatic-phase amphibians, terrestrial-phase amphibians and 

mammals. RQ values for terrestrial invertebrates potentially exceed the LOC for this 

taxon. RQ values for non-vascular aquatic plants do not exceed the LOC. The effects 

determination for indirect effects to the CRLF due to effects on its prey base is “may 

affect.” Due to a lack of effects data for vascular plants exposed to dicofol, potential risk 

of dicofol to the designated critical habitat of the CRLF cannot be quantified and 

potential indirect effects to the CRLF through effects to its habitat cannot be discounted. 

Therefore, the determination for indirect effects to the CRLF through effects to its habitat 

is “may affect.” In addition, dicofol can potentially result in effects to the CRLF’s 

aquatic and terrestrial habitats based on potential impacts to its principal constituent 

elements (PCEs). 

Refinement of all “may affect” determinations results in: a “LAA” determination based 

on direct effects to the aquatic and terrestrial-phase CRLF, indirect effects to the CRLF 

based on effects to its prey and indirect effects to the CRLF based on effects to its habitat 

(Table 1). Consideration of CRLF critical habitat indicates a determination of “habitat 

modification” for aquatic and terrestrial designated critical habitats (Table 2). 
Table 1. Description of evidence supporting effects determination for dicofol use in California. Assessment endpoints include su

reproduction of CRLF individuals. 

Assessment 

Endpoint 

Effects 

Determination

Basis for Determination 

Direct effects to 

CRLF 

 -Acute RQs for aquatic-phase CRLF exceed the LOC for all uses of dicofol, except Bermuda gra- Analysis of individual effects indicates that up to 1 in 2 individual CRLF could experience m

dicofol in the aquatic habitat. - Chronic RQs for aquatic-phase CRLF exceed the LOC for all uses of dicofol, except Bermuda g

- Chronic EECs in the aquatic environment are above levels where growth effects were observed i

- Acute and chronic RQs for aquatic-phase CRLF consuming aquatic organisms contaminateaccumulation) exceed LOCs. - Refined acute, dose-based RQs (derived using T-HERPS) for medium sized CRLF consuming s

LOCs for all uses of dicofol. - Refined acute, dietary-based RQs (derived using T-HERPS) for CRLF consuming small insectexceed LOCs for several uses of dicofol. - Chronic dietary-based RQs for CRLF exceed LOCs for all uses of dicofol, for CRLF consumininsects, mammals and terrestrial-phase amphibians). - Chronic, dietary-based EECs are above levels where reduced number of eggs laid was observppm). 

Indirect effects to 

tadpole CRLF 

via reduction of 

prey (i.e., algae) 

RQ values for algae are below the LOC for all uses of dicofol. 

Indirect effects to 

juvenile CRLF 

via reduction of 

prey (i.e., 

invertebrates) 

- Acute RQs for aquatic invertebrates exceed the LOC the majority of dicofol uses. - The likelihood of individual acute effects to aquatic invertebrates is ≤3%. Based on this, indirect 

acute effects to aquatic invertebrates is discountable. - Chronic RQs for aquatic invertebrates do not exceed the LOC for dicofol use on cucurbits, peppeornamentals, turf and outside buildings. - Chronic RQs for aquatic invertebrates exceed the LOC for dicofol use on beans, citrus, cotton, gstone fruits, strawberry, walnuts, and pecans. 

Indirect effects to 

adult CRLF via 

reduction of prey 

(i.e., 

invertebrates, 

fish, frogs, mice) 

LAA 

- Acute RQs for aquatic invertebrates exceed the LOC the majority of dicofol uses. - The likelihood of individual acute effects to aquatic invertebrates is ≤3%. Based on this, indirect acute effects to aquatic invertebrates is discountable. - Chronic RQs for aquatic invertebrates do not exceed the LOC for dicofol use on cucurbits, peppeornamentals, turf and outside buildings. - Chronic RQs for aquatic invertebrates exceed the LOC for dicofol use on beans, citrus, cotton, gstone fruits, strawberry, walnuts and pecans. -Acute RQs for aquatic-phase amphibians and fish exceed the LOC for all uses of dicofol, except buildings. 

14 
Assessment 

Endpoint 

Effects Basis for Determination 

Determination

- Use of dicofol on beans, citrus, cotton, hops, mint, pome fruits, strawberries, walnuts, and peca

individual mortality (from acute exposures) to fish and aquatic-phase amphibians. -Use of dicofol on cucurbits, grapes, pepper, stone fruits, tomatoes, Bermuda grass, ornamentals, in <10% chance of effects to an individual fish and aquatic-phase amphibians representing prey of - Chronic RQs for fish and aquatic-phase amphibians exceed the LOC for all uses of dicofol, eoutside buildings. - Because the LD50 used in deriving RQs for terrestrial invertebrates is not quantified, RQs for acu

terrestrial invertebrates to dicofol potentially exceed the LOC of 0.05 for all uses. 

- Given that dicofol is intended for control of insects, it has the potential to impact non-target inse

-For use of dicofol on grapes, mint, hops, peppers, tomatoes, cucurbits, ornamentals, turf and Bresult in a chance of individual mortality to <10% of terrestrial insects. Therefore, indirect effect

effects to terrestrial invertebrates resulting from these dicofol uses are considered discountable. - Use of dicofol on citrus, pome fruits, strawberries, walnuts, pecans, beans, cotton and stone ≥10% of mortality to small invertebrates. Although there is uncertainty in the actual effects oinvertebrates, given that no LD50 was established, mortality to small insects resulting from dicofpotential to result in indirect effects to the CRLF. - RQ values representing acute exposures to terrestrial mammals exceed the LOC (0.1) for all uses turf, outside buildings and Bermuda grass - Use of dicofol on citrus and pome fruits could potential result in 10.7% mortality to individual dicofol use on citrus and pome fruits could potentially result in indirect effects to the CRLF dmammals. All other uses of dicofol result in ≤2.0% mortality to small mammals resulting frTherefore, indirect effects to the CRLF through potential effects to terrestrial mammals resultin

citrus and pome fruits, are considered discountable. - Chronic RQs exceed the LOC for terrestrial mammals for all uses of dicofol. Chronic EECs are for mammals where reproductive effects were observed. Therefore, chronic exposures of dicofol to indirectly affect the CRLF via impacts to terrestrial mammals serving as potential prey items. - Acute and chronic exposures of small mammals to dicofol through consumption of contaminated with dicofol have the potential to result in effects to mammals. - Acute, dose-based RQs for terrestrial-phase amphibians serving as prey to the CRLF do not exce

- Acute, dietary-based RQs for terrestrial-phase amphibians exceed the LOC for several uses. - Analysis of the likelihood of individual mortality using acute dietary-based RQs for terrestrial am

of dicofol result in ≤2% chance of effects to an individual terrestrial amphibian representing prey 

impact of the indirect effects to terrestrial-phase CRLFs via acute effects on terrestrial amphibians 

dicofol. - Chronic, dietary-based RQs exceed the LOC by factors ranging 2x to 474x. Therefore, for all dicindirect effects to the CRLF resulting from chronic effects to terrestrial frogs. 

Indirect effects to 

CRLF via 

-Due to a lack of quantitative effects data for non-target plants exposed to dicofol, potential ri

terrestrial habitats of the CRLF cannot be quantified and effects of dicofol to plants cannot be disc

15 
16 

Assessment 

Endpoint 

Effects 

Determination

Basis for Determination 

reduction of 

habitat and/or 

primary 

productivity 

(i.e., plants) 

-Qualitative data suggest that dicofol may result in phytotoxicity. -There is one reported incident involving effects of dicofol to plants. -Dicofol exposures to plants have the potential to cause indirect effects to aquatic phase CLRF thr

Table 2. Summary of effects determination for CRLF critical habitat based on uses of dicofol in California.Assessment Endpoint 

Effects Determination 

Basis for Determination 

Modification of aquatic-phase primary constituent elements 

 Dicofol has the potential to modify habitat based on the aquatic-phase PCEs.

- Dicofol has the potential to directly affect the aquatic-phase CRLF (See Table 1). - Dicofol has the potential to indirectly affect the aquatic-phase CRLF through effects to its prey (see Table 1). -Effects of dicofol to plants making up the aquatic habitat of the CRLF cannot be discounted. 

Modification of terrestrial-phase primary constituent elements 

Habitat Effects

Dicofol has the potential to modify habitat based on the terrestrial-phase PCEs.

- Dicofol has the potential to directly affect the terrestrial-phase CRLF (See Table 1). - Dicofol has the potential to indirectly affect the terrestrial-phase CRLF through effects to its prey (see Table 1). -Effects of dicofol to plants making up the terrestrial habitat of the CRLF cannot be discounted. 
Based on the conclusions of this assessment, a formal consultation with the U. S. Fish 

and Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

When evaluating the significance of this risk assessment’s direct, indirect, and adverse 

habitat modification effects determinations, it is important to note that pesticide 

exposures and predicted risks to the species and its resources (i.e., food and habitat) are 

not expected to be uniform across the action area. In fact, given the assumptions of drift 

and downstream transport (i.e., attenuation with distance), pesticide exposure and 

associated risks to the species and its resources are expected to decrease with increasing 

distance away from the treated field or site of application. Evaluation of the implication 

of this non-uniform distribution of risk to the species would require information and 

assessment techniques that are not currently available. Examples of such information and 

methodology required for this type of analysis would include the following: 

• Enhanced information on the density and distribution of CRLF life stages 

within specific recovery units and/or designated critical habitat within the 

action area. This information would allow for quantitative extrapolation 

of the present risk assessment’s predictions of individual effects to the 

proportion of the population extant within geographical areas where those 

effects are predicted. Furthermore, such population information would 

allow for a more comprehensive evaluation of the significance of potential 

resource impairment to individuals of the species. 

• Quantitative information on prey base requirements for individual aquaticand terrestrial-phase frogs. While existing information provides a 

preliminary picture of the types of food sources utilized by the frog, it 

does not establish minimal requirements to sustain healthy individuals at 

varying life stages. Such information could be used to establish 

biologically relevant thresholds of effects on the prey base, and ultimately 

establish geographical limits to those effects. This information could be 

used together with the density data discussed above to characterize the 

likelihood of adverse effects to individuals. 

• Information on population responses of prey base organisms to the 

pesticide. Currently, methodologies are limited to predicting exposures 

and likely levels of direct mortality, growth or reproductive impairment 

immediately following exposure to the pesticide. The degree to which 

repeated exposure events and the inherent demographic characteristics of 

the prey population play into the extent to which prey resources may 

recover is not predictable. An enhanced understanding of long-term prey 

responses to pesticide exposure would allow for a more refined 

determination of the magnitude and duration of resource impairment, and 

together with the information described above, a more complete prediction 

of effects to individual frogs and potential modification to critical habitat. 

17 
2.0 Problem Formulation 

Problem formulation provides a strategic framework for the risk assessment. By 

identifying the important components of the problem, it focuses the assessment on the 

most relevant life history stages, habitat components, chemical properties, exposure 

routes, and endpoints. The structure of this risk assessment is based on guidance 

contained in U.S. Environmental Protection Agency’s (EPA’s) Guidance for Ecological 

Risk Assessment (U.S. EPA 1998a), the Services’ Endangered Species Consultation 

Handbook (U.S. FWS/NMFS 1998) and is consistent with procedures and methodology 

outlined in the Overview Document (U.S. EPA 2004) and reviewed by the U.S. Fish and 

Wildlife Service and National Marine Fisheries Service (U.S. FWS/NMFS 2004). 

2.1. Purpose 

The purpose of this endangered species assessment is to evaluate potential direct and 

indirect effects on individuals of the federally threatened California red-legged frog 

(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of 

dicofol on the following: beans (dry, snap, and lima), citrus (specifically, grapefruit, 

kumquats, lemons, limes, oranges, tangelos, and tangerines), cotton, cucurbits 

(specifically, cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and 

summer squash), grapes, hops, mint, pecans, peppers, pome fruits (specifically, apples, 

crabapples, pears, and quince), stone fruits (specifically, apricots, sweet and sour 

cherries, nectarines, peaches, plums, and prunes), strawberries, tomatoes, walnuts, 

Bermuda grass, turf/ornamental uses (specifically, turf grasses, nursery stock, flowers, 

shade trees, woody shrubs and vines, and sod farms) and outside building surfaces (nonagricultural). In addition, this assessment evaluates whether use on these sites is 

expected to result in effects to the species’ designated critical habitat. This ecological 

risk assessment has been prepared consistent with a settlement agreement in the case 

Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 02-1580-JSW(JL) 

entered in Federal District Court for the Northern District of California on October 20, 

2006. 

In this assessment, direct and indirect effects to the CRLF and potential effects to its 

designated critical habitat are evaluated in accordance with the methods described in the 

Agency’s Overview Document (U.S. EPA 2004). Screening-level methods include use 

of standard models such as GENEEC, PRZM-EXAMS, T-REX, TerrPlant, and 

AgDRIFT, all of which are described at length in the Overview Document (U.S. EPA 

2004). Use of such information is consistent with the methodology described in the 

Overview Document (U.S. EPA 2004), which specifies that “the assessment process may, 

on a case-by-case basis, incorporate additional methods, models, and lines of evidence 

that EPA finds technically appropriate for risk management objectives” (Section V, page 

31 of U.S. EPA 2004). 

In accordance with the Overview Document, provisions of the ESA, and the Services’ 

Endangered Species Consultation Handbook, the assessment of effects associated with 

registrations of dicofol is based on an action area. The action area is the area directly or 

18 
indirectly affected by the federal action. It is acknowledged that the action area for a 

national-level FIFRA regulatory decision associated with a use of dicofol may potentially 

involve numerous areas throughout the United States and its Territories. However, for 

the purposes of this assessment, attention will be focused on relevant sections of the 

action area including those geographic areas associated with locations of the CRLF and 

its designated critical habitat within the state of California. As part of the “effects 

determination,” one of the following three conclusions will be reached regarding the 

potential use of dicofol in accordance with current labels: 

• “No effect”; 

• “May affect, but not likely to adversely affect”; or 

• “May affect and likely to adversely affect”. 

Designated critical habitat identifies specific areas that have the physical and biological 

features, known as primary constituent elements or PCEs, essential to the conservation of 

the listed species. The PCEs for CRLFs are aquatic and upland areas where suitable 

breeding and non-breeding aquatic habitat is located, interspersed with upland foraging 

and dispersal habitat. 

If the results of initial screening-level assessment show no direct or indirect effects (no 

LOC exceedances) upon individual CRLFs or upon the PCEs of the species’ designated 

critical habitat, a “no effect” determination is made for use of dicofol as it relates to this 

species and its designated critical habitat. If, however, potential direct or indirect effects 

to individual CRLFs are anticipated or effects may impact the PCEs of the CRLF’s 

designated critical habitat, a preliminary “may affect” determination is made for the 

FIFRA regulatory action regarding dicofol. 

If a determination is made that use of dicofol within the action area(s) associated with the 

CRLF “may affect” this species or its designated critical habitat, additional information is 

considered to refine the potential for exposure and for effects to the CRLF and other 

taxonomic groups upon which these species depend (e.g., aquatic and terrestrial 

vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.). Additional 

information, including spatial analysis (to determine the geographical proximity of CRLF 

habitat and dicofol use sites) and further evaluation of the potential impact of dicofol on 

the PCEs is also used to determine whether effects to designated critical habitat may 

occur. Based on the refined information, the Agency uses the best available information 

to distinguish those actions that “may affect, but are not likely to adversely affect” from 

those actions that “may affect and are likely to adversely affect” the CRLF. This 

information is presented as part of the Risk Characterization in Section 5 of this 

document. 

The Agency believes that the analysis of direct and indirect effects to listed species 

provides the basis for an analysis of potential effects on the designated critical habitat. 

Because dicofol is expected to directly impact living organisms within the action area 

(defined in Section 2.7), critical habitat analysis for dicofol is limited in a practical sense 

to those PCEs of critical habitat that are biological or that can be reasonably linked to 

19 
biologically-mediated processes (i.e., the biological resource requirements for the listed 

species associated with the critical habitat or important physical aspects of the habitat that 

may be reasonably influenced through biological processes). Activities that may modify 

critical habitat are those that alter the PCEs and appreciably diminish the value of the 

habitat. Evaluation of actions related to use of dicofol that may alter the PCEs of the 

CRLF’s critical habitat form the basis of the critical habitat impact analysis. Actions that 

may affect the CRLF’s designated critical habitat have been identified by the Services 

and are discussed further in Section 2.6. 

 

2.2. Scope 

Dicofol is an organochlorine, broad-spectrum acaricide, insecticide, and miticide 

currently registered nationwide for application to a variety of crops, including: beans 

(dry, snap, and lima), citrus (specifically, grapefruit, kumquats, lemons, limes, oranges, 

tangelos, and tangerines), cotton, cucurbits (specifically, cantaloupes, cucumbers, 

melons, pumpkins, watermelons, and winter and summer squash), grapes, hops, mint, 

pecans, peppers, pome fruits (specifically, apples, crabapples, pears, and quince), stone 

fruits (specifically, apricots, sweet and sour cherries, nectarines, peaches, plums, and 

prunes), strawberries, tomatoes, walnuts, Bermuda grass, turf/ornamental uses 

(specifically, turf grasses, nursery stock, flowers, shade trees, woody shrubs and vines, 

and sod farms) and outside building surfaces (non-agricultural). Application rates range 

from 0.4 – 3 lbs a.i./A with no more than one application per year for food crops. Dicofol 

may be applied as an aerial or ground spray. The current technical formula containing 

dicofol was reregistered in 1998. The terms of reregistration included cancellation of 

residential uses, with remaining uses limited to one annual application, and application 

rate reductions. The current labels for products containing dicofol comport with the 

changes implemented through reregistration and are being used to define parameters of 

the action being assessed in this ecological risk assessment and effects determination. 

Prior to 1990, dicofol contained approximately 10% DDT since DDT is an intermediate 

in the production of dicofol; however, refinements in the manufacturing process have 

reduced contamination in the current formulation to less than 0.1 % DDT contamination. 

The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory 

action) is an approved product label. The label is a legal document that stipulates how 

and where a given pesticide may be used. Product labels (also known as end-use labels) 

describe the formulation type (e.g., liquid or granular), acceptable methods of application, 

approved use sites, and any restrictions on how applications may be conducted. Thus, the 

use of dicofol in accordance with the approved product labels for California is “the 

action” relevant to this ecological risk assessment. 

Although current registrations of dicofol allow for use nationwide, this ecological risk 

assessment and effects determination addresses currently registered uses of dicofol in 

portions of the action area that are reasonably assumed to be biologically relevant to the 

CRLF and its designated critical habitat. Further discussion of the action area for the 

CRLF and its critical habitat is provided in Section 2.7. 

20 
Major degradates of the two isomers of dicofol are the o,p'- and p,p' isomers of 

dichlorobenzophenone (DCBP); 1, 1-(p-ch1orophenyl-) 2,2-dichloroethanol (FW-152); 

dichlorobenzhydrol (DCBH); hydroxyl-dichlorobenzophenone (OH-DCBP); and 

chlorobenzoic acid (CBA). DCBP was identified in the hydrolysis, photolysis and 

metabolism studies while the others were only present in metabolism studies. The 

structures of dicofol and its major degradates are provided in Appendix A. There are 

currently no submitted studies addressing the environmental fate and transport of these 

major degradates. In addition, no empirical data are available to define the toxicities of 

these degradates to non-target organisms. In order to characterize the relative toxicities 

of these degradates to dicofol, the Ecosar1

 model was run. The result indicates that the 

toxicities of DCBP, FW-152, DCBH and OH-DCBP are within an order of magnitude of 

dicofol (for a full description of the results, see Section 4.2). Therefore, these degradates 

were considered to be of concern for this risk assessment. It is assumed in this 

assessment that for aquatic animals, total residues are of equal toxicity to that of the 

parent. 

The Agency does not routinely include in its risk assessments an evaluation of mixtures 

of active ingredients, either those mixtures of multiple active ingredients in product 

formulations or those in the applicator’s tank. In the case of the product formulations of 

active ingredients (that is, a registered product containing more than one active 

ingredient), each active ingredient is subject to an individual risk assessment for 

regulatory decision regarding the active ingredient on a particular use site. If effects data 

are available for a formulated product containing more than one active ingredient, they 

may be used qualitatively or quantitatively in accordance with the Agency’s Overview 

Document and the Services’ Evaluation Memorandum (U.S. EPA 2004; U.S. 

FWS/NMFS 2004). 

Registered products that contain dicofol do not list any other active ingredients on their 

labels. However, as mentioned earlier, prior to 1990, dicofol contained approximately 

10% DDT. Refinements in the manufacturing process have reduced contamination in the 

current formulation to less than 0.1 % DDT contamination. No other data on mixtures 

including dicofol are available. 

2.3. Previous Assessments 

In November 1998, EPA completed its Registration Eligibility Decision (RED) for 

dicofol. EPA concluded that the available field data suggested that dicofol did not pose 

significant adverse effects on avian reproduction and did not present an unreasonable risk 

to ecosystems. However, based on laboratory data, the potential for such effects 

appeared significant for certain species. Dicofol was found to be moderately to slightly 

toxic on an acute exposure basis to terrestrial animals and practically non-toxic to honey 

bees on an acute contact exposure basis. In laboratory studies dicofol was also shown to 

cause reproductive effects in avian and mammalian species. Dicofol was found to be 

highly toxic on an acute basis to both cold and warm water species of fish and freshwater 

 

1

 USEPA 2009. Ecological Structure Activity Relationships (ECOSAR) version 1.00a. Office of Pollution 

Prevention and Toxic. http://www.epa.gov/oppt/newchems/tools/21ecosar.htm 

21 
invertebrates and was very highly toxic to estuarine/marine invertebrates. Additionally, 

laboratory studies showed that dicofol had some potential to bioaccumulate in fish, but 

that dicofol residues depurated relatively quickly. Because of its apparent structural 

similarity to DDT, dicofol has been identified as a potential endocrine disrupter. 

However, based on the data available, no conclusions could be made regarding the 

potential for dicofol to act as an endocrine disrupter (USEPA, 1998b). 

2.4. Stressor Source and Distribution 

2.4.1. Environmental Fate Assessment 

Based on the available environmental fate data for dicofol, this chemical is not expected 

to persist in the environment, with half-lives less than 90 days, depending upon the 

specific environmental conditions. However, studies submitted on the fate of dicofol do 

not provide sufficient information to estimate persistence of dicofol degradates in the 

environment. As a result, conservative estimates for persistence of dicofol (considering 

the parent and major degradates) are as high as 313 days. The primary route of 

dissipation is soil metabolism and the primary route of transport is surface runoff. 

Dicofol occurs in formulated end-use products as two isomers, o,p'-dicofol and p,p'-

dicofol, at a ratio of 1:4.5. Major degradates of dicofol include the o,p'- and p,p'-isomers 

of DCBP, FW-152, DCBH, OH-DCBP, and CBA. 

22 
Table 3 lists the environmental fate properties of the dicofol isomers. The o,p'-isomer 

hydrolyzed with half-lives of 47 days, 0.33 days, and 0.006 days at pHs 5, 7 and 9, 

respectively (MRID 40042033). An aerobic soil metabolism study showed that the o,p'-

isomer degraded with half-life of 8.5 days in a loam soil under slightly alkaline 

conditions (pH = 7.5, MRID 41094201). Parent plus major residues degraded with a halflife of 186 days. An anaerobic soil metabolism study showed that the o,p'-isomer 

degraded with half-life of 6 days in a silt loam soil under slightly alkaline conditions (pH 

= 7.9, MRID 43908701). Adsorption data indicate that the o,p’-isomer is not very 

mobile, with a majority of the o,p’-dicofol remaining in the upper 2 inches of the soil 

columns. Less than 2.5% of o,p’-dicofol was found in leachate (MRID 41509802). 

The p,p'-isomer hydrolyzed with half-lives of 85 days, 2.8 days and 0.018 days at pHs 5, 

7 and 9, respectively (MRIDs 40042032, 40460105). An aerobic soil metabolism study 

showed that the p,p'-isomer degraded with a half-life of 32 days in a silt loam soil under 

slightly alkaline conditions (pH = 7.8, MRID 41050701). Parent plus major residues 

degraded with a half-life of 313 days. An anaerobic soil metabolism study showed that 

the p,p'-isomer degraded with half-life of less than 30 days in a silt loam soil under 

slightly alkaline conditions (pH = 7.8, MRID 40042039). Adsorption data indicate that 

the p,p’-isomer is not very mobile (MRID 41509801). A regression analysis between the 

Kd and organic carbon content values indicated a high r-squared value (0.98) and 

statistical significance (<0.01). To assess the appropriateness of the Koc model, the 

coefficient of variation for the Koc (CV = 19) was compared to the coefficient of variation 

for Kd (CV = 58). Since the CV for the Koc was less than the CV for Kd, the average Koc

of 7,060 mL/g was used (Kashuba et al. 2006). For o,p’-dicofol, the majority of dicofol 

remained in upper 2 inches of soil columns, with less than 2.5% of dicofol found in 

leachate. 

Of the major dicofol degradates, DCBP was identified in the hydrolysis, photolysis and 

metabolism studies, while the other degradates were only present in metabolism studies. 

Table 4 summarizes the maximum amount of the individual degradates that were observed 

in submitted environmental fate studies for dicofol and when the maximum amount 

occurred. There are currently no submitted studies quantifying the environmental fate 

and transport (e.g., half-lives) of the major degradates of dicofol individually. 

Available registrant-submitted data indicate that dicofol has potential to bioaccumulate in 

aquatic ecosystems. Dicofol has a octanol-water partitioning coefficient (Kow) of 1.15 x 

10-6 (MRID 00141578). In a bioconcentration study, parent p,p'-dicofol residues in 

bluegill sunfish resulted in bioconcentration factors of 6,600 in fillet, 17,000 in viscera, 

and 10,000 in whole fish. The half-life of elimination (depuration) was estimated to be 33 

days (MRID 265330). 

23 
Based on the available fate data, the major routes of dissipation for dicofol are hydrolysis 

under neutral and alkaline conditions, and aerobic and anaerobic soil metabolism under 

slightly alkaline conditions (pH from 7.5 to 7.9), with the o,p'-isomer degrading more 

quickly. Dicofol can be classified as slightly mobile (Kashuba, et al. 2006) and has the 

potential to bioaccumulate in the environment. Leaching and photodegradation are not 

expected to be significant routes of dissipation. Based on dicofol’s vapor pressure 

(3.9 x 10-7 torr), low levels of volatilitization are possible, but not expected. Dicofol can 

be expected to partition between the gas and particle phases in the atmosphere, and is 

likely to exist largely in the particle phase, potentially contributing to its long-range 

transport. Given dicofol’s Kow and Koc values, it is anticipated that dicofol that enters 

surface water through soil erosion, runoff, or spray drift will have an affinity to reside in 

the sediment. Anaerobic soil metabolism studies indicate that dicofol will degrade 

relatively rapidly in sediment with a half-life less than 30 days. It is unclear how dicofol 

degradates would partition in the water column; however, estimates of the Kow values 

(9,120-77,625) and Koc values (1,933-8,950) 2 using EPISuite indicate a similar affinity 

for the sediment. As there are no data quantifying the fate and transport of the dicofol 

degradates, two stressors will be examined in this assessment: the parent compound (both 

isomers of dicofol) and the total residues of concern (both isomers of dicofol and their 

degradates). Based on toxicity data, the degradate CBA will not be considered in the 

total residues of concern (see Section 4.2.1). 

 

2

 USEPA 2009. Estimation Program Interface (EPI) Suite version 4.0. Office of Pollution Prevention and 

Toxics. http://www.epa.gov/oppt/exposure/pubs/episuitedl.htm 

24 
Table 3. Summary of dicofol environmental fate properties. 

Chemical/Fate 

Parameter 

Value 

o,p’-dicofol 

Value 

p,p’-dicofol 

MRID1 Study 

Classification 

Molecular weight 370.5 g/mol 

Vapor pressure (20°C) 3.9x10-7 torr 

Water solubility 

(25°C) 1.32 mg/L 

00141704 

00142595 Acceptable 

Kow 1.15 x 106

 00141578 Acceptable 

Hydrolysis half-life 

 pH 5 

 pH 7 

 pH 9 

47 days 

3.3 x 10-1 days 

6.3 x 10-3 days 

85 days 

2.8 days 

1.8 x 10-2 days 

40042033 

40042032 

40460105 

Acceptable 

Acceptable 

Acceptable 

Direct Aqueous 

Photolysis2

 half-life 27.5 days 244 days 

40849702 

40849701 

Acceptable 

Acceptable 

Soil Photolysis halflife 56 days 21 days 

40042037 

40042036 

Supplemental 

Supplemental 

Aerobic Soil 

Metabolism half-life 

8.5 days (parent) 

104.5 days (parent 

and major degradates) 

32 days (parent) 

313 days (parent and 

major degradates) 

41094201 

41050701 

Acceptable 

Acceptable 

Anaerobic Soil 

Metabolism half-life 6 days < 30 days 

43908701 

40042039 

Acceptable 

Supplemental 

Leaching & 

Adsorption/Desorption 

Majority of parent 

remained in upper 2 

inches of soil 

columns. ≤2.5% of 

parent found in 

leachate. 

Koc=7,060 mL/g 

41509802 

41509801 

Acceptable 

Acceptable 

Terrestrial Field 

Dissipation half-life 3.7, 22 days 4.7, 72 days 

41381801 

42118601 

Supplemental 

Supplemental 

1. First MRID listed corresponds to data for o,p’-dicofol, while the second MRID corresponds to data for p,p’-

dicofol. 

2. Data corrected for dark control. 

25 
Table 4. Summary of dicofol degradates observed in submitted environmental fate studies for dicofol. 

Data represent % of total residue detected as specific degradate and study day residues were 

measured. 

Fate Study 

 Dicofol 

Isomer FW-1521 DCBP2 DCBH3 OH-DCBP4 CBA5 MRID 

o,p’ ND 

53% 

Day 1 

ND ND ND 40042033 

Hydrolysis 

 pH 7 p,p’ ND 

50% 

Day 7 

ND ND ND 40042032 

o,p’ ND 

26% 

Day 30 

ND ND ND 40849702 Direct 

Aqueous 

Photolysis1

 p,p’ ND 

7% 

Day 30 

ND ND ND 40849701 

o,p’ ND 

29% 

Day 30 

ND ND ND 40042036 

Soil 

Photolysis p,p’ ND 

25% 

Day 30 

ND ND ND 40042037 

o,p’ 

31% 

Day 31 

19% 

Day 275 

12% 

Day 366 

12% 

Day 92 

14% 

Day 92 

41094201 

Aerobic Soil 

Metabolism p,p’ 

45% 

Day 62 

18% 

Day 275 

ND 

17% 

Day 275 

ND 41050701 

o,p’ 

43% 

Day 30 

<10% 

Day 1 

15% 

Day 30 

ND ND 43908701 Anaerobic 

Soil 

Metabolism p,p’ 

38% 

Day 60 

5.4% 

Day 0 

6.4% 

Day 60 

ND ND 40042039 

ND = not detected 

1

 1,1-(p-ch1orophenyl-) 2,2-dichloroethanol 2

 Dichlorobenzophenone 

3

 Dichlorobenzhydrol 

4

 Hydroxyl-dichlorobenzo-phenone 

5

 Chlorobenzoic acid

2.4.2. Environmental Transport Assessment 

Potential transport mechanisms include runoff in soluble and soil-bound forms, spray 

drift, and atmospheric transport in soil-bound residues leading to deposition into nearby 

or more distant ecosystems. 

Dicofol is expected to have limited mobility in the environment and a low potential to 

migrate to groundwater. In soil column leaching experiments in sand, sandy loam, and 

clay loam (MRID 41509802), 75 to 98% of the applied radioactivity of the o,p'-dicofol 

isomer remained in the upper 1 or 2 inches of the columns. Less than 3% of the applied 

radioactivity was in the leachate. Batch equilibrium studies on the p,p'-isomer resulted 

in organic carbon sorption coefficients of 7,060 mL/goc, (MRID 41509801). Two 

supplemental leaching studies conducted on p,p'-dicofol suggest that the chemical does 

not significantly leach under the testing conditions (IDs GS0021002 and GS0021007). 

26 
No data are available on the mobility of aged dicofol or on the mobility of the major 

degradates of dicofol. Based on the results of the terrestrial field dissipation studies, it 

appears that dicofol metabolites are not very mobile under normal dicofol use conditions. 

Depending on soil, site and meteorological conditions dicofol may be transported off-site 

in soil-bound erosion from runoff. 

Although supplemental, two terrestrial field dissipation studies confirm the results of the 

laboratory persistence and mobility studies. These studies suggest that dicofol does not 

persist in the field for long periods (on an order of several days to several weeks). In a 

dissipation study on cotton in Madera, California (MRID 41381801), dicofol residues had 

a DT50 value (the length of time required for 50% of the parent to dissipate from the 

surface 6-inches of the soil) of less than 7 days. In a second dissipation study on 

strawberries in Thermal, California (MRID 42118601), the rate of dissipation was slower 

(DT50s of 22 days for o,p'-dicofol and 72 days for p,p'-dicofol). Dicofol dissipated from 

the upper 6 inches in the Madera study site at a rate that was an order of magnitude faster 

than that of the Thermal site, despite the fact that the soils at the Thermal site had an 

alkaline pH more favorable to hydrolysis (8.4 at Thermal versus 6.2 at Madera) and a 

higher organic matter content (0.8% at Thermal versus 0.2% at Madera). Greater 

amounts of irrigation were used in the cotton study (44.28 inches of water over the first 

228 days in Madera versus 27.04 inches of water over 365 days). Results of these studies 

suggest that hydrolysis at the Madera site may have played a greater role than at the 

Thermal site, where metabolism appeared to be the dominant route of dissipation in the 

field. Neither dicofol nor its residues moved significantly below 6 inches in either study. 

The major degradates observed in these field studies, o,p' and p,p'-DCBP, o,p'-DCBH, 4-

CBA, and p,p'-FW 152. Analysis of the data indicates that the half-lives for the major 

degradates, o,p’-DCBP and p,p’-DCBP, were between 29 and 45 days, and 55 and 132 

days, respectively. 

A number of studies have documented atmospheric transport and re-deposition of 

pesticides from the Central Valley to the Sierra Nevada Mountains (Fellers et al. 2004; 

Sparling et al. 2001; LeNoir et al. 1999; McConnell et al. 1998). Prevailing winds blow 

across the Central Valley eastward to the Sierra Nevada Mountains, transporting airborne 

industrial and agricultural pollutants into the Sierra Nevada ecosystems (Fellers et al.

2004; LeNoir et al. 1999; McConnell et al. 1998). Several sections of critical habitat for 

the CLRF are located east of the Central Valley. The magnitude of transport via 

secondary drift depends on dicofol’s ability to be mobilized into air and its eventual 

removal through wet and dry deposition of particles and photochemical reactions in the 

atmosphere. Therefore, physicochemical properties of dicofol that describe its potential 

to enter the air from water or soil, pesticide use data, modeled estimated concentrations in 

water and air, and available air monitoring data from the Central Valley and the Sierra 

Nevada Mountains are considered in evaluating the potential for atmospheric transport of 

dicofol to locations where it could impact the CRLF. 

Because of its low vapor pressure and persistence in the air (estimated half-life > 2 days), 

the United Nations Economic Commission for Europe’s (UNECE) Convention on Longrange Transboundary Air Pollution has indicated that dicofol has the potential for long 

27 
range transport (Rasenberg et al. 2003). According to the report, “dicofol is expected to 

partition between the gas and particle phases in the atmosphere and is likely to exist 

largely in the particle phase.” 

2.4.3. Mechanism of Action 

According to the World Health Organization (WHO, 1996), dicofol produces stimulation 

of axonal transmission of nerve signals, believed to be related to inhibition of ATPases in 

the central nervous system (CNS). The signs of toxicity are consistent with CNS 

depression. However, the Insecticide Resistance Action Committee (IRAC) has recently 

classified the mode of action for dicofol as unknown or uncertain (IRAC, 2008). 

2.4.4. Use Characterization 

Analysis of labeled use information is the critical first step in evaluating the federal 

action. The current labels for dicofol represent the FIFRA regulatory actions; therefore, 

labeled use and application rates specified on the label form the basis of this assessment. 

The assessment of use information is critical to the development of the action area and 

selection of appropriate modeling scenarios and inputs. 

Dicofol is an organochlorine, broad-spectrum acaricide, insecticide, and miticide 

currently registered nationwide for application on a variety of crops and non-agricultural 

uses. Table 5 presents the uses and corresponding application rates and methods of 

application considered in this assessment. The reported application rates represent the 

maximum application rate used in any crop/use site within each group. The information 

was extracted from existing product labels (EPA Registration Numbers 11603-26, 66222-

21, 66222-56, and 66222-95). Dicofol is used for non-residential purposes only. 

Table 5. Methods and rates of application of currently registered uses of dicofol in California1. 

Use (Application Method) 

Max. Single 

Appl. Rate 

(lb a.i./A) 

Application Method(s) 

Beans (dry, snap, lima) 1.5 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Citrus2 3 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Cotton 1.5 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Cucurbits3 0.625 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Grapes 1.25 ULV, Aircraft and ground sprayer 

Hops 1.165 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Mint/Peppermint/Spearmint 1.25 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

28 
Use (Application Method) 

Max. Single 

Appl. Rate 

(lb a.i./A) 

Application Method(s) 

Pecans 2 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Peppers 0.75 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Pome Fruits4 3 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Stone Fruits5 1.5 ULV, Aircraft and ground sprayer 

Strawberries 2 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Tomatoes 0.75 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Walnuts (English/black) 2 ULV, Aircraft, Hi- and low-volume ground 

sprayer 

Bermuda grass 0.4 Hi- and low-volume ground sprayer 

Turf grasses 0.5 Hi- and low-volume ground sprayer 

Sod farms 0.5 Hi- and low-volume ground sprayer 

Ornamentals6 0.5 Hi- and low-volume ground sprayer 

Outside building surfaces 0.5 Hi- and low-volume ground sprayer 

1. Applications of dicofol are limited to no more than one per year on any one field. 

2. Specifically: grapefruit, kumquats, lemons, limes, oranges, tangelos, and tangerines. 

3. Specifically: cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash. 

4. Specifically: apples, crabapples, pears, and quince. 

5. Specifically: apricots, sweet and sour cherries, nectarines, peaches, plums, and prunes. 

6. Specifically: nurseries, flowers, and shade trees. 

Figure 2 below shows the estimated poundage of dicofol uses across the United States. 

The map was downloaded from a U.S. Geological Survey (USGS), National Water 

Quality Assessment Program (NAWQA) website 

(http://water.usgs.gov/nawqa/pnsp/usage/maps/). 

29 
Figure 2. Estimated national agricultural use of dicofol for 2002. 

The Agency’s Biological and Economic Analysis Division (EPA/OPP/BEAD) provides 

an analysis of both national- and county-level usage information (Kaul and Jones, 2006) 

using state-level usage data obtained from USDA-NASS3

, Doane (www.doane.com; the 

full dataset is not provided due to its proprietary nature) and the California’s Department 

of Pesticide Regulation Pesticide Use Reporting (CDPR PUR) database4

 . CDPR PUR is 

considered a more comprehensive source of usage data than USDA-NASS or EPA 

proprietary databases, and thus the usage data reported for dicofol by county in this 

California-specific assessment were generated using CDPR PUR data. Eight years 

(1999-2006) of usage data were included in this analysis. Data from CDPR PUR were 

obtained for every pesticide application made on every use site at the section level 

(approximately one square mile) of the public land survey system. EPA/OPP/BEAD 

summarized these data to the county level by site, pesticide, and unit treated. Calculating 

county-level usage involved summarizing across all applications made within a section 

and then across all sections within a county for each use site and for each pesticide. The 

county level usage data that were calculated include: average annual pounds applied, 

 

3

 United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical 

Use Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop 

and state. See http://www.usda.gov/nass/pubs/estindx1.htm#agchem. 4

 The California Department of Pesticide Regulation’s Pesticide Use Reporting database provides a census 

of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm. 

