UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

September 15, 2015 

MEMORANDUM 

Subject: Registration Review: Ecological Risk Assessment for Terbufos 

PC Code: 105001 

DP Barcode: 407573 

From: MichaelLowit, Ph.D.,Ecologist ~~/~ 9/t)(<"° _ Faruque Khan, Ph.D., Senior Fate Scientist ~L~-' c; Ir r/r rSujatha Sankula, Ph.D., Branch Chief ~ ~ ~-er\ I~ 1-SEnvironmental Risk Branch I ~v-....__ - Ck :.;;.>? _ 

Environmental Fate and Effects Division (7 07P) 

To: Matthew Manupella, Chemical Review Manager 

Tom Myers, Team Leader 

Kevin Costello, Branch Chief 

Risk Management and Implementation Branch II 

Pesticide t..e-Evaluation Division (7508P) 

The Environmental Fate and Effects Division (EFED) conducted an ecological risk assessment 

for the Registration Review of terbufos, a systemic organophosphate used as an insecticide and 

nematicide to control a variety of pests on com, sorghum, and sugar beet. The assessment is 

attached. 
1

REGISTRATION REVIEW

ECOLOGICAL RISK ASSESSMENT AND 

EFFECTS DETERMINATION

Terbufos

CAS Number: 13071-79-9

PC Code: 105001

Prepared by:

Michael Lowit, Ph.D., Ecologist

Faruque Khan, Ph.D., Senior Fate Scientist

Reviewed by:

Edward Odenkirchen, Ph.D., Senior Science Advisor

Stephen Wente, Ph.D., Biologist

Meghan Radtke, Ph.D., Biologist

Sujatha Sankula, Ph.D., Branch Chief

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch I

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460
2

I. Executive Summary

Terbufos is a systemic organophosphate insecticide-nematicide used to control a variety of pests 

on corn (field and sweet corn), grain sorghum, and sugar beet. Terbufos was first registered in 

1974 and was most recently reviewed in 1999 (USEPA, 1999; reregistration eligibility decision 

document (RED)). Previous risk assessments concluded that ecological risks to aquatic and 

terrestrial organisms were of concern to the Agency. Specifically, the fish kill incidents 

associated with the use of terbufos on corn was a major consideration in the risk mitigation plan 

outlined in the 2001 Interim Reregistration Eligibility Decision (IRED; USEPA, 2001) for 

terbufos. Mitigation efforts included a reduction in the application rate for sorghum, a label 

requirement for maintaining setbacks and vegetative buffers adjacent to terbufos treated areas, 

the removal of the “over the top” application for European corn borer control on corn, and a 

label change for banded applications on corn (use a 7 inch band over the row, in front of the 

press wheel, and incorporate into the top 1 inch of soil).

The relatively high vapor pressure (3.16E-04 mm Hg at 25°C) and Henry's Law Constant (2.46

E-05 atm m3

/mol) of terbufos suggest that some of the parent compound will dissipate by 

volatilization from moist soil and water bodies into the atmosphere. Terbufos is also susceptible 

to degradation and transformation by both abiotic and biotic processes. Terbufos is moderately 

mobile to slightly mobile in soil. Three major degradates were identified in the environmental 

fate studies: terbufos sulfoxide, terbufos sulfone, and formaldehyde. Terbufos sulfoxide and 

terbufos sulfone have low soil partition coefficient (Kd) values ranging from 0.40 to 2.93 mL/g 

and DT50s of 136 to 174 days in soil suggesting that they are more mobile and persistent than 

terbufos in the environment.

Terbufos is very highly toxic to fish, aquatic invertebrates, and mammals, highly toxic to birds, 

and moderately toxic to bees on an acute basis. Chronic effects are observed in both aquatic 

and terrestrial animals at low concentrations. Some effects are observed in plants; however, 

toxicity to plants is relatively low compared to animals. Available data indicate that two major 

degradates (terbufos sulfoxide and terbufos sulfone) are similar to terbufos in toxicity; thus, 

they are considered degradates of concern. Field data show avian and mammalian mortality 

associated with terbufos use. In addition, there are a large number of reported fish kills 

attributed to the use of terbufos. 

This assessment considers the most up to date toxicology and fate data, uses current exposure 

models including those exploring pathways not quantitatively assessed in past risk assessments 

(e.g., drinking water and inhalation exposure), and considers the most recent labels (including a 

newer formulation, 20G), incident information, and monitoring data. Based on the latest 

information, conclusions of this assessment are substantially similar to those of the RED. An 

acute and chronic risk concern is expected for direct effects to both listed and non-listed species 

of birds, mammals, fish, aquatic invertebrates, and terrestrial invertebrates. The Agency does not 

currently have the capability to quantitatively assess the effectiveness of the required vegetative 

buffers; however, based on a review of research studies it was hypothesized that buffers may 

reduce the loading of total toxic residues of terbufos in aquatic systems between 50% and 90%. 

Although loading may be reduced up to 90%, the overall risk concerns for fish and aquatic 

invertebrates remain because risk quotients (RQs) remain above the levels of concern (LOC)

after accounting for those reductions. Previous assessments did not consider risk to plants due to 
3

a lack of data. This assessment concludes that there is not a risk concern for direct effects to 

aquatic and terrestrial plants. In conclusion, consistent with past assessments there is a risk 

concern for aquatic organisms and terrestrial wildlife including listed species for the labeled uses 

of terbufos. 

Table 1. Summary of Direct and Indirect Effects Associated with Registered Uses of 

Terbufos

Taxon

Risk Concern for

Direct Effects?

Risk Concern for 

Indirect Effects to 

Non-Listed Listed Listed Species?

Birds, reptiles, and terrestrial-phase amphibians Yes Yes Yes

Mammals Yes Yes Yes

Terrestrial invertebrates (honeybees)1 Yes Yes Yes

Terrestrial (upland and semi-aquatic) plants – monocots No No Yes

Terrestrial (upland and semi-aquatic) plants – dicots No No Yes

Freshwater fish and aquatic-phase amphibians Yes Yes Yes

Marine/estuarine fish Yes Yes Yes

Freshwater invertebrates Yes Yes Yes

Marine/estuarine invertebrates Yes Yes Yes

Aquatic vascular plants No No Yes

Aquatic non-vascular plants No N/A N/A 1 Honeybee is used as a surrogate for terrestrial invertebrates. Honeybees were not assessed quantitatively due to a 

lack of oral (dietary) toxicity data for adults or larvae; however, risk is expected for terrestrial invertebrates given 

that terbufos is an insecticide.

N/A = Not applicable. There are no aquatic non-vascular plant species that are listed at this time. 

II. Use Characterization and Methods of Application

Terbufos is used on corn, sorghum, and sugar beet to control a variety of insects and nematodes. 

Use data from 2004-2012 indicate an annual average domestic use of approximately 740,000 

pounds of terbufos active ingredient (USEPA, 2014). Terbufos is applied in bands, in-furrow, or 

knifed-in. All uses require ground application and soil incorporation to a specified depth 

depending on the use. The timing of application is at-planting, at-bedding, postemergence, or at 

cultivation. Terbufos is applied only one time a year for all uses. The labels provide rates in 

terms of lb ai/A and lb ai/1000 ft row. On a per acre basis, the maximum application rate for 

corn is 1.3 lb ai/A except for a Special Local Need (SLN) registration (NC920001) in North 

Carolina that allows use on corn up to 2.6 lb ai/A. The maximum application rates for sorghum 

and sugar beet are 1.695 lb ai/A and 1.96 lb ai/A, respectively. Use information was obtained 

from the chemical profile produced by the Biological and Economic Analysis Division (BEAD). 

EFED used application scenarios that result in maximum exposure from a given use for the risk 

assessment. 

In addition to the technical product, there are three registered end-use granular formulations: 

Counter®CR (EPA Reg. No 241-314), Counter®15G (EPA Reg. No. 5481-545), and 

Counter®20G (EPA Reg. No. 5481-562).

As a result of the terbufos IRED (USEPA, 2001), setbacks and buffers were added to terbufos 

product labels. The following distances are to be maintained: (1) a 500 ft vegetative buffer 

between the treated area and surface water on neighboring land, (2) a 500 ft vegetative buffer 
4

between a standpipe drain outlet and surface water on neighboring land, (3) a 66 ft setback 

between the treated area and entry points to surface water bodies on non-highly erodible soils 

and a 300 ft setback on highly erodible soils, (4) a 66 ft setback between the treated area and 

standpipes on terraced fields as well as a 66 ft vegetative buffer between the tile outlet and 

surface water bodies, and (5) a restriction on loading, rinsing, and washing equipment within 300 

ft of surface water bodies or within 50 ft of wells unless conducted on an impervious surface. All 

setbacks must be planted with a crop or seeded with grass or other suitable cover. All vegetative 

buffers must be seeded with grass or other suitable cover.

III. Summary of Environmental Fate

3.1 Terbufos

Selected physical, chemical and environmental fate properties of terbufos are listed in Table 2. 

The solubility of terbufos in water is 5.4 mg/L at 25oC. The relatively high vapor pressure 

(3.16E-04 mm Hg at 25°C) and Henry's Law Constant of 2.46 E-05 atm m3

/mol suggest that 

terbufos will dissipate by diffusion from moist soil and water into the atmosphere, but the 

amount that may volatilize will vary depending on the use site conditions and the application

method. Volatilization may be a major dissipation route for terbufos that remains on the soil 

surface after incorporation. However, vapor-phase terbufos is susceptible to atmospheric 

degradation by reaction with photochemically-produced hydroxyl radicals; the half-life in air is 

estimated to be 0.53 hours (EPISUITE 4.1). Terbufos residue were not detected in rain or snow 

samples monitored in several states (IA, IN, NY, OH and WV) (Majewski and Capel, 1995). 

Terbufos is susceptible to transformation by both abiotic and biotic processes. All DT50 values 

were calculated using nonlinear regression and single first order (SFO), double first order in 

parallel (DFOP), or intermediate order rate equation (IORE) equations (USEPA, 2012a).

Appendix A provides estimated DT50s for the submitted environmental fate studies. The 

hydrolysis half-life for terbufos is less than 2 days in the typical range of environmental pH 

values (5, 7, and 9). In another study, terbufos hydrolyzed with a half-life of less than 2 weeks at 

pH 4, 7, and 9. However, in an aerobic aquatic metabolism study, terbufos degraded in the water 

column with a half-life of less than 2 days, which is consistent with the results from the recent 

hydrolysis study (MRID 44862502). The metabolic half-life of terbufos in aerobic soil ranges 

from 5.9 to 10.2 days and in anaerobic soil is 67.5 days. Kd values ranging from 5.42 to 14.6 

mL/g suggest that terbufos is moderately mobile to slightly mobile in soil, according to a 

classification scheme of the Food and Agricultural Organization of the United Nations (USEPA, 

2006a). 

The terrestrial field data indicate that terbufos dissipated in the field with half-lives of 6.01 days 

in loamy soil from Illinois, 56.8 days in sandy loam soil from Colorado, and 22.2 days in sandy 

loam from California. Except for the Colorado soil, these half-lives are comparable to findings 

from the aerobic soil metabolism study discussed above (DT50s <11 days). Data from the open 

literature (Felsot, et al., 1982) reported field half-lives of 11-16 days for terbufos in silt loam and 

silty clay loam soils when terbufos was applied at a rate of 1.0 lb ai/A.
5

The log Kow (n-Octanol–water partition coefficient) of 4.71 indicates potential bioaccumulation 

of terbufos in aquatic organisms. The maximum terbufos bioaccumulation factors in bluegill 

sunfish were 320, 940, and 680X in edible tissues, non-edible tissue, and whole fish, 

respectively. At the end of the 14-day depuration period, the reduction in residues was 84% for 

fillet tissue and 93% for visceral tissue and whole fish. The single first order elimination rate 

was calculated as KT = 0.31 d-1 (DT50 = 2.24 days). Two major metabolites were identified: 

terbufoxon (CL94221) and a methane related compound (CL202474).

Table 2. Physical, Chemical and Environmental Fate Properties of Terbufos

Property Value Source 

(Classification)

Common name Terbufos MRID 41297901 

CAS Registry No. 13071-79-9 ---

PC Code 105001 ---

Chemical name (CAS) S-[[(1,1-dimethylethyl)thio]methyl]O,OdiethylphosphorodithioateMRID 41297901

SMILES notation CCOP(=S)(OCC)SCSC(C)(C)C EPISUITE 4.11

IUPAC name S-tert-butylthiomethyl O,O-diethyl 

phosphorodithioate

TOXNET

Synonyms CL 92100, AC 92100 MRID 41373604 

and 44862501

Structure TOXNET

Molecular formula C9H21O4P1S3 MRID 41297901

Physical and Chemical Properties

Molecular weight 288.4 MRID 41297901

Physical state Clear liquid MRID 41049502 

(Acceptable)

Vapor pressure 3.16 x 10-4 mm Hg (25oC)

6.98 x 10-4 mm Hg (35oC)

12.4 x 10-4 mm Hg (45oC)

MRID 41049502 

(Acceptable)

Henry’s Law constant 2.22E-05 atm m3/mol USEPA, 2009
6

Property Value Source 

(Classification)

Specific gravity/density 1.11g/ml @ 20oC MRID 41049502 

(Acceptable)

Solubility in water 5.4 mg/L @ 25oC in distilled water

5.6 mg/L in water solution buffered at pH 7

4.5 mg/L in water solution buffered at pH 10

MRID 41049502 

(Acceptable)

log Kow 4.71 MRID 41049502 

(Acceptable)

Laboratory accumulation in fish

bioaccumulation factor (BCF)

(Lepomis macrochirus)

320X in edible tissues

940X non-edible (viscera) tissues

680X whole fish

At the end of the 14-day depuration period, the 

reduction in residues was 84% for edible tissue, 

93% for whole fish, and 93%for visceral tissue.

MRID 41373606 

and 41773605

(Acceptable)

Environmental Fate Properties

Hydrolysis half-life

pH = 4

pH = 7

pH = 9

 pH = 5

pH = 7

 pH = 9

 

11.2 days (SFO) @ 25°C

11.4 days (SFO) @ 25°

C

13.1 days (SFO) @ 25°

C

2.52 days (SFO) @ 20°

C

[1.8 days (SFO) @ 25°

C]2

2.17 days (SFO) @ 20°

C

[1.5 days (SFO) @ 25°

C] 2

2.56 days (SFO) @ 20°

C

[1.8 days (SFO) @ 25°

C] 2

Major Degradate

Formaldehyde (Max 96.1% @ day 1.6; pH 9.0)

MRID 00087694

(Acceptable)

MRID 44862501

(Acceptable)

Photolysis half-life in air 0.53 hours (12 hour day; 1.5E6 OH/cm3) EPISUITE4.11

Photolysis half-life in water 1.77 days (SFO) @ 25°C

Major Degradate

Formaldehyde (Max 71.9% @ day 6)

MRID 00161567 

and 41181101

(Supplemental)

Aerobic soil metabolism half-life 

(25 °C)

5.85 days (silt loam) (SFO) @ 25 °C

10.2 days (silt loam) (SFO) @ 25 °C

Major Degradates

Terbufos Sulfoxide (Max 52.3 % @ day 30)

Terbufos Sulfone (Max 20.1 % @ day 60)

CO2 (Max 46 % @ day 365)

MRID 00156853 

and 41749801

(Acceptable)
7

Property Value Source 

(Classification)

Anaerobic soil metabolism half-life 67.5 days (Silt loam) (SFO) @ 25 °C

Volatile organic residue 38.6% @ day 60

Major degradates

Terbufos Sulfoxide (Max 10.5% @ day 15)

CO2 (Max 53 % @ day 60)

MRID 41749801

(Acceptable)

Aerobic aquatic metabolism half-life 

for total system 

Total System

Loam sediment

24.2 days (IORE (20±2°C)

[19.7days (IORE) @ 25°

C] 2

Sand Sediment

[3.66 days (SFO) @ (20±2°C)] 3

[2.6 days (IORE) @ 25°

C] 2,3

Volatile organic residue (41.5% @ day 30)

Major degradates

Terbufos Sulfoxide (Max 11% @ day 100)

CO2 (Max 53 % @ day 100)

MRID 44672004

(Supplemental)

Aerobic aquatic metabolism half-life 

in aqueous phase (natural pond water)

0.762 days (IORE) @ 20±2°C

[0.6 days (IORE) @ 25°C] 2

1.03 days (SFO) @ 20±2°C

[0.8 days (IORE) @ 25°

C] 2

Major Degradate

Degradate A (unidentified) (Max 33.8% @ day 2)

CO2 (Max 43.6% @ day 30)

MRID 44862502

(Supplemental)

Soil adsorption coefficient 

Kd (L/kg)

Adsorption4

Kd (L/kg)

5.42 (AR Loamy sand)

11.4 (IN Silt loam)

13.0 (NJ Sandy loam)

14.6 (WI Loam)

MRID 41373604

(Acceptable)

Terrestrial field dissipation half-life 6.01 days (IORE) in Arcola, IL

56.8 days (IORE) in Greeley, CO

22.2 days (IORE) in Hanford, CA

No major degradates were reported

MRID 00087708

(Acceptable)

MRID 00087706

(Acceptable)

MRID 41883101

(Supplemental)

1 http://www.epa.gov/opptintr/exposure/pubs/episuite.htm

2 DT50s values are Arrhenius-adjusted temperature @ 25°C for exposure model inputs. 3 DT50s values are recommended. DT50s model inputs from the kinetic guidance. 4 Since the correlation (r2

) between organic carbon and Kd is 0.33, Koc is not appropriate for terbufos.
8

3.2 Terbufos Degradates

Three major degradates, excluding CO2, were identified in the environmental fate studies: 

terbufos sulfoxide (maximum 52.3%), formaldehyde (maximum 96.1%), and terbufos sulfone

(maximum 20.1%). Limited data are available on persistence and mobility for the degradates 

terbufos sulfoxide and terbufos sulfone (Table 3). Terbufos sulfoxide and terbufos sulfone have 

low Kd values ranging from 0.40 to 2.93 mL/g and DT50s of 136 to 174 days in soil. These 

values suggest that these degradates are more mobile and persistent than terbufos in the 

environment. Terbufoxon, terbufoxon sulfoxide, terbufoxon sulfone, des-ethyl terbufos 

sulfoxide, and des-ethyl terbufos sulfone were also observed and formed less than 3.1% in 

environmental fate studies. The oxons (terbufoxon, terbufoxon sulfoxide, terbufoxon sulfone) 

were only identified in the anaerobic soil metabolism study and only as minor degradates. 

Although oxon degradates are more toxic than some organophosphates, ecological structure 

activity relationship (ECOSAR) toxicity estimates suggest that terbufos oxons are orders of 

magnitude less toxic than terbufos to fish and invertebrates and about an order of magnitude less 

toxic to algae (USEPA, 2013). Therefore, the oxons were not considered degradates of concern 

given the anticipated low exposure and the estimated toxicity compared to terbufos. Structures 

and percent formation of degradation products in various environmental fate studies are provided 

in Appendix B.

Table 3. Physical, Chemical and Environmental Fate Properties of Terbufos Sulfoxide and 

Terbufos Sulfone

Property Value Source 

(Classification)

Terbufos Sulfoxide

Common name Terbufos Sulfoxide MRID 44862501

CAS Registry No. 10548-10-4

Chemical name (CAS) S-[[(1,1-dimethylethyl)sulfinyl]methyl]O,Odiethylphosphorodithioate

SMILES notation CCOP(=S)(OCC)SCS(=O)C(C)(C)C EPISUITE1

Synonyms CL 94301, AC 94301 MRID 41373604 

and 44862501

Structure EPISUITE1
9

Property Value Source 

(Classification)

Molecular formula C9H21O3P1S3

Molecular weight 304.42

Vapor pressure 3.42 E-05mm Hg (25oC)

Henry’s Law constant 9.13E-08 atm m3/mol

Solubility in water 1100 mg/L @ 20oC in distilled water

log Kow 2.21

Hydrolysis half-life

 pH = 5

pH = 7

pH = 9

33.2 days (SFO) @ 40°C

[93.9 days (SFO) @ 25°

C]2

23.2 days (SFO) @ 40°

C

[65.1 days (SFO) @ 25°

C] 2

18.5 days (SFO) @ 40°

C

[13.3 days (SFO) @ 25°C] 2

MRID 44862501

(Acceptable)

Aerobic soil metabolism half-life 

(25°C)

136 days (Silt loam) (SFO) @ 25 °C MRID 00156853 

(Acceptable)

Soil adsorption coefficient 

Kd (L/kg)

Adsorption3

Kd (L/kg)

0.4 (AR Loamy sand)

2.83 (IN Silt loam)

0.50 (NJ Sandy loam)

0.75 (WI Loam)

MRID 41373604

(Acceptable)

Terbufos Sulfone

Common name Terbufos Sulfone MRID 44862501

CAS Registry No. 56070-16-7

Chemical name (CAS) S-[[(1,1-dimethylethyl)sulfonyl]methyl]O,Odiethylphosphorodithioate

SMILES notation C(C)(C)(C)S(=O)(=O)CSP(=S)(OCC)OCC EPISUITE1

Synonyms CL94320, AC 94320 MRID 41373604 

and 44862501
10

Property Value Source 

(Classification)

Structure EPISUITE1

Molecular formula C9H21O4P1S2

Molecular weight 320.42

Vapor pressure 7.88 E-06 mm Hg (25oC)

Henry’s Law constant 4.10E-08 atm m3/mol

Solubility in water 408 mg/L @ 19°C

log Kow 2.48

Hydrolysis half-life

 pH = 5

 

 pH = 7

 pH = 9

21.2 days (SFO) @ 40°

C

[60.0 days (SFO) @ 25°

C] 2

15.5 days (SFO) @ 40°

C]

[43.8 days (SFO) @ 25°

C] 2

14.7 days (SFO) @ 20°

C]

[10.4 days (SFO) @ 25°C] 2

MRID 44862501

(Acceptable)

Aerobic soil metabolism half-life 174 days (Silt loam) (SFO) @ 25 °C MRID 00156853 

(Acceptable)

Soil adsorption coefficient 

Kd (L/kg)

Adsorption3

Kd (L/kg)

0.55(AR Loamy sand)

2.93 (IN Silt loam)

0.69 (NJ Sandy loam)

0.86 (WI Loam)

MRID 41373604

(Acceptable)

1 http://www.epa.gov/opptintr/exposure/pubs/episuite.htm

2 DT50s values are Arrhenius-adjusted temperature @ 25°C for exposure model inputs. 3 Since the correlation (r2

) between organic carbon and Kd is ≤ 0.66, the Koc is not appropriate for terbufos 

sulfoxide and terbufos sulfone.
11

IV. Summary of Ecological Effects

Terbufos is moderately to very highly acutely toxic to both aquatic and terrestrial animals based 

on available toxicity studies. In general, studies with end use products show similar toxicity to 

the technical grade active ingredient (TGAI) although in some cases organisms may be slightly 

more sensitive to end use products. Registrant submitted toxicity studies are not available for 

degradation products; however, submitted ancillary information about terbufos sulfone and 

terbufos sulfoxide toxicity to Daphnia magna is discussed below in addition to data identified in 

the ECOTOXicology database. Available data indicate similar toxicity of terbufos, terbufos 

sulfone, and terbufos sulfoxide.

Toxicity endpoints and values used to calculate RQs are reported in Table 4. All available 

studies including additional details are provided in Appendix C. A summary of available data 

follows Table 4. Studies identified in the ECOTOXicology database that reported a more 

sensitive endpoint were reviewed and are also discussed below. Finally, toxicity data for 

mixtures (i.e., terbufos plus at least one other pesticide) were identified in the ECOTOXicology 

database. The majority of those studies show that terbufos enhances the toxicity of herbicides to 

terrestrial plants. Mixture data are summarized below and additional details are provided in 

Appendix D.

Table 4. Terbufos Toxicity Endpoints and Values Used for RQ Calculations 

Species Exposure 

Scenario

% AI Toxicity MRID

Bluegill sunfish 

(Lepomis 

macrochirus)

96 hr

(static) 86 LC50 = 0.77 (0.72-0.83)1 μg ai/L 00087718

ELS NA

NOAEC = 0.10 μg ai/L

Estimate based on acute-to-chronic ratio using 

rainbow trout data2

NA

Waterflea

(Daphnia magna)

48 hr

(static) 88.6 EC50 = 0.17 (0.15-0.19)1 μg ai/L 00101495

21 day LifeCycle 

(flowthrough)

98.4

NOAEC = 0.030 μg ai/L

LOAEC = 0.076 μg ai/L based on growth and 

reproduction (reduced body length and number of 

offspring)

00162525

Sheepshead minnow 

(Cyprinodon 

variegatus)

96 hr 98.4 LC50 = 1.6 (0.77-3.2)1 μg ai/L 00162524

ELS NA

NOAEC = 0.14 μg ai/L

Estimate based on acute-to-chronic ratio using 

rainbow trout data2

NA

Mysid shrimp

(Americamysis 

bahia)

96 hr (static) 98.4 LC50 = 0.22 (0.14-0.35)1 μg ai/L 00162523

NA NA

NOAEC = 0.041 μg ai/L

Estimate based on acute-to-chronic ratio using 

daphnia data2

NA
12

Species Exposure 

Scenario

% AI Toxicity MRID

Freshwater Algae 

(Pseudokirchneriella 

subcapitata)

96 hr

(static) 89.3

EC50 >1.85 mg ai/L 

NOAEC = 0.399 mg ai/L

LOAEC = 1 mg ai/L based on effects to cell density, 

area under the growth curve, average specific growth 

rate, and yield.

48689902

Duckweed

(Lemma gibba) 7 day 89.3

EC50 > 4.20 mg ai/L 

NOAEC = 0.280 mg ai/L

LOAEC = 0.630 mg ai/L based on frond number, 

growth rate of frond number, and yield of frond 

number

48689901

Northern Bobwhite 

Quail 

(Colinus 

virginianus)

Single oral 

dose 89.6 LD50 =28.6 (22.2-55.9)1 mg ai/kg bw 00106551

8 days

(5 days 

treatment and 

3 days 

observation)

86 LC50 = 143 (103-214)1 ppm ai 00087717

Mallard Duck 

(Anas 

platyrhynchos)

Single oral 

dose 15

LD50 = 88 (0-215)1 mg formulation/kg bw

LD50 =13.2 (0-32.3)1 mg ai/kg bw

40660705

Onegeneration 

Reproduction 

Study

89.6

NOAEC = 5 ppm ai

LOAEC = 15 ppm ai based on a possible biologically 

significant (but not statistically significant) effect on 

embryo viability.

