Risks of Aldicarb Use to Federally Listed 

Endangered California Red Legged Frog 

(Rana aurora draytonii)

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Authors: 

Jonathan Angier 

Fred Jenkins 

Jeannette Martinez 

Red Legged Frog Steering Committee 

Reviewed by: 

Donna Randall, Senior Effects Scientist 

Dana Spatz, Senior Chemist/Branch Team Leader 

Nelson Thurman, Senior Fate Scientist 

Approved by: 

Tom Bailey, Branch Chief 

Environmental Risk Branch, 2 

Environmental Fate and Effects Division 

Environmental Fate and Effects Division 

Office of Pesticide Programs 

Washington, D.C. 20460 

July 17 , 2007 
ii

TABLE OF CONTENTS 

1. Executive Summary............................................................................... 1

2. Problem Formulation .......................................................................... 12

2.1 Purpose............................................................................................................. 12 

2.2 Scope................................................................................................................. 14 

2.3 Previous Assessments...................................................................................... 15 

2.4 Stressor Source and Distribution .................................................................. 17 

2.4.1 Environmental Fate Assessment............................................................ 18 

2.4.2 Environmental Transport Assessment.................................................. 20 

2.4.3 Mechanism of Action.............................................................................. 21 

2.4.4 Use Characterization .............................................................................. 21 

2.5 Assessed Species.............................................................................................. 26 

2.5.1 Distribution.............................................................................................. 27 

2.5.2 Reproduction........................................................................................... 32 

2.5.3 Diet ........................................................................................................... 32 

2.5.4 Habitat ..................................................................................................... 33 

2.6 Designated Critical Habitat ........................................................................... 34 

2.7 Action Area...................................................................................................... 36 

2.8 Assessment Endpoints and Measures of Ecological Effect ......................... 39 

2.8.1. Assessment Endpoints for the CRLF.................................................... 39 

2.8.2. Assessment Endpoints for Designated Critical Habitat...................... 41 

2.9 Conceptual Model........................................................................................... 45 

2.9.1 Risk Hypotheses...................................................................................... 45 

2.9.2 Diagram ................................................................................................... 46 

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

2.10.1 Exposure Analysis................................................................................... 49 

2.10.2 Effects Analysis....................................................................................... 51 

2.10.3 Action Area Analysis.............................................................................. 52 

3 Exposure Assessment........................................................................... 54

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

3.2 Aquatic Exposure Assessment....................................................................... 54 

3.2.1 Conceptual Model of Exposure.............................................................. 54 

3.2.2 Existing Monitoring Data....................................................................... 54 

3.2.3 Modeling Approach ................................................................................ 55 

3.2.3.1 Model Inputs........................................................................................ 55 

3.2.3.2 Results.................................................................................................. 57 

3.2.4 Additional Modeling Exercises Used to Characterize Potential 

Exposures................................................................................................................. 58 

3.2.5 Comparison of Modeled EECs with Available Monitoring Data....... 59 

3.3 Terrestrial Plant Exposure Assessment.................................................... 60 

3.4 CRLF Terrestrial Phase Exposure Assessment....................................... 61 

4. Effects Assessment ............................................................................... 63

4.1 Taxa specific toxicological endpoints and LOCs.......................................... 63 

4.2 Evaluation of Ecotoxicity Studies.................................................................. 65 

4.2.1 Toxicity to Terrestrial Plants................................................................. 66 
iii

4.3 Acute-to-Chronic Ratio Derivation for the CRLF....................................... 67 

4.4 N-Methyl Carbamate Toxicological Data for Frogs.................................... 69 

4.5 Aquatic Freshwater Plants............................................................................. 70 

4.6 Acute-to-Chronic Ration Derivation for Freshwater Invertebrates.......... 70 

4.7 Probit Analysis................................................................................................ 70 

4.8 Review of Ecological Incident Information System (EIIS)......................... 71 

4.9 Sensitivity Distribution................................................................................... 71 

4.9.1 Freshwater Fish....................................................................................... 71 

4.9.2 Freshwater Invertebrate ........................................................................ 72 

5 Risk Characterization.......................................................................... 75

5.1 Risk Estimation............................................................................................... 75 

5.1.1 Direct Effects........................................................................................... 76 

5.1.2 Indirect Effects........................................................................................ 79 

5.1.2.1 Evaluation of Potential Indirect Effects via Reduction in Food 

Items 80 

5.1.2.2 Evaluation of Potential Indirect Effects via Reduction in Habitat 

and/or Primary Productivity ............................................................................. 81 

5.2 Risk Description.............................................................................................. 84 

5.2.1 Direct Effects to the California Red Legged Frog ............................... 85 

5.2.1.1 Direct Effects to the Aquatic Phase of the CRLF ............................ 85 

5.2.1.2 Direct Effects to the Terrestrial Phase of the CRLF ....................... 87 

5.2.2 Indirect Effects via Reduction in Food Items....................................... 88 

5.2.2.1 Indirect Effects to the Terrestrial Phase of the CRLF.................... 88 

5.2.2.2 Indirect Effects via Reduction of Aquatic Primary Productivity... 90 

5.2.2.3 Indirect Effects via Alteration in Terrestrial Plant Community.... 90 

5.2.3 Secondary Poisoning of CRLF by Consuming Terrestrial 

Invertebrates Contaminated with Aldicarb Residues......................................... 91 

5.3 Final Effects Determination................................................................... 93 

6. Uncertainties....................................................................................... 100

6.1 Exposure Assessment Uncertainties............................................................ 100 

6.1.1 Maximum Use Scenario........................................................................ 100 

6.1.2 Modeling Inputs.................................................................................... 100 

6.1.2.1 Action Area........................................................................................ 101 

6.2.1.2 Aquatic Exposure Estimates............................................................ 102 

6.1.2.3 PRZM Modeling Inputs and Predicted Aquatic Concentrations. 102 

6.3 Effects Assessment Uncertainties ................................................................ 103 

6.3.1 Age Class and Sensitivity of Effects Thresholds................................ 103 

6.3.2 Use of Acute Freshwater Invertebrate Toxicity Data for the Midge 103 

6.3.3 Extrapolation of Long-term Environmental Effects from Short-Term 

Laboratory Tests................................................................................................... 103 

6.3.4 Residue Levels Selection....................................................................... 104 

6.3.5 Dietary Intake........................................................................................ 104 

6.3.6 Sublethal Effects.................................................................................... 104 

6.3.7 Location of Wildlife Species................................................................. 105 

6.4 Assumptions Associated with the Acute LOCs.......................................... 105 
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6.5 Usage Uncertainties ...................................................................................... 105 

7. References........................................................................................... 107

Appendix A: T-REX Modeling Outputs 

Appendix B: TerrPlant Modeling Outputs 

Appendix C: Earthworm Fugacity Modeling Outputs 

Appendix D: ECOTOX Run (Oct 2004 – Dec 2006) Accepted Papers 

Appendix E: ECOTOX Run (Oct 2004 – Dec 2006) Acceptable Data 

Appendix F: ECOTOX Run (Oct 2004 – Dec 2006) Excluded Papers 

Appendix G: ECOTOX (2006 RSLERA run) Acceptable Papers 

Appendix H: ECOTOX (2006 RSLERA run) Included by ECOTOX but rejected 

by OPP EFED 

Appendix I: ECOTOX (2006 RSLERA run) Excluded Papers 

Appendix J: Updated Species information 

Appendix K: Intentionally left blank 

Appendix L: Environmental Fate Data Requirements 

Appendix M: PRZM-EXAMS Model Runs: Output Files 

Appendix N: Aldicarb Degradation and Persistence 

Appendix O: Intentionally left blank 

Appendix P: Summary of Available Persistence Data for Aldicarb and its 

Sulfoxide and Sulfone Degradates 

Appendix Q: Intentionally left blank 

Appendix R: Spatial Summary for Terrestrial and Aquatic Uses 

Attachment 1: CRLF Life History

Attachment 2: CLRF Baseline Status and Cumulative Effects
v

LIST OF TABLES 

Table 1 Summarizes the effects determinations for direct effect of aldicarb to any of the 

life-stages of the CRLF in Eight Recovery Units. .............................................................. 4 

Table 2 Summarizes the effects determinations for indirect effect of aldicarb to any of 

the life-stages of the CRLF in Eight Recovery Units. ........................................................ 5 

Table 3 Summarizes the effects determinations for effects to the critical habitat the 

CRLF in recovery units one thru eight. .............................................................................. 5 

Table 4 National Labels Supporting Aldicarb Uses and Maximum Application Rates ... 22 

Table 5 California DPR Aldicarb Use, summarized by crop/use for 2001-2005 ............ 24 

Table 6 California Red-legged Frog Recovery Units with Overlapping Core Areas and 

Designated Critical Habitat............................................................................................... 29 

Table 7 Summary of Assessment Endpoints and Measures of Ecological Effects for 

Direct and Indirect Effects of Aldicarb and its Degradates on the California Red Legged 

Frog................................................................................................................................... 40 

Table 8 Summary of Assessment Endpoints and Measures of Ecological Effect for 

Primary Constituent Elements of Designated Critical Habitat ......................................... 43 

Table 9 Generic Aldicarb Inputs Used in PRZM-EXAMS Runs.................................... 56 

Table 10 Specific Inputs for Individual PRZM-EXAMS Runs....................................... 57 

Table 11 Results of Individual PRZM-EXAMS Runs With 85% Soil Incorporation..... 57 

Table 12 Results of Individual PRZM-EXAMS Runs With 99% Soil Incorporation..... 58 

Table 13 Aldicarb Acute and Chronic Ecotoxicological Values Listed in 2005 RED and 

Used for RQ Calculations in this Assessment .................................................................. 63 

Table 14 Aldicarb Sulfoxide Acute Ecotoxicological Values Used for RQ calculations in 

this Assessment................................................................................................................. 64 

Table 15 Specific LOCs Used in this Assessment........................................................... 65 

Table 16 Ecotox Study for Formulated Aldicarb Used for RQ Calculations in this 

Assessment (Oct 2004 - Dec 2006) .................................................................................. 66 

Table 17 Avian N-Methyl Carbamate Data..................................................................... 69 

Table 18 N-Methyl Carbamate Toxicological Data for Amphibians .............................. 69 

Table 19 Freshwater Acute Invertebrate Toxicity Data and Species and Genus Mean 

Acute Values..................................................................................................................... 73 

Table 20 Summary of Aldicarb Direct Effects RQs for the CRLF.................................. 78 

Table 21 Aldicarb Sulfoxide Direct Effects to the CRLF................................................ 79 

Table 22 Summary of Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via 

Acute and Chronic Effects on Aquatic Dietary Items(1).................................................. 82 

Table 23 Summary of Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via 

Acute Effects on Terrestrial Dietary Items(1) .................................................................... 83 

Table 24 Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via Direct Acute 

Effects on Aquatic and Terrestrial Habitat Components .................................................. 84 

Table 25 Summarizes the effects determinations for direct effect of aldicarb to any of the 

life-stages of the CRLF in Eight Recovery Units. ............................................................ 93 

Table 26 Summarizes the effects determinations for indirect effect of aldicarb to any of 

the life-stages of the CRLF in Eight Recovery Units. ...................................................... 94 

Table 27 Summarizes the effects determinations for effects to the critical habitat the 

CRLF in recovery units one thru eight. ............................................................................ 94 
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LIST OF FIGURES

Figure 1 Chemical structure of aldicarb and its oxidative transformation products......... 18 

Figure 2 Aldicarb Use Areas (includes row crops and orchards) in California, with 

Recovery Units.................................................................................................................. 23 

Figure 3 Aerial Extent of Known and Potential (Cultivated Land) Section 3 and 24c 

Aldicarb Use in California................................................................................................ 26 

Figure 4 Recovery Units, Core Area, Critical Habitat, and Occurrence Designation for 

CRLF................................................................................................................................. 31 

Figure 5 CRLF Reproductive Events by Month............................................................... 32 

Figure 6 Spatial Overlap of Aldicarb Action Area with CRLF Critical Habitat. ............ 38 

Figure 7 Conceptual Model for Aldicarb Effects on Aquatic Phase of the CRLF .......... 47 

Figure 8 Conceptual Model for Aldicarb Effects on Terrestrial Phase of CRLF ............ 48 

Figure 9 Conceptual Model for Aldicarb Effects on Aquatic Component of CRLF 

Critical Habitat.................................................................................................................. 48 

Figure 10 Conceptual Model for Aldicarb Effects on Terrestrial Component of the CRLF 

Critical Habitat.................................................................................................................. 49 

Figure 11 Comparison of structures of N-methyl carbamates......................................... 67 

Figure 12 Cumulative Acute Sensitivity Distribution of Freshwater Invertebrates to 

Aldicarb............................................................................................................................. 74 
1

1. Executive Summary 

Aldicarb is an insecticide, acaricide, and nematicide in the carbamate group of 

cholinesterase inhibitors. It is registered for use in California for both agricultural and 

non-agricultural purposes. These uses include: alfalfa, cotton, dried beans, sugar beet, 

sorghum, soybean, sweet potato, pecan, peanut, citrus, and ornamentals. 

Granular aldicarb use in California entails a variety of application techniques and varies 

greatly in amounts applied, number of applications, application intervals, and timing of 

applications according to usage. Typically, the granules are spread on the surface and 

incorporated into the soil by ‘shanking in’, ‘working into the soil’, ‘covering with soil’, 

and/or ‘wetting in’. Applications directly ‘in-furrow’ are also performed for some crops 

(e.g. sweet potato), but may be followed by later applications that are less effectively 

soil-incorporated. For the aquatic portion of this assessment, most applications were 

conservatively assumed to result in only 85% soil incorporation. Certain application 

techniques – specifically, in-furrow applications and banded applications that utilize 

state-of-the-art methods (such as positive displacement and immediate soil incorporation) 

– may theoretically result in incorporation efficiencies of 99%. However, crops that 

require additional applications after maturity cannot reasonably be expected to achieve 

99% incorporation efficiency and are difficult to model jointly, so in cases where there 

are multiple applications in a single year (that also include post-emergent applications) an 

assumption of 85% incorporation (even if the first application could potentially be 99% 

effective) is more conservative than applying a 99% efficiency for all applications. To 

address this uncertainty, most model runs were conducted using both 85% and 99% 

incorporation efficiencies; all results are reported herein. 

There are two aldicarb degradates of concern, aldicarb sulfoxide and aldicarb sulfone, 

that are also considered in this assessment. These degradates appear to form primarily in 

the shallow subsurface (although some may also form within plant tissue) and are 

potentially more mobile and persistent than the parent. As a conservative assumption, all 

three forms (parent aldicarb, sulfoxide, and sulfone) are considered as a single constituent 

for aquatic exposure estimates because of the longer degradate half-lives. Parent only is 

considered for terrestrial exposure because of its higher toxicity to animals, the likelihood 

that most exposure would be to whole granules, and because less of the degradate is 

expected to occur directly on the surface. 

Alidcarb and its major toxic degradates of concern may move through the environment 

and be transported away from the site of application. Aldicarb and its degradates may 

potentially be transported as a component of runoff (dissolved in water or sorbed onto 

solids) or groundwater and end up in proximate surface water bodies. Historically, 

aldicarb and its major toxic degradates appears to be more likely to be found in 

groundwater than surface water. Although groundwater per se is not evaluated herein, it 

is nonetheless significant because discharging groundwater is likely to support low-order 

streams, wetlands, and intermittent ponds – environments that are favorable to California 

Red-Legged Frogs (CRLFs). Long-term chronic concentrations derived from the PRZM-
2

EXAMS model should reflect background concentrations that might be found in 

discharged groundwater/stream baseflow. Based on the product formulation and physical 

and chemical properties of aldicarb, atmospheric long range transport is not considered 

an exposure pathway of concern. While bioaccumulation of aldicarb or its major toxic 

degradates in animals through the food chain is also not expected to be a significant 

exposure pathway (i.e., aldicarb and its degradates are expected to be rapidly metabolized 

at sublethal levels), secondary acute exposure is still a concern. Aldicarb is very highly 

toxic, and ingestion of a single granule is sufficient to result in death, with a delayed 

reaction time that potentially provides a window of opportunity for an exposed animal to 

move offsite before it is incapacitated or dies. Any granules not fully sorbed in the gut 

and metabolized in such animals potentially pose a secondary acute risk to a predator. In 

addition, dissolved aldicarb may be present in pools of water that typically form on the 

ground following an intense rainfall. Based on information on the extent of daily 

movements within a home range of small to medium size mammals (potential CRLR 

prey items), the potential extent of offsite movement was conservatively set to the upper 

range of one mile. 

There were insufficient monitoring data to support an aquatic evaluation based on 

concentrations found in water samples; specifically there were no targeted monitoring 

data on aldicarb for this region. Thus, there are no values available that would be 

considered consistent with high-end (‘peak’) exposure concentrations expected in surface 

water – although positive aldicarb detections from non-targeted data sets may be 

indicative of lower-end exposure concentrations. Therefore, it was necessary to estimate 

exposure (and risk) based on modeled results. The initial aquatic estimation was based 

on standard PRZM-EXAMS operating methods described in the Overview Document 

(US EPA, 2004), using pre-existing scenarios as well as scenarios devised specifically for 

the CRLF (depending on crop type). The EXAMS outputs were then processed further to 

delineate an aquatic Action Area within which potential (direct and indirect) effects to 

relevant (plant and/or animal) species might result in their being adversely affected – 

regardless of the presence or absence of CRLFs in that area. Post-processing of EXAMS 

outputs included estimating dilution that would be expected to occur within a stream 

channel, extended downstream to a point where concentrations are predicted to drop 

below a level at which there is an expected impact on any aquatic plant or animal species. 

In terms of direct effects, aquatic acute and chronic RQs are exceeded for the following 

modeled uses: dried bean, cotton, soybean (banded applications), pecan, peanut, alfalfa, 

and sugar beet. Sugar beet is the higher risk scenario and drives the overall risk in the 

aquatic environment and RQ/LOC exceedance based on sugar beet are used to determine 

the aquatic (downstream dilution) action area. Terrestrial acute and chronic RQs for onsite exposure are exceeded for all modeled scenarios: citrus, cotton, soybean, pecan, and 

sugar beet. Terrestrial acute and chronic risks off-site are not above levels of concern. 

Citrus drives the risk in the on-site terrestrial environment, followed by cotton. The 

initial area of concern for aldicarb is determined by including all potential crop land 

(agricultural and non-agricultural) from the 2002 National Land Cover Data (NLCD) and 

where aldicarb use has not been off-labeled (i.e. Del Norte and Humboldt Counties). The 
3

Agency extended this area by 1 mile (home range of a CRLF prey item) to include the 

distance a CRLF prey item could fly (Haskell et al., 2002) before succumbing to aldicarb 

effects. This one mile zone around crop land will account for part of the action area 

where aldicarb secondary poisoning effects, for predators ingesting birds, can be 

expected (extent of zone for small mammals likely to feed on fields is smaller). 

Based on all available lines of evidence and the highest risk scenario, the Agency 

concludes a “likely to adversely affect” (LAA) determination for direct effects to the 

terrestrial and aquatic phase of the CRLF via mortality, growth, or reproduction in 

recovery units where exposure to aldicarb occurs; a “not likely to adversely affect” for 

direct effects to the terrestrial and aquatic phase of the CRLF via mortality, growth, or 

reproduction in recovery units where aldicarb could potentially be used, and the Agency 

determined LOC exceedances but CAL DPR PUR data informs that aldicarb has not been 

used from 2001 through 2005. The Agency concludes a LAA determination for indirect 

effects to the California Red Legged Frog based on expected adverse effects to the prey 

base of the CRLF.. The Agency also concludes a LAA determination for all designated 

critical habitats in recovery units 1, 3, 4, 5, 6, and 7 based on adverse effects expected to 

the terrestrial and aquatic animal components of the critical habitat. There is no 

designated critical habitat in recovery units 2 and 8. 

Based on the highest risk scenario, the Agency also concludes that aldicarb is likely to 

indirectly adversely affect the terrestrial and aquatic phases of the CRLF by potentially 

negatively impacting the available prey items, for terrestrial prey this affect is limited to 

on-site exposures. This conclusion is based on the premise that there were LOC 

exceedances for all the potential prey items for the terrestrial (on-site) and aquatic phases 

of the CRLR for sugar beets. 

No LOC exceedances are predicted for aldicarb sulfoxide based on modeled EECs and 

available freshwater fish and freshwater invertebrate endpoint values. The Agency 

concludes a “no effects” determination for direct effects of aldicarb sulfoxide to the 

aquatic phase of the CRLF. 

The Agency also concludes a “no effects” determination for indirect effects to the aquatic 

phase of the CRLF via direct effects to aquatic plants in all recovery units. Lastly, the 

Agency concludes there is a “no effects” determination for indirect effects to the CRLF 

via direct effects to terrestrial plants and terrestrial plants growing in semi-aquatic areas 

(e.g., wetlands, saturated riparian zones, etc.) in all recovery units and critical habitat. 

Key uncertainties and data gaps that affect conclusions about direct and indirect effects 

on California Red-Legged Frogs (and therefore the effects determination conclusions) 

include: 1) Lack of targeted monitoring data, which does not allow for direct comparison 

with model results – thus there is no means by which to definitively check the aquatic 

exposure estimates. However, monitoring data that are available indicate that, when 

present, sample concentrations are consistent with low-end model results, and may reflect 

‘background’ levels in use areas; 2) Dilution factors used to establish the aquatic Action 
4

Area were based upon drainage area rather than stream flow – thus requiring a number of 

simplifying assumptions that should be conservative and protective, but that nonetheless 

increases the likelihood of error (whereas stream flow would be a direct measure of 

actual dilution potential); 3) Information provided regarding aldicarb usage in California 

may be inaccurate, inconsistent, or contradictory, but is the best available at this time; 4) 

use of most sensitive freshwater and terrestrial animal endpoint values to calculate RQs, 

which are one of several lines of evidence used to make direct and indirect effects 

determinations; 5) use of surrogate species (bird) to assess risk to aquatic and terrestrial 

phase amphibians T-REX overestimates risk to small frogs by using the LD50 for small 

birds and underestimates risk to large frogs by using the LD50 for medium birds. 

Considering the uncertainties and unknowns, it is believed that this assessment provides 

the most accurate and reasonably protective risk evaluation currently possible. 

Effects determinations for aldicarb direct effect, indirect effects, and effects to the critical 

habitat based on the highest risk scenario, sugar beet, and on-site effects to terrestrial prey 

items are displayed in Tables 1-3, below. Following the tables, effects determinations for 

individual registered crop uses and for on-site and off-site exposure of terrestrial prey 

items are delineated. 

Table 1 Summarizes the effects determinations for direct effect of aldicarb to any of the life-stages of 

the CRLF in Eight Recovery Units. 

Life stages include aquatic (eggs, larvae, tadpoles) and terrestrial phase of CRLF (young and adult frogs). 

The assessment endpoints are growth, survival, and reproduction of CRLF individuals. 

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

2 NLAA Based on lack of spatial overlap with Action Area (AA), frog habitat, and 

occurrence sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

3 NLAA Based on lack of spatial overlap with Action Area (AA), frog habitat, and 

occurrence sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

4 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

5 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF; 

6 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

7 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

8 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

* Summarize the effects determination by Recovery Unit, based upon the most conservative of the effects 

determinations. Summation by specific crops, more specific to on-site usage, is provided in the following 

text. 
5

Table 2 Summarizes the effects determinations for indirect effect of aldicarb to any of the life-stages of 

the CRLF in Eight Recovery Units. 

The life stages include aquatic (eggs, larvae, tadpoles) and terrestrial phase of CRLF (young and adult frogs). 

The indirect effects include effects to habitat including effect to primary productivity, prey, and riparian 

habitat. 

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

2 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF food 

sources 

3 NLAA Based on lack of spatial overlap with AA 

4 NLAA Based on lack of spatial overlap with AA 

5 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

6 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

7 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF food 

sources 

8 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

* Summarize the effects determination by Recovery Unit, based upon the most conservative of the effects 

determinations. Summation by specific crops, more specific to on-site usage, is provided in the following 

text. 

Table 3 Summarizes the effects determinations for effects to the critical habitat the CRLF in recovery 

units one thru eight. 

The effects entail effects to growth and survival of terrestrial and aquatic plant and animal components. 

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

2 NE No designated critical habitat in Recovery Unit (RU)

3 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat 

4 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat 

5 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

6 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

7 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat.. 

8 NE No designated critical habitat in RU

*Summarize the effects determination by Recovery Unit, based upon the most conservative of the effects 

determinations. Summation by specific crops, more specific to on-site usage, is provided in the following 

text. 
6

Aquatic Phase CRLF and Critical Habitat: 

No Effect

Soybean (in-furrow and/or positive displacement applications only), Citrus, and 

Sorghum 

Citrus, sorghum and soybean (but only when applied in-furrow with immediate soil 

incorporation or in-furrow with positive displacement) uses were determined to have “no 

effect” directly or indirectly on the aquatic-phase of the CRLF or the aquatic-phase of the 

critical habitat. This determination was based on the results of the risk assessment where 

all direct and indirect assessment endpoints of the aquatic-phase CRLF and its aquaticphase critical habitat were either below endangered LOCs (i.e., no exceedences of LOCs 

for aquatic animals) or judged based on the best available information to not be affected 

(i.e., off-field terrestrial plant components of critical habitat and aquatic plants judged to 

not be affected, based on estimated exposure concentrations that were lower than a ‘no 

observable effect’ level for limited toxicity data). Although application rates for citrus 

are fairly high (4.95 lb a.i./A) and incorporation efficiency only 85%, low rainfall rates 

and other factors in citrus production areas of California contribute to relatively low 

aquatic exposure and risk estimates. For Sorghum use, low application rates (1 lb a.i./A) 

and high incorporation efficiency (in-furrow application, 99%) contribute to minimal 

aldicarb residues being exported into surface waters or off-field terrestrial habitat. When 

compared to less efficient application methods with approximately 85% soil 

incorporation (e.g., banded applications), the use of more efficient application techniques 

(e.g., in-furrow, positive displacement) results in higher incorporation efficiencies (99%), 

and concomitant exposure estimations well below LOCs for soybean. 

Ornamentals (container grown) indoors 

There is no exposure pathway by which aldicarb applied to ornamentals in containers 

grown indoors may reach and expose the aquatic-phase of the CRLF or its critical habitat 

(i.e., no run-off, no atmospheric transport, no CRLF or its critical habitat indoors). 

Therefore this use is determined to have “no effect” on the aquatic-phase of the CRLF or 

its critical habitat. 

May Affect but Not Likely to Adversely Affect

Ornamentals (field grown—no containers) and Sweet Potato 

Aldicarb registered uses on containerless field-grown ornamentals and sweet potato were 

identified as “may affect” because the acute RQ values for aquatic invertebrates exceeded 

the acute endangered LOC, the chronic RQ values exceeded the chronic LOC, and the 

chronic RQ for aquatic invertebrates exceeded the chronic LOC for sweet potato use. 

However, based on consideration of a number of factors, the level of effect both directly 

and indirectly to the aquatic-phase of the CRLF and its aquatic critical habitat for these 

assessment endpoints was determined to be discountable. Off-site terrestrial plant 

components of critical habitat and aquatic plants were judged to not be affected based on 
7

the best available information that estimated exposure concentrations were lower than ‘no 

observable effect levels’ (based on limited toxicity data). Therefore, aldicarb uses on 

containerless field-grown ornamentals and sweet potato were determined to “not likely 

adversely affect” the aquatic-phase of the CRLF and its critical habitat. 

Direct effects to the aquatic-phase of the CRLF were considered discountable because the 

acute endangered RQ values did not exceed the endangered species LOC; while the 

chronic RQ value of 1 was exceeded, this exceedence was considered not significant and 

essentially indistinguishable from the no observable effect level. For example, the 

chronic RQ of 1.1 for containerless field grown ornamentals based on significant figures 

is not distinguishable from 1 (i.e., EEC/NOAEC = 0.49/0.46 ≅ 0.5/0.5 = 1), the level 

equivalent to no observable effects. In addition, ornamental usage is not extensive, and 

any potential impact on a water body adjacent to an application area would likely be 

minor, fleeting, and spatially very limited. 