30 
average annual area treated, and average and maximum application rate across all eight 

years. The units of area treated are also provided where available. 

 

Eight years (1999-2006) of usage data from CDPR PUR were obtained for every difocol 

application made on every use site in California at the field level. Total annual pounds 

applied and total annual area treated were calculated at the county level by site and 

pesticide active ingredient. Pesticide usage was also aggregated across all observations 

for eight years for each chemical-county-unit-treated combination. Because pesticide 

applications are made in different area units, the units of area treated are provided where 

available. Years in which there is no reported use in a county are included as zeros in the 

calculation of the eight-year averages for pounds and area treated. Averages reflect years 

without use. 

In California between 1999 and 2006, the majority of dicofol applied was used on cotton 

(64%), with lesser percentages applied to beans (13%), citrus (6%), and grapes (5%). 

Overall usage of dicofol in California fell from 1999 to 2002 to roughly 182,000 lbs/year, 

then increased to 212,000 lbs/year in 2004, and decreased to 101,000 lbs in 2006. 

Approximately 20% of dicofol applied in California is used in the 20 counties that 

contain CRLF critical habitat areas. A summary of dicofol usage for all California use 

sites is provided below in Table 6. These rates are consistent with the maximum 

application rates specified on the label and used in the modeling analysis, depicted in 

Table 9, with a few exceptions. For cucurbits, the maximum label application rate is 

0.625 lbs dicofol/A, while the application rates depicted in the CDPR PUR database were 

above this level. This can be attributed to an outlier reported for 1999 in San Joaquin 

County where 50 acres of squash were reportedly treated with 2,815 lbs of dicfol. For 

tomatoes, the maximum label application rate is 0.75 lbs dicofol/A, while the CDPR PUR 

reported application rates are above this level. Data available in the CDPR PUR database 

for tomatoes is divided into two groups, tomatoes and tomato processing. It appears that 

the use rates for tomato processing applications are increasing the values derived from 

the CDPR PUR database, as the statistical application rates data for tomatoes all fall 

below the maximum label rate, while all of the statistics for tomato processing are above 

the maximum label use rate. For Bermuda grass, the maximum label rate is 0.4 lbs 

dicofol/A. There was only one reported value for Bemuda grass in the CDPR PUR 

database for 0.48 lbs dicofol/A. Lastly, the maximum label application rate for 

ornamentals is 0.5 lbs dicofol/A. Outdoor flowers, transplants, and plants in containers 

were grouped into this category. It’s unclear as to how the area treated, reported in acres 

or square feet, was estimated in the database. As such, an underestimation in the area 

treated could result in an application rate higher than the maximum label rate. It should 

be noted that the uses considered in this risk assessment represent all currently registered 

uses according to a review of all current labels. No other uses are relevant to this 

assessment. Any other reported use, such as may be seen in the CDPR PUR database, 

represent either historic uses that have been canceled, mis-reported uses, or mis-use. 

Historical uses, mis-reported uses, and misuse are not considered part of the federal 

action and, therefore are not considered in this assessment. 

31 
Table 6. Summary of California Department of Pesticide Registration (CDPR) Pesticide Use 

Reporting (PUR) data and calculated annual application rates (1999 - 2006) for currently registered 

dicofol uses.1

 

Site Name 

Annual 

Average 

Pounds 

Avg App 

Rate 

(lbs ai/acre) 

Avg 95th% 

App Rate 

(lbs ai/acre) 

Avg 99th% 

App Rate 

(lbs ai/acre) 

Avg Max App 

Rate 

(lbs ai/acre) 

Beans (dry, snap, lima) 28,568 1.27 1.46 1.46 1.46 

Citrus2 13,427 2.26 2.70 2.70 2.70 

Cotton 142,539 1.01 1.25 1.25 1.25 

Cucurbits3 6,853 0.77 1.26 1.26 1.26 

Grapes 11,642 1.10 1.26 1.26 1.26 

Mint/Peppermint/Spearmint 138 0.87 1.00 1.00 1.00 

Peppers 184 0.66 0.71 0.71 0.71 

Pome Fruits4 1,769 1.64 1.89 1.89 1.89 

Stone Fruits5 7,676 1.34 1.55 1.55 1.55 

Strawberries 1,327 1.01 1.36 1.36 1.36 

Tomatoes 1,008 0.78 0.93 0.93 0.93 

Walnuts (English/black) 7,013 1.75 2.00 2.00 2.00 

Bermuda grass 90 0.48 0.48 0.48 0.48 

Ornamentals6 582 0.93 1.24 1.24 1.24 

1. Dicofol was not applied to hops, pecans, turf, sod farms, or outside building surfaces from 1999-2006, according to 

the PUR database. 

2. Specifically: grapefruit, lemons, oranges, tangelos, and tangerines. 

3. Specifically: cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash. 

4. Specifically: apples and pears. 

5. Specifically: apricots, cherries, nectarines, peaches, plums, and prunes. 

6. Specifically: outdoor flowers and plants. 

2.5. Assessed Species 

The CRLF was federally listed as a threatened species by U.S. FWS effective June 24, 

1996 (U.S. FWS 1996). It is one of two subspecies of the red-legged frog and is the 

largest native frog in the western United States (U.S. FWS 2002). A brief summary of 

information regarding CRLF distribution, reproduction, diet, and habitat requirements is 

provided below. Further information on the status, distribution, and life history of and 

specific threats to the CRLF is provided in Attachment 1. 

Final critical habitat for the CRLF was designated by U.S. FWS on April 13, 2006 (U.S. 

FWS 2006; 71 FR 19244-19346). Further information on designated critical habitat for 

the CRLF is provided in Section 2.6. 

32 
2.5.1. Distribution 

The CRLF is endemic to California and Baja California (Mexico) and historically 

inhabited 46 counties in California including the Central Valley and both coastal and 

interior mountain ranges (U.S. FWS 1996). Its range has been reduced by about 70%, 

and the species currently resides in 22 counties in California (U.S. FWS 1996). The 

species has an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings 

and Hayes 1994); however, nearly all of the known CRLF populations have been 

documented below 1,050 meters (3,500 feet) (U.S. FWS 2002). 

Populations currently exist along the northern California coast, northern Transverse 

Ranges (U.S. FWS 2002), foothills of the Sierra Nevada (5-6 populations), and in 

southern California south of Santa Barbara (two populations) (Fellers 2005a). Relatively 

larger numbers of CRLFs are located between Marin and Santa Barbara Counties 

(Jennings and Hayes 1994). A total of 243 streams or drainages are believed to be 

currently occupied by the species, with the greatest numbers in Monterey, San Luis 

Obispo, and Santa Barbara counties (U.S. FWS 1996). Occupied drainages or watersheds 

include all bodies of water that support CRLFs (i.e., streams, creeks, tributaries, 

associated natural and artificial ponds, and adjacent drainages), and habitats through 

which CRLFs can move (i.e., riparian vegetation, uplands) (U.S. FWS 2002). 

The distribution of CRLFs within California is addressed in this assessment using four 

categories of location including recovery units, core areas, designated critical habitat, and 

known occurrences of the CRLF reported in the California Natural Diversity Database 

(CNDDB) that are not included within core areas and/or designated critical habitat 

(Figure 3). Recovery units, core areas, and other known occurrences of the CRLF from 

the CNDDB are described in further detail in Attachment I, and designated critical habitat 

is addressed in Section 2.6. Recovery units are large areas defined at the watershed level 

that have similar conservation needs and management strategies. The recovery unit is 

primarily an administrative designation, and land area within the recovery unit boundary 

is not exclusively CRLF habitat. Core areas are smaller areas within the recovery units 

that comprise portions of the species’ historic and current range and have been 

determined by U.S. FWS to be important in the preservation of the species. Designated 

critical habitat is generally contained within the core areas, although a number of critical 

habitat units are outside the boundaries of core areas, but within the boundaries of the 

recovery units. Additional information on CRLF occurrences from the CNDDB is used 

to cover the current range of the species not included in core areas and/or designated 

critical habitat, but within the recovery units. 

Other Known Occurrences from the CNDBB 

The CNDDB provides location and natural history information on species found in 

California. The CNDDB serves as a repository for historical and current species location 

sightings. Information regarding known occurrences of CRLFs outside of the currently 

occupied core areas and designated critical habitat is considered in defining the current 

33 
range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb_info.html for additional 

information on the CNDDB. 

Recovery Units

1. Sierra Nevada Foothills and Central Valley

2. North Coast Range Foothills and Western 

Sacramento River Valley

3. North Coast and North San Francisco Bay

4. South and East San Francisco Bay

5. Central Coast

6. Diablo Range and Salinas Valley

7. Northern Transverse Ranges and Tehachapi

Mountains

8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River

2. Yuba River- S. Fork Feather River

3. Traverse Creek/ Middle Fork/ American R. Rubicon

4. Cosumnes River

5. South Fork Calaveras River*

6. Tuolumne River*

7. Piney Creek*

8. Cottonwood Creek

9. Putah Creek – Cache Creek*

10. Lake Berryessa Tributaries

11. Upper Sonoma Creek

12. Petaluma Creek – Sonoma Creek

13. Pt. Reyes Peninsula

14. Belvedere Lagoon

15. Jameson Canyon – Lower Napa River

16. East San Francisco Bay

17. Santa Clara Valley

18. South San Francisco Bay

19. Watsonville Slough-Elkhorn Slough

20. Carmel River – Santa Lucia

21. Gablan Range

22. Estero Bay

23. Arroyo Grange River

24. Santa Maria River – Santa Ynez River

25. Sisquoc River

26. Ventura River – Santa Clara River

27. Santa Monica Bay – Venura Coastal Streams

28. Estrella River

29. San Gabriel Mountain*

30. Forks of the Mojave*

31. Santa Ana Mountain*

32. Santa Rosa Plateau

33. San Luis Ray*

34. Sweetwater*

35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map

Recovery Units

1. Sierra Nevada Foothills and Central Valley

2. North Coast Range Foothills and Western 

Sacramento River Valley

3. North Coast and North San Francisco Bay

4. South and East San Francisco Bay

5. Central Coast

6. Diablo Range and Salinas Valley

7. Northern Transverse Ranges and Tehachapi

Mountains

8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River

2. Yuba River- S. Fork Feather River

3. Traverse Creek/ Middle Fork/ American R. Rubicon

4. Cosumnes River

5. South Fork Calaveras River*

6. Tuolumne River*

7. Piney Creek*

8. Cottonwood Creek

9. Putah Creek – Cache Creek*

10. Lake Berryessa Tributaries

11. Upper Sonoma Creek

12. Petaluma Creek – Sonoma Creek

13. Pt. Reyes Peninsula

14. Belvedere Lagoon

15. Jameson Canyon – Lower Napa River

16. East San Francisco Bay

17. Santa Clara Valley

18. South San Francisco Bay

19. Watsonville Slough-Elkhorn Slough

20. Carmel River – Santa Lucia

21. Gablan Range

22. Estero Bay

23. Arroyo Grange River

24. Santa Maria River – Santa Ynez River

25. Sisquoc River

26. Ventura River – Santa Clara River

27. Santa Monica Bay – Venura Coastal Streams

28. Estrella River

29. San Gabriel Mountain*

30. Forks of the Mojave*

31. Santa Ana Mountain*

32. Santa Rosa Plateau

33. San Luis Ray*

34. Sweetwater*

35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map

Figure 3. Recovery unit, core area, critical habitat, and occurrence designations for CRLF. 

34 
2.5.2. Reproduction 

CRLFs breed primarily in ponds; however, they may also breed in quiescent streams, 

marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (U.S. FWS 2002), 

CRLFs breed from November through late April. Peaks in spawning activity vary 

geographically; Fellers (2005b) reports peak spawning as early as January in parts of 

coastal central California. Eggs are fertilized as they are being laid. Egg masses are 

typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails 

(Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and 

Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size 

between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after 

fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported 

to be infrequent and most mortality is associated with the larval stage (particularly 

through predation by fish); however, predation on eggs by newts has also been reported 

(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles 

(terrestrial-phase), typically between May and September (Jennings and Hayes 1994, 

U.S. FWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until 

the following year) (Fellers 2005b, U.S. FWS 2002). Males reach sexual maturity at 2 

years, and females reach sexual maturity at 3 years of age; adults have been reported to 

live 8 to 10 years (U.S. FWS 2002). Figure 4 depicts CRLF annual reproductive timing. 

J F M A M J J A S O N D

Light Blue = Breeding/Egg Masses

Green = Tadpoles (except those that over-winter)

Orange = Young Juveniles

Adults and juveniles can be present all year

J F M A M J J A S O N D

Light Blue = Breeding/Egg Masses

Green = 

Orange = Young Juveniles

Adults and juveniles can be present all year

Tadpoles (except those that over-winter)

Figure 4. CRLF reproductive events by month. 

2.5.3. Diet 

Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied 

specifically, it is assumed that their diet is similar to that of other frog species, with the 

aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus 

(U.S. FWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar 1980) 

via mouthparts designed for effective grazing of periphyton (Wassersug 1984; 

Kupferberg et al. 1994; Kupferberg 1997; Altig and McDiarmid 1999). 

Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs 

greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial35 
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the 

shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study 

examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as 

many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda, 

Insecta, and Mollusca. The most commonly observed prey species were larval alderflies 

(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp). 

The preferred prey species, however, was the sowbug (Hayes and Tennant 1985). This 

study suggests that CRLFs forage primarily above water, although the authors note other 

data reporting that adults also feed under water, are cannibalistic, and consume fish. For 

larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs, 

and fish, although aquatic and terrestrial invertebrates were the most numerous food 

items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at 

night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985). 

2.5.4. Habitat 

CRLFs require aquatic habitat for breeding, but also use other habitat types including 

riparian and upland areas throughout their life cycle. CRLF use of their environment 

varies; they may complete their entire life cycle in a particular habitat or they may utilize 

multiple habitat types. Overall, populations are most likely to exist where multiple 

breeding areas are embedded within varying habitats used for dispersal (U.S. FWS 2002). 

Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.

1997). Dense vegetation close to water, shading, and water of moderate depth are habitat 

features that appear especially important for CRLF (Hayes and Jennings 1988). 

Breeding sites include streams, deep pools, backwaters within streams and creeks, ponds, 

marshes, sag ponds (land depressions between fault zones that have filled with water), 

dune ponds, and lagoons. Breeding adults have been found near deep (0.7 m) still or 

slow moving water surrounded by dense vegetation (U.S. FWS 2002); however, the 

largest number of tadpoles have been found in shallower pools (0.26 – 0.5 m) (Reis 

1999). Data indicate that CRLFs do not frequently inhabit vernal pools, as conditions in 

these habitats generally are not suitable (Hayes and Jennings 1988). 

CRLFs also frequently breed in artificial impoundments such as stock ponds, although 

additional research is needed to identify habitat requirements within artificial ponds (U.S. 

FWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation closely associated 

with deep-water pools bordered with cattails and dense stands of overhanging vegetation 

(http://www.fws.gov/endangered/features/rl_frog/rlfrog.html#where). 

In general, dispersal and habitat use depends on climatic conditions, habitat suitability, 

and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The 

foraging quality of the riparian habitat depends on moisture, composition of the plant 

community, and presence of pools and backwater aquatic areas for breeding. CRLFs can 

be found living within streams at distances up to 3 km (2 miles) from their breeding site 

and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up 

to 77 days (U.S. FWS 2002). 

36 
During dry periods, the CRLF is rarely found far from water, although it will sometimes 

disperse from its breeding habitat to forage and seek other suitable habitat under downed 

trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to 

Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter 

as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as 

refugia; these cracks may provide moisture for individuals avoiding predation and solar 

exposure (Alvarez 2000). 

2.6. Designated Critical Habitat 

In a final rule published on April 13, 2006, 34 separate units of critical habitat were 

designated for the CRLF by U.S. FWS (U.S. FWS 2006; FR 51 19244-19346). A 

summary of the 34 critical habitat units relative to U.S. FWS-designated recovery units 

and core areas (previously discussed in Section 2.5) is provided in Attachment 1. 

‘Critical habitat’ is defined in the ESA as the geographic area occupied by the species at 

the time of the listing where the physical and biological features necessary for the 

conservation of the species exist, and there is a need for special management to protect 

the listed species. It may also include areas outside the occupied area at the time of 

listing if such areas are ‘essential to the conservation of the species.’ All designated 

critical habitat for the CRLF was occupied at the time of listing. Critical habitat receives 

protection under Section 7 of the ESA (Section 7) through prohibition against destruction 

or adverse modification with regard to actions carried out, funded, or authorized by a 

federal Agency. Section 7 requires consultation on federal actions that are likely to result 

in the destruction or adverse modification of critical habitat. 

To be included in a critical habitat designation, the habitat must be ‘essential to the 

conservation of the species.’ Critical habitat designations identify, to the extent known 

using the best scientific and commercial data available, habitat areas that provide 

essential life cycle needs of the species or areas that contain certain primary constituent 

elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to, 

space for individual and population growth and for normal behavior; food, water, air, 

light, minerals, or other nutritional or physiological requirements; cover or shelter; sites 

for breeding, reproduction, rearing (or development) of offspring; and habitats that are 

protected from disturbance or are representative of the historic geographical and 

ecological distributions of a species. The designated critical habitat areas for the CRLF 

are considered to have the following PCEs that justify critical habitat designation: 

• Breeding aquatic habitat; 

• Non-breeding aquatic habitat; 

• Upland habitat; and 

• Dispersal habitat. 

Further description of these habitat types is provided in Attachment 1. 

37 
Occupied habitat may be included in the critical habitat only if essential features within 

the habitat may require special management or protection. Therefore, U.S. FWS does not 

include areas where existing management is sufficient to conserve the species. Critical 

habitat is designated outside the geographic area presently occupied by the species only 

when a designation limited to its present range would be inadequate to ensure the 

conservation of the species. For the CRLF, all designated critical habitat units contain all 

four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in 

April 2006. The FR notice designating critical habitat for the CRLF includes a special 

rule exempting routine ranching activities associated with livestock ranching from 

incidental take prohibitions. The purpose of this exemption is to promote the 

conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate 

of conversion to other land uses that are incompatible with CRLF conservation. See 

Attachment I for a full explanation on this special rule. 

U.S. FWS has established adverse modification standards for designated critical habitat 

(U.S. FWS 2006). Activities that may destroy or adversely modify critical habitat are 

those that alter the PCEs and jeopardize the continued existence of the species. 

Evaluation of actions related to use of dicofol that may alter the PCEs of the CRLF’s 

critical habitat form the basis of the critical habitat impact analysis. According to U.S. 

FWS (2006), activities that may affect critical habitat and therefore result in adverse 

effects to the CRLF include, but are not limited to the following: 

(1) Significant alteration of water chemistry or temperature to levels beyond the 

tolerances of the CRLF that result in direct or cumulative adverse effects to 

individuals and their life-cycles. 

(2) Alteration of chemical characteristics necessary for normal growth and viability 

of juvenile and adult CRLFs. 

(3) Significant increase in sediment deposition within the stream channel or pond or 

disturbance of upland foraging and dispersal habitat that could result in 

elimination or reduction of habitat necessary for the growth and reproduction of 

the CRLF by increasing the sediment deposition to levels that would adversely 

affect their ability to complete their life cycles. 

(4) Significant alteration of channel/pond morphology or geometry that may lead to 

changes to the hydrologic functioning of the stream or pond and alter the timing, 

duration, water flows, and levels that would degrade or eliminate the CRLF 

and/or its habitat. Such an effect could also lead to increased sedimentation and 

degradation in water quality to levels that are beyond the CRLF’s tolerances. 

(5) Elimination of upland foraging and/or aestivating habitat or dispersal habitat. 

(6) Introduction, spread, or augmentation of non-native aquatic species in stream 

segments or ponds used by the CRLF. 

(7) Alteration or elimination of the CRLF’s food sources or prey base (also 

evaluated as indirect effects to the CRLF). 

As previously noted in Section 2.1, the Agency believes that the analysis of direct and 

indirect effects to listed species provides the basis for an analysis of potential effects on 

the designated critical habitat. Because dicofol is expected to directly impact living 

38 
organisms within the action area, critical habitat analysis for dicofol is limited in a 

practical sense to those PCEs of critical habitat that are biological or that can be 

reasonably linked to biologically mediated processes. 

2.7. Action Area 

For listed species assessment purposes, the action area is considered to be the area 

affected directly or indirectly by the federal action and not merely the immediate area 

involved in the action (50 CFR 402.02). It is recognized that the overall action area for 

the national registration of dicofol is likely to encompass considerable portions of the 

United States based on the large array of agricultural uses. However, the scope of this 

assessment limits consideration of the overall action area to those portions that may be 

applicable to the protection of the CRLF and its designated critical habitat within the state 

of California. The Agency’s approach to defining the action area under the provisions of 

the Overview Document (U.S. EPA 2004) considers the results of the risk assessment 

process to establish boundaries for that action area with the understanding that exposures 

below the Agency’s defined Levels of Concern (LOCs) constitute a no-effect threshold. 

For the purposes of this assessment, attention will be focused on the footprint of the 

action (i.e., the area where pesticide application occurs), plus all areas where offsite 

transport (i.e., spray drift, downstream dilution, etc.) may result in potential exposure 

within the state of California that exceeds the Agency’s LOCs. 

Deriving the geographical extent of this portion of the action area is based on 

consideration of the types of effects that dicofol may be expected to have on the 

environment, the exposure levels to dicofol that are associated with those effects, and the 

best available information concerning the use of dicofol and its fate and transport within 

the state of California. Specific measures of ecological effect for the CRLF that define 

the action area include any direct and indirect toxic effect to the CRLF and any potential 

effects to its critical habitat, including reduction in survival, growth, and fecundity as 

well as the full suite of sublethal effects available in the effects literature. Therefore, the 

action area extends to a point where environmental exposures are below any measured 

lethal or sublethal effect threshold for any biological entity at the whole organism, organ, 

tissue, and cellular level of organization. In situations where it is not possible to 

determine the threshold for an observed effect, the action area is not spatially limited and 

is assumed to be the entire state of California. 

The definition of action area requires a stepwise approach that begins with an 

understanding of the federal action. The federal action is defined by the currently labeled 

uses for dicofol. An analysis of labeled uses and review of available product labels was 

completed. Several of the current labels are special local needs (SLN) labels for states 

other than California and several currently labeled uses on FIFRA section 3 labels are 

restricted to specific states other than California and therefore, are excluded from this 

assessment. For those uses relevant to the CRLF, the analysis indicates that, for dicofol, 

the following agricultural uses are considered as part of the federal action evaluated in 

this assessment: beans (dry, snap, and lima), citrus (specifically, grapefruit, kumquats, 

lemons, limes, oranges, tangelos, and tangerines), cotton, cucurbits (specifically, 

cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer 

39 
squash), grapes, hops, mint, pecans, peppers, pome fruits (specifically, apples, 

crabapples, pears, and quince), stone fruits (specifically, apricots, sweet and sour 

cherries, nectarines, peaches, plums, and prunes), strawberries, tomatoes, and walnuts. In 

addition, the following non-food and non-agricultural uses are considered: Bermuda 

grass, turf/ornamental uses (specifically, turf grasses, nursery stock, flowers, shade trees, 

woody shrubs and vines, and sod farms) and outside building surfaces (nonagricultural). 

Following a determination of the assessed uses, an evaluation of the potential “footprint” 

of dicofol use patterns (i.e., the area where pesticide application occurs) is determined. 

This “footprint” represents the initial area of concern, based on an analysis of available 

land cover data for the state of California. The initial area of concern is defined as all 

land cover types and the stream reaches within the land cover areas that represent the 

labeled uses described above. A map representing all the land cover types that make up 

the initial area of concern for dicofol is presented in Figure 5. In this figure, potential 

uses of dicofol on all field crops as well as orchards and vineyards are represented by the 

cultivated crops landcover data obtained from NLCD. In addition, potential use areas of 

dicofol on tree fruits and grapes are represented by the orchard and vineyard land cover 

data obtained from California GAP. Turf uses of dicofol are depicted as a derived NLCD 

class based on developed classes and the impervious surface layer with corrections 

applied. Additional information on the landcover data used to define the initial area of 

concern is provided in Appendix B. 

40 
Figure 5. Initial area of concern for crops described by agricultural landcover which corresponds to 

potential dicofol use sites. This map represents the area potentially directly affected by the federal 

action. 

41 
Once the initial area of concern is defined, the next step is to define the potential 

boundaries of the action area by determining the extent of offsite transport via spray drift 

and runoff where exposure of one or more taxonomic groups to the pesticide exceeds the 

listed species LOCs. As previously discussed, the action area is defined by the most 

sensitive measure of direct and indirect ecological toxic effects including reduction in 

survival, growth, reproduction, and the entire suite of sublethal effects from valid, peerreviewed studies. 

Once the potential boundaries of the area of concern are defined, the next step is to 

compare the extent of that area with the results of the screening-level risk assessment. In 

this assessment, transport of dicofol through erosion and spray drift is considered in 

deriving quantitative estimates of dicofol exposure to CRLF, its prey and its habitats. 

Since this screening-level risk assessment defines taxa that are predicted to be exposed 

through runoff and drift to dicofol at concentrations above the Agency’s Levels of 

Concern (LOC), there is a need to expand the action area to include areas that are 

affected indirectly by this federal action. Because of the lack of a NOAEC in several 

chronic toxicity studies with birds, described later in Section 4.3.1, the action area for 

dicofol is established as the entire state of California. Additional analysis related to the 

intersection of the dicofol action area and CRLF habitat used in determining the action 

area is described in section 5.2.5 and in Appendix B. 

2.8. Assessment Endpoints and Measures of Ecological Effect 

Assessment endpoints are defined as “explicit expressions of the actual environmental 

value that is to be protected.”5

 Selection of the assessment endpoints is based on valued 

entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of 

its designated critical habitat), the ecosystems potentially at risk (e.g., waterbodies, 

riparian vegetation, and upland and dispersal habitats), the migration pathways of dicofol 

(e.g., runoff, spray drift, etc.), and the routes by which ecological receptors are exposed 

to dicofol (e.g., direct contact, etc.). 

2.8.1. Assessment Endpoints for the CRLF 

Assessment endpoints for the CRLF include direct toxic effects on the survival, 

reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of 

the prey base or effects to its habitat. In addition, potential effects to critical habitat is 

assessed by evaluating potential effects to PCEs, which are components of the habitat 

areas that provide essential life cycle needs of the CRLF. Each assessment endpoint 

requires one or more “measures of ecological effect,” defined as changes in the attributes 

of an assessment endpoint or changes in a surrogate entity or attribute in response to 

exposure to a pesticide. Specific measures of ecological effect are generally evaluated 

based on acute and chronic toxicity information from registrant-submitted guideline tests 

that are performed on a limited number of organisms. Additional ecological effects data 

from the open literature are also considered. It should be noted that assessment endpoints 

 

5

 U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001. 

42 
are limited to direct and indirect effects associated with survival, growth, and fecundity, 

and do not include the full suite of sublethal effects used to define the action area. 

According the Overview Document (U.S. EPA 2004), the Agency relies on acute and 

chronic effects endpoints that are either direct measures of impairment of survival, 

growth, or fecundity or endpoints for which there is a scientifically robust, peer reviewed 

relationship that can quantify the impact of the measured effect endpoint on the 

assessment endpoints of survival, growth, and fecundity. 

A complete discussion of all the toxicity data available for this risk assessment, including 

resulting measures of ecological effect selected for each taxonomic group of concern, is 

included in Section 4 of this document. A summary of the assessment endpoints and 

measures of ecological effect selected to characterize potential assessed direct and 

indirect CRLF risks associated with exposure to dicofol is provided in Table 7. 

43 
Table 7. Assessment endpoints and measures of ecological effects for dicofol.

Assessment Endpoint Measures of Ecological Effects3

Aquatic-Phase CRLF (Eggs, larvae, juveniles, and adults)1

Direct Effects 

1. Survival, growth, and reproduction of 

CRLF 

1a. LC50 = 53.0 μg/L, based on most sensitive acute 

exposure data available for fish 

1b. NOAEC = 4.4 μg a.i./L, based on most sensitive 

chronic exposure data available for fish 

Indirect Effects and Critical Habitat Effects 

2. Survival, growth, and reproduction of 

CRLF individuals via indirect effects on 

aquatic prey food supply (i.e., fish, freshwater 

invertebrates, non-vascular plants) 

2a. EC50 = 140 μg/L, based on most sensitive acute 

exposure data available for aquatic invertebrates 

2b. NOAEC = 19 μg a.i./L, based on most sensitive 

chronic exposure data available for aquatic invertebrates 

2c. LC50 = 53.0 μg/L, based on most sensitive acute 

exposure data available for fish 

2d. NOAEC = 4.4 μg a.i./L, based on most sensitive 

chronic exposure data available for fish 

2e. EC50 > 5,000, <10,000 μg/L, based on available data 

for green algae 

3. Survival, growth, and reproduction of 

CRLF individuals via indirect effects on 

habitat, cover, food supply, and/or primary 

productivity (i.e., aquatic plant community) 

3a. EC50 > 5,000, <10,000 μg/L, based on available data 

for green algae 

4. Survival, growth, and reproduction of 

CRLF individuals via effects to riparian 

vegetation 

No data are available to quantify an endpoint to represent 

effects of dicofol exposures to vascular plants. 

Terrestrial-Phase CRLF (Juveniles and adults) 

Direct Effects 

5. Survival, growth, and reproduction of 

CRLF individuals via direct effects on 

terrestrial phase adults and juveniles 

4a. LD50 = 265 mg a.i./kg bw, based on most sensitive 

acute oral exposure data available for birds2 

4b. LC50 = 903 ppm, based on most sensitive subacute 

dietary exposure data available for birds2 

4c. NOAEC = 1 ppm, based on most sensitive chronic 

exposure data available for birds2 

Indirect Effects and Critical Habitat Effects 

6. Survival, growth, and reproduction of 

CRLF individuals via effects on terrestrial 

prey (i.e., terrestrial invertebrates, small 

mammals , and frogs) 

5a. LD50>50 μg a.i./bee, based on most sensitive acute 

oral exposure data available for terrestrial invertebrates 

5b. LD50 = 587 mg/kg-bw, based on most sensitive acute 

oral exposure data available for mammals 

5c. NOAEC = 5 ppm, based on most sensitive chronic 

exposure data available for mammals 

5d. LD50 = 265 mg a.i./kg bw, based on most sensitive 

acute oral exposure data available for birds2 

5e. LC50 = 903 ppm, based on most sensitive subacute 

dietary exposure data available for birds2 

5f. NOAEC = 1 ppm, based on most sensitive chronic 

exposure data available for birds2

7. Survival, growth, and reproduction of 

CRLF individuals via indirect effects on 

habitat (i.e., riparian and upland vegetation) 

No data are available to quantify an endpoint to represent 

effects of dicofol exposures to vascular plants. 

1

 Adult frogs are no longer in the “aquatic phase” of the amphibian life cycle; however, submerged adult frogs are 

considered “aquatic” for the purposes of this assessment because exposure pathways in the water are considerably 

different that exposure pathways on land. 

2

 Birds are used as surrogates for terrestrial phase amphibians. 

3

See Table 22 and Table 27 for citations and additional information.

44 
2.8.2. Assessment Endpoints for Designated Critical Habitat 

As previously discussed, designated critical habitat is assessed to evaluate actions related 

to the use of dicofol that may alter the PCEs of the CRLF’s critical habitat. PCEs for the 

CRLF were previously described in Section 2.6. Actions that may modify critical habitat 

are those that alter the PCEs and jeopardize the continued existence of the CRLF. 

Therefore, these actions are identified as assessment endpoints. It should be noted that 

evaluation of PCEs as assessment endpoints is limited to those of a biological nature (i.e., 

the biological resource requirements for the listed species associated with the critical 

habitat) and those for which dicofol effects data are available. Adverse modification to 

the critical habitat of the CRLF includes, but is not limited to, those listed in Section 2.6. 

Measures of such possible effects by labeled use of dicofol on critical habitat of the 

CRLF are described in Table 8. Some components of these PCEs are associated with 

physical abiotic features (e.g., presence and/or depth of a water body, or distance between 

two sites), which are not expected to be measurably altered by use of pesticides. 

Assessment endpoints used for the analysis of designated critical habitat are based on the 

adverse modification standard established by U.S. FWS (2006). 

45 
Table 8. Summary of dicofol assessment endpoints and measures of ecological effect for primary 

constituent elements of designated critical habitat1

. 

Assessment Endpoint Measures of Ecological Effect3

Aquatic-Phase CRLF PCEs (Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat) 

Alteration of channel/pond morphology or geometry 

and/or increase in sediment deposition within the 

stream channel or pond: aquatic habitat (including 

riparian vegetation) provides for shelter, foraging, 

predator avoidance, and aquatic dispersal for juvenile 

and adult CRLFs. 

No data are available to quantify an endpoint to represent 

effects of dicofol exposures to vascular plants. 

Alteration in water chemistry/quality including 

temperature, turbidity, and oxygen content necessary 

for normal growth and viability of juvenile and adult 

CRLFs and their food source.

1e. EC50 > 5,000, <10,000 μg/L, based on available data for 

green algae 

No data are available for assessing the effects of exposures 

of dicofol to vascular plants. 

Alteration of other chemical characteristics necessary 

for normal growth and viability of CRLFs and their 

food source. 

1a. LC50 = 53.0 μg/L, based on most sensitive acute 

exposure data available for fish 

1b. NOAEC = 4.4 μg a.i./L, based on most sensitive 

chronic exposure data available for fish 

1c. EC50 = 140 μg/L, based on most sensitive acute 

exposure data available for aquatic invertebrates 

1d. NOAEC = 19 μg a.i./L, based on most sensitive 

chronic exposure data available for aquatic invertebrates 

1e. EC50 > 5,000, <10,000 μg/L, based on available data for 

green algae 

Reduction and/or modification of aquatic-based food 

sources for pre-metamorphs (e.g., algae) 

1e. EC50 > 5,000, <10,000 μg/L, based on available data for 

green algae 

Terrestrial-Phase CRLF PCEs (Upland Habitat and Dispersal Habitat) 

Elimination and/or disturbance of upland habitat; 

ability of habitat to support food source of CRLFs: 

Upland areas within 200 ft of the edge of the riparian 

vegetation or dripline surrounding aquatic and riparian 

habitat that are comprised of grasslands, woodlands, 

and/or wetland/riparian plant species that provides the 

CRLF shelter, forage, and predator avoidance 

No data are available to quantify an endpoint to represent 

effects of dicofol exposures to vascular plants. 

Elimination and/or disturbance of dispersal habitat: 

Upland or riparian dispersal habitat within designated 

units and between occupied locations within 0.7 mi of 

each other that allow for movement between sites 

including both natural and altered sites which do not 

contain barriers to dispersal 

No data are available to quantify an endpoint to represent 

effects of dicofol exposures to vascular plants. 

Reduction and/or modification of food sources for 

terrestrial phase juveniles and adults 

2a. LD50>50 μg a.i./bee, based on most sensitive acute 

exposure data available for terrestrial invertebrates 

2b. LD50 = 587 mg/kg-bw, based on most sensitive acute 

oral exposure data available for mammals 

2c. NOAEC = 5 mg/kg-bw, based on most sensitive chronic 

exposure data available for mammals 

2d. LD50 = 265 mg a.i./kg bw, based on most sensitive 

acute oral exposure data available for birds2

 

2e. LC50 = 903 mg/kg-bw, based on most sensitive 

subacute dietary exposure data available for birds2

 

2f. NOAEC = 1 mg/kg-bw, based on most sensitive chronic 

exposure data available for birds2

46 
Assessment Endpoint Measures of Ecological Effect3

Alteration of chemical characteristics necessary for 

normal growth and viability of juvenile and adult 

CRLFs and their food source. 

3a. LD50 = 265 mg a.i./kg bw, based on most sensitive 

acute oral exposure data available for birds2

 

3b. LC50 = 903 mg/kg-bw, based on most sensitive 

subacute dietary exposure data available for birds2

 

3c. NOAEC = 1 mg/kg-bw, based on most sensitive chronic 

exposure data available for birds2

1 Physico-chemical water quality parameters such as salinity, pH, and hardness are not evaluated because these 

processes are not biologically mediated and, therefore, are not relevant to the endpoints included in this assessment. 

2Birds are used as surrogates for terrestrial phase amphibians. 

3 See Table 22 and Table 27 for citations and additional information.

2.9. Conceptual Model 

2.9.1. Risk Hypotheses 

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in 

assessment endpoints) and may be based on theory and logic, empirical data, 

mathematical models, or probability models (U.S. EPA 1998a). For this assessment, the 

risk is stressor-linked, where the stressor is the release of dicofol to the environment. The 

following risk hypotheses are presumed for this endangered species assessment: 

The labeled use of dicofol within the action area may: 

• directly affect the CRLF by causing mortality or by adversely affecting growth or 

fecundity; 

• indirectly affect the CRLF by reducing or changing the composition of food 

supply; 

• indirectly affect the CRLF or affect designated critical habitat by reducing or 

changing the composition of the aquatic plant community in the ponds and 

streams comprising the species’ current range and designated critical habitat, thus 

affecting primary productivity and/or cover; 

• indirectly affect the CRLF or affect designated critical habitat by reducing or 

changing the composition of the terrestrial plant community (i.e., riparian habitat) 

required to maintain acceptable water quality and habitat in the ponds and streams 

comprising the species’ current range and designated critical habitat; 

• affect the designated critical habitat of the CRLF by reducing or changing 

breeding and non-breeding aquatic habitat via effects to water quality parameters, 

habitat morphology, and/or sedimentation; 

• affect the designated critical habitat of the CRLF by reducing the food supply 

required for normal growth and viability of juvenile and adult CRLFs; 

• affect the designated critical habitat of the CRLF by reducing or changing upland 

habitat within 200 ft of the edge of the riparian vegetation necessary for shelter, 

foraging, and predator avoidance; 

• affect the designated critical habitat of the CRLF by reducing or changing 

dispersal habitat within designated units and between occupied locations within 

47 
0.7 mi of each other that allow for movement between sites including both natural 

and altered sites which do not contain barriers to dispersal; or, 

• affect the designated critical habitat of the CRLF by altering chemical 

characteristics necessary for normal growth and viability of juvenile and adult 

CRLFs. 

2.9.2. Diagram 

The conceptual model is a graphic representation of the structure of the risk assessment. 

It specifies the dicofol release mechanisms, biological receptor types, and effects 

endpoints of potential concern. The conceptual models for aquatic and terrestrial 

exposures are shown in Figure 6 and in Figure 7, respectively, which include the 

conceptual models for the aquatic and terrestrial PCE components of critical habitat. 

Exposure routes shown in dashed lines are not quantitatively considered because the 

contribution of those potential exposure routes to potential risks to the CRLF and 

modification to designated critical habitat is expected to be negligible. 