00161574

Brown-headed 

Cowbird 

(Molothrus ater)

Single oral 

dose 20

LD50 = 85 (46-151)1 mg formulation/kg bw

LD50 = 16.9 (9.2-30.1)1 mg ai/kg bw

41508804

Rat

Acute Oral

89.7 LD50 = 1.25 (0.98-1.52) 1 mg ai/kg bw (female) 44021601

19 LD50 = 0.836 mg ai/kg bw (female) 47512801

2-generation 

reproduction 89.6

NOAEC(L) = 1 ppm ai (0.07-0.09 mg ai/kg bw/day)

LOAEC(L) = 2.5 ppm ai (0.18-0.24 mg ai/kg bw/day) 

based on decreased pregnancy, decreased male 

fertility, decreased body weight gain in adult females 

during lactation, and decreased pup weights

43649402

Honeybee 

(Apis mellifera) Acute contact TGAI LD50 = 4.09 μg ai/bee 00066220

Cabbage, Carrot, 

Cucumber, Lettuce, 

Soybean, Tomato, 

Corn, Oat, Onion, 

Ryegrass

Tier 1 

Seedling 

Emergence

89.3

EC25 >2.04 lb ai/A

NOAEC = 2.04 lb ai/A

Applies to monocots and dicots

48710801

1

Range is 95% confidence interval.

2 See Table C-1, Appendix C, for calculations.

ELS = Early life stage; NA = not applicable
13

4.1 Aquatic Organisms

Acute Toxicity to Freshwater Fish

TGAI

Several acute toxicity studies with different species are available. Toxicity may be 

underestimated because the available studies reported nominal concentrations and terbufos may 

degrade by hydrolysis and photolysis during a 96 hr exposure period. Bluegill sunfish is the 

most sensitive species tested with acute toxicity ranging from 96 hr LC50 = 0.77 to 3.8 μg ai/L 

(MRID 00037483, 00085176, 00087718, and 40098001). Rainbow trout acute toxicity ranged 

from 96 hr LC50 = 7.6 to 9.4 μg ai/L (MRID 00037483 and 40098001). Fathead minnow 

showed a 96 hr LC50 = 390 μg ai/L (MRID 40098001). Brown trout showed a 96 hr LC50 = 20 

μg ai/L (MRID 00087718). Channel catfish showed a 144 hr LC50 = 9.6 μg ai/L (MRID 

00085176). Sublethal effects included partial loss of equilibrium and pectoral fin erection; 

however, it is not clear if these effects were observed in surviving fish or fish that eventually 

died and most studies did not report any sublethal effects.

End use product

The 15% granular formulation of terbufos (Counter 15G) is comparable in acute toxicity to 

technical grade terbufos. The 96 hr LC50 = 1.8 (95% confidence interval of 1.5-2.3) μg ai/L for 

bluegill sunfish and the 96 hr LC50 = 8.9 μg ai/L (95% confidence interval of 7.2-11.1) for 

rainbow trout (MRID FE0TER04 and FE0TER05). Sublethal effects were not reported for 

surviving fish.

A second study with a 15% granular formulation of terbufos (product not specified) showed 

similar results (MRID 40098001) for toxicity to rainbow trout and blugill sunfish. The 96 hr 

LC50 = 1.7 (95% confidence interval of 1.2-2.4) μg ai/L for bluegill sunfish and the 96 hr LC50 = 

8.8 μg ai/L (95% confidence interval of 6.4-12.1) for rainbow trout. Data were also reported for 

fathead minnow (96 hr LC50 = 150; 95% confidence interval of 101-223 μg ai/L) and channel 

catfish (96 hr LC50 = 1800; 95% confidence interval of 1230-2640 μg ai/L). Sublethal effects 

were not reported.

Chronic Toxicity to Freshwater Fish

An early life-stage study with rainbow trout (MRID 41475802) showed reduced wet weight and 

length at concentrations 1.4 μg ai/L and higher. A significant reduction of 60 day post hatch 

survival was observed at concentrations of 2.7 μg ai/L and higher. A majority of fish at 2.7 and 

5.3 μg ai/L showed sublethal effects throughout the study including resting on their lateral 

surfaces, hypersensitivity, loss of equilibrium, irregular respiration, dark discoloration, surfacing, 

and quiescence. In addition, several fish in various concentrations developed spinal curvature 

and malformed otic capsules. The study NOAEC = 0.64 μg ai/L.

A second study with rainbow trout (MRID 40009301) did not produce a NOAEC because no 

effects were observed at the highest test concentration (1.4 μg ai/L).
14

In addition to the available registrant submitted studies, an open literature study (Call et al., 

1989) was identified in the ECOTOXicology database that reported a more sensitive endpoint; 

therefore, the study was reviewed. The NOAEC = 0.34 μg ai/L and the LOAEC = 0.56 μg ai/L 

based on reduced length of juvenile fathead minnows (Pimephales promelas). Wet weight was 

reduced at higher test concentrations. The study authors questioned the biological significance 

of the observed effects (5-5.5% reduction) and set the study NOAEC at 1.96 μg ai/L. The study 

was classified as qualitative in part because of high variability in measured test concentrations. 

Therefore, results are not used to calculate RQ values but are incorporated into the risk 

characterization.

Bluegill sunfish sensitivity to terbufos on a chronic basis was estimated using an acute to chronic 

ratio (ACR) because it is the most acutely sensitive species. The ACR was based on rainbow 

trout (acute and chronic toxicity) and bluegill sunfish (acute toxicity) data (see Table C-1 in 

Appendix C for calculation). The estimated NOAEC = 0.10 μg ai/L

Chronic Toxicity to Aquatic-phase Amphibians

One open literature study on aquatic-phase amphibians was identified in the ECOTOXicology 

database. Fish are typically used as surrogates for aquatic-phase amphibians; however, this 

study was reviewed because under-represented taxonomic classes including aquatic-phase 

amphibians have been selected for further refinement in preliminary risk assessments, even if 

these taxa show less sensitivity than surrogate species. The southern bellfrog showed delayed 

development (Gosner stage) and metamorphosis when exposed to 10 μg terbufos sulfone/L 

(nominal) for ten weeks (Choung et al., 2011a). Terbufos was not tested. The study was 

classified as qualitative in part because only one terbufos sulfone concentration was tested; thus,

an evaluation of dose-response cannot be determined. Therefore, results are not used to calculate 

RQ values but are incorporated into the risk characterization.

 

Acute Toxicity to Marine/Estuarine Fish

Two acute toxicity studies are available for sheepshead minnow. Toxicity ranged from 96 hr 

LC50 = 1.6 to 3.2 μg ai/L (MRID 00162524 and 41373602). Sublethal effects were observed in 

both studies and included loss of equilibrium, floating at the surface, forward pointing pectoral 

fins, erratic swimming, labored respiration, quiescence, fish at the bottom of the test chamber, 

and surfacing.

Chronic Toxicity to Marine-Estuarine Fish

No data are available for the chronic toxicity of terbufos to estuarine/marine fish. Therefore, a 

NOAEC for estuarine/marine fish of 0.14 μg/L was calculated using the acute toxicity endpoint 

for sheepshead minnow and an ACR for freshwater fish (i.e., rainbow trout) (see Table C-1 in 

Appendix C for calculation).
15

Acute Toxicity to Freshwater Invertebrates

TGAI

Daphnia magna is the most sensitive species tested with acute toxicity ranging from 48 hr LC50

= 0.17 to 0.4 μg ai/L (MRID 00101495 and 40098001); the majority of individuals displaying 

sublethal effects (erratic swimming and lying on the bottom) were deceased by 48 hours. 

Gammarus pseudolimnaeus showed a 96 hr LC50 = 0.2 μg ai/L (MRID 40098001). Chironomus 

plumosus showed a 48 hr LC50 = 1.4 μg ai/L (MRID 40098001). Crayfish showed a 96 hr LC50

= 8 μg ai/L (MRID 00085176); sublethal effects were not reported for surviving individuals. 

In addition to the available registrant submitted studies for freshwater invertebrates, two open 

literature studies were identified in the ECOTOXicology database that reported a more sensitive 

endpoint. Both studies were classified as qualitative (described below); therefore, the results are 

not used to calculate RQ values but are incorporated into the risk characterization.

The freshwater invertebrate, Ceriodaphnia cf dubia, showed a 48 hr EC50 = 0.121 to 0.142 μg 

ai/L and a 96 hr EC50 = 0.074 to 0.078 μg ai/L (Choung et al., 2011b). The ranges represent the 

EC50 values from two independent tests. A second set of experiments was conducted that 

reported only 96 hr EC50 values; these values were similar to those from the first set of 

experiments. Sublethal effects were not reported. The study also reported on toxicity of 

degradation products (discussed below) and pesticide mixtures (discussed below). The study 

was classified as qualitative because exposure concentrations were not reported and exposure 

concentrations were not verified by analytical measurement with exception of the highest test 

concentration.

Gammarus pseudolimnaeus showed a range of 96 hr LC50s from 0.08 to 1.24 μg ai/L (Howe et 

al., 1994) based on a range of pH (6.5 – 9.5) and temperature (7 to 17°C) conditions. Toxicity 

(LC50 = 0.17 μg ai/L) was esentially the same as that observed in MRID 40098001 (LC50 = 0.20 

μg ai/L; 95% confidence interval = 0.1-0.3 μg ai/L) under the same conditions (pH 7.4–7.5 and 

17°C). At 96 hr, toxicity tended to increase with increasing temperature and change in pH away 

from near neutral (i.e., 7.5). However, overall there was not a statistically significant effect of 

pH on toxicity. Similarly, there was no difference in toxicity at 12 and 17°C; however, toxicity 

at those temperatures was significantly greater than that at 7°C. Sublethal effects were not 

reported. The study was classified as qualitative for various reasons including but not limited to 

questions about control mortality, exposure concentrations were not reported, and exposure 

concentrations were not verified by analytical measurement with exception of the highest and 

lowest test concentration at the beginning of the experiment.

End Use Product

The 15% granular formulation of terbufos (Counter 15G) is comparable in acute toxicity to 

technical grade terbufos. The 48 hr LC50 = 0.9 (95% confidence interval of 0.8-1.2) μg ai/L for 

Daphnia magna (MRID FE0TER06). Sublethal effects were not reported.
16

Chronic Toxicity to Freshwater Invertebrates

A 21-day life cycle study with Daphnia magna (MRID 00162525) showed reduced body length

and number of offspring at 0.076 μg ai/L, the highest test concentration. The NOAEC = 0.030 

μg ai/L. Daphnids, some of which may have later died, were observed lying on the bottom or 

quiescent toward the end of the experiment (day 19 and 21).

Degradation Products

Several sources of information suggest that terbufos sulfoxide and terbufos sulfoxone are similar 

to terbufos in their acute toxicity to aquatic invertebrates.

Toxicity studies are not available; however, the registrant submitted information about the 

toxicity of terbufos sulfone and terbufos sulfoxide to Daphnia magna based on a screening study 

(MRID L000037). The registrant reported a 48 hr EC50 = 1 μg ai/L for terbufos sulfone and the 

48 hr EC50 = 2.1 μg ai/L for terbufos sulfoxide. No sublethal effects were reported. The 

information is taken at face value and suggests that the degradates are similar to terbufos in acute 

toxicity.

In addition to the available registrant submitted information, there are two open literature studies 

that reported toxicity of terbufos sulfoxide and terbufos sulfone in comparison to terbufos. One 

study reported toxicity to Ceriodaphnia cf dubia (Choung et al., 2011b; discussed above). 

Terbufos sulfoxide showed a 48 hr EC50 = 0.489 to 0.594 μg ai/L and a 96 hr EC50 = 0.360 to 

0.363 μg ai/L. Terbufos sulfone showed a 48 hr EC50 = 0.324 to 0.381 μg ai/L and a 96 hr EC50

= 0.148 to 0.222 μg ai/L. The ranges represent the EC50 value from two independent tests. 

These values are within a factor of 5x of the terbufos toxicity observed in concurrently 

conducted studies. A second and third set of experiments were conducted that reported only 96 

hr EC50 values; these values were similar to those from the first set of experiments. No sublethal 

effects were reported.

The second study reported toxicity to Chironomus tepperi (Choung et al., 2010). There was not 

a statistically significant difference in the toxicity of terbufos, terbufos sulfoxide, and terbufos 

sulfone. Toxicity of the three compounds differed less than a factor of 2x. Terbufos showed a

96 hr EC50 = 1.99 to 2.27 μg ai/L, terbufos sulfoxide showed a 96 hr EC50 = 3.53 to 3.74 μg 

ai/L, and terbufos sulfone showed a 96 hr EC50 = 2.49 to 2.69 μg ai/L. The ranges represent the 

EC50 value from two independent tests. A second set of experiments was conducted that 

reported 96 hr EC50 values that were similar to those from the first set of experiments. No 

sublethal effects were reported.

Acute Toxicity to Marine/Estuarine Invertebrates 

In three 96 hr acute toxicity studies with mysid shrimp, the LC50 ranged from 0.22 to 0.54 μg

ai/L (MRID 00162523, 41297903, and 42306701). The two older studies showed excessive 

control mortality (more than 10%). One, a static test (MRID 00162523), showed 20% mortality 

in the negative control but 0% in the solvent control. The other, a flow-through test (MRID 

41297903), showed 5% mortality in the negative control but 15% in the solvent control (the 
17

study author indicated that dead organisms were not located and suggested that the loss was due 

to misplacement of organisms during transfer between vessels at test initiation). Although the 

control mortality raises questions about the toxicity values of the older studies, the three studies 

show consistent results under different exposure conditions (static vs. flow-through) with LC50

values differing by only 2.5X. Sublethal effects included quiescence, lying on the bottom, 

surfacing, loss of equilibrium, erratic swimming, gyrating motions, and lethargy.

Eastern oyster (Crassostrea virginica) showed a 96 hr EC50 = 201 μg ai/L (MRID 42381501). 

Chronic Toxicity to Marine-Estuarine Invertebrates 

No data are available for the chronic toxicity of terbufos to estuarine/marine invertebrates. 

Therefore, a chronic toxicity endpoint for estuarine/marine invertebrates of 0.041 μg/L was 

calculated using the acute toxicity endpoint for mysid shrimp and an ACR for freshwater 

invertebrates (i.e., Daphnia magna) (see Table C-1 in Appendix C for calculation). 

Aquatic Plants

Two toxicity studies are available for non-vascular plants. A study with a freshwater green algae 

showed a 96 hr EC50 >1.85 mg ai/L (MRID 48689902). The NOAEC = 0.399 mg ai/L and the 

LOAEC = 1.00 mg ai/L based on reduced cell density, area under the growth curve, average 

specific growth rate, and yield. A study with a marine diatom showed a 96 hr EC50 >1.01 mg 

ai/L and the NOAEC ≥ 1.01 mg ai/L (MRID 48939101). Statistically significant adverse effects 

were not observed in this study. Although this study had guideline deviations that likely 

confounded the results (e.g., excessive variation in initial cell density), the study is sufficient to 

indicate that there is likely no inhibition within the range of concentrations tested. Data are not 

available for freshwater diatom or bluegreen algae species.

In addition to the available registrant submitted studies for non-vascular aquatic plants, an open 

literature study (Tien and Chen, 2012) was identified in the ECOTOXicology database that 

reported a more sensitive endpoint for non-vascular aquatic plants. The freshwater diatom, 

Nitzschia sp, showed a 96 hr EC50 = 0.59 to 1.51 mg ai/L. Two other test species showed less 

sensitivity: Oscillatoria sp. (96 hr EC50 = 7.99 mg ai/L) and Chlorella sp. (96 hr EC50 = 41.16 

mg ai/L). The study was classified as qualitative in part because of a lack of information about 

growth in the controls. Therefore, the results are not used to calculate RQ values, but are 

incorporated into the risk characterization.

A vascular plant study with duckweed showed an EC50 > 4.20 mg ai/L (MRID 48689901). The 

NOAEC = 0.280 mg ai/L and the LOAEC = 0.630 mg ai/L based on frond number, growth rate 

of frond number, and yield of frond number. Inhibition was observed at higher concentrations 

for area under the curve and biomass.
18

4.2 Terrestrial Organisms

Acute Oral Toxicity to Birds

TGAI

The acute oral LD50 = 28.6 (22.2-55.9; 95% confidence interval) mg ai/kg bw for bobwhite quail

(MRID 00106551) when exposed to the TGAI. Observed sublethal effects included lethargy 

progressing to depression, reduced reaction to external stimuli, loss of coordination, lower limb 

weakness, prostrate posture, loss of righting reflex, salivation, and lower limb rigidity. 

Three open literature studies identified in the ECOTOXicology database reported a more 

sensitive endpoint. Bobwhite quail showed acute oral toxicity ranging from an LD50 = 15 (95% 

confidence interval = 12-19 and slope = 7.9) (Hill and Camardese, 1984) to 24.4 (95% 

confidence interval = 18.1-31.8 and slope = 5.1) mg ai/kg bw (Brewer et al., 1996). Observed 

sublethal effects reported by Brewer et al. (1996) were consistent with those reported in other 

studies: all dosed birds exhibited lethargy, wing droop, piloerection and diarrhea whereas birds 

receiving higher doses were ataxic and prostrate prior to death. Wolfe and Kendall (1998) 

examined toxicity of different age classes of red-winged blackbirds and starling; in general both 

species showed increasing LD50s with increasing age. Adult red-winged blackbirds showed an 

LD50 = 2.06 (95% confidence interval = 1.52-3.53) mg ai/kg bw and nestlings (0-11 days old) 

showed sensitivity ranging from an LD50 = 0.36 to 3.33 mg ai/kg bw. Starlings were less 

sensitive: adults showed an LD50 = 204 (95% confidence interval = 130-350) mg ai/kg bw and 

nestlings (0-19 days old) showed sensitivity ranging from an LD50 = 2.3 to 60.8 mg ai/kg bw. 

Red-winged blackbird nestlings showed behaviors such as failure to beg, vocalize, and respond 

to parental stimulation and some of those birds were thrown out of the nest. The study also 

reported reduced plasma and brain cholinesterase activity from exposure to terbufos. The three 

open literature studies were classified as qualitative for various reasons including but not limited 

to: (a) a general lack of details about experimental design (Brewer et al., 1996), (b) limited dose 

levels were tested for red-winged blackbirds, dose levels were not reported (range only) or 

verified by analytical measurement, and there was a loss of birds due to illness or escape at 

dosing (Wolfe and Kendall, 1998), and (c) dose levels were not reported or verified by analytical 

measurement (Hill and Camardese, 1984). Therefore, results are not used to calculate RQ values 

but are incorporated into the risk characterization.

End Use Product

Results for formulated product testing also show that terbufos is highly toxic to birds on an acute 

oral basis (MRID 40660705, 40660706, 40660707, 40660708, 41508802, 41508803, 41508804, 

and 41508805). The product Counter 15G showed an LD50 = 43.5-44.3 mg ai/kg bw (290-295 

mg formulation/kg bw)1 for bobwhite quail, an LD50 =13.2 mg ai/kg bw (88 mg formulation/kg 

bw) for mallard duck, and an LD50 = 22.2 mg ai/kg bw (148 mg formulation/kg bw) for brownheaded cowbird. Although greater sensitivity was not observed (TGAI vs TEP tested in the same 

study), it is noted that Hill and Camardese (1984), as discussed above, tested bobwhite quail with 

Counter 15G and showed an LD50 = 26 mg ai/kg bw. The product Counter CR showed an LD50

 1 Range based on two studies.
19

= 47.6 mg ai/kg bw (238 mg formulation/kg bw) for bobwhite quail and an LD50 = 16.9 mg ai/kg 

bw (85 mg formulation/kg bw) for brown-headed cowbird. The product Counter 20P showed an 

LD50 = 50 mg ai/kg bw (250 mg formulation/kg bw) for bobwhite quail and an LD50 = 32.2 mg 

ai/kg bw (161 mg formulation/kg bw) for mallard duck. Sublethal effects observed in these 

studies are consistent with those observed in response to oral dosing with the TGAI (see 

Appendix C for details by study).

Acute Dietary Toxicity to Birds

Bobwhite quail is the most sensitive species tested on an acute dietary basis with an LC50 = 143 

(125-201; 95% confidence interval) ppm ai (MRID 00087717) and 157 ppm ai (103-214; 95% 

confidence interval) ppm ai (MRID 00160387) – both based on nominal test concentration. 

Bobwhite quail showed decreased locomotor activity, feather erection, loss of righting reflex, 

depression (lethargy), reduced reaction to sound and movement, wing droop, loss of 

coordination, prostrate posture, lower limb rigidity, ruffled appearance, lower limb weakness, 

reduced body weight gain, and reduced food consumption.

Mallard duck was tested on an acute dietary basis and showed an LC50 = 153 (117-198; 95% 

confidence interval) ppm ai (MRID 00087717) and 697 ppm ai (584-1616; 95% confidence 

interval) ppm ai (MRID 00035120) – both based on nominal test concentrations. Mallard ducks 

showed decreased locomotor activity, feather erection, loss of righting reflex, reduced body 

weight, and reduced food consumption.

Chronic Toxicity to Birds

Available studies do not clearly define a NOAEC. Studies with bobwhite quail and mallard duck 

(MRID 00097892 and 00085177) showed possible effects on viable embryos of eggs set at 2 

ppm ai. Mallard duck also showed decreasing body weight at both 2 and 20 ppm ai throughout 

the study in contrast to the control birds, which gained weight. However, the results of these 

studies cannot be confirmed due to a lack of pen by pen data.

A second study with mallard duck showed a possible NOAEC = 5 ppm ai based on an effect (not 

statistically significant) on embryo viability at 15 ppm ai (MRID 0161574). A second study with 

bobwhite quail showed no effects at 30 ppm ai, the highest test concentration tested (MRID 

00161573).

Phorate, the closest chemical analog to terbufos, showed a NOAEC = 5 ppm ai for mallard duck 

(MRID 00158334). The subacute dietary toxicity of phorate to mallard duck (LC50 = 240 ppm 

ai, MRID 00022923) is also similar to the toxicity of terbufos. Given that a NOAEC is not 

clearly defined for terbufos, an approximate NOAEC of 5 ppm ai is assumed based on the 

combined information from the available terbufos and phorate studies. Risk conclusions would 

not change if the NOAEC was lower than 2 ppm ai as suggested by the study results that could 

not be confirmed (MRID 0097892 and 00085177).
20

Acute Oral Toxicity to Mammals

TGAI

The acute oral LD50 = 1.25 (0.98-1.52; 95% confidence interval) mg ai/kg bw for female rats

(MRID 44021601) when exposed to the TGAI. Observed sublethal effects included tremors, 

salvation, exophthalmos (bulging of the eye), and decreased activity. All survivors appeared 

normal 9 days after dosing. 

End Use Product

Results for formulated product testing also show that terbufos is very highly toxic to mammals 

on an acute oral basis (MIRD 47512801) and that the 20G formulation is slightly more toxic than

the TGAI. The product Counter 20G showed an LD50 = 0.836 mg ai/kg bw for female rats

(confidence intervals could not be calculated). 

Chronic Toxicity to Mammals

A 2-generatation reproduction study with rats showed a NOAEC(L) = 1 ppm ai (0.07-0.09 mg 

ai/kg bw/day) for maternal/offspring and reproductive effects (MRID 43649402). The 

LOAEC(L) = 2.5 ppm ai (0.18-0.24 mg ai/kg bw/day) based on decreased pregnancy rate, 

decreased male fertility, decreased body weight gain in adult females during lactation, and 

decreased pup weights. Cholinesterase inhibition was observed at 1 ppm ai and higher (NOAEC 

= 0.5 ppm ai).

Terrestrial Invertebrates

The acute contact LD50 = 4.09 μg ai/bee when exposed to the TGAI (MRID 00066220). Acute 

and chronic oral toxicity data (adult or larvae) are not available for terbufos or phorate, the 

structural analog of terbufos.

Terrestrial plants

In a Tier I seedling emergence study, no statistically significant inhibition was observed in any of 

the ten tested species (MRID 48710801). The EC25 > 2.04 lb ai/A and the NOAEC = 2.04 lb 

ai/A for both monocots and dicots. A vegetative vigor study is not available.

The majority of open literature studies show no effects to terrestrial plants at the tested 

concentrations. However, a small number show phytotoxicity effects (other than growth or 

survival) or reduced yield in field studies that may indicate greater sensitivity than registrant 

submitted data; thus, these studies are discussed qualitatively in the risk characterization. 

Greenhouse grown corn treated at both 0.98 and 1.96 lb ai/A showed increased chlorosis (7 day 

old corn) and decreased tissue zinc concentration (at harvest); a NOAEC was not reported for 

these endpoints (Matocha and Hopper, 2001). Testing was conducted on 15G and CR

formulations. Reduced chlorophyll (28 day old corn; 15G only) and plant height (7 day old 

corn) were observed for both test concentrations early in the experiment; however, both variables 
21

showed recovery compared to the control at time points thereafter. Two field studies showed 

effects of terbufos on plant yield (reduced numbers of sugar beet plants at 1.78 lb ai/A; Downard 

et al., 1999 and kenaf plants at 2 lb ai/A; Barillas-Argueta, 1993); however, the observed effects 

were isolated and there is inherent uncertainty as to the cause of effects in field studies. Yield 

was only impacted in a single instance in either study (single year and location); kenaf was tested 

in two years at a single location and sugar beet was tested in two years at three different 

locations. In addition, Downard et al. (1999) tested both 15G and CR formulations at each 

location/year except the single instance that showed reduced yield. In that case, the test material 

was only reported as “terbufos”. There were no additional effects on kenaf (plant diameter, 

height, and weight; Barillas-Argueta, 1993) or sugar beet (injury index, root yield, and sucrose 

characteristics; Downard et al, 1999). 

 

4.3 Simulated and/or Actual Field Tests

Several field studies provide information on impacts to non-target organisms following 

application of terbufos. Among the limitations of field studies is the issue with false negatives 

(i.e., the failure to identify animals impacted by exposure to terbufos). This is in part because 

findings are highly dependent upon the probability of locating a dead animal on the treated field, 

the probability of locating a dead animal before it is removed from the treated field by a 

scavenger, and the probability that a moribund animal moved off the treated field by itself.

1. Terrestrial Field Study. Counter 15G applied to corn fields at 1 lb ai/A at time of plant 

showed minimal acute effects on wildlife (two dead birds); however carcass searches, residue 

analyses, and miscellaneous wildlife observations were very limited (MRID 00085178, 

00085180, and 00087726).

2. Simulated Field Study, exposure to treated soil. Ring-necked pheasants were exposed to soil 

treated with Counter 15G at a rate equivalent to 1 to 5 lb ai/A and residues were not detected in 

soil 22 days after the initial exposure. No poisoning symptoms were observed during 55 days of 

observation following treatment. Two of three birds exposed to a simulated spill died within 12 

hours of the initial exposure (MRID 00085179, 00085183, and FEOTEROl).

3. Terrestrial Field Study. Terbufos was applied at planting at 2.6 lb ai/A and 10 weeks later as a 

broadcast aerial application at 1 lb ai/A to a cornfield in Maryland. Following the at-planting 

application, several species of wildlife were observed dead (one bluebird, one morning dove, two 

snakes, and one turtle) or alive and exhibiting signs of cholinergic poisoning (one blue jay, one 

robin, and one brown-headed cowbird). The affected blue jay and dead bluebird contained 

residues of 0.24 and 0.15 ppm, respectively. Seven feather spots were also found indicating a 

dead bird that was consumed by a predator. Following the aerial application, surveys identified 

eight dead birds, one affected bird, 14 dead mammals (mouse, rat, woodchuck, shrew, raccoon, 

and rabbit), one dead reptile, six feather spots, one fur spot, and several dead fish. Detectable 

levels of terbufos residues in the affected and dead animals ranged from 0.09 to 8.47 ppm 

(MRID BAOTEROl and 145854).