Loss of fish or aquatic invertebrates as dietary resources was considered discountable 

based on several factors affecting the frequency and duration of exposure and the 

magnitude of effect. For example, both of these uses are limited to a single application 

per year, with sweet potato application occurring at plant and ornamentals occurring at 

any time prior to or during an infestation but again limited by the label to a single 

application per year. Therefore, any potential impact on a water body adjacent to an 

application area would likely be minor and fleeting. The acute endangered LOC for fish 

is not exceeded for either use. Although the chronic LOC is exceeded, as discussed in the 

preceding paragraph these exceedences are essentially equivalent to the no observable 

adverse effect level. Additionally, other fish species are not as sensitive (e.g., fathead 

minnow), so any potential impact would be limited in both magnitude and number of 

species involved. For aquatic invertebrates, while the acute endangered LOC was 

exceeded, the likelihood that an individual would be affected for the most sensitive 

species was one-in-over a million (based on default slope of 4.5). Additionally, based on 

the invertebrate species sensitivity distribution, over 80 percent of the aquatic 

invertebrates would be even less sensitive. The chronic LOC was not exceeded for the 

ornamentals and was at the LOC of 1 for sweet potato use, which is equivalent to no 

observable effect on invertebrates. 

Ornamentals (container grown) outdoors 

Outdoor container grown ornamental use was considered to “not likely adversely affect” 

the aquatic-phase CRLF or its aquatic-phase critical habitat. This determination was 

based on the determination for containerless field grown ornamentals used as a surrogate. 

Surface water exposure concentrations are expected to be lower than that for 

containerless field grown ornamentals. This reduction is attributable to containers which 

are expected to physically reduce run-off of aldicarb and its major toxic degradates and 

lower application rates as compared to containerless field grown ornamentals. In 

addition, ornamental usage is not extensive, and any potential impact on a water body 

adjacent to an application area would likely be minor, fleeting, and spatially very limited. 
8

May Affect and Likely to Adversely Affect

Dried Beans, Soybean (banded applications), Peanut, Pecans, Cotton, Alfalfa, 

Sugar beet 

Aldicarb registered uses on dried beans, soybean, peanut, pecan, cotton, alfalfa, and sugar 

beet were identified as “may affect” and “likely to adversely affect” the CRLF directly 

because both the acute endangered LOC and chronic LOC were exceeded for amphibian 

assessment endpoints (fish used as surrogate) and indirectly because fish and aquatic 

invertebrate acute and chronic LOC values were exceeded. 

It should be noted that for many of these crops, use of more efficient application 

techniques (i.e., ones that yield 99% vs. 85% incorporation) would result in exposure 

estimations well below the LOC for most categories (see Table 12). Although this might 

be impractical or impossible for some current uses (e.g., peanut application post-pegging, 

cotton application at bloom, pecan), in other cases (e.g., soybean, dried bean) achieving 

an incorporation efficiency of 99% results in acceptable levels of risk, and should be 

possible with appropriate application techniques (possibly requiring label changes). 

Terrestrial Phase CRLF and Critical Habitat: 

No Effect

Ornamentals (container grown) indoors 

There is no exposure pathway by which aldicarb applied to ornamentals in containers 

grown indoors may reach and expose the terrestrial-phase of the CRLF or its terrestrial 

critical habitat (i.e., no run-off, no atmospheric transport, no CRLF or its critical habitat 

indoors). Therefore this use is determined to have “no effect” on the aquatic-phase of the 

CRLF or its critical habitat. 

May Affect but Not Likely to Adversely Affect

Off-site All Outdoor Uses 

Off-site exposure for all outdoor registered uses was identified as “may affect” because 

an individual terrestrial-phase CRLF that ingested a granule transported off-site in the gut 

(incidental ingestion) or on the fur of a small mammal would potentially be effected. All 

other off-site exposure of the terrestrial-phase CRLF (i.e., bioaccumulation in terrestrial 

invertebrates or mammalian dietary items) and its critical habitat (i.e., loss of dietary 

resources, riparian or upland plants) to aldicarb and its major toxic residues are below 

LOCs. Because exposure of a terrestrial-phase CRLF to a granule carried in a smallmammal off-field was considered unlikely and no other off-site exposure of the 

terrestrial-phase CRLF or its critical habitat were above LOCs, exposure off-site for all 

outdoor uses was considered discountable and therefore “not likely to adversely affect” 

either directly or indirectly the terrestrial-phase of the CRLF or its critical habitat. 
9

Risks to terrestrial environments outside the zone of application for granular aldicarb are 

mainly limited to re-deposition of aldicarb residues in lower-lying areas affected by 

aldicarb runoff from nearby fields. However, calculations of the approximate amount of 

aldicarb potentially deposited as a result of registered aldicarb use (based on the highest 

risk scenario, cotton at 5 lbs a.i./A) indicate that concentrations (~ 10-6 mg a.i./kg soil) 

would be several orders of magnitude below those that would exceed the LOC. 

Exposure off-site of a CRLF to a granule in the gut or on the fur of small mammal was 

considered unlikely because it is doubtful that the series of events needed to coincide for 

an actual exposure event to occur would be frequent, if they occurred at all. First, 

aldicarb is applied to most crops once per year, and infrequently for the others (i.e., 

cotton at most three times and sugar beets and peanuts at most two times per year). 

Second, the duration of the integrity of a granule in the field is limited as it is fragile, and 

readily dissolves in water⎯ irrigation or rainfall dissolves the granule and moves it down 

into the soil profile. Therefore the window of opportunity for a small mammal (as 

potential CRLF prey) to be exposed on field to a granule is limited to a few days a year. 

While it is considered likely that some small mammals may be exposed to aldicarb during 

this window, it is unlikely that a significant number of small mammals would then 

subsequently move off-site, and not die before encountering a CRLF (biological 

description does not indicate it feeds on carrion). 

May Affect and Likely to Adversely Affect

On-site All Crops 

On-site exposure for all outdoor registered uses was identified as “may affect” and 

“likely to adversely affect” the terrestrial-phase of the CRLF because the acute LOC was 

exceeded for the direct amphibian measurement endpoint (birds) and for indirect effects 

(i.e., loss of small mammals, and on-site terrestrial invertebrates) for all uses. 

Bioaccumulation was demonstrated to not be a pathway of concern. This effects 

determination is based on the assumption that terrestrial-phase CRLF will come onto the 

treated site and that on-site resources are considered a critical component that supports 

CRLF (i.e., invertebrates and insects on the field that the farmer is trying to eliminate are 

considered critical to the support of the CRLF) and that the field is considered part of the 

critical habitat. A number of the uses are applied on fields that have been prepared for 

planting and should be relatively barren of cover for the CRLF at the time of aldicarb 

application (i.e., sorghum, sweet potato, dried bean, and soybean). 

Pooling the crop and aquatic- and terrestrial-phase specific analyses the following 

summarizes the effects determination by crop. 

• A “No Effect” (“NE”) determination was concluded for indoor container grown 

ornamentals because there is no exposure pathway for aldicarb to reach either the 

aquatic- or terrestrial-phase of the CRLF or its critical habitat. 
10

• A “Not Likely to Adversely Affect” (“NLAA”) determination was concluded for 

soybean (in-furrow and/or positive displacement applications only), citrus, and 

sorghum uses based on the lack of direct and indirect, acute and chronic effects to 

the aquatic-phase of the CRLF and its critical habitat and the lack of or 

discountable direct and indirect, acute and chronic effects to off-site CRLF, or to 

its critical habitat. 

• A “Not Likely to Adversely Affect” (“NLAA”) determination was concluded for 

containerless field-grown ornamentals, outdoor container grown ornamentals, and 

sweet potato based on the lack of direct or discountable direct and indirect, acute 

and chronic effects to the aquatic-phase of the CRLF and its critical habitat and 

the lack of or discountable direct and indirect, acute and chronic effects to off-site 

terrestrial-phase CRLF, or to its critical habitat. 

• A “Likely to Adversely Affect” (“LAA”) determination was concluded for dried 

beans, soybean (banded applications), peanut, pecans, cotton, alfalfa, and sugar 

beet based on direct acute and chronic effects to the aquatic-phase of the CRLF, 

and indirect effects to fish and aquatic invertebrates (food resources to aquaticand terrestrial-phase of the CRLF) and its critical habitat. However, there is no 

direct and indirect, acute and chronic effects to off-site terrestrial-phase CRLF, or 

its critical terrestrial habitat. 

• A “LAA” determination was concluded for all uses if terrestrial-phase CRLF will 

come onto the treated site and that on-site resources are considered a critical 

component that supports CRLF (i.e., invertebrates and insects on the field that the 

farmer are trying to eliminate are considered critical to the support of the CRLF) 

and that the field is considered part of the critical habitat. 

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 
11

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 adverse modification to critical 

habitat. 
12

2. 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. This assessment was completed in accordance with the August 5, 

2004 Joint Counterpart Endangered Species Act (ESA) Section 7 Consultation 

Regulations specified in 50 CFR Part 402 (USFWS/NMFS 2004; FR 69 47762). The 

structure of this risk assessment is based on guidance contained in U.S. EPA’s Guidance

for Ecological Risk Assessment (U.S. EPA 1998), the Services’ Endangered Species 

Consultation Handbook (USFWS/NMFS 1998) and procedures outlined in the Overview 

Document (U.S. EPA 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 

aldicarb on alfalfa (Section 24c), dried beans (Section 3), citrus, cotton (Section 3), 

peanuts (Section 3), pecan (Section 3 and 24c), sorghum (Section 3), soybean (Section 3), 

sugar beet (Section 3), sweet potato(Section 3), and ornamentals. In addition, this 

assessment evaluates whether these actions can be expected to result in the destruction or 

adverse modification of the species’ critical habitat. Key biological information for the 

CRLF is included in Section 2.5, and designated critical habitat information for the 

species is provided in Section 2.6 of this assessment. This ecological risk assessment has 

been prepared as part of the Center for Biological Diversity (CBD) vs. EPA et al. (Case 

No. 02-1580-JSW(JL)) settlement entered in the Federal District Court for the Northern 

District of California on October 20, 2006. It is one in a series of endangered species 

effects determinations for pesticide active ingredients involved in this litigation. 

In this endangered species assessment, direct and indirect effects to the CRLF and 

potential adverse modification to its critical habitat are evaluated in accordance with the 

methods (both screening level and species-specific refinements, when appropriate) 

described in the Agency’s Overview Document (U.S. EPA 2004). Use of such 

information is consistent with the guidance provided 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 aldicarb are based on an action area. The action area is considered to be 

the area directly or indirectly affected by the federal action, as indicated by the 

exceedance of Agency Levels of Concern (LOCs) used to evaluate direct or indirect 

effects. It is acknowledged that the action area for a national-level FIFRA regulatory
13

decision associated with a use of aldicarb 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 for registration of aldicarb at the use sites described in 

this document to affect CRLF individuals and/or result in the destruction or adverse 

modification of designated CRLF critical habitat: 

• “No effect”; 

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

• “May affect and likely to adversely affect”. 

Critical habitat identifies specific areas that have the physical and biological features, 

(known as primary constituent elements or PCEs) essential to the conservation of 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 (Section 2.6). 

If the results of initial screening-level assessment methods 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 the FIFRA regulatory 

action regarding aldicarb as it relates to this species and its designated critical habitat. If, 

however, direct or indirect effects to individual CRLFs are anticipated and/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 aldicarb. 

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

the CRLF “may affect” this species and/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 overlay of CRLF habitat with 

aldicarb use) and further evaluation of the potential impact of aldicarb on the PCEs is 

also used to determine whether destruction or adverse modification 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 

and/or the PCEs of its designated critical habitat. 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. 
14

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

(defined in Section 2.7), critical habitat analysis for aldicarb 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 (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 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 aldicarb 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 and 

jeopardize the continued existence of the species have been identified by the Services and 

are discussed further in Section 2.6. 

2.2 Scope 

Aldicarb (2-methyl-2-(methylthio)propionaldehyde O-(methylcarbamoyl)oxime), also 

known by the trade name TEMIK®, is a granular pesticide that was first registered for use 

on cotton in 1970. Aldicarb is an insecticide, acaricide, and nematicide, and is used in 

California on a variety of crops. Currently registered crop uses in California include: 

alfalfa, cotton, dried beans, citrus, sugar beet, sorghum, soybean, sweet potato, pecan, 

and peanut. County level usage data for aldicarb were obtained from California’s 

Department of Pesticide Regulation Use Reporting (CDPR PUR) database. Reported 

usage information considered in this assessment spans from 2001-2005 and is for the 

following commodities: alfalfa, cotton, dried beans, citrus, sugar beet, sorghum, sweet 

potato, pecan, and ornamentals. 

There are a number of uses reported in the CDPR PUR database (37 records out of 

14,960 records or 0.2% of the database) that either are misuses or entry errors in the 

database for they are not supported by past or current state (Section 24c) or national 

(Section 3) labels for aldicarb. These uses are not part of the FIFRA regulatory action and 

have not been included in this assessment but are identified here for completeness: 

landscape maintenance (1 record), soil fumigation/preplant (2 records), tomato 

processing (1 record), rights of way (1 record), almonds (1 record), corn (forage-fodder) 

(9 records), corn (human consumption) (2 records), and structural pest control (1 

record). Aldicarb was also used in research (i.e., research commodity record) in 2004 (1 

record, 23.1 lbs to 11 acres), in 2002 (2 records, 11.55 lbs to 5.5 acres, and 10.95 lbs to 

an unknown number of acres), and in 2001 (1 record, 4.5 lbs to unknown number of 

acres); the research occurred in Fresno and Tulare Counties. This use will be excluded as 

well from this assessment. Experimental use permits are federal actions that are taken for 

specific research projects which are typically of limited use and acreage. Each 

experimental use is considered on a case-by-case basis, limited to the year that the permit 

was granted; ESA effects would be considered at the time when experimental use permits 

are granted. 
The end result of the EPA pesticide registration process (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 or 

potential use of aldicarb in accordance with the approved product labels for California is 

“the action” being assessed. 

This ecological risk assessment is for currently registered uses of aldicarb 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. 

Consideration of degradates is an integral part of this risk assessment. There are two 

degradates of concern, aldicarb sulfoxide and aldicarb sulfone, that appear to form 

primarily in the shallow subsurface (although they may also be produced within plants 

that have systemically appropriated the parent chemical). Based on acute toxicity studies 

for freshwater fish, the relative toxicity relationship is: aldicarb > aldicarb sulfoxide > 

aldicarb sulfone. Based on the acute toxicity for freshwater invertebrates, the relative 

toxicity relationship is: aldicarb ≈ aldicarb sulfoxide > aldicarb sulfone. Total toxic 

residues (parent aldicarb + aldicarb sulfoxide + aldicarb sulfone) were modeled and 

evaluated in this screening-level assessment for aquatic exposure. Assuming 100 % of 

aldicarb parent in the terrestrial environment is a more conservative exposure assumption 

than modeling residues that are less toxic; therefore, this assessment does not consider 

degradates in the terrestrial environment. 

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; USFWS/NMFS 

2004). Aldicarb does not have any registered products that contain multiple active 

ingredients. 

There are many variables within the landscape covered by this risk assessment that can 

affect predicted exposure to (and ultimately effects of) aldicarb in any given area; even 

within contiguous Red-Legged Frog critical habitats in California there is great 

variability in land use and cover, topography, and precipitation. 

2.3 Previous Assessments

15
16

Two previously published, relevant risk assessments for aldicarb are the aldicarb 

Registration Eligibility Document (US EPA, May 2005) and revised RED (US EPA, 

September 2006). Key conclusions on exposure and risks to terrestrial and aquatic 

wildlife as well as relevant data gaps as they relate to these two assessments are listed 

here. For specific details not mentioned in this assessment, these documents can be 

consulted. Risk conclusions were consistent and remained unchanged between 

assessments. 

Exposure and Risk to Terrestrial Organisms:

• The cotton scenario (4.05 lbs ai/A; banded sidedress, 1 application) poses the 

highest use risk in the terrestrial environment to mammals and birds due to 

aldicarb levels in soil (highest acute RQ for small birds = 6400), followed by 

potato, sugar beet, peanuts and dry beans (RQ for small birds = 3000, 2800, 2800, 

2600, respectively). 

• The acute risk, acute restricted use, and acute endangered species LOCs for birds 

and mammals are exceeded for all target crops (cotton, dry beans, sorghum, 

peanuts, potatoes, soybeans, sugar beets, sweet potatoes, citrus, pecans, 

ornamentals) due to aldicarb levels in soil at both maximum allowed label rates 

(1.05 to 10.05 lbs ai/A) and average use rates (0.6 to 3.1 lbs ai/A). 

• Acute levels of concern are consistently exceeded by a factor of greater than 100 

and are frequently exceeded by more than 1000. 

• Granules left exposed on the surface appear to be the main source of exposure, 

but other sources such as residues of aldicarb taken up by plants and soil 

invertebrates (e.g., earthworms) may also serve as a means of exposure. 

• A single granule of TEMIK® 15G can kill a small bird 

• Reproductive effects to birds at sub-lethal levels could not be assessed because of 

the lack of reproductive studies with aldicarb or its degradates, due in part to high 

acute toxicity. It has been difficult to design an experiment that utilizes a dose 

low enough not to acutely intoxicate adult birds. 

• Reduction in seedling emergence and vegetative vigor to non-target terrestrial 

plants from runoff could not be assessed because of the lack of seedling 

emergence and vegetative vigor toxicity tests. Label identified the potential for 

impact to certain crop plants. 

Exposure and Risk to Aquatic Organisms

• The cotton scenario (4.05 lbs ai/A; 1 application) poses the highest use risk in the 

aquatic environment to aquatic invertebrates and fish due to estimated levels of 

aldicarb and its degradates in surface water from runoff (highest acute and chronic 

RQs for freshwater invertebrates = 1.4 and 26.6, respectively), followed by 
17

pecans, soybeans, citrus, and potato (acute and chronic RQs of 0.60, 0.36, 0.15, 

0.07 and 11.40, 6.76, 2.80, 1.40, respectively). 

• There is acute risk for freshwater fish and invertebrates and estuarine/marine fish 

and invertebrates for all of the registered uses (list) with the exception of potatoes 

for freshwater fish and invertebrates and estuarine/marine fish. 

• Based on the use of an estimated NOAEC for reproductive effects in freshwater 

fish, the chronic level of concern is also exceeded for freshwater fish (larval and 

juvenile survival) for cotton, pecan, and soybean use patterns. 

• Based on the use of an estimated NOAEC for reproductive effects in 

estuarine/marine fish, the chronic level of concern is exceeded for 

estuarine/marine fish for all crop scenarios. 

• Aldicarb residues are most likely to exceed levels of concern for fish and aquatic 

invertebrates in low-order streams because these streams are dominated by 

baseflow conditions (where 100% of stream flow consists of discharged 

groundwater), and most of the toxic residues are believed to form within the 

subsurface (especially within the saturated zone) and are conveyed by 

groundwater. Higher-order streams are sustained by much larger contributing 

land areas, so there should be a greater dilution effect. 

• In addition to risk based exposure estimates from modeling, there were also 

exceedances of the Agency levels of concern based on surface water residue 

monitoring data. 

2.4 Stressor Source and Distribution 

Chemical and Physical Properties

 Common Name: Aldicarb 

Chemical Name: 2-methyl-2(methylthio)propionaldehyde 

O-(methylcarbamoyl)oxime 

 CAS No. 116-06-3 

 PC Code: 098301 

 Molecular Formula: C7 H14 N2O2S 

 Molecular Weight: 190.2 g/mol 

 Density: 1.2 g/cm3

 

 Melting Point: 100N

C 

 Boiling Point: decomposes above 100N

C 

 Vapor Pressure: 2.55 x 10-5 mm Hg at 25o

C 

 Water Solubility: 6,000 mg/L(pH 7, 25 o

C) 

 Henry's Law Const.: 1.7x10-10 atm m3

/mole 

 Octanol/Water Partition Coefficient (KOW): 14 

 Formulations: Granules (e.g. Active ingredient 15.0%, 

Inert ingredients 85.0%) 
Aldicarb

Aldicarb Sulfone

Aldicarb Sulfoxide

C H 3 S

CC H N

C H 3

O

C

N

C H 3

H

H 3C O

C H 3 S

C

C H

N

C H 3

O

C

N

C H 3

H

O

O

H 3C

C H 3 S

C

C H

N

C H 3

O

C

N

C H 3

H

H O 3C

OO

Figure 1 Chemical structure of aldicarb and its oxidative transformation products

2.4.1 Environmental Fate Assessment 

Aldicarb rapidly degrades to aldicarb sulfoxide and aldicarb sulfone – both of which are 

as toxic or nearly as toxic as, and are more persistent than, the parent. Other aldicarb 

degradates may form as well, but are substantially less toxic and/or produced only in 

small amounts (<5%) and so are not included in this evaluation. Aerobic soil metabolism 

is the primary dissipation route for parent aldicarb in unsaturated soil. Half-lives for 

parent aldicarb range from 1 to 28 days (MRIDs 00102051, 00093642, 00080820, 

00093640, 00053366, 00101934, 00035365, and 00102071). There is currently 

insufficient data to accurately estimate the formation and dissipation rates of the 

sulfoxide and sulfone degradates. However, the rapid oxidation of parent aldicarb to 

these forms, and their substantially greater persistence than the parent, have been well 

documented in the published literature (e.g. Bull et al., 1970; Smelt et al., 1979). 

Laboratory studies suggest that degradation of all three aldicarb forms (parent, sulfoxide, 

and sulfone) to relatively non-toxic, non-carbamate residues (oximes and nitriles) occurs 

slowly (t1/2 up to 3 months) in aerobic soils, as a result of soil-catalyzed hydrolysis rather 

than aerobic metabolism (Lightfoot et al., 1987; Bank and Tyrrell, 1984). Parent aldicarb 

is generally stable to hydrolysis, slowly hydrolyzing only at a pH of 9 (MRID 00102065). 

Aldicarb sulfoxide hydrolyzed more quickly (t1/2 = 2.3 days) at pH 9 than at pH 7 (about 

6% at 28 days) (MRID 00102066). Aqueous photolysis rapidly degraded aldicarb to 

oxime and nitrile forms (i.e. with a t1/2 of four days: MRID 42498201). However, this 

process will only be dominant in clear, shallow waters, and will not affect residues in the 

subsurface. 

While there is limited information on aerobic metabolism in aquatic environments, a 

18
19

published laboratory study (Vink et al., 1997) reported half-lives ranging from 70 to 173 

days in surface waters in the Netherlands. The fate of parent aldicarb under anaerobic 

aquatic conditions (particularly groundwater) is of less concern than that of the 

degradates (aldicarb sulfoxide and aldicarb sulfone), which have been detected in 

groundwater long after application of the parent chemical had ceased. Published studies 

have reported increased degradation rates under low redox conditions, perhaps due to 

catalysis by reduced metal species in these environments (Bromilow et al., 1986). For 

example, Smelt et al. (1983) reported laboratory half-lives of aldicarb sulfone and 

sulfoxide ranging from 2 to 131 days in Dutch subsoils under “anaerobic conditions” 

(310 mV), and from 84 to 1100 days under aerobic conditions. Given this information, it 

is likely that aldicarb sulfoxide and aldicarb sulfone, which degrade relatively slowly in 

aerobic soil (MRID 44005001), can gradually leach into groundwater and continue to 

provide detectable levels of these materials over long time periods. 

In published field studies, dissipation half-lives for total carbamate residues in soil have 

ranged from approximately 0.3 to 5 months in the unsaturated zone, and 1 to 36 months 

in the saturated zone (Jones and Estes, 1995), in apparent contradiction to the observation 

of faster degradation under anaerobic (saturated) conditions. The reasons for the extreme 

variability in reported transformation rates (3 hours to 36 months) for aldicarb residues 

under anaerobic/saturated conditions are not known, but may be related to temperature, 

pH, and the presence of soils for surface catalysis (Lightfoot, et al., 1987). Also, not all 

saturated zones are necessarily anoxic; if they are shallow, there can be sufficient 

interaction with the unsaturated zone such that the groundwater may be sub-oxic or even 

atmosphere-equilibrated (oxic). Monitoring data in areas with historical aldicarb 

contamination confirm the high persistence of total aldicarb residues in some 

groundwater. For example, twenty years after cessation of aldicarb use on Long Island, 

NY, aldicarb sulfone and sulfoxide are still the most frequently detected pesticide 

compounds in groundwater there (Suffolk County Dept. of Health Services, 2000). 

In this assessment, ‘total aldicarb residues’ – consisting of parent aldicarb, the degradate 

aldicarb sulfoxide, and the degradate aldicarb sulfone – are considered for the aquatic 

assessment. This is done partly because the sulfoxide and sulfone degradates are nearly 

as toxic as the parent and are more mobile and persistent. For aquatic exposures the 

parent aldicarb may undergo some transformation to the sulfoxide and sulfone residues 

between the time of application to the soil and a runoff event. Therefore, by including 

both transformation products in addition to the parent and by modeling the combined 

residues using the most mobile and persistent fate parameters and comparing estimated 

exposures to the most toxic endpoint, we are accounting for the maximum potential 

exposure of aldicarb residues in the aquatic environment. In the case of terrestrial 

exposure, though, the higher toxicity of the parent and expectation that on-site surface 

residues of greatest concern will consist mostly of parent (especially whole granules) lead 

to an assumption of parent-only exposure in the terrestrial arena. That is, in the terrestrial 

environment the highest potential exposure will occur at the time of application before 

transformation, when parent aldicarb only is present. By assuming parent-only exposures 

and the higher toxicity of the parent, we are being similarly protective for the terrestrial 

environment. 
2.4.2 Environmental Transport Assessment 

Parent aldicarb is most likely to be transported off-site as a component of field runoff. 

Following a rain event, aldicarb may reach aquatic environments as sheet and channel 

flow from areas of application, since aldicarb is moderately persistent in terrestrial 

environments and soluble in water. It is unlikely, though, that undissolved granules will 

reach surface water bodies. The toxic degradates (aldicarb sulfoxide and aldicarb 

sulfone) are more prone to move vertically down through the soil profile, and potentially 

into groundwater, as they form primarily in the shallow subsurface. Groundwater that 

contains aldicarb residues may then be discharged into surface waters as baseflow. If the 

receiving groundwater is cool, acidic, and oxic, the sulfoxide and sulfone degradates will 

be very persistent and capable of long-distance subsurface transport. 

Aldicarb and its oxidation products are all highly mobile in soil. Aldicarb itself has 

Freundlich Kads values ranging between 0.20 ml/g (for sand) and 0.60 ml/g (for clay) 

(MRID 42498202). Aldicarb sulfoxide has Freundlich Kads values between 0.17 ml/g 

(sandy loam soil) and 0.36 ml/g (sandy clay loam) (MRID 43560301). Aldicarb sulfone 

had slightly lower values, ranging between 0.12 ml/g and 0.22 ml/g for the same set of 

soils as the sulfoxide (MRID 43560302). Degradation rates for combined aldicarb 

residues (parent plus sulfoxide plus sulfone) were calculated based upon the available 

information; details may be found in Appendix N & P. 

Potential transport mechanisms include pesticide surface water runoff, and secondary 

drift of volatilized or soil-bound residues leading to deposition onto nearby or more 

distant ecosystems. The magnitude of pesticide transport via secondary drift depends on 

the pesticide’s ability to be mobilized into air and its eventual removal through wet and 

dry deposition of gases/particles and photochemical reactions in the atmosphere. A 

number of studies have documented atmospheric transport and redeposition of pesticides 

from the Central Valley to the Sierra Nevada mountains (Fellers et al., 2004, Sparling et 

al., 2001, LeNoir et al., 1999, and McConnell et al., 1998). Prevailing winds blow across 

the Central Valley eastward to the Sierra Nevada mountains, transporting airborne 

industrial and agricultural pollutants into Sierra Nevada ecosystems (Fellers et al., 2004, 

LeNoir et al., 1999, and McConnell et al., 1998). Therefore, physicochemical properties 

of the pesticide that describe its potential to enter the air from water or soil (e.g., Henry’s 

Law constant and vapor pressure), pesticide use, modeled estimated concentrations in 

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

Nevadas are considered in evaluating the potential for atmospheric transport of aldicarb 

to habitat for the CRLF. Because aldicarb is applied as a granule and its potential to enter 

the air from water or soil is considered insignificant based on Henry’s Law constant and 

vapor pressure). 