Stressor

Source

Receptors

Attribute

Change

Dicofol isomers, degradates, and DDT applied to use site

Spray drift

Fish/aquatic-phase 

amphibians

**Piscivorous mammals 

and birds 

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae

Reduction in prey

Modification of PCEs

related to prey availability

Habitat integrity

Reduction in primary productivity

Reduced cover

Communit y change

Modif ication of PCEs related to 

habit at

Surface water/

Sediment

Runoff

Aquatic Animals

Invertebrates

Vertebrates

Exposure

Media

Uptake/gills 

or integument

Ingestion Ingestion

Long range 

atmospheric 

transport

Wet/dry deposition

Soil Groundwater

Uptake/gills 

or integument

Aquatic Plants

Non-vascular

Vascular

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways see 

Figure 7

Figure 6. Conceptual model for dicofol effects on aquatic-phase of the CRLF. 

48 
Stressor

Source

Receptors

Attribute

Change

Dicofol isomers, degradates, and DDT applied to use site

Direct

application Spray drift

Birds/terrestrialphase 

amphibians/

reptiles/mammals

Terrestrial 

insects

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey

Modification of PCEs

related to prey availability

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Modification of PCEs related to 

habitat

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs)

Runoff

Mammals/ 

Birds

Exposure

Media

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport

Root uptake

Wet/dry deposition

Terrestrialphase 

amphibians

Ingestion

Figure 7. Conceptual model for dicofol effects on terrestrial phase of the CRLF. 

2.10. Analysis Plan 

In order to address the risk hypothesis, the potential for direct and indirect effects to the 

CRLF, its prey, and its habitat is estimated. In the following sections, the use, 

environmental fate, and ecological effects of dicofol are characterized and integrated to 

assess the risks. This is accomplished using a risk quotient (ratio of exposure 

concentration to effects concentration) approach. Although risk is often defined as the 

likelihood and magnitude of adverse ecological effects, the risk quotient-based approach 

does not provide a quantitative estimate of likelihood and/or magnitude of an adverse 

effect. However, as outlined in the Overview Document (U.S. EPA 2004), the likelihood 

of effects to individual organisms from particular uses of dicofol is estimated using the 

probit dose-response slope and either the level of concern (discussed below) or actual 

calculated risk quotient value. 

49 
2.10.1. Measures of Exposure 

The environmental fate properties of dicofol along with available monitoring data 

indicate that runoff and spray drift are the principle potential transport mechanisms of 

dicofol to the aquatic and terrestrial habitats of the CRLF. In this assessment, transport 

of dicofol through runoff and spray drift is considered in deriving quantitative estimates 

of dicofol exposure to CRLF, its prey and its habitats. Because of its low vapor pressure 

and persistence in the air (T1/2 > 2 days), dicofol has the potential for long range transport. 

It should be noted, however, that recent ambient air monitoring in agricultural 

communities in California does not indicate volatilization of dicofol (See Section 

3.2.4.2). 

Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of dicofol using maximum labeled application rates 

and methods of application. The models used to predict aquatic EECs are the Pesticide 

Root Zone Model coupled with the Exposure Analysis Model System (PRZM/EXAMS). 

The model used to predict terrestrial EECs on food items is T-REX. The model used to 

derive EECs relevant to terrestrial and wetland plants is TerrPlant. These models are 

parameterized using relevant reviewed registrant-submitted environmental fate data. 

Additionally, the Generic Estimated Environmental Concentration Model (GENEEC2) 

was used to characterize the potential impacts due to the DDT manufacturing 

intermediate in dicofol (see Appendix F). 

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are simulation models 

coupled with the input shell pe5.pl (Aug 2007) to generate daily exposures and 1-in-10 

year EECs of dicofol that may occur in surface water bodies adjacent to application sites 

receiving dicofol through runoff and spray drift. PRZM simulates pesticide application, 

movement and transformation on an agricultural field and the resultant pesticide loadings 

to a receiving water body via runoff, erosion and spray drift. EXAMS simulates the fate 

of the pesticide and resulting concentrations in the water body. The standard scenario 

used for ecological pesticide assessments assumes application to a 10-hectare agricultural 

field that drains into an adjacent 1-hectare water body, 2-meters deep (20,000 m3

 volume) 

with no outlet. PRZM/EXAMS was used to estimate screening-level exposure of aquatic 

organisms to dicofol. The measure of exposure for aquatic species is the 1-in-10 year 

return peak or rolling mean concentration. The 1-in-10 year peak is used for estimating 

acute exposures of direct effects to the CRLF, as well as indirect effects to the CRLF 

through effects to potential prey items, including: algae, aquatic invertebrates, fish and 

frogs. The 1-in-10-year 60-day mean is used for assessing chronic exposure to the CRLF 

and fish and frogs serving as prey items; the 1-in-10-year 21-day mean is used for 

assessing chronic exposure for aquatic invertebrates, which are also potential prey items. 

GENEEC2 Version 2.0 is a screening-level model used in pesticide aquatic ecological 

risk assessments. Similar to PRZM/EXAMS, GENEEC2 uses the soil/water partition 

coefficient and degradation kinetic data to estimate runoff from a ten hectare field into a 

one hectare by two meter deep “standard” pond. 

50 
Exposure estimates for the terrestrial-phase CRLF and terrestrial invertebrates and 

mammals (serving as potential prey) assumed to be in the target area or in an area 

exposed to spray drift are derived using the T-REX model (version 1.3.1, 12/07/2006). 

This model incorporates the Kenega nomograph, as modified by Fletcher et al. (1994), 

which is based on a large set of actual field residue data. The upper limit values from the 

nomograph represented the 95th percentile of residue values from actual field 

measurements (Hoerger and Kenega 1972). For modeling purposes, direct exposures of 

the CRLF to dicofol through contaminated food are estimated using the EECs for the 

small bird (20 g) which consumes small insects. Dietary-based and dose-based exposures 

of potential prey (small mammals) are assessed using the small mammal (15 g) which 

consumes short grass. The small bird (20g) consuming small insects and the small 

mammal (15g) consuming short grass are used because these categories represent the 

largest RQs of the size and dietary categories in T-REX that are appropriate surrogates 

for the CRLF and one of its prey items. Estimated exposures of terrestrial insects to 

dicofol are bound by using the dietary based EECs for small insects and large insects. 

Birds are currently used as surrogates for terrestrial-phase CRLF. However, amphibians 

are poikilotherms (body temperature varies with environmental temperature) while birds 

are homeotherms (temperature is regulated, constant, and largely independent of 

environmental temperatures). Therefore, amphibians tend to have much lower metabolic 

rates and lower caloric intake requirements than birds or mammals. As a consequence, 

birds are likely to consume more food than amphibians on a daily dietary intake basis, 

assuming similar caloric content of the food items. Therefore, the use of avian food 

intake allometric equation as a surrogate to amphibians is likely to result in an overestimation of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore, 

T-REX (version 1.3.1) has been refined to the T-HERPS model (v. 1.0), which allows for 

an estimation of food intake for poikilotherms using the same basic procedure as T-REX 

to estimate avian food intake. 

The spray drift model AgDRIFT is used to assess exposures of terrestrial phase CRLF 

and its prey to dicofol deposited on terrestrial habitats by spray drift. In addition to the 

buffered area from the spray drift analysis, the downstream extent of dicofol that exceeds 

the LOC for the effects determination is also considered. 

KABAM (KOW (based) Aquatic BioAccumulation Model) v.1.0 is used to estimate 

potential bioaccumulation of dicofol in freshwater aquatic food webs and subsequent 

risks to mammals and birds via consumption of contaminated aquatic prey. In this case, 

exposures to birds are used as a surrogate for CRLF consuming aquatic organisms that 

have bioaccumulated dicofol and its degradates of concern. 

Lastly, in order to characterize the long range transport potential (LRTP) of dicofol and 

its degradates, the OECD Pov and LRTP Screening Tool was used. Three chemicals 

known to move via long range transport, DDT, aldrin and endrin, were also modeled to 

provide a context for the dicofol-estimated LRTP. It should be noted that OPP is not able 

to quantify the extent to which dicofol and its degradates will undergo long-range 

51 
atmospheric transport once it has been released from a treatment site and, as such, cannot 

quantify the amount of exposure that could potentially occur to nontarget animals distant 

from the use sites. 

2.10.2. Measures of Effect 

Data identified in Section 4 are used as measures of effect for direct and indirect effects 

to the CRLF. Data were obtained from registrant submitted studies or from literature 

studies identified by ECOTOX. The ECOTOXicology database (ECOTOX) was searched 

in order to provide more ecological effects data and in an attempt to bridge existing data 

gaps. ECOTOX is a source for locating single chemical toxicity data for aquatic life, 

terrestrial plants, and wildlife. ECOTOX was created and is maintained by the U.S. EPA, 

Office of Research and Development, and the National Health and Environmental Effects 

Research Laboratory's Mid-Continent Ecology Division. 

The assessment of risk for direct effects to the terrestrial-phase CRLF makes the 

assumption that toxicity of dicofol to birds is similar to or less than the toxicity to the 

terrestrial-phase CRLF. The same assumption is made for fish and aquatic-phase CRLF. 

Algae, aquatic invertebrates, fish, and amphibians represent potential prey of the CRLF 

in the aquatic habitat. Terrestrial invertebrates, small mammals, and terrestrial-phase 

amphibians represent potential prey of the CRLF in the terrestrial habitat. Aquatic, semiaquatic, and terrestrial plants represent habitat of CRLF. 

The acute measures of effect used for animals in this screening level assessment are the 

LD50, LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, 

given all at once, that is estimated to cause the death of 50% of the test organisms. LC 

stands for “Lethal Concentration” and LC50 is the concentration of a chemical that is 

estimated to kill 50% of the test organisms. EC stands for ‘Effective Concentration’ and 

the EC50 is the concentration of a chemical that is estimated to produce a specific effect in 

50% of the test organisms. Endpoints for chronic measures of exposure for listed and 

non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for ‘No 

Observed-Adverse-Effect-Level’ and refers to the highest tested dose of a substance that 

has been reported to have no harmful (adverse) effects on test organisms. The NOAEC 

(i.e., ‘No-Observed-Adverse-Effect-Concentration’) is the highest test concentration at 

which none of the observed effects were statistically different from the control. The 

NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute 

exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants). 

It is important to note that the measures of direct and indirect effects to the CRLF and its 

designated critical habitat are associated with impacts to survival, growth, and fecundity, 

and do not include the full suite of sublethal effects used to define the action area. 

According the Overview Document (USEPA 2004), the Agency relies on effects 

endpoints that are either direct measures of impairment of survival, growth, or fecundity 

or endpoints for which there is a scientifically robust, peer reviewed relationship that can 

quantify the impact of the measured effect endpoint on the assessment endpoints of 

survival, growth, and fecundity. 

52 
2.10.3. Integration of Exposure and Effects 

Risk characterization is the integration of exposure and ecological effects characterization 

to determine the potential ecological risk from agricultural and non-agricultural uses of 

dicofol, and the likelihood of direct and indirect effects to CRLF in aquatic and terrestrial 

habitats. The exposure and toxicity effects data are integrated in order to evaluate the 

risks of adverse ecological effects on non-target species. For the assessment of dicofol 

risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity 

values. EECs are divided by acute and chronic toxicity values. The resulting RQs are 

then compared to the Agency’s levels of concern (LOCs) (U.S. EPA 2004) (see 

Appendix C). 

For this endangered species assessment, listed species LOCs are used for comparing RQ 

values for acute and chronic exposures of dicofol directly to the CRLF. If estimated 

exposures directly to the CRLF of dicofol resulting from a particular use are sufficient to 

exceed the listed species LOC, then the effects determination for that use is ‘may affect’. 

When considering indirect effects to the CRLF due to effects to animal prey (aquatic and 

terrestrial invertebrates, fish, frogs, and mice), the listed species LOCs are also used. If 

estimated exposures to CRLF prey of dicofol resulting from a particular use are sufficient 

to exceed the listed species LOC, then the effects determination for that use is a ‘may 

affect.’ If the RQ being considered also exceeds the non-listed species acute risk LOC, 

then the effects determination is an LAA. If the acute RQ is between the listed species 

LOC and the non-listed acute risk species LOC, then further lines of evidence (i.e. 

probability of individual effects, species sensitivity distributions) are considered in 

distinguishing between a determination of NLAA and a LAA. When considering indirect 

effects to the CRLF due to effects to algae as dietary items or plants as habitat, the nonlisted species LOC for plants is used because the CRLF does not have an obligate 

relationship with any particular aquatic and/or terrestrial plant. If the RQ being 

considered for a particular use exceeds the non-listed species LOC for plants, the effects 

determination is ‘may affect.’ Further information on LOCs is provided in Appendix C. 

2.10.4. Data Gaps 

There are currently no submitted studies quantifying the environmental fate and transport 

of the major degradates of dicofol individually. Additionally, aerobic and anaerobic soil 

metabolism studies were conducted using slightly alkaline (pH from 7.5 to 7.9) soil, so 

soil metabolism studies under acidic soil conditions are missing. It should also be noted 

that a study on photodegradation in air for dicofol and its degradates has not been 

submitted. 

 

No data are available for assessing the effects of exposures of dicofol to freshwater 

vascular plants. Generally, data for duckweed (Lemna gibba) are used to assess these 

effects. 

53 
In addition, no data are available to quantify an endpoint to represent effects of dicofol 

exposures to riparian and terrestrial vegetation (vascular plants), which are generally 

represented by effects data for terrestrial agricultural crop species. 

Limited data are available to determine the toxicity of dicofol’s major degradates to 

aquatic or terrestrial organisms. 

3.0 Exposure Assessment 

Dicofol is formulated as a wettable powder and emulsifiable formulation. Application 

equipment includes: ground application, aerial application, and various sprayers (highand low-volume. Risks from ground boom and aerial applications are expected to result 

in the highest off-target levels of dicofol due to generally higher spray drift levels. 

Ground boom and aerial modes of application tend to use lower volumes of application 

applied in finer sprays than applications coincident with sprayers and spreaders and thus 

have a higher potential for off-target movement via spray drift. 

 

3.1. Label Application Rates and Intervals 

Dicofol labels may be categorized into two types: labels for manufacturing uses 

(including technical grade dicofol and its formulated products) and end-use products. 

While technical products, which contain dicofol of high purity, are not used directly in 

the environment, they are used to make formulated products, which can be applied in 

specific areas to control mites. The formulated product labels legally limit dicofol’s 

potential use to only those sites that are specified on the labels. 

Currently registered agricultural and non-agricultural uses of dicofol within California 

include: beans (dry, snap, and lima), citrus (specifically, grapefruit, kumquats, lemons, 

limes, oranges, tangelos, and tangerines), cotton, cucurbits (specifically, cantaloupes, 

cucumbers, melons, pumpkins, watermelons, and winter and summer squash), grapes, 

hops, mint, pecans, peppers, pome fruits (specifically, apples, crabapples, pears, and 

quince), stone fruits (specifically, apricots, sweet and sour cherries, nectarines, peaches, 

plums, and prunes), strawberries, tomatoes, walnuts, Bermuda grass, turf/ornamental uses 

(specifically, turf grasses, nursery stock, flowers, shade trees, woody shrubs and vines, 

and sod farms) and outside building surfaces (non-agricultural). The model scenarios and 

application input parameters for the uses included in this risk assessment are summarized 

in Table 9. 

54 
Table 9. Dicofol uses and application information for the CRLF risk assessment1

. 

Crop 

Uses 

Represented 

by Scenario 

PRZM/EXAMS 

Scenario 

Application 

Rate 

(lbs 

a.i./acre)

Number of 

Applications 

Application 

Interval 

Application 

Method 

Beans 

(dry, green, 

lima) 

CA row crop 

RLF 1.5 1 Annually 

ULV, 

Aerial, 

ground 

Citrus 

Grapefruit, 

kumquats, 

lemons, 

limes, 

oranges, 

tangelos, 

tangerines 

CA citrus 3 1 Annually 

ULV, 

Aerial, 

ground 

Cotton CA cotton 1.5 1 Annually 

ULV, 

Aerial, 

ground 

Cucurbits 

Cantaloupes, 

cucumbers, 

melons, 

pumpkins, 

watermelons, 

winter and 

summer 

squash 

CA melons RLF 0.625 1 Annually 

ULV, 

Aerial, 

ground 

Grapes CA wine grapes 

RLF 1.25 1 Annually 

ULV, 

Aerial, 

ground 

Hops OR hops 1.165 1 Annually 

ULV, 

Aerial, 

ground 

Mint 

Mint, 

peppermint, 

spearmint 

OR mint 1.25 1 Annually 

ULV, 

Aerial, 

ground 

Pecans CA almonds 2 1 Annually 

ULV, 

Aerial, 

ground 

Peppers CA row crop 

RLF 0.75 1 Annually 

ULV, 

Aerial, 

ground 

Pome fruits 

Apples, 

crabapples, 

pears, quince 

CA fruit 3 1 Annually 

ULV, 

Aerial, 

ground 

Stone fruits 

Apricots, 

sweet and 

sour 

cherries, 

nectarines, 

peaches, 

plums, 

prunes 

CA fruit 1.5 1 Annually 

ULV, 

Aerial, 

ground 

55 
Crop 

Uses 

Represented 

by Scenario 

PRZM/EXAMS 

Scenario 

Application 

Rate 

(lbs 

a.i./acre)

Number of 

Applications 

Application 

Interval 

Application 

Method 

Strawberries CA strawberries 

(non-plastic) 2 1 Annually 

ULV, 

Aerial, 

ground 

Tomatoes CA tomato 0.75 1 Annually 

ULV, 

Aerial, 

ground 

Walnuts CA almonds 2 1 Annually 

ULV, 

Aerial, 

ground 

Bermudagrass CA turf RLF 0.4 1 Annually Ground 

Turf grasses CA turf RLF 0.5 1 Annually Ground 

Sod farm turf CA turf RLF 0.5 1 Annually Ground 

Ornamentals 

Nurseries, 

ornamentals, 

flowers, 

shade trees 

CA nursery 0.5 1 Annually Ground 

Outside 

building 

surfaces 

CA impervious 

RLF and CA 

turf RLF 

0.5 1 Annually Ground 

1. Uses assessed based on maximum label rates for registered dicofol products. 

The labels for dicofol also specify that applications using ground equipment should not 

be made within 25 feet, or by air within 150 feet, of lakes, reservoirs, rivers, permanent 

streams, marshes, natural ponds, estuaries, or commercial fish farm ponds. The spray 

drift buffer zone is 450 feet when ultra low volume application is made. 

3.2. Aquatic Exposure Assessment 

3.2.1. Modeling Approach 

Aquatic exposures are quantitatively estimated for all of assessed uses using scenarios 

that represent high exposure sites for dicofol use in California. Each of these sites 

represents a 10-hectare field that drains into a 1-hectare pond that is 2 meters deep and 

has no outlet. Exposure estimates generated using the standard pond are intended to 

represent a wide variety of vulnerable water bodies that occur at the top of watersheds 

including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural 

ponds, and intermittent and first-order streams. As a group, there are factors that make 

these water bodies more or less vulnerable than the standard surrogate pond. Static water 

bodies that have larger ratios of drainage area to water body volume would be expected 

to have higher peak EECs than the standard pond. These water bodies will be either more 

shallow or have larger drainage areas (or both). Shallow water bodies tend to have 

limited storage capacity, and thus, tend to overflow and carry pesticide in their discharge 

whereas the standard pond has no discharge. As watershed size increases beyond 10 

hectares, at some point, it becomes unlikely that the entire watershed is planted to a 

single crop and which is all concurrently treated with the pesticide. Headwater streams 

56 
can also have peak concentrations higher than the standard pond, but these peaks in 

pesticide concentrations tend to persist for only short periods of time and are then carried 

downstream. 

Crop-specific management practices for all of the assessed uses of dicofol were used for 

modeling, including application rates, buffer widths and resulting spray drift values 

modeled from AgDRIFT and the first application date for each crop. The date of first 

application was developed based on several sources of information including data 

provided by EPA/OPP/BEAD, a summary of individual applications from the CDPR 

PUR data, and Crop Profiles maintained by the USDA. A sample of the distribution of 

dicofol applications to cotton from the CDPR PUR data for 2004 used to pick an 

application date is shown in Figure 8. More detail on the crop profiles and the previous 

assessments may be found at: http://www.ipmcenters.org/CropProfiles/. 

In defining the date of application, available CDPR PUR data were analyzed to determine 

the time period when greater than 90% of applications took place. An initial first 

application date was then selected from the month at the beginning of this range. Then, 

the corresponding PRZM/EXAMS scenarios used in the modeling effort were examined 

and dates for crop emergence, maturation, and harvest were evaluated. As mites usually 

rely on leaves and fruit as food sources, the midpoint date between emergence and 

maturation was estimated. If the crop scenario indicated that the crop was grown all year, 

a date of January 15th was selected to result in a conservative EEC that would result from 

increased rainfall experienced in California during the winter months. If the 

PRZM/EXAMS midpoint date occurred within the time period of the CDPR PUR 90%, 

then the PRZM/EXAMS midpoint date was used as the date of first application. 

Otherwise, the initial CDPR PUR date was used. For example, according to the CDPR 

PUR data, 90% of the dicofol use on cotton was between May and August, and May 3rd

was selected as the initial date of first application. In the PRZM/EXAMS scenario for 

California cotton, crop emergence occurs on May 1st and crop maturation occurs on 

September 20th, with a midpoint around July 11th. As this midpoint lies within the range 

of the 90% data obtained from CDPR PUR, July 11th was selected as the first application 

date for modeling purposes. 

57 
0

500

1000

1500

2000

2500

3000

3500

4000

4500

5/3/2004

5/10/20045/17/20045/24/20045/31/2004

6/7/2004

6/14/20046/21/20046/28/2004

7/5/2004

7/12/20047/19/20047/26/2004

8/2/20048/9/2004

8/16/2004

Pounds Applied

Figure 8. Summary of applications of dicofol to cotton in 2004 from CDPR PUR data. 

Once the separate PRZM/EXAMS runs for o,p’- and p,p’-dicofol are finished, the daily 

EECs are summed to generate a total daily parent dicofol EEC. This was done to 

facilitate comparison of the various EECs to the appropriate endpoints, which were based 

on total dicofol. Average 21-day, 60-day, and annual EECs of these total daily dicofol 

EECs were calculated. Maximum values were then estimated for each year and 1-in-10 

year return peak and rolling means for the 21-day, 60-day, and annual concentrations 

were estimated for each scenario. The same analyses were conducted for the o,p’- and 

p,p’-dicofol and degradate scenarios. 

3.2.2. PRZM Scenarios 

PRZM scenarios used to model aquatic exposures resulting from applications of specific 

uses are identified in Table 9. In cases where a scenario does not exist for a specific use, 

it is necessary to assign a surrogate scenario. Those surrogates are assigned to be most 

representative of the use being considered. Justifications for assignments of surrogates 

are defined below. 

Row crop scenario 

This scenario is intended to represent production of carrots, beans, peppers and other 

crops in CA, and is therefore, directly relevant to these uses. 

58 
Citrus scenario 

This scenario is intended to represent applications of pesticides to oranges, grapefruit, 

kumquats, lemons, limes, taneglos, and tangerines in CA and is therefore, directly 

relevant to this use. 

Cotton scenario 

This scenario is intended to represent applications of pesticides to cotton in CA and is 

therefore, directly relevant to this use. 

Melon scenario 

This scenario is intended to represent applications of pesticides to cantaloupes, 

cucumbers, melons, pumpkins, watermelons, winter and summer squash in CA and is 

therefore, directly relevant to this use. 

Wine grapes scenario

From 2002 to 2007, CA PUR data indicate that dicofol was used mostly on grapes grown 

for wine production, as opposed to grapes grown for consumption, in 31 counties. This 

scenario is intended to represent applications of pesticides to wine grapes in CA and is 

therefore, directly relevant to this use. 

Hops 

This scenario, developed based on a hops vineyard in the Pacific Northwest, represents a 

vineyard located north of the area where hops are grown in CA Since the locations 

where hops are grown in CA are mostly in the northern part of the state, this scenario was 

deemed appropriate for modeling hops grown in CA. 

Mint 

According to NASS data, mint (grown for oil) has been grown in Lassen, Shasta and 

Siskiyou Counties. These counties are located in northern CA, bordering OR. Although 

this scenario represents a field located north of the area where mint is grown in CA, it 

was developed based on a mint field in the Pacific Northwest. Since the locations where 

mint is grown in CA are in the northern part of the state, this scenario was deemed 

appropriate for modeling mint grown in CA. 

Almond scenario 

This scenario is intended to represent almond production in CA and is therefore, directly 

relevant to this use. Walnuts and pecans are nut trees with similar practices and have been 

assigned to this scenario. 

59 
Fruit scenario 

The CA fruit scenario represents a deciduous fruit tree orchard in Fresno County, which 

is located in the Central Valley. This scenario is intended to represent non-citrus fruit, 

including apples, crabapples, pears, quince, apricots, sweet and sour cherries, nectarines, 

peaches, plums, and prunes. 

Strawberry scenario 

This scenario is intended to represent applications of pesticides to strawberries, nontarped, in CA. While the majority of strawberry growers use tarps, this scenario is 

considered a conservative approach and is therefore, directly relevant to this use. 

Tomato scenario 

This scenario is intended to represent applications of pesticides to tomatoes in CA and is 

therefore, directly relevant to this use. 

Turf scenario 

This scenario is intended to represent applications of pesticides to sod farms, parks, 

recreational fields, grass for seed, and golf courses in CA and is therefore, directly 

relevant to this use. 

Nursery scenario 

This scenario is intended to represent applications of pesticides in outdoor nurseries in 

CA and is therefore, directly relevant to this use. 

Outside buildings 

Two scenarios were used to assess this use pattern: CA impervious and CA turf. The 

label indicates that to control clover mites, “thoroughly spray the outside walls, 

foundations, and windowsills and plants and lawn at the base of infested buildings.” For 

the 10-hectare scenario used in PRZM/EXAMS, it was assumed that a building was at the 

center of each hectare. Each building was assumed to be a square measuring 15,000 

square feet, with turf on three sides of the building and impervious surface on one side. It 

was assumed a 10-foot swath was treated on the sides with turf and that the side with the 

impervious surface would be treated up to a height of three feet along the building wall. 

This results in approximately 3.75% of the watershed being treated. A detailed 

description of the rationale for this value is provided in Appendix D.

60 
3.2.3. Model Inputs 

The appropriate chemical-specific PRZM input parameters are selected from reviewed 

environmental fate data submitted by the registrant (Table 3) and in accordance with 

EFED water model input parameter selection guidance (U.S. EPA 2002). The input 

parameters selected are similar to those used in the 1998 dicofol RED (U.S. EPA, 1998b). 

A summary of the chemical specific model inputs used in this assessment are provided in 

Table 10 and Table 11. 

Table 10. Summary of PRZM/EXAMS environmental fate data used for aquatic exposure inputs for 

o,p’-dicofol. 1

Fate Property Value (unit) MRID (or source) Comment 

Molecular Weight 370.5 g/mole 00141704; 00142595 

Henry’s constant 1.44 x 10-7 atmm3

/mol 

Estimated using VP, MW 

and solubility: 

HLC=VPxMW/Sol 

Vapor Pressure 3x10-7 torr 00141704; 00142595 

Solubility in Water 1.32 mg/L 00141704; 00142595 

Photolysis in Water 27.5 days 40849702 

Aerobic Soil 

Metabolism Halflives 

25.5 days (parent) 

313.5 days (total) 41094201 3x single value 

Hydrolysis 3.3 x 10-1 days 40042033 

Aerobic Aquatic 

Metabolism 

(water column) 

51 days (parent) 

627 days (total) -- Assumed: 2x aerobic soil half-life 

Anaerobic Aquatic 

Metabolism 

(benthic) 

0 d -- Assumed stable, no 

reviewed data 

Koc 7,060 mL/g 41509802 

≤2.5% of parent found in 

leachate. Used value 

from p,p’-dicofol. 

1 – Inputs determined in accordance with EFED “Guidance for Chemistry and Management Practice Input 

Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides” dated February 28, 

2002 

61 
Table 11. Summary of PRZM/EXAMS environmental fate data used for aquatic exposure inputs for 

p,p'-dicofol. 1

Fate Property Value (unit) MRID (or source) Comment 

Molecular Weight 370.5 g/mole 00141704; 00142595 

Henry’s constant 1.44 x 10-7 atmm3

/mol 

Estimated using VP, MW 

and solubility, 

HLC=VPxMW/Sol 

Vapor Pressure 3x10-7 torr 00141704; 00142595 

Solubility in Water 1.32 mg/L 00141704; 00142595 

Photolysis in Water 244 days 40849701 

Aerobic Soil 

Metabolism Halflives 

96 days (parent) 

939 days (total) 41050701 3x single value 

Hydrolysis 2.8 days 40042032 

Aerobic Aquatic 

Metabolism (water 

column) 

192 days (parent) 

1,878 days (total) 2x aerobic soil half-life 

Anaerobic Aquatic 

Metabolism 

(benthic) 

0 d Assumed stable, no 

reviewed data 

Koc

7060 mL/g 41509801 Average Koc

1 – Inputs determined in accordance with EFED “Guidance for Chemistry and Management Practice Input 

Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides” dated February 28, 

2002 

For p,p'-dicofol, a regression analysis between the Kd and organic carbon content values 

indicated a high r-squared value (0.98) and statistical significance (<0.01). To assess the 

appropriateness of the Koc model, a comparison of the coefficient of variation for the Koc.

(CV = 19) was compared to the coefficient of variation for Kd (CV = 58). Since the CV 

for the Koc was less than the CV for Kd, the average Koc of 7060 mL/g was used (Kashuba 

et al. 2006). For o,p’-dicofol, the majority of dicofol remained in upper 2 inches of soil 

columns, with less than 2.5% of dicofol found in leachate. As a result, a Koc of 0 was 

used during modeling. 

 

As depicted in Table 3, the aerobic soil half-lives for the parent dicofol isomers were 

significantly less than the half-lives estimated for the total residues of parent and 

degradates of concern (8.5 vs. 104.5 days for o,p’-dicofol and 32 vs 313 days for p,p’-

dicofol). As these values indicate a significant increase in persistence in the 

environment, separate model runs were conducted for the parent isomers and the parent 

plus degradate. 

For the PRZM input “chemical application method” (CAM), a value of 2 was selected to 

represent foliar applications. For aerial applications, using the 150-foot buffer zone 

stipulated on the label, an application efficiency of 0.95 was derived using AgDrift, with 

62 
a spray drift fraction of 0.039. For ground applications, using the 25-foot buffer zone 

stipulated on the label, an application efficiency of 0.99 was derived using AgDrift, with 

a spray drift fraction of 0.027. For ULV applications, using the 450-foot buffer zone 

required on the label, an application efficiency of 0.727 was derived using AgDrift, with 

a spray drift fraction of 0.109, for orchards (e.g., citrus, pome fruit, and stone fruit), and 

an application efficiency of 0.72 was derived using AgDrift, with a spray drift fraction of 

0.117, for other crops. It should be noted that if the buffer zone for ULV is not used, 

spray drift fractions increase to 0.5 for both orchards and crops. Parameters used in the 

derivation of the application efficiency and spray drift for ULV applications are discussed 

further in Appendix P. 

3.2.4. Model Results 

The aquatic EECs for the various scenarios and application practices for the sum of the 

o,p' and p,p' isomers of dicofol and for total dicofol (e.g., including degradates) are listed 

in Table 12 and Table 13. Example PRZM/EXAMS outputs are available in Appendix E. 

Table 12. Aquatic EECs (μg/L) for Dicofol Uses in California, Total o,p’ and p,p’ Isomers. 

Crop/Application 

Represented

Application 

Rate 

(lbs a.i./acre)

Date of First 

Application Scenario Peak EEC

21-day 

average 

EEC 

60-day 

average 

EEC

Beans Aerial 1.5 May-01 CA row crop RLF 3.24 0.46 0.18 

Beans Ground 1.5 May-01 CA row crop RLF 2.25 0.32 0.12 

Beans ULV 1.5 May-01 CA row crop RLF 9.72 1.38 0.53 

Citrus Aerial 3.0 January-15 CA citrus 6.44 0.97 0.42 

Citrus Ground 3.0 January-15 CA citrus 4.46 0.69 0.31 

Citrus ULV 3.0 January-15 CA citrus 17.97 2.58 1.03 

Cotton Aerial 1.5 July-11 CA cotton irrig 3.44 0.65 0.29 

Cotton Ground 1.5 July-11 CA cotton irrig 2.46 0.52 0.25 

Cotton ULV 1.5 July-11 CA cotton irrig 9.87 1.52 0.60 

Cucurbit Aerial 0.625 June-23 CA melons RLF 1.34 0.19 0.07 

Cucurbit Ground 0.625 June-23 CA melons RLF 0.93 0.13 0.05 

Cucurbit ULV 0.625 June-23 CA melons RLF 4.03 0.57 0.21 

Grape Aerial 1.25 June-11 CA wine grape 2.69 0.39 0.15 

Grape Ground 1.25 June-11 CA wine grape 1.86 0.27 0.10 

Grape ULV 1.25 June-11 CA wine grape 8.06 1.15 0.44 

Hops Aerial 1.165 May-31 OR hops 2.51 0.38 0.17 

Hops Ground 1.165 May-31 OR hops 1.74 0.27 0.13 

Hops ULV 1.165 May-31 OR hops 7.54 1.09 0.43 

Mint Aerial 1.25 June-04 OR mint 2.69 0.39 0.16 

Mint Ground 1.25 June-04 OR mint 1.86 0.27 0.11 

Mint ULV 1.25 June-04 OR mint 8.05 1.15 0.44 

Pepper Aerial 2.0 May-11 CA row crop RLF 1.61 0.23 0.09 

Pepper Ground 2.0 May-11 CA row crop RLF 1.12 0.16 0.06 

Pepper ULV 2.0 May-11 CA row crop RLF 4.83 0.69 0.26 

Pome Fruit Aerial 3.0 June-05 CA fruit 6.44 0.91 0.34 

Pome Fruit Ground 3.0 June-05 CA fruit 4.46 0.63 0.24 

63 
Crop/Application 

Represented

Application 

Rate 

(lbs a.i./acre)

Date of First 

Application Scenario Peak EEC

21-day 

average 

EEC 

60-day 

average 

EEC

Pome Fruit ULV 3.0 June-05 CA fruit 17.97 2.55 0.96 

Stone Fruit Aerial 1.5 May-08 CA fruit 3.24 0.46 0.18 

Stone Fruit Ground 1.5 May-08 CA fruit 2.24 0.32 0.12 

Stone Fruit ULV 1.5 May-08 CA fruit 9.05 1.29 0.48 

Strawberry Aerial 2.0 January-15 CA strawberry (nonplastic) RLF 6.09 1.71 0.92 

Strawberry Ground 2.0 January-15 CA strawberry (nonplastic) RLF 5.97 1.57 0.87 

Strawberry ULV 2.0 January-15 CA strawberry (nonplastic) RLF 13.10 2.67 1.22 

Tomato Aerial 0.75 June-07 CA tomato 1.61 0.23 0.09 

Tomato Ground 0.75 June-07 CA tomato 1.12 0.16 0.06 

Tomato ULV 0.75 June-07 CA tomato 4.83 0.69 0.26 

Walnut/Pecan Aerial 2.0 June-08 CA almond 4.38 0.67 0.29 

Walnut/Pecan Ground 2.0 June-08 CA almond 3.07 0.48 0.22 

Walnut/Pecan ULV 2.0 June-08 CA almond 12.97 1.87 0.73 

Bermuda grass Ground 0.4 January-15 CA turf RLF 0.60 0.10 0.04 

Ornamentals Ground 0.5 January-15 CA nursery 1.77 0.39 0.18 

Turf/Sod Farm Ground 0.5 January-15 CA turf RLF 0.75 0.13 0.05 

Outside Buildings 0.5 January-15 CA impervious RLF & CA turf RLF 0.15 0.025 0.01 

Table 13. Aquatic EECs (μg/L) for Dicofol, Parent and Degradate Uses in California. 

Crop/Application 

Represented

Application 

Rate 

(lbs a.i./acre)

Date of First 

Application Scenario Peak EEC

21-day 

average 

EEC 

60-day 

average 

EEC

Beans Aerial 1.5 May-01 CA row crop RLF 20.55 18.42 17.76 

Beans Ground 1.5 May-01 CA row crop RLF 18.09 16.58 16.11 

Beans ULV 1.5 May-01 CA row crop RLF 36.51 30.74 28.77 

Citrus Aerial 3.0 January-15 CA citrus 21.64 17.89 16.61 

Citrus Ground 3.0 January-15 CA citrus 16.49 13.93 13.13 

Citrus ULV 3.0 January-15 CA citrus 55.15 44.58 40.99 

Cotton Aerial 1.5 July-11 CA cotton irrig 22.86 21.17 20.52 

Cotton Ground 1.5 July-11 CA cotton irrig 20.46 19.39 18.93 

Cotton ULV 1.5 July-11 CA cotton irrig 38.84 33.25 31.31 

Cucurbit Aerial 0.625 June-23 CA melons RLF 7.81 7.01 6.74 

Cucurbit Ground 0.625 June-23 CA melons RLF 6.78 6.23 6.01 

Cucurbit ULV 0.625 June-23 CA melons RLF 14.82 12.44 11.63 

Grape Aerial 1.25 June-11 CA wine grape 15.39 13.81 13.26 

Grape Ground 1.25 June-11 CA wine grape 13.33 12.22 11.84 

Grape ULV 1.25 June-11 CA wine grape 29.15 24.37 22.74 

Hops Aerial 1.165 May-31 OR hops 22.70 21.27 20.47 

Hops Ground 1.165 May-31 OR hops 21.03 20.11 19.45 

Hops ULV 1.165 May-31 OR hops 33.88 29.41 27.99 

Mint Aerial 1.25 June-04 OR mint 18.81 17.62 16.81 

Mint Ground 1.25 June-04 OR mint 17.12 16.05 15.52 

Mint ULV 1.25 June-04 OR mint 32.57 27.83 26.26 

Pepper Aerial 2.0 May-11 CA row crop RLF 10.29 9.23 8.90 

Pepper Ground 2.0 May-11 CA row crop RLF 9.05 8.32 8.09 

64 
Crop/Application 

Represented

Application 

Rate 

(lbs a.i./acre)

Date of First 

Application Scenario Peak EEC

21-day 

average 

EEC 

60-day 

average 

EEC

Pepper ULV 2.0 May-11 CA row crop RLF 18.21 15.34 14.37 

Pome Fruit Aerial 3.0 June-05 CA fruit 24.32 20.57 19.26 

Pome Fruit Ground 3.0 June-05 CA fruit 18.69 16.08 15.18 

Pome Fruit ULV 3.0 June-05 CA fruit 57.34 46.74 43.13 

Stone Fruit Aerial 1.5 May-08 CA fruit 12.06 10.17 9.50 

Stone Fruit Ground 1.5 May-08 CA fruit 9.20 7.91 7.44 

Stone Fruit ULV 1.5 May-08 CA fruit 28.73 23.40 21.57 

Strawberry Aerial 2.0 January-15 CA strawberry (nonplastic) RLF 42.51 39.77 39.11 

Strawberry Ground 2.0 January-15 CA strawberry (nonplastic) RLF 41.13 37.81 37.41 

Strawberry ULV 2.0 January-15 CA strawberry (nonplastic) RLF 59.64 52.07 50.05 

Tomato Aerial 0.75 June-07 CA tomato 7.72 6.77 6.44 

Tomato Ground 0.75 June-07 CA tomato 6.38 5.72 5.49 

Tomato ULV 0.75 June-07 CA tomato 16.54 13.70 12.73 

Walnut/Pecan Aerial 2.0 June-08 CA almond 25.28 22.82 21.99 

Walnut/Pecan Ground 2.0 June-08 CA almond 21.88 20.20 19.64 

Walnut/Pecan ULV 2.0 June-08 CA almond 47.75 40.25 37.70 

Bermuda grass Ground 0.4 January-15 CA turf RLF 2.66 2.31 2.21 

Ornamentals Ground 0.5 January-15 CA nursery 7.16 6.48 6.29 

Turf/Sod Farm Ground 0.5 January-15 CA turf RLF 3.31 2.87 2.74 

Outside Buildings 0.5 January-15 CA impervious RLF & CA turf RLF 0.38 0.31 0.29 

3.2.5. Available Monitoring Data 

A critical step in the process of characterizing EECs is comparing the modeled estimates 

with available surface water monitoring data. Monitoring data for dicofol from the 

USGS NAWQA program (http://water.usgs.gov/nawqa) were not available. Surface 

water and sediment monitoring data from the California Department of Pesticide 

Regulation (CDPR) were available and are considered in this assessment. No air 

monitoring data were located. 