4. Terrestrial Field Study. Three seasons of field research were conducted from 1987 to 1989 in 

south central Iowa to assess the environmental exposure of terbufos and its effects on wildlife in 

a corn agro-ecosystem. Terbufos was applied at 1.3 lb ai/A in bands and in furrows at the time of 
22

planting of corn. Monitoring and biochemical sampling techniques showed relatively low 

exposure to most species sampled. Nonetheless, mortalities were observed and individuals 

showed reduced brain ChE activity and the presence of terbufos residues (including degradation 

products) in the GI tract. Results from starling nest box monitoring in the second year suggest 

some effects in reproduction parameters and third year passerine blood plasma ChE activity

showed a significant difference between in-furrow treatment sites and controls in blue jay 

(MRID 40985501 and 41475801). 

5. Simulated Field Study. A study was conducted to compare the effects of Counter 15G to 

Counter CR on bobwhite quail and brown-headed cowbirds. Terbufos was applied at time of 

corn planting in pens using band and in-furrow applications. Despite study limitations, the results 

suggest that both formulations could impact non-target wildlife species. All treatment pens 

showed higher mortality rates than controls (MRID 41508801 and 41849201).

4.4 Toxicity of Mixtures

There are not any terbufos products formulated with another active ingredient. However, 

numerous studies were identified in the open literature that examined the toxicity of terbufos 

combined with at least one other pesticide (see Appendix D). The majority of these studies 

compared the effects of pesticide mixtures on terrestrial plants, typically corn. These 

experiments compared toxic effects when terbufos was applied alone to toxic effects when 

terbufos was applied along with common herbicides to determine if the interaction was neutral, 

increased toxicity (i.e., additive or synergistic effect) or decreased toxicity (antagonistic effect). 

It is well established that terbufos and other OP insecticides can have a synergistic interaction 

with acetolactate synthase (ALS) inhibitor herbicides such as sulfonylureas. The majority of the 

reviewed studies showed that combined exposure of terbufos and ALS inhibitor herbicides (e.g., 

nicosulfuron, primisulfuron, rimsulfuron, prosulfuron, chlorimuron, and flumetsulam) increased 

toxicity to plants; however, terbufos did not increase toxicity of all ALS herbicides (e.g.

imazaquin) under experimental conditions. Likewise, terbufos interacted with other types of 

herbicides including photosynthesis inhibitors, growth regulators, shoot and root growth 

inhibitors, and PPO inhibitors to increase toxicity of some herbicides (e.g., metribuzin, cycloate, 

and oryzalin) but not others (e.g., atrazine, clopyralid, 2,4-D, metolachlor, alachlor, and 

acifluorfen). In general, many factors impacted the effects of terbufos-herbicide mixtures 

including but not limited to the presence of safeners, application rate, application timing, 

terbufos formulation and method of application, effect endpoint, and experimental site location. 

A smaller number of studies tested the effects of mixtures on aquatic organisms. Increased 

toxicity to fish was observed from exposure to mixtures of terbufos with either permethrin or 

atrazine. Mixtures of atrazine and terbufos increased the toxicity of terbufos to one aquatic 

invertebrate species (Ceriodaphnia dubia) but not another (Chironomus tepperi). The toxicity

of terbufos sulfone and terbufos sulfoxide to aquatic invertebrates was not impacted by mixtures 

with atrazine. Similarly, there was no evidence of synergism when frogs were exposed to a 

mixture of terbufos sulfone and atrazine. Finally, mixtures of terbufos and other 

organophosphate chemicals (chlorpyrifos and methamidophos) showed antagonistic interactions 

on toxicity (decreased) to individual species (Oscillatoria sp. and Chlorella sp.) and multi 
23

species assemblages of algae. In contrast, terbufos and methamidophos may have had a 

synergistic interaction on the toxicity to the multi species assemblage.

 

4.5 Incident Information

The RED (USEPA, 1999) reported that terbufos was the leading cause of fish kill incidents 

reported to EPA for any pesticide applied to corn and ranked fourth in fish kill incidents reported 

to EPA for any pesticide applied to any crop. Additional terbufos related incidents were

obtained from the Ecological Incident Information System (EIIS, v 2.1.1), the Aggregate 

Incident Data System, and the Avian Incident Monitoring System (AIMS)2 on May 19, 20143

. 

Incidents occurring after 1999 are typical of those previously reported. There is not enough 

information provided in the incident reports to determine which if any aquatic incidents reported 

after 1999 reflect mitigation efforts resulting from the RED. The reports indicate that some 

incidents prior to 1999 occurred despite the use of buffer strips, which were not required at that 

time. After 1999, there were four reported incidents with fish, two with birds, and one with 

mammals in the EIIS database. Two plant damage incidents are reported in the EIIS database; 

however, in both cases two herbicides were applied in addition to terbufos. Previous 

assessments of terbufos incidents did not include those identified in the Aggregate Incident Data 

System or AIMS. Both of these databases revealed incidents prior to and after the RED. 

Focusing on incidents since the RED, there were five minor wildlife incidents, three bird 

incidents (not included in EIIS), and six minor plant incidents. Unlike the EIIS database, few 

details are reported about incidents in the other two databases. 

The majority of reported fish incidents occurred prior to the RED. There are several key points 

about the aquatic incidents reported in the EIIS database: 

• The majority of incidents are associated with use on corn. 

• Incidents are associated with various methods of application and two of the three granular 

formulations (Counter 15G and Counter CR). No incidents have been reported for 20G,

which was registered more recently.

• The majority of incidents occurred in 5 corn belt states (IA, IN, IL, NE, OH). 

• Incidents involve mortality from 20 to 90,000 fish.

• Large grassy buffer strips (300-1000 ft) did not prevent incidents in some cases.

• Incidents generally occurred 2 days to 3 weeks after application.

• In some of the incidents, rainfall was reported as occurring over a period of days to 

weeks prior to the incident. Based on the limited weather information provided, the 

Agency believes the incidents could be associated with normal spring rain events, as 

opposed to unusually severe rainfall events over a short period of time. 

The updated incident list is provided in Appendix E.

 2 http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm 3 It was confirmed that no additional incidents were added to the EIIS or the Aggregate Incident databases between 

May 19, 2014 and August 25, 2015. The AIMS database was not accessible on August 25, 2015.
24

V. Aquatic LOC Assessment

5.1 Exposure Estimates 

The Surface Water Concentration Calculator (SWCC v 1.106) model4 was used to generate 

estimated environmental concentrations (EECs) for the Tier II aquatic exposure assessment. The 

SWCC is a graphical user interface that runs the Pesticide Root Zone Model (PRZM, v 5, 

November 15, 2006) and the Variable Volume Water Body Model (VVWM, 3/6/2014) (USEPA, 

2006b). Simulations are run for multiple (usually 30) years and the EECs represent peak values 

that are expected once every ten years based on the thirty years of daily values generated during 

the simulation. Separate EECs were generated for residues of concern: terbufos, terbufos 

sulfone, and terbufos sulfoxide. The SWCC model was parameterized using relevant use and 

environmental fate data for terbufos, terbufos sulfone, and terbufos sulfoxide according to the 

EFED input parameter guidance for water modeling (USEPA, 2009). Application rates for 

terbufos sulfone and terbufos sulfoxide were determined by adjusting the application rate of 

terbufos by the maximum percentage of degradate formed and the molecular weight ratio of 

terbufos to the degradate. The residue summation method (USEPA, 2008a) was used to estimate 

the 1-in-10 year exposure concentrations for total toxic residues (TTRs) representing the 

combined exposure to the residues of concern (terbufos, terbufos sulfone, and terbufos 

sulfoxide). EXCEL was used to post-process estimated EECs generated for terbufos, terbufos 

sulfone, and terbufos sulfoxide. One inch incorporation of granular terbufos was modeled to 

represent the typical incorporation depth for all labeled application methods (in furrow, banded, 

and knifed-in).

Current terbufos labels require certain setback distances or vegetative buffers between treated 

areas and surface water. A well maintained vegetative buffer could potentially intercept sediment 

laden with terbufos via runoff from a treated field. However, the current surface water model 

does not have the capability to account for the prescribed setbacks or vegetative buffer distances; 

thus, the SWCC model generated EECs are considered upper bound aquatic exposures. While 

there is good evidence that buffers can reduce pesticide movement into water bodies to some 

extent, there is still a great deal of uncertainty regarding the performance of buffers, which 

includes but is not limited to proper design and placement and the duration of their efficacy. 

Many studies have been conducted to document the effectiveness of various types of vegetative 

buffers, commonly known as vegetative filter strips (VFS). Based on a review of available 

research, EFED hypothesized that the use of VFS may reduce loading of total toxic residues of 

terbufos in aquatic systems by 50% to 90% (see USEPA, 2015 for a full discussion).

Input parameters and representative results of SWCC modeling are provided in Appendix F. 

The highest and lowest EECs based on TTR for various scenarios and application rates are 

provided in Table 5. 

 4 http://www.epa.gov/oppefed1/models/water
25

Table 5. Estimated Environmental Concentrations (EECs) of Total Toxic Residues of 

Terbufos (TTR1,2) for Surface Water and Benthic Layer Based on Selected Crop Scenarios

Use

Scenario 

(modeled rate)

Application 

Method

Peak EEC

(μg/L)

3

21-DayEEC 

(μg/L)

3

60-Day EEC

(μg/L)

3

TTR in Surface Water 

Corn:

MScorn_STD

ORsweetcorn_OP

(1 app. X 1.30 lb ai/acre)

Ground 

(Incorporated)

23.40

5.52

17.00

4.95

15.50

3.63

Corn:

NCcornW_OP

NCcornE_STD

(1 app. X 2.6 lb ai/acre)

24.80

15.50

21.40

11.30

18.70

9.08

Sugar beet:

MNsugarbeet_STD

CAsugarbeetWirrg_OP

(1 app. X 1.96 lb ai/acre)

14.20

9.84

8.03

8.27

6.30

6.89

Sorghum:

TXsorghum_OP

KSsorghum_STD

(1app. X 1.695 lb ai/acre)

35.70

12.30

21.90

9.83

18.50

8.30

TTR in Benthic Layer (Pore Water) 

Corn:

MScorn_STD

ORsweetcorn_OP

(1 app. X 1.30 lb ai/acre)

Ground

(Incorporated)

17.60

2.37

16.80

2.31 --

Corn:

NCcornW_OP

NCcornE_STD

(1 app. X 2.6 lb ai/acre)

11.20

6.04

11.20

5.67 --

Sugar beet:

MNsugarbeet_STD

CAsugarbeetWirrg_OP

(1 app. X 1.96 lb ai/acre)

4.91

4.25

4.89

4.23 --

Sorghum:

TX sorghum_OP 

KS sorghum_STD

(1app. X 1.695 lb ai/acre)

12.50

5.88

11.40

5.86 --

1 Terbufos plus its major degradates, terbufos sulfone and terbufos sulfoxide. 2 EECs do not account for required vegetative buffers and setback distances.

3 SWCC modeled values are the highest and lowest TTR EECs for each crop and application rate.
26

5.2 RQ Values

Acute and chronic LOCs for fish and invertebrates are exceeded for use of terbufos on corn, 

sorghum, and sugar beet (Table 6). A range of RQs was presented for each use representing the 

use scenario resulting in the lowest and highest EECs. Acute RQs for fish range from 3-46 and 

chronic RQs for fish range from 26-187. Acute RQs for aquatic invertebrates range from 11-210 

and chronic RQs for aquatic invertebrates range from 56-730. The listed species LOC (1) is not 

exceeded for aquatic plants (vascular or non-vascular). 

Table 6. Aquatic RQs for Use of Terbufos1,2,3,4,5

Taxonomic Group Crop (application rate)

Corn

(1.3 lb ai/A)

NC Corn

(2.6 lb ai/A)

Sugar Beet

(1.96 lb ai/A)

Sorghum

(1.695 lb ai/A)

Freshwater 

Animals

Fish (acute) 7-30 20-32 13-18 16-46

Fish (chronic) 36-155 91-187 63-69 83-185

Invertebrate (acute) 33-138 91-146 58-84 72-210

Invertebrate (chronic) 165-567 377-713 268-276 328-730

Benthic Invertebrate 

(acute) 14-104 36-66 25-29 35-74

Benthic Invertebrate 

(chronic) 77-560 189-373 141-163 195-380

Marine/

Estuarine 

Animals

Fish (acute) 3-15 10-16 6-9 8-22

Fish (chronic) 26-111 65-134 45-49 59-132

Invertebrate (acute) 25-106 70-113 45-65 56-162

Invertebrate (chronic) 121-415 276-522 196-202 240-534

Benthic Invertebrate 

(acute) 11-80 27-51 19-22 27-57

Benthic Invertebrate 

(chronic) 56-410 138-273 104-119 143-278

Algae (listed species)6 0.01-0.06 0.04-0.10 0.02-0.04 0.03-0.09

Aquatic Vascular plants (listed 

species)6 0.02-0.08 0.06-0.10 0.04-0.05 0.04-0.13

1 EECs do not account for required vegetative buffers and setback distances.

2 Range is based on use scenarios resulting in the lowest and highest EECs for each crop as provided in Table 5. 

For example, the acute fish RQ range for corn (1.3 lb ai/A) is based on the peak EEC from the ORsweetcorn_OP 

scenario (5.52 μg/L) and MScorn_STD (23.40 μg/L). 3 Acute RQs were calculated using the peak EEC, chronic fish RQs were calculated using the 60-day EEC, and 

chronic invertebrate RQs were calculated using the 21-day EEC. Benthic invertebrate EECs were calculated using 

porewater EECs.

4 RQs were calculated using toxicity endpoints presented in Table 4. The listed species RQ for aquatic plants is 

based on the NOAEC value. Waterflea and Mysid shrimp data were used to calculate RQs for benthic invertebrates 

because those were the most sensitive invertebrate species and the available data for benthic invertebrates were 

based on water column concentrations (not spiked sediment).

5 RQs greater than 1 are rounded to the nearest whole number.

6 RQs were not calculated for non-listed species because RQs for listed species do not exceed the LOC of 1.0.

BOLD indicates that the RQ is greater than or equal to the LOC for aquatic animals (acute listed species LOC = 

0.05 or the chronic LOC = 1.0) or aquatic plants (listed species LOC = 1.0).
27

5.3 Monitoring Data

The occurrence of terbufos in surface water and groundwater was summarized in the IRED 

(USEPA, 2001). For surface water, a total of 5198 samples from the United States Geological 

Survey (USGS) National Water Quality Assessment (NAWQA) database were analyzed for 

terbufos. Terbufos was detected in 17 surface water samples with concentrations ranging from 

0.02 to 0.56 μg/L. Terbufos groundwater monitoring information was available from several 

sources including the registrant, NAWQA, states, and EPA's Pesticides in Groundwater 

Database. These data represent 4,563 samples from 13 states; of these there were 20 detections 

of terbufos that ranged from 0.011 to 20.0 μg/L. Terbufos degradates were not included as 

analytes for surface water or groundwater monitoring.

A surface water and groundwater monitoring study (MRID 46873301) was conducted for

terbufos, terbufos sulfone, and terbufos sulfoxide by the registrant. The study was required by 

the terbufos IRED (USPEA, 2001) to confirm concentrations of terbufos, terbufos sulfone, and 

terbufos sulfoxide in drinking water sources. The Agency review of this study (USEPA, 2008b) 

is summarized as follows. For the surface water, a total of 502 samples were collected from 33 

sites between 1999 and 2005. For the groundwater, 73 samples were collected from 2003 to 

2005. From 1999 to 2003, samples from numerous watersheds were provided by the NAWQA 

program. In surface water, terbufos and terbufos oxon were not detected above the reporting 

limits in any samples. Terbufos sulfoxide was detected in four samples at 0.092 to 0.205 μg/L, 

with an additional nine estimated detections of 0.045 to 0.262 μg/L. Terbufos sulfone was 

detected in six samples at 0.046 to 0.114 μg/L, with 30 additional estimated detections of 0.012 

to 0.034 μg/L. There were no detections of terbufos or any degradates in any of the groundwater 

samples. 

USGS-NAWQA monitoring data from 2006 to the present were accessed on March 18, 2014 to 

evaluate the post-IRED trend of terbufos, terbufos sulfone, and terbufos sulfoxide concentrations 

in surface water and groundwater. This dataset included filtered surface water and groundwater 

monitoring data that were not available in a previously reviewed 2008 monitoring study of 

terbufos and its degradates in drinking water (USEPA, 2008b). For surface water, a total of 6740 

water samples were analyzed for terbufos. Terbufos was detected in only one sample and the 

concentration was 0.02 μg/L. There were two detections of 0.07 μg/L and 0.17 μg/L terbufos 

sulfone out of 6198 surface water samples. For groundwater, a total of 3582 water samples were 

analyzed for terbufos. Terbufos was detected in one sample with a concentration of 0.01 μg/L. 

There were no detections of terbufos sulfone in any of the groundwater samples. 

Post-IRED detections and concentrations of terbufos in surface water and groundwater samples 

are lower than the pre-IRED monitoring data. The Agency implemented several mitigation and 

risk management measures necessary to address human health and environmental risks 

associated with the uses of terbufos during the IRED process. In particular, the application rate 

for sorghum was reduced from 1.96 lb ai/A to 1.696 lb ai/A and a vegetative buffer was required 

between the treated area and surface water bodies to mitigate terbufos exposure in surface water. 

The reduced rate for sorghum and the implementation of vegetative buffers may have resulted in 

fewer detections and lower concentrations of terbufos and its degradates in surface water and 

groundwater.
28

The NAWQA program recently began monitoring the quality of source water and finished water 

of aquifers and major rivers used by some of the larger community water systems in the United 

States (Carter et al., 2010). There were 295 anthropogenic organic compounds (AOCs) 

including terbufos and terbufos sulfone monitored during 2002–2010 for the Source WaterQuality Assessment (SWQA) studies. The SWQA studies are intended to complement drinkingwater monitoring required by Federal, State, and local programs, which focus primarily on posttreatment compliance monitoring. A total of 221 surface water samples were analyzed for 

terbufos and terbufos sulfone. There were no detections of terbufos or terbufos sulfone in any 

samples. 

Monitoring data for surface water, groundwater, and sediment from the California Department of 

Pesticide Regulation (CDPR) were searched on March 18, 2014. Terbufos was detected in only 

one sample and the concentration was 0.04 μg/L out of 2538 surface water samples. There were 

no detections of terbufos or its degradates in any of the groundwater samples.

There are some limitations with the non-targeted monitoring data cited above. Critical 

information is not available to determine how well sampling events at the monitoring sites 

correspond with terbufos applications. The sampling frequency may be sufficient for estimating 

long-term average concentrations for chronic toxicity endpoints but is inadequate for estimating 

peak exposures for acute endpoints. The monitoring results can provide a lower bound of 

anticipated exposures from terbufos residues in water bodies in terbufos use areas.

VI. Terrestrial LOC Assessment

6.1 Birds and Mammals

Dietary Ingestion (granules)

T-REX (Terrestrial Residue Exposure Model, v 1.5.2)5 was used to estimate avian and mammal 

dietary exposure to terbufos granules based on the LD50/ft2 method. Risk was assessed based on 

toxicity to the TGAI and to formulations when data indicated greater toxicity. Representative 

model input and output are shown in Appendix G.

The acute and chronic LOCs are exceeded for use of terbufos on corn, sorghum, and sugar beet

(Table 7 and 8). The acute listed and non-listed species LOCs are exceeded for 20g and 100g 

birds (all uses). RQs are at or exceed the listed species acute LOC (0.1) for birds in the 1000g 

size class (all uses). RQs exceed the non-listed species acute LOC (0.5) for birds in the 1000g 

size class for uses with the 15G granule (all NC corn uses and banded uses on corn, sorghum, 

and sugar beet). All uses exceed the listed and non-listed species acute LOCs for all considered 

size classes of mammals (15-1000g). The chronic LOC (1) is exceeded for all uses (birds and 

mammals). Available acute dose-based toxicity data for some granule formulations indicates 

greater toxicity than the TGAI; thus, RQs are greater when based on granule toxicity. Banded 

application methods result in higher RQs than in-furrow or knifed-in application methods.

 5 http://www.epa.gov/oppefed1/models/terrestrial
29

Table 7. Avian RQs for Use of Terbufos1,2

Use Application 

Method 

(timing) 

lb ai/

1000 

ft row

Product Band 

width 

(in)

Toxicity3 RQ (acute dose)4 RQ 

(chronic)5 0.02 kg 

bird

0.1 kg

bird

1 kg 

bird

Corn Banded 

(at planting) 

0.15 15G (NC) 7 TGAI 42 7 0.47 63

15G 127 20 1 N/A

0.075 CR TGAI 21 3 0.23 31

CR 30 5 0.32 N/A

15G TGAI 21 3 0.23 31

15G 63 10 0.69 N/A

20G 5 TGAI 30 5 0.33 44

4 37 6 0.41 55

In furrow

(at planting)

0.15 15G (NC) 1 TGAI 20 3 0.22 116

15G 59 9 0.66 N/A

0.075 CR TGAI 10 2 0.11 58

CR 14 2 0.15 N/A

15G TGAI 10 2 0.11 58

15G 30 5 0.33 N/A

20G TGAI 10 2 0.11 58

Banded 

(postemergence 

and at 

cultivation)

0.075 CR 7 TGAI 21 3 0.23 124

CR 30 5 0.32 N/A

15G TGAI 21 3 0.23 124

15G 63 10 0.69 N/A

20G TGAI 21 3 0.23 124

Sorghum Knifed in 

(at bedding and 

at planting)

0.065 CR 1 TGAI 9 1 0.09 13

CR 12 2 0.13 N/A

0.066 15G TGAI 9 1 0.10 13

15G 26 4 0.30 N/A

0.065 20G TGAI 9 1 0.09 13

Banded 

(at planting)

0.065 CR 7 TGAI 18 3 0.20 27

CR 25 4 0.28 N/A

0.066 15G TGAI 18 3 0.20 27

15G 55 9 0.60 N/A

0.065 20G TGAI 18 3 0.20 27

0.066 15G 5 TGAI 26 4 0.29 38

15G 77 12 0.87 N/A

0.065 20G TGAI 25 4 0.28 38

Sugar 

beet

Modified in 

furrow and 

knifed in

(at planting)

0.075 CR 1 TGAI 10 2 0.11 15

CR 14 2 0.15 N/A

15G TGAI 10 2 0.11 15

15G 30 5 0.33 N/A

20G TGAI 10 2 0.11 15

Banded

(at planting and 

postemergence)

CR 7 TGAI 21 3 0.24 32

CR 30 5 0.34 N/A

15G TGAI 21 3 0.24 32

15G 64 10 0.72 N/A

20G TGAI 21 3 0.24 32

CR 5 TGAI 30 5 0.33 175

CR 42 7 0.46 N/A

15G TGAI 30 5 0.33 175

15G 89 14 0.99 N/A

20G TGAI 30 5 0.33 175
30

1 Product application methods (timing, lb ai/1000 ft row, band width) were obtained from the most recent product 

labels.

2 RQs greater than 1 (acute) or 2 (chronic) are rounded to the nearest whole number.

3 Acute toxicity based on TGAI, Bobwhite quail LD50 = 28.6 mg ai/kg/bw; 15G, Mallard duck LD50 = 13.21 mg 

ai/kg bw; 20CR Cowbird LD50 = 16.9 mg ai/kg bw 4 RQs are based on data from single oral dose toxicity studies. Results from dietary studies can be converted to dose 

equivalent toxicity values; these values result in RQs (not shown) that are similar to those based on single oral dose 

toxicity studies. Example conversion for LC50 = 143 mg ai/kg diet (MRID 00087717): mg ai/kg bw = (mg ai/kg diet 

* daily food intake)/kg bw. daily food intake = 0.0582 * bw^0.651 (source: SIP v 1.0 manual). bw = 0.157 kg 

(source: mean value from MRID 00087717). LD50 = 15.8 mg ai/kg bw = (143 mg ai/kg diet * 0.017 kg/day)/0.157

kg bw

5 The dietary-based chronic toxicity value (NOAEC = 5 mg ai/kg diet; MRID 0161574) was converted to a dose 

equivalent toxicity value. mg ai/kg bw = (mg ai/kg diet * daily food intake)/kg bw. daily food intake = 0.0582 * 

bw^0.651 (source: SIP v 1.0 manual). bw = 1.136 kg (source: mean value from MRID 0161574). NOAEL= 0.278 

mg ai/kg bw = (5 mg ai/kg diet * 0.0632 kg/day)/1.136 kg bw

BOLD indicates that the RQ is greater than or equal to the acute listed species LOC (0.1) or the chronic LOC (1.0).

N/A indicates that chronic toxicity data were not available for the formulation. TGAI = technical grade active 

ingredient. CR, 15G, and 20G refer to Counter (terbufos) formulations. 15G (NC) = North Carolina special local 

needs label for 15G.

Table 8. Mammalian RQs for Use of Terbufos1,2

Use Application 

Method 

(timing) 

lb ai/

1000 

ft row

Product Band 

width 

(in)

Toxicity3 RQ (acute dose) RQ 

0.015 (chronic)

kg4

0.035 

kg4

1 kg4

Corn Banded 

(at planting) 

0.15 15G (NC) 7 TGAI 422 224 18 249

0.075 CR, 15G 211 112 9 124

20G 5 TGAI 296 157 13 174

20G 440 233 19 N/A

4 TGAI 370 196 16 218

20G 551 292 24 N/A

In furrow

(at planting)

0.15 15G (NC) 1 TGAI 197 104 8 116

0.075 CR, 15G 99 52 4 58

20G 99 52 4 58

20G 147 78 6 N/A

Banded 

(postemergence 

and at 

cultivation)

0.075 CR, 15G 7 TGAI 211 112 9 124

20G 211 112 9 124

20G 315 167 14 N/A

Sorghum Knifed in 

(at bedding and 

at planting)

0.065 CR 1 TGAI 85 45 4 50

0.066 15G 86 45 4 50

0.065 20G 85 45 4 50

20G 127 67 5 N/A

Banded 

(at planting)

0.065 CR 7 TGAI 182 96 8 107

0.066 15G 184 97 8 108

0.065 20G 182 96 8 107

20G 271 144 12 N/A

0.066 15G 5 TGAI 257 136 11 151

0.065 20G 255 135 11 150

20G 380 201 16 N/A
31

Use Application 

Method 

(timing) 

lb ai/

1000 

ft row

Product Band 

width 

(in)

Toxicity3 RQ (acute dose) RQ 

0.015 (chronic)

kg4

0.035 

kg4

1 kg4

Sugar 

beet

Modified in 

furrow and 

knifed in

(at planting)

0.075 CR, 15G 1 TGAI 99 52 4 58

20G 99 52 4 58

20G 148 78 6 N/A

Banded

(at planting and 

postemergence)

CR, 15G 7 TGAI 212 113 9 125

20G 212 113 9 125

20G 316 168 14 N/A

CR, 15G 5 TGAI 297 157 13 175

20G 297 157 13 175

20G 443 235 19 N/A 1 Product application methods (timing, lb ai/1000 ft row, band width) were obtained from the most recent product 

labels.