20
2.4.3 Mechanism of Action 

Aldicarb is a systemic insecticide, acaricide, and nematicide. It is a potent cholinesterase 

(ChE) inhibitor causing inhibition of erythrocyte acetylcholinesterase (RBC ChE) as well 

as plasma butyryl ChE by binding to the active site of the enzyme. Acetylcholinesterase 

is an enzyme necessary for the degradation of the neurotransmitter acetylcholine (ACh) 

and subsequent cessation of synaptic transmission. Inhibition of these enzymes in 

animals (i.e. terrestrial and aquatic invertebrates, fish, birds, amphibians, reptiles, 

mammals) results in the accumulation of ACh at cholinergic nerve endings and continual 

nerve stimulation leading to death. 

2.4.4 Use Characterization 

National (Section 3) uses for aldicarb are presented in Table 4, with label maximum 

application rates. Use on potato1 and sugarcane2 is prohibited in California on the Section 

3 label (EPA Reg. No. 264-330). In California, dry beans and sorghum have the lowest 

allowed maximum application rates (7 lbs of product/A), while pecans, citrus, and sugar 

beet have the highest allowed maximum application rates among all crop uses permitted 

in the state (33 lbs, 33 lbs, and 28 lbs of product/A, respectively). For aldicarb use on dry 

beans in California, the target pests, which differ slightly from the rest of the states, are 

leafhoppers, Mexican bean beetle, mites, and nematodes. For the use on sugar beet in 

California, the target pests do not differ from the rest of the country; but California has 

restrictions on application window for sugar beet and dry beans from May 1 through 

September 1. For aldicarb use on sorghum, there are no restrictions on the Section 3 label 

for California. For aldicarb use on citrus, the Section 3 restriction for California refers to 

the application window only (May 1 through September 1). The use on pecans is 

restricted by the Section 24c label and restricts the maximum application per acre to 33 

lbs of product (4.95 lbs a.i.) per acre. 

 

1

 Label permits use on potato only in Florida, Pacific Northwest, and the following counties in Utah 

(Beaver, Boxelder, Cache, Carbon, Davis, Duchesne, Iron, Millard, lute, Salt Lake, Sanpete, Sevier, 

Uintah, Utah, Wasatch, Washington, and Weber) and Nevada (Humboldt, Pershing) 

2

 Label permits use on sugarcane in Louisiana only 

21
Table 4 National Labels Supporting Aldicarb Uses and Maximum Application Rates

National - Section 3 Registration

Site

Max 1 Time 

appl rate 

(lbs/A)

Max appl 

rate/year 

(lbs/A)

Max # 

appl/year

Citrus 33 33 1

Cotton 20 33 3

Dry Beans 14 14 1

Peanuts 20 20 1

Pecans 67 67 1

Potato* 20 20 1

Sorghum 7 7

Soybean 20 20 1

Sugarbeet 27 33 3

Sugarcane* 20 20 1

Sweet Potat

1

o 20 20 1

label for nectarine not found; thus not included in table

*off labeled in California

Figure 2 shows an overlay of where aldicarb was used in 2001 through 2005 (source: 

California Department of Pesticide Regulation Use Reporting (CAL DPR); map shows 

land in California which is under crop cultivation (based on National Land Cover Data 

(NLCD) 2002), describing, based on best available information, the aerial extent of 

potential aldicarb use in California. Del Norte and Humboldt Counties (northwest corner 

of state) have been off labeled since 1983. 

22
Figure 2 Aldicarb Use Areas (includes row crops and orchards) in California, with Recovery Units 

23
Analysis of labeled use information is the critical first step in evaluating the federal 

action. The current label for aldicarb represents the FIFRA regulatory action; 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. 

The Agency’s Biological and Economic Analysis Division (BEAD) provides an analysis 

of both national- and county-level usage information (BEAD, December 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 aldicarb by county in this 

California-specific assessment were generated using CDPR PUR data. Usage data are 

averaged together over the years 2000 to 2005 to calculate average annual usage statistics 

by county and crop for aldicarb, including pounds of active ingredient applied and base 

acres treated. California State law requires that every pesticide application be reported to 

the state and made available to the public. The summary of aldicarb usage for all use 

sites, including both agricultural and non-agricultural, is provided below in Table 5. 

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 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, misreported uses, and misuse are not considered part of the federal action and, therefore, are 

not considered in this assessment. 

Table 5 California DPR Aldicarb Use, summarized by crop/use for 2001-2005

AVG 

Annual 

Pounds 

Applied 

Use 

AVG 

Annual 

Area 

Treated 

Max. Avg. 

Application 

Rate (lb 

ai/A) 

Max. 95 

Percentile 

Application 

Rate (lb 

ai/A) 

Max. 99 

Percentile 

Application 

Rate (lb 

ai/A) 

Max. 

Maximum 

Application 

Rate (lb 

ai/A) 

Alfalfa 350.1 271.8 ac 2.18 2.69 2.69 2.69 

Almond 63.0 30.0 ac 2.10 2.10 2.10 2.10 

Bean, Dried 630.0 694.6 ac 1.06 2.10 2.10 2.10 

Corn (Forage -Fodder) (a) 76.2 73.0 ac 0.86 2.10 2.10 2.10 

Corn, Human Consumption (a) 45.4 60.5 ac 0.75 0.75 0.75 0.75 

Cotton 234450.4 219023.3 ac 1.24 2.25 2.25 28.52 

Landscape Maintenance (a) 0.2 Na 0.00 0.00 0.00 0.00 

Nectarine 0.5 1.0 ac 0.45 0.45 0.45 0.45 

N-Grnhs Flower 0.4 7400.0 sq ft 0.00 0.00 0.00 0.00 

N-Grnhs Plants In Containers 0.4 22705.0 sq ft 0.00 0.00 0.00 0.00 

 

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. 

24
Use 

AVG 

Annual 

Pounds 

Applied 

AVG 

Annual 

Area 

Treated 

Max. Avg. 

Application 

Rate (lb 

ai/A) 

Max. 95 

Percentile 

Application 

Rate (lb 

ai/A) 

Max. 99 Max. 

Percentile Maximum 

Application Application 

Rate (lb Rate (lb 

ai/A) ai/A) 

N-Outdr Flower 0.0 1425.0 sq ft 0.00 0.00 0.00 0.00 

N-Outdr Plants In Containers 801.1 19219.1 ac 4.45 5.00 5.00 5.00 

N-Outdr Transplants 19.3 6.5 ac 2.94 3.37 3.37 3.37 

Pecan 5099.5 1067.4 ac 4.95 4.95 5.82 5.82 

Research Commodity 11.4 4.1 2.10 2.10 2.10 2.10 

Soil Fumigation/Preplant (a) 233.3 385.8 ac 0.90 0.90 0.90 0.90 

Sorghum/Milo 16.5 8.0 ac 2.06 2.06 2.06 2.06 

Structural Pest Control (a) 0.1 na 0.00 0.00 0.00 0.00 

Sugarbeet 85.5 67.7 ac 1.31 2.40 2.40 2.40 

Tomato, Processing (a) 10.5 17.5 ac 0.60 0.60 0.60 0.60 

All Uses 241893.7 272460.2 ac 4.95 5.00 5.82 28.52 

(a) Use reports in Cal DPR PUR that represent misuse or misreporting are excluded from this assessment 

(b) Uses excluded in this assessment because they will not affect CRLF 

25
Figure 3 Aerial Extent of Known and Potential (Cultivated Land) Section 3 and 24c Aldicarb Use in 

California 

2.5 Assessed Species 

The CRLF was federally listed as a threatened species by USFWS effective June 24, 

1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest 

native frog in the western United States (USFWS 2002). A brief summary of information 

26
regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in 

Sections 2.5.1 through 2.5.4, respectively. 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 USFWS on April 13, 2006 

(USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat 

for the CRLF is provided in Section 2.6. 

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 (USFWS 1996). Its range has been reduced by about 70%, and 

the species currently resides in 22 counties in California (USFWS 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) (USFWS 2002). 

Populations currently exist along the northern California coast, northern Transverse 

Ranges (USFWS 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 (USFWS 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) (USFWS 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 (see 

Figure 4). Recovery units, core areas, and other known occurrences of the CRLF from the 

CNDDB are described in further detail in this section, 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 USFWS 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 

27
to cover the current range of the species not included in core areas and/or designated 

critical habitat, but within the recovery units. 

Recovery Units 

Eight recovery units have been established by USFWS for the CRLF. These areas are 

considered essential to the recovery of the species, and the status of the CRLF “may be 

considered within the smaller scale of the recovery units, as opposed to the statewide 

range” (USFWS 2002). Recovery units reflect areas with similar conservation needs and 

population statuses, and therefore, similar recovery goals. The eight units described for 

the CRLF are delineated by watershed boundaries defined by US Geological Survey 

hydrologic units and are limited to the elevational maximum for the species of 1,500 m 

above sea level. The eight recovery units for the CRLF are listed in Table 6 and shown 

in Figure 4. 

Core Areas 

USFWS has designated 35 core areas across the eight recovery units to focus their 

recovery efforts for the CRLF (see Figure 4). Table 6 summarizes the geographical 

relationship among recovery units, core areas, and designated critical habitat. The core 

areas, which are distributed throughout portions of the historic and current range of the 

species, represent areas that allow for long-term viability of existing populations and 

reestablishment of populations within historic range. These areas were selected because 

they: 1) contain existing viable populations; or 2) they contribute to the connectivity of 

other habitat areas (USFWS 2002). Core area protection and enhancement are vital for 

maintenance and expansion of the CRLF’s distribution and population throughout its 

range. 

For purposes of this assessment, designated critical habitat, currently occupied (post1985) core areas, and additional known occurrences of the CRLF from the CNDDB are 

considered. Each type of locational information is evaluated within the broader context 

of recovery units. For example, if no labeled uses of aldicarb occur (or if labeled uses 

occur at predicted exposures less than the Agency’s LOCs) within an entire recovery unit, 

that particular recovery unit would not be included in the action area and a “no effect” 

determination would be made for all designated critical habitat, currently occupied core 

areas, and other known CNDDB occurrences within that recovery unit. Historically 

occupied sections of the core areas are not evaluated as part of this assessment because 

the USFWS Recovery Plan (USFWS 2002) indicates that CRLFs are extirpated from 

these areas. A summary of currently and historically occupied core areas is provided in 

Table 6 (currently occupied core areas are bolded). While core areas are considered 

essential for recovery of the CRLF, core areas are not federally-designated critical 

habitat, although designated critical habitat is generally contained within these core 

recovery areas. It should be noted, however, that several critical habitat units are located 

outside of the core areas, but within the recovery units. The focus of this assessment is 

currently occupied core areas, designated critical habitat, and other known CNDDB 

28
CRLF occurrences within the recovery units. Federally-designated critical habitat for the 

CRLF is further explained in Section 2.6. 

Table 6 California Red-legged Frog Recovery Units with Overlapping Core Areas and Designated 

Critical Habitat. 

Recovery Unit 1

(Figure 2.a) Core Areas 2,7 (Figure 2.a) Critical Habitat 

Units 3

Currently 

Occupied 

(post-1985) 

4

Historically 

Occupied 4

Cottonwood Creek (partial) 

(8) -- 9

Feather River (1) BUT-1A-B 9

YUB-1 Yuba River-S. Fork Feather 9

River (2) 

-- NEV-16

-- Traverse Creek/Middle Fork 9

American River/Rubicon (3) 

Consumnes River (4) ELD-1 9

S. Fork Calaveras River (5) -- 9

Tuolumne River (6) -- 9

Piney Creek (7) -- 9

Sierra Nevada 

Foothills and Central 

Valley (1) 

(eastern boundary is 

the 1,500m elevation 

line) 

-- East San Francisco Bay 9

(partial)(16) 

Cottonwood Creek (8) -- 9

Putah Creek-Cache Creek (9) -- 9

-- Jameson Canyon – Lower 9

Napa Valley (partial) (15) 

Belvedere Lagoon (partial) 

(14) -- 9

North Coast Range 

Foothills and 

Western Sacramento 

River Valley (2) 

-- Pt. Reyes Peninsula (partial) 9

(13) 

-- Putah Creek-Cache Creek 9

(partial) (9) 

NAP-1 Lake Berryessa Tributaries 9

(10) 

Upper Sonoma Creek (11) -- 9

-- Petaluma Creek-Sonoma 9

Creek (12) 

Pt. Reyes Peninsula (13) MRN-1, MRN-2 9

Belvedere Lagoon (14) -- 9

North Coast and 

North San Francisco 

Bay (3) 

SOL-1 Jameson Canyon-Lower 9

Napa River (15) 

-- CCS-1A6

ALA-1A, ALA1B, STC-1B 

East San Francisco Bay 9

(partial) (16) 

-- STC-1A6

South and East San 

Francisco Bay (4) 

SNM-1A South San Francisco Bay 9

(partial) (18) 

South San Francisco Bay 

(partial) (18) 

SNM-1A, SNM2C, SCZ-1 

9 Central Coast (5) 

Watsonville Slough- Elkhorn SCZ-2 5 9

29
Slough (partial) (19) 

MNT-2 Carmel River-Santa Lucia 9

(20) 

Estero Bay (22) -- 9

-- SLO-86

Arroyo Grande Creek (23) -- 9

-- Santa Maria River-Santa 9

Ynez River (24) 

MER-1A-B, 

STC-1B 

East San Francisco Bay 9

(partial) (16) 

-- SNB-16, SNB-26

Santa Clara Valley (17) -- 9

MNT-1 Watsonville Slough- Elkhorn 9

Slough (partial)(19) 

-- Carmel River-Santa Lucia 9

(partial)(20) 

Gablan Range (21) SNB-3 9

Diablo Range and 

Salinas Valley (6) 

Estrella River (28) SLO-1A-B 9

SLO-86 -- 

STB-4, STB-5, 

STB-7 

Santa Maria River-Santa 9

Ynez River (24) 

Sisquoc River (25) STB-1, STB-3 9

Ventura River-Santa Clara 

River (26) 

VEN-1, VEN-2, 

VEN-3 

9

Northern Transverse 

Ranges and 

Tehachapi Mountains 

(7) 

LOS-16 -- 

-- Santa Monica Bay-Ventura 9

Coastal Streams (27) 

San Gabriel Mountain (29) -- 9

Forks of the Mojave (30) -- 9

Santa Ana Mountain (31) -- 9

Santa Rosa Plateau (32) -- 9

San Luis Rey (33) -- 9

Sweetwater (34) -- 9

Southern Transverse 

and Peninsular 

Ranges (8) 

Laguna Mountain (35) -- 9 1

 Recovery units designated by the USFWS (USFWS 2000, pg 49). 

2

 Core areas designated by the USFWS (USFWS 2000, pg 51). 

3

 Critical habitat units designated by the USFWS on April 13, 2006 (USFWS 2006, 71 FR 19244-19346). 

4

 Currently occupied (post-1985) and historically occupied core areas as designated by the USFWS 

(USFWS 2002, pg 54). 

5

 Critical habitat unit where identified threats specifically included pesticides or agricultural runoff 

(USFWS 2002). 

6

 Critical habitat units that are outside of core areas, but within recovery units. 7

 Currently occupied core areas that are included in this effects determination are bolded. 

30
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 

Figure 4 Recovery Units, Core Area, Critical Habitat, and Occurrence Designation for CRLF 

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 

31
range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb_info.html for additional 

information on the CNDDB.

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 (USFWS 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, 

USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until 

the following year) (Fellers 2005b, USFWS 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 (USFWS 2002). Figure 5 depicts CRLF annual reproductive timing. 

Figure 5 CRLF Reproductive Events by Month

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 

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 

(USFWS 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 terrestrialphase CRLFs is thought to be aquatic and terrestrial invertebrates found along the 

32
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 (USFWS 2002). 

Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al. 

1997), and dense vegetation close to water and shading 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 (USFWS 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 

(USFWS 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 (USFWS 2002). 

33
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 USFWS (USFWS 2006; FR 51 19244-19346). A summary 

of the 34 critical habitat units relative to USFWS-designated recovery units and core 

areas (previously discussed in Section 2.5.1) is provided in Table 6. 

‘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 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. 

Please note that a more complete description of these habitat types is provided in 

Attachement 1. 

34
Occupied habitat may be included in the critical habitat only if essential features within 

the habitat may require special management or protection. Therefore, USFWS 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. Please 

see Attachment 1 for a full explanation on this special rule. 

USFWS has established adverse modification standards for designated critical habitat 

(USFWS 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 aldicarb that may alter the PCEs of the CRLF’s critical habitat 

form the basis of the critical habitat impact analysis. According to USFWS (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) 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. 

(3) 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. 

(4) Elimination of upland foraging and/or aestivating habitat or dispersal habitat. 

(5) Introduction, spread, or augmentation of non-native aquatic species in stream 

segments or ponds used by the CRLF. 

(6) 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 aldicarb is expected to directly impact living 

organisms within the action area, critical habitat analysis for aldicarb is limited in a 

35
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 aldicarb 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. Deriving the geographical extent of this portion of the action area is the 

product of consideration of the types of effects that aldicarb may be expected to have on 

the environment, the exposure levels to aldicarb that are associated with those effects, 

and the best available information concerning the use of aldicarb and its fate and 

transport within the 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 aldicarb. An analysis of labeled uses and review of available product labels was 

completed. This analysis indicates that for aldicarb the following uses are considered as 

part of the federal action evaluated in this assessment: 

• Alfalfa (for seed) 

• Citrus 

• Cotton 

• Dried bean 

• Sugar beet 

• Sorghum 

• Sweet potato 

• Peanut 

• Pecan 

• Soybean 

• Ornamentals (field-grown, no containers) 

In all these cases granular aldicarb is applied directly onto/into the soil and is usually 

soil-incorporated. 

After determination of which uses will be assessed, an evaluation of the potential 

“footprint” of the use pattern should be determined. This “footprint” represents the initial 

area of concern and is typically based on available land cover data. Local land cover data 

available for the state of California were analyzed to refine the understanding of potential 

aldicarb use. However, no areas are excluded from the final action area based on usage 

and land cover data. The initial area of concern is defined as all land cover types that 

represent the labeled uses described above. The borders of all cultivated land have been 

36
extended outward by 1 mile to account for secondary poisoning effects by listed 

terrestrial wildlife. This zone represents at most the home range for a small bird (Haskell 

et al., 2002), and is used here synonymously with “the distance a small mammal could 

travel away from a site containing aldicarb” before falling prey to an adult CRLF. This 

constitutes the terrestrial portion of the aldicarb action area. 

Once the initial area of concern is defined, the next step is to compare the extent of that 

area with the results of the screening level risk assessment. The screening level risk 

assessment will define which taxa, if any, are predicted to be exposed at concentrations 

above the Agency’s Levels of Concern (LOC). The screening level assessment includes 

an evaluation of the environmental fate properties of aldicarb to determine which routes 

of transport are likely to have an impact on the CRLF. 

The physical/chemical properties of aldicarb are such that the dominant route of exposure 

is likely to be granules on the land surface. While there may be transient peaks in surface 

water bodies following large rain events that occur soon after application, both modeling 

and monitoring data indicate that this is probably not as common an occurrence. There is 

possible concern about infiltration into groundwater and subsequent discharge of tainted 

groundwater into water bodies inhabited by CRLFs. While this potential effect is not 

specifically incorporated into the delineation of the Action Area, some implications are 

discussed in section 3.2. 

LOC exceedances are used to describe how far effects may be seen from the initial area 

of concern. Factors considered include: spray drift (N/A for aldicarb), downstream runoff, atmospheric transport (N/A for aldicarb), etc. This information is incorporated into 

GIS and a map of the action area is created. Figure 6 shows the spatial overlap of the 

aldicarb action area with all designated area for critical habitat in the eight recovery 

zones. 

37
Figure 6 Spatial Overlap of Aldicarb Action Area with CRLF Critical Habitat. 

38
Subsequent to defining the action area, an evaluation of usage information was conducted 

to determine the area where use of aldicarb may impact the CRLF. This analysis is used 

to characterize where predicted exposures are most likely to occur but does not preclude 

use in other portions of the action area 

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.,. water bodies, 

riparian vegetation, and upland and dispersal habitats), the migration pathways of 

aldicarb and its major degradates (e.g., runoff, infiltration, etc.), and the routes by which 

ecological receptors are exposed to aldicarb-related contamination (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 and/or modification of its habitat. In addition, potential destruction and/or 

adverse modification of 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. 

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 aldicarb and its major degradates is 

provided in Table 7. 

 

5

 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001. 

39
Table 7 Summary of Assessment Endpoints and Measures of Ecological Effects for Direct and 

Indirect Effects of Aldicarb and its Degradates on the California Red Legged Frog

Measures of Ecological Effects6 Assessment Endpoint 

(Data Sources Reviewed) 

Specific Selected Toxicity Value 

(basis) 

Aquatic Phase 

(eggs, larvae, tadpoles, juveniles, and adults)a

1a. Most sensitive fish or 

amphibian acute LC50 (guideline 

or ECOTOX) 

1a. Bluegill sunfish 96-hr LC50 = 52 

ppb ai 

(most sensitive fish value) 

1b. Most sensitive fish or 

amphibian chronic NOAEC 

(guideline or ECOTOX) 

1b. Bluegill sunfish early-life stage 

NOAEC = 0.46 ppb ai 

(estimated using ACR) 

1. Survival, growth, and 

reproduction of CRLF 

individuals via direct 

effects on aquatic phases 

1c. Most sensitive fish or 

amphibian early-life stage data 

1c. same as 1b. 

2a1. Bluegill sunfish 96-hr LC50 = 52 

ppb ai (most sensitive fish value) 

2a2. Chironomus tentans 48-hr EC50 = 

20 ppb ai 

(most sensitive invertebrate value) 

2a. Most sensitive (1) fish, (2) 

aquatic invertebrate, and (3) 

aquatic plant EC50 or LC50 

(guideline or ECOTOX) 

2a3. Marine diatom 96-hr EC50 > 5000 

ppb ai 

(only algal value available) 

2b1. C. tentans reproduction NOAEC 

= 1 ppb ai (estimated using ACR) 

2. Survival, growth, and 

reproduction of CRLF 

individuals via effects to 

food supply (i.e.,

freshwater invertebrates, 

non-vascular plants) 

2b. Most sensitive (1) aquatic 

invertebrate and (2) fish chronic 

NOAEC (guideline or ECOTOX) 2b2. Bluegill sunfish NOAEC = 0.46 

ppb ai 

(estimated using ACR) 

3a. Most sensitive vascular plant 

acute EC50 (duckweed guideline 

test or ECOTOX vascular plant) 

3. Survival, growth, and 3a. No data available 

reproduction of CRLF 

individuals via indirect 

effects on habitat, cover, 

and/or primary 

productivity (i.e., aquatic 

plant community) 

3b. Most sensitive non-vascular 

plant acute EC50 (freshwater algae 

or diatom guideline or similar 

ECOTOX) 

3b. Marine diatom 96-hr EC50 > 5000 

ppb ai 

(only available algal test, used marine 

as surrogate for freshwater) 

4a1. Pearl millet seedling emergence 

21-d NOAEC = 2.05 lbs ai/A 

(No seedling emergence EC25 values 

available, used the only available plant 

study endpoint) 

4a. Distribution of (1) seedling 

emergence and (2) vegetative 

vigor monocot EC25 values 

(seedling emergence and 

vegetative vigor guidelines or 

similar ECOTOX) 4a2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

4b1. No seedling emergence study 

data available 

4. Survival, growth, and 

reproduction of CRLF 

individuals via effects to 

riparian vegetation, 

required to maintain 

acceptable water quality 

and habitat in ponds and 

streams comprising the 

species’ current range. 4b. Distribution of (1) seedling 

emergence and (2) vegetative 

vigor EC25 values for dicots 

(seedling emergence, vegetative 

vigor guidelines, or similar 

ECOTOX)7

4b2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

 

6

 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in 

Appendices D through F.

7

 The available information indicates that the California red-legged frog does not have any obligate 

relationships. 

40
Measures of Ecological Effects6 Assessment Endpoint 

(Data Sources Reviewed) 

Specific Selected Toxicity Value 

(basis) 

Terrestrial Phase (Juveniles and adults)

5a. Most sensitive birdb or 

terrestrial-phase amphibian acute 

LC50 or LD50 (guideline or 

ECOTOX) 

5a. Mallard duck LD50 = 1 mg ai/kgbw 

(most sensitive bird test as surrogate 

for terrestrial-phase amphibian) 

5. Survival, growth, and 

reproduction of CRLF 

individuals via direct 

effects on terrestrial 

phase adults and juveniles 5b. Most sensitive birdb

 or 

terrestrial-phase amphibian 

chronic NOAEC (guideline or 

ECOTOX) 

5b. Mallard duck reproduction 

NOAEC = 0.49 mg ai/kg-bw 

(Extrapolated using ACR) 

6a1. Honey bee acute contact LD50 = 

0.285 μg ai/bee 

(most sensitive terrestrial invertebrate)

6a. Most sensitive terrestrial (1) 

invertebrate and (2) vertebrate 

acute EC50 or LC50 (guideline or 

ECOTOX)c 6a2. rat LD50 = 0.9 mg ai/kg-bw 

(most sensitive terrestrial mammalian)

6b1. No chronic NOAEC data for 

terrestrial invertebrates 

6. Survival, growth, and 

reproduction of CRLF 

individuals via effects on 

prey (i.e.,terrestrial 

invertebrates, small 

terrestrial vertebrates, 

including mammals and 

terrestrial phase 

amphibians) 

6b. Most sensitive terrestrial (1) 

invertebrate and (2) vertebrate 

chronic NOAEC (guideline or 

ECOTOX) 

6b2. rat 2-generation reproduction 

study NOAEC = 0.4 mg/kg-bw 

7a1. Pearl millet seedling emergence 

21-d NOAEC = 2.05 lbs ai/A 

(No seedling emergence EC25 values 

available, used the only available plant 

study endpoint) 

7a. Distribution of (1) seedling 

emergence and (2) vegetative 

vigor EC25 values for monocots 

(seedling emergence, vegetative 

vigor guideline or similar 

ECOTOX study) 7a2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

7b1. No seedling emergence study 

data available 

7. Survival, growth, and 

reproduction of CRLF 

individuals via indirect 

effects on habitat (i.e.,

riparian vegetation) 

7b. Distribution of (1) seedling 

emergence and (2) vegetative 

vigor EC25 values for dicots 

(seedling emergence, vegetative 

vigor, or ECOTOX)5

7b2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable a

 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 than exposure pathways on land. 

b

 Birds are used as surrogates for terrestrial phase amphibians. c

 Although the most sensitive toxicity value is initially used to evaluate potential indirect effects, 

sensitivity distribution is used (if sufficient data are available) to evaluate the potential impact to food 

items of the CRLF.

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 aldicarb 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 destroy or adversely 

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 aldicarb effects data are available. 

41
Assessment endpoints and measures of ecological effect selected to characterize potential 

modification to designated critical habitat associated with exposure to aldicarb are 

provided in Table 8. Adverse modification to the critical habitat of the CRLF includes 

the following, as specified by USFWS (2006) and previously discussed in Section 2.6: 

1. Alteration of water chemistry/quality including temperature, turbidity, and 

oxygen content necessary for normal growth and viability of juvenile and 

adult CRLFs. 

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. 

4. Significant alteration of channel/pond morphology or geometry. 

5. Elimination of upland foraging and/or aestivating habitat, as well as 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. 

Measures of such possible effects by labeled use of aldicarb 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 USFWS (2006). 