Dicofol 

A study was conducted in 1993 (Domagalski 1996) that assessed the levels of dicofol in 

the San Joaquin River and its tributaries during the irrigation season. Water samples 

were collected at 22 sites within the perennial reach of the San Joaquin River in the San 

Joaquin Valley. All sampling locations were selected downstream of the confluence of 

the San Joaquin River and the Salt Slough. All sites were sampled during two synoptic 

surveys that occurred during March and August 1993. A subset of these sites was 

sampled more frequently (twice-monthly or monthly) for the period of March through 

September 1993. The sampling sites with the greatest frequency were the Central 

California Irrigation District Canal, Orestimba Creek, the Spanish Grant Drain, and the 

Salt Slough. From the study, it appears that 79 samples were collected from March to 

September 1993. All samples collected between March and June of 1993 were below the 

65 
level of detection (0.05 μg/L). From June to September, 33 samples had levels of dicofol 

above the detection limit, with the highest concentration of 2.5 μg/L from a sample 

collected at the Orestimba Creek site. 

NAWQA monitoring data were not available for dicofol from California surface waters 

(USGS 2008). 

CDPR maintains a database of monitoring data of pesticides in CA surface waters. The 

sampled water bodies include rivers, creeks, urban streams, agricultural drains, the San 

Francisco Bay delta region and storm water runoff from urban areas. The database 

contains data from 51 different studies by federal (including the USGS NAWQA 

program), state and local agencies as well as groups from private industry and 

environmental interests. Data are available from 1990-2006 for 46 counties for several 

pesticides and their degradates. Data for dicofol are included in this database (CDPR 

2008). 

From 1990-2006, 618 samples from surface waters were analyzed for dicofol in the 

CDPR database. Of these, dicofol was detected in 11 (1.8%) of the samples, with a 

maximum concentration of 0.27 μg/L. These samples included 131 different sites in 16 

counties; including counties where CRLF core areas and critical habitat are located. 

Dicofol was not reported in the sediment samples that were collected over this timeframe. 

It should be noted that these results are not from targeted monitoring studies. 

The Pesticides in Ground Water Data Base (U.S. EPA 1992) shows no detections of 

dicofol in limited sampling in several States, including California, (1634 wells sampled 

between 1979 and 1991). 

Dicofol Degradates 

NAWQA monitoring data were available for one degradate of dicofol, p,p’-DCBP. 

Twenty samples of p,p'-DCBP were collected from 2003 to 2005, with a maximum 

estimated concentration of 0.69 μg/L (detection limit unknown). It should be noted that 

the original source of the p,p’-DCBP detections (e.g., where the active ingredient came 

from) is unknown, as p,p'-DCBP is also a degradate of chlorobenzilate, chloropropylate, 

and DDT.

The CDPR database did not contain monitoring data of dicofol degradates in surface 

water or sediment. 

3.3. Aquatic Bioaccumulation Assessment 

Available data on the octanol-water partition coefficient Kow = 1.15 x 106

, (MRID 

00141580) and bioconcentration factors (BCFs) for dicofol indicate that this pesticide 

may accumulate in aquatic food webs. KABAM v.1.0 was used to estimate 

concentrations of dicofol in tissues of aquatic organisms resulting from bioaccumulation. 

Available empirical and modeling estimates of bioaccumulation of dicofol in aquatic 

organisms are described below. 

66 
3.3.1. Estimated BCF values 

In order to estimate BCF values for aquatic organisms accumulating dicofol, KABAM 

was run, using a Kow of 1.15 x 106

 (log(Kow) = 6.06) to represent the partitioning of 

dicofol to aquatic organisms. It was assumed that the concentration of dissolved oxygen 

in water was 10 mg/L (near saturation) and the water temperature was 20o

C. The body 

characteristics of organisms in the model trophic levels are depicted in Table 14. The 

resulting BCF values for these trophic levels are depicted in Table 15. Output files from 

KABAM are provided in Appendix G. 

Table 14. Characteristics of model aquatic organisms used to derive BCF values. 

Trophic Level 

Wet Weight 

(kg) 

% 

lipids 

% Non-lipid 

organic matter % Water 

phytoplankton N/A 2.0% 8.0% 90.0% 

zooplankton 1.0E-07 3.0% 12.0% 85.0% 

benthic invertebrates 1.0E-04 3.0% 21.0% 76.0% 

filter feeders 1.0E-03 2.0% 13.0% 85.0% 

small fish 1.0E-02 4.0% 23.0% 73.0% 

medium fish 1.0E-01 4.0% 23.0% 73.0% 

large fish 1.0E+00 4.0% 23.0% 73.0% 

Table 15. Estimated BCF values for parent dicofol in aquatic organisms. 

Trophic Level 

Total BCF 

(μg/kg-ww)/(μg/L) 

Phytoplankton 55,112 

Zooplankton 39,268 

Benthic Invertebrates 42,884 

Filter Feeders 28,188 

Small Fish 55,170 

Medium Fish 55,170 

Large Fish 55,170 

3.3.2. Empirical BCF data 

In a 28-day laboratory BCF study with bluegill sunfish (Lepomis macrochirus) exposed 

to p,p'-dicofol, a BCF of 10,000 was observed in whole fish. In this study, steady state 

was not reached. The estimated steady-state BCF for dicofol was 25,000, which is within 

a factor of 2.2 of the estimated BCF for fish (Table 15). In this study, parent dicofol 

represented >94% of the radioactivity measured after the 28-day exposure, suggesting 

that metabolism of dicofol was minimal. FW-152 and OH-DCBH were detected in tissue 

samples, each comprising as much as 4.7% of the overall radioactivity measured at the 

time (MRID 265330). 

In an early life stage test with the aquatic invertebrate, Hyalella azteca and the fathead 

minnow (Pimephales promelas), mean 28-day BCF values of 10,000 (±3000) and 3,700 

67 
(±800), respectively, were observed (GS0021-017). As the duration of this study was 

insufficient to allow the test organisms to reach steady-state, it is expected that if the 

duration had been extended, observed BCF values would have increased. 

In a full life cycle test with the fathead minnow, the highest observed BCF value was 

43,000, which was observed in F0 females after 296 days of exposure to dicofol (MRID 

42628901). This value is within a factor of 1.3 of estimated BCF value for fish (i.e., 

55,000). 

3.3.3. Bioaccumulation modeling 

KABAM was run in default mode (see user’s guide for full description), with a Log Kow 

= 6.06, a KOC = 7060 L/kg-oc (see Table 10) and surface water and pore water EECs of 

0.26 and 0.066 μg/L, respectively. These PRZM/EXAMS-generated EECs are based on 

the average of yearly average concentrations of dicofol parent from ULV dicofol 

applications to strawberries. These EECs were selected because they represent the 

highest annual EECs predicted for any use of dicofol and result in the highest predicted 

accumulation of dicofol in tissues of aquatic organisms. The average water temperature 

(13oC) for this scenario was used to simulate the water temperature of the abiotic 

compartment of KABAM. It was assumed that metabolism of dicofol by aquatic 

organisms did not occur. This assumption is supported by the available BCF study with 

p,p'-dicofol, where parent dicofol represented >94% of the radioactivity measured after 

the 28-day exposure and metabolism was minimal (MRID 265330). The resulting 

concentrations of dicofol in tissues of aquatic organisms are provided in Table 16. Output 

files from KABAM are provided in Appendix G. These values are used to derive RQs 

based on dose-based and dietary-based exposures of aquatic-phase CRLF to dicofol 

through consumption of contaminated aquatic prey (See section 5.1). 

Table 16. Concentrations of dicofol parent in tissues of aquatic organisms (estimated using KABAM). 

Trophic level Total concentration (μg/kg-ww) 

Phytoplankton 10,559 

Zooplankton 11,838 

Benthic Invertebrates 15,191 

Filter Feeders 10,301 

Small Fish 39,027 

Medium Fish 82,949 

Large Fish 290,605 

KABAM’s predictions of bioaccumulation in aquatic systems are most sensitive to the 

Kow value of the assessed pesticide, with accumulation increasing as the Kow increases. 

No empirical data were available to define the Kow values of dicofol’s residues of 

concern, so EPISuite v.4.0 was used to estimate Kow values for the 4 degradates of 

concern (Table 17). Review of the estimated Kow values of dicofol’s residues of concern 

indicates that dicofol transforms to residues that have lower Kow values, and thus lower 

68 
accumulation potential in aquatic organisms. KABAM was used to estimate the 

bioaccumulation of dicofol’s total residues of concern, by considering PRZM/EXAMS 

generated aquatic EECs for total residues and the Log Kow values of dicofol’s degradates 

of concern. KABAM was run again in default mode (see user’s guide for full 

description), with Log Kow = 3.96, 4.0, 4.44, 4.89, and 6.06 (measured), to represent the 

partitioning of OH-DCBP, DCBH, DCBP, FW-152 and dicofol, respectively in aquatic 

organisms. A Koc = 7060 L/kg-oc (see Table 10) and surface water and pore water EECs 

of 41 and 17 μg/L, respectively. These EECs are based on the average of yearly average 

concentrations of dicofol parent derived from ULV applications of dicofol to 

strawberries, as modeled using PRZM/EXAMS. As discussed earlier, these EECs were 

selected because they represent the highest annual EECs predicted for any use of dicofol 

and result in the highest predicted accumulation of dicofol in tissues of aquatic 

organisms. The resulting concentrations of dicofol in tissues of aquatic organisms are 

provided in Table 18. Output files from KABAM are provided in Appendix G. In 

reality, dicofol and its residues of concern would be subject to uptake by aquatic 

organisms. Therefore, the overall bioaccumulation of dicofol’s total residues would be a 

mixture of dicofol and its 4 residues and would therefore fall between the tissue residue 

concentrations estimated for OH-DCBP and dicofol that are provided in Table 18. 

Table 17. Estimated Log Kow values of dicofol's residues of concern.

Chemical Log Kow* 

Dicofol 5.81 

DCBP 4.44 

FW-152 4.89 

DCBH 4.00 

OH-DCBP 3.96 

*Estimated using EPISuite v.4.0. 

Table 18. Concentrations of dicofol total residues of concern in tissues of aquatic organisms (μg/kgww; estimated using KABAM). Concentrations were estimated using Log Kow values representative 

of the different dicofol residues of concern. 

Trophic level 

Log Kow = 

3.96 

(OH-DCBP) 

Log Kow = 

4.00 

(DCBH) 

Log Kow = 

4.44 

(DCBP) 

Log Kow = 

4.89 

(FW-152) 

Log Kow = 

6.06 

(dicofol) 

Phytoplankton 1.7E+04 1.9E+04 5.2E+04 1.5E+05 1.7E+06 

Zooplankton 1.3E+04 1.4E+04 3.9E+04 1.1E+05 1.9E+06 

Benthic Invertebrates 1.4E+04 1.5E+04 4.2E+04 1.2E+05 2.4E+06 

Filter Feeders 9.0E+03 9.9E+03 2.7E+04 7.9E+04 1.6E+06 

Small Fish 1.8E+04 2.0E+04 5.5E+04 1.7E+05 6.2E+06 

Medium Fish 1.8E+04 2.0E+04 5.8E+04 1.9E+05 1.3E+07 

Large Fish 1.9E+04 2.1E+04 6.4E+04 2.4E+05 4.6E+07 

69 
3.4. Terrestrial Animal Exposure Assessment 

3.4.1. Modeling Approach 

T-REX (Version 1.4.1) is used to calculate dietary and dose-based EECs of dicofol for 

the CRLF and its potential prey (e.g. small mammals and terrestrial insects) inhabiting 

terrestrial areas. EECs used to represent the CRLF are also used to represent exposure 

values for frogs serving as potential prey of CRLF adults. T-REX simulates a 1-year time 

period. 

Terrestrial EECs for dicofol were derived for the uses and corresponding application rates 

summarized in Table 19. According to dicofol labels, only 1 application of dicofol is 

allowed per year on any one field, so only 1 application per year was modeled for each 

use. One foliar dissipation half-life value specific to dicofol (6 days based on application 

to alfalfa in CA) is available in Willis and McDowell (1987). Because a single half-life 

value is insufficient to derive a foliar dissipation half-life specific to dicofol, the EFED 

default foliar dissipation half-life of 35 days is used based on the work of Willis and 

McDowell (1987). This value falls within the range of observed dissipation half-lives for 

dicofol measured in 3 studies (9-61 days, see section 3.4.1 below). The maximum 

application rate for each use is modeled in T-REX and upper bound EECs are used for 

RQ calculations. An example output from T-REX is available in Appendix H. 

Table 19. Input parameters to T-REX used to generate dicofol EECs for terrestrial animals. 

Use Application Rate 

(lbs a.i./A) 

Citrus,1 Pome Fruits2 3 

Strawberries, Walnuts (English/black), Pecans 2 

Beans, cotton, Stone Fruits3 1.5 

Grapes, mint4 1.25 

Hops 1.165 

Peppers, Tomatoes 0.75 

Cucurbits5 0.625 

Ornamentals,6 Turf grasses, Sod farms, Outside building 

surfaces 0.5 

Bermuda grass 0.4 1

 grapefruit, lemons, oranges, tangelos, and tangerines 

2

 apples and pears 

3

 apricots, cherries, nectarines, peaches, plums, and prunes 

4

 mint, peppermint and spearmint 

5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6

 nurseries and flowers 

For modeling purposes, exposures of the CRLF, as well as other frog species serving as 

prey to the CRLF, to dicofol through contaminated food are estimated using the EECs for 

70 
the small bird (20 g) which consumes small insects. Dietary-based and dose-based 

exposures of potential prey are assessed using the small mammal (15 g) which consumes 

short grass. Upper-bound Kenega nomogram values reported by T-REX for these two 

organism types are used for derivation of EECs for the CRLF and its potential prey 

(Table 20). 

As indicated above, T-REX is also used to calculate EECs for terrestrial insects exposed 

to dicofol. Dietary-based EECs calculated by T-REX for small and large insects (units of 

μg a.i./g) are used to bound an estimate of exposure to terrestrial insects. Available acute 

contact toxicity data for bees exposed to dicofol (in units of μg a.i./bee), are converted to 

μg a.i./g (of bee) by multiplying by 1 bee/0.128 g. Dietary-based EECs for terrestrial 

insects are later compared to the adjusted acute contact toxicity data for bees in order to 

derive RQs. Dietary-based EECs for small and large insects reported by T-REX as well 

as the resulting adjusted EECs are available in

71 
Table 21. 

Table 20. Upper-bou enega Nomogram E and Do of the 

CRLF e Applications of dicofol for Current Uses in Californ

nd K ECs for Dietary- se-based Exposures

 and its Prey to Singl ia. 

EECs for CRLF EECs for Prey 

(smal mals) l mam

Use Dietary-based Dose-ba EC sed E Dietary-based Dose-based EEC 

EEC (ppm) (mg/kg-bw) EEC (ppm) (mg/kg-bw) 

Citrus Fruits2 ,

1 Pome 405 461 720 686 

Strawberries, Walnuts 

(English/black), Pecans 270 308 480 458 

Beans, cotton, Stone Fruits3 203 231 360 343 

Grapes, mint4 168 192 300 286 

Hops 157 179 281 267 

Peppers, Tomatoes 101 115 180 172 

bits5 Cucur 84.4 96.1 150 143 

Ornamentals, Turf grasses, 6 

Sod farms, Outside building 

surfaces 67.5 76.9 120 114 

Bermuda grass 54.0 61.5 96.0 91.5 

1 grapefruit, lemons, oranges, tangelos, and tangerines 

2 apples and pears 

3 apricots, cherries, nectarines, peaches, plums, and prunes 

4 mint, peppermint and spearmint 

5 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6 nurseries and flowers 

72 
Table 21. Dicofol EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to 

Terrestrial Invertebrate Prey Items. 

Use Small Insect EEC Large Insect EEC 

Citrus,1 Pome Fruits2 405 45.0 

Strawberries, Walnuts 

(English/black), Pecans 270 30.0 

Beans, cotton, Stone Fruits3 203 22.5 

Grapes, mint4 169 18.8 

Hops 157 17.5 

Peppers, Tomatoes 101 11.3 

Cucurbits5 84.4 9.38 

Ornamentals,6 Turf grasses, Sod 

farms, Outside building surfaces 67.5 7.50 

Bermuda grass 54.0 6.00 1

 grapefruit, lemons, oranges, tangelos, and tangerines 

2

 apples and pears 

3

 apricots, cherries, nectarines, peaches, plums, and prunes 

4

 mint, peppermint and spearmint 5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6

 nurseries and flowers 

3.4.1. Field Studies 

Comprehensive ecological monitoring studies of dicofol residues were conducted for 

three years in California cotton fields (1990-92; MRIDs 41785102, 41857301, and 

42285503), Florida citrus groves (1989-91; MRIDs 41785103, 41845605, 42091501, and 

42437301), and New York apples orchards (1989-91; MRIDs 41845604, 42285501, and 

42721301). Areas and crops selected had a previous history of heavy dicofol use and a 

high likelihood for exposure to non-target organisms. Application rates typified those 

most commonly used by the growers and not necessarily the maximum label rates. 

Observed residue concentrations were variable and declined exponentially after 

application. The highest mean concentrations were typically found immediately 

following ap

e Florida c

plication on the treated area, usually on the treated crop foliage, except for 

itrus site. Residues of p,p'-dicofol on the non-crop area were typically 1 to 2 

rders of magnitude below those found in the crop areas. In the crop areas, the highest 

ean concentration of p,p'-dicofol measured were 97 ppm for foliage (New York), 78 

ppm on grass (Florida) and 0.56 ppm for soil (New York). The highest mean 

concentration of p,p'-dicofol measured in the abiotic matrices for the non-crop area were 

9.7 ppm for grass (Florida), 5.9 ppm on foliage (Florida), and 0.1 ppm for soil (California 

and Florida). Foliage residues in the crop areas declined from 3-year means of 92, 97 and 

74 ppm immediately after application, to 0.05, 16 and 24 ppm 90 days later for cotton, 

orchards, and citrus, respectively. Foliage residues in non-crop areas declined from 3-

year means of 0.6, 5.2, and 5.9 ppm immediately after application to 0.09, 0.9, and 0.55 

ppm after 90 days for cotton, orchards, and citrus, respectively. Mean grass residues 

declined from 0.47, 5.1, and 9.7 ppm immediately after application, to 0.04, 0.08, and 

0.54 ppm 90 days later for cotton, orchards, and citrus, respectively. 

th

o

m

73 
Residues of p,p'-dicofol were detected in the foliage of crops and dissipated with a halflife ranging of 9, 41, and 61 days for cotton, orchard, and citrus foliage respectively. 

Grass residues declined from 3-year means of 48 and 78 ppm immediately after 

application, to 0.15 and 2.3 ppm 90 days later for orchards and citrus, respectively. 

Dissipation half-lives of p,p'-dicofol on orchard and citrus grass were 12 and 21 days, 

respectively. The observed foliar dissipation half-lives for dicofol are comparable to the 

35-day default value used to represent the foliar dissipation half-life of dicofol in the TREX model. 

3.5. Accumulation of Dicofol Residues on Soil 

Because dicofol and its degradates are moderately persistent in soil (aerobic soil halflives greater than 104 days) and do not have a tendency to leach from soil, a screening 

analysis was conducted to characterize the levels of dicofol in the soil of a treated site 

after 30 years of applications. 

Ground application to pome fruits was selected for the screening analysis, as it was 

expected to result in highest soil concentrations of dicofol compared to any other use 

(b o 

str

levels of EECs in the aquatic exposure assessment. PRZM/EXAMS runs were conducted 

and total soil concentrations were estimated for the upper 10 cm soil horizon. As with 

the aquatic exposure assessment, both the o,p'- and p,p' isomers of dicofol were run 

separately and the results combined in a postprocessor. The 1-in-10-year peak 

concentrations in the soil for total dicofol were 11,952 and 7,770 mg/m3

 for pome fruits 

and strawberries, respectively. The 1-in-10- year peak concentrations in the pore water 

for total dicofol were 176 and 115 mg/m3 for pome fruits and strawberries, respectively. 

Annual average peak dicofol soil concentrations increased for the first fifteen years of the 

simulation, then reached a plateau at an average annual peak concentration in the soil at 

10,170 and 6,600 mg/m3

 for pome fruits and strawberries, respectively, and in the pore 

water at 150 and 98 mg/m3 for pome fruits and strawberries, respectively (Figure 9 and 

Figure 10). 

ased on the highest application rate and application efficiency). Aerial application t

awberries was selected for the screening analysis, as this scenario produced the highest 

74 
Peak Dicofol Concentrat

14000

ions in Soil Over Time

8000

6000 8000 10000 12000

Soil Conc (mg/m3)

10000

12000

0

2000

4000

6000

0 2000 4000

Figure 9. Concentration of total residues of dicofol in soil treated with dicofol for 30 years. X axis 

represents time in days. Soil modeled in PRZM using CA strawberries and CA fruit scenarios. 

Pome Fruit, Ground App Strawberry, Aerial App

Peak Dicofol Concentrations in Pore Water Over Time

0

Figure 10. Concentration of total residues of dicofol in pore water of soil treated with dicofol for 30 

years. X axis represents time in days. Soil modeled in PRZM using CA strawberries and CA fruit 

scenarios. 

0

0

0

0

0

0

0

0

0

0 2000 4000 6000 8000 10000 12000

2

4

6

8

10

12

14

16

18

20

Pore Water Conc (mg/m3)

0

Pome Fruit, Ground App Strawberry, Aerial App

75 
3.6. Terrestrial Bioaccumulation Assessment 

ggs. 

 ppm for reptiles/amphibians (Florida), 0.9 ppm for 

irds (Florida), and 0.26 ppm for fish (Florida). Dicofol was found at a concentration of 

compared with the nesting 

ccess for these species. Yearly geometric mean p,p'-dicofol residues ranged from 

can robin eggs in New 

lowest in 

ns for p,p'-FW152 residues 

eans exceeded 0.03 ppm only in eggs of the eastern screech 

ppm). Yearly geometric means for p,p'-

 residues ranged from 0.004 ppm (starling in California) to 0.1651 ppm (eastern 

The estimated octanol-air partition coefficient (KOA) of 1010 (EPIsuite v.4.0) suggests that 

bioaccumulation of dicofol in air breathing organisms is possible (Kelly et al. 2007). At 

this time, modeling tools are unavailable to quantify the bioaccumulation of dicofol in 

terrestrial organisms. However, relevant monitoring studies involving dicofol have been 

conducted. 

Comprehensive ecological monitoring studies of dicofol residues were conducted for 

three years in California cotton fields (1990-92; MRIDs 41785102, 41857301, and 

42285503), Florida citrus groves (1989-91; (MRIDs 41785103, 41845605, 42091501, 

and 42437301), and New York apples orchards (1989-91; (MRIDs 41845604, 42285501, 

and 42721301). Areas and crops selected had a previous history of heavy dicofol use and 

a high likelihood for exposure to non-target organisms. Application rates typified those 

most commonly used by the growers and not necessarily the maximum label rates. 

Dicofol residues were monitored in soil, plant foliage, fish, mammals, reptiles, 

amphibians, earthworms, birds, and bird e

In crop areas, the highest mean concentrations of p,p'-dicofol measured in the biotic 

matrices were 1.4 ppm for small mammals (Florida), 3.9 ppm for terrestrial invertebrates 

(California), and 3.8 ppm for reptiles/amphibians (Florida). In non-crop areas, highest 

mean concentrations were 0.3 ppm for small mammals (New York), 0.76 ppm for 

terrestrial invertebrates (Florida), 0.38

b

1-2 ppm in earthworms in New York. 

Eggs were collected from thirteen avian species and were analyzed for residues and 

eggshell thickness (MRIDs 41764801, 41764802, 41845601, 41845602, 41845603, 

42285501, 42285505, and 42721302). These data were

su

0.0027 ppm (several species in California) to 0.46 ppm (Ameri

York). Yearly means were highest in New York (0.01-0.46 ppm), and 

California (<LOD to 0.02 ppm). Yearly geometric mea

ranged from 0.002 ppm (mourning dove in California) to 0.218 ppm (eastern screech owl 

in Florida). Three year m

owls in Florida and robins in New York (0.0947 

DCBP

screech owl in Florida). Three year means exceeded 0.03 ppm only in eggs of eastern 

screech owls in Florida and New York (0.1093 and 0.0648 ppm, respectively), New York 

robins (0.0374 ppm), and Florida mockingbirds (0.0431 ppm). Except for p,p'-FW152 

concentrations in the eastern screech owl in Florida, geometric mean metabolite residue 

concentrations were generally lower than for p,p'-dicofol. None of the yearly geometric 

means for dicofol, p,p'-FW152, or p,p'-DCBP exceeded 0.5 ppm. 

76 
4.0 Effects Assessment 

This assessment evaluates the potential for dicofol to directly or indirectly affect the 

CRLF or modify its designated critical habitat. As discussed in Section 2.7, assessment 

endpoints for the CRLF effects determination include direct toxic effects on the survival, 

reproduction, and growth of CRLF, as well as indirect effects, such as reduction of the 

prey base or effects to its habitat. In addition, potential effects to critical habitat is 

assessed by evaluating effects to the PCEs, which are components of the critical habitat 

reas that provide essential life cycle needs of the CRLF. Direct effects to the aquatics described in the Agency’s Overview Document (U.S. EPA 2004), the most sensitive 

 on data generated from guideline studies 

bmitted by the registrant, and from open literature studies that meet the criteria for 

ironmental chemical concentration/dose or application rate is 

reported; and 

n 

e registrant-submitted data are considered. The degree to which open literature data are 

uantitatively or qualitatively characterized for the effects determination is dependent on 

hether the information is relevant to the assessment endpoints (i.e., maintenance of 

 

a

phase of the CRLF are based on toxicity information for freshwater fish, while terrestrialphase effects are based on avian toxicity data, given that birds are generally used as a 

surrogate for terrestrial-phase amphibians. Because the frog’s prey items and habitat 

requirements are dependent on the availability of freshwater fish and invertebrates, small 

mammals, terrestrial invertebrates, and aquatic and terrestrial plants, toxicity information 

for these taxa are also discussed. Acute (short-term) and chronic (long-term) toxicity 

information is characterized based on registrant-submitted studies and a comprehensive 

review of the open literature on dicofol. 

A

endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa 

include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, aquatic 

plants, birds (surrogate for terrestrial-phase amphibians), mammals, terrestrial 

invertebrates, and terrestrial plants. 

Toxicity endpoints are established based

su

inclusion into the ECOTOX database maintained by EPA/Office of Research and 

Development (ORD) (U.S. EPA 2004). In order to be included in the ECOTOX 

database, papers must meet the following minimum criteria: 

o the toxic effects are related to single chemical exposure;6

o the toxic effects are on an aquatic or terrestrial plant or animal species; 

o there is a biological effect on live, whole organisms; 

o a concurrent env

o there is an explicit duration of exposure.

Data that pass the ECOTOX screen are evaluated along with the registrant-submitted 

data, and may be incorporated qualitatively or quantitatively into this endangered species 

assessment. In general, effects data in the open literature that are more conservative tha

th

q

w

 

 The studies that have information on mixtures are listed in the bibliography as rejected due to the 

presence of mixtures. These studies are evaluated by EFED when applicable to the assessment; however, 

the data is not used quantitatively in the assessment. 

6

77 
CRLF survival, reproduction, and growth) identified in Section 2.8. For example, 

ehavi fications are be qua ly e ecause 

quantitative relationships between modifica d species survival, 

reproduction, and/or growth are not available. Although the effects determination relies 

re r r

portant to note that the 

ts s t

sidered action dicofol. 

fol ECOTOX database on 10/31/08 were considered 

 Ci all open ture not considered as part of this 

they were either rejected by the ECOTOX screen or accepted by 

t not used (e.g., the endpoint is less sensitive) are included in Appendix I. 

 include r reje ha

 those that were not eval endan

ed s readsheet of the available accepted ECOTO

ll suite of lethal and sublethal endpoints is presented in . 

ludes a s a d

nt-submitted and open literature toxicity information, other sources 

including

indi

e conducted to further refine the characterization of potential ecological 

ciated with exposure to dicofol. A summary of the available incident 

formation for dicofol is provided below. 

in study reports, sublethal effects 

obs acute toxicity studies a this effects characterization. 

ublethal effects raise concern abo f dicofol; however, it is not 

to quantitatively link these effects to the selected assessment endpoints for the 

F (i.e., survival, growth, and re dividuals and maintenance of 

ore, pot ffects on specific taxa are 

valuated qualitatively. Definitive endpoints, such as LC50s are used for quantifying 

ent. 

.1. 

endpoints such as b or modi likely to

tions and re

e

litative

uction in

valuated, b

on endpoints that a

reproduction, it is im

elevant to the assessm nt endpoi

full suite of su

nts of su

blethal endpoints potentially 

vival, growth, or

available in the effec

endpoints) are con

literature (regardle

 to define the 

s of their sig

 area for 

nificance o the assessment 

Toxicity data for dico

for this assessment.

assessment because 

ECOTOX bu

available in the

tations of litera

Appendix I also

ECOTOX screen and

assessment. A detail

data, including the fu

s a rationale fo ction of those 

uated as part o

studies t

f this

t did not pass the 

gered species risk 

X open literature 

Appendix J

p

Appendix K inc

In addition to registra

of informatio

ummary of the hum n health effects data for icofol. 

n, 

the probability of an 

System (EIIS), ar

effects asso

 use of the acute probit dose response relationship to establish 

vidual effect and reviews of the Ecological Incident Information

in

It should be noted that where data were provided 

erved during re described in 

These s

possible 

ut the effects o

listed CRL

l habitat PCEs). Theref

production of in

critica ential sublethal e

e

RQs in this assessm

4 Toxicity of dicofol to aquatic organisms 

Table 22 summarizes the most sensitive aquatic toxicity endpoints for the CRLF, based 

on an evaluation of the available studies as previously discussed. Toxicity to aquatic fish 

and invertebrates is categorized using the system shown in Table 23 (U.S. EPA 2004). 

78 
Table 22. Freshwater toxicity profile for dicofol. 

Assessment Endpoint Species Toxicity 

Value Used in 

Risk 

Source 

(MRID) 

Comment 

Assessment 

Acute Direct Toxicity to 

A

Oncorhynchus clarkii LC50 = 53.0 40098001 Slope not available 

quatic-Phase CRLF (cutthroat trout) μg/L 

Chronic Direct Toxicity to 

Aquatic-Phase CRLF 

Oncorhynchus mykiss

(rainbow trout)

NOAEC 

./

42063001 LOAEC = 7.9 μg 

a.i./L based on 

dec

= 4.4 

μg a.i L 

reased length 

Indirect Toxicity to 

A

A

F

(

Daphnia magna 

) 

50 =

g/L 

40042057 Slope not available 

quatic-Phase CRLF via (waterflea

cute Toxicity to 

reshwater Invertebrates 

i.e. prey items) 

EC 140 

μ

I

A

C

F

(

 azteca 

(amphipod) 

OAE

 a.i./L

S00

6

28-da

33 μg d 

on decreased 

surviv

ndirect Toxicit

quatic-Phase CRLF via 

y to Hyalella

hronic Toxicity to 

reshwater Invertebrates 

i.e. prey items) 

N C = 19 G

μg

21-

01

y LOAEC =

 a.i./L, base

al

I

A

T

A

s acutus

) 

C50 > 

10,000

sh

i 1

Effec

and 

observ

ndirect Toxicity to Scenedesmu

quatic-Phase CRLF via (green alga

oxicity to Non-vascular 

quatic Plants 

E 5,000, Kri

< μg/L mar

naku

977 

ts to biomass

growth

ed 

I

Aquatic-Phase CRLF via 

Toxicity to Vascular 

A

No data are available to quantify an endpoint to represent effects of dicofol 

exposures to vascular plants.

ndirect Toxicity to 

quatic Plants 

Table 23. Categories of acute toxicity for aquatic organisms. 

LC50 (mg/L) Toxicity Category 

< 0.1 Very highly toxic 

> 0.1 - 1 Highly toxic 

> 1 - 10 Moderately toxic 

> 10 - 100 Slightly toxic 

> 100 Practically nontoxic 

4.1.1. Toxicity of re ater Fish 

l t ity data not availa for aq se a , 

 ar d as a su to estim irect chro o 

ater toxicity data are also used to asses dir ts 

RL Effects to hwater fish sulting sure

affect the CRLF via reduction in available food. As discussed in Section 

2.5.3, over 50% of the prey mass of the CRLF may consist of vertebrates such as mice, 

ogs, and fish (Hayes and Tennant 1985). 

Dicofol to F shw

Given that dicofo oxic are ble uatic-pha mphibians

freshwater fish data

the CRLF. Freshw

e use

 fish

rrogate ate d acute and

s potential in

nic risks t

ect effec

of dicofol to the C

could indirectly 

F. fres re from expo to dicofol 

fr

Available acute toxicity data for freshwater fish exposed to dicofol include 96-h LC50

values ranging 53-603 μg /L (Table 24). Therefore, dicofol is classified (Table 23) as 

79 
very highly to highly toxic to freshwater fish on an acute exposure basis. The most 

sensitive freshwater species tested is cutthroat trout, with a 96-hour LC50 value of 53 

μg/L (MRID: 400980-01), is used for deriving risk quotients for the CRLF and fish 

serving as prey to the adult CRLF. 

Table 24. Acute toxicity data (96-h LC50) for freshwater fish exposed to dicofol.

Species (common name) LC50 value 

(μg/L) 

95% 

confidence 

interval 

(μg/L) 

Slope Source (MRID) 

Oncorhynchus clarkii (cutthroat trout) 53.0 41-68 NA 40098001 

O. clarkia (cutthroat trout) 158 100-250 NA 40098001 

O. clarkii (cutthroat trout) 53.1 41.3-68.2 15.6 GS0021002 

Salvelinus namaycush (lake trout) 86.9 53.1-142.0 NA GS0021001 

S. namaycush (lake trout) 87 53-142 40098001 

O. mykiss (rainbow trout) 124.3 95.0-181.0 3.8 41695401 

Ictalurus punctatus (channel catfish) 360 290-447 10.8 40098001 

Micropterus salmoides (largemouth bass) 395 NA NA 40098001 

Pimephales promelas (fathead minnow) 509 492-533 12.2 GS0021018 

Lepomis macrochirus (bluegill sunfish) 510 420-640 10.3 GS0021004 

Lepomis macrochirus (bluegill sunfish) 520 421-642 NA 40098001 

Pimephales promelas (fathead minnow) 603 577-631 NA ECOTOX # 12859

NA = not available 

Several chronic studies are available where freshwater fish were exposed to dicofol 

(Table 25). Available chronic studies for rainbow trout (Oncorhynchus mykiss) and 

fathead m below. From these studies, the 

mos ed growth, is a 95-day NOAEC value 

f 4.4 μg/L (MRID: 42063001). This value is used for deriving risk quotients for the 

innows (Pimephales promelas) are described

t sensitive chronic endpoint, based on decreas

o

CRLF and fish serving as prey to the adult CRLF. 

Table 25. Chronic toxicity data for freshwater fish exposed to dicofol.

Species (common name) Duration of 

Study (days) 

NOAEC (μg/L) LOAEC 

(μg /L) 

Observed Source 

Effects (MRID) 

Oncorhynchus mykiss

(rainbow trout) 

95 4.4 7.9 Decreased 

length 

42063001 

Oncorhynchus mykiss

(rain

99 4.6 9.1 Decreased 

th 

43383902 

bow trout) leng

Pimephales promelas 296 4.52 8.82 Impacted 42628901 

(fathead minnow) reproduction 

Pimephales promelas

(fathead minnow) 

28 19 39 Decreased 

survival and 

growth 

GS0021-016 

In an early life stage test with rainbow trout, growth (length) was significantly reduced 

(4.8% compared to controls) in fish (at 35-days post-hatch) exposed to concentrations of 

7.9 (±1.0) μg a.i./L. The resulting NOAEC for this study was 4.4 μg a.i./L (MRIDs 

80 
42063001). In an additional early life stage test conducted with rainbow trout resulted in 

reduced growth (length was decreased 4.8% compared to controls) of fish (36-day old) 

exposed to 9.1 μg a.i./L dicofol. The resulting NOAEC for this study was 4.6 μg a.i./L 

(MRID 43383902). 

In an early life stage test with fathead minnows, survival and growth were significantly 

(±3.8) μg a.i./L (GS0021-016). In a full life 

cycle study (296 days) with the fathead minnow, mean ha ccess of

g was significan sed ./L treat ared

ecrease). Also, signif effects to rep duction were o erved in the 

ion exposed to 8.82 μg , including d sed number s/pair, decrea

f spawns per mating pair and decreased number of reproductive days per mati

e resulting NOAEC for this study was 4.52 μg a.i./L (MRID 42628901). 

 of Dicofol to Freshwater Invertebrates 

icofol is classified highly toxic to freshwater invertebrates, based on an acute toxicity 

-016). 

s 

his risk assessment (i.e., to derive RQ values for the degradates), but 

r to compare the relative toxicitites of dicofol and its major environmental 

decreased in fish exposed to concentrations of 39 (±6.3) μg a.i./L for 28 days. The 

resulting NOAEC for this study was 19 

tching su the F1

eneration tly decrea at 8.82 μg a.i ment comp to controls 

(13% d icant ro bs F0

generat a.i./L ecrea of egg sed 

number o ng 

pair. Th

4.1.2. Toxicity

D

study with Daphnia magna (MRID 40042057), where an EC50 of 140 μg/L was observed. 

Chronic toxicity data are available for the amphipod, Hyalella azteca. The NOAEC for 

this study was 19 (±2.2) μg a.i./L, based on a decrease in survival (70% mortality, 

compared to 0% in controls) in animals exposed to 33 (±2.2) μg a.i./L for 28 days 

(GS0021

4.1.3. Toxicity of Dicofol to Aquatic Plants 

Data are available from the scientific literature involving exposures of dicofol to the 

green alga, Scenedesmus acutus. Based on observed decreases in biomass and growth 

rates, the EC50 is estimated to lie between 5,000 and 10,000 μg/L (Krishnakumari 1977). 