2 RQs greater than 1 (acute) or 2 (chronic) are rounded to the nearest whole number.

3 Acute toxicity based on TGAI, Rat LD50 = 1.25 mg ai/kg/bw; 20G, rat LD50 = 0.836 mg ai/kg bw. Chronic dose 

based toxicity based on TGAI, NOAEL = 0.07 mg ai/kg bw. 4 Mammal body weight

BOLD indicates that the RQ is greater than or equal to the acute listed species LOC (0.1) or the chronic LOC (1.0).

N/A indicates that chronic toxicity data were not available for the formulation. TGAI = technical grade active 

ingredient. CR, 15G, and 20G refer to Counter (terbufos) formulations. 15G (NC) = North Carolina special local 

needs label for 15G.

Dietary Ingestion (contaminated fish)

KABAM (KOW (based) Aquatic BioAccumulation Model, v 1.0)6 was used to estimate potential

bioaccumulation of terbufos in freshwater aquatic food webs and risk to piscivorus mammals and 

birds that consume terbufos contaminated fish. The model bases bioaccumulation in the food 

web on the octanol-water coefficient (Kow) of the chemical and the estimated surface water and 

pore water concentrations of the chemical. Although terbufos, terbufos sulfoxide, and terbufos 

sulfone show similar toxicity, risk was assessed based on exposure to terbufos alone because the 

bioaccumulation potential of terbufos is much greater than that of terbufos sulfoxide and terbufos 

sulfone (terbufos log Kow = 4.71, terbufos sulfone log Kow = 2.48 (EPISUITE estimate), and 

terbufos sulfoxide log Kow = 2.21 (EPISUITE estimate)). Bioaccumulation based on TTR EECs 

and the bioaccumulation potential of terbufos would overestimate bioaccumulation in the food 

web. The bioaccumulation potential is assumed to be low for terbufos sulfone and terbufos 

sulfoxide based on their Kow values. 

The assessment is based on the assumption that terbufos is not metabolized by aquatic organisms 

(input parameter km = 0 d-1

). The elimination rate constant value (kT = 0.31 d-1) estimated from 

the laboratory BCF study is similar to the sum of the KABAM estimated loss rate constants (i.e., 

k2 + kG = 0.36 d-1) based on fish weight and water temperature from the BCF study.

7 The results 

 6 http://www.epa.gov/oppefed1/models/water

7 The estimated loss rate constants (k2 and kg) were generated using the KABAM model. All default parameters 

were used, with two exceptions: (1) the large fish was parameterized to represent the average body weight of the fish 

in the BCF study (6.4 g) and (2) the average temperature of the study (22 °C) was entered as the model water 

temperature.
32

of this comparison indicate that metabolism is not a substantial mechanism of depuration and 

supports the assumption that km = 0 d-1

. 

RQs were calculated for the crop scenario resulting in the lowest and highest EECs (21 day 

averaging period) for each use of terbufos (Appendix F; Table F-4); as discussed above, EECs 

are based on terbufos only. Representative KABAM model results are presented in Appendix 

H.

Results from KABAM indicate a risk concern for piscivorus birds and mammals for use of 

terbufos (Table 9). For mammals, all uses, crop scenarios, mammal size classes, and functional 

feeding groups exceed the LOC on an acute and chronic basis. For birds, the chronic LOC is 

exceeded only for the crop scenario resulting in the highest EEC estimates for corn and sorghum. 

Acute RQs for birds exceed the listed species acute LOC but not the non-listed species LOC and 

only for smaller birds in two feeding groups (represented by sandpipers and rails) for the crop 

scenario resulting in the highest EECs for each use of terbufos.

Table 9. Piscivorous Wildlife RQs for Use of Terbufos1,2

Crop 

(application 

rate)

Wildlife Species Acute RQ Chronic RQ

Dose Based Dietary Based Dose Based Dietary Based

Corn

(1.3 lb ai/A)

Mammalian

fog/water shrew 0.06-1 N/A 2-31 0.28-6

rice rat/star-nosed mole 0.08-2 N/A 2-38 0.28-6

small mink 0.11-2 N/A 3-52 0.42-8

large mink 0.12-2 N/A 3-57 0.42-8

small river otter 0.13-2 N/A 3-61 0.42-8

large river otter 0.15-3 N/A 4-73 0.47-9

Avian

sandpipers 0.01-0.28 <0.01-0.04 N/A <0.1-1.1

cranes <0.01-0.02 <0.01-0.04 N/A <0.1-1.2

rails <0.01-0.15 <0.01-0.05 N/A <0.1-1.3

herons <0.01-0.03 <0.01-0.05 N/A <0.1-1.4

small osprey <0.01-0.04 <0.01-0.06 N/A <0.1-1.6

white pelican <0.01-0.02 <0.01-0.06 N/A <0.1-1.8

NC Corn

(2.6 lb ai/A)

Mammalian

fog/water shrew 0.51-0.52 N/A 13 2

rice rat/star-nosed mole 0.62-0.65 N/A 16 2

small mink 0.86-0.89 N/A 21-22 3-4

large mink 0.95-0.98 N/A 24-25 3-4

small river otter 1 N/A 25-26 3-4

large river otter 1 N/A 32-34 4

Avian

sandpipers 0.12 0.02 N/A 0.46-0.48

cranes <0.01 0.02 N/A 0.48-0.50

rails 0.06 0.02 N/A 0.54-0.56

herons 0.01 0.02 N/A 0.57-0.59

small osprey 0.02 0.02 N/A 0.69-0.71

white pelican <0.01 0.03 N/A 0.79-0.84
33

Crop 

(application 

rate)

Wildlife Species Acute RQ Chronic RQ

Dose Based Dietary Based Dose Based Dietary Based

Sugar beet

(1.96 lb ai/A)

Mammalian

fog/water shrew 0.25-0.28 N/A 6-7 1.1-1.2

rice rat/star-nosed mole 0.31-0.34 N/A 8-9 1.1-1.3

small mink 0.42-0.47 N/A 11-12 1.7-1.9

large mink 0.47-0.52 N/A 12-13 1.7-1.9

small river otter 0.50-0.56 N/A 13-14 1.7-1.9

large river otter 0.65-0.69 N/A 16-17 2

Avian

sandpipers 0.06 <0.01 N/A 0.23-0.25

cranes <0.01 <0.01 N/A 0.24-0.26

rails 0.03 ≤0.01 N/A 0.27-0.30

herons <0.01 0.01 N/A 0.28-0.31

small osprey ≤0.01 0.01 N/A 0.34-0.37

white pelican <0.01 0.01 N/A 0.40-0.43

Sorghum

(1.695 lb ai/A)

Mammalian

fog/water shrew 0.35-0.96 N/A 9-24 1.5-4

rice rat/star-nosed mole 0.43-1 N/A 11-29 1.6-4

small mink 0.59-2 N/A 15-40 2-6

large mink 0.66-2 N/A 16-44 2-6

small river otter 0.71-2 N/A 18-47 2-6

large river otter 0.86-2 N/A 21-55 3-7

Avian

sandpipers 0.08-0.22 0.01-0.03 N/A 0.32-0.86

cranes ≤0.01 0.01-0.03 N/A 0.34-0.90

rails 0.04-0.12 0.01-0.04 N/A 0.37-1.0

herons <0.01-0.02 0.01-0.04 N/A 0.40-1.1

small osprey 0.01-0.03 0.02-0.05 N/A 0.48-1.3

white pelican ≤0.01 0.02-0.05 N/A 0.53-1.4 1 Range is based on use scenarios resulting in the lowest and highest terbufos EECs for each crop as provided in 

Appendix F, Table F-4. For example, the RQ range for corn is based on the 21 day EECs (terbufos only) from the 

ORsweetcorn_OP scenario (0.13 μg/L surface water; 0.34 μg/L pore water) and MScorn_STD (2.44 μg/L surface 

water; 8.74 μg/L pore water).

2 RQs greater than 1 (acute) or 2 (chronic) are rounded to the nearest whole number.

BOLD indicates that the RQ is greater than or equal to the acute listed species LOC (0.1) or the chronic LOC (1.0).

Inhalation

The Screening Tool for Inhalation Risk (STIR v1.0)8 was used to provide an upper bound 

estimate of bird and mammal exposure to terbufos through vapor inhalation. There is no spray 

drift exposure (droplet inhalation) because terbufos is applied as a granule. The screening 

suggests that terbufos use has the potential for significant vapor inhalation risk (the ratio of vapor 

concentration in the air to the inhalation LD50 exceeds the screening threshold of 0.1). Model 

inputs and output are presented in Appendix I.

 8 http://www.epa.gov/oppefed1/models/terrestrial
34

Drinking Water

The Screening Imbibition Program (SIP v.1.0)

8 was used to calculate an upper bound estimate of 

bird and mammal exposure to terbufos in drinking water. The screening indicates potential acute 

and chronic risk to birds and mammals through the consumption of terbufos-contaminated 

drinking water. Model results are presented in Appendix J.

6.2 Terrestrial and Semi-Aquatic Plants

TerrPlant (v 1.2.2)8 was used to calculate EECs for characterizing exposure to terrestrial and 

semi-aquatic plants through run-off of terbufos. There is no spray drift exposure because 

terbufos is applied as a granule. The listed species LOC of 1 is not exceeded for any use. Input 

and output for the maximum application rate (NC use on corn) are shown in Appendix K.

VII. Risk Characterization

7.1 Aquatic Organisms

Aquatic Fish and Invertebrates

The standard modeling approach based on exposure to total toxic residues (terbufos, terbufos 

sulfoxide, and terbufos sulfone) indicates an acute and chronic risk concern for fish and aquatic 

invertebrates from use of terbufos on corn, sorghum, and sugar beet (Table 6). TTR was used 

to calculate EECs because terbufos sulfoxide, and terbufos sulfone are more persistent than 

terbufos and available toxicity data indicate that they are similar in toxicity to terbufos. 

Concerns about adverse effects to aquatic organisms from terbufos use are strongly supported by 

widespread fish kill incidents. Aquatic incidents prior to the RED do not necessarily reflect any 

of the mitigation which now requires implementation of vegetative buffers and setbacks 

between the treated field and water bodies. Buffers may make aquatic incidents less likely to 

occur and it is noted that the number of reported fish incidents per year has declined since the 

RED; however, this does not necessarily indicate a lack of incidents or reduced risk. Reliance 

on the frequency of incidents may significantly underestimate the extent of the actual impacts. 

Adverse ecological effects cannot be assumed to be reliably detected and reported. Before an 

incident can be reported, it must be observed and attributed to terbufos. Reproductive effects or 

other sublethal effects, effects on eggs or small age classes, or impacts on relatively small 

species (invertebrates, amphibians, or small fish species) are likely to escape immediate 

detection. For example, the only invertebrate species cited in terbufos related incidents is 

crayfish, which is a relatively conspicuous invertebrate. Toxicity data indicate that invertebrates 

are more sensitive to terbufos than fish; thus, effects on invertebrates can be assumed when fish 

kill incidents are reported but the absence of fish incidents does not indicate an absence of 

adverse effects on invertebrates.

In many cases, incident reports for fish kills associated with terbufos use on corn indicate that

residues of terbufos, terbufos sulfone, or terbufos sulfoxide were detected at levels in the surface 

water of static systems that are similar to those predicted by modeling of static water systems 

(Appendix E, Table E-1 and Appendix F, Table F-4). Surface water concentrations observed 
35

in the incident reports reflect a wide range of variables including but not limited to application 

rate and method, time elapsed between application and water sampling, distance of the water 

body from the application site, and the size of the water body relative to that of the treated field. 

Monitoring data generally show lower concentrations of terbufos in flowing water systems than 

predicted through modeling for static water systems, but non-targeted sampling is unlikely to 

capture peak concentrations (see Section V). Nonetheless, monitoring information indicates 

that concentrations of terbufos, terbufos sulfone, and terbufos sulfoxide sometimes reach levels 

in flowing water systems that would adversely affect aquatic animals. For instance, more recent 

NAWQA monitoring data show surface water concentrations of terbufos up to 0.02 μg/L and 

terbufos sulfone concentrations up to 0.17 μg/L, which are high enough to trigger an acute risk 

concern for aquatic invertebrates.

Several open literature studies showed greater acute (freshwater invertebrates) and chronic 

(freshwater fish) toxicity than demonstrated in registrant submitted studies (discussed in Section 

IV). RQs were not calculated because the studies were classified as qualitative. These data do 

not change the risk conclusions; however, it does suggest that acute risk to freshwater 

invertebrates and chronic risk to freshwater fish may be greater than indicated by toxicity based 

on registrant submitted data. 

In addition, one open literature study showed adverse developmental effects on southern bell 

frogs exposed to 10 μg terbufos sulfone/L for 10 weeks. Assuming that terbufos and terbufos 

sulfoxide are similar in toxicity to terbufos sulfone as for other taxa, then adverse effects may be 

reasonably expected to occur given that 60-day TTR surface water EECs range from 3.63 to

18.70 μg/L.

The quantitative risk assessment (i.e., calculation of RQs) is based on upper bound EECs that do 

not consider the labeled setbacks and vegetative buffers. It is assumed that buffers will reduce 

loading to aquatic systems due to run-off from treated fields; thus, risk to aquatic organisms may 

be reduced with use of buffers. Although currently available models cannot account for the 

impact of vegetative buffers (see Section V for discussion), the potential impact of buffers is 

characterized by calculating how effective they would need to be to reduce EECs and thus RQs 

below LOCs. While there is good evidence that buffers can reduce pesticide movement into 

water bodies to some extent, there is still a great deal of uncertainty regarding the performance of 

buffers, which includes but is not limited to proper design and placement and the duration of 

their efficacy. Based on a review of available research, EFED hypothesized that the use of 

vegetative buffers may reduce loading of total toxic residues of terbufos in aquatic systems by 

50% to 90% (see USEPA, 2015 for a full discussion). In comparison, loading would need to be 

reduced more than about 93% to 99.9% for RQs to be below LOCs, depending on the crop, 

taxonomic group (fish or invertebrate; freshwater or marine/estuarine species), listed or nonlisted species status, and LOC (acute or chronic). There is only one exception that requires 

loading reductions less than the hypothesized maximum of 90%. A vegetative buffer would 

need to reduce the “no buffer” EECs by ≥ 85% for the scenario with the lowest surface water 

EECs (5.52 μg/L; corn; ORsweetcorn_OP scenario) to be below the acute non-listed species 

LOC for marine/estuarine fish (Figure 1). For all other scenarios, loading would need to be 

reduced more than 90% for the RQ to be below the acute non-listed species LOC for 

marine/estuarine fish. Overall, available information suggests that loading may be reduced up to 
36

90% with the use of vegetative buffers; however, the overall risk concerns for fish and aquatic 

invertebrates remain because RQs remain above the LOCs after accounting for those reductions. 

 Figure 1.

Aquatic plants

The LOC (1.0) is not exceeded for listed aquatic plants (RQs ≤ 0.13) from any labeled use. 

Although EC50s were not established in the available studies, there is not a risk concern for nonlisted plants given that there is not a risk concern for listed plants. Although there is open 

literature data for a freshwater diatom (Nitzschia sp.) that showed a more sensitive EC50 value 

than registrant submitted data, the reported EC50 value is higher than the NOAEC values in the 

registrant submitted data which did not trigger a risk concern for listed species. Although the 

NOAEC was not reported, there is little uncertainty in the risk conclusions of this assessment 

because there are not currently any listed algal species. That same study also tested two other 

algal species that showed less sensitivity to terbufos. Based on the weight of the available 

evidence, there is not a risk concern for aquatic vascular or non-vascular plants. 

7.2 Terrestrial Organisms

Birds and Mammals

There are several potential sources of terbufos exposure to birds and mammals. Granules may be 

ingested directly by birds foraging for seed and grit at or below the soil surface on treated areas. 

The similarity of the granules to natural forage or grit has been suggested as an important 

characteristic which may influence ingestion of granules. Grit preferences are expected to vary 
37

among avian species and may depend on variables including size, shape, texture, and color. 

Birds and mammals may also ingest granules adhered to the surface of invertebrate prey items 

such as earthworms and grubs or accidentally ingest granules when foraging for seeds and 

insects. Piscivorous birds and mammals may be exposed to terbufos residues in contaminated 

fish. Other routes of exposure for both birds and mammals include ingestion of contaminated 

drinking water, vapor inhalation, and dermal exposure through contact with treated soil. The 

weight of evidence from the assessment of various pathways supports an acute and chronic risk 

concern for birds and mammals from labeled uses of terbufos.

The standard modeling scenario for consumption of granules (LD50/ft2 method) indicates an 

acute and chronic risk concern for evaluated size classes of birds and mammals for use on corn, 

sorghum, and sugar beet (Table 7 and 8). While the LD50/ft2 method has no ecological meaning, 

it is used as a means to characterize the level of exposure in a relatively small foraging area; 

therefore, the likelihood of risk. Available acute dose-based toxicity data for granules indicates 

greater toxicity than TGAI; thus, RQs are greater when based on granule toxicity. 

Banded application methods result in higher RQs than in-furrow or knifed-in application 

methods. Soil incorporation using conventional commercial equipment greatly reduces the 

number of exposed granules, but does not eliminate potential exposure. The risk assessment 

assumes that 15% of granules are exposed and available for banded applications and 1% are 

exposed for in-furrow and knifed-in applications. However, varying numbers of exposed 

granules may result from each type of use specified on terbufos labels. 

Exposure values were estimated for along treated rows where some type of incorporation is 

concurrent with application. The number of granules that may be found in turn areas at row ends 

where application equipment is raised from the soil may be considerably higher than along rows. 

Label directions specify incorporating product that is visible on the soil surface in turn areas; 

however, it may not be practical to do this immediately after granules are deposited and the level 

of incorporation may not be equal to that along the rows. Therefore, risk at row ends may be 

greater than suggested by risk along treated rows.

The likelihood of consuming enough terbufos to cause adverse effects is related in part to the 

number of granules containing that dose and the number of granules readily available for 

foraging. The fewer the number of granules and the higher the availability, the greater the risk 

concern. In general, very few granules are required to reach either the acute listed or non-listed 

species LOCs (Appendix L). The number of exposed granules is relatively high in comparison. 

For birds, the listed species acute LOC is exceeded consuming <1 to 125 granules, depending on 

the bird weight and terbufos product (CR, 15G, or 20G).

9

 For mammals, the listed species acute 

LOC is exceeded consuming <1 to 10 granules, depending on the mammal weight and terbufos 

product. Exceedance of the non-listed species acute LOC requires consuming 5 times as many 

granules. For a given use, the formulation also impacts the likelihood of consuming enough 

granules to exceed the acute LOCs; a fewer number of CR granules are required than 20G or 

15G granules due primarily to their larger size.10

 9 Range is based on formulation toxicity when available instead of TGAI toxicity. 10 Difference in formulation toxicity is also a factor. Although there is not a complete formulation toxicity dataset 

for either birds or mammals, available information suggests that differences in granule size may be the primary 

factor differentiating the formulations in terms of the number of consumed granules that result in a risk concern.
38

Results from KABAM indicate a risk concern for piscivorus birds and mammals for all uses of 

terbufos. The results suggest that mammals are more at risk than birds. This assessment is based 

on the assumption that terbufos is not metabolized by aquatic organisms in the food chain. The 

assumption is supported by results from the BCF study in conjunction with KABAM estimates 

of loss rate constants which indicate that metabolism is not a substantial mechanism of 

depuration for fish (see Section 6.1); nonetheless, risk may be overestimated to the extent that 

terbufos is metabolized in different compartments of the aquatic food chain. Although exposure 

concentrations in water may be high enough to cause mortality in sensitive individuals and 

species of fish and invertebrates, the potential for bioaccumulation in the food chain may occur 

in less sensitive individuals and species. In addition, the assessment was based on EECs that do 

not consider the labeled setbacks and vegetative buffers. Currently available models cannot 

account for the impact of these buffers (see Section V for discussion). The potential impact of 

the buffers was characterized by calculating how effective they would need to be to reduce EECs 

below the level of concern. Buffers need to be very effective at reducing runoff to eliminate the 

risk concern; however, in some cases the buffers may be effective enough. As discussed above, 

it is hypothesized that buffers may reduce loading between 50% and 90%. RQs would be below 

the acute and chronic LOCs for the scenario with the lowest bioaccumulation potential 

(ORsweetcorn_OP scenario) if loading is reduced by 75% compared to the “no buffer” EECs. In 

contrast, the scenario with the highest bioaccumulation potential (MScorn_STD) would require a 

95% reduction in loading compared to the “no buffer” EECs to eliminate the risk concern for 

birds (acute and chronic) and for mammals on an chronic dietary basis while RQs would remain 

above the acute and chronic LOC on a dose basis for mammals even with a 95% reduction in 

loading.

The STIR model indicates a potential risk to birds and mammals from vapor inhalation. This is 

not unexpected given that terbufos is highly toxic (acute inhalation) and semi-volatile. The 

screen assumes a maximum vapor concentration in air at saturation for 1 hour; therefore, it 

represents an upper-bound exposure value and provides a conservative estimate of exposure at 

the screening level. The screen indicates that the ratio of vapor concentration (at saturation) to 

inhalation toxicity is 108x above the screening threshold of 0.1 for mammals and 40x above the 

threshold for birds (based on an estimated inhalation toxicity value). Although avian inhalation 

toxicity data would be useful for better addressing potential risk, it is likely to show that terbufos 

is highly toxic (as it is to mammals); therefore, indicating a potential risk through vapor 

inhalation exposure. The vapor pressure (3.16 x 10-4 mm Hg) and Henry’s Law Constant (2.22 x 

10-5 atm m3/mol) suggest that some terbufos will dissipate by diffusion into the atmosphere; 

however, the amount will likely vary depending on site conditions, application methods, and the 

rate of photodegradation in the atmosphere. For example, exposure from volatilization may be 

greater for terbufos that remains on the soil surface after incorporation (i.e., along rows and at the 

end of rows) than for terbufos that is incorporated into the soil. Likewise, lightly incorporated 

applications may result in greater exposure than applications requiring deeper incorporation. 

Vapor phase exposure estimates can be refined using a flux rate measured at a representative use 

site coupled with an air dispersion model (e.g., AERSCREEN or PERFUM). EFED 

recommends submission of a field volatility study to refine exposure estimates. 

Given the results of the conservative screening, exposure to terbufos through volatilization may 

or may not be a sole cause of adverse effects to non-target animals; however, the screening does 
39

suggest that when aggregated with other routes of exposure (i.e., diet, drinking water, and 

dermal), terbufos exposure through vapor inhalation may contribute to a total exposure that has 

potential for effects to non-target animals.

The SIP model indicates a potential risk to birds and mammals from acute and chronic exposure 

to terbufos contaminated drinking water. This screening is qualitative, is based on drinking 

water exposure alone, and is based on several conservative assumptions which add considerable 

uncertainty to this risk conclusion (see Appendix J). Nonetheless, when aggregated with other 

routes of exposure (i.e., diet, inhalation, and dermal), terbufos exposure through drinking water 

may contribute to a total exposure that has potential for effects to non-target animals.

The open literature data for acute toxicity to birds (discussed in Section IV) were not used 

quantitatively in the risk assessment. The data would not change general conclusions about 

acute risk to birds; however, it does suggest that acute risk may be greater than that indicated by 

acute toxicity of the TGAI to bobwhite quail (MRID 00106551).

Overall, the weight of available evidence supports an acute and chronic risk concern for birds 

and mammals from the labeled use of terbufos. The risk concern based on the LD50/ft2

assessment is supported by field studies. In addition, bird and mammal incidents are reported in 

the three incident databases (EIIS, Aggregate Incident Data System, and AIMS), although it is 

noted that some reported in EIIS may be misuse or misapplications of terbufos. Screening level 

drinking water and vapor phase exposure estimates suggest a potential risk concern as well. 

Finally, there is a potential risk concern for piscivorus birds and mammals from consuming 

terbufos contaminated fish. Cumulative exposure to terbufos from multiple pathways may be an 

important consideration in the risk of terbufos even if each pathway contributes a small amount 

to total exposure given that terbufos is highly toxic to birds and very highly toxic to mammals.

Non-Target Terrestrial Invertebrates

Terbufos is a systemic granular pesticide, thus it is translocated into plant tissues after soil 

applications. Exposure of honeybees to systemic pesticides via soil applications is expected to 

result primarily from translocation to plant tissues (pollen, nectar, exudates, and honeydew); 

therefore, it is assumed that the primary route of exposure is through diet (USEPA, 2012b). 

Exposure may occur from visiting plants on the treatment field. Plants off the treated field may 

also contain residues if run-off occurs. Bees could be exposed through direct contact with 

exposed granules; however, this exposure pathway is much less likely and the proposed Tier I 

exposure methods do not include a methodology for addressing this exposure pathway. Dietary 

risk could not be assessed because acute and chronic oral toxicity (adult or larval) data are not 

available for terbufos or phorate, the structural analog of terbufos. Although risk cannot be 

quantified it is reasonable to expect risk to honeybees given that terbufos is an insecticide and 

that it is systemic. Submission of acute and chronic oral toxicity data (adult and larval) would be 

useful for refining and characterizing the degree of risk.
40

Terrestrial Plants

The LOC (1.0) is not exceeded for listed plants located in dry or semi-aquatic locations (RQs ≤ 

0.13) from any labeled use. There is no risk from spray drift because the products are applied as 

a granule. Vegetative vigor toxicity data were not available; however, given the mode of action 

of terbufos it is assumed that the seedling emergence data are likely representative of potential 

effects on growth of older plants. Although an EC25 was not established in the available 

seedling emergence study, there is no risk concern for non-listed plants given that there is no risk 

concern for listed plants.

Some open literature data suggest that effects to plants (phytotoxicity other than growth and 

survival and field yield) may occur at rates lower to or equal to the 2 lb ai/A NOAEC observed 

in the registrant submitted data. Effects were observed at concentrations from 1-2 lb ai/A; 

however, NOAECs were not established. Chlorosis (7 day old corn) and decreased tissue Zn 

concentration (at harvest) were observed in corn while treated plants showed growth 

(chlorophyll, height, and weight) that was similar to or greater than control plants later in the 

growing season. Two field studies showed effects on yield; however, there is inherent 

uncertainty as to the cause of these effects and the effects did not occur consistently from year to 

year or site to site. 