42
Table 8 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary 

Constituent Elements of Designated Critical Habitat

Assessment Endpoint Measures of Ecological 

Effect8

(Data Sources Reviewed) 

Specific Selected Toxicity Value 

(basis) 

Aquatic Phase PCEs

(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat) 

a. Most sensitive aquatic plant 

EC50 (guideline or similar 

ECOTOX study) 

a. Marine diatom 96-hr EC50 > 5000 

ppb ai 

(only available algal test, used marine 

as surrogate for freshwater) 

b1. Pearl millet seedling emergence 

21-d NOAEC = 2.05 lbs ai/A 

(No seedling emergence EC25 values 

available, used the only available plant 

study endpoint) 

b. Distribution of terrestrial 

monocot (1) seedling 

emergence and (2) vegetative 

vigor EC25 values (seedling 

emergence and vegetative 

vigor guidelines or similar 

ECOTOX studies) 

b2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

c1. No seedling emergence study data 

available 

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. 

c. Distribution of terrestrial 

dicot (1) seedling emergence 

and (2) vegetative vigor EC25

values (seedling emergence 

and vegetative vigor guidelines 

or similar ECOTOX studies)

c2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

a. Most sensitive EC50 values 

for aquatic plants (guideline or 

similar ECOTOX studies) 

a. Marine diatom 96-hr EC50 > 5000 

ppb ai 

(only available algal test, used marine 

as surrogate for freshwater) 

b1. Pearl millet seedling emergence 

21-d NOAEC = 2.05 lbs ai/A 

(No seedling emergence EC25 values 

available, used the only available plant 

study endpoint) 

b. Distribution of terrestrial 

monocot (1) seedling 

emergence and (2) vegetative 

vigor EC25 values (seedling 

emergence and vegetative 

vigor guidelines or similar 

ECOTOX studies) 

b2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

c1. No seedling emergence study data 

available 

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.9

c. Distribution of terrestrial 

dicot (1) seedling emergence 

and (2) vegetative vigor EC25

values (seedling emergence 

and vegetative vigor guidelines 

or similar ECOTOX studies)

c2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

 

8

 All toxicity data reviewed for this assessment are included in Appendices D through F. 9

 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. 

43
Assessment Endpoint Measures of Ecological 

Effect8

(Data Sources Reviewed) 

Specific Selected Toxicity Value 

(basis) 

a1. Bluegill sunfish 96-hr LC50 = 52 

ppb ai (most sensitive fish value) 

a. Most sensitive EC50 or LC50 

values for (1) fish or aquaticphase amphibians and (2) 

aquatic invertebrates (guideline 

or similar ECOTOX study) 

a2. C. tentans 48-hr EC50 = 20 ppb ai 

(most sensitive invertebrate value) 

b1. Bluegill sunfish early-life stage 

NOAEC = 0.46 ppb ai 

(estimated using ACR) 

Alteration of other chemical 

characteristics necessary for 

normal growth and viability of 

CRLFs and their food source. 

b. Most sensitive reproductive 

NOAEC values for (1) fish or 

aquatic-phase amphibians and 

(2) aquatic invertebrates 

(guideline or similar ECOTOX 

studies)

b2. C. tentans reproduction NOAEC = 

1 ppb ai (estimated using ACR) 

Reduction and/or modification of 

aquatic-based food sources for 

pre-metamorphs (e.g., algae) 

a. Most sensitive aquatic plant 

EC50 (guideline or ECOTOX) 

a. Marine diatom 96-hr EC50 > 5000 

ppb ai 

(only available algal test, used marine 

as surrogate for freshwater) 

Terrestrial Phase PCEs 

(Upland Habitat and Dispersal Habitat) 

a1. Pearl millet seedling emergence 

21-d NOAEC = 2.05 lbs ai/A 

(No seedling emergence EC25 values 

available, used the only available plant 

study endpoint) 

a. Distribution of terrestrial 

monocot (1) seedling 

emergence and (2) vegetative 

vigor EC25 values (seedling 

emergence and vegetative 

vigor guidelines or similar 

ECOTOX studies) a2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

b1. No seedling emergence study data 

available 

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 

b. Distribution of terrestrial 

dicots (1) seedling emergence 

and (2) vegetative vigor EC25

values (seedling emergence 

and vegetative vigor guidelines 

or similar ECOTOX studies)

b2. Granular formulation so effect of 

residues on foliar vegetation is not 

applicable 

c1a. rat LD50 = 0.9 mg ai/kg-bw 

(most sensitive terrestrial mammalian) 

c1b. rat 2-generation reproduction 

study NOAEC = 0.4 mg/kg-bw 

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 

c. Most sensitive food source 

acute EC50 or LC50 and 

NOAEC values for terrestrial 

vertebrates (mammals) and 

invertebrates, birds or 

terrestrial-phase amphibians, 

and freshwater fish. c2a. Honey bee acute contact LD50 = 

0.285 μg ai/bee 

(most sensitive terrestrial invertebrate) 

c2b. No chronic NOAEC data for 

terrestrial invertebrates 

Reduction and/or modification of 

food sources for terrestrial phase 

juveniles and adults 

c3a. Mallard duck LD50 = 1 mg ai/kgbw 

(most sensitive bird test as surrogate 

for terrestrial-phase amphibian) 

Alteration of chemical 

characteristics necessary for 

normal growth and viability of 

juvenile and adult CRLFs and 

their food source. 

c3b. Mallard duck reproduction 

NOAEC = 0.49 mg ai/kg-bw 

(Extrapolated using ACR)

44
 

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, 1998). For this assessment, the 

risk is stressor-linked, where the stressor is the release of aldicarb to the environment. 

The following risk hypotheses are presumed for this endangered species assessment: 

• Labeled uses of aldicarb within the action area may directly affect the CRLF by 

causing mortality or by adversely affecting growth or fecundity; 

• Labeled uses of aldicarb within the action area may indirectly affect the CRLF by 

reducing or changing the composition of food supply; 

• Labeled uses of aldicarb within the action area may indirectly affect the CRLF 

and/or adversely modify 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; 

• Labeled uses of aldicarb within the action area may indirectly affect the CRLF 

and/or adversely modify 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; 

• Labeled uses of aldicarb within the action area may adversely modify the 

designated critical habitat of the CRLF by reducing or changing breeding and nonbreeding aquatic habitat (via modification of water quality parameters, habitat 

morphology, and/or sedimentation); 

• Labeled uses of aldicarb within the action area may adversely modify the 

designated critical habitat of the CRLF by reducing the food supply required for normal 

growth and viability of juvenile and adult CRLFs; 

• Labeled uses of aldicarb within the action area may adversely modify 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. 

• Labeled uses of aldicarb within the action area may adversely modify the 

designated critical habitat of the CRLF by reducing or changing 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. 

• Labeled uses of aldicarb within the action area may adversely modify the 

designated critical habitat of the CRLF by altering chemical characteristics necessary for 

normal growth and viability of juvenile and adult CRLFs. 

45
2.9.2 Diagram 

The conceptual model is a graphic representation of the structure of the risk assessment. 

It specifies the stressor (aldicarb), release mechanisms, biological receptor types, and 

effects endpoints of potential concern. The conceptual models for aquatic and terrestrial 

phases of the CRLF are shown in Figures 7 and 8, and the conceptual models for the 

aquatic and terrestrial PCE components of critical habitat are shown in Figures 9 and 10. 

Exposure routes shown in dashed lines are not quantitatively considered because the 

resulting exposures are expected to be so low as not to cause adverse effects to the CRLF. 

Exposure Pathways and Routes in Aquatic Phase Conceptual Model

Eggs, larvae, tadpoles, juveniles, and adult frogs may potentially absorb across their 

membranes or gills and integuments dissolved aldicarb and its two major degradates 

(aldicarb sulfoxide, aldicarb sulfone) in surface water. 

Aquatic animals that serve as prey to the juvenile and adult CRLF may be exposed via 

gills and their integument to aldicarb and its two major toxic degradates in surface water. 

Aquatic vascular and non-vascular plants may sorb to their membranes or transfer across 

their membranes dissolved aldicarb and its major degradates in surface water. 

Terrestrial plants in semi-aquatic areas (i.e. wetlands, riparian zones) may uptake 

dissolved aldicarb and its major degradates from soil pore water, surface water, or 

groundwater. 

The exposure pathways discussed here in the aquatic phase conceptual model are 

modified to address attributes assessed in aquatic component of critical habitat and PCEs 

in conceptual model 13. 

46
Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Red-legged Frog

Eggs Juveniles

Larvae Adult

Tadpoles

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

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 2.c

Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Red-legged Frog

Eggs Juveniles

Larvae Adult

Tadpoles

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

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 2.c

Figure 7 Conceptual Model for Aldicarb Effects on Aquatic Phase of the CRLF 

Exposure Pathways and Routes in Terrestrial Phase Conceptual Model

Juvenile and adult frogs may experience dermal exposure to soil residues of aldicarb and 

its two major toxic degradates when seeking refuge in ground crevices from solar 

radiation or traversing across soils with aldicarb-related residues. 

Juvenile and adult frogs may also incidentally ingest soil residues of aldicarb and its two 

major degradates along with prey items. 

CRLF prey items, small mammals (mice) and terrestrial insects, may uptake across their 

dermal/cuticle soil residues of aldicarb and its two major degradates. 

The exposure pathways discussed here in the terrestrial phase conceptual model are 

modified to address attributes assessed in terrestrial component of critical habitat and 

PCEs in conceptual model 14. 

47
Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Direct

application

Red-legged Frog

Juvenile

Adult

Terrestrial 

insects

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs)

Runoff

Mammals

Exposure

Media

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport

Root uptake

Wet/dry deposition

Amphibians

Ingestion

Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Direct

application

Red-legged Frog

Juvenile

Adult

Terrestrial 

insects

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs)

Runoff

Mammals

Exposure

Media

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport

Root uptake

Wet/dry deposition

Amphibians

Ingestion

Figure 8 Conceptual Model for Aldicarb Effects on Terrestrial Phase of CRLF 

Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Red-legged Frog

Eggs Juveniles

Larvae Adult

Tadpoles

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food sources

Reduction in algae

Reduction in prey

Habitat quality and channel/pond 

morphology or geometry

Adverse water quality changes

Increased sedimentation

Reduced shelter

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 and 

Upland plants

terrestrial exposure 

pathways and PCEs

see Figure 2.d

Community

Reduced seedling 

emergence or vegetative 

vigor (Distribution)

Habitat 

PCEs

Other chemical 

characteristics

Adversely modified 

chemical characteristics

Population 

Yield

Reduced yield

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Stressor

Source

Receptors

Attribute

Change

Aldicarb applied to use site

Red-legged Frog

Eggs Juveniles

Larvae Adult

Tadpoles

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food sources

Reduction in algae

Reduction in prey

Habitat quality and channel/pond 

morphology or geometry

Adverse water quality changes

Increased sedimentation

Reduced shelter

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 and 

Upland plants

terrestrial exposure 

pathways and PCEs

see Figure 2.d

Community

Reduced seedling 

emergence or vegetative 

vigor (Distribution)

Habitat 

PCEs

Other chemical 

characteristics

Adversely modified 

chemical characteristics

Population 

Yield

Reduced yield

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Figure 9 Conceptual Model for Aldicarb Effects on Aquatic Component of CRLF Critical Habitat 

48
Stressor

Source

Attribute

Change

Habitat 

PCEs

Aldicarb applied to use site

Direct

application

Red-legged Frog

Juvenile

Adult

Terrestrial 

insects

Food resources

Reduction in food 

sources

Elimination and/or disturbance of 

upland or dispersal habitat

Reduction in primary productivity

Reduced shelter

Restrict movement

Terrestrial plants

grasses/forbs, fruit, 

seeds (trees, shrubs)

Runoff

Mammals

Exposure

Media and

Receptors

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport

Root uptake

Wet/dry deposition

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Other chemical 

characteristics

Adversely modified 

chemical characteristics

Population

Reduced survival

Reduced growth

Reduced reproduction

Community

Reduced seedling emergence 

or vegetative vigor 

(Distribution)

Stressor

Source

Attribute

Change

Habitat 

PCEs

Aldicarb applied to use site

Direct

application

Red-legged Frog

Juvenile

Adult

Terrestrial 

insects

Food resources

Reduction in food 

sources

Elimination and/or disturbance of 

upland or dispersal habitat

Reduction in primary productivity

Reduced shelter

Restrict movement

Terrestrial plants

grasses/forbs, fruit, 

seeds (trees, shrubs)

Runoff

Mammals

Exposure

Media and

Receptors

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport

Root uptake

Wet/dry deposition

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Other chemical 

characteristics

Adversely modified 

chemical characteristics

Population

Reduced survival

Reduced growth

Reduced reproduction

Community

Reduced seedling emergence 

or vegetative vigor 

(Distribution)

Figure 10 Conceptual Model for Aldicarb Effects on Terrestrial Component of the CRLF Critical 

Habitat

2.10 Analysis Plan 

Analysis of risks to the California Red-Legged Frog (both direct and indirect) and to its 

critical habitat will be assessed according to the Overview Document (EPA, 2004) and 

Agency guidance for ecological risk assessments. 

2.10.1 Exposure Analysis 

Risks (direct effects) to the aquatic phase CRLF will be assessed by comparing modeled 

surface water exposure concentrations of aldicarb and its sulfoxide and sulfone 

degradates to acute and chronic (early life stage hatching success and growth) effect 

concentrations for aquatic phase amphibians (or surrogate freshwater fish) from 

laboratory studies (see the Effects Analysis section below). Risks (direct effects) to 

aquatic dietary food resources (aquatic invertebrates, algae) of the aquatic phase CRLF or 

risks (direct effects) to aquatic habitat that support the CRLF will also be assessed by 

comparing modeled surface water exposure concentrations of total aldicarb residues to 

laboratory established effect levels appropriate for the taxa. 

Long-range transport of aldicarb is highly unlikely, given the chemical characteristics, 

formulation, and application methods. A vapor pressure of 2.5 x 10-5 mm Hg and Henry’s 

Law Constant of 1.7x10-10 atm m3

/mole mean that aldicarb is not likely to volatilize and be 

49
transported offsite in the atmosphere. As a soil-incorporated granule, there is no spray 

drift, and a very limited amount of aldicarb is available at the surface. Whole granules 

dissolve readily, and will not move offsite intact (unless adhered to the integument of an 

organism, which should nevertheless limit the total amount transported). Some aldicarb 

residues may be transported as a component of field runoff, but dilution by receiving 

water bodies should limit the extent of long-range transport via surface water. While 

aldicarb residues may be subject to long-range transport through groundwater (which 

may be discharged to the surface some distance away from the application area), the 

greater the distance traveled, the more dilution is likely to occur and the greater 

opportunity for degradation. Thus, Agency believes that risk of long-range transport of 

aldicarb is minimal. 

Surface water concentrations of aldicarb residues will be quantified using a model, 

PRZM-EXAMS. For the screening assessment, the standard EXAMS water body of 2 

meters maximum depth, and 20,000 cubic meters volume, will be used. Since spray drift 

is expected to be minimal because aldicarb is applied as a granule to the ground, the 

model accounts for loading of aldicarb into the surface water via run-off and erosion. 

Agricultural scenarios appropriate for labeled aldicarb uses will be used to account for 

local soils, weather and growing practices which impact the magnitude and frequency of 

aldicarb loading to the surface water. Maximum labeled application rates, with 

maximum number of applications and shortest intervals, will be used to help define (1) 

the Action Area within California for the Federal Action and (2) for evaluating effects to 

the CRLF. 

Concentrations of aldicarb estimated by PRZM-EXAMS represent aldicarb loading in 

water bodies adjacent to any treated field and assume that the concentration applies to 

any water body within the treated area. Aldicarb residues are also estimated for waters 

downstream from the treated areas by assuming dilution with stream water (derived from 

land area) from unaffected sources, propagating downstream, until a point is reached 

beyond which there are no relevant LOC exceedances. Once the distribution of predicted 

stream water concentrations is obtained, it is further processed using a model that 

calculates expected dilution in the stream according to contributing land area. As the 

land area surrounding the field on which aldicarb is applied is enlarged, it encompasses a 

progressively greater drainage area; in effect, a progressively larger ‘sub-watershed’ is 

created, with a concomitant increase in dilution at the drainage point. This drainage point 

moves down-gradient along the stream channel as the sub-watershed is expanded. At a 

certain point the predicted stream concentrations will become sufficiently diluted; the 

region beyond this then falls outside the Action Area. 

Risks to the terrestrial phase CRLF will be assessed by comparing modeled exposure to 

effect concentrations from laboratory studies. Exposure in the terrestrial phase will be 

quantified using the TREX model, which automates the calculation of dietary exposure 

according to the Hoerger-Kenaga nomogram, as modified by Fletcher et al., 1994. The 

nomogram tabulates the 90th and 50th percentile exposure expected on various classes of 

food items, and scales the exposure (in dietary terms) to the size and daily food intake of 

50
several size classes of birds and mammals. Birds are also used as surrogates to represent 

reptiles and terrestrial-phase amphibians. 

2.10.2 Effects Analysis 

Aldicarb Toxicity (Including Major Toxic Degradates): 

As previously discussed in Section 2.8.1 and 2.8.2, assessment endpoints for the CRLF 

include direct toxic effects on survival, reproduction, and growth of the species itself, as 

well as indirect effects, such as reduction of the prey base and/or modification of its 

habitat. Direct effects to the CRLF are based on toxicity information for freshwater fish 

and birds, which are generally used as a surrogate for aquatic and terrestrial phase 

amphibians, respectively. The open literature will be screened also for available 

amphibian toxicity data. If no such data are available for aldicarb, then toxicity data for 

other N-Methyl carbamates will be screened to see if amphibian toxicity data are 

forthcoming that would allow making inferences with respect to aldicarb toxicity. 

Indirect effects to the CRLF are assessed by looking at available toxicity information of 

the frog’s prey items and habitat requirements (freshwater invertebrates, freshwater 

vertebrates, aquatic plants, terrestrial invertebrates, terrestrial vertebrates, and terrestrial 

plants). 

Aldicarb’s toxicity dataset is incomplete; chronic avian studies are lacking. Other NMethyl carbamates were therefore screened for available chronic bird data that could 

used to derive a carbamate avian acute to chronic ratio (ACR). Plant Tier I and Tier II 

guideline studies are not available for aldicarb, therefore the open literature was screened 

for similar toxicological data. 

Acute (short-term) and chronic (long-term) toxicity information for aldicarb and its 

degradates is characterized based on registrant-submitted studies and an updated review 

of the open literature. An extensive review of the open literature was done for the recent 

aldicarb screening level ecological risk assessment (May 2005). Based on an updated 

review of the open literature for October 2004 through December 2006, if new and more 

sensitive or otherwise relevant toxicological data were available, this information was 

included and used in this assessment to modify the Action Area and evaluate direct and 

indirect effects to the CRLF and its critical habitat. 

Where there are data gabs, estimates for these values may be extrapolated for the same 

taxa for other N-methyl carbamates, or extrapolated within taxa based on relationships 

within taxa for aldicarb or for N-methyl carbmates. To help refine the risk 

characterization, species sensitivity distributions may be established for prey (e.g., 

aquatic invertebrates) and for the CRLF (using surrogate species) if enough data are 

available. N-Methyl carbamate data was used to derive an ACR for use on birds 

(surrogate for terrestrial phase amphibians). Other sources of information, including use 

of the acute probit dose response relationship to establish the probability of an individual 

effect and reviews of the Ecological Incident Information System (EIIS), were conducted 

to further refine the characterization of potential ecological effects associated with 

51
exposure to granular aldicarb. A summary of the available freshwater and terrestrial 

ecotoxicity information, the community-level endpoints, species’ sensitivity distributions, 

use of the probit dose response relationship, and the incident information for aldicarb are 

provided in Sections 4.1 through 4.4. 

Toxicity studies for aldicarb degradates (where available) will be discussed for exposure 

to the aquatic phase of the CRLF and incorporated into this risk assessment. 

Product Formulations Containing Multiple Active Ingredients: 

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; USFWS/NMFS 

2004). 

Aldicarb does not have any registered products that contain multiple active ingredients. 

2.10.3 Action Area Analysis 

The Action Area for the federal action is the geographic extent of exceedance of Listed 

species Levels of Concern (LOC) for any taxon or effect (plant or animal, acute or 

chronic, direct or indirect) resulting from the maximum label-allowed use of aldicarb. To 

define the extent of the Action Area, the following exposure assessment tools will be 

used where appropriate: PRZM-EXAMS, TREX, AgDrift, and ArcGIS (a geographic 

information system (GIS) program). Other tools may be used as required if these are 

inadequate to define the maximum extent of the Action Area. 

The initial area of concern (or terrestrial action area) is assumed to be all agricultural 

land, orchards, and vineyards where granular aldicarb could potentially be applied and 

the area surrounding these areas where secondary poisoning effects are expected to be 

visible. Secondary poisoning to listed species could result if listed species consumes all 

or part of the poisoned prey. A model for secondary poisoning effects is in development 

by the Agency. However, from that model, which relies on allometric relationships that 

relate body weight to food consumption and body weight to home range, it was 

preliminarily determined that a CRLF prey item bird could travel approximately one mile 

from the field before dying from aldicarb poisoning. Thus, a one-mile buffer is applied 

around cultivated land to account for secondary poisoning effects to wildlife from 

aldicarb granular exposure. 

52
In order to determine the extent of the action area downstream from the initial area of 

concern, the Agency will need to complete the screening level risk assessment. Once all 

aquatic risk quotients (RQs) are calculated, the Agency determines which RQ to level of 

concern (LOC) ratio is greatest for all aquatic organisms (plant and animal). For 

example, if both fish and aquatic plants have the same RQ of 1, the fish RQ to LOC ratio 

(1/0.05) would be greater than for plants (1/1). Therefore, the Agency would identify all 

stream reaches downstream from the initial area of concern where the PCA for the land 

uses identified for aldicarb are greater than 1/20, or 5%. All streams identified as 

draining upstream catchments greater than 5% of the land class of concern, will be 

considered part of the action area. 

53
3 Exposure Assessment 

3.1 Label Application Rates and Intervals 

In California, aldicarb is registered for use on cotton, dry beans, peanuts, pecans, 

sorghum, soybean, sugar beet, sweet potato, alfalfa (for seed), citrus, and field-grown 

ornamentals (no containers). Application rates are listed in Table 10. Only cotton and 

sugar beet allow more than one application per season; up to 3 applications may be used 

for these crops. Application intervals are not specified on the labels. Instead, cotton 

applicators are instructed to apply “once at planting, at first squaring, and between first 

squaring and bloom.” Use directions for sugar beet simply list an application window 

from 3/1-9/1. The best estimate that could be construed from these explanations, plus 

additional research, indicates a likely average application interval of 30 days. 

3.2 Aquatic Exposure Assessment 

Aldicarb rapidly degrades in the aquatic environment to aldicarb sulfoxide and aldicarb 

sulfone, both of which are toxic to aquatic organisms. Therefore, exposure to all 3 of 

these forms of aldicarb (parent + sulfoxide + sulfone) must be considered. Direct 

application of aldicarb to streams, lakes, and ponds is forbidden by product labels. 

However, following a rain event, aldicarb may reach aquatic environments in runoff from 

areas of application, since aldicarb is moderately persistent in terrestrial environments 

and soluble in water. It is unlikely that whole, intact granules will reach the aquatic 

environment because of the highly soluble nature of the compound (granules will 

dissolve rather than be transported intact) and the application methods (direct application 

onto field, typically with soil incorporation). Groundwater discharged to the surface 

(mostly in low-lying areas) could result in additional exposure to aldicarb residues, 

independent of rainfall and runoff conditions.

3.2.1 Conceptual Model of Exposure 

The basic conceptual model for aldicarb exposure includes terrestrial on-site exposure to 

granules at (and just below) the surface, indirect exposure to fauna that have been 

exposed and may transport aldicarb (internally or externally) off-site, and aquatic 

exposure to aldicarb in surface water (as a component of runoff/erosion from a treated 

field). Exposure to dissolved granules in pooled surface water or damp soil within or 

adjacent to a treated field is also considered. However, potential exposure to aldicarb in 

discharged groundwater (e.g., as baseflow) is not explicitly considered. 

3.2.2 Existing Monitoring Data 

Aldicarb is one of the pesticides for which monitoring is routinely performed; however, 

no targeted monitoring regimes in California have been implemented. Only non-targeted 

monitoring data are available. These data are not specifically tied to periods of aldicarb 

use or even to areas where such use is allowed. Thus, it is not suitable for evaluating the 
impact of aldicarb use on affiliated waterways. At best, the non-targeted data can 

establish a lower bound for potential aldicarb surface water exposure. 

Nationally, the USGS NAWQA database (1992-2001) indicates that aldicarb has been 

detected in surface water approximately 0.2% of the time. The highest concentration 

detected was 0.5 ug/L (Martin et al., 2001). However, results of targeted monitoring in 

smaller streams suggest that aldicarb may occasionally pose a contamination hazard. For 

example, Williams and Harris (1996) found substantially higher aldicarb concentrations 

in small southeastern streams after a rainfall event (concentrations up to 430, 68, and 14 

μg/l for aldicarb, aldicarb sulfoxide, and aldicarb sulfone, respectively). Absent a 

sampling regime specifically targeted to aldicarb use in California, surface water 

modeling will be employed to estimate environmental concentrations. 

The detection rate for aldicarb residues in CA groundwater (~0.1%) appeared to be 

similar to surface water (~0.2%), but, where detected, concentrations in groundwater 

were often much higher. Based on well monitoring in California reported by CA-DPR, 

conducted from 1986-1999, groundwater concentrations of aldicarb sulfoxide ranged 

from 0.05-1281 ug/L and aldicarb sulfone from 0.06-13.2 ug/L 

(http://www.cdpr.ca.gov/docs/empm/pubs/ehapreps/eh0308.pdf). Evidence for 

persistence of aldicarb residues in California groundwater has been documented by the 

presence of aldicarb sulfoxide and aldicarb sulfone in well water samples from counties 

(Humboldt and Del Norte) where aldicarb use had been suspended 

(http://www.cdpr.ca.gov/docs/empm/pubs/ehapreps/eh9001.pdf). 

3.2.3 Modeling Approach 

Risk quotients (RQs) were initially based on EECs derived using the Pesticide Root Zone 

Model/Exposure Analysis Modeling System (PRZM-EXAMS) standard ecological pond 

scenario according to the methodology specified in the Overview Document (U.S. EPA, 

2004). Where LOCs for direct/indirect effects and/or adverse habitat modification are 

exceeded based on the modeled EEC using the static water body (i.e., “may affect”), 

refined modeling may be used to differentiate “may affect, but not likely to adversely 

affect” from “may affect and likely to adversely affect” determinations for the CRLF and 

its designated critical habitat. 

The general conceptual model of exposure for this assessment is that the highest 

exposures are expected to occur in the headwater streams adjacent to agricultural fields. 

Many of the streams and rivers within the action area defined for this assessment are in 

close proximity to agricultural use sites. 

3.2.3.1 Model Inputs 

Generic PRZM-EXAMS inputs are listed in Table 9. Specific inputs (application rates, 

application intervals, etc.) used for individual crop/noncrop model runs that were used in 

this assessment are listed in Table 10. 

55
Degradation of parent compound aldicarb to aldicarb sulfoxide, and, subsequently, 

aldicarb sulfoxide to aldicarb sulfone, each occur at different rates and to varying extents 

under different conditions. Since each compound is toxic, and each is formed from the 

previous, it is necessary to treat the half-lives for all additively. Thus, half-lives used for 

modeling the environmental fate of aldicarb account for degradation of parent through 

each degradate of concern, for a half-life reflecting total toxic residues. The range for 

field dissipation of total aldicarb residues considered in this document, derived from 

Jones and Estes, 1995, is 15-105 days. The aerobic soil half-life used for model inputs, 

however, is 55 days, derived from the upper 90th pct bound on mean for total aldicarb 

residue half-lives from 19 soils (see Appendix N). 