No data are available involving exposures of aquatic vascular plants to dicofol. 

4.2. Toxicity of Dicofol’s Degradates to Aquatic Organisms 

4.2.1. Toxicity of Dicofol’s Degradates to Aquatic Animal

Empirical data are not available for exposure of aquatic animals to dicofol’s major 

degradates (DCBP, FW-152, DCBH, OH-DCBP and CBA). In order to characterize the 

relative toxicity of dicofol and its major degradates, ECOSAR v. 1.0 (USEPA 2009) was 

run to estimate acute LC50 and chronic toxicity values for fish and aquatic invertebrates. 

ECOSAR predicted acute and chronic values for the parent and degradates are not used 

quantitatively in t

rathe

81 
degradates. ECOSAR estimates of acute and chronic toxicity for fish and daphnids 

indicate that DCBP, FW-152, DCBH and OH-DCBP are similar (i.e., estimated LC50 and 

chronic values are within an order of magnitude) to that of dicofol. ECOSAR estimates 

cofol, with estimated LC50 and chronic 

96-h LC50 chronic value 48-h LC50 chronic value 

indicate that CBA may be of lesser toxicity than di

values for CBA being several orders of magnitude greater than dicofol (Table 26). 

Table 26. Estimated acute and chronic toxicity values (μg/L) for fish and daphnids exposed to dicofol 

and its degradates (as calculated by ECOSAR).

Chemical Fish Fish Daphnid Daphnid 

Dicofol1 274 9 8 21 

DCBP2 1391 171 1124 192 

FW-152 1027 50 79 1 40 

DCBH 42 231 1 3037 139 2

OH-DCBP 1472 1088 206 3 8 

CBA2 844098 88987 488560 58244 1

Benzyl alcohol clas

2

Neutral organic clas

3

Phenols class 

s 

s 

C5 e o 53

ted v falls within this range. The ECOSAR estimated 

chronic value of 9 μg /L also falls within the range of available NOAE

ofol erte CO m

nitude availabl pirical EC50 e 

μg/L). 

nt s of aqu onm

FW d O Because the estimated acute and 

ity of CBA is several orders of magnitude less than that of dicofol and the 

A is not considered to date of concern

ent that for l residues are of equal tox

 acute toxicity data used t toxicity of the 

uatic animals are selected based on the most sensitive values available for 

hron data av exp fr

sed to so used sent the chronic toxicity of the total 

 organisms. 

of Dicofol’s Degr

ata are available from the scientific literature involving separate exposures of DCBP 

nd DCBH to the green alga, Chlorella vulgaris. At concentrations of 1000 μg/L, 

ecreases in chlorophyll a and biomass were not observed compared to controls. At 

0,000 μg/L, decreases in chlorophyll a and biomass were observed (Subba-Rao and 

lexander 1980). 

Ninety-six hour L

ECOSAR estima

0 values for fish

alue of 274 μg/L

xposed to dic fol range -603 μg/L. The 

Cs 4.4-19 μg/L for 

ated acute value is 

(48-h EC50 = 140 

fish exposed to dic

2 orders of mag

. For aquatic inv

 lower than the 

brates, the E

e em

SAR esti

valu

In this risk assessme

as: dicofol, DCBP, 

, the total residue

-152, DCBH an

concern for

H-DCBP. 

atic envir ents are defined 

chronic toxic

other degradates, CB

this assessm

the parent. The

 be a degra . It is assumed in 

icity compared to 

total residues of 

aquatic animals, tota

o represent the

dicofol to aq

dicofol exposures. C

invertebrates expo

ese

ic toxicity ailable for 

to repre

osures of eshwater fish and 

 dicofol are al

residues to th

4.2.2. Toxicity adates to Aquatic Plants 

D

a

d

1

A

82 
No data are available involving exposures of aquatic vascular plants to dicofol’s major 

degradat

4.3. Toxicity of dicofol to terrestrial organisms 

Tabl s the most sensitive terrestrial toxicity endpoints for the CRLF, based 

on a of registrant submit s and the scien re. Acute 

toxic nimals is catego sing the classification system shown in 

Table 28 (U.S. EPA 2004). Toxicity categories for terrestrial plants have not been 

defined. 

abl l. 

es. 

e 27 summarize

n evaluation ted studie tific literatu

ity to terrestrial a rized u

T e 27. Terrestrial toxicity profile for dicofo

Endpoint Species 

Toxicity Value 

Used in Risk 

Assessment 

Source 

(MRID) Comment 

Acut

Terre

Average body weight of 

1135 g for this species from 

Tot 

e Direct Toxicity to 

strial-Phase CRLF 

pheasant 

(Phasianus 

colchicus) 

LD50 = 265 mg 

a.i./kg bw 160000 Dunning 1984 used in 

REX. Slope data are n

available. 

Ring-necked 

Suba

Terre

cute Direct Toxicity to 

strial-Phase CRLF 

Japanese quail 

(Coturnix japonica) LC50 = 905 ppm ECOTOX# 

35240 Available slope is 5.92

Chro

Terre (Falco sparverius) ppm 

41934001 

 on 

thickness. Body weight for 

this species is 0.100 kg 

from Dunning 1984. 

nic Direct Toxicity to 

trial-Phase CRLF 

American kestrel NOAEC = 1 

LOAEC = 3 ppm based

8% decrease in egg shell 

s

Indirect Tox

Terrestrial-Pha (via 

acute toxi

prey item

 rat

g g 40731204 No slope is available. 

icity to 

se CRLF 

city alian to mamm

s) 

Laboratory

(Rattus norve icus) 

LD

m 50 = 587 

/kg-bw 

Indirect Tox

Terre

chron

mamm ms) 

L tory r

NOAEC = 5 

ppm 

.4 mg/kg/ ) 

4160

LO m; based 

on emic and 

ffects. 

icity to 

strial-Phase CRLF (via 

ic toxicity to 

alian prey ite

abora at 

(0 day

6601 

AEC = 25 pp

 parental syst

reproductive e

Indire

Terre (via 

acute ial 

invert

y bee

(Apis mellifera) 

D50>50

a.i./bee 0500 LD ent to >391 μg a.i./g of bee 

ct Toxicity to

strial-Phase CRLF

 toxicity to terrestr

ebrate prey items) 

Hone L μg 1991 50 is equival

Indire

Terre

Phase

terres

No data are available to quantify this endpoint 

ct Toxicity to 

strial- and Aquatic-

 CRLF (via toxicity to

trial plants) 

83 
Table 28. Categories of acute toxicity for avian and mammalian studies. 

Toxicity Category Oral LD50 (mg/kg) Dietary LC50 (ppm) 

Very highly toxic < 10 < 50 

Highly toxic 10 - 50 50 - 500 

Moderately toxic 51 - 500 501 - 1000 

Slightly toxic 501 - 2000 1001 - 5000 

Practically non-toxic > 2000 > 5000 

4.3.1. Toxicity of Dicofol to Birds 

An acute oral toxicity study with ring-necked pheasant (Phasianus colchicus) established 

an LD50 of 265 (211-334) mg ai/kg bw (MRID 160000). This indicates that dicofol is 

moderately toxic to avian species on an acute oral exposure basis. 

Available subacute dietary toxicity data for birds exposed to dicofol include 8-day LC50

values ranging 905-3010 ppm (Table 29). Therefore, dicofol is classified (Table 28) as 

moderately to slightly toxic to birds on a subacute dietary exposure bas

a

is. Data are 

vailable for 4 species of birds exposed to dicofol. The most sensitive species is the 

e of 905 ppm (ECOTOX # 35240). 

T eri qu r the C serving to 

the adult CRLF. 

toxic a (LC50) bird

Japanese quail (Coturnix japonica), with an LC50 valu

his value is used for d ving risk otients fo RLF and frogs as prey 

Table 29. Subacute dietary ity dat for s exposed to dicofol.

Species 

(common name) 

95% 

LC50 va lue 

(ppm) 

confidence 

interval 

(μppm) 

In of itial age

test birds 

(days) 

Slope Source 

Coturnix japonica

(Japanese quail) 905 723-1140 C35 1 5.92 E OTOX# 240 

C. japonica 1237 979-1578 4.89 GS0021010 (Japanese quail) 7 

C. japonica 

(Japanese quail) 1418 1232-1628 12 4.13 00022923 

C. japonica 

 (Japanese quail) 1545 1360-1739 14 7.95 GS0021011 

Anas platyrhynch

(mallard duck) 

os 1651 1356-2029 10 5.64 00022923 

C. japonica 

(Japanese quail) 1746 1377-2255 21 5.37 GS0021012 

Phasianus colchicus 

(ring-necked pheasant) 2126 1892-2387 16 7.38 00022923 

Colinus virginianus

(bobwhite quail) 3010 2635-3424 15 4.31 00022923 

84 
Several chronic studies are available where birds were exposed to dicofol (Table 30). 

Available chronic studies included data on American kestrel (Falco sparverius), eastern 

screech owls (Otus asio), ring doves (Streptopelia risoria), mallard ducks (Anas 

platyrhynchos) and northern bobwhite quail (Colinus virginianus). From these studies, 

the most sensitive chronic toxicity endpoint is a NOAEC of 1 ppm based on reproductive 

effects to the American kestrel. This value is based on a LOAEC where effects to egg 

shells were observed. There is some uncertainty in relying upon observed effects to egg 

shells to represent effects to reproduction of the CRLF, since the CRLF does not produce 

eggs with hardened shells. However, observed effects in bird eggs caused by parental 

exposures to dicofol could result in other effects to amphibian eggs that are unrelated to 

egg shell thickness but do affect the composition of the egg coatings that regulate osmotic 

alance in eggs. In addition, effects to other endpoints that directly relate to amphibians, 

 the adult CRLF. Another consideration is that 

icofol produces similar effects in birds as DDT/DDE. This endpoint has clear 

b

including decreased numbers of eggs laid and feminization of male chicks were observed 

at 40 ppm. In the two studies where these effects were observed in birds, a NOAEC was 

not established, i.e., effects were measured at all levels tested. Therefore the available 1 

ppm NOAEC is used for deriving risk quotients for the CRLF and terrestrial frogs (e.g.,

the Pacific tree frog) serving as prey to

d

population level effects as demonstrated with bald eagles exposed to DDT. 

Table 30. Chronic toxicity data for birds exposed to dicofol.

Species (common name) NOAEC 

(ppm) 

LOAEC 

(ppm) Observed Effects Source 

Falco sparverius 1 3 

(American kestrel) 

Decreased egg shell thickness 

(8%) 

MRID 

41934001 

Otus asio (eastern screech 

owls) 

none 7.2 Decreased shell weight (11.7-

13.5%) and thickness (7.6-11%) 

of eggs 

Wienmeyer et 

al. 1989 

Anas platyrhynchos

(mallard duck) 

10 40 Increased number of cracked 

eggs (12%) 

MRID 

41231301 

Streptopelia risoria (ring 

dove)

none 40 Decreased egg-shell thickness 

and egg production, increased 

number of cracked eggs 

(11.2%) 

Schwarzbach 

et al. 1988 

F

(A

alco sparverius None 40 

merican kestrel) increase in eggs lost, potential 

feminization of male chicks 

al. 1996 

Decreased number of eggs laid, MacLellan et 

Anas platyrhynchos

(mallard duck)

10 none none GS0021-014 

Colinus virginianus

(northern bobwhite quail) 

120 none none MRID 

40042055 

In a reproduction study with the American kestrel, eggshells were thinned by 8% in 

parent birds fed 3 ppm technical dicofol for up to 175 days. Shell weight was also 

reduced by 9% at concentrations as low as 10 ppm. The resulting NOAEC for the study 

d 

s 

nerations. Female birds in the first generation treated with 20 mg/kgwas 1 ppm (MRID 41934001). In a second study with captive American kestrels, paire

females were given daily oral doses of 0, 5 and 20 mg/kg-bw of dicofol. This study wa

conducted over 2 ge

85 
bw (10.98%) compared to 

ontrols. Female birds in the second generation treated with 5 mg/kg-bw had an increase 

 male 

ffspring with abnormal gonads. Histological examination of male gonads indicated a 

osed to 40 ppm dicofol in a reproductive study. Observed effects at 

is level included significant reductions in egg shell thickness (9% less than to controls), 

 a reproduction study with mallard ducks exposed to technical grade dicofol, egg shell 

stren f cracked eggs compared to 

ont her effects were observed 

ith northern bobwhite quail exposed to technical grade dicofol, 

produced eggs with significantly reduced shell thickness 

c

in number of eggs lost and a decrease in total number of eggs laid compared to controls. 

Female birds of the first and second generation treated with 5 mg/kg-bw produced

o

thickened cortex and a significant increase in primordial germ cells present in male 

offspring of females treated with 5 mg/kg-bw. The authors suggested that this 

histological evidence indicated feminization of male offspring (MacLellan et al. 1996). 

As 5 mg/kg-bw was the lowest treatment level, a NOAEL could be established for this 

study. On a dietary exposure basis, a dose of 5 mg/kg-bw/day is approximately 

equivalent to 40 mg/kg-diet/day7

. 

In a reproduction study with eastern screech owls, birds were exposed to 7.2 ppm dicofol 

in feed. At this concentration, shell weight was reduced on average by 12-14% compared 

to controls. Also, egg shell thickness was reduced by 8-11% on average, compared to 

controls. Since only one treatment group was involved in this study, a NOAEC could not 

be determined (Wienmeyer et al. 1989). 

Ring doves were exp

th

increased numbers of cracked eggs (14.3 more than controls), and decreased egg 

production (13% less than controls). In addition, 14.3% of clutches produced by the 

treated group contained only single eggs, as compared to 1.8% of clutches produced by 

the control group (Schwartzbach et al. 1988). 

In

gth was significantly reduced (12% increase in number o

c rols) at 40 ppm, resulting in a NOAEC of 10 ppm. No ot

during this study (MRID 41231301). In another reproductive study with mallard ducks, 

birds treated with 5 ppm and 10 ppm showed no significant effects to reproduction 

compared to controls. Effects considered in this study included number of eggs laid, 

eggs cracked, eggs embryonated, survival of embryos and hatchling survival. Egg shell 

thickness data were not reported (GS0021-014). 

 

In a reproduction study w

no significant effects to reproduction were observed relative to controls. Effects 

considered in this study included eggs laid, eggs cracked, egg shell thickness, eggs set, 

viable embryos, survival of embryos and hatchling survival. The highest treatment level 

of this study was 120 ppm (MRID 40042055). 

 

7

 The available dose-based value (5 mg/kg-bw) is multiplied by the body weight (BW) of the bird (0.111 

kg, from Dunning 1984) and then divided by the food intake rate. The food intake rate (FI, in kg/day), is 

lculated according to: (*0582.0 )1993 . 651.0

ca FI = BW USEPA

86 
4.3.2. Toxicity of Dicofol to Mammals 

Available acute toxicity data for the laboratory rat indicates that dicofol is slightly toxic 

to mammals on an acute oral exposure basis (LD50=587 mg/kg, MRID 40731204). 

In a two-generation reproduction study, groups of laboratory rats (25/sex/group) were fed 

ectively). For parental systemic toxicity, the NOAEC was 5 ppm (0.4 

tive 

xicity, the NOAEC was 5 ppm (0.4 mg/kg-bw/day) and the LOAEC was 25 ppm 

1 females, 

 For offspring toxicity, the 

dditional chronic toxicity data for mammals (rats and mice) exposed to dicofol were 

rted data corresponded to higher NOAEC 

, NOAEC = 5 ppm (0.4 mg/kg/day); MRID 

bee; MRID 05001991). An acute oral LD50 for 

ees has also been reported as >10 μg a.i./bee (MRID 05001991). In a study where a 1% 

restrial Plants 

an endpoint to represent effects of dicofol 

xposures to vascular plants. However, there are several studies available in the 

scientific literature to qualitatively describe effects of dicofol on vascular plants. 

diets containing dicofol (93.3%) at dose levels of 0, 5, 25, 125 or 250 ppm (equivalent to 

0.4, 1.9, 9.5, or 18.9 mg/kg-bw/day for males and 0.4, 2.1, 10.5, or 20.5 mg/kg-bw/day 

for females, resp

mg/kg-bw/day) and the LOAEC was 25 ppm (1.9/2.1 mg/kg-bw/day for M/F) based upon 

histopathological changes in P and F1 livers (hypertrophy of centrilobular hepatocytes 

with associated vacuolation) and F1 ovaries (increased vacuolation). For reproduc

to

(1.9/2.1 mg/kg-bw/day in M/F), based on the ovarian vacuolation in the F

which was judged to be an effect on reproductive physiology. 

NOAEC could be defined at 25 ppm (1.9/2.1 mg/kg-bw/day for M/F) and the LOAEC at 

125 ppm (9.5/10.5 mg/kg-bw/day for M/F), based on decreased F2 pup viability 

(increased numbers of stillborn pups, postnatal day 0-4 pup deaths, and total litter loss) 

(MRID 41606601). 

A

available in ECOTOX. However, all repo

values than that used in this assessment (i.e.

41606601). Therefore, these data were not considered further for this assessment. 

4.3.3. Toxicity of Dicofol to Terrestrial Invertebrates 

Dicofol is classified as practically nontoxic to honey bees (Apis mellifera) on an acute 

contact exposure basis (LD50>50 μg a.i./

b

solution of a formulated product containing 18.5% dicofol was applied directly to honey 

bee hives through saw cuts in the frame, no abnormal mortality was observed in worker 

bees (MRID 05009244). 

For the purpose of this assessment, the acute contact honey bee endpoint is used to 

represent effects to terrestrial invertebrates. This toxicity value is converted to units of 

μg a.i./g (of bee) by multiplying by 1 bee/0.128 g resulting in an LD50 >391 μg a.i./g. 

4.3.4. Toxicity of Dicofol to Ter

There are no data are available to quantify 

e

87 
In a study involving 15 types of ornamental plants, dicofol applied as a spray resulted in 

phytotoxicity to begonias. No effects were observed to the other 14 ornamental plants 

In a study involving the papaya (Carica papaya), 0.125% of a formulation including 

rowth and resulted in leaf burn (Sherman and Sanchez 1968). 

r its 

egradates to terrestrial organisms. 

June of 2000 in Tulare 

County that the observed plant damage was 

associated with exposure to dicofol was considered possible. The legality of the use was 

undetermin

dustry, and discharged process wastewater into the unlined wastewater pond. This 

included in the test, including antirrhinum, asters, carnation, chrysanthemum, cineraria, 

coleus, cyclamen, dahlia, geranium, petunia, polyanthus, ,saintpaulia, violets and zinnia 

(Dennis and Edwards 1963). 

When neanthe bella palm (Chamaedorea elegans) was exposed to dicofol, phytotoxicity 

was observed. Dicofol applied to 6 other species of plants did not cause phytotoxicity 

(Knauss 1971). 

 

dicofol affected plant g

4.4. Toxicity of dicofol degradates to terrestrial organisms 

There are no data available from registrant-submitted studies or in the scientific literature 

to evaluate the potential toxicity of dicofol degradates to terrestrial organisms. In 

addition, there are no models or tools available to estimate the toxicity of dicofol o

d

4.5. Incident Database Review for Dicofol 

A search of the EIIS (Environmental Incident Information System) database for 

ecological incidents (run on February 24, 2009) identified 1 incident associated with the 

use of dicofol. This incident involved plant damage to 10 acres of oranges treated 

directly with dicofol and chlorpyrifos. The incident occurred in 

 of California. The certainty (likelihood) 

ed (Incident # I013563-010). 

In 1980, a wastewater pond maintained by the Tower Chemical Company (TCC) 

overflowed into an onsite drainage ditch which flowed downstream into the Gourd Neck 

of Lake Apopka. Lake Apopka is the fourth largest freshwater lake (12,500 ha) in the 

state of Florida and has been designated as one of Florida's most polluted. From 1957 to 

1981, TCC manufactured and stored various pesticides, used primarily in the citrus 

in

discharge included dicofol, as much as 15% of DDT and its metabolites (DDD, DDE, and 

chloro-DDT), and sulfuric acid. Studies subsequent to the upset showed a dramatic 

decline in the American alligator population during the 1980s that continued into the mid 

to late 1990s (Guillette et al. 1994). 

88 
5.0 Risk Characterization 

Risk characterization is used to determine the fo and irec o 

the CRLF or for m ation to its designated l ha om the use of dicofol in 

CA. The risk characterization provides an e ion ( n 5.1 a des ion 

(Section 5.2) of the likelihood of adverse effects; articulate asse t assum ns, 

l ns, and uncertainties; and synthesizes an overall conclusion regarding the 

likelihood of adverse effects to the CRLF or its designated critical habitat ( ‘no 

effect,’ ‘likely to adversely affect,’ or ‘may affe t not to ad ly affe

5.1. Risk Estimation 

Risk is estimated by calculating the ratio of e re to ty. T atio is isk 

q Q), which is then compared to pre-established acute and chronic levels of 

c category evaluated ( dix C or ac posure the 

CRLF and its animal prey in aquatic habitats, as well as terrestrial in rates, the LOC 

is 0.05. For acute exposures to the CRLF and als, OC i The L for 

c well as acute exposures to plants is 1.0. 

R by calculating the ratio of 

xposure to toxicity using 1-in-10 year EECs based on the label-recommended dicofol 

. 

terrestrial insects, small mammals and terr se are ated based on 

exposures resulting from applications of dicofol (Table 20 and 

Risk characterization is the integration of the exposure and effects characterizations. 

 potential 

 critica

r direct 

bitat fr

/or ind t effects t

odific

stimat Sectio ) and cript

s risk ssmen ptio

imitatio

i.e., 

ct, bu likely verse ct’). 

xposu toxici his r the r

uotient (R

oncern (LOCs) for each Appen ). F ute ex s to 

verteb

 mamm the L s 0.1. OC

hronic exposures to CRLF and its prey, as 

isks to the aquatic-phase CRLF and its prey are estimated

e

usage scenarios summarized in Section 2.4.4 and the appropriate aquatic toxicity

endpoint from Section 4.1. Risks to the terrestrial-phase CRLF and its prey (e.g

estrial-pha frogs) estim

89 
Table 21) and the appropriate toxicity endpoint from Section 4.4. 

5.1.1.1. t Effects to Aquati L

Direct effects to the aquatic-phase CRLF are based on peak EECs of total dicofol 

r in the standard pond and the lowest a xicit e fo water In 

order to assess direct chronic risks to the CRLF, 60-day EECs of total dicofol residues 

(including dicofol, DCBP, FW-152, DCBH, and OH-DCBP) and the lowest chronic 

toxicity value for freshwater fish are used. 

Acute and chronic RQs for the aquatic-phase F res from

U cations of dicofol are provided ble able and Table 33

respectively. For exposures involving dicofol s deg s of rn, RQ all 

uses of dicofol exceed the acute listed species (0.05 the tion of fol 

use on Bermuda grass and outside buildings. for c exp s to th LF 

r fo ses, Ber grass, and 

outside buildings. Although RQs for aerial applications are higher than those for ground 

a and aerial applications, both 

s aquatic-phase CRLF. 

5.1.1. Exposures in the Aquatic Habitat 

Direc c-Phase CR F 

esidues cute to y valu r fresh fish.

 CRL ulting aerial, ground and 

LV appli in Ta 31, T 32, 

and it radate conce s for

LOC ), with excep dico

 RQs hronic osure e CR

e all uses exceed the LOC (1.0) sulting from r all u except muda turf 

pplications, for all uses of dicofol that have both ground 

ets of RQs exceed levels of concern for the

Table 31. Acute and chronic RQs for aquatic-phase CRLF resulting from AERIAL applications of 

dicofol. EECs are based on parent and degradates of concern. 

Use Peak EEC 

(μg/L) 

60-day 

(μg/L) 

Acute 

RQ1

Chronic 

RQ2

Beans 17.77 15.47 0.343 3.54

Citrus 17.50 13.29 0.333 3.04

Cotton 18.02 16.27 0.343 3.74

Cucurbit 6.32 5.37 0.123 1.24

Grape 13.15 11.17 0.253 2.54

Hops 19.67 17.50 0.373 4.04

Mint 16.47 14 3 4 .56 0.31 3.3

Pepper 8.91 7.74 0.173 1.84

Pome Fruit 20.73 16.26 0.39 3.7 3 4

Stone Fruit 9.97 7.76 0.193 1.84

Strawberry 37.39 0.713 7.64 33.41 

Tomato 6.30 5.16 123 1.24 0.

Walnut/Pecan 20. 18.0 .393 .14 77 6 0 4 1

Based on 96-h LC50 = 53 μ tthroat t

AEC = 4.4 μg/ inbow tro

 endan pecies le ncern 5) 

onic risk level o rn (RQ>

g/L for cu rout 2

Based on NO L for ra ut 3

 Exceeds acute risk to gered s vel of co (RQ>0.0 4

 Exceeds chr f conce 1.0) 

90 
Table 32. Acute and chronic RQs for aquatic-phase CRLF resulting from GROUND applications of 

icofol. EECs are based on parent and degradates of concern. 

nic 

2

d

Use Peak EEC 

(μg/L) 

60-day 

(μg/L) 

Acute 

RQ1

Chro

RQ

Beans 15.87 14.27 0.303 3.24

Citrus .53 53 12.99 10 0.2 2.44

Cotton 14.9 3 16.01 9 0.30 3.44

Cucurbit 5.52 4.77 1.14 0.103

Grape 11. 10.07 213 31 0. 2.34

Hops 18.35 16.69 0.353 3.84

Mint 15. 13.50 293 14 0. 3.14

Pepper 8.23 7.43 163 1. 4 0. 7

Pome Fruit 15. 12.25 293 40 0. 2.84

Stone Fruit 7.60 6.05 143 1. 4 0. 4

Strawberry 36. 32.15 693 36 0. 7.34

Tomato 5.2 4.41 103 2 0. 1.04

Walnut/Pecan 17. 16.02 343 94 0. 3.64

Bermuda grass 2.3 1.93 4 1 0.04 0.44 

Ornamentals 6.09 5.25 113 0. 1.24

Turf/Sod Farm 2.88 2.40 0.0543 0.55 

Outside Buildings 0.354 0.248 0.0067 0.056 1

Based on 96-h LC50 = 53 μg/L for cutthroat trout 2

Based on NOAEC = 4.4 μg/L for rainbow trout 

3

 Exceeds acute risk to endangered species level of concern (RQ>0.05) 4

 Exceeds chronic risk level of concern (RQ>1.0) 

Table 33. Acute and chronic RQs for aquatic-phase CRLF resulting from ULV applications of 

dicofol. EECs are based on parent and degradates of concern. 

Use Peak EEC 

(μg/L) 

60-day 

(μg/L) 

Acute 

RQ1

Chronic 

RQ2

Beans 31.80 25.26 0.603 5.74

Citrus 45.13 33.29 0.853 7.64

Cotton 31.57 25.23 0.603 5.74

Cucurbit 12.14 9.41 0.233 2.14

Grape 25.28 19.80 0.483 4.54

Hops 29.66 24.58 0.563 5.64

Mint 28.76 23.28 0.543 5.34

Pepper 15.88 12.61 0.303 2.94

Pome Fruit 3 4 48.90 36.56 0.92 8.3

Stone Fruit 23.78 17.68 0.453 4.04

Strawberry 51.32 43.81 0.973 104

Tomato 13.70 10.35 0.263 2.44

Walnut/Pecan 40.15 31.59 0.763 7.24

1

Based on 96-h LC50 = 53 μg/L for cutthroat trout 2

Based on NOAEC = 4.4 μg/L for rainbow trout 

3

 Exceeds acute risk to endangered species level of concern (RQ>0.05) 4

 Exceeds chronic risk level of concern (RQ>1.0) 

91 
As discussed above in section 3.3, dicofol has the potential to accumulate in tissues of 

d 

r 

to define the risks of aquatic-phase CRLF g lank lgae c 

invertebrates and fish, KABAM was used to d Q v r sm .4 g), um 

(37 g) and large (238 g) aquatic-phase CRLF. we sum are co ent 

with those incorporated into T-HERPS. Diet a tions assigned to each of these size 

classes are provided in Table 34. The resultin alue he C re pro in 

T ceed the LO or ac se ba nd 

chronic, dietary-based exposures to the CRLF ingesting dicofol through consum of 

c inated aquatic prey (that have accumula ofol)

T t assumptions of small, medium and larg tic-ph LF u BAM

Diet

aquatic organisms. Since aquatic-phase CRLF consume algae, aquatic invertebrates an

fish, CRLF could be exposed to dicofol accumulated in the tissues of these prey. In orde

 consumin

erive R

phytop

alues fo

ton (a

all (1

), benthi

 medi

 Body ight as ptions nsist

ssump

g RQ v s for t RLF a vided

able 35. RQ values for all size classes ex C f ute-do sed a

ption

ontam ted dic . 

able 34. Die e aqua ase CR sed in KA . 

 for: 

Trophic level in diet small CRLF 

1 

small CRLF 

2 

ed 

LF 1 RLF 

large 

 1

large 

CRLF 2 

m

CR

med 

C 2 CRLF

phytoplankton 100.0% 0.0% .0% 0% 0.0% 0.0% 0 0.

zooplankton 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

benthic invertebrates 0.0% 100.0% 100.0% 0.0% 100.0% 0.0% 

filter feeders 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

small fish 0.0% 0.0% 0.0% 100.0% 0.0% 0.0% 

medium fish 0.0% 0.0% 0.0% 0.0% 0.0% 100.0% 

large fish 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

Total 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 

Table 35. Acute and chronic RQs for aquatic-phase C xpose ofol throu

c ion of aquatic organisms which have accum dicofo

Size Classes of CRLF se 

 RQ1

Acut

Dieta

ased

Chronic, Dietary 

Ba 3

RLF e d to dic (parent) gh 

onsumpt ulated l. 

Acute, Do

Based

e, 

ry 

 RQ2 B sed RQ

small CRLF 1 4 0.63 0.012 115

small CRLF 2 4 0.38 0.017 155

med CRLF 1 0.073 0.017 155

med CRLF 2 4 0.17 0.043 395

large CRLF 1 0.029 0.017 155

large CRLF 2 4 0.14 0.0924 835

1

 Based on LD50 = 265 mg/kg-bw (for ring-necked pheasant) 

l) 

 concern (RQ>0.1) 

 Exceeds chronic risk level of concern (RQ>1.0)

2

 Based on LC50 = 903 ppm (for Japanese quai 3

 Based on NOAEC = 1 ppm (for American kestrel) 

4

 Exceeds acute risk to endangered species level of 5

92 
Indirect effects of dicofol to the aquatic-phase CRLF (t s) vi uction onvascular aquatic plants in its diet are based on peak EECs he st d pond the 

lowest toxicity value (EC50) for aquatic non-va plan Q va enerate ing 

EECs representing total residues of dicofol ( ) a s tha 1 for ses, 

which is below the LOC (1.0) for non-vascular c pla

Indirect acute effects to the aquatic-phase CR ia ef ebr in 

aquatic habitats are based on peak EECs of tota fol re in th dard p and 

the lowest acute toxicity value for freshwater tebrates. For chronic risks, 21-day 

E al dicofol residues and the lowest chronic toxicity value verteb

used to derive RQs. 

Acute and chronic RQs for the aquatic invert s res from al, ground and 

U ovided ble able and Table 38

r fol exceed the acute listed species LOC (0.05) for 

a ermuda grass, ornamentals, 

turf and outside buildings. RQs for chronic exposures to the CRLF from all uses of 

icofol exceed LOC (1.0), except cucurbits, peppers, tomatoes, Bermuda grass, 

rnamentals, turf and outside buildings. 

5.1.1.2. Indirect Effects to Aquatic-Phase CRLF through effects to prey 

adpole a red in n

from t andar and

scular ts. R lues g d us

Table 12 re les n 0.0 all u

 aquati nts. 

LF v fects to prey (invert ates)

l dico sidues e stan ond 

 inver

ECs of tot for in rates are 

ebrate ulting aeri

LV applications of dicofol are pr in Ta 36, T 37, 

espectively. RQs for all uses of dico

quatic invertebrates, with the exception of dicofol use on B

d

o

Table 36. Acute and chronic RQs for aquatic invertebrates resulting from AERIAL applications of 

dicofol. EECs are based on parent and degradates of concern. 

Use Peak EEC 

(μg/L) 

21-day 

(μg/L) 

Acute 

RQ1

Chronic 

RQ2

Beans 17.77 16.16 0.133 0.85 

Citrus 17.50 14.40 0.123 0.76 

Cotton 18.02 16.81 0.133 0.88 

Cucurbit 6.32 5.63 0.045 0.30 

Grape 3 13.15 11.78 0.09 0.62 

19.67 18.51 0.143 Hops 0.97 

Mint 16.47 15.58 0.123 0.82 

Pepper 8.91 8.09 0.0643 0.43 

Pome Fruit 20.73 17.51 0.153 0.92 

Stone Fruit 9.97 8.37 0.0713 0.44 

Strawberry 37.39 34.68 0.273 1.84

Tomato 6.30 5.49 0.045 0.29 

Walnut/Pecan 20.77 18.80 0.153 0.99 1

Based on 48-h EC50 = 140 μg/L for daphnid 2

Based on NOAEC = 19 μg/L for amphipod 

3

 Exceeds acute risk to endangered species level of concern (RQ>0.05) 4

 Exceeds chronic risk level of concern (RQ>1.0) 

93 
Table 37. Acute and chronic RQs for aquatic invertebrates resulting from GROUND applications of 

dicofol. 

Peak EEC 21-day Acute 

RQ1

Chronic 

RQ2

EECs are based on parent and degradates of concern.

Use (μg/L) (μg/L) 

Beans 15.87 14.69 0.113 0.77 

Citrus 12.99 10.87 0.0933 0.57 

Cotton 16.01 15.36 0.113 0.81 

Cucurbit 5.52 4.98 0.04 0.26 

Grape 11.31 10.39 0.0813 0.55 

Hops 18.35 17.45 0.133 0.92 

Mint 15.14 14.22 0.113 0.75 

Pepper 8.23 7.66 0.0593 0.40 

Pome Fruit 15.40 13.13 0.113 0.69 

Stone Fruit 7.60 6.48 0.0543 0.34 

Strawberry 36.36 33.38 0.263 1.84

Tomato 5.22 4.65 0.037 0.24 

Walnut/Pecan 17.94 16.52 0.133 0.87 

Bermuda grass 2.31 2.02 0.016 0.11 

Ornamentals 6.09 5.51 0.044 0.29 

Turf/Sod Farm 2.88 2.52 0.021 0.13 

Outside Buildings 0.354 0.281 0.0025 0.015 1

Based on 48-h EC50 = 140 μg/L for daphnid 

d on NOAEC = 19 μg/L for amphipod. 3 endangered species level o n (RQ>0.05

0) 

2

Base

 Exceeds acute risk to 

4

 Exceeds chronic risk l

f r conce ) 

evel of concern (RQ>1.

Table 38. Acute and chronic RQs for aquatic inv tes resultin ULV applicat 

d EECs are based on parent and degradat ncern. 

Use EEC 

g/L) 

2

(μ

Acute 

RQ1

onic 

Q2

ertebra g from ions of

icofol. es of co

Peak

(μ

1-day 

g/L) 

Chr

R

Beans 31.80 2 0.233 1.44 7.04 

Citrus 45.13 3 0.323 1.94 6.41 

Cotton 31.57 2 0.233 1.44 7.01 

C 12.14 10.18 0.0873 ucurbit 0.54 

G 8 21.29 0.183 1.14 rape 25.2

Hops 29.66 25.90 0.213 1.44

Mint 28.76 24.71 0.213 1.34

Pepper 15.88 13.49 0.113 0.71 

Pome Fruit 48.90 39.92 0.353 2.14

Stone Fruit 23.78 19.38 0.173 1.04

S .31 0.373 2.44 trawberry 51.32 45

Tomato 13.70 11.27 0.103 0.59 

40.15 33.92 0.293 1.8 W 4 alnut/Pecan 1

Based on 48-h EC50 = 140 μg/L for daphnid 

Based on NOAEC = 19 μg/L for amphipod 

 Exceeds acute risk to endangered species level of concern (RQ>0.05) 4

 Exceeds chronic risk level of concern (RQ>1.0) 

2

3

94 
Fish and frogs also represent potential prey items of adult aquatic-phase CRLFs. RQs 

associated 

used to assess potential indirect effects to the CRLF based on a reduction in freshwater 

sh and frogs as food items. As noted above, exposures involving dicofol and its 

effects of dicofol to vascular aquatic plants, 

Q values for vascular aquatic plants cannot be derived. 

with acute and chronic direct toxicity to the CRLF (Table 31 and Table 32) are 

fi

degradates of concern (DCBP, FW-152, DCBH, and OH-DCBP), RQs for all uses of 

dicofol exceed the acute listed species LOC (0.05), with the exception of dicofol use on 

Bermuda grass and outside buildings. RQs for chronic exposures to the CRLF resulting 

from all uses exceed the LOC (1.0) for all uses, except Bermuda grass, turf and outside 

buildings. 

5.1.1.3. Indirect Effects to Aquatic-Phase CRLF through effects to habitat 

Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the 

most sensitive non-vascular and vascular plant toxicity endpoints. RQ values generated 

for non-vascular plants using EECs representing total residues of dicofol (Table 12) are 

less than 0.01 for all uses, which is below the LOC of 1.0 for non-vascular aquatic plants. 

Since no data are available to quantify the 

R

95 
5.1.2. Exposures in the Terrestrial Habitat 

5.1.2.1. Direct Effects to Terrestrial-Phase CRLF 

acute risks to the terrestrial-phase CRLF are derived by considering dose- 

 T-RE a small bird (20 g) consumi all 

0) and acute oral and subacute dietary toxicity endpoints for avian 

otential direct chronic risks of dic the terrestrial-phase CRLF are derived 

considering dietary-based exposures m d in T-RE r a small bird (20g) 

all invertebrates and the low ailable chr oxicity data f rds. 

re divided by toxicity values to estim ronic diet Qs. Acute dose-

 (0.1 all uses of l, with RQs e ing 

factors ranging between 4.3 to

for most uses, with the exceptio use on cuc ornamentals, turf and 

s exceed the LOC (1.0) for all uses of dicofol, 

dicofol to 

X. 

Potential direct 

and dietary-based EECs modeled in X for ng sm

invertebrates (Table 2

species. P ofol to

by odele X fo

consuming sm est av onic t or bi

EECs a ate ch ary-based R

based RQs (Table 39) exceed the LOC

the LOC by 

) for 

32X. Acute dietary-based RQs exceed the 

dicofo xceed

LOC (0.1) n of urbits,

Bermuda grass. Chronic dietary-based RQ

by factors ranging 54 to 405X (Table 39). 