Only two incidents reported for terbufos in the EIIS database involve effects on plants (corn) and 

both were likely caused by joint application of other herbicides. In one case the herbicide 

application was a misuse. In both cases flumetsulam, an ALS-herbicide, was one of two 

herbicides applied along with terbufos. Terbufos and other OP insecticides increase the risk of 

plant injury in corn plants due to toxic effects of ALS-herbicides. As such, the terbufos labels 

provide warnings about the timing of application of terbufos and ALS-herbicides. This 

interaction occurs because terbufos and ALS-herbicides are degraded by the same enzyme 

system; thus, the presence of terbufos may reduce the rate of degradation of the herbicide and 

allow it to accumulate in the plant to toxic levels.11 Six incidents of minor plant damage are 

reported in the Aggregate Incident Data System. Details of these incidents are not reported; 

however, it is certainly possible that they could be related to co-exposure with herbicides given 

the known interaction of certain herbicides with terbufos.

Based on the weight of evidence there is little risk concern for direct effects to terrestrial plants 

from the labeled uses of terbufos with the exception of terbufos potentially increasing the 

toxicity of herbicides such as ALS-inhibitors when both terbufos and the herbicide are taken up 

by a plant in sufficient quantities.

VIII. Risk to Listed Species

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the 

National Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department 

of Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks 

to listed species from pesticides. The Interim Approaches were developed jointly by the 

agencies in response to the National Academy of Sciences’ (NAS) recommendations and reflect 

 11 http://www.weeds.iastate.edu/mgmt/qtr00-1/opinteractions.htm
41

a common approach to risk assessment shared by the agencies as a way of addressing scientific 

differences between the EPA and the Services. The NAS report outlines recommendations on 

specific scientific and technical issues related to the development of pesticide risk assessments 

that EPA and the Services must conduct in connection with their obligations under the 

Endangered Species Act (ESA) and the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA). 

The joint Interim Approaches were released prior to a stakeholder workshop held on November

15, 2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 

Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and 

Evaluation Group (SFIREG) meetings, and held a stakeholder workshop in April 2014, allowing 

additional opportunities for stakeholders to comment on the Interim Approaches. As part of a 

phased, iterative process for developing the Interim Approaches, the agencies will also consider 

public comments on the Interim Approaches in connection with the development of upcoming 

Registration Review decisions. The details of the joint Interim Approaches are contained in the 

white paper “Interim Approaches for National-Level Pesticide Endangered Species Act 

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 

Report,” dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, this preliminary risk assessment for terbufos does not contain a 

complete ESA analysis that includes effects determinations for specific listed species or 

designated critical habitat. Although EPA has not yet completed effects determinations for 

specific species or habitats, for this preliminary assessment EPA conducted a screening-level 

assessment for all taxa of non-target wildlife and plants that assumes for the sake of the 

assessment that listed species and designated critical habitats may be present in the vicinity of 

the application of terbufos. This screening level assessment will allow EPA to focus its future 

evaluations on the types of species where the potential for effects exists once the scientific 

methods being developed by the agencies have been fully vetted. This screening-level risk 

assessment for terbufos indicates potential risks of direct effects to listed mammals, birds, 

terrestrial invertebrates, fish, and aquatic invertebrates on all of its registered use sites. Listed 

species of aquatic and terrestrial plants may also be affected through indirect effects because of 

the potential for direct effects on listed and non-listed species upon which such species may rely. 

Potential direct effects on listed mammals, birds, terrestrial invertebrates, fish, and aquatic 

invertebrates from the use of terbufos may be associated with modification of Primary 

Constituent Elements (PCEs) of designated critical habitats, where such designations have been 

made. Once the agencies have fully developed and implemented the scientific methods 

necessary to complete risk assessments for endangered and threatened (listed) species and their 

designated critical habitats, these methods will be applied to subsequent analyses for terbufos as 

part of completing this registration review. 

IV. Endocrine Disruptor Screening Program

As required by FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA), EPA reviews 

numerous studies to assess potential adverse outcomes from exposure to chemicals. 
42

Collectively, these studies include acute, subchronic and chronic toxicity, including assessments 

of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. 

These studies include endpoints which may be susceptible to endocrine influence, including 

effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual 

maturation, fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For 

ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, 

developmental and reproductive effects in different taxonomic groups. As part of registration 

review of terbufos, EPA reviewed these data and selected the most sensitive endpoints for 

relevant risk assessment scenarios from the existing hazard database. However, as required by 

FFDCA section 408(p), terbufos is subject to the endocrine screening part of the Endocrine 

Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list 

of chemicals identified for EDSP screening was published on June 14, 201312 and includes some 

pesticides scheduled for registration review and chemicals found in water. Neither of these lists 

should be construed as a list of known or likely endocrine disruptors. 

Terbufos and terbufos sulfone (degradation product) are on List 2. List 2 represents the next set 

of chemicals for which EPA intends to issue test orders/data call-ins in the near future. For 

further information on the status of the EDSP, the policies and procedures, the lists of chemicals, 

future lists, the test guidelines and the Tier 1 screening battery, please visit the website.13

 12 http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 13 http://www.epa.gov/endo/
43

X. References

Note: Open literature toxicity study references from the ECOTOXicology database are listed in 

Appendix M.

Carter, J.M., Kingsbury, J.A., Hopple, J.A., and G.C. Delzer. 2010. Concentration Data for 

Anthropogenic Organic Compounds in Groundwater, Surface Water, and Finished Water of 

Selected Community Water Systems in the United States, 2002–10. U.S. Geological Survey Data 

Series 544.

Felsot, A., L. Wei, and J. Wilson. 1982. Environmental Chemodynamic Studies with Terbufos

(Counter) Insecticide in Soil under Laboratory and Field Conditions. Journal of Environmental 

Science and Health. Vol. B17(6), pp. 649-673.

Majewski, M.S. and P.D. Capel. 1995. Pesticides in the Atmosphere-Distribution, Trends, and 

Governing Factors. Pesticides in the Hydrologic System. Ann Arbor Press, Inc, Chelsea, MI.

USEPA. 1999. Revised EFED RED Chapter. August 26, 1999. DP 257287+

.

USEPA. 2001. Interim Reregistration Eligibility Decision [Terbufos]. September 2001.

USEPA. 2006a. Standardized Soil Mobility Classification Guidance. U.S. Environmental 

Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide 

Programs, Environmental Fate and Effects Division. April 21, 2006.

USEPA. 2006b. (P)RZM (E)XAMs Model Shell, Version 5.0. November 15, 2006. 

Environmental Fate and Effects Division. Office of Pesticide Programs. Office of Chemical 

Safety and Pollution Prevention. U.S. Environmental Protection Agency. 

http://www.epa.gov/oppefed1/models/water/

USEPA. 2008a. White Paper on Methods for Assessing Ecological Risks of Pesticides with 

Persistent, Bioaccumulative and Toxic Characteristics. Office of Chemical Safety and Pollution 

Prevention. U. S. Environmental Protection Agency. 

http://www.epa.gov/scipoly/sap/meetings/2008/october/sap_pbt_whitepaper_final_Oct_7_08d.pdf

USEPA. 2008b. Data Evaluation Record on a 167-1/Drinking water Monitoring study of 

Terbufos. MRID 46873301. DP 332141.

USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides, Version 2.1. U.S. Environmental Protection Agency, Office of 

Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate 

and Effects Division. October 22, 2009. 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm
44

USEPA. 2012a. Standard Operating Procedure for Using the NAFTA Guidance to Calculate 

Representative Half-life Values and Characterizing Pesticide Degradation. U.S. Environmental 

Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide 

Programs, Environmental Fate and Effects Division. November 30, 2012. 

http://www.epa.gov/oppefed1/ecorisk_ders/degradation_kinetics/NAFTA_Degradation_Kinetics.htm

USEPA. 2012b. White Paper in Support of the Proposed Risk Assessment Process for Bees, 

September 11 – 14, 2012.

USEPA. 2013. Data on Terbufos and Its Environmental Transformation Products in Support of 

the ROCKS. DP 416458.

USEPA. 2014. Usage Report in Support of a Registration Review for Terbufos. February 11, 

2014. DP 417801.

USEPA. 2015. Adjusted Time-Series Distribution of the Total Toxic Residues of Terbufos from 

Use on Sorghum to Account for the Theoretical Loading Reduction of Terbufos and its 

Degradates to Surface Water in the Presence of Label-Prescribed Vegetative Buffers. DP 

428089.
45

Appendix A: DT50s Submitted Environmental Fate Studies

Hydrolysis (MRID 44862501)

Temperature adjusted DT50 @ 25o C is 1.5 days.

The following guidance was used in calculating temperature adjusted DT50s (USEPA, 2009).
46

Aquatic Photolysis (MRID 41181101)

Estimated DT50 is 1.77 days @ 25o C.
47

Aerobic Soil Metabolism (MRID 00156853)

Aerobic Soil Metabolism (MRID 41181101)

The 90th percentile DT50 is 14.7 days.
48

Aerobic Aquatic Metabolism (MRID 44672204)

The temperature adjusted 90th percentile DT50 @ 25o C is 36.2 days.
49

Anaerobic Soil Metabolism (MRID 41749801)

Terrestrial Field Dissipation (MRID 0087708)
50

Terrestrial Field Dissipation (MRID 0087706)

Terrestrial Field Dissipation (MRID 41883101 and 41883102)
51

Hydrolysis (MRID 44862501)

Temperature adjusted DT50 @ 25o C is 65.1 days.

Aerobic Soil Metabolism (MRID 00156853)
52

Hydrolysis (MRID 44862501)

Temperature adjusted DT50 @ 25o C is 43.8 days.

Aerobic Soil Metabolism (MRID 00156853)
53

Appendix B: Degradate Formation in Fate Studies

Table B-1. Terbufos and Its Environmental Transformation Products

Common Name

(Synonym) Chemical Name Chemical Structure Study Type MRID Maximum %AR1 (day)

Final %AR1

(day)

Parent

Terbufos

(AC 92100)

S-[[(1,1-

dimethylethyl)thio]methyl]O,Odiethylphosphorodithioate

CAS No.: 13071-79-9

Formula: C9H21O4P1S3

MW: 288.4 g/mol

SMILES:

CCOP(=S)(OCC)SCSC(C)(C)C

Hydrolysis

00087694

NA

117.7-22.63 

(28d)

44862501 7.22-16.6 

(1.6-30 d)

Aqueous 

photolysis

00161567 3.2 (6 d)

44927918 11.3 (7 d)

Aerobic soil 00156853 NR

Anaerobic soil 41749801 82.7 (60 d)

Aerobic aquatic

metabolism 448625022 0.5-12 (161-189 d)

Terrestrial field 

dissipation 00087708 0.02 (100 d)

Major (>10%) Transformation Products

Formaldehyde

(Degradate A)3

Formaldehyde

Formula: CH2O

CAS No.: 000050-00-0

MW: 30.03 g/mol 

SMILES: O=C 

Hydrolysis 00087694 69.9 (28 d) 69.9 (28 d)

44862501 96.1 (1.6 d) 96.1 (1.6 d)

Aqueous 

photolysis

00161567 71.9 (6 d) 71.9 (6 d)

448625022 33.8 (2 d) NR (30 d)

448625023 16.9 (30 d) 16.9 (30 d)

448625023 35.2 (30 d) 35.2 (30 d)

41181101 Detected, not quantified

Terbufos sulfoxide

(CL 94301)

S-[[(1,1-

dimethylethyl)sulfinyl]methyl]

O,O-diethylphosphorodithioate

Formula: C9H21O3P1S3

MW: 304.42 g/mol

SMILES: 

[CCOP(=S)(OCC)SCS(=O)C

(C)(C)C

Aerobic soil 00156853 52.3 (30 d) 5.9 (365 d)

Anaerobic soil 41749801 6.2 (15 d) 3.8 (60 d)

Aerobic aquatic 44862502 2 9.98 (3 d) NR (30 d)

Terrestrial field 

dissipation 00087708 0.580 0.02 (100 d)
54

Common Name

(Synonym) Chemical Name Chemical Structure Study Type MRID Maximum %AR1 (day)

Final %AR1

(day)

Terbufos sulfone 

(CL94320)

S-[[(1,1-

dimethylethyl)sulfonyl]methyl]

O,O-diethylphosphorodithioate

Formula: C9H21O4P1S3

MW: 320.42g/mol

SMILES: 

CCOP(=O)(OCC)SCS(=O)(=O)

C(C)(C)C

Aerobic soil 00156853 20.1 (60 d) 2.3 (365 d)

Anaerobic soil 41749801 4.0 (15 d) 3.7 (60 d)

Aerobic aquatic 448625022 1.82 (30 d) 1.82 (30 d)

Terrestrial field 

dissipation 00087708 0.12 (80 d) 0.02 (100 d)

Carbon dioxide Carbon dioxide

Formula: CO2

MW: 44.1 g/mol

SMILES: O=C=O

O O

Aerobic soil 00156853 46 (365 d) 46 (365 d)

Anaerobic soil 41749801 3.1 (30 d) 2.0 (60 d)

Aerobic aquatic 448625022 61.8 (30 d) 61.8 (30 d)

Minor (<10%) Transformation Products

Terbufoxon

(CL94221)

S-[[(1,1-

dimethylethyl)thio]methyl]O,Odiethylphosphorothioate

Formula: C9H21O3P1S2

MW: 272.36 g/mol

SMILES: 

C(C)(C)(C)SCSP(=O)(OCC)O

CC

Anaerobic soil 41749801 1.7 (15 d) 1.3 (60 d)
55

Common Name

(Synonym) Chemical Name Chemical Structure Study Type MRID Maximum %AR1 (day)

Final %AR1

(day)

Terbufoxon

sulfoxide

(CL94365)

S-[[(1,1-

dimethylethyl)sulfinyl]methyl]

O,O-diethylphosphorothioate

Formula: C9H21O4P1S2

MW: 288.36 g/mol

SMILES: 

C(C)(C)(C)S(=O)CSP(=O)(OC

C)OCC

Aerobic soil 00156853 0.5 (7 d) ND (365 d)

Anaerobic soil 41749801 2.6 (60 d) 2.6 (60 d)

Terbufoxon sulfone

(CL94302)

S-[[(1,1-

dimethylethyl)sulfonyl]methyl]

O,O-diethylphosphorothioate

Formula: C9H21O4P1S2

MW: 304.36 g/mol

SMILES:

C(C)(C)(C)S(=O)(=O)CSP(=O)

(OCC)OCC

Anaerobic soil 41749801 3.1 (30 d) 2.0 (60 d)

Des-ethyl terbufos 

sulfoxide

(CL 1008534)

S-[[(1,1-

dimethylethyl)sulfonyl]methyl]

O,O-diethyl ester

Formula: C7H17O3P1S3

MW: 276.37 g/mol

SMILES:

C(C)(C)(C)S(=O)CSP(O)(=S)O

CC

Aerobic aquatic 448625022 2.14 (7 d) ND (30 d)
56

Common Name

(Synonym) Chemical Name Chemical Structure Study Type MRID Maximum %AR1 (day)

Final %AR1

(day)

Des-ethyl terbufos 

sulfone 

(CL 1008533)

S-[[(1,1-

dimethylethyl)sulfonyl]methyl]

O-ethyl ester

Formula: C7H17O4P1S3

MW: 276.37 g/mol

SMILES: 

C(C)(C)(C)S(=O)(=O)CSP(O)(

=S)OCC

Aerobic aquatic 448625022 2.85 (14 d) ND (30d)

Unextracted Residues

Unextracted 

residues NA NA Anaerobic soil 41749801 9.2 (60 d) 9.2 (60 d)

NA = not applicable; NR = not reported; ND = not detected

BOLD = formation > 10% of that applied

1 Applied radioactivity

2 No sediment was used in the study.

3 Designated as “Degradate A” in hydrolysis study.
57

Appendix C: Submitted Toxicity Data

Table C-1. Summary of Toxicity of Terbufos to Aquatic Animals 

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Bluegill sunfish 

(Lepomis 

macrochirus)

96 hr

(static)

86

LC50 = 0.77 (0.72-

0.83)1 μg ai/L (nom)2

Probit slope = 14.35 

(8.33-20.38) 1 

Sublethal effects: 

pectoral fin erection,

and partial loss of 

equilibrium

00087718

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

Unknown if sublethal 

effects observed in 

surviving fish.

NOAEC = 0.37 μg 

ai/L

LOAEC = 0.65 μg 

ai/L (mortality and 

sublethal effects)

86.3

LC50 = 3.8 (2.8-4.9)1 

μg ai/L (nom) 

(binomial test)

00037483

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

No sublethal effects 

reported for surviving 

fish.

NOAEC = 2.8 μg 

ai/L

LOAEC = 3.7 μg ai/L 

(mortality)

96 hr

(flowthrough)88.6

LC50 = 0.87 (0.77-

1.0)1 μg ai/L (nom)2

Probit slope = 5.48 

(3.69-7.28) 1 

00085176

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

No sublethal effects 

reported for surviving 

fish.

NOAEC = 0.32 μg 

ai/L

LOAEC = 0.42 μg 

ai/L (mortality)

96 hr

(static)

88 LC50 = 1.1 (0.8-1.6)1 

μg ai/L (nom) 40098001

Very 

Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

9 independent tests; 

96 hr LC50 ranged 

from 1.1 to 2.4 μg 

ai/L (nom)

15

LC50 = 1.7 (1.2-2.4)1 

μg ai/L (nom)

Sublethal effects and 

NOAEC not reported.

LC50 = 12.3 (9.8-

15.2)1 μg 

formulation/L (nom)

Probit slope = 5.4 

(3.1-7.6) 1 

LC50 = 1.8 (1.5-2.3)1 

μg ai/L (nom)

FE0TER04

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

Counter 15G

No sublethal effects 

reported.

NOAEC = 3.7 μg 

formulation/L

LOAEC = 5.6 μg 

formulation/L 

(mortality)

NA NA NOAEC = 0.10 μg 

ai/L3 NA NA NA

Acute to Chronic ratio 

based on rainbow trout 

data.
58

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Brown trout

(Salmo trutta)

96 hr

(static) 86

LC50 = 20 (12-34)1 

μg ai/L (nom)2

Probit slope = 1.47 

(0.95-1.98) 1 

Sublethal effects: 

partial loss of 

equilibrium

00087718

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

Unknown if sublethal 

effects observed in 

surviving fish.

NOAEC = 3.2 μg 

ai/L

LOAEC = 10 μg ai/L 

(mortality and 

sublethal effects)

Channel Catfish 

(Ictalurus 

punctatus)

144 hr 

(flowthrough)88.6

LC50 = 9.6 (8.5-

11.07)1 μg ai/L 

(nom) (moving 

average)2

00085176

Very 

Highly 

Toxic

Supplemental 

(test 

concentrations 

were not 

measured)

No sublethal effects 

reported for surviving 

fish.

NOAEC = 4 μg ai/L

LOAEC = 5 μg ai/L 

(mortality)

Test conducted for 

144 hrs. Toxicity at 

144 hrs was slightly 

greater than at 96 hrs.

96 hr

(static) 15 LC50 = 1800 (1230-2640)1 μg ai/L (nom) 40098001 Moderately 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

Fathead minnow 

(Pimephales 

promelas)

96 hr

(static)

88 LC50 = 390 (237-

643)1 μg ai/L (nom) 40098001 Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

15 LC50 = 150 (101-

223)1 μg ai/L (nom)

Rainbow trout 

(Oncorhynchus 

mykiss or Salmo 

gairdneri*)

96 hr

(static)

86.3

LC50 = 9.4 (7.7-

11.4)1 μg ai/L (nom)

Probit slope = 6.2 

(3.4-8.9)1 μg ai/L

00037483

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

No sublethal effects 

reported for surviving 

fish.

NOAEC = 4.9 μg 

ai/L

LOAEC = 7.5 μg ai/L 

(mortality)

*Salmo gairdneri

88 LC50 = 7.6 (6-9.7)1 

μg ai/L (nom)

40098001

Very 

Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

9 independent tests; 

96 hr LC50 ranged 

from 7.6 to 15.3 μg 

ai/L (nom)

*Salmo gairdneri

15 LC50 = 8.8 (6.4-

12.1)1 μg ai/L (nom)

Sublethal effects and 

NOAEC not reported.

*Salmo gairdneri
59

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Rainbow trout 

(Oncorhynchus 

mykiss or Salmo 

gairdneri*)

96 hr

(static) 15

LC50 = 59.7 (48.1-

74.3)1 μg 

formulation/L (nom)

Probit slope = 5.5 

(3.2-7.9)1 μg 

formulation/L

LC50 = 8.9 (7.2-

11.1)1 μg ai/L (nom)

FE0TER05

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

Counter 15G

No sublethal effects 

reported for surviving 

fish.

NOAEC = 21 μg 

formulation/L

LOAEC = 32 μg 

formulation/L 

(mortality)

*Salmo gairdneri

ELS

98.5 NOAEC ≥ 1.4 μg 

ai/L (mm) 40009301 NA Supplemental *Salmo gairdneri

98.99

NOAEC = 0.64 μg 

ai/L (mm)

LOAEC = 1.4 μg 

ai/L (mm) based on 

reduced wet weight 

and length

41475802 NA (“Core”)

Acceptable

Effects at highest two 

test concentrations 

(2.7 and 5.3 μg ai/L): 

reduced survival, 

resting on lateral 

surfaces, 

hypersensitivity, loss 

of equilibrium, 

irregular respiration, 

dark discoloration, 

surfacing, and 

quiescence. Several 

fish at various 

concentrations 

developed spinal 

curvature and 

malformed otic 

capsules.

*Oncorhynchus mykiss
60

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Waterflea

(Daphnia magna)

48 hr

(static)

88.6

EC50 = 0.17 (0.15-

0.19)1 μg ai/L (mm)

Sublethal effects: 

erratic swimming, 

lying on bottom.

00101495

Very 

Highly 

Toxic

Supplemental

(test material 

was unstable)

Majority of the 

daphnids displaying 

sublethal effects were 

deceased at 48 hr.

NOAEC = 0.107 μg 

ai/L

LOAEC = 0.185 μg 

ai/L (mortality and 

sublethal effects)

88 EC50 = 0.4 (0.3-0.5)1

μg ai/L (nom) 40098001

Very 

Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

15

EC50 = 6.2 (5.1-7.7)1

μg formulation/L 

(nom)

Probit slope = 6.6 

(3.5-9.6)1 

EC50 = 0.9 (0.8-1.2)1

μg ai/L (nom)

FE0TER06

Very 

Highly 

Toxic

Supplemental

(test 

concentrations 

were not 

measured)

Counter 15G

Sublethal effects not 

reported.

NOAEC = 2.1 μg 

formulation/L

LOAEC = 3.2 μg 

formulation/L 

(mortality)

21 day 

LifeCycle 

(flowthrough)

98.4

NOAEC = 0.030 μg 

ai/L (mm)

LOAEC = 0.076 μg 

ai/L (mm) based on 

growth and 

reproduction 

(reduced body length 

and number of 

offspring)

00162525 NA (“Core”)

Acceptable

Some daphnids were 

observed lying on the 

bottom/ quiescent on 

day 19; those 

organism appear to 

have been deceased 

by day 21. Two 

additional daphnids 

showed the same 

effects on day 21.

Gammarus 

pseudolimnaeus

96 hr

(static) 88 LC50 = 0.20 (0.1-0.3)1 μg ai/L (nom) 40098001

Very 

Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

Chironomus 

plumosus

48 hr

(static) 88 EC50 = 1.4 (1.0-2.0)1 

μg ai/L (nom) 40098001

Very 

Highly 

Toxic

Myer and 

Ellersieck, 

1986

Sublethal effects and 

NOAEC not reported.

Crayfish 

(Procambarus 

clarkii)

96 hr

(flow 

through)

88.6

LC50 = 8.0 (6.9-

10.2)1 μg ai/L 

(nom)2

Probit slope = 3.36 

(2.34-4.38) 1 

00085176

Very 

Highly 

Toxic

Supplemental 

(test 

concentrations 

were not 

measured)

No sublethal effects 

reported for surviving 

crayfish.

NOAEC = 2.4 μg 

ai/L

LOAEC = 3.2 μg ai/L

(mortality)
61

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Sheepshead 

minnow 

(Cyprinodon 

variegatus)

96 hr

(static) 98.4

LC50 = 1.6 (0.77-

3.2)1 μg ai/L (mm) 

(binomial test)

Sublethal effects: 

surfacing, loss of 

equilibrium, and fish 

at the bottom of the 

test chamber. 

00162524

Very 

Highly 

Toxic

Supplemental 

(due to low 

dissolved 

oxygen 

concentrations 

at 96 hr)

NOAEC < 0.37 μg 

ai/L

LOAEC ≤ 0.37 μg 

ai/L (sublethal 

effects)

At the lowest test 

concentration, 

sublethal effects 

(only observed at 96 

hr) may have been 

due to stress from 

low dissolved 

oxygen, terbufos, or 

both.

96 hr

(flowthrough)98

LC50 = 3.2 (2.7-

3.7)1 μg ai/L (mm)

Probit slope = 7.1 

(3.8-10.4) 1 μg ai/L

Sublethal effects: 

loss of equilibrium, 

floating at the 

surface, forward 

pointing pectoral 

fins, erratic 

swimming, labored 

respiration, 

quiescence, fish at 

the bottom of the test 

chamber, and 

surfacing. 

41373602

Very 

Highly 

Toxic

(“Core”)

Acceptable 

NOAEC < 1.4 μg 

ai/L

LOAEC ≤ 1.4 μg ai/L 

(sublethal effects)

NA NA NOAEC = 0.14 μg 

ai/L4 NA NA NA

Acute to Chronic ratio 

based on rainbow trout 

data.

Mysid shrimp

(Americamysis 

bahia)

96 hr 

(static) 98.4

LC50 = 0.22 (0.14-

0.35)1 μg ai/L (mm)

Probit slope = 2.51 

(1.44-3.58) 1 

Sublethal effects: 

quiescence, lying on 

bottom, and 

surfacing

00162523

Very 

Highly 

Toxic

Supplemental 

(MRID 

00162523 and 

41297903

primarily due 

to excessive 

control 

mortality in 

either the 

negative or 

solvent 

control but not 

both)

NOAEC = 0.07 μg 

ai/L

LOAEC = 0.13 μg 

ai/L (mortality and 

sublethal effects; 

taking control 

mortality into 

consideration)

Sublethal effects 

observed at 0.13 to 

0.59 μg ai/L.
62

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEC /LOAEC 

for acute studies

Mysid shrimp

(Americamysis 

bahia)

96 hr 

(flowthrough)

98

LC50 = 0.40 (0.34-

0.48)1 μg ai/L (mm) 

(moving average)

Sublethal effects: 

quiescence, lying on 

bottom, surfacing, 

and loss of 

equilibrium

41297903

Very 

Highly 

Toxic

Supplemental 

(see MRID 

00162523 

above)

NOAEC = 0.15 μg 

ai/L

LOAEC = 0.24 μg 

ai/L (mortality; 

taking control 

mortality into 

consideration)

Sublethal effects 

observed at 0.35 and 

0.71 μg ai/L.

99.9

LC50 = 0.543 (0.474-

0.623)1 μg ai/L (mm) 

(Untrimmed 

Spearman-Kärber)

Sublethal effects: 

erratic swimming, 

gyrating motions, 

and lethargy

42306701

Very 

Highly 

Toxic

Acceptable

NOAEC = 0.225 μg 

ai/L

LOAEC = 0.441 μg 

ai/L (mortality and 

sublethal efffects)

NA NA

NOAEC = 0.041 

μg/L5 NA NA NA

Acute to Chronic 

ratio based on 

daphnia data.