Table 9 Generic Aldicarb Inputs Used in PRZM-EXAMS Runs

Input Parameter Value Reference/Comment 

Molecular Weight 190.2 g/mol MRID 00152095 

Henry’s Law Constant 1.7 E-10 atm-m3

/mol Acc 255979 

Vapor Pressure 2.6 E-5 @ 25°C MRID 00152095 

Solubility 6,000 mg/L Acc 255979 

Kd 0.12 Minimum non-sand value for aldicarb 

sulfone (MRID 43560302) 

Hydrolysis 

pH 5, stable (0) 

pH 7, stable (0) 

pH 9, 60 days 

Parent hydrolyzed only at pH 9 (MRID 

00102065) – degradates may hydrolyze 

more rapidly at neutral-to-high pH 

Aqueous Photolysis Half-life 4 days MRID 42498201 

Water Half-life 12 days 

MRID 44592107. Single acceptable 

guideline study for parent / sulfoxide / 

sulfone (4days) x 3; corresponds w/ 

DT90 

Benthic Half-life 24 days No data; use 2X aerobic aquatic half-life

Soil Half-life 55 days 

Upper 90th pct bound on mean for 

combined parent+sulfoxide+sulfone 

half-life from 19 soils 

FILTRA, UPTKF, PLVKRT, PLDKRT 0 Default values 

FEXTRC 0.0 Soil incorporated 

Additional Notes Modeled total aldicarb residues 

Half-life input values based on 

combined aldicarb residues; lowest Kd

of the 3 chemicals used for mobility. 

Assumes equal toxicity of parent, 

degradates 

56
Table 10 Specific Inputs for Individual PRZM-EXAMS Runs

Crop/Noncrop 

Modeled 

Application Rate 

(lbs product/A) 

Number of 

Applications 

(per season) 

Comments 

Sugar beet 14 2 Used 2 applications at maximum one-time 

rate 

Pecan 33 1 Used “CAalmond” scenario 

Soybean 20 1 Used “CARowCrop” scenario 

Cotton 14 1 Used maximum one-time rate 

Cotton 7 3 Used 3 applications; however, first 2 

applications were set only 1 day apart to 

approximate a single application at the max 

one-time rate (14 lbs/A), followed by a third 

application after 30 days (at 7 lbs/A) for a 

max seasonal total of 21 lbs/A 

Citrus 33 1 

Sweet potato 30* 1 Used “CAPotato” scenario 

Dried bean 21* 1 Used “CARowCrop” scenario 

Alfalfa (seed) 20 1 

Sorghum 7 1 Used “CAWheat” scenario; 99% soil 

incorporation only 

Peanut 30* 1 Used “CARowCrop” scenario 

Ornamentals (field 

grown, no 

containers) 

50* 1 Used “CANursery” scenario; 99% soil 

incorporation only – positive displacement 

required 

* Only ‘10g’ (10%) formulation use allowed – all others utilize the ‘15g’ (15%) formulation. 

3.2.3.2 Results 

 

Model runs for the model input parameters listed in Tables 9 & 10 are shown in Table 11, 

below. 

Table 11 Results of Individual PRZM-EXAMS Runs With 85% Soil Incorporation 

COTTON-1 application: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

6.8352 6.5129 5.5533 3.5314 2.5216 0.62953 

Average of yearly averages: 0.139943

COTTON-3 applications: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

7.6324 7.1959 5.9147 3.45 2.3772 0.59044 

Average of yearly averages: 0.152104 

SOYBEAN: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

6.1421 5.8186 4.4673 2.5769 1.8282 0.45514 

Average of yearly averages: 0.181126 

PECAN: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

7.373 6.9331 5.3896 3.1468 2.2254 0.55532

Average of yearly averages: 0.226344 

57
SUGARBEET: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

11.377 10.8066 8.6342 5.425 3.9293 1.00713 

 Average of yearly averages: 0.279823 

Citrus: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.371 0.317 0.181 0.0823 0.0564 0.0141 

 Average of yearly averages: 0.004684 

Sweet Potato: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

1.385 1.3017 0.9959 0.5642 0.39333 0.097279 

Average of yearly averages: 0.0202545596666667 

Peanut: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

6.4341 6.119 5.044 3.3383 2.5214 0.66757 

 Average of yearly averages: 0.281116203333333 

Dried Bean: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

4.5047 4.2833 3.5313 2.3365 1.7652 0.46739

 Average of yearly averages: 0.196776023333333 

Alfalfa (for seed):

Peak 96 hr 21 Day 60 Day 90 Day Yearly

10.048 9.5516 8.4132 5.2773 3.7682 0.94253

 Average of yearly averages: 0.296203966666667 

3.2.4 Additional Modeling Exercises Used to Characterize Potential 

Exposures 

For purposes of comparison, and where specialized application techniques (e.g., positive 

displacement, in-furrow) are required, the following scenarios were modeled with 99% 

incorporation efficiency. Results are listed in Table 12. 

Table 12 Results of Individual PRZM-EXAMS Runs With 99% Soil Incorporation 

Sorghum: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.664 0.62995 0.52367 0.31246 0.22142 0.055175 

 Average of yearly averages: 0.0337101333333333 

Field-Grown Ornamentals (no containers): 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.90759 0.8685 0.72054 0.49119 0.37888 0.102639

 Average of yearly averages: 0.0277671827 

COTTON-1 application: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.455 0.4335 0.3697 0.2352 0.1679 0.04194 

Average of yearly averages: 0.0093270679

58
COTTON-3 applications: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.5108 0.4816 0.3959 0.2309 0.1593 0.03951 

Average of yearly averages: 0.0101877812 

SOYBEAN: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.4095 0.388 0.2978 0.1718 0.1219 0.03034

Average of yearly averages: 0.0120820702 

PECAN: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.4912 0.4622 0.3593 0.2099 0.1484 0.03704

Average of yearly averages: 0.015090452 

SUGARBEET: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.7577 0.7194 0.5749 0.3611 0.2616 0.06709 

 Average of yearly averages: 0.01864548122 

Citrus: 

Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.02469 0.02113 0.01204 0.00548 0.00376 0.000943

 Average of yearly averages: 0.00031204619

3.2.5 Comparison of Modeled EECs with Available Monitoring Data 

There are insufficient targeted monitoring data from California to allow a meaningful 

comparison with modeled EECs. However, it can be assumed that what little sampling 

data do exist under-represents real expected surface water aldicarb peaks (which are 

almost certainly much higher). Thus, the Agency is reliant on modeling data for this 

assessment. Based on the untargeted national data, it would appear that ,where detected, 

aldicarb residues in surface waters may be 1-2 orders of magnitude lower than indicated 

by the ‘peak’ or ‘acute’ modeled EECs, but possibly reflective of ‘background’ or 

‘chronic’ EEC surface water concentrations in aldicarb use areas. This appears to be 

roughly consistent with observed differences between background concentrations for 

other chemicals also detected in surface waters (as would be expected from non-targeted 

sampling) and peak concentrations detected during (targeted) sampled post-application 

runoff events. 

Detected concentrations of aldicarb residues in California well water were sometimes 

higher than would be predicted using the OPP-EFED tier 1 groundwater screening 

model, SciGrow. This model should give an estimate of likely high-end exposure due to 

registered usage. However, the highest predicted Environmental Exposure Concentration 

(EEC) obtained from the SciGrow model, using the greatest quantity applied (5 lb a.i./A 

– for Ornamental use) and a conservative KOC value of 4.9 (reflecting total residues), was 

37.3 ug/L. Thus, risk to groundwater may be greater than indicated from model results. 

Considering the greater persistence and mobility of the sulfoxide and sulfone degradates, 

59
and the historical evidence of widespread long-term groundwater contamination (both 

nationally and in certain counties in California), the impact of discharged tainted 

groundwater on receiving surface water bodies cannot be ignored. 

Surface Water Impacts: Available surface water monitoring data indicate that impacts to 

fish and aquatic invertebrates as a result of aldicarb (including the sulfone and sulfoxide 

products) are likely to be confined to smaller (lower-order) streams in high use areas. 

Widespread contamination of surface water is not expected in larger (higher-order) 

streams. In NAWQA monitoring sites, aldicarb and its sulfone and sulfoxide 

transformation products were detected infrequently at low concentrations. 

Ground Water Impacts: Aldicarb residues may be persistent in groundwater. Therefore, 

there is the potential for exposure to aldicarb residues (particularly aldicarb sulfoxide and 

aldicarb sulfone) in discharged groundwater. This is especially true for small streams, 

low-order riparian zones, and wetlands, which may be largely dependant on consistent 

groundwater discharge in addition to intermittent storm runoff to sustain ponding and 

flow conditions. These shallow water bodies are also important habitat for CRLFs. 

Groundwater can thus present a constant, low-level source of aldicarb residues in 

sensitive environments.

3.3 Terrestrial Plant Exposure Assessment 

Aldicarb is an insecticide/miticide, and thus, registrants have not been required to submit 

Tier I plant studies under the old Agency guidelines. This explains that the only available 

information on effects of aldicarb on plants comes either from crop growers (anecdotal) 

or from the open literature. There was one acceptable open literature plant study for the 

pearl millet which was used for RQ calculations in the terrestrial plant section of the risk 

estimation section. This one species (monocot) was used to represent terrestrial plants 

and terrestrial plants growing in semi-aquatic areas. How representative pearl millet is of 

all other terrestrial plant species remains unknown. 

TerrPlant (v.1.2.2) was used to assess risk to terrestrial plant and terrestrial plants 

growing in semi-aquatic areas. The model assumes complete incorporation of granules 

into the ground, which is an unrealistic assumption, especially for crops where 

applications occur after plants have emerged and root systems have already begun to 

establish. 85% incorporation for some crops (i.e. citrus) is still a generous assumption. 

Therefore, risk calculated for terrestrial plants may be underestimated. 

TerrPlant input parameters for the model included: (1) terrestrial plant toxicity values; (2) 

application rate; (3) runoff, based on chemical solubility; and (4) soil incorporation depth. 

The model provides estimates of exposure concentrations and risk quotients (RQs) for 

non-listed and listed terrestrial and semi-aquatic plants. A detailed explanation of the 

model as well as the modeling inputs and outputs for estimating terrestrial and semiaquatic plant exposure risks to aldicarb are summarized in Appendix B. Only one 

application is considered in this assessment due to model limitations. 

60
3.4 CRLF Terrestrial Phase Exposure Assessment 

Terrestrial exposures from granular applications (mg ai/square foot)10 for the California 

red-legged frog will be estimated using the Tier 1 model, T-REX Version 1.3.1 (T-REX, 

2007). In addition, a banded granular application assumes that 100% of the granules are 

unincorporated on the ground. Risk to terrestrial animals from ingesting granules will be 

based on LD50/ft2 values. The LD50/ft2 values are calculated using avian toxicity value 

(adjusted LD50 of the assessed animal and its weight c-lasses; the bird toxicity data is 

used as surrogate data for the CRLF) and the EEC (mg ai/ft2

) and are directly compared 

with Agency’s levels of concern (LOCs). Since aldicarb is used only for granular 

applications, exposures to animals from foraging on food items with aldicarb residues 

(short and tall grass, broadleaves, seeds) are not estimated because no spray drift is 

produced (granular application assumes 0% drift) that settles on the foliar surfaces of 

those food items. Details of the TREX model along with the input and output results are 

presented in Appendix A. 

Additionally, using the TREX model to estimate risk to the terrestrial phase of the CRLF 

may potentially be an overly conservative method of risk estimation. This is primarily 

because the CRLF is not expected to readily ingest as many granules as a foraging bird 

(as simulated by the TREX model) which may either: 1) mistakenly select an aldicarb 

granule to consume instead of grit that will aid in digestion or 2) incidentally consume 

aldicarb granules while ingesting other food items on the ground. The CRLF does not 

intentionally ingest grit. Thus, it is not expected to mistakenly ingest aldicarb granular 

for grit. However, the CRLF may incidentally ingest aldicarb granules that may be fixed 

to a prey item such as a mammal, bird, or frog. Because the amphibians typically have 

slower metabolisms than avian species, amphibians have lower feeding rates than birds. 

Thus, the CRLF red-legged frog is not expected to consume as many granules as a bird. 

Consequently, the TREX model may overestimate the risk of aldicarb exposure to the 

CRLF. However, the CRLF may potentially be exposed to aldicarb via other routes such 

as thru the skin or drinking water contaminated with aldicarb. Currently, there is no 

approved method available to EFED for capturing these routes of exposure. Thus, the 

TREX calculations will be assumed to capture these other routes of exposure to the 

CRLF. Thus, this assumption may address the potential over estimation calculations of 

the TREX model. 

Off-site Terrestrial Risk from Aldicarb Runoff: 

Risks to terrestrial environments outside the zone of application for granular aldicarb are 

mainly limited to re-deposition of aldicarb residues in lower-lying areas affected by 

aldicarb runoff from nearby fields. It is not expected that significant amounts of whole 

granules will be exported offsite, except those small amounts that may adher to the skin, 

fur, or feathers (integument) of organisms passing through a treated field. While aldicarb 

residues could potentially be transported as a component of runoff, and be re-deposited 

 

10 mg ai/ft2 = application rate x % active ingredient x 453,590 mg/lb x % incorporation 

 no. of rows/acre x row length x bandwidth 

61
into environments occupied by the CRLF the transported amount is limited. Calculations 

of the approximate amount of aldicarb potentially deposited as a result of registered 

aldicarb use (based on high application and low incorporation rate scenarios) indicate that 

concentrations in off-site soil would be several orders of magnitude below those that 

would trigger risk. Specifically, aldicarb concentrations in runoff water and loading to 

off-site soils (based upon the results of the TerrPlant model) were used to calculate the 

approximate amount of aldicarb residues that might be found in soil receiving runoff 

from a treated field under a high-use (4.95 lb ai/A) scenario. Assuming an affected soil 

depth of 1 inch (from surface), a soil bulk density of 1 g/cm3

 (average soil bulk density of 

1.2 g/cm3

 rounded to 1.0 for simplicity), and an initial terrestrial off-site concentrations of 

0.09 lb ai/A, it was determined that the quantity of aldicarb in soil in ‘receiving’ areas 

would be very low – on the order of 10-6 mg ai/kg soil. 

62
4. Effects Assessment 

Aldicarb ecological effects data and ecological effects data for its major toxic degradates, 

available from registrant and public literature as discussed in the Analysis Plan (Section 

2.10.2), and their use for calculating RQ values are summarized in this Section. Specific 

values selected from registrant submitted data and the public literature for the 

measurement endpoints, and the basis for their selection, are also discussed (Tables 13-

16). In addition extrapolation methods were used to fill the data gap for reproductive 

effects on aquatic vertebrates and birds, the extrapolation methods used are described. 

4.1 Taxa specific toxicological endpoints and LOCs 

Results of the Effects Assessment performed for the 2006 revised screening level 

ecological risk assessment, which are also appropriate for measurement endpoint values 

for the CRLF effects determination,, are listed in Table 13. The basis for the selection in 

the 2006 revised screening level ecological risk assessment are also identified in Table 

13. No new registrant data has been submitted since the revised aldicarb chapter has 

been finished. The updated review of public literature, which is discussed in Section 4.2, 

did not result in any more sensitive measurement endpoint values than those values 

already identified in 2006, and no aldicarb amphibian toxicity data was found. However, 

a seedling emergence and growth test for a terrestrial monocot plant, pearl millet, was 

found in open literature and the selected measurement endpoint included in Table 13. A 

review of this study is briefly summarized in Section 4.2.1. Additionally, based on avian 

acute and chronic toxicity ratios for other N-methyl carbamates, an avian chronic 

NOAEL for aldicarb was extrapolated. The extrapolation approach used is described in 

Section 4.3 and the estimated value provided in Table 13. The avian chronic NOAEL is 

used as a surrogate for estimating risk for the terrestrial-phase CRLF. Additionally, a 

NOAEL was estimated for freshwater invertebrates using ACR value for aldicarb 

(Section 4.6). 

Table 13 Aldicarb Acute and Chronic Ecotoxicological Values Listed in 2005 RED and Used for RQ 

Calculations in this Assessment

Assessment Endpoint and Species 

from Selected Study 

Measurement Endpoint 

Value 

Basis for selection MRID/Reference 

Bluegill sunfish (representing 

aquatic vertebrate prey and surrogate 

for aquatic phase CRLF) 

96-hr LC50 = 52 ppb ai Most sensitive 96-hr LC50

value 

MRID40098001, 

Meyer & 

Ellersieck, 1986 

Bluegill sunfish (representing 

aquatic vertebrate prey and surrogate 

for aquatic phase CRLF) 

Estimated chronic 

NOAEC = 0.46 ppb ai 

Extrapolated NOAEC: 96-h 

LC50 for bluegill sunfish (52 

ppb ai) divided by ACR(a)

(fathead minnow 48-h EC50 of 

8860 ppb ai divided by 

NOAEC of 78 ppb ai) 

Chironumus tentans (representing 

aquatic invertebrate prey of CRLF) 

48-hr EC50 = 20 ppb ai Most sensitive <96-hr LC50(b)

acute value 

Moore et. al., 1998

C. tentans (representing aquatic 

invertebrate prey of CRLF) 

Chronic NOAEC = 1 ppb ai Extrapolated using an ACR 

approach 
Assessment Endpoint and Species 

from Selected Study 

Measurement Endpoint 

Value 

Basis for selection MRID/Reference 

Marine diatom (surrogate for 

freshwater algae, both a dietary item 

for CRLF larva and a Habitat 

Component of CRLF)

96-hr EC50 > 5000 ppb ai Most sensitive algal <96-hr 

EC50 (where effect is measure 

of biomass and growth rate) 

MRID 40228401 

(US EPA, 1986) 

Mallard duck acute oral 

(surrogate for terrestrial phase of 

CRLF) 

LD50 = 1 mg ai/kg-bw Most sensitive avian acute oral 

value 

MRID 00107398 

Mallard duck reproduction 

(surrogate for terrestrial phase of 

CRLF)

NOAEC = 0.49 mg/kg-bw Extrapolated NOAEC: N/A 

Rat acute oral/ rat (representing 

mammalian prey of CRLF) 

LD50 = 0.9 mg ai/kg bw Most sensitive mammalian 

acute oral value 

MRID 00057333 

Rat reproduction (representing 

mammalian prey of CRLF) 

Chronic NOAEL = 0.4 

mg/kg bw(c), decreased 

parental body weight gain 

(2-generation reproduction 

study) 

Most sensitive mammalian 

reproduction NOAEC value 

MRID 42148401 

Mallard duck acute oral (Terrestrialphase CRLF)LD50 = 1 mg ai/kg-bw Most sensitive avian acute oral 

value 

MRID 00107398 

Mallard reproduction (Terrestrialphase CRLF)Estimated chronic 

NOAEL = 0.49 mg ai/kg bw

Acute oral LD50 for mallard 

duck (1mg ai/kg-bw) divided 

by ACR (N-methyl carbamate 

acute geometric mean of 

1223.2 ppm ai divided by Nmethyl carbamate chronic 

geometric mean of 137.3 ppm 

ai) 

Honey bee (representing terrestrial 

invertebrate prey of CRLF) 

Acute contact LD50 = 0.285 

ug/bee 

Most sensitive acute contact 

beneficial insect value 

MRID00036935 

Pearl millet (representing terrestrial 

plant habitat PCE component)

Seedling emergence and 

growth 21-d NOAEC 2.05 

lbs ai/A 

Only existing seedling 

emergence data for plants 

Kennedy 2002; see 

Section 4.2.1 

(a) ACR = acute to chronic ratio 

(b) For cladocerans, standards for an immobilization effect (EC50), that is considered a surrogate for mortality, are used 

in place of a lethality endpoint (LC50). 

(c) Toxicity value is similar to acute oral LD50 in rats and suggests that mammals that survive acute aldicarb exposure 

may suffer adverse reproductive effects from chronic exposure. 

Table 14 shows the acute ecotoxicological values, based upon the toxic degradate of 

concern aldicarb sulfoxide, that were used for calculating RQs. Table 15 gives the acute 

and chronic LOCs that were used in this assessment. 

Table 14 Aldicarb Sulfoxide Acute Ecotoxicological Values Used for RQ calculations in this 

Assessment

Species Endpoint MRID/Reference 

Aldicarb Sulfoxide 

Rainbow trout 96-hr LC50 = 7,140 ppb ai MRID 45592115 

Daphnid (adults) 48-hr EC50 = 43 ppb ai Foran et al., 1985 

64
Table 15 Specific LOCs Used in this Assessment

Taxa Acute LOC Chronic LOC 

Avian1 (terrestrial phase amphibians) 0.1 1 

Mammalian2 0.1 1 

Terrestrial plants3 1 

Aquatic Animals4 0.05 1 

Terrestrial Insects5 0.05* 

*The Agency has not established LOCs for terrestrial insects. This assessment will use the ratio of 0.05 as a cut-off 

value for making effects determinations. 

Toxicity values used in RQ calculations: 

1

 LD50 and estimated NOAEL, respectively 2

 LD50 and NOAEL, respectively 3

 EC50 for non-listed and NOAEC for endangered 4

 LC/EC50 and estimated and reproductive NOAEC, respectively (the acute designation is not applicable for plants) 5

 LD50

4.2 Evaluation of Ecotoxicity Studies 

Open literature data considered in this assessment include those obtained prior to October 

2004 for the 2006 revised screening level ecological risk assessment (U.S. EPA, 2006) as 

well as updated information obtained since the last ECOTOX run (Oct 2004 through Dec 

2006). ECOTOX data of the 2006 revised SLERA and not considered for RQ 

calculations in the CRLF assessment are included in appendices G through I of this 

assessment. 

In order to be included in ECOTOX, papers must meet the following initial, minimum 

criteria: 

(1) the toxic effects are related to single chemical exposure; 

(2) the toxic effects are on an aquatic or terrestrial plant or animal species; 

(3) there is a biological effect on live, whole organisms; 

(4) a concurrent environmental chemical concentration/dose or application 

rate is reported; and 

(5) there is an explicit duration of exposure 

Data that pass the ECOTOX screen are further evaluated for scientific soundness 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 than the registrant-submitted data are considered if they meet 

Agency guidelines for scientific soundness and use for quantitative purposes. The degree 

to which open literature data are quantitatively or qualitatively characterized is dependent 

on whether the information is relevant to the assessment endpoints (i.e., maintenance of 

CRLF survival, reproduction, and growth) identified in Section 2.8.1. For example, 

endpoints such as behavior modifications are likely to be qualitatively evaluated, because 

quantitative relationships between modifications and reduction in species’ survival, 

reproduction, and/or growth are not available. 

65
Results of ECOTOX updated search for aldicarb 

A brief summary and table of open literature data deemed acceptable for use in RQ 

calculations is presented below. All additional ECOTOX information (acceptable, not 

acceptable, and excluded studies) is provided in Appendices E through F and not 

included in this chapter. No additional studies found in the updated ECOTOX search had 

lower endpoint values than values presented in the 2006 revised screening level 

ecological risk assessment or were deemed otherwise relevant for the purpose of this 

assessment. Thus, studies listed in Appendix D (accepted papers) are a compilation of 

accepted and potentially rejected papers because no further analysis went into sorting out 

papers that had higher endpoint values than what was already available. 

Table 16 Ecotox Study for Formulated Aldicarb Used for RQ Calculations in this Assessment (Oct 

2004 - Dec 2006)

Species Endpoint MRID/Reference Number 

Pearl millet 21-d NOAEC = 2.05 lbs ai/A, 

decreased seedling emergence 

Kennedy, 2002 

4.2.1 Toxicity to Terrestrial Plants 

Kennedy (2002) exposed seeds of the pearl millet cereal [Pennisetum glaucum (L.)] to 

15% Temik® at 2.05 lbs ai/A, 3.08 lbs ai/A, and 4.1 lbs ai/A in a randomized complete 

block experiment with three replications (repeated twice under greenhouse conditions) to 

determine effects of in-furrow insecticides on seedling emergence and growth of this 

feedgrain crop. The seeds were watered once 7 days after sowing; emergence was 

determined at day 10; growth of seedlings was determined at day 21. In the first 

treatment (2.05 lbs ai/A), as compared to the control, no effects on seedling emergence 

were observed. Reductions in seedling emergence were observed at 3.08 lbs ai/A (actual 

% reduction not reported), and 4.1 lbs ai/A (57% reduction in emergence). The study did 

not identify what the minimum significant difference detected was for seedling 

emergence. Furthermore, Kennedy reports that pearl millet seeds surviving past the 

seedling emergence stage did not have their dry weight significantly reduced by aldicarb. 

This information seems to be in line with reports from agricultural growers who state that 

use of aldicarb has increased their crop yield (biomass), likely from reduced pest 

pressure. 

Labeled application rate data for at plant provides ancillary information regarding levels 

considered by the registrant as not reducing yield. Application rates at planting are 1.0 lb 

ai/A for sorghum; 2.1 lbs ai/A for dried bean, cotton, and sugar beet; and 3.0 lbs ai/A for 

soybeans, peanuts, and sweet potato. Additionally there are established crops that are 

exposed at levels of upto 5 lbs ai/A such as citrus and containerlesss field-grown 

ornamentals. 

The NOAEL for seedling emergence (2.05 lbs ai/A) was selected for screening effects to 

terrestrial plants. 

66
4.3 Acute-to-Chronic Ratio Derivation for the CRLF 

The following section presents the methodology used in deriving an avian ACR for Nmethyl carbamates, the group to which aldicarb belongs. The resulting avian 

reproduction NOAEL was used as a surrogate for the terrestrial-phase amphibian (U.S. 

EPA 2006). There was data for three N-methyl carbmates evaluated for this 

extrapolation. These N-methyl carbamates (methomyl, methiocarb, and thiodicarb) were 

chosen because they are the only chemicals for which acute dose-based as well as chronic 

toxicological data are readily available and have been reviewed previously for scientific 

soundness. Where there were multiple studies for a given species (e.g., mallard duck 

and/or bobwhite quail) and endpoint (e.g., acute and chronic toxicity) the average was 

calculated for each chemical. 

All three N-methyl carbamates share with aldicarb the active N-methyl carbamate moiety 

(carbamate cation is double bonded to an oxygen with a hydrogen (H) at the R1 position 

on the nitrogen (N), a methyl group (CH3) at the R2 position on the N and an oxygen at 

the R3 position on the carbon) (Figure 11); thiodicarb is a dimmer of methomyl and 

transforms to the carbamate. Thiodicarb is known to more readily metabolize to the 

carbamate in insects than mammals. The R3 group attached to the oxygen differs and 

may be an akyl group, aryl group, oxime derivative or some other more complex group. 

The N-methyl carbamates share the ability to inhibit cholinesterase through a specific 

pathway and therefore share similar symptomology during acute and chronic exposure. 

Other 'carbamate' pesticides do not share the same common mechanism. Carbamates 

whose R1 and R2 groups are larger than hydrogen and a methyl group tend to posses a 

much reduced, if at all, anticholinesterase activity. Structural differences at the R3 group 

between N-methyl carbamates result in differences of affinity for cholinesterases, 

differences in toxicokinetics and toxicodynamics and therefore differences in potency. 

Aldicarb Methiocarb Methomyl Thiodicarb

N-methyl carbamate

Structural backbone

Figure 11 Comparison of structures of N-methyl carbamates 

67
Dietary ACR Calculations (Acute LC50/Chronic NOAEC): 

Methomyl (Mallard duck): 19.6 mg/kg-bw : 50 mg/kg-bw = 0.39* 

Methomyl (Bobwhite quail): 24.2 mg/kg-bw : 78.5 mg/kg-bw = 0.31* 

Methiocarb: 16.4 mg/kg-bw : 50 mg/kg-bw = 0.33* 

Thiodicarb: 2023 mg/kg-bw : 1000 mg/kg-bw = 2.02 

Three of the preceeding ACRs are not valid, the chronic endpoint value is higher than the 

acute mortality endpoint value: 0.39 (Methomyl); 0.31 (Methomyl); (0.33). Methiocarb. 

The fact that chronic endpoint values were higher than acute mortality endpoint values is 

most likely due to the fact that the studies were conducted by different laboratories. 