Table 39. Acute an

the terrestrial-phas

d chronic, dietary-based RQs and dose-based RQs for direct effects of 

e CRLF. RQs calculated using T-RE

Use Acute, Dosebased7

Acute, Dietary- Chronic, Dietarybased8 based9

Citrus,1 Pome Fruits2 3.210 0.4510 40511

Strawberries, Walnuts (English/black), 2.1310 0.3010 27011

Pecans 

Beans, cotton, Stone Fruits3 1.5910 0.2210 20311

Grapes, mint4 1.3310 0.1910 16911

Hops 1.2410 0.1710 15711

Peppers, Tomatoes 0.8010 0.1110 10111

Cucurbits5 0.6610 0.09 8411

Ornamentals,6 Turf grasses, Sod farms, 

Outside building surfaces 0.5310 0.07 6711

Bermuda grass 0.4310 0.06 5411

1

 grapefruit, lemons, oranges, tangelos, and tangerines 

2

 apples and pears 3

 apricots, cherries, nectarines, peaches, plums, and prunes 

4

 mint, peppermint and spearmint 

5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6

 nurseries and flowers 

7

 Based on LD50 = 265 mg/kg-bw (for ring-necked pheasant) 8

 Based on LC50 = 903 ppm (for Japanese quail) 9

 Based on NOAEC = 1 ppm (for American kestrel) 

10 Exceeds acute risk to endangered species level of concern (RQ>0.1) 11 Exceeds chronic risk level of concern (RQ>1.0) 

96 
s to Terrestrial-Phase CRLF through Effects to 

Prey 

itats, the honey bee is used as a surrogate for 

rrestrial invertebrates. EECs (μg a.i./g of bee) calculated by T-REX for small and large 

inate, i.e., the LD50 value exceeds the 

pressed as less than (<) values. For small insect 

fol, RQ values potentially exceed the acute 

sk LOC (RQ>

5.1.2.2. Indirect Effect

In order to assess the risks of dicofol applications to terrestrial invertebrates, which are 

considered prey of CRLF in terrestrial hab

te

insects are divided by the calculated toxicity value (LD50) for terrestrial invertebrates, 

which is >391 μg a.i./g of bee. The resulting RQ values for large insect and small insect 

exposures bound the potential range of exposures for terrestrial insects to dicofol. Since 

the acute contact toxicity estimate is indeterm

highest dose tested (LD50>50μg/bee) the resulting toxicity value for terrestrial 

invertebrate is also indeterminate (LD50>391 μg a.i./g of bee). As such, RQ values based 

on these indeterminate values are ex

exposures, RQ values range <1.04 to <0.138. For large insect exposures, RQ values 

range <0.115 to <0.0153. For all uses of dico

ri 0.05) for terrestrial insects. 

are used. Acute and chronic effects are 

stimated using the most sensitive acute (rat LD50=587 mg/kg-bw) and chronic (rate 

toxicity values and RQs used to assess direct effects to the CRLF. Acute dose-based RQs 

exceed the LOC (0.1) for all uses of dicofol, with RQs exceeding the LOC by factors 

nging between 4.3 to 32X. Acute dietary-based RQs exceeded the LOC (0.1) for most 

cofol, by factors 

nging 54 to 405X (Table 39). 

As described above, to assess risks of dicofol to prey (small mammals) of larger 

terrestrial-phase CRLF, dietary-based and dose-based exposures modeled in T-REX for a 

small mammal (15g) consuming short grass 

e

NOAEC 5 mg/kg diet; 0.4 mg/kg-bw/day) mammalian toxicity data. EECs are divided by 

the toxicity values to estimate acute and chronic dietary-based RQs as well as acute dosebased RQs. Acute dose-based RQ values exceed the listed species acute risk LOC 

(RQ>0.1) for the majority of dicofol uses. Across all uses, chronic dose-based and 

dietary-based RQs exceed the chronic risk LOC (RQ>1.0) (Table 40). 

An additional prey item of the adult CRLF is other species of frogs. In order to assess 

risks to these organisms, dietary-based and dose-based exposures modeled in T-REX for 

a small bird (20g) consuming small invertebrates are used. These are the same EECs, 

ra

uses, with the exception of use on cucurbits, ornamentals, turf and Bermuda grass. 

Chronic dietary-based RQs exceed the LOC (1.0) for all uses of di

ra

97 
Table 40. RQs for determining indirect effects to the terrestrial-phase CRLF through effects to 

potential prey items, specifically small terrestrial mammals consuming short grass. 

Use Acute, 

dose-based7

Chronic, 

dose-based8

Chronic, 

dietary-based9

Citrus,1 Pome Fruits2 0.5310 78111 14411

Str lish/black), Pecans 0.3510 52111 9611 awberries, Walnuts (Eng

Beans, cotto , Stone Fruits3 0.2710 39011 7211 n

apes, mint4 0.2210 32511 6011 Gr

Hops 0.2110 30311 5511

Peppers, Tomatoes 0.1310 19511 3611

curbits5 0.1110 16311 3011 Cu

Or

bu

namentals,6 Turf grasses, Sod farms, Outside 

ilding surfaces 0.09 13011 2411

Bermuda grass 0.07 10411 1911

1

 gra

2

 apples and pears 

3

 apri

4

 m

5

 c

6

 n

7

 B

8

 B

9

 B

10 E ies level of concern (RQ>0.1) 11 Exceeds chronic risk level of concern (RQ>1.0) 

pefruit, lemons, oranges, tangelos, and tangerines 

cots, cherries, nectarines, peaches, plums, and prunes 

int, peppermint and spearmint 

antaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

urseries and flowers

ased on LD50 for laboratory rat = 587 mg/kg. 

ased on chronic NOAEL for laboratory rat = 0.4 mg/kg-bw. 

ased on chronic NOAEC for laboratory rat = 5 ppm. 

xceeds acute risk to endangered spec

5.1.2.3. Indirect Effects to Terrestrial-Phase CRLF through Effects to 

lant toxicity endpoints. Since no data are available to quantify the effects 

f dicofol to terrestrial plants, these RQ values cannot be derived and risk is presumed. 

od sources for 

rrestrial-phase juveniles and adults. Because these endpoints are also being assessed 

lative to the potential for indirect effects to aquatic- and terrestrial-phase CRLF, the 

ffects determinations for indirect effects from the potential loss of food items are used as 

ination for potential effects to designated critical habitat. 

Habitat (plants) 

Indirect effects to the CRLF via direct toxicity to terrestrial plants are estimated using the 

most sensitive p

o

 5.1.3. Primary Constituent Elements of Designated Critical Habitat 

For dicofol use, the assessment endpoints for designated critical habitat PCEs involve a

reduction and/or modification of food sources necessary for normal growth and viability

of aquatic-phase CRLFs, and/or a reduction and/or modification of fo

te

re

e

the basis of the effects determ

98 
5.1.3.1. Aquatic-Phase 

constituent 

elem gnated or the

effects to aquatic and/or terrestria

• Alteration of c ediment 

ition within the stre channel or 

r shelter, forag

adult CRLFs. 

Alteration in water chemistry/quality

oxygen content necessary for normal gro

CRLFs and their food source. 

• Reduction and/or modification of aquatic-based food sources for pre-metamorphs 

(e.g., algae). 

ck of data to quan tial eff

o ay affect aquatic-phase PCEs 

d/or terrestrial p

assessment. 

The remaining aquatic-phase PCE is “altera ther chemical characteristics 

necessary for normal growth and viability of CR

the impact of dicofol on this PCE (i.e., alterati

freshwater fish and invertebrate toxicity endpo

vascular plants, are used as measures of effects. lculated 

in Section 5.1.1. Based on LOC exceedances for

aquatic invertebrates to total residues of dicofol,

PCEs of designated habitat related to effe chemical 

characteristics necessary for normal growth and viability of CRLFs and their food source. 

5.1.3.2. Terrestrial-Phase 

assessment endpoints for the terre

fec

ance of upland 

nd areas with riparian 

etation or dripline surrounding aquatic and riparian habitat that are comprised 

s and

d predator avoida

ance of dispers l habitat: Upland or riparian dispersal 

 units and between occupied locations within 0.7 mi of 

Three of the four assessment endpoints for the aquatic-phase primary 

ents (PCEs) of desi critical habitat f

l plants: 

 CRLF are related to potential 

hannel/pond morphology or geometry and/or increase in s

depos am pond: aquatic habitat (including riparian 

vegetation) provides fo ing, predator avoidance, and aquatic 

dispersal for juvenile and 

• including temperature, turbidity, and 

wth and viability of juvenile and adult 

Based on a la tify poten

l m

ects of dicofol to aquatic and terrestrial 

plants, it is assumed that dicof of designated habitat 

related to effects on aquatic an

later in the risk description of this 

lants. This assumption will be refined 

tion of o

LFs and their food source.” To assess 

on of food sources), acute and chronic 

ints, as well endpoints for aquatic nonRQs for these endpoints were ca

acute and chronic exposures of fish and 

 use of dicofol may affect aquatic-phase 

cts of alteration of other 

The first two strial-phase PCEs of designated critical 

habitat for the CRLF are related s to terrestrial plants: 

• Elimination and/or disturb

source of CRLFs: Upla

veg

to potential ef t

habitat; ability of habitat to support food 

in 200 ft of the edge of the

of grasslands, woodland

CRLF shelter, forage, an

• Elimination and/or disturb

habitat within designated

, and/or wetl /riparian plant species that provides the 

nce 

a

99 
each other that allow for movement between sites including both natural and 

altered sites which do not contain barriers to dispersal 

 on a lack of data to quantif strial plants, it is 

assumed that dicofol may affe abitat related to 

i ption wi

d terrestrial-phase PCE is “reduction and/or modification of food sources for 

terrestrial phase juveniles and ad To assess

and chronic toxicity endpoints for birds, mamm restrial invertebrates are used 

as measures of effects. RQs for these endpoints were calculated in Section 5.1.2. Based 

dances for acute and chronic expo

restrial-phase P

f food sources for terrestrial phase juveniles and adults.” 

The fourth terrestrial-phase PCE is based on alteration of chemical characteristics 

necessary for normal growth and viability of ju

source. Based on LOC exceedances for acute and chronic exposures of frogs to dicofol, 

 may affect terrestrial-phase PCEs

r

.2. Risk Description 

he risk description synthesizes an overall conclusion regarding the likelihood of adverse 

pacts leading to an effects determination (i.e., “no effect,” “may affect, but not likely 

d 

The direct and indirect effect LOCs are y affect the PCEs of the 

CRLF’s critical habitat. affect” 

ding d

e 41 for direct and

ted critical habitat for the CRLF. 

Based y potential effects of dicofol to terre

ct terrestrial-phase PCEs of designated h

effects on terrestrial plants. Th

of this assessment. 

The thir

s assum ll be refined later in the risk description 

ults.” the impact of dicofol on this PCE, acute 

als, and ter

on LOC excee sures of frogs and mammals to dicofol, 

use of dicofol may affect ter CEs of designated habitat related to 

“reduction and/or modification o

venile and adult CRLFs and their food 

use of dicofol of designated habitat related to effects of 

alteration of other chemical cha sary for normal growth and viability of 

CRLFs and their food source. 

acteristics neces

5

T

im

to adversely affect,” or “likely to adversely affect”) for the CRLF and its designate

critical habitat. 

 exceeded and dicofol ma

 Therefore, the Agency concludes a preliminary “may

determination for the FIFRA regulatory

estimation results are provided in Tabl

and in Table 42 for the PCEs of designa

 action regar icofol. A summary of the risk 

 indirect effects to the CRLF 

100 
fol - direct and indirec

Assessment Endpoint LOC 

Exceedances? Descripti

Table 41. Risk estimation summary for dico t effects to the CRLF. 

on of Results of Risk Estimation 

Aquatic-Phase CRLF (eggs, larvae, tadpoles, juveniles, and adults) 

Direct Effects 

Survival, growth, and reproduction 

of CRLF individuals via direct 

effects on aquatic phases 

Yes Acute RQs exceed the LOC for exposures of aquatic-phase 

CRLF resu

outside bui

Chronic RQ

CRLF res es of dicofol, except use on 

Bermuda g , turf and outside buildings. 

Acute and

aquatic org

accumulati

lting from all uses of dicofol, except applications to 

ldings. 

s exceed the LOC for exposures of aquatic-phase 

ulting from all us

rass

 chronic RQs for aquatic-phase CRLF consuming 

anisms contaminated with dicofol (resulting from 

on) exceed LOCs. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects to 

food supply (i.e., freshwater 

invertebrates, non-vascular plants) 

yes RQ values below the LOC for all uses. 

Acute RQ

invertebrat

Bermuda g

buildings. 

Chronic R aquatic 

invertebrates resulting from the majority of dicofol uses, except 

atoes, Bermuda grass, ornamentals, turf 

de buildings. 

e RQs 

to outside buil h and 

aquatic-phase amphibians resulting. 

Chronic RQs exceed the LOC for exposures of fish and 

aquatic-phase amphibians resulting from all uses of dicofol, 

except use on Bermuda grass, turf and outside buildings. 

for algae are

s exceed the LOC for exposures of aquatic 

es resulting from the majority of dicofol uses, except 

rass, ornamentals, turf and applications to outside 

Qs exceed the LOC for exposures of

cucurbits, peppers, tom

and applications to outsi

Acut for all uses of dicofol modeled, except applications 

dings exceed the LOC for exposures of fis

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

habitat, cover, and/or primary 

productivity (i.e., aquatic plant 

community) 

Undetermined RQ values 

No data are available to derive RQs representative of the 

effects of dicofol on vascular plants. 

for algae are below the LOC for all uses. 

Indirect Effects Un

Survival, growth, and reproduction 

of CRLF individuals via effects to 

riparian

determ

 vegetation, required to 

maintain acceptable water quality 

and habitat in ponds and streams 

comprising the species’ current 

No data are 

effects of di

ined available to derive RQs representative of the 

cofol on vascular plants. 

101 
Assessment Endpoint LOC 

Excee D dances? escription of Results of Risk Estimation 

range. 

Terrestrial-Phase CRLF (Juveniles and adults) 

Direct Effects 

Survival, growth, and reproduction 

of CRLF individuals via direct 

effects on terrestrial phase adults and 

juveniles 

Yes Acute and 

CRLF for all uses of 

chronic RQs exceed the LOC for terrestrial-phase 

dicofol. 

Indirect 

Yes 

Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

prey (i.e., terrestrial invertebrates, 

small terrestrial mammals and 

terrestrial phase amphibians) 

For terrestr

the LOC. 

Acute RQs

exceed the

turf, outsid

Chronic RQ

exceed the 

Acute and the LOC for terrestrial-phase 

amphibians

ial invertebrates, RQs for all uses potentially exceed 

 for small terrestrial mammals exposed to dicofol 

 LOC for all uses of dicofol, except ornamentals, 

e building surfaces and Bermuda grass. 

s for small terrestrial mammals exposed to dicofol 

LOC for all uses of dicofol. 

chronic RQs exceed

 for all uses of dicofol. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

habitat (i.e., riparian vegetation) 

Undetermined No data a e 

effects of di

re available to derive RQs representative of th

cofol on vascular plants. 

Table 42. Risk estimation summary for dicofol – PCEs of designated critical habitat for the CRLF. 

Assessment Endpoint Habitat Effects? Description of Results of Risk Estimation 

Aquatic-Phase CRLF PCEs 

(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)

Alteration of channel/pond morphology or Undetermined No data are available to derive RQs rep

geometry and/or increase in sediment 

resentative 

of the effects of dicofol on vascular plants. 

deposition within the stream channel or 

pond: aquatic habitat (including riparian 

vegetation) provides for shelter, foraging, 

predator avoidance, and aquatic dispersal 

for juvenile and adult CRLFs. 

Alteratio

includi g

content necess

viability o

their food s

presentative 

s. 

n in water chemistry/quality 

n temperature, turbidity, and oxygen 

ary for normal growth and 

ile and adult CRLFs and 

Undetermined No data are available to derive RQs re

of the effects of dicofol on vascular plant

f juven

ource. 

102 
Assessment Endpoint Habitat Effects? Description of Results of Risk Estimation 

Alteration of other chemical characteristics 

necessary for normal growth and viability of 

Yes Acute and chronic RQs for aquatic

CRLFs and their food source. dicofol (resulting from accumulation) 

-phase CRLF 

consuming aquatic organisms contaminated with 

exceed LOCs. 

Acute RQs exceed the LOC for exposures of aquatic 

rity of dicofol 

ntals, turf and 

 buildings. 

Chronic RQs exceed the LOC for exposures of 

aquatic invertebrates resulting from the majority of 

dicofol uses, except cucurbits, peppers, tomatoes, 

Bermuda grass, ornamentals, turf and applications to 

outside buildings. 

sures of fish 

 from all 

s to outside 

nic RQs exceed the LOC for exposures of fish 

and aquatic-phase amphibians resulting from all uses 

rass, turf and 

invertebrates resulting from the majo

uses, except Bermuda grass, orname

applications to outside

Acute RQs exceed the LOC for expo

and aquatic-phase amphibians resulting

uses of dicofol, except application

buildings. 

Chro

of dicofol, except use on Bermuda g

outside buildings. 

Reduction and/or modification of aquaticbased food sources for pre-metamorphs 

(e.g., algae) 

Undetermined No data are available to derive RQs r

of the effects of dicofol on vascular plant

epresentative 

s. 

Terrestrial-Phase CRLF PCEs 

(Upland Habitat and Dispersal Habitat)

Elimination and/or disturbance 

abitat; ability of habitat to supp

of upland 

ort food 

urce of CRLFs: Upland areas within 200 

 of the edge of the riparian vegetation or 

ripline surrounding aquatic and riparian 

abitat that are comprised of grasslands, 

oodlands, and/or wetland/riparian plant 

ecies that provides the CRLF shelter, 

rage, and predator avoidance 

Undetermined No data are available to derive RQs representative 

h of the effects of dicofol on vascular plants. 

so

ft

d

h

w

sp

fo

E

h

limination and/or disturbance of dispersal 

abitat: Upland or riparian dispersal habitat 

ithin designated units and between 

ccupied locations within 0.7 mi of each 

ther that allow for movement between sites 

cluding both natural and altered sites 

hich do not contain barriers to dispersal 

Undetermined No data are available to derive RQs representative 

of the effects of dicofol on vascular plants. 

w

o

o

in

w

Reduction and/or modification of food 

urces for terrestrial phase juveniles and 

ults 

Yes For terrestrial invertebrates, RQs for all uses 

potentially exceed the LOC. 

Acute RQs for small terrestrial mammals exposed 

to dicofol exceed the LOC for all uses of dicofol, 

except ornamentals, turf, outside building surfaces 

so

ad

103 
Assessment Endpoint Habitat Effects? Description of Results of Risk Estimation 

an

Ch

to

d Ber

ro s for s ammals exposed 

 dico ceed th ses of dicofol. 

Acute chronic RQs exceed the LOC for 

terrestrial-phase amphibians for all uses of dicofol. 

muda grass. 

mall terrestrial m

e LOC for all u

nic RQ

fol ex

 and 

A of chemic aracteristics 

n for normal gro d viability of 

j and adult CRL d their od 

s

Ye Acute chroni he LOC for 

terrest hase CRLF l uses of dicofol. 

For terrestrial inver r all uses 

poten xceed th 

Acute for small terrestrial mammals exposed 

to dicofol exceed the C for all uses of dicofol, 

except ornamentals side building surfaces 

and B a grass. 

Chro s for sm ammals exposed 

to dic ceed th r all uses of dicofol. 

Acu chron eed the LOC for 

terrestrial-phase amphibians for all uses of dicofol. 

lteration al ch

ecessary wth an

uvenile Fs an fo

ource. 

s and c RQs exceed t

rial-p for al

tebrates, RQs fo

tially e e LOC.

 RQs 

LO

, turf, out

ermud

nic RQ all terrestrial m

ofol ex e LOC fo

te and ic RQs exc

Following a “may affect” determination, additional information is considered to refine 

the potential for exposure at the predicted levels based on the life history characteristics 

(i.e., habitat range, feeding preferences, etc.) of the CRLF. Based on the best available 

information, the Agency uses the refined evaluation to distinguish those actions that 

“may affect, but are not likely to adversely affect” from those actions that are “likely to 

adversely affect” the CRLF and its designated critical habitat. 

The criteria used to make determinations that the effects of an action are “not likely to 

adversely affect” the CRLF and its designated critical habitat include the following: 

• Significance of Effect: Insignificant effects are those that cannot be meaningfully 

measured, detected, or evaluated in the context of a level of effect where ‘take’ 

occurs for even a single individual. ‘Take’ in this context means to harass or 

harm, defined as the following: 

 Harm includes significant habitat modification or degradation that 

results in death or injury to listed species by significantly impairing 

behavioral patterns such as breeding, feeding, or sheltering. 

 Harass is defined as actions that create the likelihood of injury to listed 

species to such an extent as to significantly disrupt normal behavior 

104 
patterns which include, but are not limited to, breeding, feeding, o

sheltering. 

r 

• Likelihood of the Effect Occurring: Discounta ect thos e 

extremely unlikely to occur. 

Adverse Nature of Effect

ble eff s are e that ar

• : Effects that holly icial t any rse 

ot considered adverse. 

A description of the risk and effects determinat r each he es ed as ent 

endpoints for the CRLF and its designated critical habitat is provided below. 

. Direct Effects 

As discussed in the risk estimation section, RQ all us dico cept da 

g for aquatic-phase CRLFs exposed to total 

r

otal residues of dicofol to the aquatichase CRLF. The determination for all other uses of dicofol is ‘may effect’ for direct 

Based on an analysis of the likelihood of individual mo ons g th f 

acute RQs exceeding the LOC for aquatic-p RL 54-0 and u the 

probit dose-response of 4.5 (default assumption chan mor o CR ge 

f 8

 individuals to 1 in 2 individuals (Table 43). indic hat 

a ase CRLF could potentially be affe by ac xpos dico An 

e output calculating the analysis of the likelihood of individual mo is 

provided in Appendix M. 

are w benef u witho adve

effects are n

ion fo of t tablish sessm

5.2.1

5.2.1.1. Aquatic-Phase CRLF 

s for es of fol, ex Bermu

rass and outside buildings exceed LOCs

e ination for use of dicofol on Bermuda grass and 

utside buildings is ‘no effect’ for direct effects of t

sidues of dicofol. Therefore, the determ

o

p

effects of total residues of dicofol to the aquatic-phase CRLF. 

rtality c

Fs (0.0

iderin

.97), 

e range o

hase C sing 

), the ce of tality t

 This 

LF ran

rom 1 in 1.7x10 ates t

quatic-ph cted ute e ures to fol. 

xample rtality

105 
Table 43. Acute RQs and for aquatic-phase CRLF resulting from applications of dicofol. EECs 

based on parent and degradates of concern. 

are 

Use ULV application Aerial application Gro plica und ap tion 

Acute 

RQ1

Chance of 

individual 

mortality 

(1 in...) 

Acute 

RQ1

nce 

ividua

rtality

 in...) 

e 

RQ1

Chance

individu

mortali

(1 in...

Cha of 

ind l Acut

mo 

(1

 of 

al 

ty 

) 

Beans 0.60 6 0.34 57 0.30 107 

Citrus 0.85 3 0.33 66 0.25 297 

Cotton 0.60 6 0.34 57 0.30 107 

Cucurbit 0.23 491 0.12 58,519 0.10 294,319 

Grape 0.48 13 0.25 297 0.21 84 

Hops 0.56 8 0.37 38 0.35 50 

Mint 0.54 9 0.31 91 0.29 129 

Pepper 0.30 107 0.17 3,744 0.16 5853

Pome Fruit 0.92 2 0.39 30 0.29 129 

Stone Fruit 0.45 17 0.19 1,706 0.14 16,417

Strawberry 0.97 2 0.71 4 0.69 4 

Tomato 0.26 236 0.12 58,519 0.10 294,319 

Walnut/Pecan 0.76 3 0.39 30 0.34 57 

Bermuda grass NA NA NA NA 0.044 1.94x109 

Ornamentals NA NA NA NA 0.11 124,594 

Turf/Sod Farm NA NA NA NA 0.054 1.71x108 

Outside Buildings NA NA NA NA 0.0067 1.52x1022 1

Based on 96-h LC50 = 53 μg/L for cutthroat trout 

NA = not applicable

Chronic RQs for the majority of dicofol uses (all except Bermuda grass, turf and outside 

buildings) exceed the LOC (1.0) by factors of 1.1X to 10X, depending upon the use and 

application method (Table 31-Table 33). EECs are sufficient to exceed the LOAEC (7.9 

i.e., DCBP, FW152, DCBH and OH-DCBP) are equivalent to dicofol in toxicity to the aquatic-phase 

RLF. This assumption adds uncertainty to the risk assessment as the actual toxicity of 

μg/L, based on growth effects) for the majority of dicofol uses, with the exception of 

Bermuda grass, ornamentals, turf and outside buildings. 

Exposures of aquatic-phase CRLF are to dicofol are quantified in terms of total residues 

of dicofol. RQs are derived using the most sensitive toxicity data available for fish 

exposed to dicofol. It is assumed that dicofol’s degradates of concern (

C

dicofol’s degradates to the CRLF is unknown. If exposures involving parent dicofol 

alone are considered, resulting acute RQs for the aquatic-phase CRLF exceed the listed 

species LOC (0.05) for all uses of dicofol, except Bermuda grass ornamentals, turf and 

outside buildings (Table 44 - Table 46). Therefore, acute exposures to parent dicofol 

alone are sufficient to be of concern for mortality to the aquatic-phase CRLF. RQs for 

chronic exposures of the CRLF to parent dicofol alone do not exceed the LOC (1.0). 

106 
Table 44. Acute and chronic RQs for aquatic-phase CRLF resulting from AERIAL applications of 

dicofol. EECs are based on parent dicofol only. 

Peak EEC 60-day Acute Chronic 

Crop (μg/L) (μg/L) RQ1 RQ2

Beans 3.25 0.18 0.0613 0.040 

Citrus 6.46 0.42 0.123 0.095 

Cotton 3.48 0.29 0.0663 0.066 

Cucurbit 1.34 0.07 0.025 0.016 

Grape 2.70 0.15 0.0513 0.033 

Hops 2.52 0.16 0.048 0.037 

Mint 2.70 0.15 0.0513 0.035 

Pepper 1.61 0.09 0.030 0.020 

Pome Fruit 6.46 0.34 0.123 0.077 

Stone Fruit 3.25 0.17 0.061 0.040 3

Strawberry 6.41 0.93 0.123 0.21 

Tomato 1.61 0.09 0.030 0.020 

Walnut/Pecan Aerial 4.41 0.29 0.0833 0.065 1

Based on 96-h LC50 = 53 μg/L for cutthroat trout 2

Based on NOAEC = 4.4 μg/L for rainbow trout 

3

 Exceeds acute risk to endangere pecies LOC (RQ>0.05) d s

Tab ase CRLF resulting f ROUND ap of 

dic

le 45. Acute and chronic RQs for aquatic-ph

ofol. EECs are based on dicofol only

rom G plications 

. 

Cr

Peak EEC 

(μg/L) 

60-d

(μg

Acute 

RQ1

onic 

Q2 op 

ay 

/L) 

Chr

R

Beans 2.26 0.1 0.043 8 2 0.02

Ci 4.47 0.3 0.0843 trus 2 0.072 

Cotton 2.49 0.2 0.047 6 5 0.05

Cucurbit 0.93 0.0 0.018 1 5 0.01

Grape 1.87 0.10 0.035 023 0.

Hops 1.74 0.1 0.033 8 2 0.02

Mint 1.87 0.11 0.035 0.025 

Pepper 1.12 0.06 0.021 0.014 

Po 4.47 0.24 0.0843 me Fruit 0.053 

Stone Fruit 2.25 0.12 0.042 0.028 

Str 6.34 0.89 0.123 awberry 0.20 

Tomato 1.12 0.06 0.021 0.014 

3.09 0.22 0.0583 Walnut/Pecan 0.050 

Bermudagrass 0.60 0.04 0.011 0.0095 

Ornamentals 1.78 0.18 0.034 0.041 

Turf/Sod Farm 0.75 0.05 0.014 0.012 

Outside Buidlings 0.152 0.010 0.0029 0.0023 1

Based on 96-h LC50 = 53 μg/L for cutthroat trout 2

Based on NOAEC = 4.4 μg/L for rainbow trout 

3

 Exceeds acute risk to endangered species LOC (RQ>0.05) 

107 
Table 46. Acute and chronic RQs for aquatic-phase CRLF resulting from ULV applications of 

dicofol. EECs are based on parent dicofol only.

Crop 

Peak EEC 60-day Acute Chronic 

(μg/L) (μg/L) RQ1 RQ2

Beans 9.75 0.52 0.18 0.1 3 2 

18.02 1.03 0.343 Citrus 0.23 

Cotton 9.92 0.60 0.193 0.14 

Cucurbit 4.04 0.21 0. 3 076 0.048 

Grape 8.08 0.43 0.153 0.10 

Hops 7.56 0.43 0.14 0.1 3 0 

Mint 8.07 0.44 0.15 0.1 3 0 

Pepper 4.85 0.26 0.091 0.0 3 59 

Pome Fruit 18.02 0.94 0.34 0.2 3 1 

Stone Fruit 9.08 0.48 0.17 0.1 3 1 

Strawberry 13.17 1.23 0.25 0.2 3 8 

Tomato 4.85 0.25 0.091 0.05 3 8 

Walnut/Pecan 13.02 0.72 0.25 0.1 3 6 1

Based on 96-h LC50 = 53 μg/L for cutthroa

(RQ>0.05) 

t trout 2

Based on NOAEC = 4.4 μg/L for rainbow trout 

3

 Exceeds acute risk to endangered species LOC 

Aquatic EECs account for direct toxicity to the CRLF through contact with dicofol 

nd its degradates 

ncern are expected to partition to aquatic 

F can also be exposed to dicofol and its 

inated prey items. Acute and chronic RQ values 

enerated using KABAM (Table 35) are above LOCs, indicating that exposure of 

-REX calculated acute dose-based RQs, acute dietary-based RQs and chronic dietaryased RQs exceed their respective LOCs, resulting in a “may affect” determination for all 

ses. In order to explore influences of amphibian-specific food intake equations on 

otential dose-based and dietary-based exposures of the terrestrial-phase CRLF to 

dicofol, T-HERPS is used. Modeling with T-HERPS incorporates the same application 

rates, intervals and number of applications for each use as defined for modeling using TREX (Table 19). Since applications of dicofol for all uses result in exposures sufficient to 

exceed the LOC for direct effects to the terrestrial-phase CRLF, the T-HERPS model was 

used to estimate EECs and subsequent risks to the terrestrial-phase CRLF based on 

amphibian-specific equations. These refined EECs and RQs were used to distinguish 

present in the water column. Given the high Log Kow of dicofol (>6) a

of concern (>4), dicofol and its residues of co

organisms. Therefore, the aquatic-phase CRL

residues through consumption of contam

g

aquatic-phase CRLF to dicofol through consumption of aquatic organisms which have 

accumulated dicofol is of concern for the CRLF. 

Based on the above information, for all uses of dicofol, except Bermuda grass and outside 

buildings, the effects determination for direct effects to the aquatic-phase CRLF is 

“LAA” based on potential acute mortality and chronic growth effects. The determination 

for use of dicofol on Bermuda grass and outside buildings is “no effect” for direct effects 

of total residues of dicofol to the aquatic-phase CRLF. 

5.2.1.2. Terrestrial-Phase CRLF 

T

b

u

p

108 
“NLAA” and “LAA” determinations. An example output from T-HERPS is available in 

Appendix N. 

RQs are calc d for the terrestrial CR t d t. I

be noted that although dietary-base alu c y do

er do not take into acco imals 

at depending on the forage item animal has to 

if g nu lev the food item. If di

 adjusted to acc for d ntia consum n, the ad

 would likely approximate the dose-based RQ value. 

res 

Refined dose-based RQs for small sized (1.4 F consuming insects do not e

the acute listed species LOC (0.1) for dicofol (Table 47). 

Table 47. Refined dose-based RQs for 1.4 g CRLF consuming different food items. EECs calculated 

using T-HERPS. 

Use Small Insects Large Insects 

ulate -phase

d RQ v

LF on

es are 

he basis of

onsiderabl

ose and die

lower than

t should 

se-based 

RQ values, the form consume 

differing amo

unt that different-sized an

unts of food and th , an 

consume varying amounts due to d ferin trition els in etarybased RQ values are ount iffere l food ptio justed 

RQ value

Acute exposu

g) CRL xceed 

7

Citrus,1 Pome Fruits2 0.06 0.01 

Strawberries, Walnuts (English/black), Pecans 0.04 <0.01 

Beans, cotton, Stone Fruits3 0.03 <0.01 

Grapes, mint4 0.02 <0.01 

Hops 0.02 <0.01 

Peppers, Tomatoes 0.01 <0.01 

Cucurbits5 0.01 <0.01 

Ornamentals,6 Turf grasses, Sod farms, Outside building 

surfaces 0.01 <0.01 

Bermuda grass 0.01 <0.01 1

 grapefruit, lemons, oranges, tangelos, and tangerines 

2

 apples and pears 

3

 apricots, cherries, nectarines, peaches, plums, and prunes 

4

 mint, peppermint and spearmint 

5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6

 nurseries and flowers 

7

 Based on LD50 = 265 mg/kg-bw (for ring-necked pheasant) 

Refined dose-based RQs for medium-sized (37 g) CRLF consuming small herbivorous 

ammals exceed the acute listed species LOC (0.1) for all uses of dicofol. RQs exceed 

e LOC by factors of 2.3 to 16.9x. Based on an analysis of the likelihood of individual 

ortality considering the range of acute dose-based RQs for medium terrestrial-phase 

RLFs consuming small herbivore mammals (0.23-1.69), and using the default probit 

dose-response of 4.5, the chance of mortality to these CRLF range from 1 out of 491 

individuals to 100%. RQs for medium-sized CRLF consuming insects and terrestrialphase amphibians do not exceed the acute listed species LOC (Table 48). This indicates 

that medium-sized CRLF could potentially be affected by acute exposures to dicofol. 

m

th

m

C

109 
Table 48. Revised dose-based RQs7

 for 37 g CRLF consuming different food items. EECs calculated 

using T-HERPS. 

Use Insects Insects Mammals Insecti 

Mammals Am

Small Large Small 

Herbivore 

Small 

vore

Small 

Terrestrialphase 

phibians 

Citrus,1 Pome Fruits2 0.06 0.01 1.698 0.118 <0.01 

Strawberries, Walnuts (English/black), 

Pecans 0.04 <0.01 1.138 0.07 <0.01

Beans, cotton, Stone Fruits3 0.03 <0.01 0.858 0.05 <0.01

Grapes, mint 

4 0.02 <0.01 0.718 0.04 <0.01

Hops 0.02 <0.01 0.668 0.04 <0.01

Peppers, Tomatoes 0.01 <0.01 0.428 0.03 <0.01

Cucurbits5 0.01 <0.01 0.358 0.02 <0.01

Ornamentals,6 Turf grasses, Sod farms, 

Outside building surfaces 0.01 <0.01 0.288 0.02 <0.01

Bermuda grass 0.01 <0.01 0.238 0.01 <0.01 1

 grapefruit, lemons, oranges, tangelos, and tangerines 

2

 apples and pears 

3

 apricots, cherries, nectarines, peaches, plums, and prunes 

rmint 4

 mint, peppermint and spea

5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

50 easant) 8

 Exceeds acute endangered species LOC (RQ>0.1) 

6

 nurseries and flowers 

7

 Based on LD = 265 mg/kg-bw (for ring-necked ph

Refined dose-based RQs for large-sized (238 g) CRLF consuming small, herbivore 

mammals are exceeded for some uses of dicofol (Table 49). Based on an analysis of the 

likelihood of individual mortality considering the range of acute dose-based RQs 

exceeding the LOC for large terrestrial-phase CRLFs consuming small herbivore 

mammals (0.10-0.26), and using the default probit dose-response of 4.5, the chance of 

mortality to these CRLF range from 1 in 294,319 individuals to 1 in 236 individuals. 

RQs for large-sized CRLF consuming insects and terrestrial-phase amphibians do not 

exceed the acute listed species LOC (Table 49). This indicates that large-sized terrestrialphase CRLF could potentially be affected by acute exposures to dicofol resulting from 

several uses. 

110 
Table 49. Revised dose-based RQs7

 for 238 g CRLF consuming different food items. EECs calculated 

Use Small 

Insects 

Large 

Insects 

Small 

Herbivore 

Small 

Insecti 

ll 

Terrestrialusing T-HERPS. 

Sma

Mammals 

vore

Mammals phase 

Amphibians 

Citrus,1 Pome Fruits2 0.04 <0.01 0.268 0.02 <0.01

Strawberries, Waln

Pecans 

uts (English/black), 0.03 <0.01 0.188 0.01 <0.01

Beans, cotton, Stone Fruits3 0.02 <0.01 0.138 0.01 <0.01

Grapes, mint 

4 0.02 <0.01 0.118 0.01 <0.01

Hops 0.01 <0.01 0.108 0.01 <0.01

Peppers, Tomatoes 0.01 <0.01 0.07 <0.01 <0.01

Cucurbits5 0.01 <0.01 0.05 <0.01 <0.01

Ornament ls,6 a Turf

Outside buil

 grasses, Sod farms, 

din surfaces g 

0.01 <0.01 0.04 <0.01 <0.01

Bermuda grass 0.01 <0.01 0.04 <0.01 <0.01 1

 grapefruit, lemons, orang 2

 apples and pea

es, tangelos, and tange

nes 

and winter and summer squash 

rines 

rs 3

 apricots, cherries, nectarines, peaches, plums, and pru

4

 mint, peppermint and spearmint 5

 cantaloupes, cucumbers, melons, pumpkins, watermelons, 

6

 nurseries and flowers 

7

 Based on LD50 = 265 mg/kg-bw (for ring-necked pheasant) 8

 Exceeds acute endangered species LOC (RQ>0.1) 

R

m

efined acute dietary-based RQs for CRLFs consuming small insects and herbivorous 

ammals exceed the acute listed species LOC (0.1) for most uses of dicofol (the 

excepti . Based on an analysis of the 

kelihood of individual mortality considering the range of acute dietary-based RQs 

ons include ornamentals, turf and Bermuda grass)

li

exceeding the LOC for terrestrial-phase CRLFs consuming small herbivore mammals 

(0.11-0.53), and using the probit dose-response of 5.92 (Table 27), the chance of 

mortality to these CRLF range from 1 in 1.4x108

 individuals to 1 in 19 individuals. For 

CRLFs consuming large insects, terrestrial-phase amphibians and small insectivorous 

mammals, the acute LOC is not exceeded for any use (Table 50). This indicates that 

CRLF could potentially be affected by acute exposures to dicofol. 

111 
Table 50. Re RLF consuming different food items. EECs 

lculated using T-HERPS. 