Eastern oyster

(Crassostrea 

virginica)

96 hr 

(flowthrough)89.2

EC50 = 201 μg ai/L 

(176-231)1 μg ai/L 

(mm) (moving 

average)

42381501 Highly 

Toxic

(“Core”)

Acceptable

NOAEC < 54 μg ai/L 

(22 to 29% inhibition 

compared to negative 

control at lowest 

three test levels)

mm = mean measured; nom = nominal concentration; NA = not applicable

– See DERs for more complete explanations of study classifications.

1

Range is 95% confidence interval. 

2 It is uncertain if test concentrations were adjusted for purity of the test material. 3 Bluegill sunfish sensitivity to terbufos on a chronic basis was estimated using an acute to chronic ratio (ACR) because it is the 

most acutely sensitive species. The ACR was based on rainbow trout (acute and chronic toxicity) and bluegill sunfish (acute 

toxicity) data. Numerous acute TGAI toxicity endpoints were available for rainbow trout (10) and bluegill sunfish (12) from 

reliable studies. An average toxicity value from these studies was used given that the range was 2X (rainbow trout) to 3X (bluegill 

sunfish), resulting in an ACR of 16.7. One open literature study (Call et. al, 1989) reported a NOAEC (0.34 μg ai/L) for fathead 

minnow about two times lower than that of the rainbow trout (0.64 μg ai/L, MRID 41475802). The study by Call et al. was 

classified as qualitative and was not used to calculate an ACR. Nonetheless, results from the Call et al. study support the ACR 

based on the rainbow trout data; an ACR of 4.5 was reported for fathead minnow based on exposure to terbufos while a mean ACR

of 10.4 (range of 4.5 to 27.9) was reported for fathead minnow based on terbufos plus four other organophosphate chemicals. The 

reported ACR of 4.5 is based on a NOAEC of 1.96 μg ai/L because Call et al. questioned the biological significance of the observed 

effects on length at lower concentrations; the ACR was 38.2 assuming a NOAEC of 0.34 μg ai/L. 4 Sheepshead minnow sensitivity to terbufos on a chronic basis was estimated using an ACR because data were not available. The 

ACR was based on rainbow trout (acute and chronic toxicity) and sheepshead minnow (acute toxicity) data. See footnote 3

regarding use of rainbow trout data to estimate the ACR of 16.7. Two equally reliable acute studies were available for sheepshead 

minnow; an average acute toxicity value from these studies was used to estimate chronic toxicity to sheepshead minnow given that 

the range of acute toxicity values was 2X. 

5 Mysid sensitivity to terbufos on a chronic basis was estimated using an ACR because data were not available. The ACR was 

based on daphnia (acute and chronic toxicity) and mysid (acute toxicity) data. Two equally reliable acute studies with the TGAI 

were available for daphnia and three were available for mysid. An average acute toxicity value was used for each species when 

calculating the ACR given the small range of acute values (2.4X for daphnia and 2.5X for mysid).
63

Table C-2. Summary of Toxicity of Terbufos to Aquatic Plants 

Species Exposure 

Scenario

% 

AI

Toxicity MRID Toxicity 

Category

Classification

Freshwater Algae 

(Pseudokirchneriella 

subcapitata)

96 hr

(static) 89.3

EC50 >1.85 mg ai/L (im)

NOAEC = 0.399 mg ai/L 

(im)

LOAEC = 1 mg ai/L based 

on effects to cell density, 

area under the growth curve, 

average specific growth 

rate, and yield.

48689902 NA Acceptable

Marine Diatom 

(Skeletonema grethae) 96 hr 89.3

EC50 > 1.01 mg ai/L (im)

NOAEC ≥ 1.01 mg ai/L 

(im)

48939101 NA

Supplemental 

(numerous deviations 

including excessive 

variation of initial cell 

density among 

treatment groups)

Duckweed

(Lemma gibba) 7 day 89.3

EC50 > 4.20 mg ai/L 

NOAEC = 0.280 mg ai/L

LOAEC = 0.630 mg ai/L 

based on frond number, 

growth rate of frond 

number, and yield of frond 

number

48689901 NA Acceptable 

im = initial measured; NA = not applicable

– See DERs for more complete explanations of study classifications.

Table C-3. Summary of Toxicity of Terbufos to Terrestrial Animals

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

Single oral 

dose 89.6

LD50 =28.6 (22.2-55.9)1

mg ai/kg bw

Probit slope = 4.35 

(1.56-7.13)

Sublethal effects: 

clinical signs (lethargy 

progressing to 

depression, reduced 

reaction to external

stimuli, loss of 

coordination, lower limb 

weakness, prostrate 

posture, loss of righting 

reflex, salivation, and 

lower limb rigidity)

00106551 Highly 

toxic

(“Core”)

Acceptable

Sublethal effects 

observed at some 

point during the 

exposure period at 

all doses (≥ 6.81 

mg ai/kg bw). 

Mortality 

observed at doses 

≥ 14.7 mg ai/kg 

bw.
64

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

Single oral 

dose 20

LD50 = 250 (147-464)1

mg formulation/kg bw

LD50 = 50 (29.4-92.8)1

mg ai/kg bw

Sublethal effects: 

clinical signs (ataxia, 

lethargy, inability to 

walk when aroused, and 

weakness), reduced 

body weight, and 

decreased food 

consumption (day 1-3, 

all test concentrations 

with surviving birds)

40660708

Highly 

toxic 

(ai basis)

(“Core”)

Acceptable

Counter 20P

NOAEL < 29.4 

mg ai/kg bw

LOAEL ≤ 29.4 

mg ai/kg bw 

(sublethal effects)

Body weight 

decreased in all 

treatment groups 

from day 1-3 or 7. 

Body weight 

increased 

thereafter, 

recovering to that 

of control birds by 

day 21 in the 

second and third 

highest treatment 

groups (higher 

treatment groups 

showed 100% 

mortality).

LD50 = 238 (180-310)1

mg formulation/kg bw

LD50 = 47.6 (35.9-62)1

mg ai/kg bw

Probit slope = 3.52 

(1.99-5.04)

Sublethal effects: 

clinical signs at 

unspecified treatment 

levels (lethargy, ataxia, 

diarrhea, anorexia, 

noticeable weight loss, 

inability to stand, and 

weak appearance) and 

reduced body weight 

and feed consumption in 

all treatment groups

41508802

Highly 

toxic

(ai basis)

Acceptable

Counter CR

NOAEL < 20 mg 

ai/kg bw

LOAEL ≤ 20 mg 

ai/kg bw 

(mortality, body 

weight, and feed 

consumption)
65

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

Single oral 

dose 15

LD50 = 295 (215-464)1

mg formulation/kg bw

LD50 = 44.3 (32.3-

69.6)1 mg ai/kg bw

Sublethal effects: 

clinical signs (ataxia, 

lethargy, inability to 

stand/walk when 

aroused, dyspnea, 

muscle tremors, 

piloerection, and 

paralysis), reduced body 

weight, and reduced 

food consumption (day 

1-3 or 7, all test 

concentrations)

40660707

Highly 

toxic 

(ai basis)

(“Core”)

Acceptable

Counter 15G

NOAEL < 22.1 

mg ai/kg bw

LOAEL ≤ 22.1 

mg ai/kg bw 

(sublethal effects)

Body weight 

decreased in all 

treatment groups 

from day 1-3. 

Body weight 

increased 

thereafter but by 

day 21 only the 

lowest treatment 

group weight 

recovered to that 

of the control 

birds. 

LD50 = 290 (245-344)1

mg formulation/kg bw

LD50 = 43.5 (36.7-

51.6)1 mg ai/kg bw

Probit slope = 8.61 

(4.31-12.9)

Sublethal effects: 

clinical signs in all 

treatment groups 

(lethargy, ataxia, 

diarrhea, anorexia, and 

inability to walk) and 

reduced feed 

consumption in the 

highest three test 

concentrations not 

showing 100% mortality 

(day 0-3)

41508803

Highly 

toxic 

(ai basis)

Acceptable

Counter 15G

NOAEL < 15 mg 

ai/kg bw

LOAEL ≤ 15 mg 

ai/kg bw (clinical 

signs)
66

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Northern 

Bobwhite Quail 

(Colinus 

virginianus)

8 days (5 days 

treatment and 

3 days 

observation)

86

LC50 = 143 (103-214)1

ppm ai (moving 

average) (nom)2

Sublethal effects: 

decreased locomotor 

activity, feather 

erection, loss of righting 

reflex, and reduced food 

consumption

00087717 Highly 

toxic

Supplemental

(test 

concentrations 

not measured 

or 

demonstrated 

to be stable)

NOAEC < 25 ppm 

ai

LOAEC ≤ 25 ppm 

ai (mortality and 

sublethal effects)

87.8

LC50 = 157 (125-201)1

ppm ai (nom)

Probit slope = 7.2 (3.2-

11.2)

Sublethal effects: 

depression (lethargy), 

reduced reaction to 

sound and movement, 

wing droop, loss of 

coordination, prostrate 

posture, lower limb 

rigidity, ruffled 

appearance, lower limb 

weakness, reduced body 

weight gain, and 

reduced food 

consumption

00160387 Highly 

toxic

Supplemental

(test 

concentrations 

not measured 

or 

demonstrated 

to be stable)

NOAEC = 56.2 

ppm ai

LOAEC = 100 

ppm ai (mortality 

and clinical signs)

Some sublethal 

effects 

disappeared by the 

end of the 

experiment.

Onegeneration 

Reproduction 

Study

89 NOAEC < 2 ppm ai 

(nom)2 00085177

NA

Supplemental

(test 

concentrations 

not measured 

or 

demonstrated 

to be stable

and lack of 

pen-by-pen 

data)

Possible effects on 

viable embryos of 

eggs set at 2 ppm 

ai. Results cannot 

be confirmed due 

to a lack of pen by 

pen data for 

statistical analysis.

89.6 NOAEC ≥ 30 ppm ai

(nom) 00161573 (“Core”)

Acceptable

No effects 

observed at 

highest test 

concentration.
67

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Mallard Duck 

(Anas 

platyrhynchos)

Single oral 

dose

20

LD50 = 161 (68-316)1

mg formulation/kg bw

LD50 = 32.2 (13.6-

63.2)1 mg ai/kg bw

Sublethal effects: 

lethargy, ataxia, and 

reduced food 

consumption (day 0-3, 

all test concentrations)

40660706

Highly 

toxic

(ai basis)

(“Core”)

Acceptable

Counter 20P

NOAEL < 13.6 

mg ai/kg bw

LOAEL ≤ 13.6 

mg ai/kg bw 

(reduced food 

consumption)

15

LD50 = 88 (0-215)1 mg 

formulation/kg bw

LD50 = 13.2 (0-32.3)1

mg ai/kg bw

Sublethal effects: 

dyspnea, lethargy, 

immobility, emesis, and 

reduced food 

consumption (day 0-3, 

all test concentrations)

40660705

Highly 

toxic 

(ai basis)

(“Core”)

Acceptable

Counter 15G

NOAEL < 6.96 

mg ai/kg bw

LOAEL ≤ 6.96 

mg ai/kg bw 

(mortality and 

sublethal effects)

Mallard Duck 

(Anas 

platyrhynchos)

8 days (5 days 

treatment and 

3 days 

observation)

86

LC50 = 153 (117-198)1

ppm ai (nom)2

Probit slope = 5.45 

(2.33-8.57)

Sublethal effects: 

decreased locomotor 

activity, feather 

erection, loss of righting 

reflex, and reduced food 

consumption (all test 

concentrations)

00087717 Highly 

toxic

Supplemental

(test 

concentrations 

not measured 

or 

demonstrated 

to be stable)

NOAEC < 100 

ppm ai

LOAEC ≤ 100 

ppm ai (mortality 

and sublethal 

effects)

Increasing food 

avoidance with 

increasing dose

86

LC50 = 697 (584-1616)1

ppm ai (moving 

average) (nom)2

Sublethal effects: 

reduced body weight 

and food consumption 

(all test concentrations)

00035120 Moderately 

toxic Supplemental

NOAEC < 100 

ppm ai

LOAEC ≤ 100 

ppm ai (sublethal 

effects)

Body weight and 

food consumption 

showed recovery 

after exposure 

period

Study author 

calculated LC50 = 

520 ppm ai
68

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Mallard Duck 

(Anas 

platyrhynchos)

Onegeneration 

Reproduction 

Study

89 NOAEC < 2 ppm ai

(nom)2 00097892

NA

Supplemental

(test 

concentrations 

not measured 

or 

demonstrated 

to be stable

and lack of 

pen-by-pen 

data)

Possible effects on 

viable embryos of 

eggs set at 2 ppm 

ai and other 

variables at 20 ai

ppm. Results 

cannot be 

confirmed due to a 

lack of pen by pen 

data for statistical 

analysis. It is also 

noted that body 

weight decreased 

at 2 and 20 ppm ai 

and increased in 

the control 

throughout the 

study.

89.6

NOAEC = 5 ppm ai

(nom)

LOAEC = 15 ppm ai

(nom)*

00161574 (“Core”)

Acceptable

*Possible 

biologically 

significant (but 

not statistically 

significant) effect 

on embryo 

viability.

Domestic Hen 

(Gallus gallus 

domesticus)

Single oral 

dose 88.8 NA 46293202 NA Invalid

Brown-headed 

Cowbird 

(Molothrus ater)

Single oral 

dose 20

LD50 = 85 (46-151)1 mg 

formulation/kg bw

LD50 = 16.9 (9.2-30.1)1

mg ai/kg bw

Probit slope = 1.59 

(0.81-2.37)

Sublethal effects: 

clinical signs at 

unspecified treatment 

levels (lethargy, 

hypersalivation, ataxia, 

inability to walk or fly, 

shaking, lying on the 

side, tachypnea, and 

agape mouth) and body 

weight (increase only)

41508804

Highly 

toxic 

(ai basis)

Acceptable

Counter CR

NOAEL < 3.5 mg 

ai/kg bw

LOAEL ≤ 3.5 mg 

ai/kg bw 

(mortality)
69

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Brown-headed 

Cowbird 

(Molothrus ater)

Single oral 

dose 15

LD50 = 148 (100-235)1

mg formulation/kg bw

LD50 = 22.2 (15.0-

35.3)1 mg ai/kg bw

Probit slope = 2.63 

(1.46-3.79)

Sublethal effects: 

clinical signs showed 

remission by day 4 

(lethargy, 

hypersalivation, ataxia, 

anorexia, difficulty or 

inability walking or 

flying, and agape 

mouth), and reduced 

feed consumption 

occurred intermittently 

at the top two doses

41508805

Highly

toxic 

(ai basis)

Acceptable

Counter 15G

NOAEL = 6.96 

mg ai/kg bw

LOAEL = 10.2 

mg ai/kg bw 

(mortality and 

clinical signs)

Honeybee 

(Apis mellifera) Acute contact TGAI

LD50 = 4.09 μg ai/bee

Probit slope = 3.54 μg 

ai/bee

00066220 Moderately 

toxic

(“Core”)

Acceptable
70

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Rat Acute Oral

89.7

LD50 = 1.25 (0.98-

1.52)1 mg ai/kg bw 

(female)

LD50 = 2.87 (2.33-

4.30)1 mg ai/kg bw 

(male)

Sublethal effects: 

tremors, salvation, 

exophthalmos, and 

decreased activity. All 

survivors appeared 

normal 9 days after 

dosing.

44021601

Very 

Highly 

Toxic

Acceptable

19

LD50 = 0.836 mg ai/kg 

bw (female)*

LD50 = 3.3 mg ai/kg bw 

(male)

Sublethal effects: 

tremors, exophthalmos, 

salivation, 

chromodacyrorrhea, 

ventral surface staining, 

diarrhea, decreased 

activity, blood around 

nose, diuresis, and 

ataxia

47512801

Very 

Highly 

Toxic

Acceptable

Counter 20G

Sublethal effects 

were observed in 

animals that did 

not survive except 

for males in the 

2.4 mg ai/kg bw 

(12.5 mg/kg bw) 

dose level. 

Recovery of those 

animals generally 

occurred by three 

days after dosing.

*Confidence 

intervals could not 

be calculated due 

to 0 and 100% 

mortality for 

sequential doses 

(e.g., 0% mortality 

at 0.59 mg ai/kg 

bw and 100% 

mortality at 1.18 

mg ai/kg bw for 

females).
71

Species Exposure 

Scenario

% AI Toxicity MRID Toxicity 

Category

Classification Comments and 

NOAEL/ 

LOAEL or 

NOAEC/ 

LOAEC for 

acute studies

Rat 2-generation 

reproduction 89.6

Reproductive Effects

NOAEC(L) = 1 ppm ai 

(0.07 – 0.09 mg ai/kg 

bw/day)

LOAEC(L) = 2.5 ppm ai 

(0.18 – 0.24 mg ai/kg 

bw/day) based on 

decreased pregnancy 

rate and male fertility

Maternal/Offspring 

Effects

NOAEC(L) = 1 ppm ai 

(0.09 mg ai/kg bw/day)

LOAEC(L) = 2.5 ppm ai 

(0.22 – 0.24 mg ai/kg 

bw/day) based on 

decreased body weight 

gain in adult females 

during lactation and 

lower pup weights

43649402 NA Acceptable

Cholinesterase 

inhibition

NOAEC(L) = 0.5 

ppm ai (0.04 mg 

ai/kg bw/day)

LOAEC(L) = 1 

ppm ai (0.09 mg 

ai/kg bw/day) 

based on ≥ 50% 

inhibition in 

female plasma 

levels

Range of dose per 

body weight 

reflects weights of 

study animals 

(male and female)

1

Range is 95% confidence interval. 

2 It is uncertain if test concentrations were adjusted for purity of the test material.

NA = not applicable

– See DERs for more complete explanations of study classifications.

Table C-4. Summary of Toxicity of Terbufos to Terrestrial Plants

Species Exposure 

Scenario

% 

AI

Toxicity MRID Toxicity 

Category

Classification

Cabbage, Carrot, 

Cucumber, 

Lettuce, Soybean, 

Tomato, Corn, 

Oat, Onion, and 

Ryegrass

Tier 1 

Seedling 

Emergence

89.3

EC25 >2.04 lb ai/A (m)

NOAEC = 2.04 lb ai/A

Applies to monocots and 

dicots 48710801 NA

Supplemental 

(tested TGAI 

instead of TEP and 

tested fewer than the 

minimum 

recommended 

number of seeds per 

treatment level)

m = measured; NA = not applicable

– See DER for more complete explanations of study classifications.
72

Appendix D: Summary of Mixture Toxicity Data

Table D-1. Summary of Open Literature Studies on Toxicity of Mixtures1 of Terbufos and Other Pesticides2

Citation Chemicals tested1 Test species Summary3

Baerg, 1994 Terbufos, Terbufos 

Sulfone, Nicosulfuron, 

Chlorimuron, 

Bentazon, 

Imazethapyr, 

Malathion, and 

Cinnamic Acid

Corn Terbufos inhibited nicosulfuron metabolism in corn. Terbufos sulfone 

inhibited the metabolism of nicosulfuron and imazethapyr but not bentazon 

in corn. Terbufos sulfone inhibited P450 activity; that is, the hydroxylation 

of nicosulfuron, chlorimuron, bentazon, and imazethapyr (but not cinnamic 

acid) and the desulfuration of malathion in corn.

Biales et al., 2011 Terbufos and 

Permethrin

Fathead minnow Increased mortality was observed in the mixture compared to only terbufos 

or permethrin exposure. Twenty-four proteins were found to be 

differentially expressed among all three treatments (mixture, only terbufos, 

and only permethrin).

Castro-Escobar et al., 

1996

Terbufos, 

Nicosulfuron, and 

Primisulfuron

Corn (Zea mays) Corn injury from nicosulfuron and primisulfuron increased with an increased 

application rate of terbufos. Plant height following application of 

nicosulfuron and primisulfuron showed an inverse relationship with 

increased application rate of terbufos (i.e., plant height decreased with 

increased terbufos rate). 

Choung et al., 2011a Terbufos sulfone and 

Atrazine

Southern Bell Frog The authors concluded that atrazine did not interact synergistically with 

terbufos sulfone. Terbufos sulfone alone and as a mixture significantly 

slowed larval development and ultimately delayed metamorphosis. 

Choung et al., 2010 Terbufos, Terbufos 

sulfone, Terbufos 

sulfoxide, and Atrazine 

Chironomus tepperi No interaction was observed between atrazine (25 μg/l) and mixtures with 

either terbufos, terbufos sulfone, or terbufos sulfoxide.

Choung et al., 2011b Terbufos, Terbufos 

sulfone, Terbufos 

sulfoxide, and Atrazine 

Ceriodaphnia dubia The addition of atrazine (10 μg/l) significantly increased the toxicity of 

terbufos. The toxicity of terbufos sulfone was unaffected by atrazine, 

whereas the results for terbufos sulfoxide were equivocal.

Diehl et al., 1995 Terbufos and 

Nicosulfuron

Corn (Zea mays) Fresh corn weight was reduced more from exposure to a mixture of terbufos 

and nicosulfuron than to exposure of either terbufos or nicosulfuron alone. 

Plant metabolism of nicosulfuron was slowed by the presence of terbufos.
73

Citation Chemicals tested1 Test species Summary3

Diehl and Stoller,

1995

Terbufos and 

Nicosulfuron

Corn (Zea mays) Terbufos, applied to the soil at planting, interacted with nicosulfuron applied 

postemergence to injure corn and reduce grain yield. No visual injury or 

yield reductions were noted in corn treated with nicosulfuron alone. The 

terbufos 15G formulation caused greater corn injury than did the Counter

20CR (terbufos) formulation at each rainfall timing when sprayed with 

nicosulfuron.

Downard et al., 1999 Terbufos, Trisulfuron, 

Desmedipham, and, 

Phenmedipham

Sugar beet 

(Beta vulgaris)

In some cases toxicity to sugar beet (% injury) was significantly increased 

when plants were exposed to terbufos + trisulfuron and terbufos + 

trisulfuron + desmedipham + phenmedipham compared to exposure to 

individual chemicals or the herbicides mixture. The impact of the mixture 

(enhanced toxicity or no effect vs exposure to individual chemicals or 

herbicide mixtures) varied by factors including experimental site location 

and year, pesticide application concentration, terbufos formulation, and 

terbufos application method. Mixtures did not increase adverse effects on 

population number, root yield, sucrose content, or extractable sucrose.

Exposure to terbufos + desmedipham + phenmedipham did not result in 

enhanced or decreased toxicity to any measured endpoint. In a few cases, 

exposure to terbufos + herbicide(s) increased root yield, sucrose content, 

and/or extractable sucrose.

Foster and Brust,

1995

Terbufos and Methyl 

bromide

Watermelon citrullus 

lanatus; striped and 

spotted cucumber 

beetle

Watermelon growth and yield were similar in terbufos only treatments and 

controls. Exposure to a mixture of methyl bromide and terbufos resulted in 

similar watermelon growth and yield as exposure to methyl bromide alone.

Frazier and Nissen, 

1994

Terbufos, Benoxacor, 

CGA-185072, MON13900, and 

Primisulfuron

Corn (Zea mays) Exposure to a mixture of primisulfuron and terbufos reduced shoot dry 

weight and shoot length compared to the negative control and either 

compound alone. Preemergence applications of the safeners CGA-185072 

and MON-13900 significantly reduced stunting effects on corn from the 

combined exposure to primisulfuron and terbufos; however, shoot weight 

and length remained reduced compared to the negative control. Benoxacor 

had no safening effect. 

Green and Ulrich, 

1994

Terbufos and 

Rimsulfuron

Corn (Zea mays; 

inbred and hybrid 

varieties)

Terbufos applied with rimsulfuron significantly reduced growth (weight) in

three of four varieties of corn compared to exposure to either compound 

alone. 

Hein and Wilson, 

1995 

Terbufos, Cycloate, 

Ethofumesate, and 

Diethatyl

Sugar beet Yields decreased when terbufos was applied with cycloate treated plots. On 

ethofumesate and diethatyl treated plots, root yield also decreased.

Holshouser et al.,

1991

Terbufos and CGA136872 (sulfonylurea 

herbicide)

Corn (five hybrids) All hybrids showed increased injury and reduced yield after CGA-136872 

was applied in combination with terbufos (in-furrow application). Injury 

increased with increased application rate of CGA-136872. 
74

Citation Chemicals tested1 Test species Summary3

Kapusta and Krausz, 

1992

Terbufos and 

Nicosulfuron

Corn (Zea mays) Terbufos applied in-furrow at planting interacted with nicosulfuron applied 

post to cause significant injury 25 to 60 days after planting in 1989 and 

1990. Injury decreased significantly when nicosulfuron was applied at later 

growth stages of corn. Plant population was not affected by the combined 

exposure to terbufos and nicosulfuron. Corn ear number and grain yield in 

1989 and 1990 were lower in plots treated with terbufos at planting and 

nicosulfuron applied at the three leaf stage than in plots treated with only 

nicosulfuron. There were no differences in the height of corn, ear number, or 

grain yield when nicosulfuron was applied at the seven-leaf stage regardless 

of terbufos application in 1989 and 1990.

Kwon et al., 1995 Terbufos,

Nicosulfuron, 

Primisulfuron, and 

Piperonyl butoxide 

(PBO)

Corn (six hybrids) Toxicity to corn (reduced height and/or increased % injury) increased when 

plants were exposed to terbufos + nicosulfuron, terbufos + primisulfuron, 

terbufos + nicosulfuron + PBO, and terbufos + primisulfuron + PBO 

compared to toxicity of single chemicals. Toxicity of terbufos + PBO was 

not enhanced compared to toxicity of each chemical alone.