Therefore, the thiodicarb ACR (2.02) was used to derive a mallard duck (the most acutely 

sensitive bird) chronic NOAEL for aldicarb as follows: 

The (aldicarb) mallard duck LC50 used in this assessment is 1 mg/kg-bw, and the 

thiodicarb acute-to-chronic ratio of 2.02 is used to calculate the final estimated NOAEL 

for aldicarb. 

bwkgmg bwkgmg

ACR

LCanimalTest Estimated NOAEL = − − = = /49.0

02.2

50 /1

The estimated avian (terrestrial phase amphibian) NOAEL is practically identical to the 

measured chronic mammalian NOAEL for rats (0.4 mg/kg); acute terrestrial phase 

amphibian LD50 is practically identical to the acute LD50 (0.9 mg/kg) for rats. This lends 

additional support in using the estimated NOAEL to make qualitative risk 

characterizations for chronic effects of aldicarb to the CRLF. The fact that acute and 

estimated chronic endpoint value are very close together with estimated chronic endpoint 

slightly lower suggests that if a bird (or amphibian) survives acute exposure to aldicarb, 

chronic reproductive effects can be expected. 

68
Table 17 Avian N-Methyl Carbamate Data

Chemical Species 

& Acute 

Endpoint 

14-d LD50

(mg/kgbw) 

Avg 

Value 

(ppm) 

MRIDs/ 

Labs 

NOAEL

(ppm) 

Avg 

Value 

(ppm) 

MRIDs/ 

Labs 

Species/ 

Chemical 

Specific 

ACR 

Methiocarb Bobwhite, 

14-d LD50

19.6 19.6 40560018 

REF (1983)

50* 50 00128119 

MCC 

(1982) 

0.39 – not 

valid 

Mallard, 

14-d LD50

15.9 00160000 

FWS (1984)

Mallard, 

14-d LD50

16.8 

16.4 

ACC233993 

DUP (1970)

50* 50 41898601 

WLI 

(1991) 

0.33 – not 

valid 

137 41898602 

WLI 

(1991) 

Methomyl 

Bobwhite, 

14-d LD50

24.2 24.2 00161886 

WLI (1983)

20* 

78.5 

N.R. 

0.31 – not 

valid 

Thiodicarb Bobwhite, 

14-d LD50

2023 2023 92185002 

WLI (1978)

1000 1000 43313003 

BLA 1994 

2.02 

N.R. = not reported 

* acute measurement endpoint is lower than chronic measurement endpoint 

4.4 N-Methyl Carbamate Toxicological Data for Frogs 

No toxicological data on frogs is available for aldicarb; and there is very limited 

amphibian toxicity data for other N-methyl carbamates in the public literature (Table 18). 

For other wildlife (e.g., avians, mammals, fish, invertebrates) aldicarb is typically among 

the most toxic of the N-methyl carbamates, along with carbofuran. Thus, the 

ecotoxicological frog data presented in Table 18 likely under represents aldicarb’s acute 

oral toxicity and the 96-hr lethal concentration to this taxa. While the data is limited a 

comparison of these amphibian N-methyl carbmate toxicity values to those of the 

surrogate taxa support the assumption that the selected surrogates are at least as sensitive 

if not more sensitive than amphibians for N-methyl carbamates. For example, the 

Mallard Duck acute oral LD50 value of 7.4 mg ai/kg-bw for propoxur (ACC 94546) is 80 

times more toxic than the propoxur acute oral LD50 of 595 mg ai/kg-bw for the Bullfrog 

(Table 18), and the Bluegill Sunfish 96-hr LC50 of 210 ppb (MRID 400980-01) for 

methiocarb is 41 times more toxic than the Leopard frog methiocarb 96-hr LC50 of 8700 

ppb (Table 18). 

Table 18 N-Methyl Carbamate Toxicological Data for Amphibians 

Chemical Species Endpoint Reference 

Propoxur Bullfrog (adult) 14-d LD50 = 595 mg ai/kg bw Hudson et al., 1984 

Methiocarb Leopard frog 

(larva) 

96-hr LC50 = 8.7 ppm Armitage, 1984 

69
4.5 Aquatic Freshwater Plants 

Aquatic freshwater plant data is not available for aldicarb and is a data gap; thus, the 

Agency will use the marine diatom study to characterize potential risk to all aquatic 

plants in this risk assessment (riparian plants were assessed using the results on pearl 

millet (Kennedy 2002). 

4.6 Acute-to-Chronic Ration Derivation for Freshwater Invertebrates 

The most acutely sensitive freshwater invertebrate species was Chironomus tentans (20 

ppb ai) (Moore et al. 1998). However, there was no reproduction and emergence study 

found in the literature for this species. Since for aldicarb there was both an acute 48-hr 

EC50 for Daphnia magna immobilization and a 21-d reproduction NOAEC, this 

information was used to calculate an ACR of 20. The estimated NOAEC for C. tentans is 

1 ppb ai (estimated NOAEC = 48-hr EC50/ACR = 20/20 = 1 ppb). 

4.7 Probit Analysis 

The Agency uses the probit dose response relationship as a tool for providing additional 

information on the listed animal species acute levels of concern (LOC) and on calculated 

RQ values, when the acute LOC is not exceeded. The listed LOC evaluated is 0.05 for 

aquatic animals. Interpretation is presented in terms of the chance of an individual event 

(i.e., mortality or immobilization) should exposure at the EEC actually occur resulting in 

an RQ equivalent to the LOC or higher. The probit analysis is performed specifically by 

using either the slope of the dose response relationship available from the toxicity study 

used to establish the acute toxicity measurement endpoints for each taxonomic group, or 

if this information is not available the default slope. In addition to a single effects 

probability estimate based on the mean slope for a taxa, upper and lower estimates of the 

effects probability are also provided to account for variance in the slope. The upper and 

lower bounds of the effects probability are based on available information on the 95% 

confidence interval of the slope. A statement regarding the confidence in the 

applicability of the assumed probit dose response relationship for predicting individual 

event probabilities is also included. Studies with good probit fit characteristics (i.e., 

statistically appropriate for the data set) are associated with a high degree of confidence. 

Conversely, a low degree of confidence is associated with data from studies that do not 

statistically support a probit dose response relationship. In addition, confidence in the 

data set might be reduced by high variance in the slope (i.e., large 95% confidence 

intervals), despite good probit fit characteristics. 

Individual effect probabilities are calculated using an Excel spreadsheet tool IECV1.1 

(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP, 

Environmental Fate and Effects Division (June 22, 2004). The tool performs calculations 

based on user inputs of the mean slope estimate (and the 95% confidence bounds of that 

estimate) as the slope parameters. The summary of probabilities of an individual to 

demonstrate an effect using probit slope relationships can be found in the Risk Estimation 

section of the Risk Characterization for the acute listed LOC and RQ. 

70
4.8 Review of Ecological Incident Information System (EIIS) 

Twenty-nine ecological incidents, dating from 1988 to 2005, related to aldicarb poisoning 

have been reported and summarized in the 2006 revised screening level ecological risk 

assessment. Only the two new incidents reported in the database since 2005 are listed 

here. These two new incidents, summarized below, came about due to illegal use of 

alidcarb. 

On January 3, 2006 a man in Floyd County (GA) found his dog severely sick (I017085-

001). The following day, his other dog was found dead near his home. The next day, a 

ranger of the Georgia Department of Natural Resources (GA DNR) found two opossum 

carcasses in the same area where his dog had died. Necropsies were performed on the 

two opossums; the gastrointestinal contents of one of them contained 96 ppm of aldicarb 

and the other contained 185 ppm aldicarb. Further study of the area led to the discovery 

of a dead white-tailed deer that had been dumped on the property. The ranger 

investigating the deaths feels that the deer, too badly decomposed to analyze for pesticide 

residues, was the source of the aldicarb in the animals that were killed. He said that 

Temik was not sold locally, and that the main crop grown in the area was corn, for which 

Temik is not registered. He suspects that the deer carcass was baited with aldicarb and 

placed to kill coyotes. 

On March 27, 2006, one dog and two black vultures were found near a partiallyconsumed carcass of a cottontail rabbit (I017462-001). The incident occurred on 

municipal property that was used by the town of Hoinsville, Georgia, for disposal of 

wastewater from a sewage treatment plant. Analysis of the vulture and rabbit found that 

brain cholinesterase levels were significantly depressed in both animals, indicating that 

both had ingested an anticholinesterase chemical. Toxicological analysis found 43 ppm 

aldicarb in the stomach of the rabbit and "greater than 0.1 ppm" of aldicarb sulfoxide in 

the liver of the vulture. The testimony of a local GA DNR employee as well as a GIS 

analysis done by EFED indicated that very little or no land in the vicinity was planted in 

crops on which aldicarb is registered for use. Thus, while there is little doubt that the 

animals were poisoned by alidcarb, the most likely scenario is that the animals were 

poisoned by illegal baiting or some other illegal use of aldicarb. 

4.9 Sensitivity Distribution 

4.9.1 Freshwater Fish 

Of all the freshwater fish data reviewed by the Agency (registrant submitted studies as 

well as open literature studies) in the 2006 revised screening level ecological risk 

assessment, only three studies were classified as ‘acceptable’ or ‘supplemental’ according 

to guidelines. Not enough data were available to develop a sensitivity distribution of 

freshwater fish 96-h LC50 values. 

71
4.9.2 Freshwater Invertebrate 

An acute freshwater species sensitivity distribution was constructed using acute toxicity 

values for freshwater invertebrates from registrant and open literature studies. The kinds 

of data desired for an acute species sensitivity distribution generally consist of 96-h LC50

values for invertebrates except for cladocerans. The desired measurement endpoint for 

daphnids and other cladocerans is the 48-h EC50 based on percentage of organisms 

immobilized plus percentage of organisms killed. These kinds of data are consistent with 

FIFRA guideline studies and acute toxicity data measurement endpoints for water quality 

criteria (Stephens et al., 1985). Freshwater acute toxicity data for aldicarb identified as 

scientifically sound and useable quantitatively from the RED and this effects 

determination are listed in Table 19. Aldicarb acute invertebrate data excluded from the 

analysis include those tests where controls were insufficient or not reported (Margin et 

al., 1988; Pantani et al., 1997), tests with single-celled organisms, these are not 

considered acute tests (Edmiston et al., 1984); and tests with saline environmental 

conditions (Song and Brown, 1998). A 24-hr EC50 value for Daphnia magna was 

included along with the 48-hr values because it was lower than some 48-hr values. The 

only scientifically sound Chironomus riparius and Chironomus tetans acute toxicity data 

was for 24 hour and 48 hour exposures, respectively, rather than 96 hours. The 96-h 

acute values for these Chironomous spp. are expected to be lower and may therefore 

result in an underestimation of the concentration where the lower tail lies (e.g., 

underestimation of the concentration at and below which 0.05 of a fraction of the taxa 

lie). 

Where there were multiple results for a single species, a species mean acute value 

(SMAV) was calculated by taking the geometric mean of the data for that species. Where 

there were multiple results for a genus, a genus mean acute value (GMAV) was 

calculated by taking the geometric mean of the SMAV. The method of calculating 

SMAV and GMAV for constructing the sensitivity distribution is consistent with Office 

of Water quality criteria development (Stephan et al., 1985). The use of GMAVs is used 

to prevent data sets from being biased by overabundance of species in one or a few 

genera, given that on the average, species within a genus are generally much more 

toxicologically similar than species in different genera (Stephen et al., 1985). The 

GMAVs are assumed to be log normally distributed. The mean (3.1261) and standard 

deviation (1.4411) of the log transformed GMAVs were used to calculate the sensitivity 

distribution (Figure 12). The 5, 25, 50 and 75 percent of the freshwater invertebrate taxa 

fall at and below 6, 143, 1337, and 12557 ppb aldicarb, respectively. The 95% lower 

confidence limit for the 0.05 fraction is (mean-standard deviation * t0.05,5; 3.1261 –

1.4411*2.015=2 ppb). 

72
Table 19 Freshwater Acute Invertebrate Toxicity Data and Species and Genus Mean Acute Values 

Species Genus 

96-hr 

LC50

(a)

(ppb) 

Log 

96-hr 

LC50

Species

Mean(b)

Acute 

(ppm) 

Genus

Mean(b)

Acute 

(ppm) Reference 

Pila globosa Pila 175000 5.243 175000 175000 Singh and Agarwal, 1981 

Lymnaea acuminate Lymnaea 11500 4.061 11500 11500 Singh and Agarwal, 1981 

Hyalella azteca Hyalella 3990 3.601 3990 3990 Moore et al., 1998 

Aedes aegypti, 27oC Aedes 290 2.462 280 280 Song et al., 1997 

Aedes aegypti, 20oC 270 2.431 Song et al., 1997 

Daphnia magna, 20oC Daphnia 583 2.766 253 121 Moore et al., 1998 

Daphnia magna 411 2.614 Acc. No. 098663 

Daphnia magna(c) 228 2.358 Sturm and Hansen, 1999 

Daphnia magna, 27oC 75 1.875 Song et al., 1997 

Daphnia Laevis juvenile 65 1.813 58 Foran et al., 1985 

Daphnia Laevis adult 51 1.708 Foran et al., 1985 

Chironomus riparius(d), pH 4 Chironomus 17 1.230 22 21 Suorsa and Fisher, 1986 

Chironomus riparius(d), pH 6 21 1.322 Suorsa and Fisher, 1986 

Chironomus riparius(d), pH 8 28 1.447 Suorsa and Fisher, 1986 

Chironomus tetans(e) 20 1.301 20 Moore et al., 1998 

(a) Tests with daphnids and other cladocerans are 48-hr EC50 based on percentage of organisms immobilized plus percentage of 

organisms killed (Stephan et al., 1985) 

(b) Geometric mean 

(c) Result is a 24-hr value which may underestimate the desired 48-h EC50 measurement endpoint 

(d) Test conducted using 4th instar rather than 2nd or 3rd instar which are considered a more sensitive midge life stage (Stephan et al., 

1985) and result is a 24-hr value which may underestimate the desired 96-h LC50 measurement endpoint 

(e) Result is a 48-hr value which may underestimate the desired 96-h LC50 measurement endpoint 

73
Figure 12 Cumulative Acute Sensitivity Distribution of Freshwater Invertebrates to Aldicarb

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1 10 100 1000 10000 100000 1000000

Aldicarb Concentration (ppb)

Probability

0.95 1.645 5.4968 313,874

0.90 1.282 4.9736 94,110

0.80 0.842 4.3396 21,855

0.75 0.675 4.0989 12,557

0.70 0.524 3.8813 7,608

0.60 0.253 3.4907 3,096

0.50 0 3.1261 1,337

0.40 -0.253 2.7615 577

0.30 -0.524 2.3710 235

0.25 -0.675 2.1541 143

0.20 -0.842 1.9127 82

0.10 -1.282 1.2787 19

0.05 -1.645 0.7555 6

LC50

Log Probability Zp LC50

0.95 1.645 5.4968 313,874

0.90 1.282 4.9736 94,110

0.80 0.842 4.3396 21,855

0.75 0.675 4.0989 12,557

0.70 0.524 3.8813 7,608

0.60 0.253 3.4907 3,096

0.50 0 3.1261 1,337

0.40 -0.253 2.7615 577

0.30 -0.524 2.3710 235

0.25 -0.675 2.1541 143

0.20 -0.842 1.9127 82

0.10 -1.282 1.2787 19

0.05 -1.645 0.7555 6

LC50

Log Probability Zp LC50

Log LC50 = 3.1261 - 1.4411(zp) where zp is the standard normal deviate

Pila (snail) (LC50 = 175,000)

Lymnaea (snail) (LC50 = 11,500)

Hyalella (amphipod) (LC50 = 3,990)

Aedes (mosquito) (LC50 = 280)

Daphnia (cladoceran) (LC50 = 121)

Chironomus (midge) (LC50 = 21)

74
5 Risk Characterization 

Risk characterization is the integration of the exposure and effects characterizations to 

determine the potential ecological risk from varying aldicarb use scenarios within the 

action area and likelihood of direct and indirect effects on the CRLF. The risk 

characterization provides an estimation and a description of the likelihood of adverse 

effects; articulates risk assessment assumptions, limitations, and uncertainties; and 

synthesizes an overall conclusion regarding the effects determination (i.e., “no effect,” 

“likely to adversely affect,” or “may affect, but not likely to adversely affect”) for the 

CRLF. 

5.1 Risk Estimation 

Risk was estimated by calculating the ratio of estimated environmental concentrations 

(EECs; see Table 11) and the appropriate toxicity endpoint. This ratio is the risk quotient 

(RQ), which is then compared to pre-established acute and chronic levels of concern 

(LOCs) for each category evaluated (Tables 15). 

Aquatic screening level RQs are based on the most sensitive endpoints for each 

assessment endpoint (Tables 7, 8 and 13) and modeled surface water concentrations from 

the following scenarios of aldicarb: 

• Citrus (1 application @ 33 lbs of product/A) 

• Cotton (1 application @ 21 lbs of product/A) 

• Cotton (3 applications @ 7 lbs of product/A each with a 30 day interval between 

applications) 

• Soybean (1 application @ 20 lbs of product/A) 

• Pecan (1 application @ 33 lbs of product/A) 

• Sugar beet (2 applications @ 14 lbs of product/A with a 30 day interval between 

applications) 

• Sweet potato (1 application @ 30 lbs of product/A – Temik 10g only) 

• Dried bean (1 application @ 21 lbs of product/A– Temik 10g only) 

• Alfalfa (1 application @ 20 lbs of product/A) 

• Sorghum (1 application @ 7 lbs of product/A) 

• Peanut (1 application @ 30 lbs of product/A– Temik 10g only) 

• Ornamentals (1 application @ 50 lbs of product/A– Temik 10g only) 

Terrestrial screening level RQs for the terrestrial phase of the CRLF and small 

mammalian prey are based on the most sensitive endpoints and EECs/sq ft for the 

following scenarios11 as modeled by T-REX (ver.1.3.1): 

• Citrus (1 application @ 33 lbs of product/A, 85% incorporation efficiency) 

 

11 Alfalfa was not modeled in the terrestrial risk assessment because its application rate, application 

method, and RQs are representative of RQs derived for the peanut and soybean scenarios. 

75
• Cotton (3 applications @ 7 lbs of product/A, 30 day interval between 

applications, 85% incorporation efficiency) 

• Dry beans (1 application @ 7 lbs of product/A, 99% incorporation efficiency) 

• Peanuts (1 application @ 20 lbs of product/A, 99% incorporation efficiency) 

• Sorghum (1 application @ 7 lbs of product/A, 99% incorporation efficiency) 

• Soybean (1 application @ 20 lbs of product/A, 99% incorporation efficiency) 

• Sugar beet (2 applications @ 14 lbs of product/A, 30 day interval between 

applications, 85% incorporation efficiency) 

• Sweet potato (1 application @ 14 lbs of product/A, 99% incorporation efficiency) 

Application of aldicarb to pecans could not be adequately modeled using T-REX because 

the model assumes that aldicarb is applied by shanking in below the dripline of the tree. 

Based on information provided by OPP BEAD, (pecan trees are grown up to 60 feet; 30 

feet spacing within row; canopies touching; little space between canopies of adjacent 

rows), the Agency calculated LD50/sq ft for pecans based on ‘shanking-in’ application, 

band with of 6.25”, and 72” row spacing (space between adjacent canopies). 

 

Terrestrial screening level RQs for terrestrial invertebrates and terrestrial phase of the 

CRLF (due to secondary poisoning) are based on the highest estimated aldicarb 

concentrations in soil from all use scenarios (see T-REX) as estimated by the most 

sensitive endpoints and the Earthworm Fugacity model. Terrestrial plant RQs are based 

on the most sensitive endpoint and EECs as modeled by TerrPlant (ver.1.2.2). EECs will 

be calculated for all labeled uses permitted in California. 

In cases where the screening level RQ exceeds one or more LOC, additional factors, 

including CRLF life history characteristics, probit dose-response analysis (IEC V1.1), 

and species sensitivity distribution are considered and used to characterize the potential 

for aldicarb to affect the CRLF. Risk estimations of direct and indirect effects of aldicarb 

to the CRLF are provided in section 5.1.1 and 5.1.2, respectively. 

5.1.1 Direct Effects 

Risk to the aquatic stage of the CRLF is driven by the sugar beet scenario and generated 

acute and chronic RQs of 0.22 and 11.79, respectively (LOC ≥0.05 and ≥1). Due to lack 

of a dose response slope value, individual probabilities of mortality were bracketed by 

evaluating a slope of 2 (high probability of individual mortality) and a value of 9 (low 

probability of individual mortality). The aquatic acute listed LOC (0.05) at default slope 

95% bounds of 2 and 9 correspond to a probability of individual mortality of 1 individual 

in 216 and 1 individual in 1.8E+31, respectively. One of the reasons it is difficult to get a 

slope is because of the almost all or none response observed in most studies. Therefore, 

the slope actually is expected to tend more towards 2 than 9. Probabilities for the 

calculated RQ values above the acute listed LOC (0.05) but below the acute LOC (0.5) 

for all assessments at the default average slope of 4.5 and the 95% lower bound slope of 2 

are provided in Table 

76
Risk to the terrestrial phase of the CRLF is driven by aldicarb use on citrus, followed by 

cotton, with an acute LD50/sq ft (RQ) of 2978 and 468 for small and large red legged 

frogs, respectively (LOC ≥0.1). For the pecan scenario, it was assumed based on mature 

orchard information from BEAD, that adult tree canopies within the same row touch, and 

therefore shanking of aldicarb granules into the soil in one continuous row as modeled by 

T-Red’s LD50/sq ft method became a reasonable assumption. It was further assumed that 

trees between rows leave a 72” gap between canopies of adjacent rows of trees, and that 

this distance was the row spacing between rows. Chronic RQs could not be calculated by 

the LD50/sq foot method of the T-REX model, but the estimated NOAEL of 0.11mg ai/kg 

bw will be qualitatively discussed in the risk description section. Direct toxicity to the red 

legged frog by way of secondary poisoning exposure from terrestrial invertebrates is not 

expected to lead to LOC exceedances (LOC ≥0.05). 

. 

77
Table 20 Summary of Aldicarb Direct Effects RQs for the CRLF

Effects 

to CRLF 

Surrogate 

Species 

Toxicity 

Value 

Scenarios RQ Probability 

of 

Individual 

Effect 

(Default 

slope = 4.5) 

LOC 

Exceedance 

Aquatic Phase CRLF 

Acute 

Direct 

Toxicity 

Bluegill 

sunfish 

96-h 

LC50= 52 

ppb ai 

Citrus 

Cotton (1) 

Cotton (3) 

Soybean 

Pecan 

Sugar beet 

0.0071 

0.13 

0.15 

0.12 

0.14 

0.22 

>1-in-4.3E8 

1-in-30,000 

1-in-9,600 

1-in-58,000 

1-in-16,000 

1-in-648 

No 

Yes 

Yes 

Yes 

Yes 

Yes 

Chronic 

Direct 

Toxicity 

Bluegill 

sunfish/Fathead 

minnow ACR 

Estimated 

NOAEC= 

0.46 ppb 

ai 

Citrus 

Cotton (1)

Cotton (3) 

Soybean 

Pecan 

Sugar beet 

0.81 

7.68 

7.50 

5.60 

6.84 

11.79 

Not 

applicable 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Terrestrial phase CRLF 

Sm 

frog6

Lg 

frog6

Acute 

Direct 

Toxicity 

Mallard duck LD50= 1 

mg/kgbw 

Citrus 

Cotton 1, 4

Dry Beans3

Peanuts3

Pecans5

Sorghum3

Soybean3

Sugarbeet2,3

Sweet 

potato3 

2978 

1599 

84 

180 

571 

185 

150 

1158 

84.23 

467 

251 

13 

28 

89 

29 

23 

181 

13 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Acute 

Direct 

Toxicity 

via 

Secondary 

poisoning 

Mallard duck LD50= 1 

mg/kgbw 

Citrus 0.0017 No 

Bolded scenarios are the highest risk in the aquatic or terrestrial environment and bolded RQ values exceed LOC values 1 T-REX does not allow for different application rates; thus the modeling run generating the highest RQs was chosen 

for final RQs in Table 24, which was for 3 applications @ 7 lbs/A 2

 Three applications are allowed for sugar beet with a maximum 1 time application rate of 14 lbs/A and a total of 28 

lbs/yr. The modeling run generating the highest RQs was chosen for final RQs in Table 24 3

 Incorporation efficiency 99% 

4

 incorporation efficiency 85% 

5

 LD50/sq ft calculated assuming granules shanked in, row spacing between canopy of trees in adjacent rows 72”. 6

small refers to a 20 g bird; a small CRLF however would be around 50g. Therefore this RQ estimate may be higher 

than expected. Large refers to a 100g bird; a large CRLF may weigh up to 100 g. Therefore, this RQ estimate may be 

lower than expected. 

78
Aldicarb Degradates and Direct toxicity to the Red Legged Frog 

Aldicarb sulfoxide has been classified as moderately toxic on an acute basis to freshwater 

fish (MRID 45592115). Based on the one study available, it can be assumed that aldicarb 

sulfoxide is not likely to pose a risk to the aquatic phase of the red legged frog. None of 

the scenarios modeled (combined aquatic EECs for parent and degradates were used in 

these calculations) lead to LOC exceedances (LOC ≥0.05). 

Table 21 Aldicarb Sulfoxide Direct Effects to the CRLF

Effects 

to 

CRLF 

Surrogate 

Species 

Toxicity 

Value 

Scenarios RQ Probability 

of 

Individual 

Effect 

LOC 

Exceedance 

Acute 

direct 

toxicity 

Rainbow trout 96-hr LC50 

= 7,140 ppb 

ai 

Citrus 

Cotton (1) 

Cotton (3) 

Soybean 

Pecan 

Sugar beet 

0.00005 

0.001 

0.001 

0.0009 

0.001 

0.002 

At LOC of 

0.05 and 

slopes of 2 

and 9 

1 in 216 

1 in 1.8E+31 

No 

5.1.2 Indirect Effects 

Pesticides have the potential to exert indirect effects upon listed species by inducing 

changes in structural or functional characteristics of affected communities. Perturbation 

of forage or prey availability and alteration of the extent and nature of habitat are 

examples of indirect effects. 

In conducting a screen for indirect effects, direct effects LOCs for each taxonomic group 

(freshwater and terrestrial vertebrates, freshwater and terrestrial invertebrates, terrestrial 

plants) are employed to make inferences concerning the potential for indirect effects upon 

listed species that rely upon non-listed organisms in these taxonomic groups as resources 

critical to their life cycle (U.S. EPA, 2004). This approach used to evaluate indirect 

effects to listed species is endorsed by the Services (USFWS/NMFS, 2004b). If no direct 

effect listed species LOCs are exceeded for non-endangered organisms that are critical to 

the California Red Legged Frogs life cycle, the concern for indirect effects to the CRLF 

is expected to be minimal. 

If LOCs are exceeded for freshwater and terrestrial vertebrates as well as invertebrates 

that are prey items of the CRLF, there is a potential for aldicarb to indirectly affect the 

frogs by reducing available food supply. In such cases, the dose response relationship 

from the toxicity study used for calculating the RQ of the surrogate prey item is analyzed 

to estimate the probability of acute effects associated with an exposure equivalent to the 

EEC. Generally, the greater the probability that exposures will produce effects on a taxa, 

the greater the concern for potential indirect effects for listed species dependant upon that 

taxa (U.S. EPA, 2004). However, life history characteristics of each taxa affected and 

serving as prey to the CRLF will have to be considered in conjunction with the 

probability of exposure. In addition, the species’ sensitivity distribution for aquatic 

invertebrates can be used to further refine an effects determination. 

79
As an insecticide, indirect effects to CRLFs from potential effects on primary and 

secondary consumers are a principle concern. Furthermore, aldicarb has shown to have 

deleterious effects on seedling emergence in terrestrial plants, and therefore, potential 

effects on terrestrial plants growing in semi-aquatic areas is of concern as well. Based on 

the emergence data, aldicarb’s systemic nature, and its positive effects on biomass in 

terrestrial plants, it can be concluded that potential effects on primary productivity of 

aquatic vascular plants is of concern as well. This risk assessment will address risk to 

aquatic vascular plants in a qualitative way because of lack of data. 