-

s 

vised acute dietary-based RQs7 for C

ca

Use Small 

Insects 

Large 

Insects 

Small 

Herbivore 

Mammals 

Small 

Insectivore 

Mammals 

Small 

Terrestrial

phase 

Amphibian

s,1 Pome Fruits2 0.458 0.05 0.528 Citru 0.03 0.02 

Straw

Pecans 0.308 0.03 0.358 0.02 0.01 berries, Walnuts (English/black), 

Beans, cotton, Stone Fruits 0.01 3 0.228 0.02 0.268 0.02 

Grapes, mint 0.01 4 0.198 0.02 0.228 0.01 

Hops 178 0.02 0.208 0. 0.01 0.01

Peppers, Tomatoes 8 0.11 0.01 8 0.13 0.01 <0.01 

Cucurbits5 0. 0.01 09 0.11 0.01 <0. 8 01

Ornamentals,6 Turf gras m

Outside building surfaces 

ses, Sod far s, 0.07 0.01 0.09 0.01 <0.01

Berm rass uda g 0.06 0.01 0.07 <0.01 <0.01 1

 grap mons, oranges, t s, and ta nes 

2

 appl ears 

3

 apri ries, nectarines es, plum prunes 

4

 mint nt and spearm

5

 cant cumbers, me mpkins rmelon nter an er squa

6

 nurs flowers 

7

 Bas C50 = 905 ppm (f nese qua 8

 Exc ute endangered sp OC (RQ>0.1) 

efruit, le angelo ngeri

es and p

cots, cher , peach s, and

, peppermi

aloupes, cu

int 

lons, up , wate s, and wi d summ sh 

eries and 

ed on L or Japa il) 

eeds ac ecies L

Chronic exposures 

R chronic diet ased R r CR ceed hronic specie C 

( ses of ol and all foo s pote y cons

( the a ble chr study re American kestrel were exposed to 

d NOAEC s 1 ppm nd the EC wa ppm, on de d 

e ess. C arison e LOA directly hronic dietary-based EECs 

all u suffic to 

effects were observed in the laboratory. 

ved effects to egg shells to represent 

ction of the CRLF, since the CRLF does not produce eggs with shells. 

 other chronic studies with birds, decreased number of eggs laid was observed in ring 

efined ary-b Qs fo LFs ex the c listed s LO

1.0) for all u dicof for d item ntiall umed by the CRLF 

Table 51). In vaila onic whe

icofol, the wa , a LOA s 3 based crease

ggshell thickn omp of th EC to c

f ming food i indicate that EECs for 

oductive 

or CRLF consu all tems ses are ient 

exceed the concentration where repr

There is some uncertainty in relying upon obser

effects to reprodu

In

doves and American kestrel feed 40 ppm dicofol. EECs from all uses of dicofol for CLRF 

consuming small insects and small herbivore mammals are still sufficient to exceed this 

level where decreased number of offspring was observed in birds. 

Based on the above information, for all uses of dicofol, the effects determination for 

chronic effects to the terrestrial-phase CRLF is “LAA” based on potential reproductive 

effects. 

112 
Table 51. Revised chronic dietary-based RQs7

 for CRLF consuming different food items. EECs 

calculated using T-HERPS. 

Use Small 

Insects Insects 

S

Herbivore 

Mammals 

In re 

Mammals 

ll 

strialase 

ibians 

Large mall Small 

sectivo

Sma

Terre

ph

Amph

Citru ruits2 4058

 4 47 .18 s,1 Pome F 5.08 48 30.0v 14

Straw Walnuts (English/black), 

Pecan 270v 3 31 berries, 8

s 

0.08 68 19388 9.37

Bean , Stone Fruits3 2038

 2 23 8 s, cotton 2.58 78 14.88 7.03

Grape 1698 s, mint 1 19 4 8.88 88 8 12.48 5.86

Hops 1578

 1 18 8 7.58 48 11.58 5.46

Peppe 1018

 1 11 8 rs, Tomatoes 1.28 98 7.418 3.51

Cucu 84.48

 9 98 8 rbits5 .388 .88 6.188 2.93

Ornam f grasses, Sod farms, 

Outsi 67.58

 7 79 entals, 8 6 Tur

de building surfaces .508 .18 4.948 2.34

Berm 54.08

 6 63 8 uda grass .008 .38 3.958 1.87 1

 grap s 2

 appl

3

 apr prunes 4

 min ppermint and spearmint 

5

 can

6

 nur

7

 Based on NOAEC = 1 ppm (for American kestrel) 

8

 Exceeds chronic risk LOC .0) 

efruit, lemons, oranges, tangelos, and tangerine

es and pears 

icots, cherries, nectarines, peaches, plums, and 

t, pe

taloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

series and flowers 

 (RQ>1

) 

As discussed in Section 2.5.3, the diet of ta e CRL com prim of 

unicellular nonvascular aquatic plants and detritus. Juvenile CRLF consume ily 

aquatic and terrestrial invertebrates. The diet of adult CRLF is com f aq d 

terrestrial invertebrates, fish, frogs and mice. These prey groups are considered in 

d indirect effects to the CRLF caused by direct effects to its prey. 

.2.1. Algae (non-vascular plants

RQ values for algae are below the LOC for a es of ol. T sults in a “no 

e ination for indirect effects to t RLF 

d

5.2.2. Indirect Effects (through effects to prey

dpol F is posed arily 

primar

posed o uatic an

etermining

5.2 ) 

ll us dicof his re

ffect” determ he C due to exposures of algae to 

icofol. 

113 
5.2.2.2. Aquatic Invertebrates 

Based on an analysis of the likelihood of ind rta ng a Qs f c 

invertebrates and a probit dose-response of 4 fault like of in ual 

mortality for each use is available in Table 52. on t alysi uses o fol 

result in less than or equal to a 3% chance of ef to an i dual inve tes 

representing prey of the CRLF. 

Table 52. Acute RQs and associated likelihood of indiv effects uatic ate

r g from applications of dicofol. EECs are based on parent a rada ncern

ULV application Ae pplicat pl

ividual mo

e

lity usi

) 

cute R or aquati

.5 (d , the lihood divid

Based

f

his an s, all f dico

ects ndivi aquatic rtebra

idual for aq invertebr s 

esultin nd deg tes of co . 

rial a ion Ground ap ication 

Use 

Acute RQ1

Likelihood 

of 

individual 

acute 

effect (%) 

Acut

Like 

indi 

acute effect 

(

A 1

Likelihood 

individual 

acute effect 

e RQ1

lihood

of 

vidual

%) 

cute RQ

of 

(%) 

Beans 0.233 0.2 0.133

 <0.1 0.113 <0.1

Citrus 0.323 1.3 0.123

 <0.1 0.0933 <0.1

Cotton 0.233 0.2 0.133 <0.1 0.113

 <0.1

Cucurbit 0.0873 <0.1 0.045 <0.1 0.039 <0.1

Grape 0.183 <0.1 0.0943

 <0.1 0.0813 <0.1

Hops 0.213 0.1 0.143

 <0.1 0.133 <0.1

Mint 0.213 0.1 0.123

 <0.1 0.113 <0.1

Pepper 0.113 <0.1 0.0643

 <0.1 0.0593 <0.1

Pome Fruit 0.353 2.0 3 3 0.15 <0.1 0.11 <0.1

Stone Fruit 0.17 0713

 <0.1 0.0543 <0.1 3 <0.1 0.

Strawberry 0.373 2.6 0.273

 0.5 0.263 0.4 

Tomato 0.103 <0.1 0.045 <0.1 0.037 <0.1

Walnut/Pecan 0.293 0.8 0.153

 <0.1 0.133 <0.1

Bermuda grass NA NA NA NA 0.016 <0.1

Ornamentals NA NA NA NA 0.044 <0.1

Turf/Sod Farm NA NA NA NA 0.021 <0.1

Outside Buildings NA NA NA NA 0.0025 <0.1 1

Based on 48-h EC50 = 140 μg/L for daphnid. 2

Based on NO

3

 Exceeds acu

A = not applicable

cept cucurbits, peppers, tomatoes, Bermuda 

entals, turf and outside buildings (Table 53 - Table 55). Chronic exposures 

of dicofol parent are insufficient to exceed the LOC (1.0). 

AEC = 19 μg/L for amphipod. 

te risk to endangered species LOC (RQ>0.05) 

N

Exposures of aquatic invertebrates to dicofol are quantified in terms of total residues of 

dicofol. RQs are derived using the most sensitive toxicity data available for aquatic 

invertebrates exposed to dicofol. It is assumed that dicofol’s degradates of concern (i.e., 

DCBP, FW-152, DCBH and OH-DCBP) are equivalent to dicofol in toxicity to aquatic 

invertebrates. This assumption adds uncertainty to the risk assessment, the toxicity of 

dicofol’s degradates to aquatic invertebrates is unknown. If exposures involving dicofol 

only are considered, acute RQs for the aquatic invertebrates CRLF exceed the listed 

species LOCs (0.05) for all dicofol uses, ex

grass, ornam

114 
Table 53. Acute and chronic RQs for aquatic invert om AERI

n dicofol only. 

ebrates resulting fr AL applications of 

dicofol. EECs are based o

Crop Peak E

L

Acute 1

EC 

) 

21-day 

(μg/ (μg/L) RQ

Chronic 

RQ2

Beans 3.25 0.46 0.023 0.024 

Citrus 6.46 .97 46 51 0 0.0 0.0

Cotton 3.48 .64 25 34 0 0.0 0.0

Cucurbit 1.34 .19 10 10 0 0.0 0.0

Grape 2.70 38 19 0 0. 0.0 0.02

Hops 2.52 .38 18 20 0 0.0 0.0

Mint 2.70 .39 19 20 0 0.0 0.0

Pepper 1.61 .23 12 12 0 0.0 0.0

Pome Fruit 6.46 90 46 8 0. 0.0 0.04

Stone Fruit 3.25 .46 23 24 0 0.0 0.0

Strawberry 6.41 .76 46 2 1 0.0 0.09

Tomato 1.61 23 12 12 0. 0.0 0.0

Walnut/Pecan Aerial 4.41 66 0. 0.031 5 0.03 1

Based on 48-h EC

2 50 = 1 /L for dap . 

 = 19 for amph 

40 μg hnid

Based on NOAEC μg/L ipod.

Table 54. Acute and chr RQs for aquatic inver tes resu from G appl 

d ased icofol onl

Peak EEC 

(μg/L) 

21-day 

(μg/L) 

Acute 

RQ1

Chronic 

RQ2

onic tebra lting ROUND ications of

icofol. EECs are b on d y. 

Crop 

Beans 2.26 0.32 0.016 0.017 

Citrus 4.47 0.69 0.032 0.036 

Cotton 2.49 0.51 0.018 0.027 

Cucurbit 0.93 0.13 0.0067 0.0069 

Grape 1.87 0.27 0.013 0.014 

Hops 1.74 0.27 0.012 0.014 

Mint 1.87 0.27 0.013 0.014 

Pepper 1.12 0.16 0.0080 0.0084 

Pome Fruit 4.47 0.63 0.032 0.033 

Stone Fruit 2.25 0.32 0.016 0.017 

Strawberry 6.34 1.62 0.045 0.085 

Tomato 1.12 0.16 0.0080 0.0083 

Walnut/Pecan 3.09 0.48 0.022 0.025 

Bermuda grass 0.60 0.10 0.0043 0.0054 

Ornamentals 1.78 0.39 0.013 0.020 

Turf/Sod Farm 0.75 0.13 0.0053 0.0067 

Outside Buildings 0.152 0.025 0.0011 0.0013 1

Based on 48-h EC50 = 140 μg/L for daphnid. 2

Based on NOAEC = 19 μg/L for amphipod. 

115 
Table 55. Acute and chronic RQs for aquatic invertebrates resulting from ULV applications of 

dicofol. EECs are based on dicofol only. 

Crop Peak EEC 

(μg/L) 

21-day 

(μg/L) 

Acute 

RQ1

Chronic 

RQ2

Beans 9.75 1.38 0.0703 0.073 

Citrus 18.02 2.58 0.133 0.14 

Cotton 9.92 1.49 0.0713 0.079 

Cucurbit 4.04 0.56 0.029 0.030 

Grape 8.08 1.14 0.0583 0.060 

Hops 7.56 1.08 0.0543 0.057 

Mint 8.07 1.15 0.0583 0.060 

Pepper 4.85 0.69 0.035 0.036 

Pome Fruit 18.02 2.52 0.133 0.13 

Stone Fruit 9.08 1.28 0.065 7 3 0.06

Strawberry 13.17 0.0943 2.70 0.14 

Tomato 4.85 0.68 0.035 0.036 

Walnut/Pecan 0. 3 13.02 1.85 093 0.097 1

Based on 48-h EC50 = 140 μg/L for daphnid. 

9 μg/L for amphipod. 

 (RQ

2

Based on NOAEC = 1

3

 Exceeds acute risk to endangered species LOC >0.05) 

C tal residues of dic r the ty of ol use but 

cucurbits, peppers, tomatoes, Bermuda grass entals, turf and outside buildings) are 

sufficient to exceed the LOC (1.0). For ULV ation cofol on, po ruit, 

s walnuts/pecans, EECs are ient t ed th EC ( /L) 

for chronic effects to aquatic invertebrates. 

Based on the above information, the imp

CRLFs via acute effects on aquatic invertebrates is discountable for all uses of dicofol. 

T bits, peppers, tomatoes, Bermuda grass, 

o and outside buildings) have the potential to result in chronic exposures 

t especially when dicofol is applied via 

U

5.2.2.3. Fish and Aquatic-Phase Amphibians 

Based on an analysis of the likelihood of individual mortality considering the range of 

acute RQs exceeding the LOC for fish and aquatic-phase amphibians (0.05-0.71), and 

sing the probit dose-response of 4.5 (default assumption), likelihood of individual 

lt in 

ss than a 10% chance of effects to an individual fish and aquatic-phase amphibians 

representing prey of the CRLF. 

hronic RQs based on to ofol fo majori dicof s (all

, ornam

 applic s of di to cott me f

trawberries, and suffic o exce e LOA 33 μg

act of the indirect effects to aquatic-phase 

he majority of dicofol uses (all but cucur

rnamentals, turf 

hat may result in effects to aquatic invertebrates, 

LV methods. 

u

mortality for each use is available in Table 56. Based on this analysis, use of dicofol on 

beans, citrus, cotton, hops, mint, pome fruit, strawberries and walnuts/pecans results in 

greater than a 10% likelihood of individual mortality. All other uses of dicofol resu

le

116 
Table 56. Acute RQs and likelihood of individual mortality for fish and aquatic-phase amphibians 

resulting from applications of dicofol. EECs are based on parent and degradates of concern. 

ULV application Aerial application Ground application 

Use 

Acute 

RQ1

Likelihood 

of individual 

mortality 

(%) 

Acute 

RQ1

Likelihood 

of individual 

mortality 

(%) 

Acute 

RQ1

Likelihood of 

individual 

mortality (%) 

Beans 0.60 16 0.34 1.8 0.30 0.9 

Citrus 0.85 38 0.33 1.5 0.25 0.3 

Cotton 0.60 16 0.34 1.8 0.30 0.9 

Cucurbit 0.23 0.2 0.12 <0.1 0.10 <0.1 

Grape 0.48 7.6 0.25 0.3 0.21 0.1 

Hops 0.56 13 0.37 2.6 0.35 2.0 

Mint 0.54 11 0.31 1.1 0.29 0.8 

Pepper 0.30 0.9 0.17 <0.1 0.16 <0.1 

Pome Fruit 0.92 44 0.39 3.3 0.29 0.8 

Stone Fruit 0.45 5.9 0.19 0.1 0.14 <0.1 

Strawberry 0.97 48 0.71 25.2 0.69 23 

Tomato 0.26 0.4 0.12 <0.1 0.10 <0.1 

Walnut/Pecan 0.76 30 0.39 3.3 0.34 1.8 

Ber rass NA NA NA muda g NA 0.044 <0.1 

Ornamentals NA NA NA NA 0.11 <0.1 

Turf/Sod Farm NA NA NA NA 0.054 <0.1 

Outside Buildings NA NA NA NA 0.0067 <0.1 1

Bas LC = 53 μg/L for cutthroat trout 

NA =

Chronic RQs for fish and aquatic-phase am or the majority of dicofol uses (all 

exce ceed the LOC (1.0) by factors of 

1.1X cient to 

exceed the LOAEC (7.9 μg/L, based on growth effects) for the majority of dicofol uses, 

with ntals, turf and outside buildings. 

e acute risk LOC (RQ>

ed on 96-h 50

 not applicable 

phibians f

pt Bermuda grass, turf and outside buildings) ex

 to 10X, depending upon the use (Table 31 - Table 33). EECs are suffi

 the exception of Bermuda grass, orname

5.2.2.4. Terrestrial Invertebrates 

As noted above, for small insect exposures, RQ values range <1.04 to <0.138. For large 

insect exposures, RQ values range <0.115 to <0.0153. For all uses of dicofol, RQ values 

potentially exceed th 0.05) for terrestrial insects. Because the 

te 

he 

t 

LD50 used in deriving RQs for terrestrial invertebrates is not quantified, RQs for acu

exposures of small and large terrestrial invertebrates to dicofol potentially exceed t

LOC of 0.05 for all uses. 

Based on an analysis of the likelihood of individual mortality considering the range of 

acute RQs potentially exceeding the LOC (0.05 to <1.04), and using the default probi

dose-response of 4.5, the chance of mortality to terrestrial invertebrates range from less

than 0.1% to 53% (Table 57). For use of dicofol on grapes, mint, hops, peppers, 

tomatoes, cucurbits, ornamentals, turf and Bermuda grass, dicofol exposures result in a 

117 
chance of individual mortality to less than 10% of terrestrial insects. Therefore, indirect 

s

7

 and associated likelihood of individual effects to terrestrial invertebrates due to 

icofol exposures. 

effects to the CRLF through potential effects to terrestrial invertebrates resulting from 

these dicofol uses are considered discountable. Use of dicofol on citrus, pome fruits, 

strawberries, walnuts, pecans, beans, cotton and stone fruits could potentially result in 

indirect effects to greater than 10% of small invertebrates. Although there is uncertainty 

in the actual effects of these exposures to terrestrial invertebrates, given that no LD50 was 

established, mortality to small insects resulting from dicofol applied to these crops has 

the potential to result in indirect effects to the CRLF, especially considering that dicofol 

is intended for control of insects. 

Table 57. RQ

d

Small Insect Large Insect

Use 

RQ 

Likelihood 

of individual 

acute effect 

(%) 

RQ acute effect 

(%) 

Likelihood 

of individual 

Citrus,1 Pome Fruits2 <1.04 <53.10 <0.12 <0.1 

Strawberries, Walnuts (English/black), Pecans <0.69 <23.40 <0.08 <0.1 

Beans, cotton, Stone Fruits3 <0.52 <10.10 <0.06 <0.1 

Grapes, mint4 <0.43 <4.95 <0.05 <0.1 

Hops <0.40 <3.67 <0.04 <0.1 

Peppers, Tomatoes <0.26 <0.42 <0.03 <0.1 

Cucurbits5 <0.22 <0.15 <0.02 <0.1 

Ornamentals,6 Turf grasses, Sod farms, Outside 

building surfaces <0.17 <0.1 02 1 <0. <0.

Bermuda grass <0.14 <0.1 .02 1 <0 <0.

1 grapefruit, lemons, oranges, tangelos, and tangerines 

2 apples and pears 

3 apricots, cherries, nectarines, peaches, plums, and prunes 

4 mint, peppermint and spearmint 

5 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and s r squash umme

6 nurseries and flowers 

7 Based on LD50 >391 μg a.i./g for honey bee 

RQ 0.1) for 

all uses of dicofol except: ornamentals, turf, outside buildings and Bermuda grass (Table 

). fol to terrestrial mammals. 

5.2.2.5. Mammals 

values representing acute exposures to terrestrial mammals exceed the LOC (

58 Therefore, there is potential for acute effects of dico

118 
Based on an analysis of the likelihood of individual mortality using acute dose-based 

RQs for terrestrial mammals and a probit dose-response of 4.5 (default value), the 

kelihood of individual mortality for each use is available in Table 58. Based on this 

able 58. Acute dose-based RQs and associated likelihood of individual effects to small terrestrial 

dose-based7 individual acute 

eff

li

analysis, the majority of dicofol uses result in less than a 10% chance of effects to an 

individual terrestrial mammal representing prey of the CRLF. Only the highest RQ 

(from citrus and pome fruits) result in estimations of likelihood of individual effects 

which represents a significant indirect effect to the CRLF (10.7%). Therefore, the impact 

of the indirect effects to terrestrial-phase CRLFs via acute effects on small mammals is 

discountable for all uses of dicofol, except citrus and pome fruits. 

T

mammals (consuming short grass) due to dicofol exposures. 

Use Acute, Likelihood of 

ect (%) 

Citrus,1 Pome Fruits2 0.53 10.7

Strawberries, Walnuts (English/black), Pecans 0.35 2.0

Beans, cotton, Stone Fruits3 0.27 0.5 

Grapes, mint4 0.22 0.2

Hops 0.21 0.1

Peppers, Tomatoes 0.13 <0.1

Cucurbits 0.11 <0.1 5

Ornamentals,6 Turf grasses, Sod farms, Outside building 0.09 <0.1

surfaces

Bermuda grass 0.07 <0.1 

1 grapefruit, lemons, oranges, tangelos, and tangerines 

2 apples and pears 

3 apricots, cherries, nectarines, peaches, plums, and prunes 

and winter and summer squash 

4 mint, peppermint and spearmint 

5 cantaloupes, cucumbers, melons, pumpkins, watermelons, 

6 nurseries and flowers

7

Based on LD50 for laboratory rat = 587 mg/kg. 

s for terrestrial mammals exceed the LOC (1.0) 

y factors of 19X to 781X, depending upon the use (Table 40). EECs are sufficient to 

ures of terrestrial animals to pesticides 

rough consumption of foliar surfaces of crops and insects on the treated site. The 

model ial animals resulting from 

ulated the pesticide in their 

Dose-based and dietary-based chronic RQ

b

exceed the LOAEC (25 ppm, based on reproductive effects) for all uses by factors of 4X 

or greater. Based on this information, chronic exposures of dicofol from all uses have the 

potential to indirectly affect the CRLF via impacts to terrestrial mammals serving as 

potential prey items. 

The T-REX model is useful for assessing expos

th

cannot be used to assess pesticide exposures to terrestr

consumption of soil dwelling invertebrates which have accum

tissues. In order to explore the potential exposures of mammals to total residues of 

dicofol that have accumulated in earthworms inhabiting dicofol treatment sites, a simple 

fugacity approach was employed to estimate dicofol concentrations in earthworms and 

subsequent exposures to mammals consuming earthworms. This approach is explained in 

detail in Appendix O. 

119 
Based on PRZM estimated dicofol concentrations of 10 and 0.16 g/m3 in soil and soil 

pore water, respectively (Figure 9 and Figure 10), the estimated concentration of dicofol 

in earthworms is 2914 ppm. This translates to a dose-based EEC of 2778 mg/kg-bw, 

hich exceeds the LD50 for rats of 587 mg/kg-bw. If it is assumed that a 20g mammal 

Table 59 7

consuming 

gs 

consuming

w

consumes only earthworms, its chronic dietary based and dose-based exposures would be 

approximately 100X and 1000X, respectively, above levels where reproductive effects 

were observed in rats (25 ppm, MRID 41606601). Therefore, acute and chronic 

exposures of small mammals to dicofol through consumption of contaminated 

earthworms from fields treated with dicofol have the potential to result in effects to 

mammals. 

5.2.2.6. Terrestrial-Phase Amphibians 

In order to explore influences of amphibian-specific food intake equations on potential 

dose-based and dietary-based exposures of amphibians (prey of CRLF) to dicofol, the THERPS model is used. The Pacific tree frog (Hyla regilla) is used to represent the 

amphibian prey species. The weight of the animal is assumed to be 2.3 g, and its diet is 

assumed to be composed of small and large insects. For frogs consuming small and 

large insects, the acute LOC (0.1) is not exceeded for dicofol (Table 59). 

. Acute dose-based RQs for terrestrial-phase frogs (prey) exposed to dicofol. 

Use Frogs Fro

Small 

Insects 

Large 

Insects 

Citrus,1 Pome Fruits2 0.04 <0.01 

Strawberries, Walnuts (English/black), Pecans 0.04 <0.01

Beans, cotton, Stone Fruits3 0.03 <0.01

Grapes, mint4 0.02 <0.01

Hops 0.02 <0.01

Peppers, Tomatoes 0.01 <0.01

Cucurbits 0.01 <0.01 5

Ornamentals,6 Turf grasses, Sod farms, Outside building surfaces 0.01 <0.01

Bermuda grass 0.01 <0.01

1 grapefruit, lemons, oranges, tangelos, and tangerines 

2 apples and pears 

3 apricots, cherries, nectarines, peaches, plums, and prunes 

4 mint, peppermint and spearmint 

5 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6 nurseries and flowers 

7 Based on LD50 = 265 mg/kg-bw (for ring-necked pheasant) 

Acute dietary-based RQs for the CRLF, which do not account for the weight of the 

animal being assessed, can also be used to assess risks to the terrestrial frog prey (Table 

50). For frogs which consume small insects, RQs exceed the acute LOC (0.1) for the 

majority of dicofol uses, with the exception of use on cucurbits, ornamentals, turf, outside 

120 
buildings and Bermuda grass. For frogs which consume large insects, the acute LOC is 

not exceeded for dicofol. 

Based on an analysis of the likelihood of individual mortality using acute dietary-based 

RQs for terrestrial amphibians and a probit dose-response of 5.92, the likelihood of 

individual mortality for each use is available in Table 60. Based on this analysis, all uses 

of dicofol result in ≤2% chance of effects to an individual terrestrial amphibian 

representing prey of the CRLF. Therefore, the impact of the indirect effects to terrestrialphase CRLFs via acute effects on terrestrial amphibians is discountable for all uses of 

dicofol. 

Table 60. Acute dietary-based RQs for terrestrial-phase frogs (prey) consuming small insects and 

likelihood of individual effects chance resulting from dicofol exposures. RQs calculated using THERPS. 

Use Acute, dietarybased RQ7

Likelihood of 

individual acute 

effect (%) 

Citrus,1 Pome Fruits2 0.45 2.0 

Strawberries, Walnuts (English/black), Pecans 0.30 0.1 

Beans, cotton, Stone Fruits3 0.22 <0.1 

Grapes, mint4 0.19 <0.1

Hops 0.17 <0.1

Peppers, Tomatoes 0.11 <0.1

Cucurbits5 0.09 <0.1

Ornamentals,6 Turf grasses, Sod farms, Outside building surfaces 0.07 <0.1

Bermuda grass 0.06 <0.1

1 grapefruit, lemons, oranges, tangelos, and tangerines 

2 apples and pears 

3 apricots, cherries, nectarines, peaches, plums, and prunes 

4 mint, peppermint and spearmint 

5 cantaloupes, cucumbers, melons, pumpkins, watermelons, and winter and summer squash 

6 nurseries and flowers 

7 Based on LC50 = 903 ppm (for Japanese quail)

Chronic dietary-based RQs for the CRLF, which do not account for the weight of the 

animal being assessed, can also be used to assess risks to the terrestrial frog prey (Table 

51). Chronic RQs for the frog exceed the LOC (1.0) by factors ranging from 2X to 474X. 

Therefore, for all dicofol uses, there is potential for indirect effects to the CRLF resulting 

from chronic effects to terrestrial amphibians. 

5.2.3. Indirect Effects (through effects to habitat) 

quatic plants serve several important functions in aquatic ecosystems. Non-vascular 

quatic plants are primary producers and provide the autochthonous energy base for 

A

a

aquatic ecosystems. Vascular plants provide structure as attachment sites and refugia for 

many aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In 

121 
addition, vascular plants also provide primary productivity and oxygen to the aquatic 

ecosystem. Rooted plants help reduce sediment loading and provide stability to 

nearshore areas and lower streambanks. In addition, vascular aquatic plants are 

portant as attachment sites for egg masses of CRLFs. 

addition to providing habitat and cover for invertebrate and vertebrate prey items of the 

F, terr eta lso es s for LF ove predators 

 through 

primary produ n. v n 

cover during dispersal. Riparian vegetati s ta integrity of 

systems by pr ing b th sta erv a b fil sed 

nutrients, and contami efo re e w ed, rvi n 

source. 

to a lack fec , p l ri dico pla nno uan 

itative eff data st t plic of dicofol m ult i toto 

ever, due a lac deta vid , the relati 

tween effect serve app n ra dicofol cannot be defined. In addition, 

involving effects of dicofol to plants. Although effects of 

ofol on pla anno antified, effects of dicofol on plan not coun 

5.2.4. P ary ituen men

As discussed e, ef of d l to co ng t uatic terre l 

habitats of the CRLF cannot be discounted. Also, exposures of dicofol to the CRLF and 

ave the potent aff CR The e, dic is likely to re 

s to the CRLF’s aquatic and terrestria itats d on ntial im acts to 8 

5.2.5. Area of Effects 

itial ar f conc for d fol wa n 2.7 d 

picted in Figure 5 of the problem formul n. A p depicting the overlap of this 

itial area of concern an RLF h tat is d ted in ure 1 ecaus the la f 

AEC in several chronic toxi cribed in Section 4.3.1), the 

on area for dicofol is establishe the en state o aliforn 

im

Terrestrial plants serve several important habitat-related functions for the CRLF. In 

CRL

while foraging. Terrestrial plants also provi

estrial veg tion a provid helter

de energy to the terrest

the CR and c

rial ecosystem

r from

ctio Upland egetatio including grassland and woodlands provides 

on help to main in the aquatic

ovid ank and ermal bility, s ing as uffer to ter out iment,

nants b re they ach th atersh and se ng as a energy

Due 

ual

 of ef ts data otentia sk of fol to nts ca t be q tified.

Q ects sugge hat ap ations ay res

ies

n phy xicity,

how

e

 to k of il pro ed in the available stud onship

b

there is one reported incident 

s ob d and licatio tes of

dic nts c t be qu ts can be dis ted. 

rim Const t Ele ts of Designated Critical Habitat 

abov fects icofo plants mprisi he aq and stria

its prey h ial to ect the LF. refor ofol sult in

effect l hab base pote p all

PCEs. 

The in ea o ern ico s previously discussed in Sectio an

de atio ma

in d C abi epic Fig 1. B e of ck o

a NO city studies with birds (des

acti d as tire f C ia.

122 
Figure 11. Intersection between dicofol use areas and CRLF habitat. 

Available pesticide use data from California indicate that dicofol has been used in 

counties which contain CRLF habitat. Out of 58 counties in California, 33 contain some 

123 
124 

portion of CRLF critical habitat or core areas. According to use data for 1999-2006, all o

the 33 counties con

f 

taining CRLF areas have reported past uses of dicofol. From 1999-

2006, 8 of these counties had >1000 pounds of d n

Table 61. Summary of CDPR pesticide use reporting b fol (annual pounds of dicofol 

applied from 1999 to 2006). 

County 

RLF 

at/cor

eas 

sent?

2001 2003 4 2005 

icofol applied a

y county for dico

nually (Table 61). 

Are C

habit e 1999 2000 ar

pre

2002 200 2006

FRESNO yes 123,090 100,221 75,201 5 3 1,56 49,215 63,344 60,967 27,191

TULARE no 53,026 62,227 39,640 3 3 42,234 4 07 35,060 ,155 5,51 3,5 10

KINGS yes 35,692 44,112 18,674 2 4 5,11 27,709 3 10 1,0 29,124 7,807 

MERCED yes 23,932 25,490 19,746 1 0 7,07 18,552 2 07 7,7 19,666 22,032 

KERN yes 32,442 22,994 9,345 1 8 0,33 8,726 5,966 12,774 5,828 

STANISLAUS yes 17,860 23,376 14,536 1 5 3,81 11,925 1 22 3,8 7,120 5,330 

SAN JOAQUIN yes 22,647 15,153 3,379 4,895 3,527 5,582 4,839 5,924 

MADERA no 12,042 6,208 4,369 3,019 2,037 54 5,358 938 2,4 4,

MONTEREY yes 7,057 4,058 4,504 1,523 802 1,824 3,767 1,825 

IMPERIAL no 8,439 2,916 3,103 2,271 2,371 65 2,138 2 2,9 47

SUTTER no 2,514 3,590 3,071 4,067 2,500 46 1,580 905 1,8 2,

RIVERSIDE yes 5,996 2,466 1,913 2,046 3,140 2,694 586 1,212 

BUTTE yes 829 1,545 4,846 1,278 4,196 2,255 3,797 1,102 

YOLO no 4,652 2,585 1,511 2,466 1,771 403 431 1 34

GLENN no 2,016 645 1,066 1,273 980 618 1,226 1,170

TEHAMA yes 1,219 1,529 1,128 2,356 2,159 42 277 29 

SOLANO yes 2,353 496 1,210 1,294 833 368 663 184 

COLUSA no 1,766 224 233 770 403 1,775 756 479 

SANTA BARBARA yes 487 1,670 797 349 162 636 1,311 571 

SACRAMENTO yes 3,537 1,270 133 376 211 3 8 0 

CONTRA STA CO yes 1,432 1,107 1,282 33 301 334 0 10 

SAN LUIS OBISPO yes 1,881 1,495 198 56 4 149 3 324 

SAN DIEGO yes 449 269 385 290 496 288 235 86 

SONOMA yes 1,363 780 103 8 18 0 0 2 

SANTA CLARA yes 76 12 7 26 179 395 840 543 

ALAMEDA yes 1,667 72 35 0 0 2 0 0 

VENTURA yes 27 84 189 23 441 693 251 27 

LOS ANGELES yes 527 731 273 135 29 2 2 7 

SAN BENITO yes 813 416 55 0 0 50 0 195 

SISKIYOU no 0 0 0 0 8 494 874 149 

YUBA yes 177 11 638 47 263 7 0 0 

ORANGE yes 860 60 18 31 13 8 3 0 

MENDOCINO no 604 161 0 2 0 0 6 0 

AMADOR yes 92 16 30 0 629 0 0 0 

SAN BERN RDINO A no 211 149 86 45 29 5 5 5 

SHASTA yes 173 218 11 0 26 31 34 2 

MODOC no 0 0 0 0 0 441 20 0 

SANTA CRUZ yes 222 4 9 179 8 0 0 0 
County habitat/core 1999 2000 2001 2002 2003 2004 2005 2006 

Are CRLF 

areas 

present?

CALAVERAS no 63 8 173 123 0 0 0 0 

NAPA yes 154 0 53 0 8 0 65 0 

SAN MATEO yes 103 19 40 8 10 13 20 12 

PLACER no 42 125 1 0 1 0 1 0 

LAKE no 47 7 38 12 20 6 3 3 

EL DORADO yes 65 0 6 14 42 2 2 0 

NEVADA yes 42 7 0 4 0 0 0 0 

PLUMAS yes 12 0 0 0 0 0 0 0 

MARIPOSA no 0 6 0 0 0 0 0 0 

SIERRA no 6 0 0 0 0 0 0 0 

MARIN yes 2 0 0 0 0 0 0 0 

SAN FRANCISCO no 2 0 0 0 0 0 0 0 

HUMBOLDT no 0 1 0 0 0 0 0 0 

Total 372,704 328,533 212,033 182,430 185,981 211,738 193,809 100,862 

In order to determine the extent of the lotic (flowing) aquatic habitat directly affected in 

aquatic, the greatest ratio of the RQ to the LOC for any endpoint for aquatic organisms is 

used to determine the distance downstream for concentrations to be diluted below levels 

that would be of concern (i.e. result in RQs less than the LOC). For this assessment, this 

applies to RQs for acute exposures of total residues of dicofol to the aquatic-phase CRLF 

(and fish and aquatic-phase amphibians). The highest RQ (0.71) divided by the acute 

LOC (0.05) results in a ratio of 14.2. The maximum downstream distance from areas 

where dicofol are applied and dicofol is at concentrations that are of concern to the 

aquatic-phase CRLF is 155 km. 

EECs and relevant RQs calculated by T-HERPS and T-REX apply to sites where dicofol 

is directly applied. Since dicofol can be transported through spray drift to non-target 

reas beyond the treatment site, the CLRF and its prey located outside of direct treatment 

here the LOC is exceeded is expected to 

e less than 161 feet for aerial applications and 43 feet for ground applications. 

a

areas can still be exposed to dicofol in non-target areas. Exposure and associated risks to 

the CRLF are expected to decrease with increasing distance away from the treated field 

or site of application. 

Based on acute effects data for the terrestrial-phase CRLF, spray drift deposition of 

dicofol as low as 0.18 lbs a.i./A would be sufficient to exceed the acute listed species 

LOC for the CRLF. This is based on the highest acute RQ for terrestrial phase CRLF and 

its prey, which is 1.69 based on risks to medium sized CRLF receiving dicofol through 

consumption of small herbivore mammals. For aerial applications of dicofol to citrus and 

pome fruits, at the maximum application rate (3 lb a.i./A), spray drift is sufficient to 

exceed the LOC for as far as 161 feet from the edge of the treatment field (Table 62). 

Since 3 lb a.i./A represents the highest application rate of dicofol, for all other uses of 

dicofol, the distance from the edge of the field w

b

125 
Table 62. Single application rate not exceeding acute LOC for dietary- and dose-based exposures of 

the CRLF to dicofol. 

Distance from edge of field where LOC 

is not exceeded (in feet) for single 

application of 3 lb a.i./A2, 3

CRLF 

size1

Based 

on dose 

or diet? 

Feeding Category Highest 

application rate 

not exceeding 

LOC (lbs a.i./A) 

Ground Aerial 

medium Dose small herbivore mammals 0.18 43 161 

all Diet Small herbivore mammals 0.55 16 43 

all Diet Small insects 0.64 13 30 

large Dose small herbivore mammals 1.1 10 10 

medium Dose small insectivore mammals 2.9 3 0 

small Dose small insects >3 0 0 

medium Dose small insects >3 0 0 

large Dose small insects >3 0 0 

large Dose small insectivore mammals >3 0 0 

Small Dose large insects >3 0 0 

medium Dose large insects >3 0 0 

large Dose large insects >3 0 0 

all Diet large insects >3 0 0 

medium Dose terrestrial-phase amphibians >3 0 0 

all Diet Small insectivore mammals >3 0 0 

all Diet Terrestrial-phase amphibians >3 0 0 

large Dose terrestrial-phase amphibians >3 0 0 

1. Small is defined as 1.4 g. Medium is defined as 37 g. Large is defined as 238 g. 

2. Estimated using the terrestrial assessment of the Tier 1 version of AgDRIFT. Modeling assumed that applications 

were done using ground and aerial methods, and assuming that the droplet size distribution was “ASAE very fine to 

fine” for ground applications (high boom) and "ASAE fine to medium" for aerial applications. 

3. 3 lb a.i./A is the highest application of dicofol. This corresponds to applications to citrus and pome fruits. 

 

5.2.6. Description of Assumptions, Limitations and Uncertainties 

5.2.6.1. Exposure Assessment 

Maximum Use Scenario 

The screening-level risk assessment focuses on characterizing potential ecological risks 

resulting from a maximum use scenario, which is determined from labeled statements of 

maximum application rate and number of applications with the shortest time interval 

between applications. The frequency at which actual uses approach this maximum use 

scenario may be dependant on pest resistance, timing of applications, cultural practices, 

and market forces. 

126 
Use Characterization Uncertainties 

County-level usage data were obtained from California’s Department of Pesticide 

he standard ecological water body scenario (EXAMS pond) used to calculate potential 

d to represent conservative estimates, and to 

void underestimations of the actual exposure. The standard scenario consists of 

have higher peak EECs than the EXAMS pond. These water bodies will be 

ither smaller in size or have larger drainage areas. Smaller water bodies have limited 

he Agency acknowledges that there are some unique aquatic habitats that are not 

presentative 

f exposure to aquatic-phase CRLFs. In addition, the Services agree that the existing 

Regulation Pesticide Use Reporting (CDPR PUR) database. CDPR PUR documentation 

indicates that errors in the data may include the following: a misplaced decimal; 

incorrect measures, area treated, or units; and reports of diluted pesticide concentrations. 

In addition, it is possible that the data may contain reports for pesticide uses that have 

been cancelled. As with all pesticide usage data, there may be instances of misuse and 

misreporting. The Agency made use of the most current, verifiable information; in cases 

where there were discrepancies, the most conservative information was used. 