Kwon, 1993 Terbufos, Metolachlor, 

Alachlor, Acetochlor, 

Chlorimuron, 

Nicosulfuron, 

Primisulfuron, 

Imazaquin, and 

antidotes (CGA154281 and naphthalic 

anhydride) 

Corn Toxicity to corn (reduced height and/or increased % injury) was increased 

when plants were exposed to terbufos + chlorimuron, terbufos + 

nicosulfuron, terbufos + primisulfuron, terbufos + chlorimuron + 

metolachlor, terbufos + nicosulfuron + metolachlor, terbufos + primisulfuron 

+ metolachlor, terbufos + chlorimuron + metolachlor + CGA-154281, 

terbufos + nicosulfuron + metolachlor + CGA-154281, terbufos + 

primisulfuron + metolachlor + CGA-154281, terbufos + nicosulfuron + 

naphthalic anhydride, and terbufos + primisulfuron + naphthalic anhydride

compared to toxicity of each chemical (or combination of chemicals when 

applicable) alone. Toxicity to corn from exposure to terbufos + metolachlor, 

terbufos + alachlor, terbufos + imazaquin, terbufos + imazaquin + 

metolachlor, and terbufos + imazaquin + metolachlor + CGA-154281 was 

not enhanced compared to toxicity of each chemical (or combination of 

chemicals when applicable) alone. Toxicity to corn from exposure to 

terbufos + acetochlor was reduced compared to exposure to acetochlor alone 

(only at the 6.7 kg/ha acetochlor application rate). Toxicity of terbufos + 

primisulfuron was the same as that of primisulfuron alone for barnyard 

grass, giant foxtail, and velvetleaf.
75

Citation Chemicals tested1 Test species Summary3

Langton, 1997 Terbufos,

Flumetsulam, 

Clopyralid, 2,4-D, 

Rimsulfuron, 

Thifensulfuron, 

Halosulfuron, Safener, 

Prosulfuron, 

Primisulfuron, and 

Nicosulfuron

Corn Significant interactions between terbufos and other chemicals were observed 

in terms of effects on corn (height, yield, and stand) after exposure to 

mixtures of terbufos + flumetsulam, terbufos + nicosulfuron, terbufos + 

flumetsulam + nicosulfuron, terbufos + flumetsulam + nicosulfuron + 

pyrimisulfan, and terbufos + rimsulfuron + thifensulfuron. Terbufos did not 

show significant interactions in any other combinations of tested chemicals

(terbufos + prosulfuron + primisulfuron, terbufos + halosulfuron + safener, 

terbufos + halosulfuron, and terbufos + flumetsulam + clopyralid + 2,4-D).

Lentz et al., 1985 Terbufos and 

Metribuzin

Soybean Treatments of terbufos when combined with metribuzin produced 

significantly greater injury and reduced yield than when metribuzin or 

terbufos was applied alone.

Messaad et al., 2000 Terbufos and Atrazine Red shiner minnow 

(C. Lutrensis)

Generally, thermal tolerance of red shiner after exposure to atrazine, 

terbufos, or a mixture of both compounds decreased at both test 

temperatures compared to the control. Thermal tolerance was measured as 

the critical thermal maximum response method (CTM). There was a 

possible additive effect of the mixture observed at the highest test 

temperature/mixture concentration combination.

Messaad, 1996 Terbufos and Atrazine Red shiner minnow

(C. Lutrensis)

Overall survival was lowest for the pesticide mixture (92% at 23°C and 48% 

at 30°C) in comparison to atrazine only at 30°C (54%), terbufos (97% at 23 

°C and 91% at 30 °C) or the control (100%).

Morton, 1993 Terbufos and 

Nicosulfuron

Field and sweet corn

(Zea mays)

Exposure to nicosulfuron and terbufos increased plant injury and tiller 

formation and decreased yield and height compared to exposure to either 

compound alone. The toxicity of the mixture varied and was a function of 

many factors including application rate, application timing (nicosulfuron), 

terbufos formulation and method of application, effect endpoint, and 

experimental site location. Toxicity of the mixture was not enhanced in all 

cases.

Morton et al., 1994 Terbufos and 

Nicosulfuron

Corn (Zea mays) In two of three locations, vigor was reduced more when corn was exposed to 

both nicosulfuron and terbufos compared to nicosulfuron or terbufos alone.

Similarly, grain yield was reduced more by the mixture in some of the 

experimental groups at one of the locations. 

Noetzel and 

Kellesvig, 1993

Terbufos and 

Carbofuran

Canola (Brassica 

napus)

The combination of terbufos and carbofuran did not impact toxicity to 

canola compared to that of each chemical alone.
76

Citation Chemicals tested1 Test species Summary3

Rahman and James,

1993

Terbufos and 

Nicosulfuron

Corn (Zea mays) Damage to corn increased with increasing exposure to nicosulfuron and 

varied by terbufos application method; damage was greater when terbufos 

was applied in an open furrow or as a 17-cm band with or without 

incorporation. Despite phytotoxic effects, all plants recovered within 4 

weeks. Exposure to terbufos and nicosulfuron had no effect on crop yield 

or crop maturity compared to exposure to nicosulfuron alone. 

Simpson et al., 1994 Terbufos, 

Nicosulfuron, and 2,4-

D

Corn (Zea mays) Exposure to nicosulfuron and terbufos caused increased visual injury and 

reduced dry weight. Exposure to 2,4-D and terbufos did not result in an 

obvious increase in visual injury or reduce dry weight. Exposure to 2,4-D, 

nicosulfuron, and terbufos decreased the degree of visual injury and amount 

of reduction in dry weight caused by the nicosulfuron/terbufos interaction. 

The timing of the 2,4-D application relative to the nicosulfuron application 

impacted the safening effect on the nicosulfuron/terbufos interaction.

Smart and Bradford, 

1995

Terbufos, Prosulfuron, 

and Atrazine

Corn and Sorghum The mixture of prosulfuron and terbufos increased effects on corn height, 

injury, and leaf stage but not yield. The mixture of atrazine and terbufos did 

not impact effects on corn. Irrigated sorghum yield was reduced by 

exposure to prosulfuron and terbufos but not to atrazine and terbufos 

compared to a no herbicide control. Irrigated sorghum height and leaf stage 

were also impacted by the prosulfuron and terbufos mixture.

Tien and Chen, 2012 Terbufos, 

Chlorpyrifos, and 

Methamidophos

Diatom (Nitzschia 

sp.), cyanobacteria 

Oscillatoria sp., and 

chlorophyta (Chlorella 

sp.)

The EC50 values for the pesticide mixtures (terbufos + chlorpyrifos, terbufos 

+ methamidophos, and terbufos + chlorpyrifos + methamidophos) were 

mostly higher than those for single pesticides (antagonistic effect). Only one

mixture (terbufos + methamidophos) showed a synergistic effect and that 

effect was on a multiple algal species assemblage; in contrast this chemical 

mixture had an antagonistic effect on single species of algae.

Waldrop and Banks, 

1983

Terbufos, Acifluorfen, 

Toxaphene, BAS9052, Metribuzin, 

Metolachlor, and 

Oryzalin

Soybean (Glycine 

max)

Effects from exposure to terbufos plus either acifluorfen, toxaphene, BAS9052, or metolachlor were not significantly different from those due to 

exposure to the individual compounds. Exposure to terbufos plus either 

metribuzin or oryzalin caused increased toxicity (increased injury, decreased 

shoot and root weights, and/or decreased yield) compared to exposure to the 

individual compounds. Increased effects due to the mixture were observed 

for metribuzin in both greenhouse and field (2 years) experiments whereas 

they were observed for oryzalin in greenhouse but not field experiments. 1 The term “mixture” used in this table means that the test species was exposed at some point during the experiment to terbufos and one or more other 

pesticides. It does not necessarily mean that the chemicals were applied simultaneously. For example, terbufos may have been applied to the soil followed by 

a foliar application of an herbicide.

2 This review focuses on chemicals that were tested as mixtures with terbufos. In some cases additional chemicals were tested but not in combination with 

terbufos; these chemicals are not reported here.

3 The summary focuses on potential interactions between terbufos and other chemicals and is not intended to be a comprehensive detailing of all results.
77

Appendix E: Incident Data

Table E-1. Terbufos Aquatic Incidents (EIIS)

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Unknown1 2003 IN 50-60

300-400

Over 2000

Bass

Bluebird

Crappie

Probable. The fish kill occurred on May 8, 2003 in a pond in Grant County, IN. 

Terbufos (Counter CR) was thought to be involved. It was reported that terbufos was 

present in the pond. It was also reported that a residue of 1.46 ppm was detected but the 

compound was not specified. (I013987-001)

Unknown1 2003 IN 120

4400

6000

Bass

Bluegill

Crappie

Possible. The fish kill occurred on April 22, 2003 in two ponds in Grant County, IN. The 

granular Counter CR formulation of terbufos had been applied a nearby field. Terbufos and 

its “toxic degradates” (undefined) were detected in both ponds at concentrations > 2 ppb.

(I014116-001)

Corn 2000 IN 650

100

200

200

Bluegill

Bass 

Catfish

Crappie

Highly Probable. The fish kill occurred from June 16, 2000 to June 17, 2000 in a pond 

adjacent to a corn agricultural area in Ohio County, IN. Terbufos (Counter) had been applied 

to a corn on a nearby field. Terbufos sulfoxide (3.4-5.1 ppb) and terbufos sulfone (1.8-3.6 

ppb) were detected in the pond 34 days after application to the field. The legality of the 

incident is misuse or accidental. (I010477-002)

Corn 2000 IN 4000

300

40

Few

Bluegill

Bass 

Catfish

Crappie

Highly Probable. The fish kill occurred on May 16, 2000 in a pond adjacent to a corn 

agricultural area in Montgomery County, IN. Terbufos (Counter) had been applied to a corn 

on a nearby field. Terbufos sulfoxide (12-21 ppb) and terbufos sulfone (1.28 ppb) were 

detected in the pond 23 days after application to the field. The legality of the incident is 

misuse or accidental. (I010477-001)

Corn 1998 NE 180

20

Bluegill

Catfish

Highly Probable. The fish kill occurred in a 1 acre farm pond in Nebraska (location not 

given). Terbufos had been applied to a corn field 23 days earlier; there was a slope of 15% 

in the field. Terbufos was not detected in the water but 5 days after the incident the 

concentration of terbufos sulfoxide was 15.5 ppb and terbufos sulfone was 6.6 ppb. 

(B0000-506-02)

Corn 1998 IN 300 Bluegill Highly Probable. The fish kill occurred in a pond in a field near Greensburg, IN. Terbufos 

was not detected in the water but water concentrations of 20.8 to 22.7 ppb of terbufos 

sulfoxide and sulfone were detected 2 days after the incident. Water concentrations of 1.2-

1.3 ppb of terbufos sulfoxide were detected 47 days after the incident. (B0000-506-01)
78

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn 1998 IN 10000

3000

100

200

Bluegill 

Largemouth 

Bass

Catfish

Walleye

Possible. The fish kill occurred on June 19, 1998 in a 15 acre, 20 foot deep farm pond in 

Lagro, IN. The grower applied the CR formulation of terbufos as a T-band application at 

planting at the rate of 1.3 lb ai/A to a 75 acre corn field. The "field drains into neighbor's 

farm pond and pond overflows into reported pond incident". Analysis of water samples 

revealed no evidence of terbufos residues. (I007795-0021)

Corn 1998 IN 2000-3000

500

Bluegill

Largemouth 

Bass

Possible. The fish kill occurred on June 19, 1998 in a farm pond in Lagro, IN. The grower 

applied the 20CR formulation of terbufos as a T-band application at planting at the rate of 

1.3 lb ai/A to a 75 acre corn field. The field drains via tile into the farm pond. There is also a 

2 to 3 foot deep drainage ditch that carries runoff into the pond. Analysis of water samples 

revealed no evidence of terbufos residues. 

(I007795-001)

Corn1 1998 IN 2400

20

10

1

Bluegill

Bass

Frog

Carp

Probable. The fish kill occurred on June 18, 1998 in a farm pond in Huntington, IN. The 

grower applied the 20CR formulation of terbufos as a T-band application at planting at the 

rate of 1.3 lb ai/A to a 46 acre field. Analysis of water samples revealed terbufos sulfoxide 

and terbufos sulfone residues. (I007676-001)

Corn1 1998 IN >5000 Bluegill

Bass

Catfish

Minnow

Crappie

Probable. The fish kill occurred on June 13, 1998 in a 2 acre farm pond in LaFountaine, 

IN. The grower applied the 20CR formulation of terbufos as a T-band application at 

planting at the rate of 1.3 lb ai/A to a 76 acre field. Analysis of water samples revealed 

terbufos sulfoxide and terbufos sulfone residues. (I007924-006; I007513-006)

Corn1 1998 IN 1400 Fish Probable. The fish kill occurred on June 13, 1998 in 2 farm ponds in Lewis, IN. The grower 

applied the 20CR formulation of terbufos as a T-banded application at planting at the labeled 

rate. Analysis of water samples revealed terbufos sulfoxide and terbufos sulfone residues. 

(I007924-005; I007513-005)

Corn1 1998 IN ~1100

50-75

200

Bluegill

Bass

Crappie

Probable. The fish kill occurred on June 14, 1998 in a 3 acre farm pond in Wabash, IN. 

The grower applied the 20CR formulation of terbufos as a T-band application at planting 

at the rate of 1.3 lb ai/A. Mortality estimates for bluegill ranged from 1000- 1200. 

Analysis of water samples revealed terbufos sulfoxide and terbufos sulfone residues. 

(I007924-004; I007513-004)
79

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn1 1998 IN 1000

100

50

Bluegill 

Bass 

Walleye

Probable. The fish kill occurred on June 16, 1998 in a 2 acre farm pond in Wabash 

County, IN. The grower applied the CR formulation of terbufos as a T-band application at 

planting. Analysis of water samples revealed terbufos sulfoxide and terbufos sulfone 

residues. (I007924-003; I007513-003)

Corn1 1998 IN 5100

100

Bluegill 

Bass

Probable. The fish kill occurred on June 13, 1998 in 2 farm ponds in Chester, IN. The 

grower applied the CR formulation of terbufos as an in-furrow application at planting at 

the rate of 1.3 lb ai/A to a 38.5 acre field. Analysis of water samples revealed terbufos

sulfoxide and terbufos sulfone residues. (I007924-002; I007513-002)

Corn1 1998 IN 60

32

1

Bluegill 

Bass 

Catfish

Probable. The fish kill occurred on June 16, 1998 in a 0.8 acre farm pond in Wabash, IN. 

The grower applied the CR formulation of terbufos as a T-band application at planting at 

the rate of 1.3 lb ai/A to a 74 acre field. Analysis of water samples revealed terbufos 

sulfoxide and terbufos sulfone residues. (I007924-001; I007513-001)

Banana 

plantation 1997 Philippines NR Fish

Probable. The fish kill occurred on January 1, 1997 on agricultural land in the Philippines. 

Mortality may be linked to runoff of multiple pesticides, including the granular form of 

Counter 10G. (I006395-001)

Corn1 1997 Corn belt NR Fish Possible. American Cyanamide reported 5 fish kill incidents involving farm ponds in 

Indiana, Nebraska, and possibly other corn belt states in 1997. (I006718-001)

Corn1 1996 Corn belt NR Fish Possible. American Cyanamide reported 1 fish kill incident in the corn belt in 1996.

(I004607-001; I006718-001)

Corn1 1995 Corn belt NR Fish Possible. American Cyanamide reported 4 fish kill incidents involving farm ponds in the 

corn belt in 1995 (I002814-001; I006718-001)

Corn1 1994 Corn belt NR Fish Possible. American Cyanamide reported 7 fish kill incidents involving farm ponds in the 

corn belt in 1994 (I002814-001; I006718-001)

Corn 1994 NC 100 Bass 

Bluegill 

Crappie

Probable. On May 10, 1994, the North Carolina Department of Agriculture reported a fish 

kill incident involving approximately 100 fish that occurred in a canal that fed into the 

Pasquotank River in Pasquotank County. Terbufos (Counter CR) had been applied to a 

corn field adjacent to the canal. Residue analysis revealed 140 ppb of terbufos in the canal. 

(I003826-025; IR94-51; North Carolina Department of Agriculture)
80

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn 1994 LA 1386 Fish Probable. Terbufos and permethrin applied preplant to 3769 acres of corn. The 

Louisiana State University Medical Diagnostic Laboratory concluded that the fish were 

killed by terbufos and permethrin. (I001849-003; I001179-20)

Corn1 1993 Corn belt NR Fish Possible. American Cyanamide reported fish kill incidents at 14 farm ponds in the corn belt 

in 1993. (I002814-001; I006718-001)

Corn 1993 NC 15

15

Bass 

Bream

Highly Probable. A fish kill occurred in Clinton, NC (Sampson County) on April 6 

following application of atrazine and terbufos to a neighboring corn field approximately 

365 feet away. Water samples taken a week later revealed 2 ppb of terbufos. No analyses 

were conducted on the dead fish. (I003654-003)

Corn1 1992 Corn belt NR Fish Possible. American Cyanamide reported 2 fish kill incidents in the corn belt in 1992 

(I002814-001; I006718-001)

Corn

tobacco

1992 NC Small 

number

Bluegill Possible. A fish kill in a small pond adjacent to tobacco and corn fields in North Carolina on 

June 12, 1992. Terbufos, carbofuran, and aldicarb were applied to adjacent fields.

(I000165-052)

Banana 1992 Costa Rica 1250

300

Fish

Tilapia

Probable. Moribund fish were discovered in a river adjacent to a terbufos-treated banana 

farm. Other pesticides had also been used in the area. According to the report terbufos was 

suspected as being responsible for the fish kill. (I000286-001)

Corn1 1991 IA NR Fish Probable/Misuse. Grower in Fontanelle, Adair County, IA, reportedly left a partially used 

bag of Counter® 15G eight feet from pond. (B000170-6; I002814-002)

Corn 1991 IA 4000-

5000

Bluegill

Crappie

Small Bass

Probable. This incident involved 6 ponds in Chariton, Lucas County, IA. Residue analysis 

2 to 4 weeks after treatment showed 1-4 ppb terbufos sulfoxide in the pond. (B000170-4;

I002814-002)

Corn 1991 IA large 

number

Bluegill 

Bass 

Crappie 

Catfish

Probable. Fish kill occurred on June 9 in several ponds east of Chariton, IA. The largest 

pond (3.5 acres) was surrounded by 300-1000 feet of pasture/grassy buffer strip. Terbufos 

was applied as a banded application on an adjacent farm. Terbufos residues (1 ppb) 

recovered from pond water on July 6. No analyses made on dead fish. (B000300-41)
81

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn 1991 IA 500

400

3

Bluegill 

Bass 

Snapping 

Turtle

Probable. Fish kill occurred in 2 ponds in Milo, Warren County, IA. Incident is related to 

a study by Wildlife International. Pond was surrounded by grassy strips and steep sloped 

corn fields. Terbufos also caused a fish kill in these ponds in 1990. (B000170-005;

I002814-002)

Corn 1991 IA NR Fish Possible. A pond near corn field in Lucas County, IA experienced a fish kill in June, 

1991. No residue analysis was performed. (I000254-002: Submitted by Region VII)

Corn 1991 IA NR Bluegill 

Bass 

Crappie 

Catfish

Highly Probable. Pond near corn field in Lucas County, IA experienced fish kill in June, 

1991. Residue analysis revealed terbufos in water following kill and 3 weeks later. 

Trifluralin and Bicep also applied. (I000254-001: Submitted by Region VII)

Corn 1991 IL 1000 Bluegill Probable. Pond in Nashville, Washington County, IL experienced a fish kill. An assay 

conducted 2 weeks after treatment revealed 3 ppb terbufos sulfoxide. (I002814-002; 

I000170-001)

Corn 1991 IL 41800

38000

6318

4343

Bluegill 

Bass 

Sunfish 

Crappie

Highly Probable. On May 4, 1991, terbufos was applied at a rate of 1.3 lb ai/A on a no-till 

corn field adjacent to Taylor Lake, in Victoria, IL (Knox County). Taylor Lake is a former 

strip mine. A total of 90,461 fish were found dead. The species affected included bluegill, 

largemouth bass, green sunfish, black crappie, red-ear sunfish, and hybrid sunfish. The 

dead sunfish had the pectoral fin in the forward position across the head: which is 

considered to be a sign of OP toxicosis. An assay conducted 2 weeks after treatment 

revealed 2 to 9 ppb terbufos sulfoxide. (I005002-003; B000166-001; I002814-002; 

I000170-2; Illinois Department of Conservation,1991)

Corn 1991 IN 1500 Bluegill 

Crappie

Possible. Incident occurred in Whiteland, Brown County, IN involving 1500 bluegill and 

crappie fingerlings. No assay was conducted. (I002814-002; I000170-003)
82

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn

Tobacco

1991 NC 200+ Bluegill 

Bass

Possible. On May 10, 1991, a fish kill occurred in Onslow, North Carolina. Terbufos, 

disulfoton, ethoprop, chlorpyrifos, atrazine, and napropamide were applied to adjacent 

corn and tobacco fields. Analysis of pond water and surrounding soils found terbufos, 

chlorpyrifos, napropamide, and atrazine residues. Because the chlorpyrifos and terbufos 

residues were higher than napropamide and atrazine residues, they were considered more 

likely to have caused the kill. The crops that were associated with the fish kill were corn 

and tobacco. Terbufos was applied to the corn crop only. A corrugated pipe connects the 

fields to a drainage ditch and a concrete pipe to connect the ditch and runs under the road 

to the pond. Apparently pesticide application was applied too close to the water. 

(I000799-004; IR91-60 North Carolina Department of Culture)

Corn or 

Sorghum

1991 TX NR Fish Possible. Incident occurred on April 19, 1991 in a lake adjacent to a 500 acre treated field 

in Lamar, Texas. Assay of water samples was negative. Crop listed in report as field 

crop/grain with the pest as greenbug. (I00917-004· TDA incident No. 11-91-0017)

Corn 1990 IA 300 Bluegill Probable. Event occurred in Audubon County, IA. Terbufos sulfoxide found in residue 

analysis. (B000168-002; I002814-003)

Corn 1990 IA 200 Bluegill Probable. Event occurred in Audubon County, IA. Terbufos sulfoxide found in residue 

analysis. (B000168-001; I002814-003)

Corn 1990 IA 200+ Bluegill Probable. Event occurred in Montgomery County, IA. Field sloping towards pond. 

Terbufos sulfoxide found in residue analysis. (B000168-003; I002814-003)

Corn 1990 IA 200+ Bluegill Probable. Event occurred in Warren County, IA. Terbufos sulfoxide found in residue 

analysis. (B000168-006; I002814-003)

Corn 1990 IA 200+ Bluegill Probable. Event occurred in Milo, Warren County, IA. Incident is related to a study by 

Wildlife International. Terbufos sulfoxide found in residue analysis. (B000168-005)

Corn 1990 IA 500 Bluegill Possible. Event occurred in Washington County, IA. No residue samples taken.

(B000168-004; I002814-003)

Corn 1990 IA 200+ Bluegill Probable. Event occurred in Warren County, IA. Terbufos sulfoxide found in residue 

analysis. (B000168-006; I002814-003)
83

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn 1990 IL 150 Bluegill Possible. Event occurred in Coles County, IL. No residue samples taken. (B000168-013;

I002814-003)

Corn 1990 IL 10000-

15000

Fish Possible. Event occurred in McHenry County, IL. No residue samples taken.

(B000168-014)

Corn 1990 IL NR Bluegill Probable. Event occurred in Du Page County, IL. Terbufos found in residue analysis. 

(B000168-015)

Corn 1990 IL 20 Bluegill Probable. Event occurred in St Clair County, IL. Terbufos sulfoxide found in residue 

analysis. (B000168-0016)

Corn 1990 KS 300 Fish Probable. Event occurred in Leavenworth County, KS. Terbufos was applied in

furrow. Terbufos sulfoxide found in residue analysis. (B000168-007)

Corn 1990 MI 500-600 Bluegill Probable. Event occurred in Hillsdale County, MI. Terbufos was applied as a

banded application. Terbufossulfoxide found in residue analysis.

(B000168-008)

Corn 1990 OH 100 % in

4-5 acre 

pond

Bass, 

Bluegill

Catfish

Crappie 

Snake

Probable. On May 15, 1990, bass, bluegill, catfish, crappie, and a black snake were 

reported killed from the use of terbufos applied in-furrow at-planting on a corn field at a 

rate of 1.3 lb ai/A in Licking County, Ohio. The Ohio Department of Agriculture measured 

terbufos residues of 10 ppb. Ammonia, atrazine, and metolachlor residues were also 

found. The investigator concluded that the kill could have been caused by terbufos or 

ammonia. The total kill was reported for the 4 to 5-acre pond that was 5 to 6 feet deep

(B000168-12; 422059-01; American Cyanamid, 1992)

Corn 1990 OH NR Bluegill Probable. Event occurred in Clinton County, OH. Terbufos was applied as a 

banded application. Terbufos sulfoxide found in residue analysis. 

(B000168-010)

Corn 1990 OH 1500-

1800

Bluegill Possible. Event occurred in Darke County, OH. Terbufos was applied as a banded 

application. There was no residue analysis performed. (B000168-011)

Corn 1990 OH 10000-

15000

Bluegill Probable. Event occurred in Licking County, OH. Terbufos was applied as an in 

furrow application. Terbufos sulfoxide found in residue analysis. (B000168-009)
84

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn1

Sorghum1

1990 TX 200 Fish Probable. Incident occurred in Bell County, Texas. Investigators suspect that runoff 

from the neighbors field into tank caused the fish to die. Samples of fish analyzed 

contained terbufos. Crop listed in report as field crop/grain. Corn and sorghum are the 

most likely crops to have been involved. Metalochlor, 2,4-D, atrazine, and picloram 

were also applied to adjacent fields. (I00917-003; TDA incident No. 05-90-0034)

Corn 1989 NC 600

12

Small Fish 

Crayfish

Highly probable. On May 5, 1989, a fish kill occurred from the use of Counter 15G on 

a nearby corn field in Sampson County, NC. About 600 small fish and 12 crayfish were 

found dead in an adjacent water body. The corn field was treated on April 20. The 

metabolite of terbufos, terbufos sulfone, was detected in the water samples.

(B000169-001; IR89-40. North Carolina Department of Agriculture 1989)

Corn 1989 NC 2000+ Fish Highly probable. On April 30, 1989, thousands of fish were killed in a canal which 

feeds into the Alligator River following the application of terbufos 15G and alachlor to 

corn in Tyrell County, NC. By the time the fish kill was investigated on May 1, 1989, 

the fish had drifted into the Alligator River. Terbufos had been applied in-furrow atplanting and alachlor on top after planting. Terbufos sulfone, the metabolite of terbufos, 

was detected in soil samples. (B000164-001; R89-37. North Carolina Department of 

Agriculture, 1989)

Corn 1989 NC 400 Fish Highly probable. On May 16, 1989, about 400 fish died from the use of Counter 15G. 

Terbufos was measured in the water samples taken in a pond adjacent to a field that was 

treated with terbufos on corn. An adjacent tobacco field had been treated with ethoprop 

and pebulate, but no measurable residues were detected for those chemicals.

(B000167-001; IR89-44. North Carolina Department of Agriculture, 1989)

Corn 1985 NE 1000 Fish Possible. Terbufos was applied in a corn field in Butler County, NE on May 8, 1985. The 

water source for this pond was filtered overflow from a larger pond which had also suffered 

a fish kill at the same time. Terbufos (applied in-furrow to corn) and phorate (applied to 

sorghum) had recently been used in nearby fields above the pond. (I000598-001A; 

Nebraska Game and Parks Commission, 1985).

Corn1 1985 NE "many" Fish Possible. In 1985, terbufos was applied in a field near a pond in Richardson County, 

NE. (I000598-007, Nebraska Game and Parks Commission)
85

Crop/

Source

Year State Number

Affected

Species

Affected

Certainty Index, Summary of Incident (Reference)

Corn 1984 SC 100

100

Bass 

Bream

Possible. On April 2, 1984 a fish kill was reported in Williamsburg County, SC. 