5.1.2.1 Evaluation of Potential Indirect Effects via Reduction in Food 

Items 

Potential indirect effects from direct effects on animal food items were evaluated by 

considering the diet of the California Red Legged frog and the sensitivity distribution of 

aquatic prey organisms. Aquatic phase CRLF larvae consume algae, diatoms, and 

detritus, for which no data are available. The saltwater diatom data was used as a 

surrogate for freshwater diatoms to assess potential indirect effects on the larval stage of 

the CRLF; no other aquatic plant data are available for an indirect effects analysis of the 

aquatic phase of the CRLF. Terrestrial phase CRLFs feed on a wide range of freshwater 

and terrestrial invertebrates, and freshwater and terrestrial vertebrates, including water 

striders, sow bugs, fish, other frogs, salamanders, and small mice. While aquatic and 

terrestrial invertebrates comprise the most numerous food items, 50% of the prey mass in 

larger adult CRLFs consists of vertebrates such as mice, frogs, and fish. The RQs used to 

characterize potential indirect effects to the terrestrial and aquatic phase of the CRLF 

from direct acute and chronic effects on freshwater vertebrate and invertebrate as well as 

terrestrial vertebrate and invertebrate food sources are provided in Table 22. Acute RQs 

are based on the most sensitive toxicity endpoints of the bluegill sunfish (96-h LC50 = 52 

ppb ai), C. tentans (20 ppb ai), the rat (LD50 = 0.9 mg ai/kg-bw), and the honey bee (LD50

= 0.285 μg/bee). Chronic RQs are based on the bluegill sunfish (estimated NOAEC = 

0.46 ppb ai), and C. tentans (NOAEC = 1 ppb ai). Chronic RQs cannot be calculated by 

the LD50/sq foot method of the T-REX model; but the rat NOAEL of 0.4 mg ai/kg-bw 

will be qualitatively discussed in the Risk Description section of this assessment. 

There are acute LOC exceedances (≥ 0.05) for fish and invertebrates and aquatic animals 

from all use scenarios except citrus (low runoff PRZM-EXAMS scenario), sorghum and 

by default soybean with infurrow and positive displacement application methods only 

which have lower EECs than citrus (Table 22). Containerless field grown ornamentals 

(and by default container grown outdoor ornamentals represented by this scenario) and 

sweet potato do not exceed the acute listed LOC for fish. There are chronic LOC 

exceedences for fish and aquatic invertebrates for all scenarios except citrus (soybean 

applied infurrow and/or with positive displacement by default) and sorghum. Sugar beet 

drives both the acute and chronic risks LOC exceedances to these potential dietary 

sources of the CRLF and invertebrates and, therefore, drives the indirect effects to the 

CRLF on an overall basis. 

80
There are LOC exceedances (≥0.1, Ratio of ≥0.05 for terrestrial invertebrates) for small 

mammals and terrestrial invertebrates from all use scenarios (Table 23). Aldicarb use on 

citrus leads to the highest LOC exceedance for small mammals (LD50/sq ft =1042) 

followed by cotton, sugar beets, and pecans (LD50/sq ft =560, 405, and 200, respectively). 

Aldicarb use on citrus also produced the highest soil concentration estimated with the 

Earthworm Fugacity model (14.3 mg/kg soil); this estimated soil concentration was used 

to estimate risk to concentrations on a honey bee of 0.1g (or 0.0001 kg). The resulting 

RQ for honey bee is 5.03 (LOC = 0.05) and is representative of all terrestrial 

invertebrates on-site. An estimate of the off-site soil concentrations were estimated using 

Terrplant as discussed in Section 3.4 and resulted in concentrations below the LOC. 

Since aldicarb use on cotton has the highest reported usage in California, soil 

concentrations from this use were considered as well to estimate risk to terrestrial 

invertebrates. Aldicarb use on citrus produced a soil concentration of 1.2 mg/kg soil. 

The resulting RQ for honey bee is 0.42 and exceeds the LOC of 0.05 for terrestrial 

invertebrates for on-site soils. The off-site soil as discussed in the previous sentence will 

be below the LOC. 

5.1.2.2 Evaluation of Potential Indirect Effects via Reduction in Habitat 

and/or Primary Productivity 

Potential indirect effects on habitat and/or primary productivity were assessed using the 

RQs from a saltwater diatom. This species is used as a surrogate for freshwater diatoms 

and will only provide insight into a small part of the sensitivity spectrum of freshwater 

plant. If aquatic plant RQs exceed the Agency’s non-listed species LOC (because the 

aquatic and terrestrial phase of the CRLF relies on multiple plant species), potential 

community level effects are evaluated using the threshold concentrations (No Adverse 

Effects Levels, i.e. NOAEC). Risk quotients used to estimate potential indirect effects to 

the CRLF from effects on aquatic and terrestrial plants primary productivity are 

summarized in Table 24. 

None of the use scenarios led to LOC exceedances for freshwater aquatic plants (using 

saltwater diatom as surrogate) and terrestrial plants, or for terrestrial plants growing in 

semi-aquatic areas. Both aquatic plant and terrestrial plant RQs were <0.5 and do not 

trigger the LOC. The TerrPlant model assumes that 100% of the granules are 

incorporated, which is not a realistic assumption for all aldicarb incorporation methods. 

In reality, citrus and cotton (3 applications) are more likely to have only 85% of aldicarb 

granules incorporated (because established trees for citrus and established plants for 

second and third applications for cotton do not allow for use of the type of equipment 

necessary to achieve 99% incorporation). If TerrPlant had the ability to model partial 

granular incorporation, the resulting RQs would be higher for terrestrial plants and plants 

growing in semi-aquatic areas. 

81
Table 22 Summary of Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via Acute and Chronic 

Effects on Aquatic Dietary Items(1) 

 Efficiency Amount % EEC Fish (1, 2, 3) Invertebrate (1, 2, 3)

Crop of Method Product a.i. Peak 21-d 60-d Acute Chronic Acute Chronic 

Citrus (85%) 33 lb/A 15g 0.4 0.2 0.1 0.01 0.2 0.02 0.2 

Sorghum IF (99%) 10 lb/A/yr 10g 0.7 0.5 0.3 0.01 0.7 0.04 0.5 

 IF (99%) 7 lb/A/yr 15g 0.7 0.5 0.3 0.01 0.7 0.04 0.5 

Ornamentals 

(field-no 

contaniners) 

SD (99%) 50 lb/A/yr 10g 0.9 0.7 0.5 0.02 1.1 0.05 

4.5S (1-in-4.2E8)

2S (1-in-216)

0.7 

Sweet Potato Band (99%) 30 

lb/A/crop 

10g 1.4 1 0.6 0.03 1.3 0.07 

4.5S (1-in-9.9E6)

2S (1-in-96)

1.0 

Dried Bean Band (85%) 21 lb/A/ 

crop 

10g 4.5 3.5 2.3 0.09 

4.5S (1-in-7.9E5)

2S (1-in-55)

5.0 0.23 

4.5S (1-in-491) 

2S (1-in-9)

3.5 

Soybean (85-99%) 20 lb/A 15g 6.1 4.5 2.6 0.12 

4.5S (1-in-5.8E4)

2S (1-in-30)

5.7 0.31 

4.5S (1-in-91) 

2S (1-in-6)

4.5 

Peanut Band (85%) 30 

lb/A/crop 

10g 6.4 5 3.3 0.12 

4.5S (1-in-5.8E4)

S (1-in-30)

7.2 0.32 

4.5S (1-in-77) 

2S (1-in-6)

5.0 

Pecans (85%) 33 lb/A 15g 7.4 5.4 3.1 0.14 

4.5S (1-in-1.6E4)

2S (1-in-23)

6.7 0.37 

4.5S (1-in-39) 

2S (1-in-5)

5.4 

Cotton (85-99%) 21 

lb/A/season 

15g 7.6 5.9 3.4 0.15 

4.5S (1-in-9,600) 

2S (1-in-20)

7.4 0.38 

4.5S (1-in-34) 

2S (1-in-5)

5.9 

 6.8 5.5 3.5 0.13 

4.5S (1-in-3E4) 

2S (1-in-20)

7.6 0.34 

4.5S (1-in-57) 

2S (1-in-6)

5.5 

Alfalfa (seed) Drill (85%) 20 lb/A/yr 15g 10 8.4 5.3 0.19 

4.5S (1-in-1700) 

2S (1-in-13)

11.5 0.50 8.4 

Sugarbeet (99%) 15g 11.4 8.6 5.4 0.22 

4.5S (1-in-648) 

2S (1-in-11)

11.7 0.57 8.6 

(1) Bolded acute values exceed the acute listed LOC (0.05) and bolded chronic values exceed the chronic 

LOC (1). 

(2) Peak EECs are used for calculating acute RQs; 21-day EECs are used for invertebrate chronic RQs and 

60-day EECs for vertebrate chronic RQs. 

 (3) Fish bluegill 96-h LC50 52 ppb; NOAEC 0.46 ppb; 48-hr EC50 Chironomus tentans 20 ppb; estimated 

NOAEC 1 ppb 

82
Table 23 Summary of Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via Acute Effects 

on Terrestrial Dietary Items(1)

Indirect 

Effect to 

CRLF 

Surrogate Food 

Item Toxicity 

Value 

Use Dose or 

Concentration 

RQ LOC(2)

Exceedance

Dose LD50/sq ft 

15 g 

mam

mal 

35 g 

mam

mal 

1000 g

mam

mal 

Citrus 1042 

Cotton (3) 560 296 24 5591

Dry Beans 30 16 1.26 291

Peanuts 63 35 2.7 631

Pecans 200 106 9 2001

Sorghum 65 34 2.8 651

Soybean 53 28 2 521

Sugar beet 405 214 17 4051

Reduced 

Terrestrial 

Food via 

Acute Direct 

Toxicity

Rat 

LD50 0.9 mg a.i./kgbw

Sweet potato 1.26 16 29 291

Yes 

On-site(3) Soil 

Concentration 

Reduced 

Terrestrial 

Food via 

Acute Direct 

Toxicity 

Honey bee (0.0001 

kg) 

LD50 0.000285 mg 

a.i./bee 

Citrus 

Cotton (3) 

14.3 mg ai/kg soil 

(=0.0014 mg a.i./bee) 

1.2 mg ai/kg soil 

5.032 

0.42

Yes 

Yes 

 (1) Bolded sections represent use scenarios that are driving risk in aquatic and terrestrial environment, 

bolded RQs exceed LOC 

(2) Acute endangered LOC of 0.1 is used for terrestrial animals and the LOC of 0.05 is used for acute 

effects to terrestrial invertebrates. 

(3) Off-site soil estimated soil concentrations are below LOC of 0.05 (see Section 3.4) 

83
Table 24 Aldicarb RQs Used to Estimate Indirect Effects to the CRLF via Direct Acute Effects on 

Aquatic and Terrestrial Habitat Components

Indirect Effect to 

CRLF 

Surrogate 

Species/ Toxicity 

Value 

Use EEC RQ Exceedance and 

Risk Interpretation 

Reduced Cover to 

Aquatic Phase of 

CRLF via Direct 

Toxicity 

Marine diatom 

96-hr EC50 > 

50,000 ppb ai 

Citrus 

Cotton (3) 

Soybean 

Pecan 

Sugar beet 

0.371 

7.632 

6.142 

7.373 

11.377 

0.000007 

0.0002 

0.0001 

0.0001 

0.0002 

No 

No 

No 

No 

No 

Total loading 

to adjacent 

areas 

Total 

loading to 

semi 

aquatic 

areas 

Emerg. RQs 

adjacent 

area, 

monocots 

Emerg. RQs 

semi aquatic 

area, 

monocots 

Reduced Plant 

Stand of Terrestrial 

Habitat Component 

via Direct Toxicity 

to seedling 

emergence 

Pearl millet 21-d 

NOAEC = 2.05 

lbs ai/A 

Citrus 

Cotton 

Dry bean 

Peanut 

Pecan 

Sorghum 

Soybean 

Sugar beet 

Sweet potato

0.0825 

0.0525 

0.0175 

0.0500 

0.0825 

0.0350 

0.0500 

0.0700 

0.0350 

0.8250 

0.5250 

0.1750 

0.5000 

0.8250 

0.3500 

0.5000 

0.7000 

0.3500 

0.04 

0.03 

0.01 

0.02 

0.04 

0.02 

0.02 

0.03 

0.02 

0.40 

0.26 

0.09 

0.24 

0.4 

0.17 

0.24 

0.34 

0.17 

No 

No 

No 

No 

No 

No 

No 

No 

No 

5.2 Risk Description 

The risk description synthesizes an overall conclusion regarding the likelihood of adverse 

impacts leading to an effects determination (i.e., “no effect,” “may affect, but not likely 

to adversely affect,” or “likely to adversely affect”) for the California Red Legged frog. 

If the RQs presented in the Risk Estimation (Section 5.1.2) show no indirect effects, and 

LOCs for the CRLF are not exceeded for direct effects (Section 5.1.1), a “no effect” 

determination is made based on aldicarb’s use within the action area. If, however, 

indirect effects are anticipated and/or exposure exceeds the LOCs for direct effects, the 

Agency concludes a preliminary “may affect” determination for the CRLF. 

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 and potential community-level 

effects to aquatic plants and terrestrial plants growing in semi-aquatic areas. 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. 

The criteria used to make determinations that the effects of an action are “not likely to 

adversely affect” the CRLF 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: 

84
 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 patterns which include, but are not 

limited to, breeding, feeding, or sheltering. 

• Likelihood of the Effect Occurring: Discountable effects are those that are 

extremely unlikely to occur. For example, use of dose-response 

information to estimate the likelihood of effects can inform the evaluation 

of some discountable effects. 

• Adverse Nature of Effect: Effects that are wholly beneficial without any 

adverse effects are not considered adverse. 

A description of the risk and effects determination for each of the established assessment 

endpoints for the CRLF is provided in Sections 5.2.1 through 5.2.3. 

5.2.1 Direct Effects to the California Red Legged Frog 

5.2.1.1 Direct Effects to the Aquatic Phase of the CRLF 

Aquatic acute and chronic RQs exceeded acute listed and chronic LOCs for the following 

modeled uses within the action area: cotton, dried bean, soybean (banded applications), 

peanut, pecan, alfalfa and sugar beet. Sugar beet drives the risk in the aquatic 

environment with acute and chronic RQs of 0.22 and 12, respectively. These RQs were 

based on maximum label application rates. What constitutes typical application rates for 

the uses having LOC exceedances is unclear and can, therefore, not be discussed for 

characterization purposes. For the purpose of refinement, the CAL DPR PUR data will 

be used in conjunction with spatial CRLF data, RQ exceedances, species’ life history 

information, and more to make direct effects determinations for the CRLF. 

The probability of an individual event to the CRLF was calculated for all acute RQs 

based on the dose response curve slopes of 4.5 (default) and its lower and upper 95% 

bounds of the slope range (2 and 9) due to lack of actual probit slope values for 

individual taxa). The corresponding estimated chance of an individual acute mortality to 

the larva of the CRLF at RQs above the acute listed LOC ranging from 0.09 to 0.22 

(based on the acute toxic endpoint for surrogate freshwater fish) is 1-in-790,000 to 1-in648, respectively, for the mean slope of 4.5 (range if slope of 2 is used: 1-in-55 to 1-in11). The acute listed LOC estimated chance of an individual acute mortality for the mean 

slope is 1-in-4.2E8 (for slope of 2 and 9: 1-in-216 and 1-in-1.8E31). There is 

considerable amount of uncertainty around the probability of an individual mortality 

85
occurrence based on the default slope bounds; however, expect the slope to be more 

towards 4.5 and 2 based on the all-or-none response observed in most acute tests. In 

absence of a species’ sensitivity distribution for acute mortality endpoint values, this 

uncertainty cannot be further refined at this point. For dried beans, soybean (banded 

application), peanut, pecan, cotton, alfalfa, and sugar beet, given the high probability of 

an individual experiencing a mortality event based on the steeper slopes, and chronic RQs 

that are above the chronic LOC, aldicarb was considered likely to cause direct adverse 

effects to the aquatic phase of the CRLF where exposure to pesticide actually occurs. 

Based on the usage information provided by California Department of Pesticide 

Programs (PUR database) for 2001 through 2005, minor use of aldicarb (total amount of 

aldicarb in California has been reported (1 and 1,232 lbs/A) for the following twelve 

counties during the five year period: Alameda (1 lbs/A), Butte (854 lbs/A), Glenn (422 

lbs/A), Monterey (111 lbs/A), San Benito (157 lbs/A), San Joaquin (77 lbs/A), San Luis 

Obispo (1 lbs/A), Santa Cruz (3 lbs/A), Santa Clara (1 lbs/A), Stanislaus (5 lbs/A), Sutter 

(1,232 lbs/A), and Riverside Counties (1,202 lbs/A). Significant aldicarb use (total 

amount of aldicarb used in five years greater than 1,232 lbs/A) has been limited to the 

following nine counties: Colusa (3,574 lbs/A), Fresno (>75,000 lbs/A), Imperial (3,491 

lbs/A), Kern (>25,120 lbs/A), Kings (>75,400 lbs/A), Madera (5,014 lbs/A), Merced 

(2,909 lbs/A), Tulare (2,512 lbs/A), and Yolo (5,089 lbs/A). No aldicarb use has been 

reported for the remaining counties in California. Of the nine and twelve counties with 

highest and lowest total aldicarb use (for all commodities) listed above, the following ten 

counties are expected to clearly overlap with occurrence polygons, occurrence sections, 

critical habitat, or core areas in recovery units (RU): Alameda (RU4), Butte (RU1), 

Fresno (RU1), Merced (RU1), Monterey (RU5, RU6), San Luis Obispo (RU5, RU6), San 

Benito (RU5, RU6), Santa Cruz (RU4, RU5), Santa Clara (RU4, RU6), and Riverside 

(RU8). The remaining counties from that list are not expected to overlap with occurrence 

polygons, occurrence sections, critical habitat, or core areas: Butte, Colusa, Glenn, 

Imperial, Kern, Kings, Madera, San Joaquin, Stanislaus, Sutter, Tulare, and Yolo. The 

highest total use of aldicarb has been on cotton in Colusa (2,800 lbs/A), Fresno (74,000 

lbs/A), Imperial (3,500 lbs/A), Kern (31,500 lbs/A), Kings (74,000 lbs/A), Madera (4,700 

lbs/A), Merced (27,800 lbs/A), Riverside (1,200 lbs/A), Sutter (1,200 lbs/A), Tulare 

(22,300 lbs/A), and Yolo (5,000 lbs/A). All other aldicarb uses listed in the CAL DPR 

PUR database make up insignificant amounts when compared to aldicarb use on cotton. 

As discussed in the 2006 revised screening level ecological risk assessment, two 

incidents for freshwater fish (I003826-002 and I000799-005) related to aldicarb have 

been reported in the Environmental Incident Information System (EIIS) database (North 

Carolina (1995): one incident as a result of registered use and one of undetermined use). 

No aquatic incidents have been reported in California. 

Based on all available lines of evidence, the Agency concludes a “likely to adversely 

affect” determination for direct effects to the aquatic phase of the CRLF via mortality, 

growth, or reproduction in areas where exposure to aldicarb is expected to occur, such as 

in recovery unit 1, 5, 6, and 8, for dried bean, soybean (banded application), peanut, 

pecan, cotton, alfalfa for seed, and sugar beet. The Agency concludes a “not likely to 

adversely affect” determination for direct effects to the aquatic phase of the CRLF via 

86
growth, survival, and reproduction in recovery units 2, 3, 4, and 7 due to lack of spatial 

overlap of CRLF habitat and occurrence data with the aldicarb action area. The Agency 

concludes a “likely to adversely affect” determination for direct effects of aldicarb to the 

aquatic phase of the CRLF in RU1, RU5, RU6, RU8. 

No LOC exceedances are predicted for aldicarb degradates based on modeled EECs and 

available freshwater fish and freshwater invertebrates endpoint values. The Agency 

concludes a “no effects” determination for direct effects of aldicarb sulfoxide to the 

aquatic phase of the CRLF. 

5.2.1.2 Direct Effects to the Terrestrial Phase of the CRLF 

Terrestrial acute RQs, based on on-site exposure, are exceeded for all modeled scenarios 

(and by default the other uses they represent) within in the action area. Citrus drives the 

risk in the terrestrial environment followed by cotton with acute RQs for a small and 

large size frog of 2978 and 468, and 1599 and 251, respectively. These RQs were based 

on maximum label application rates. What constitutes typical application rates for these 

uses having LOC exceedances is unclear and can, therefore, not be discussed for 

characterization purposes. Terrestrial acute effects from aldicarb transport off-site was 

evaluated for citrus and was below the LOC; therefore by default all other scenarios, 

which result in lower exposure, also do not pose a risk of concern off-site. 

For the purpose of refinement, the CAL DPR PUR data (see discussion in Section 

5.2.1.1) will be used in conjunction with spatial CRLF data, RQ exceedances, species’ 

life history information, and more to make direct effects determinations for the CRLF. 

As previously mentioned, direct effects to the CRLF are based on avian data, which are 

used as a surrogate for terrestrial-phase amphibians. Chronic risk to the terrestrial phase 

of the CRLF could not be assessed quantitatively via the LD50/sq ft method. However, 

the following qualitative statement can be made regarding chronic risk from aldicarb 

exposure to the adult phase of the CRLF. The estimated NOAEL (0.49 mg/kg) suggests 

that if an adult frog experiences acute exposure to aldicarb (LD50 = 1mg/kg) and survives 

the incidence, chronic reproductive effects may potentially be expected. 

Based on all available lines of evidence, the Agency concludes a “not likely to adversely 

affect” determination for direct effects of aldicarb to the terrestrial phase of the CRLF via 

growth, survival, and reproduction in recovery units 2, 3, 4, and 7 due to lack of spatial 

overlap of CRLF habitat and occurrence data with the aldicarb action area. The Agency 

concludes a “likely to adversely affect” determination for direct effects of aldicarb to the 

terrestrial phase of the CRLF in RU1, RU5, RU6, RU8 considering on-site exposure. Offsite exposure does not pose a risk of concern because off-site EECs are below LOCs. 

There is no designated critical habitat in recovery units 2 and 8. 

87
5.2.2 Indirect Effects via Reduction in Food Items 

5.2.2.1 Indirect Effects to the Terrestrial Phase of the CRLF 

The results of the screening-level risk assessment for the CRLF suggest the potential for 

direct acute adverse effects to terrestrial invertebrates and vertebrates exposed on-site for 

all agricultural and non-agricultural uses. Citrus and cotton produce the greatest LOC 

exceedances for terrestrial invertebrates with acute RQs of 5.03 and 0.42, respectively. 

Aldicarb use on citrus and cotton produces RQs of 1042 and 560 for small mammals, 

2978 and 1599 for small frogs, and 468 and 251 for large frogs (LD50/sq ft RQs for 

birds). Off-site exposure levels in the terrestrial environment and riparian environment 

are below levels of concern for both terrestrial invertebrates and vertebrates for all uses. 

Soybean (in-furrow and/or positive displacement applications only), citrus, and sorghum 

do not exceed acute listed or chronic LOCs for freshwater invertebrates. Sugar beets 

produce the greatest acute and chronic LOC exceedances for freshwater invertebrates 

(0.57 and 8.63, respectively) followed by cotton (0.38 and 5.91, respectively), and pecans 

(0.37 and 5.39, respectively). Based on the highest risk scenarios, because the chronic 

LOC exceedances for some crops are above the Agency LOC, aldicarb is likely to pose a 

risk to the terrestrial prey base of the CRLF. 

Indirect Effects to CRLF via Effects to Freshwater Fish and Freshwater 

Invertebrate Prey Base 

For freshwater invertebrates, acute listed and chronic RQs exceed the LOC of 0.05 and 1, 

respectively for all uses of aldicarb except soybean (in-furrow and/or positive 

displacement application methods only), citrus, and sorghum. For freshwater fish, acute 

listed and chronic RQs exceed the LOC of 0.05 and 1, respectively for all uses of aldicarb 

except soybean (in-furrow and/or positive displacement application methods only), citrus, 

sorghum, and essentially containerless field grown ornamentals (chronic RQ ≅ 1, the no 

observable effect concentration for the ornamental scenario). Because the RQ values are 

above the Agency LOC, based on the highest risk scenarios, alidicarb is likely to pose a 

risk to the freshwater fish and freshwater invertebrate prey base of the CRLF.

Explanation of Indirect Effects Determination Based on Effects to the CRLF 

Terrestrial and Aquatic Prey Base 

Based on all available lines of evidence, the Agency concludes a “not likely to adversely 

affect” determination for indirect effects to the CRLF via aldicarb adverse effects to the 

terrestrial and aquatic prey base of the CRLF in recovery units 2, 3, 4, and 7 due to lack 

of spatial overlap of CRLF habitat and occurrence data with the aldicarb action area. 

Based on the highest risk scenarios, the Agency concludes a “likely to adversely affect” 

determination for indirect effects to the CRLF via aldicarb adverse effects to the 

terrestrial and aquatic prey base of the CRLF in RU1, RU5, RU6, RU8. The Agency also 

concludes “a like to adversely affect” to the critical habitat for RU1, RU5, RU6, RU8 of 

the CRLF because of the adverse effect expected to the terrestrial and aquatic organisms 

base which is a component of the critical habitat of the CRLF. 

88
Indirect Effects to CRLF via Effects to Aquatic Plants 

Due to lack of other aquatic plant data, the Agency had to rely on the only aquatic data 

available, an estuarine/marine species used as a surrogate for freshwater, and on making 

inferences for riparian plants from the results for terrestrial plants listed in this 

assessment (Section 5.2.4). No direct effects are predicted to aquatic plants when the 

estuarine/marine diatom is used in the RQ calculations. RQs for all use scenarios are 

well below 1 and do not indicate reason for concern. Terrestrial plant emergence RQs are 

also well below 1; highest emergence RQs for terrestrial plants growing in semi-aquatic 

areas are for the citrus and pecan scenario and are 0.4. However, the TerrPlant model 

assumes complete incorporation of granules, which is not a feasible assumption for 

aldicarb applications to citrus. Therefore, these emergence RQs may represent an 

underestimate of risk of aldicarb use to aquatic vascular plants. 

Agency concludes a “no effects” determination for indirect effects to the aquatic phase of 

the CRLF via direct effects to aquatic plants in all recovery units. 

Indirect Effects to CRLF via Effects to Mammalian and Frog Prey 

Acute RQs for small mammals exposed to on-site levels exceed the LOC of 0.1, and 

suggest that granular application of aldicarb to agricultural and non-agricultural 

commodities has the potential to indirectly affect the CRLF via reduction in the 

availability of sensitive terrestrial food items. The mammalian calculations were based 

on the rat LD50 of 0.9 mg ai/kg-bw. No comparison of the rat LD50 with other species’ 

LD50 is possible due to lack of data. Whether the 0.9 mg ai/kg-bw represents a lower or 

upper value of the sensitivity spectrum for mammals is unclear. The chronic value 

(NOAEL = 0.4 mg ai/kg-bw) suggest that where acute exposure to small mammals 

occurs and individuals survive that chronic reproductive effects can be expected. 

Acute RQs for small and large frogs exceed the LOC of 0.1, suggesting that granular 

application of aldicarb to agricultural and non-agricultural commodities has the potential 

to indirectly affect the CRLF via reduction in the availability of sensitive terrestrial food 

items. The frog calculations were base on the surrogate mallard duck LD50 of 1 mg ai/kgbw. No other data is available to assess birds’ sensitivity to acute aldicarb exposure. The 

estimated chronic NOAEL of 0.1 mg ai/kg-bw suggests that where acute exposure to 

frogs occurs and individuals survive that chronic reproductive effects may potentially 

expected. In absence of aldicarb amphibian endpoint values, other (less sensitive) Nmethyl carbamate frog data was used in conjunction with aldicarb EECs to see whether 

LOC exceedances would occur. Table 15 shows that when the amphibian endpoint for 

propoxur (carbamate class) is used that LOC exceedances occur for almost all uses of 

aldicarb. The highest LOC exceedances are for citrus (4.48 small frog and 0.70 large 

frog) and cotton (2.4 small frog and 0.38 large frog). This analysis strengthens the 

argument that aldicarb use on these crops can be expected to lead to LOC exceedances 

with an aldicarb toxicological endpoint value as well. 