Aquatic Exposure Modeling of Dicofol 

T

aquatic exposure to pesticides is intende

a

application to a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3) pond 

with no outlet. Exposure estimates generated using the EXAMS pond are intended to 

represent a wide variety of vulnerable water bodies that occur at the top of watersheds 

including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural 

ponds, and intermittent and lower order streams. As a group, there are factors that make 

these water bodies more or less vulnerable than the EXAMS pond. Static water bodies 

that have larger ratios of pesticide-treated drainage area to water body volume would be 

expected to 

e

storage capacity and thus may overflow and carry pesticide in the discharge, whereas the 

EXAMS pond has no discharge. As watershed size increases beyond 10-hectares, it 

becomes increasingly unlikely that the entire watershed is planted with a single crop that 

is all treated simultaneously with the pesticide. Headwater streams can also have peak 

concentrations higher than the EXAMS pond, but they likely persist for only short 

periods of time and are then carried and dissipated downstream. 

T

accurately captured by this modeling scenario and modeling results may, therefore, 

under- or over-estimate exposure, depending on a number of variables. For example, 

aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are 

located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency 

does not currently have sufficient information regarding the hydrology of these aquatic 

habitats to develop a specific alternate scenario for the CRLF. CRLFs prefer habitat 

with perennial (present year-round) or near-perennial water and do not frequently inhabit 

vernal (temporary) pools because conditions in these habitats are generally not suitable 

(Hayes and Jennings 1988). Therefore, the EXAMS pond is assumed to be re

o

EXAMS pond represents the best currently available approach for estimating aquatic 

exposure to pesticides (U.S. FWS/NMFS 2004). 

127 
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations 

that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone 

Model is a process or “simulation” model that calculates what happens to a pesticide in 

an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant 

anspiration of water, as well as how and when the pesticide is applied. It has two major 

and chemical transport. Water movement is simulated by the use 

f generalized soil parameters, including field capacity, wilting point, and saturation 

cted to be exceeded in the environment 

pproximately 90 percent of the time. Mobility input values are chosen to be 

uenced substantially by 

rocesses governing sediment particle delivery to (and transport within) water bodies 

(i.e., se mpounds, soil erosion is usually a major source of 

esticide loading into aquatic ecosystems. Once in an aquatic ecosystem, processes such 

tr

components: hydrology 

o

water content. The chemical transport component can simulate pesticide application on 

the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in 

the soil are estimated by simultaneously considering the processes of pesticide uptake by 

plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection, 

dispersion, and retardation. 

Uncertainties associated with each of these individual components add to the overall 

uncertainty of the modeled concentrations. Additionally, model inputs from the 

environmental fate degradation studies are chosen to represent the upper confidence 

bound on the mean values that are not expe

a

representative of conditions in the environment. The natural variation in soils adds to the 

uncertainty of modeled values. Factors such as application date, crop emergence date, 

and canopy cover can also affect estimated concentrations, adding to the uncertainty of 

modeled values. Factors within the ambient environment such as soil temperatures, 

sunlight intensity, antecedent soil moisture, and surface water temperatures can cause 

actual aquatic concentrations to differ for the modeled values. 

The temporal and spatial distribution of pesticides with persistent and bioaccumulative 

characteristics in aquatic ecosystems is expected to be infl

p

diment dynamics). For these co

p

as settling, resuspension, and burial of sediment particles can affect the distribution of 

pesticides in the water column-, pore water-, and suspended- and benthic-sediment 

compartments. Sediment dynamics can also influence pesticide bioavailability within 

these compartments, due to pesticide sorption on particulate organic carbon and 

complexation with dissolved organic carbon. Currently, OPP’s aquatic exposure 

modeling framework incorporates pesticide delivery to a standard pond from soil erosion 

and runoff using the Pesticide Root Zone Model (PRZM). In this modeling framework, 

only the pesticide mass delivered from soil erosion and runoff is considered for delivery 

to an aquatic ecosystem (i.e., the mass of soil and volume of runoff predicted by PRZM 

are not considered). Pesticide transport between the water column and the benthic region 

within the standard pond is modeled using the Exposure Analysis Modeling System 

(EXAMS) based on a set of lumped parameters that are designed to reflect the combined 

effect of multiple transport processes (e.g., diffusion, setting and resuspension). The 

current modeling framework does not consider pesticide burial in the benthic area, a 

process by which pesticide is rendered permanently unavailable for biological interaction 

due to accumulating sediment. Without consideration of burial processes, the current 

128 
modeling framework likely represents an effective screen for pesticide exposure 

assessment in both lentic (static) and lotic (flowing water) systems. 

sumed pesticide 

sidues in wildlife dietary items. These residue assumptions are believed to reflect a 

 plants in the case of grass and forage 

mpling. 

 was assumed that ingestion of food items in the field occurs at rates commensurate 

is comparable with 

onsumption during laboratory testing. In the screening process, exposure may be 

pecies were not 

Unlike spray drift, tools are currently not available to evaluate the effectiveness of a 

vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is 

highly dependent on the condition of the vegetative strip. For example, a wellestablished, healthy vegetative setback can be a very effective means of reducing runoff 

and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality 

or a setback that is channelized can be ineffective at reducing loadings. Until such time 

as a quantitative method to estimate the effect of vegetative setbacks on various 

conditions on pesticide loadings becomes available, the aquatic exposure predictions are 

likely to overestimate exposure where healthy vegetative setbacks exist and 

underestimate exposure where poorly developed, channelized, or bare setbacks exist. 

Terrestrial Exposure Modeling of Dicofol 

The Agency relies on the work of Fletcher et al. (1994) for setting the as

re

realistic upper-bound residue estimate, although the degree to which this assumption 

reflects a specific percentile estimate is difficult to quantify. It is important to note that 

the field measurement efforts used to develop the Fletcher estimates of exposure involve 

highly varied sampling techniques. It is entirely possible that much of these data reflect 

residues averaged over entire above ground

sa

It

with those in the laboratory. Although the screening assessment process adjusts dryweight estimates of food intake to reflect the increased mass in fresh-weight wildlife food 

intake estimates, it does not allow for gross energy differences. Direct comparison of a 

laboratory dietary concentration- based effects threshold to a fresh-weight pesticide 

residue estimate would result in an underestimation of field exposure by food 

consumption by a factor of 1.25 – 2.5 for most food items. 

Differences in assimilative efficiency between laboratory and wild diets suggest that 

current screening assessment methods do not account for a potentially important aspect of 

food requirements. Depending upon species and dietary matrix, bird assimilation of wild 

diet energy ranges from 23 – 80%, and mammal’s assimilation ranges from 41 – 85% 

(U.S. EPA 1993). If it is assumed that laboratory chow is formulated to maximize 

assimilative efficiency (e.g., a value of 85%), a potential for underestimation of exposure 

may exist by assuming that consumption of food in the wild 

c

underestimated because metabolic rates are not related to food consumption. 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal 

was assumed to occupy either the treated field or adjacent areas receiving a treatment rate 

on the field. Actual habitat requirements of any particular terrestrial s

129 
considered, and it was assumed that species occupy, exclusively and permanently, the 

sport

t are d. However, once in th fo rtition 

he g arti , ex ely particle 

phase, potentia buting to the long-range transport of dicofol. Partioning in the air 

st likely occur when the pesticide is applied via an aerial or ground spray, 

arly when -low v e spr Data latiliza from fo rfaces 

availab weve ee dis able residu ind at the 

r dico cotton, cucumbers, and or was 52, an days, 

y. Fo parative purposes, DDT has ge of ves on from 

.8 days (W s and M ell 

P is ble to y the extent to which dicofol and its degradates will 

o long-rang mospheric transport once it has been released from a treatm nt site, 

ism of transport will cons route of exposure for nontarget animals 

-7 o

 Europe’s 

 Air Pollution has indicated that 

ort (Rasenberg et al. 2003). According to 

n the gas and particle phases in the 

tmosphere and is likely to exist largely in the particle phase.” 

d ambient air in Lompoc (Santa Barbara County) for 31 

 is 

 largest p r seed s. CDPR d the 

pesticides during the peak use period for most of the pesticides, between May 31 and 

August 3, 2000. Durin 10-week period ected 24-hour sa s, four 

ve days per we each of the fo ing locations, located in the 

t, west, southwes d central parts of the county. The University of California, 

performed the pr laboratory analysis, using a new method developed 

 to analyze the pesticides used in L dicofol, the highest one-day 

ted as trace, meaning the concentration was halfway between the 

tection limit and the estimated quantitation lim m3

. Additionally, the 

14-day and 10-we ir concentrations for dicofol were a sted as 

., the concentration was halfway betw ethod detection l nd the 

itation lim f 1.37 ng/m3

 and 0.91 ng/m3, respectively). Collocated 

ollected du the last week of s to determine if any percentage 

ical concentrations were being missed in the analysis of the prim amples 

modeled treatment area. Spray drift model predictions suggest that this assumption leads 

to an overestimation of exposure to species that do not occupy the treated field 

exclusively and permanently. 

Long Range Tran

Based on dicofol’s vapor pressure (3.9x10-7 torr), low levels of volatility can potentially

occur, bu not expecte e air dico l can be expected to pa

between t as and p cle phases in the atmosphere isting larg in the

lly contri

would mo

particul ultra olum ays. on vo tion liar su

were not le. Ho r, thr lodge foliar e studies icate th

half-life fo

tivel

fol on

r 

anges

 n

3.2, 5.

i

d 15.6

respec com a ra half-l r clove

1.6 to 18 illi cDow 1987). 

Although OP

underg

not a

e at

quantif

e

this mechan titute a

distant from use sites. Based on its vapor pressure (3.9x10 torr @ 20 C) and persistence 

in the air (half life =3.1 days), the United Nations Economic Commission for

(UNECE) Convention on Long-range Transboundary

dicofol has the potential for long-range transp

the report, “dicofol is expected to partition betwee

a

Atmospheric Monitoring Data 

In 2000, CDPR monitore

pesticides and breakdown products, including dicofol (CDPR 2003). Lompoc County

one of the roducers of flowe s in the United State monitore

g this , DPR coll mple

consecuti

es

ek at ur monitor

northw t, an

Davis imary

specifically ompoc. For

air concentration was lis

method de it of 4 ng/

highest measured 

i.e.

ek a lso li

trace ( een the m imit a

estimated quant

samples were c

it o

ring ampling 

of the chem ary s

130 
as particulates. In all of the samples analyzed, levels of dicofol were below detection 

rotection Agency’s Environmental 

Justice Action Plan, CDPR conducted a pilot project focusing on pesticide air 

concen e, predominantly Hispanic, Fresno County farming 

ommunity of Parlier, located in the San Joaquin Valley (CDPR 2006). Fruit orchards 

nd sixty-eight ambient air samples were collected and analyzed for 

icofol. Dicofol was not detected in any of the 468, one-day concentration samples 

6 ng/m out of 53 samples collected (Yeary et al. 1993). It is not clear 

hether the detection occurred in California. 

al by a constant flow of air (wind speed of 0.02 m/s) or water 

cean water circulation speed of 0.02m/s (Scheringer et al. 2006). 

. A high TE value indicates an “optimal” 

ansport condition from the source region to remote depositional region. 

levels. 

In 2006, as part of the California Environmental P

trations in the low-incom

c

and grape vineyards were the predominant crops in the area. CDPR and the Air 

Resources Board (ARB) collected samples of ambient air at three primary schools 

throughout the 2006 calendar year. During the sampling period, approximately 6 

applications totaling 150 lbs of dicofol occurred within five miles of Parlier in 2006. 

Four hundred a

d

collected (quantitation limit = 46.3 ng/m3

). It does not appear that particulate matter, 

collected during this study, was analyzed for dicofol concentrations; given that dicofol is 

expected to be associated with particulate matter suspended in the air, the absence of 

detections may not accurately reflect the potential movement of dicofol. 

The USGS publication, Pesticides in the Atmosphere (Majewski et al. 1995) reports an 

observed concentration for kelthane (dicofol) in the air of 9.5 ng/m3

. Additionally, a 

cited study in this reference reports one detected residential outdoor ambient air 

concentration of 3

w

Modeling of Long-Range Transport Potential 

The “OECD Pov and LRTP Screening Tool” (version 2.0) was utilized in evaluating the 

overall environmental persistence (Pov), the long range transport potential (LRTP) and 

transfer efficiency (TE). The OECD Tool requires estimated degradation half lives in 

soil, water and air, and partition coefficients between air and water and between octanol 

and water as chemical-specific input parameters to calculate metrics of Pov and LRTP. 

Pov is derived from the degradation rate constants in soil, water and air to provide overall 

degradation. The resulted Pov value represents the characteristic time for disappearance 

of a chemical after releases in various media have been stopped and the overall 

degradation rate is determined by the disappearance of chemical from a medium 

(Scheringer et al., 2006). The characteristic travel distance (CTD) represents the 

potential of a chemical to be transported over long distances in air or water. In the OECD 

Tool, the CTD is the distance at which the concentration of chemical decrease to 37% 

due to transport of chemic

(o

Transfer efficiency is a dimensionless metric of potential for atmospheric transport and 

deposition of parent compound in terrestrial and aquatic environments of a remote region 

(Wegmann et al. 2007). It is a ratio between the depositional flux (mol/day) in remote 

region and emission flux from the source area

tr

131 
The OECD Tool was used in evaluating the Pov and LRTP for 3 known PBT chemicals 

DT, aldrin and endrin) and the dicofol isomers (both as the parent and parent plus 

Table 63. Ph properties used as input for estimating overall 

persistence a using the OECD Tool.

(D

degradates) using chemical-specific degradation half-lives in soil, water, and air as well 

as two partition constants, the Kow and KAW. Table 63 provides input parameters used in 

the OECD Tool. 

ysicochemical and environmental fate

nd long-range transport potential 

Name of 

Chemical 

Molecular 

Weight 

(g/mole) 

Log Kowa Log KAwa 

Half life 

in Air 

(hrs) 

Half life Half life 

in Water in Soil 

(hrs) (hrs) 

p.p’ DDT b 345.5 6.39 -3.34 170 5500 17000 

Aldrin b 364.9 4.94 -3.38 2.86 2670 3830 

Endrin b 380.9 5.44 -3.11 12.72 78840 29070 

o,p’dicofol 370.5 6.06 -7.641 74.4c 408d 612 d

p,p’-dicofol 370.5 6.06 -5.005 74.4c 1536 d 2304 d

DCBP 251 4.44e -4.359e 103e 1440e 2880e

FW-152 336 4.89e -7.187e 57.1e 4320e 8640e

DCBH 253 4.0e -6.404e 25.1e 900e 1800e

3- and 4- OHDCBP 267 3.96e -8.343e 46.8e 1440e 2880e

2 OH-DCBP 267 4.73e -5.242e 11.3e 1440e 2880e

a Maximum reported value 

b Input parameters for these chemical are based on the Reference chemicals data in the OECD 

Tool. 

c Half-life in air based on value reported in Rasenberg et al. 2003 

d The half-life in water based on PRZM/EXAM inputs 

e Maximum value derived in EPISuite for dicofol degradates. 

Although there are considerable uncertainties in the environmental fate properties of th

selected chemicals under consideration, the results (Table 64) indicate that dicofol and its 

degradates have Pov and LRTP properties similar to those of several known POPs (p,

DDT, aldrin and endrin). 

Table 64. Overall persistence and characteristic travel distances generated using the OECD Tool. 

e 

p’ 

Chemical Overall Persistence 

(Pov) 

(Days) 

Characteristic Travel 

Distance 

km (Miles) 

Transfer 

Efficiency 

(%) 

p.p’ DDT 1010 2530 (1572) 5.17 

Aldrin 225 206 (128) 0.003 

Endrin 1556 515 (320) 0.04 

o,p’-dicofol 37 2142 (1331) 9.45 

p,p’-dicofol 138 1467 (912) 3.39 

DCBP 172 1381 (858) 2.24 

FW-152 516 504 (313) 2.15 

DCBH 108 238 (148) 0.66 

3- and 4- OHDCBP 171 149 (93) 0.31 

2 OH-DCBP 173 228 (142) 0.10 

132 
Results from the OECD Tool do not indicate absolute loading of pesticides in the 

environment but help to compare model estimates for dicofol residues relative to known 

POP pesticides according to their Pov, TE, and CTD. 

Annual Emission Amounts 

There are two potential mechanisms that can result in transport of dicofol from an 

application area to the atmosphere with subsequent wet or dry deposition of the 

compound to areas distant from the initial site of application. These mechanisms include 

1) drift of dicofol during spray treatments of fields and 2) wind erosion of soil containing 

sorbed dicofol. 

From the CA PUR data, the average annual rate of dicofol applied between 1999 and 

006 was 223,511 lbs. From the AGDRIFT analysis, between 0.94% and 8.7% of the 

amount applied during aerial and ULV application, respectively, is lost due to airborne 

rift, or 2,101 to 19,450 lbs/year. Wet and dry deposition would result in removal of this 

irborne drift from the atmosphere; however, estimates of these removal processes 

timates for scavenging coefficients, particle size distributions, and settling 

velocities, and are beyond the level of this analysis. As such, a conservative estimate 

would result in all of the aerial drift, or 2,101 to 19,450 lbs/year, remaining for longrange transport. 

As dicofol has an affinity to partition to particulate matter, a potentially significant source 

of dicofol emissions from a field would be particulate matter from windblown soil 

erosion. The California Air Resources Board developed non-pasture agriculture 

particulate matter emission estimates for a number of counties in California (CARB 

1997). These emission estimates were divided by the total number of acres harvested in 

each county (USDA 2009) and then multiplied by the average annual acres of dicofol 

applied in each county (from the CA PUR data), in order to estimate the annual 

particulate matter per county where dicofol was used. The average annual amount of 

particulate matter from nonpasture windblown agricultural emissions in counties where 

dicofol was applied was 2,677 tons/year. If 90% of the dicofol applied is integrated into 

the top 1 cm of the soil, then the concentration of dicofol in the soil is 2.59 x 10-8 lbs 

dicofol/cm3 (0.9 x 223,511 lbs / [192,120 acres x 4.05 x 107 cm2/acre x 1 cm]). 

Assuming an average soil bulk density of 1.3 g/cm3, this equates to 9.03 x 10-6 lbs 

dicofol/lb soil. Multiplying this concentration by the average amount of particulate 

matter from nonpasture windblown agricultural emissions results in 48 lbs/year of dicofol 

emitted via wind erosion. 

ight volatilize 

2

d

a

require es

The average total annual amount of dicofol, not including that which m

from the soil or wate surface, that is available for long range transport is between 2,149 

and 19,500 lbs/year, or between 1 and 9% of the dicofol applied. It is worth noting that 

despite these estimates, air monitoring reported earlier showed only trace amounts of 

dicofol in the atmospheric samples collected. 

133 
DDT, DDD, DDE

In assessing the impacts of dicofol on the red-legged frog, it was assumed that the 

impacts of DDT, DDD, and DDE would be additive to those seen for dicofol’s total 

residues of concern. 

5.2.6.2. Effects Assessment 

Age Class and Sensitivity of Effects Thresholds 

It is generally recognized that test organism age may have a significant impact on the 

observed sensitivity to a toxicant. The acute toxicity data for fish are collected on 

juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on 

recommended immature age classes (e.g., first instar for daphnids, second instar for 

amphipods, stoneflies, mayflies, and third instar for midges). 

Testing of juveniles may overestimate toxicity at older age classes for pesticide active 

ingredients that act directly without metabolic transformation because younger age 

classes may not have the enzymatic systems associated with detoxifying xenobiotics. In 

so far as the available toxicity data may provide ranges of sensitivity information with 

respect to age class, this assessment uses the most sensitive life-stage information as 

measures of effect for surrogate aquatic animals, and is therefore, considered as 

protective of the CRLF. 

Use of Surrogate Species Effects Data 

Guideline toxicity tests and open literature data on dicofol are not available for frogs or 

any other aquatic-phase amphibian; therefore, freshwater fish are used as surrogate 

species for aquatic-phase amphibians. Endpoints based on freshwater fish ecotoxicity 

data are assumed to be protective of potential direct effects to aquatic-phase amphibians 

including the CRLF, and extrapolation of the risk conclusions from the most sensitive 

tested species to the aquatic-phase CRLF is likely to overestimate the potential risks to 

those species. Efforts are made to select the organisms most likely to be affected by the 

type of compound and usage pattern; however, there is an inherent uncertainty in 

extrapolating across phyla. In addition, the Agency’s LOCs are intentionally set very 

low, and conservative estimates are made in the screening level risk assessment to 

account for these uncertainties. 

In order to characterize the conservatism, of the endpoint selected to represent direct 

effects to aquatic-phase CRLF (i.e., the 96-h LC for the cutthroat trout = 53 μg/L), a 

eshwater fish (Table 24). Data were considered useful for the distribution if they are 

lassified acceptable or supplemental. Data for this distribution were collected from 

gistrant-submitted studies as well as the open literature (as identified using ECOTOX). 

nce the data set was assembled, the average of the Log10 values of the LC50 values for 

50

genus sensitivity distribution was derived using the available acute toxicity data for

fr

c

re

O

134 
a species was calculated. Then, the average of the Log10 values of the genera was 

alculated. A student’s t distribution was used to derive a genus sensitivity distribution 

l of 

he 

ta 

of 

Equation 

is 

n is 

aquatichase CRLF (LC50 = 53 μg/L) is comparable to the lower 5% of the genus sensitivity 

ating that this endpoint is protective of the lower 5th

ercentile of freshwater fish species. 

c

for with the mean and standard deviations of log-transformed acute toxicity data for al

the available genera of fish. The degrees of freedom were equal to n-1, where n is t

number of genera for which there are data available for the distribution. In this case, da

were available for 6 genera, so the distribution was established with 5 degrees 

freedom. The t-statistic was calculated for probabilities ranging 0.05-0.95 at intervals of

0.05. The log LC50 value for a specific proportion (p) of genera is calculated by 

1. The genus sensitivity distribution for 96-h LC50 values for fish exposed to dicofol 

displayed in Figure 12. Additional information relevant to this sensitivity distributio

provided in Appendix L. The endpoint selected to represent direct effects to 

p

distribution (LC50 = 49 μg/L), indic

p

Equation LCLog ( STDEVtLCLogMean ) p p .1 *

50 = 50 +

0.5

0.6

0.7

0.8

0.9

1

Pimephales

Lepomis

Micropterus

Ictalurus

0.4

0

0.1

0.2

0.3

10.0 100.0 1000.0

LC50 (ug/L)

Proportion

Figure 12. Genus sensitivity distribution for acute (96-h) exposures of fish to dicofol. 

 order to characterize the conservatism of the endpoint selected to represent direct 

ffects to terrestrial-phase CRLF (i.e., the subacute dietary toxicity endpoint for birds, 

C50 for the Japanese quail = 903 ppm), a species sensitivity distribution was derived 

using the available subacute dietary toxicity data for birds (Table 29). Data were 

considered useful for the distribution if they are classified acceptable or supplemental. 

In

e

L

Salvelinus

Oncorhynchus

135 
Data fo gistrant-submitted studies as well as the 

pen literature (as identified using ECOTOX). Once the data set was assembled, the 

ed subacute toxicity data for all of the available species within taxa. The 

egrees of freedom were equal to n-1, where n is the number of species for which there 

are data available for the distribution. In this case, data were available for 4 species, so 

the distribution was established with 3 degrees of freedom. The t-statistic was calculated 

for probabilities ranging 0.05-0.95 at intervals of 0.05. The log LC50 value for a specific 

proportion (p) of genera is calculated by Equation 1. The species sensitivity distribution 

for LC50 values for birds exposed to dicofol is displayed in Figure 13. Additional 

information relevant to this sensitivity distribution is provided in Appendix L. The 

Japanese quail toxicity endpoint selected to represent direct effects to terrestrial-phase 

CRLF is comparable to the lower 10% of the species sensitivity distribution. 

r this distribution were collected from re

o

average of the log-transformed LC50 values for a species was calculated. Unlike with the 

fish data, avian data were not averaged based on genera because no data were available 

for multiple species within the same genera. A student’s t distribution was used to derive 

a species sensitivity distribution for with the mean and standard deviations of logtransform

d

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100.0 1000.0 10000.0

LC50

Proportion

Coturnix japonica

Colinus virginianus

Phasianus colchicus

Anas platyrhynchos

Figure 13. Species sensitivity distribution for subacute exposures of birds to dicofol.

136 
Sublethal Effects 

When assessing acute risk, the screening risk assessment relies on the acute mortality 

e-by-case basis and only after careful consideration of the nature of the 

blethal effect measured and the extent and quality of available data to support 

ffect in humans that 

 similar to an effect produced by a naturally occurring estrogen, or other such 

endocrine effects as the Administrator may designate.” Following the recommendations 

of its Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC), EPA 

determined that there were scientific bases for including, as part of the program, 

androgen and thyroid hormone systems, in addition to the estrogen hormone system. 

EPA also adopted EDSTAC’s recommendation that the Program include evaluations of 

potential effects in wildlife. When the appropriate screening and/or testing protocols 

being considered under the Agency’s Endocrine Disrupter Screening Program (EDSP) 

have been developed and vetted, dicofol may be subjected to additional screening and/or 

testing to better characterize effects related to endocrine disruption. 

Location of Wildlife Species 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal 

was assumed to occupy either the treated field or adjacent areas receiving a treatment rate 

on the field. Actual habitat requirements of any particular terrestrial species were not 

considered, and it was assumed that species occupy, exclusively and permanently, the 

modeled treatment area. Spray drift model predictions suggest that this assumption leads 

to an overestimation of exposure to species that do not occupy the treated field 

exclusively and permanently. 

endpoint as well as a suite of sublethal responses to the pesticide, as determined by the 

testing of species response to chronic exposure conditions and subsequent chronic risk 

assessment. Consideration of additional sublethal data in the effects determination t is 

exercised on a cas

su

establishing a plausible relationship between the measure of effect (sublethal endpoint) 

and the assessment endpoints. However, the full suite of sublethal effects from valid 

open literature studies is considered for the purposes of defining the action area. 

Potential for Endocrine Disruption 

The extent to which dicofol may act on endocrine-mediated processes of non-target 

organisms, including CRLF is uncertain. EPA is required under the FFDCA, as amended 

by FQPA, to develop a screening program to determine whether certain substances 

(including all pesticide active and other ingredients) “may have an e

is

137 
138 

. i h i theses 

In orde o u h is s m t, it is necess t s th s y e 

defined in section 2.9.1. Based on the conclusions of this assessment, none of the 

hypoth a e je d eaning that the stated hypotheses repr n 

terms c d t e o icofol on the CRLF and its designated critical 

habitat

5.

r t

ese

of 

. 

2.7

o c

s c

dire

Add

ncl

n b

t a

ress

de t

 re

 in

ng t

is r

cte

irec

e R

k a

, m

 eff

sk H

sess

cts 

ypo

en

f d

ary o addres e ri

esen

k h

t co

poth

cern

ses

s in

nd
139 

6.0 Risk

In fulfilling d ered A 

inform ent repres

curren i sig ated

critical habitat. 

Based on the best available information, th

to Adverse ination CRLF from the fol.

Additionally, the Agency has 

CRLF desi

conclus r n

in tive y. Analysis r

dicofol action area and C

determ

potential effects to designated critical habita

cum

 Conclusions 

 its obligations under Section 7(

ailab

ly Affec

gnated critical habita

 and in 

a)(2) of

ecies risk asses

sks of dicof

e Agency makes a May Aff

for the

 CRLF and its critica

 determining use patte

. The LAA determ

t is descr

ed in Attachment 2

the En

sm

ol to the CRLF and its d

fol.

elated to the intersec

ibed in the baseline status

ang

e potential for effects to

 Summ

ination f

.

Species 

ents the bes

e

ect, and Likely 

 use of dic

aries of th

itat are p

tion of

lt in L

or the CRLF and

ct,

t data 

n

o

e risk

ese

 the 

A

 and 

the 

 

ted 

A 

ation presented in

tly av

ions and ef

inations are described in 

 this endang

sess th

RLF habitat used in

ered sp

e potentia

m

determined that there is th

t from the use of dico

inations f

, respec

Appendix B

le to as

fects determ

l r

or the

l

t (LAA) deter

Table 66

l hab

rns that resu

Table 65

ulative effects for the CRLF and is provid
Table 65. 

reproduc

Descripti dence s nation for dicofol use in California. Assessment endpoint is surviva

tion o als.

on of evi

f CRLF individu

upporting effects determi

Assessment 

Endpoint 

Effects Basis for Determination 

Determination

Dir to 

Analysis of individual effects indicates that up to 1 in 2 individual CRLF could experience m

dicofol in the aquatic habitat. - Chronic RQs for aquatic-phase CRLF exceed the LOC for all uses of dicofol, except Bermuda g

- Chronic EECs in the aquatic environment are above levels where growth effects were observed i

- Acute and chronic RQs for aquatic-phase CRLF consuming aquatic organisms contaminateaccumulation) exceed LOCs. - Refined acute, dose-based RQs (derived using T-HERPS) for medium sized CRLF consuming s

uming small insect

ce of dicofol. 

hr RLF consumin

insec

h was observ

ect effects

CRLF 

 -Acute RQs for aquatic-phase CRLF exceed the LOC for all uses of dicofol, except Bermuda gra- LOCs for all uses of dicofol. - Refined acute, dietary-based RQs (derived using T-HERPS) for CRLF consex- C

ed LOCs for several uses 

onic dietary-based RQs for CRLF exceed LOCs for all uses of dicofol, for C

ts, mammals and terrestrial-phase amphibians). 

- Cppm

ronic, dietary-based EECs are above levels where reduced number of eggs laid 

). 

Indirect e to 

tadpole CRLF 

via reduction of 

prey

ffects RQ 

 (i.e., algae) 

values for algae are below the LOC for all uses of dicofol. 

Indir

juve

via r

invertebrates) 

- Acu- The on this, indirect 

acute- Chr bits, peppe

orna- Chr , cotton, gstone , and walnuts/pecans. 

ect effects to 

nile CRLF 

eduction of 

prey (i.e., 

te RQs for aquatic invertebrates exceed the LOC the majority of dicofol uses. 

 likelihood of individual acute effects to aquatic invertebrates is ≤3%. Based 

 effects to aquatic invertebrates is discountable. 

onic RQs for aquatic invertebrates do not exceed the LOC for dicofol use on cucur

mentals, turf and outside buildings. 

onic RQs for aquatic invertebrates exceed the LOC for dicofol use on beans, citrus

 fruit, strawberry

Indirect effects to 

adul CRLF via 

redu on of prey 

(i.e., 

invertebrates, 

fish, frogs, mice) 

LAA 

- Acute RQs for aquatic invertebrates exceed the LOC the majority of dicofol uses. - The likelihood of individual acute effects to aquatic invertebrates is ≤3%. Based on this, indirect acute effects to aquatic invertebrates is discountable. - Chronic RQs for aquatic invertebrates do not exceed the LOC for dicofol use on cucurbits, peppeornamentals, turf and outside buildings. - Chronic RQs for aquatic invertebrates exceed the LOC for dicofol use on beans, citrus, cotton, gstone fruit, strawberry, and walnuts/pecans. -Acute RQs for aquatic-phase amphibians and fish exceed the LOC for all uses of dicofol, except buildings. 

t 

cti

140 
Assessment Effects 

Endpoint Determination

Basis for Determination - Use of dicofol on beans, citrindividual mortality (from acut-Use of dicofol on cucurbits, gin <10% chance of effects to an- Chronic RQs for fish and aqoutside buildings. - Because the LD50 used in deri

terrestrial invertebrates to dicof

us, cotton, hops, mint, p

e exposures) to fish and 

rapes, pepper, stone frui

 individual fish and aqu

uatic-phase amphibians 

ving RQs for terrestrial i

ol potentially

ome fruit, strawberries a

aquatic-phase amphibian

t, tomatoes, Bermuda gr

atic-phase amphibians re

exceed the LOC for all

nvertebrates is not quant

n 

s. 

as 

pr

 u 

ifi 

d walnuts/pecan

s, ornamentals, 

esenting prey of 

ses of dicofol, 

ed, RQs for acu

 exceed the

 for control of insects, it 

mint, hops, peppers, tom

 mortality to <10% of te

es resulting from these di

me fruits, strawberries, w

vertebrates. Although th

50 was established, mort

fects to the CRLF. 

exposures to terrestrial m

muda grass 

pome fruits could potenti

e fruits could potentially

icofol result in ≤2.0% 

he CRLF through potent

idered discountable. 

 for terrestrial mammals 

ve effects were observed

ia impacts to terrestrial m

small mammals to dic

result in effects to ma

strial-phase amphibian

restrial-phase amphibi

ividual mortality using

f effects to an individu

rrestrial-phase CRLFs

eed the LOC by factor

ting from chronic effec

 LOC of 0.05 for all use

has the potential to impa

atoes, cucurbits, ornam

rrestrial insects. Therefo

fol uses are considere

lnuts, pecans, beans, 

re is uncertainty in th

ity to small insects res

mmals exceed the LO

 result in 10.7% morta

esult in indirect effec

ortality to small mam

l effects to terrestrial 

r all uses of dicofol. C

Therefore, chronic ex

mmals serving as pote

ol through consumpti

mals. 

serving as prey to the 

s exceed the LOC for 

cute dietary-based RQ

terrestrial amphibian r

a acute effects on terr

anging 2x to 474x. Th

 to terrestrial frogs. 

s. 

ct 

ent 

re 

co d 

a co 

e e 

al ul 

a C 

al li 

 r ts 

m m 

ia m 

fo h 

. po 

a nti

- A of of on 

wi o m- A re s C- A er an se

- A nd a s 

of o al ep im te vi est 

di- C xc s r er 

in ul ts

 non-target inse

als, turf and Be

, indirect effect

discountable. 

tton and stone 

actual effects o

ting from dicof

(0.1) for all uses 

ty to individual 

to the CRLF d

als resulting fr

ammals resultin

ronic EECs are 

sures of dicofol 

al prey items. 

of contaminated 

RLF do not exce

veral uses. 

for terrestrial am

resenting prey 

rial amphibians 

efore, for all dic

- Given that dicofol is intended-For use of dicofol on grapes, result in a chance of individualeffects to terrestrial invertebrat- Use of dicofol on citrus, po≥10% of mortality to small ininvertebrates, given that no LDpotential to result in indirect ef- RQ values representing acute turf, outside buildings and Ber- Use of dicofol on citrus and dicofol use on citrus and pommammals. All other uses of dTherefore, indirect effects to tcitrus and pome fruits, are cons- Chronic RQs exceed the LOCfor mammals where reproductito indirectly affect the CRLF v

cute and chronic exposures 

th dicofol have the potential t

cute, dose-based RQs for tercute, dietary-based RQs for t

nalysis of the likelihood of i

dicofol result in ≤2% chance

pact of the indirect effects to 

cofol. 

hronic, dietary-based RQs e

direct effects to the CRLF res

Indirect effects to 

CRLF via 

-D ef et co 

ter ca d e nt

ue to a lack of quantitative 

restrial habitats of the CRLF 

fects data for non-targ

nnot be quantified an

plants exposed to di

ffects of dicofol to pla

fol, potential ri

s cannot be disc

141 
142 

Assessment 

Endpoint 

Effects 

Determination

Basis for Det ion erminat

reduction of 

habitat and/or

primary 

productivity 

(i.e., plants) 

-Qu ive d uggest th cofol ma lt in phytoto y. 

 o rte nv ts an

 e t e t e a R 

alitat

-There is-Dicofol

ata s

ne repo

xposures

at di

d incident i

o plants hav

y resu

ng effec

otential

xicit

of dicofol to pl

o cause indirect

olvi

the p

ts. 

ffects to aqu tic phase CL F thr

Table 66. of er n f F bi n Summary effects det minatio or CRL critical ha tat based o uses of dicofol in California.Assessment Endpoint 

Effects D o eterminati n 

Basi te s for De rmination 

Modificataquatic-pprimary celements 

ion of c h a quati C

hase 

onstituent 

 Di ofol has t e potential to modify habit t based on the a c-phase P Es.

Table 

ough 

nnot be 

- D59- Deff-Efdis

ic th o c ase C e 

). 

ic the p o ff hase r

ec rey ( e 

fe cofol e of th a

co

ofol has 

ofol has 

ts to its p

cts of di

unted. 

e potential t

otential t

see Tabl

 to plants

dire

indir

59). 

makin

ctly affe

ectly a

g up th

t the aquatic-ph

ect the aquatic-p

aquatic habitat

RLF (Se

CRLF th

e CRLF c

Modificatterrestrialprimary celements 

ec

ion of o he po m y at rrestr P

phase 

onstituent 

Habitat Eff ts

Dic fol has t tential to odif habit based on the te ial-phase CEs.

ee 

hrough 

 cannot 

- DTa- Deff-Efbe 

ic the p o tl c phase S

bl

ic the p o ec ff

ec rey ( e 

fe cofol g e str at of t F

di d. 

ofol has 

e 59). 

ofol has 

ts to its p

cts of di

scounte

otential t

otential t

see Tabl

 to plants

direc

indir

59). 

makin

y affe

tly a

up th

t the terrestrialect the terrestrial-ph

terre ial habit

 CRLF (

ase CRLF t

he CRL
143 

Based th the U. S. Fish and 

Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

modific redicted 

sks to the species and its resources (i.e., food and habitat) are not expected to be uniform across 

nuation 

with d

expecte . 

Evalua orm distribution of risk to the species would require 

formation and assessment techniques that are not currently available. Examples of such 

Enhanced information on the density and distribution of CRLF life stages within specific 

ation 

wou of the present risk assessment’s predictions of 

individual effects to the proportion of the population extant within geographical areas where 

a 

mo he significance of potential resource impairment to 

individuals of the species. 

trialpha

sources utilized by the frog, it does not establish minimal requirements to sustain healthy 

individuals at varying life stages. Such information could be used to establish biologically 

its to 

tho bove 

to c . 

Information on population responses of prey base organisms to the pesticide. Currently, 

gro irment immediately following exposure to the pesticide. The 

degree to which repeated exposure events and the inherent demographic characteristics of the 

table. 

An 

for and 

together with the information described above, a more complete prediction of effects to 

on the conclusions of this assessment, a formal consultation wi

When evaluating the significance of this risk assessment’s direct/indirect and habitat

ation effects determinations, it is important to note that pesticide exposures and p

ri

the action area. In fact, given the assumptions of drift and downstream transport (i.e., atte

istance), pesticide exposure and associated risks to the species and its resources are 

d to decrease with increasing distance away from the treated field or site of application

tion of the implication of this non-unif

in

information and methodology required for this type of analysis would include the following: 

•

recovery units and/or designated critical habitat within the action area. This inform

ld allow for quantitative extrapolation 

those effects are predicted. Furthermore, such population information would allow for 

re comprehensive evaluation of t

• Quantitative information on prey base requirements for individual aquatic- and terres

se frogs. While existing information provides a preliminary picture of the types of food

relevant thresholds of effects on the prey base, and ultimately establish geographical lim

se effects. This information could be used together with the density data discussed a

haracterize the likelihood of adverse effects to individuals

•

methodologies are limited to predicting exposures and likely levels of direct mortality,

wth or reproductive impa

prey population play into the extent to which prey resources may recover is not predic

enhanced understanding of long-term prey responses to pesticide exposure would allow 

a more refined determination of the magnitude and duration of resource impairment,

individual frogs and potential modification to critical habitat.
144 

7.0 Re

lvarez, J. 2000. Letter to the U.S. Fish and Wildlife Service providing comments on the Draft 

 – 

7-

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