89
EFED presumes that because the LOC exceedances for mammalian and frog prey items 

are well above the Agency LOC, aldicarb poses a likely risk to mammalian and 

amphibian food prey of the CRLF, if on-site mammalian and amphibian populations are 

critical to the CRLF. Off-site aldicarb concentrations are below levels of conern. 

Based on all available lines of evidence, the Agency concludes a “not likely to adversely 

affect” determination for indirect effects to the CRLF via aldicarb adverse effects to the 

mammalian and amphibian prey base of the CRLF in recovery units 2, 3, 4, and 7 due to 

lack of spatial overlap of CRLF habitat and occurrence data with the aldicarb action area. 

The Agency concludes a “likely to adversely affect” determination for indirect effects to 

the CRLF via aldicarb adverse effects to mammalian and amphibian prey base of the 

CRLF in RU1, RU5, RU6, RU8, assuming on-site prey base is critical to CRLF. The 

Agency also concludes “a like to adversely affect” to the critical habitat for RU1, RU5, 

RU6, RU8 of the CRLF because of the adverse effect expected for the mammalian and 

amphibian organisms which are a component of the critical habitat of the CRLF, 

assuming on-site is considered critical habitat. 

5.2.2.2 Indirect Effects via Reduction of Aquatic Primary Productivity 

As already stated in Section 5.2.2 (indirect effects to CRLF via direct effects to aquatic 

plants), due to lack of other aquatic plant data, the Agency had to rely on the only aquatic 

data available, an estuarine/marine species as a surrogate, and on making inferences for 

riparian plants from the results for terrestrial plants listed in this assessment (Section 

5.2.4). No direct effects are predicted to aquatic plants when the estuarine/marine diatom 

is used in the RQ calculations (see Table 26). RQs for all use scenarios are well below 1 

and do not indicate reason for concern. Terrestrial plant emergence RQs are also well 

below 1; highest emergence RQs for terrestrial plants growing in semi-aquatic areas are 

for the citrus and pecan scenario and are 0.4. However, the TerrPlant model assumes 

complete incorporation of granules, which is not a feasible assumption for aldicarb 

applications to citrus. Therefore, these emergence RQs may represent an underestimate 

of risk to aquatic vascular plants. The Agency concludes a “no effects” determination for 

indirect effects to the CRLF via direct effects to aquatic plants in all recovery units and 

critical habitat. 

5.2.2.3 Indirect Effects via Alteration in Terrestrial Plant Community 

Emergence RQs for terrestrial monocots are below the LOC of 1 for all use scenarios, 

range from 0.01 to 0.04, and do not indicate reason for concern. Emergence RQs for 

terrestrial monocots growing in semi-aquatic areas are slightly higher but also below the 

LOC of 1, and range from 0.09 (dry beans) to 0.4 (citrus). However, the TerrPlant model 

assumes complete incorporation of granules, which is not a feasible assumption for 

aldicarb applications to citrus. Therefore, the emergence RQs of 0.4 may represent an 

underestimate of risk to riparian plants. 

90
Agency concludes a “no effects” determination for indirect effects to the CRLF via direct 

effects to terrestrial plants and terrestrial plants growing in semi-aquatic areas in all 

recovery units and critical habitat. 

5.2.3 Secondary Poisoning of CRLF by Consuming Terrestrial 

Invertebrates Contaminated with Aldicarb Residues 

The Earthworm Fugacity model was used to calculate the aldicarb concentration 

(Appendix C) in soil (mg/kg). The conservative assumption was made that the 

concentration in a 1 kg of soil is equivalent to the aldicarb concentration in 1 kg of 

terrestrial invertebrate. The size of terrestrial invertebrate was set at 10 grams 

(approximate weight of a large slug); however, most invertebrates that a CRLF consumes 

will have a weight much below this value (water strider ~1g; spiders ~6mg). The citrus 

scenario resulted in the highest concentration of aldicarb in soil (14.3 mg/kg) and was 

used in estimating aldicarb concentrations in a terrestrial invertebrate of 10 grams (0.01 

kg) as follows. 

Aldicarb concentrations in a large terrestrial invertebrate:

14.3 mg ai/kg * 0.010 kg = 0.143 mg ai/lg invert 

The allometric food ingestion rate equation for amphibians/reptiles is:

FI (g/day) = =0.077 g/day = 0.000077 kg/day 773.0 *013.0 Wt

The estimated aldicarb concentration in a terrestrial invertebrate (0.0143 mg/kg), the 

LD50 for mallard duck (1mg/kg; surrogate for terrestrial phase amphibians), the daily 

mass of invertebrates eaten by an amphibian/reptilian surrogate based on range of weight 

for CRLF, the highest value cited for food water content in terrestrial animals and aquatic 

animals (87%; or dry weight of food (13%)* 7.7=100%), and the weight (upper and 

lower end; 100 g, 50 g) of a CRLF were used to calculate an RQ for the terrestrial phase 

CRLF (LOC = 0.1). The Wildlife Exposure Factor Handbook (US EPA, 1993, vol I) 

provided amphibian/reptilian insectivorous food ingestion rate equations and water 

content of food to convert dry weight to wet weight of food; USGS (2004) provided 

upper and lower bound weight of CRLF frog. These RQs measure risk to the CRLF from 

secondary poisoning exposure via terrestrial invertebrates. The calculations show that 

RQs are not significantly different for small and large adult CRLFs. The RQ for smaller 

frogs will be used for the purpose of determining direct effects to the CRLF from 

secondary poisoning exposure. 

RQ = 

CRLFbwkg

aimg

bodyweightCRLF

day

invertkg consumed

invertkg

aimg

__

_

) __

_

_ ( ∗ ÷

RQ (for 50g frog) = 

kgmg

kgmg kg day bwkg

/1

∗ ÷ _05.0)/7.7*000077.0(/143.0 =0.0017

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RQ (for 100g frog) = 

kgmg

kgmg kg bwkgday

/1

∗ ÷ _1.0)/7.7*000077.0(/143.0 =0.00085 

Based upon the RQ values calculated above, aldicarb CRLF secondary poisoning via 

earthworms contaminated with aldicarb is below the Agency LOC (LOC > 0.1). 

92
5.3 Final Effects Determination 

The following tables (25-27) summarize the effects determination by Recovery Unit, 

based upon the most conservative of the effects determinations, sugar beets, with the 

assumption of on-site exposure of CRLF and that on-site terrestrial invertebrates are a 

critical component of the diet of the CRLF and its critical habitat. Summation by specific 

crops, more specific to on-site usage, is provided in text following these tables. 

Table 25 Summarizes the effects determinations for direct effect of aldicarb to any of the life-stages of 

the CRLF in Eight Recovery Units. 

The life stages include aquatic (eggs, larvae, tadpoles) and terrestrial phase of CRLF (young and adult frogs). The 

assessment endpoints are growth, survival, and reproduction of CRLF individuals.

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

2 NLAA Based on lack of spatial overlap with Action Area (AA), frog habitat, and 

occurrence sightings, CAL DPR PUR data despite LOC exceedances to 

CRLF 

3 NLAA Based on lack of spatial overlap with Action Area (AA), frog habitat, and 

occurrence sightings, CAL DPR PUR data despite LOC exceedances to 

CRLF 

4 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

5 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF; 

6 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

7 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF 

8 LAA Based on spatial overlap with frog habitat and occurrence information, CAL 

DPR PUR data, and direct effects for both phases of CRLF 

* Summarize the effects determination by Recovery Unit, based upon the most conservative of the effects 

determinations. Summation by specific crops, more specific to on-site usage, is provided in the following 

text. 

93
Table 26 Summarizes the effects determinations for indirect effect of aldicarb to any of the lifestages of the CRLF in Eight Recovery Units. 

The life stages include aquatic (eggs, larvae, tadpoles) and terrestrial phase of CRLF (young and adult 

frogs). The indirect effects include effects to habitat including effect to primary productivity, prey, and 

riparian habitat. 

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

2 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF food 

sources 

3 NLAA Based on lack of spatial overlap with AA 

4 NLAA Based on lack of spatial overlap with AA 

5 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

6 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

7 NLAA Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to CRLF food 

sources 

8 LAA Expected indirect effects to CRLF via adverse effects to CRLF prey sources. 

* Summarize the effects determination by Recovery Unit, based upon the most conservative of the effects 

determinations. Summation by specific crops, more specific to on-site usage, is provided in the following 

text. 

Table 27 Summarizes the effects determinations for effects to the critical habitat the CRLF in 

recovery units one thru eight. 

The effects entail effects to growth and survival of terrestrial and aquatic plant and animal components. 

Recovery 

Unit 

Effects 

Determination 

Basis for Effects Determination Conclusion 

1 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

2 NE No designated critical habitat in Recovery Unit (RU) 

3 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat 

4 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat 

5 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

6 LAA Based on direct effects to terrestrial and aquatic animals which are 

components of the critical habitat. 

7 NE Based on lack of spatial overlap with AA, frog habitat, and occurrence 

sightings, CAL DPR PUR data despite LOC exceedances to animals 

components of the critical habitat.. 

8 NE No designated critical habitat in RU 

94
Aquatic Phase CRLF and Critical Habitat 

No Effect 

Soybean (in-furrow and/or positive displacement applications only), Citrus, and 

Sorghum 

Citrus, sorghum and soybean (but only when applied in-furrow with immediate soil 

incorporation or in-furrow with positive displacement) uses were determined to have “no 

effect” directly or indirectly on the aquatic-phase of the CRLF or the aquatic-phase of the 

critical habitat. This determination was based on the results of the risk assessment where 

all direct and indirect assessment endpoints of the aquatic-phase CRLF and its aquaticphase critical habitat were either below endangered LOCs (i.e., no exceedences of LOCs 

for aquatic animals) or judged based on the best available information to not be affected 

(i.e., off-field terrestrial plant components of critical habitat and aquatic plants judged to 

not be affected, based on estimated exposure concentrations that were lower than a ‘no 

observable effect’ level for limited toxicity data). Although application rates for citrus 

are fairly high (4.95 lb a.i./A) and incorporation efficiency only 85%, low rainfall rates 

and other factors in citrus production areas of California contribute to relatively low 

aquatic exposure and risk estimates. For Sorghum use, low application rates (1 lb a.i./A) 

and high incorporation efficiency (in-furrow application, 99%) contribute to minimal 

aldicarb residues being exported into surface waters or off-field terrestrial habitat. When 

compared to less efficient application methods with approximately 85% soil 

incorporation (e.g., banded applications), the use of more efficient application techniques 

(e.g., in-furrow, positive displacement) results in higher incorporation efficiencies (99%), 

and concomitant exposure estimations well below LOCs for soybean. 

Ornamentals (container grown) indoors 

There is no exposure pathway by which aldicarb applied to ornamentals in containers 

grown indoors may reach and expose the aquatic-phase of the CRLF or its critical habitat 

(i.e., no run-off, no atmospheric transport, no CRLF or its critical habitat indoors). 

Therefore this use is determined to have “no effect” on the aquatic-phase of the CRLF or 

its critical habitat. 

May Affect but Not Likely to Adversely Affect 

Ornamentals (field grown—no containers) and Sweet Potato 

Aldicarb registered uses on containerless field-grown ornamentals and sweet potato were 

identified as “may affect” because the acute RQ values for aquatic invertebrates exceeded 

the acute endangered LOC, the chronic RQ values exceeded the chronic LOC, and the 

chronic RQ for aquatic invertebrates exceeded the chronic LOC for sweet potato use. 

However, based on consideration of a number of factors, the level of effect both directly 

and indirectly to the aquatic-phase of the CRLF and its aquatic critical habitat for these 

assessment endpoints was determined to be discountable. Off-site terrestrial plant 

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components of critical habitat and aquatic plants were judged to not be affected based on 

the best available information that estimated exposure concentrations were lower than ‘no 

observable effect levels’ for limited toxicity data. Therefore, aldicarb uses on 

containerless field-grown ornamentals and sweet potato were determined to “not likely 

adversely affect” the aquatic-phase of the CRLF and its critical habitat. 

Direct effects to the aquatic-phase of the CRLF were considered discountable because the 

acute endangered RQ values did not exceed the endangered species LOC; while the 

chronic RQ value of 1 was exceeded, this exceedence was considered not significant and 

essentially indistinguishable from the no observable effect level. For example, the 

chronic RQ of 1.1 for containerless field grown ornamentals based on significant figures 

is not distinguishable from 1 (i.e., EEC/NOAEC = 0.49/0.46 ≅ 0.5/0.5 = 1), the level 

equivalent to no observable effects. In addition, ornamental usage is not extensive, and 

any potential impact on a water body adjacent to an application area would likely be 

minor, fleeting, and spatially very limited. 

Loss of aquatic fish or invertebrates as dietary resources was considered discountable 

based on several factors affecting the frequency and duration of exposure and the 

magnitude of effect. For example, both of these uses are limited to a single application 

per year, with sweet potato application occurring at plant and ornamentals occurring at 

any time prior to or during an infestation but again limited by the label to a single 

application per year. Therefore, any potential impact on a water body adjacent to an 

application area would likely be minor and fleeting. The acute endangered LOC for fish 

is not exceeded for either use. Although the chronic LOC is exceeded, as discussed in the 

preceding paragraph these exceedences are essentially equivalent to the no observable 

adverse effect level. Additionally, other fish species are not as sensitive (e.g., fathead 

minnow), so any potential impact would be limited in both magnitude and number of 

species involved. For aquatic invertebrates, while the acute endangered LOC was 

exceeded, the likelihood that an individual would be affected for the most sensitive 

species was one-in-over a million (based on default slope of 4.5). Additionally, based on 

the invertebrate species sensitivity distribution, over 80 percent of the aquatic 

invertebrates would be even less sensitive. The chronic LOC was not exceeded for the 

ornamentals and was at the LOC of 1 for sweet potato use, which is equivalent to no 

observable effect on invertebrates. 

Ornamentals (container grown) outdoors 

Outdoor container grown ornamental use was considered to “not likely adversely affect” 

the aquatic-phase CRLF or its aquatic-phase critical habitat. This determination was 

based on the determination for containerless field grown ornamentals used as a surrogate. 

Surface water exposure concentrations are expected to be lower than that for 

containerless field grown ornamentals. This reduction is attributable to containers which 

are expected to physically reduce run-off of aldicarb and its major toxic degradates and 

lower application rates as compared to containerless field grown ornamentals. In 

addition, ornamental usage is not extensive, and any potential impact on a water body 

adjacent to an application area would likely be minor, fleeting, and spatially very limited. 

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May Affect and Likely to Adversely Affect 

Dried Beans, Soybean (banded applications), Peanut, Pecans, Cotton, Alfalfa, 

Sugar beet 

Aldicarb registered uses on dried beans, soybean, peanut, pecan, cotton, alfalfa, and sugar 

beet were identified as “may affect” and “likely to adversely affect” the CRLF directly 

because both the acute endangered LOC and chronic LOC were exceeded for amphibian 

assessment endpoints (fish used as surrogate) and indirectly because fish and aquatic 

invertebrate acute and chronic LOC values were exceeded. 

It should be noted that for many of these crops, use of more efficient application 

techniques (99% vs. 85% incorporation) would result in exposure estimations well below 

the LOC for most categories (see Table 12). Although this might be impractical or 

impossible for some current uses (e.g., peanut application post-pegging, cotton 

application at bloom, pecan), in other cases (e.g., soybean, dried bean) achieving an 

incorporation efficiency of 99% results in acceptable levels of risk should be possible 

with appropriate application techniques. 

Terrestrial Phase CRLF and Critical Habitat 

No Effect 

Ornamentals (container grown) indoors 

There is no exposure pathway by which aldicarb applied to ornamentals in containers 

grown indoors may reach and expose the terrestrial-phase of the CRLF or its terrestrial 

critical habitat (i.e., no run-off, no atmospheric transport, no CRLF or its critical habitat 

indoors). Therefore this use is determined to have “no effect” on the aquatic-phase of the 

CRLF or its critical habitat. 

May Affect but Not Likely to Adversely Affect 

Off-site All Outdoor Uses 

Off-site exposure for all outdoor registered uses was identified as “may affect” because 

an individual terrestrial-phase CRLF that ingested a granule transported off-site in the gut 

(incidental ingestion) or on the fur of a small mammal would potentially be effected. All 

other off-site exposure of the terrestrial-phase CRLF (i.e., bioaccumulation in terrestrial 

invertebrates or mammalian dietary items) and its critical habitat (i.e., loss of dietary 

resources, riparian or upland plants) to aldicarb and its major toxic residues are below 

LOCs. Because exposure of a terrestrial-phase CRLF to a granule carried in a smallmammal off-field was considered unlikely and no other off-site exposure of the 

terrestrial-phase CRLF or its critical habitat were above LOCs, exposure off-site for all 

97
outdoor uses was considered discountable and therefore “not likely to adversely affect” 

either directly or indirectly the terrestrial-phase of the CRLF or its critical habitat. 

Risks to terrestrial environments outside the zone of application for granular aldicarb are 

mainly limited to re-deposition of aldicarb residues in lower-lying areas affected by 

aldicarb runoff from nearby fields. However, calculations of the approximate amount of 

aldicarb potentially deposited as a result of registered aldicarb use (based on the highest 

risk scenario, cotton at 5 lbs a.i./A) indicate that concentrations (~ 10-6 mg a.i./kg soil) 

would be several orders of magnitude below those that would exceed the LOC. 

Exposure off-site of a CRLF to a granule in the gut or on the fur of small mammal was 

considered unlikely because it is doubtful that the series of events needed to coincide for 

an actual exposure event to occur would be frequent, if they occurred at all. First, 

aldicarb is applied to most crops once per year, and infrequently for the others (i.e., 

cotton at most three times and sugar beets and peanuts at most two times per year). 

Second, the duration of the integrity of a granule in the field is limited as it readily 

dissolves in water⎯ irrigation or rainfall dissolves the granule and moves it down into 

the soil profile. Therefore the window of opportunity for a small mammal to be exposed 

on field to a granule (in terms of subsequent exposure of a CRLF to a granule) is limited 

to a few days a year. While it is considered likely that some small mammals may be 

exposed to aldicarb during this window, it is unlikely that a significant number of small 

mammals would then subsequently move off-site, and not die before encountering a 

CRLF (biological description does not indicate it feeds on carrion). 

May Affect and Likely to Adversely Affect 

On-site All Crops 

On-site exposure for all outdoor registered uses was identified as “may affect” and 

“likely to adversely affect” the terrestrial-phase of the CRLF because the acute LOC was 

exceeded for the direct amphibian measurement endpoint (birds) and for indirect effects 

(i.e., loss of small mammals, and on-site terrestrial invertebrates) for all uses. 

Bioaccumulation was demonstrated to not be a pathway of concern. This effects 

determination is based on the assumption that terrestrial-phase CRLF will come onto the 

treated site and that on-site resources are considered a critical component that supports 

CRLF (i.e., invertebrates and insects on the field that the farmer is trying to eliminate are 

considered critical to the support of the CRLF) and that the field is considered part of the 

critical habitat. A number of the uses are applied on fields that have been prepared for 

planting and should be relatively barren of cover for the CRLF at the time of aldicarb 

application (i.e., sorghum, sweet potato, dried bean, and soybean). 

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 

98
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 adverse modification to critical 

habitat. 

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6. Uncertainties 

6.1 Exposure Assessment Uncertainties 

6.1.1 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 insecticide resistance, timing of applications, cultural 

practices, and market forces. 

6.1.2 Modeling Inputs 

The standard ecological water body scenario (EXAMS pond) used to calculate potential 

aquatic exposure to pesticides is intended to represent conservative estimates, and to 

avoid underestimations of the actual exposure. The standard scenario consists of 

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 have higher peak EECs than the EXAMS pond. These water bodies will be 

either smaller in size or have larger drainage areas. Smaller water bodies have limited 

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. 

The Agency acknowledges that there are some unique aquatic habitats that are not 

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 representative 

of exposure to aquatic-phase CRLFs. In addition, the Services agree that the existing 

100
EXAMS pond represents the best currently available approach for estimating aquatic 

exposure to pesticides (USFWS/NMFS 2004). 

6.1.2.1 Action Area 

An example of an important simplifying assumption that may require future refinement is 

the assumption of uniform runoff characteristics throughout a landscape. It is well 

documented that runoff characteristics are highly non-uniform and anisotropic, and 

become increasingly so as the area under consideration becomes larger. The assumption 

made for estimating the aquatic Action Area (based on predicted in-stream dilution) was 

that the entire landscape exhibited runoff properties identical to those commonly found in 

agricultural lands in this region. However, considering the vastly different runoff 

characteristics of: a) undeveloped (especially forested) areas, which exhibit the least 

amount of surface runoff but the greatest amount of groundwater recharge; b) 

suburban/residential areas, which are dominated by the relationship between 

impermeable surfaces (roads, lots) and grassed/other areas (lawns) plus local drainage 

management; c) urban areas, that are dominated by managed storm drainage and 

impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused 

runoff (especially with row crops), a refined assessment should incorporate these 

differences for modeled stream flow generation. As the zone around the immediate 

(application) target area expands, there will be greater variability in the landscape; in the 

context of a risk assessment, the runoff potential that is assumed for the expanding area 

will be a crucial variable (since dilution at the outflow point is determined by the size of 

the expanding area). Thus, it important to know at least some approximate estimate of 

types of land use within that region. Runoff from forested areas ranges from 45 – 

2,700% less than from agricultural areas; in most studies, runoff was 2.5 to 7 times higher 

in agricultural areas (e.g., Okisaka et al., 1997; Karvonen et al., 1999; McDonald et al., 

2002; Phuong and van Dam 2002). Differences in runoff potential between 

urban/suburban areas and agricultural areas are generally less than between agricultural 

and forested areas. In terms of likely runoff potential (other variables – such as 

topography and rainfall – being equal), the relationship is generally as follows (going 

from lowest to highest runoff potential): 

Three-tiered forest < agroforestry < suburban < row-crop agriculture < urban. 

There are, however, other uncertainties that should serve to counteract the effects of the 

aforementioned issue. For example, the dilution model considers that 100% of the 

agricultural area has the chemical applied, which is almost certainly a gross overestimation. Thus, there will be assumed chemical contributions from agricultural areas 

that will actually be contributing only runoff water (dilutant); so some contributions to 

total contaminant load will really serve to lessen rather than increase aquatic 

concentrations. In light of these (and other) confounding factors, Agency believes that 

this model gives us the best available estimates under current circumstances. 

101
6.2.1.2 Aquatic Exposure Estimates 

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 a 

farmer’s field on a day-to-day basis. It considers factors such as rainfall and plant 

transpiration of water, as well as how and when the pesticide is applied. It has two major 

components: hydrology and chemical transport. Water movement is simulated by the use 

of generalized soil parameters, including field capacity, wilting point, and saturation 

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 expected to be exceeded in the environment 

approximately 90 percent of the time. Mobility input values are chosen to be 

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. 

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. 

6.1.2.3 PRZM Modeling Inputs and Predicted Aquatic Concentrations 

The inputs selected for use in the PRZM model were based upon the best available 

information regarding persistence, mobility, and formation and dissipation of major 

degradates. Nevertheless, there is intrinsic uncertainty related to the quality of data that 

were used to determine these parameters. In addition, there are issues involved in 

selecting appropriate incorporation efficiencies. Agency assumes (as stated in the 2006 

RED) that the incorporation efficiency for granular aldicarb leaves 15% on the surface, 

102
except for certain highly efficient application methods – specifically: 1) in-furrow 

applications, and; 2) banded applications that include simultaneous soil incorporation 

(and that also make use of state-of-the-art applicator tools, such as positive displacement) 

– for which an incorporation efficiency leaving only 1% available at the surface is 

assigned. Both sets of model results are presented in this document (Tables 11 & 12). 

The Agency believes that these data and input values are the best available and were 

adequate for the purposes of this (and other) aldicarb assessments. 

6.3 Effects Assessment Uncertainties 

6.3.1 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 pesticidal active 

ingredients, such as aldicarb, that act directly (without metabolic transformation) because 

younger age classes may not have the enzymatic systems associated with detoxifying 

xenobiotics. Insofar 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 California Red Legged Frog. 

6.3.2 Use of Acute Freshwater Invertebrate Toxicity Data for the Midge 

The initial acute risk estimate for freshwater invertebrates was based on the lowest 

toxicity value from Chironomus tetans studies, which showed a greater sensitivity than 

other species that are equally or more likely to be part of the diet of an adult CRLF. 

Therefore, acute RQs based on the most sensitive toxicity endpoint for freshwater 

invertebrates may represent an overestimation of potential direct risks to freshwater 

invertebrates and indirect effects to the California Red Legged Frog via a reduction in 

available food. 

6.3.3 Extrapolation of Long-term Environmental Effects from Short-Term 

Laboratory Tests 

The influence of length of exposure and concurrent environmental stressors to the 

California Red Legged Frog (i.e., urban expansion, habitat modification, decreased 

quantity and quality of water in CRLF habitat, predators, etc.) will likely affect the 

species’ response to aldicarb. Additional environmental stressors may decrease the 

CRLF’s sensitivity to the insecticide, although there is the possibility of 

additive/synergistic reactions. Timing, peak concentration, and duration of exposure are 

critical in terms of evaluating effects, and these factors will vary both temporally and 

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spatially within the action area. Overall, the effect of this variability may result in either 

an overestimation or underestimation of risk. However, as previously discussed, 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. 

6.3.4 Residue Levels Selection 

The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide 

residues in wildlife dietary items. These residue assumptions are believed to reflect a 

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 plants in the case of grass and forage 

sampling. 

6.3.5 Dietary Intake 

It was assumed that ingestion of food items in the field occurs at rates commensurate 

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. Environmental Protection Agency, 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 

is comparable with consumption during laboratory testing. In the screening process, 

exposure may be underestimated because metabolic rates are not related to food 

consumption. 

6.3.6 Sublethal Effects 

For an acute risk assessment, the screening risk assessment relies on the acute mortality 

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 assessment is exercised on a 

case-by-case basis and only after careful consideration of the nature of the sublethal 

effect measured and the extent and quality of available data to support establishing a 

104
plausible relationship between the measure of effect (sublethal endpoint) and the 

assessment endpoints. 

 

6.3.7 Location of Wildlife Species 

For this baseline terrestrial 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. 

6.4 Assumptions Associated with the Acute LOCs 

The risk characterization section of this endangered species assessment includes an 

evaluation of the potential for individual effects. The individual effects probability 

associated with the acute RQ is based on the mean estimate of the slope and an 

assumption of a probit dose response relationship for the effects study corresponding to 

the taxonomic group for which the LOCs are exceeded. 

Sufficient dose-response information was not available to estimate the probability of an 

individual effect on freshwater fish or freshwater invertebrates (two of the dietary food 

items of the CRLF). Acute ecotoxicity data from the bluegill sunfish and midge were 

used to derive RQs for freshwater fish and invertebrates. Based on a lack of doseresponse information for both species, the probability of an individual effect was 

calculated using the lowest and highest probit dose response curve slope value (2 and 9, 

respectively) to bound probability of individual effect to prey for technical grade 

aldicarb. It is unclear whether the probability of an individual effect for freshwater 

animals would be higher or lower, and therefore, the lowest slope value was chosen when 

effects determinations were made for direct effects to the prey of the CRLF. 

6.5 Usage Uncertainties 

County-level usage data were obtained from California’s Department of Pesticide 

Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002 – 

2005) were included in this analysis because statistical methodology for identifying 

outliers, in terms of area treated and pounds applied, was provided by CDPR for these 

years only. No methodology for removing outliers was provided by CDPR for 2001 and 

earlier pesticide data; therefore, this information was not included in the analysis because 

it may misrepresent actual usage patterns. 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. 

The CPDR PUR data does not include home owner applied pesticides; therefore, 

residential uses are not likely to be reported. As with all pesticide use data, there may be 

105
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. 

106
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