Terbufos, atrazine, and metalochlor were used on the adjacent corn field 2 to 3 days 

before the kill. Analysis of a water sample showed no terbufos residues but tested positive 

for atrazine and metalochlor. (B000163-001)

Corn 1981 MO NR Fish Possible. Fish kill occurred on May 29, 1981 in Krueger Pond, Lafayette County, MO 

(near the town of Alma). A one acre pond was affected. Butylate and atrazine were also 

applied to the corn field. (B000165-001; I000636-032)

Corn 1981 MO NR Bluegill 

Crappie

Possible. On June 3, 1981, terbufos was implicated in a Missouri fish kill with multiple 

pesticide use (atrazine, Sutan and terbufos). Many small bluegill and a few crappie 

reportedly were affected from the use on corn. (Missouri Department of Conservation, 

1981)

Corn 1978 IA many Fish Possible. Terbufos was applied in a corn field in Iowa in 1978. Runoff into a farm pond 

drained about 1⁄2 acre of the treated corn field. Many dead fish were found in the pond.

(Pesticide Incident Monitoring System, 1981)

Unknown1 1976 IL 20 Bluegill Possible. Around April 1976, terbufos was applied to a field across the road from a 0.8 

acre pond in Illinois. About 20 dead bluegill were found. Laboratory work did not 

confirm the presence of terbufos. (Pesticide Incident Monitoring System, 1981)

1 Crop association, if any, is uncertain.

*Some incidents were linked to specific formulations (Counter 15G and CR). The Counter 20G formulation was not specifically linked to any incidents.

NR = not reported

NOTE: hundreds interpreted as 200+; thousands as 2,000+

 soil incorporated interpreted as in-furrow application 

 surface application interpreted as banded application

 
86

Table E-2. Terbufos Terrestrial Incidents (EIIS database)

Crop/

Source

Year State Number

Affected

Species

Affected Certainty Index, Summary of Incident (Reference)

Unknown1 2008 KS 1

87

55

47

Mallard

White-fronted goose

Canada goose

Goose

Possible. Incident occurred in Rice, KS starting on December 16, 2008 and ending on 

December 23, 2008. This mortality was out of approximately 10,000 geese that were 

using the 20-acre refuge area on private ground. Two Canada geese, two Cackling 

geese, one White-fronted goose, and one Mallard were analyzed. Salt toxicosis was 

determined to be the cause of death in one Canada goose, one Cackling goose, and one 

White-fronted goose. Terbufos was detected in the gizzard content of one of the 

White-fronted geese. Strychnine was detected in a Mallard duck. (I020995-002)

Unknown1 2002 NC 5 Red wolf Possible. Incident occurred in Hyde, NC starting on March 9, 2002 and ending on 

March 14, 2002. Cause was diagnosed as toxicosis by terbufos plus scabies infection. 

(I018980-007)

Unknown1 2001 NJ 1 Cooper’s Hawk Highly Probable. Incident occurred in Burlington County, NJ on May 2, 2001. A 

necropsy showed that its brain cholinesterase activity was reduced 78% below normal, 

and the stomach contents (bird remains and two wheat seeds) had 61.8 ppm terbufos. 

The conclusion was that terbufos was the cause of death, but there was no 

determination of the source of the terbufos. (I012549-007)

Corn 1997 DE 2 Canada geese Highly Probable. Incident occurred in Felton, DE (Kent County) on May 27, 1997 in 

a 7 acre stand of field corn. The geese were feeding in the newly planted corn which 

had been treated with Counter 15G. There were heavy rains prior to the incident. 

Analysis of the stomach contents revealed 75 ppm of terbufos. (I007372-001)

Misuse 1996 Canada NR Eagles Probable/Misuse. Carcasses baited with terbufos for coyote control in Saskatoon area 

of Canada. (I004605-001; references newspaper article in Star Phoenix)
87

Crop/

Source

Year State Number

Affected

Species

Affected Certainty Index, Summary of Incident (Reference)

Corn 1996 TX 20 Swainsons hawks Highly Probable/Misapplication. An incident in occurred on April 27, 1996 near 

Dumas, Texas (King County) in which about 20 migrating Swainson's hawks were 

killed by terbufos (Counter 15G). The registrant commissioned a team of scientists to 

conduct an assessment of the incident. The unpublished report developed by that 

team has been reviewed by the Agency. The report draws the following conclusions: 

The hawks were killed while gorging on grubs (larvae of the Southern masked 

chafer) exposed in a newly plowed field. Stomach contents were found to contain 

soil, grubs, and terbufos residues ranging from 6.5 to 16 ppm. The exposure of the 

birds to terbufos resulted from failure to cover the furrows after plowing. The 

furrows were not properly covered because of equipment failure associated with 

plowing under unusually wet soil conditions. In much of the field, the corn seed and 

the terbufos granules were deposited on to the soil surface instead of inside the 

furrow. The dead hawks were discovered 7 days after planting. The conclusion of 

the report is that the incident occurred under an unusual set of conditions. 

(I003498-001; I006435C)

Corn1 1995 WI 2 Red-tailed hawk Highly Probable. An adult female and a hatchling red-tailed hawk were found at the 

base of a tree in Madison, WI. Meat taken from the crops of the hawks contained 12 

and 13 ppm terbufos. The investigator speculated that the prey of the hawks had 

been a rodent from a nearby corn field. (I002993-012; I002733-043, USFWS case 

file 2300)

 

Unknown1 1994 Canada 4 Bald eagles Highly Probable/Possible Misuse. An incident occurred in Vancouver, British 

Columbia involving 4 eagles. Analysis of the contents of the crop and stomach 

confirmed the presence of terbufos and its oxidative degradates at levels that could 

have caused the death of the eagles. Misuse is suspected because the eagles were 

found many months after the normal application time for terbufos and the significant 

amounts of terbufos (relative to the amounts of oxidative degradates). (I002486)

Unknown1 1994 NC 2 Red wolf Highly Probable/Misuse. Two dead red wolves were found near a farm in NC in 

the Fall of 1994. Analysis of the stomach contents revealed “large quantities” of 

terbufos (38 ppm), rabbit flesh, and shotgun pellets. The presence of these 3 items 

in the gut strongly supported a case of intentional poisoning. The wolves had been 

introduced by the U.S. Fish and Wildlife Service against the wishes of the owners 

of the farm. (I002484)
88

Crop/

Source

Year State Number

Affected

Species

Affected Certainty Index, Summary of Incident (Reference)

Sugarbeet1 1992 OR 5-10 Bald eagles Highly Probable/Possible Misuse. Five bald eagle carcasses were collected in March, 

1992 near Toulee Lake in the Klamath Basin Game Preserve, north of Klamath Falls 

OR. Analysis of the gut contents revealed terbufos residues. The gut content was 

mainly waterfowl. The source of the terbufos was not known. The report noted that 

sugar beet are grown in the Klamath Falls area and terbufos is registered on sugar beet. 

Ingestion of terbufos laced bovine meat as a poison bait was also speculated since the 

incident occurred prior to planting of sugar beet and the registrant does not have any 

records of sale in this area. (I000089-001; B0000-300-39, Bennett and Williams, 1996)

1 Crop association if any is uncertain.
89

Table E-3. Summary of Aggregate Incident Data for Terbufos

NOTE: Incidents in the Aggregate Incident Database may duplicate reports in EIIS or AIMS.

Package and 

Sequence #

Incident From Date Product 

Regulation #

Product Name Formulation Sum WildlifeMinorPlant 

DamageMinor

Other NonTarget

013492-00007 7/1/02 - 10/1/02 000241-00238 Counter 15G Granular 1 0 1 0

013492-00006 7/1/02 - 10/1/02 000241-00314 Counter CR Granular 4 0 4 0

012391-00006 7/1/01 - 10/31/01 000241-00314 Counter CR Granular 1 0 1 0

010544-00007 5/1/00 - 7/31/00 000241-00314 Counter CR Granular 1 1 0 0

010260-00001 6/1/00 - 6/30/00 000241-00238 Counter 15G

systemic insecticide 

nematicide

Granular 1 1 0 0

010135-00001 1/1/00 - 4/30/00 000241-00238 Counter 15G

systemic insecticide 

nematicide

Granular 3 3 0 0

008281-00006 9/1/98 - 11/30/98 000241-00241 Counter technical

poison soil 

insecticide

Technical 

Chemical

1 1 0 0

008063-00002 7/1/98 - 9/30/98 000241-00314 Counter XL

systemic insecticide 

nematicide

Granular 1 1 0 0

007883-00001 6/1/98 - 8/31/98 000241-00314 Counter XL

systemic insecticide 

nematicide

Granular 1 1 0 0
90

Table E-4. Terbufos Incidents Identified in the Avian Incident Monitoring System (AIMS)1 

Species Pesticide(s) Location Year Source(s)

Bald Eagle Terbufos Lancaster, NE 2002 FWSLE: Case 02-0330

FWSLE (INV): 2002602946

Green Jay

Turkey Vulture

Terbufos Nueces, TX 2001 FWSLE: Case 01-0268

FWSLE (INV): 2001201753

Cooper’s Hawk Terbufos Burlington, NJ 2001 EIIS: I012549-007

European Starling, 

House Sparrow

Terbufos Gratiot, MI 2000 MAHDL: 2226138

MIWDL: 000098

MIWDL: 000099

MIWDL: 000100

MIWDL: 000101

MIWDL: 000102

MIWDL: 000103

MIWDL: 000104

Canada Geese Terbufos Kent, DE 1997 EIIS: I007372-001

Eagle Terbufos Canada 1996 EIIS: I004605-001

Swainson’s Hawk Terbufos King, TX 1996 EIIS: I003498-001

Bald Eagle Terbufos Pender, NC 1996 FWSLE: Case 96-0460

FWSLE (INV): 605000193

Red-tailed Hawk Terbufos Dane, WI 1995 EIIS: I002993-012

WAHL: 516215

WIDNR: 95-54

Passerine Terbufos Bonneville, ID 1994 FWSLE: Case 94-0490

FWSLE (INV): 1375AQ

Bald Eagle Terbufos Nuckolls, NE 1993 CWS: CWS93-8

FWSW: 11500-001

Bald Eagle Terbufos Nuckolls, NE 1993 CWS: CWS93-7

FWSW: 11497-002

Bald Eagle Terbufos Klamath, OR 1992 EIIS: B0000-300-39; I000089-

001

NOTE: Incidents with an EIIS number are also listed above in Table E-2. 1 Two incidents in the AIMS database associated with terbufos are also reported in the EIIS database and are 

considered to have been caused by other pesticides; therefore, they are not reported in Table E-4. An incident from 

1998 is associated with phorate (EIIS: I002486-001) and another is from 1992 and is associated with carbofuran.

(EIIS: I000799-007 and NC: IR92-72)
91

Appendix F: SWCC Input Parameters and Representative Sample Outputs

Table F-1. SWCC Input Parameters for Terbufos

Parameter Input Value Source Comment

Application Rate 

Corn: 1.30 lb a.i/A

Sorghum: 1.68 lb ai/A

Sugar beet: 1.98 lb a.i/A

Corn: 2.6 lb a.i/A

EPA Reg# 241-314

EPA Reg# 5481-562

EPA Reg# SLN No. 

NC920001

Maximum application rates 

for specified crops based on 

the labels

Number of 

application/year 1 EPA Reg# 241-314

EPA Reg# 5481-562

Label directions

Application method Incorporated Current Labels 

Label directions and to 

simulate subsurface 

incorporation of applied 

terbufos.

Depth of Incorporation 1 inch Current labels

Label direction for corn.

For sorghum and sugar 

beet, incorporation depths 

were assumed based on 

seeding depths

Use Site Scenario 

Corn 

CA corn OP 

IA corn STD

IL corn STD 

IN corn STD 

KS corn STD

MN corn STD 

MS corn STD 

NC CornE STD 

NC CornW OP

ND Corn OP

NE corn STD 

OH corn STD 

PA corn STD 

TX corn OP 

FL sweetcorn OP 

OR Sweetcorn OP

Suger beet

CA Sugar Beet Wirrg OP 

MN Sugar Beet STD 

Sorghum

KS Sorghum STD

TX Sorghum OP 

Label directions

and available 

scenarios 

The following scenarios 

were used in generating 

EECs: 

Corn

10 standard and 5 organophosphate specific 

scenarios

Suger beet

1 standard and 1 organophosphate specific scenario

Sorghum

1 standard and 1 organophosphate specific scenario

Application Date

Relative date: 7 days prior to 

emergence date in crop 

scenarios

Label Directions ---

Spray drift fraction Not applicable EFED Guidance 

(USEPA, 2013) ---

Molecular weight 288.4 g/mole MRID 410449502 ---
92

Parameter Input Value Source Comment

Solubility in water 

(25 °C) 5.4 mg/L MRID 410449502 ---

Vapor pressure 3.16E-04 (mmHg @25°C) MRID 410449502

--- Henry’s Law constant 

(20 °C) 2.46E-05 atm.m3 /mol Footprint

Hydrolysis (t1/2)

1 1.5 days @ 25°C @ pH 7 MRID 44862501 ---

Aquatic photolysis 

(t1/2)

1 1.77 days MRID 00161567 and 

41181101 ---

Aerobic soil 

metabolism (t1/2)

1 14.7 days MRID 00156853 and 

41749801 Based on 90% of the upper 

confidence limit (UCL) of 

the mean metabolism halflife (USEPA, 2009).

Aerobic aquatic 

metabolism (t1/2)

1 37.5 days MRID 44672004

Anaerobic aquatic 

metabolism (t1/2) Stable ---

Since terbufos is sensitive 

to hydrolytic degradation, 

anaerobic aerobic aquatic 

metabolism was assumed 

stable according to the 

Input Parameter Guidance 

(USEPA, 2009).

Partition coefficient Kd 11.11 mL/g MRID 41373604 Mean Kd for 4 soils

1 DT50s were recalculated using NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in 

Environmental Media (USEPA, 2012a). Appendix A contains revised estimated half-lives.

Table F-2. SWCC Input Parameters for Terbufos Sulfoxide

Parameter Input Value Source Comment

Use Site and Scenarios 

Application Dates

See Table 5

Relative Date: 30 days after 

terbufos application

Table 5 Application dates were 

adjusted based on 

maximum terbufos 

sulfoxide formation in 

laboratory studies.

Application Rate

Corn: 0.72 lb

Corn: 1.44 lb (NC SLN 920001)

Sorghum: 0.94 lb

Sugar beet: 1.05 lb

Estimated See sample calculations 

below1

Number of applications 

per year 

1 EPA Reg# 241-314

EPA Reg# 5481-562 ---

Application method Ground --- Degradation product of 

terbufos Spray drift fraction Not applicable ---

Molecular weight 304.42 g/mole EPISUITE 4.1 ---

Solubility in water 

(25 °C) 3214 mg/L MRID 44672001 

and 44672002

Solubility of terbufos 

sulfoxide is higher than that 

of terbufos.

Vapor pressure 3.42E-05 (mmHg @25°C) EPISUITE 4.1
93

Parameter Input Value Source Comment

Henry’s Law constant 

(25 °C) 9.13E-08 atm.m3 /mol EPISUITE 4.1 Estimated using EPISUITE model

Hydrolysis (t1/2) 65.1 days @ 25°C MRID 44862501 ---

Aquatic photolysis (t1/2) Stable ---

In absence of data, assumed 

stable according to the 

Input Parameter Guidance 

(USEPA, 2009)

Aerobic soil 

metabolism (t1/2) 136 x 3 (408 days) MRID 00156853 

Single value is available. 

3X was used according to 

the Input Parameter 

Guidance (USEPA, 2009)

Aerobic aquatic 

metabolism (t1/2) Stable ---

In absence of data, assumed 

stable

Anaerobic aquatic 

metabolism (t1/2) Stable ---

Since terbufos sulfoxide is 

sensitive to hydrolytic 

degradation, anaerobic 

aerobic aquatic metabolism 

was assumed stable 

according to the Input 

Parameter Guidance 

(USEPA, 2009) 

Partition coefficient Kd 1.12 mL/g MRID 41373604 Mean Kd for 4 soils

1

Terbufos sulfoxide application rate = terbufos application rate of 1.30 lb x (0.523, the maximum conversion rate 

from the degradation of terbufos to terbufos sulfoxide in laboratory studies) x (1.055, the molecular weight ratio 

of terbufos sulfoxide to terbufos.

Table F-3. SWCC Input Parameters for Terbufos Sulfone

Parameter Input Value Source Comment

Use Site and Scenarios 

Application Dates

See Table 5

Relative Date: 60 days after 

terbufos application

Table 5 Application dates were 

adjusted based on maximum 

terbufos sulfone formation 

in the laboratory studies.

Application Rate

Corn: 0.29 lb

Corn: 0.58 lb (NC SLN 920001)

Sorghum: 0.38 lb

Sugar beet: 0.44 lb

Estimated See a sample calculations 

below1

Number of applications 

per year 

1 EPA Reg # 241-314

EPA Reg# 5481-562

Application method Ground --- Degradation product of 

terbufos Spray drift fraction Not applicable ---

Molecular weight 320.42 g/mole EPISUITE 4.1 ---

Solubility in water 

(25 °C) 407 mg/L MRID 44672001 

and 44672002

Terbufos sulfone is more 

soluble than terbufos

Vapor pressure 7.88E-06 (mmHg @25°C) EPISUITE 4.1

Estimated using EPISUITE 

model Henry’s Law constant 

(25 °C) 4.10E-08 atm.m3 /mol EPISUITE 4.1
94

Parameter Input Value Source Comment

Hydrolysis (t1/2) 43.8 days @ 25°C MRID 44862501 ---

Aquatic photolysis (t1/2) Stable --- Assumed stable

Aerobic soil metabolism 

(t1/2) 174 x 3 (522 days) MRID 00156853 

Single value is available. 

3X was used according to 

the Input Parameter 

Guidance (USEPA, 2009)

Aerobic aquatic 

metabolism (t1/2) Stable 

---- In absence of data, assumed 

stable according to the Input 

Parameter Guidance 

(USEPA, 2009)

Anaerobic aquatic 

metabolism (t1/2) Stable ---

Since terbufos sulfoxide is 

sensitive to hydrolytic 

degradation, anaerobic 

aerobic aquatic metabolism 

is assumed stable according 

to the Input Parameter 

Guidance (USEPA, 2009) 

Partition coefficient Kd 1.26 mL/g MRID 41373604 Mean Kd for 4 soils

1

Terbufos sulfone application rate = terbufos application rate of 1.30 lb x (0.201, the maximum conversion rate 

from the degradation of terbufos to terbufos sulfone in laboratory studies) x (1.11, the molecular weight ratio of 

terbufos sulfone to terbufos.

Table F-4. SWCC EECs for Terbufos, Terbufos Sulfoxide and Terbufos Sulfone for 

Various Crop Scenarios and Application Rates

Surface Water Pore Water

Scenarios Peak 4-day 21-day 60-day 90-day Peak 21-day

Concentration (μg/L)

Terbufos (Corn/Sweetcorn)

IAcornstd 7.06 2.81 0.63 0.23 0.16 5.14 3.88

ILCornSTD 7.79 3.07 0.95 0.35 0.23 3.88 3.23

INCornStd 7.44 3.25 0.93 0.34 0.23 1.83 1.47

KSCornStd 8.98 3.92 1.27 0.46 0.31 1.96 1.59

MNCornStd 5.87 2.28 0.49 0.18 0.12 1.36 1.09

MScornSTD 17.30 8.92 2.44 0.90 0.60 11.30 8.74

NCcornESTD 4.76 2.34 0.54 0.19 0.13 1.29 1.04

NECornStd 11.90 5.39 1.45 0.57 0.38 3.85 3.15

OHCornSTD 9.31 4.21 1.00 0.41 0.28 6.58 5.03

PAcornSTD 3.29 1.36 0.41 0.15 0.10 0.77 0.62

CAcornOP 1.71 0.68 0.15 0.05 0.04 0.52 0.41

FLsweetcornOP 11.50 4.22 1.03 0.47 0.69 0.46 0.38

NCcornWOP 3.86 1.65 0.40 0.16 0.11 0.42 0.35

NDcornOP 1.50 0.76 0.18 0.07 0.05 0.21 0.17

ORswcornOP 1.28 0.54 0.13 0.05 0.03 0.44 0.34
95

Surface Water Pore Water

Scenarios Peak 4-day 21-day 60-day 90-day Peak 21-day

Concentration (μg/L)

TXcornOP 4.18 1.56 0.38 0.14 0.10 1.32 1.04

2X Application Rate for North Carolina

NCcornWOP 10.60 4.80 1.18 0.44 0.30 1.51 1.25

NCcornESTD 12.50 5.07 1.11 0.43 0.29 2.10 1.74

Terbufos Sulfoxide (Corn/Sweetcorn)

IAcornstd 3.52 3.45 3.21 2.66 2.33 1.59 1.58

ILCornSTD 8.62 8.43 7.74 6.68 6.07 5.39 5.37

INCornStd 4.96 4.85 4.46 3.75 3.26 2.20 2.19

KSCornStd 15.90 15.60 14.50 12.20 10.70 7.33 7.30

MNCornStd 6.46 6.32 5.96 4.97 4.33 2.90 2.89

MScornSTD 17.00 16.60 15.80 13.40 11.70 12.70 12.70

NCcornESTD 4.26 4.16 3.84 3.18 2.77 1.97 1.96

NECornStd 11.20 10.90 10.10 8.38 7.34 5.05 5.05

OHCornSTD 7.32 7.16 6.55 5.41 4.70 3.78 3.77

PAcornSTD 4.53 4.43 4.14 3.40 2.96 2.27 2.26

CAcornOP 4.92 4.81 4.43 3.65 3.17 2.17 2.16

FLsweetcornOP 26.40 26.40 25.00 24.50 21.20 14.30 14.10

NCcornWOP 11.30 11.10 10.20 8.55 7.46 5.04 5.02

NDcornOP 5.78 5.65 5.15 4.21 3.66 2.45 2.44

ORswcornOP 1.96 1.93 1.78 1.52 1.61 1.09 1.09

TXcornOP 15.80 15.40 14.10 11.70 10.20 7.18 7.15

2X Application Rate for North Carolina

NCcornWOP 22.70 22.30 20.30 17.10 14.90 10.10 10.00

NCcornESTD 8.52 8.33 7.68 6.36 5.54 3.94 3.92

Terbufos Sulfone (Corn/Sweetcorn)

IAcornstd 3.93 3.80 3.48 2.67 2.22 1.70 1.70

ILCornSTD 4.87 4.71 4.33 3.59 3.01 2.59 2.57

INCornStd 4.61 4.46 4.03 3.07 2.54 1.69 1.68

KSCornStd 4.55 4.47 4.18 3.29 2.74 1.88 1.86

MNCornStd 4.20 4.07 3.63 2.85 2.47 1.75 1.74

MScornSTD 5.55 5.37 4.74 3.61 2.98 2.29 2.27

NCcornESTD 3.97 3.85 3.43 2.65 2.20 1.56 1.55

NECornStd 7.57 7.32 6.41 5.02 4.21 2.93 2.93

OHCornSTD 3.70 3.62 3.18 2.40 1.98 1.33 1.32

PAcornSTD 2.43 2.35 2.08 1.60 1.33 0.91 0.90

CAcornOP 1.95 1.92 1.99 1.65 1.35 0.92 0.91

FLsweetcornOP 4.78 4.63 4.43 2.67 2.21 1.61 1.44

NCcornWOP 4.23 4.09 3.59 2.75 2.29 1.56 1.55
96

Surface Water Pore Water

Scenarios Peak 4-day 21-day 60-day 90-day Peak 21-day

Concentration (μg/L)

NDcornOP 4.30 4.16 3.64 2.74 2.26 1.50 1.49

ORswcornOP 2.22 2.17 1.95 1.73 1.42 0.96 0.95

TXcornOP 10.10 9.77 8.58 6.52 5.39 4.36 4.34

2X Application Rate for North Carolina

NCcornWOP 9.76 9.44 8.29 6.36 5.28 3.59 3.57

NCcornESTD 9.16 8.88 7.91 6.13 5.07 3.61 3.58

Terbufos 

(Sorghum)

KSsorghumSTD 7.75 3.11 0.73 0.33 0.22 2.57 1.98

TXSorghumOP 19.10 7.64 1.80 0.66 0.44 10.8 8.41

Terbufos Sulfoxide (Sorghum)

KSsorghumSTD 10.50 10.20 9.54 8.13 7.11 5.25 5.22

TXSorghumOP 23.90 23.30 21.50 18.30 16.00 11.00 10.90

Terbufos Sulfone (Sorghum)

KSsorghumSTD 4.55 4.43 3.91 3.00 2.48 1.70 1.69

TXSorghumOP 6.52 6.31 5.55 4.21 3.50 2.56 2.56

Terbufos (Sugar bee

MNSugarbeetSTD 5.62 2.51 0.59 0.21 0.15 1.57 1.26

CASugarbeetwirrgOP 4.14 1.83 0.57 0.21 0.20 0.48 0.41

Terbufos Sulfoxide (Sugar beet)

MNSugarbeetSTD 7.89 7.71 7.07 5.93 5.92 3.99 3.98

CASugarbeetwirrgOP 9.18 8.98 8.27 6.87 6.00 4.21 4.20

Terbufos Sulfone (Sugar beet)

MNSugarbeetSTD 4.24 4.10 3.66 2.86 2.37 1.58 1.57

CASugarbeetwirrgOP 0.89 0.86 0.77 0.59 0.49 0.32 0.32

Table F-5. Total Toxic Residue in Water Column: TX Sorghum Scenario

Year Max 

Peak

4-day Max 14 

day

Max 21 

day

Max 30 

day

Max 60 

day

Max 90 

day

Annual

1961 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1962 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1963 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1964 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.00

1965 0.03 0.02 0.02 0.01 0.01 0.01 0.01 0.00

1966 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1967 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1968 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1969 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.00

1970 0.03 0.02 0.01 0.01 0.01 0.01 0.01 0.00
97

Year Max 

Peak

4-day Max 14 

day

Max 21 

day

Max 30 

day

Max 60 

day

Max 90 

day

Annual

1971 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1972 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1973 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01

1974 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

1975 0.04 0.03 0.03 0.03 0.03 0.03 0.02 0.01

1976 0.07 0.07 0.07 0.07 0.06 0.06 0.05 0.02

1977 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.02

1978 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01

1979 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.01

1980 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.00

1981 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00

1982 0.04 0.02 0.02 0.02 0.02 0.02 0.01 0.01

1983 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01

1984 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1985 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1986 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.01

1987 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.01

1988 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00

1989 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1990 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01

90th% (ppm) 0.04 0.02 0.02 0.02 0.02 0.02 0.02 0.01

90th% (ppb) 35.74 24.19 22.47 21.90 21.18 18.47 16.28 8.86

Table F-6. Total Toxic Residue in Benthic Layer: TX Sorghum Scenario

Year Max 

Peak

4-day Max 14 

day

Max 21 

day

Max 30 

day

Max 60 

day

Max 90 

day

Annual

1961 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.00

1962 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1963 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00

1964 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1965 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1966 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1967 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1968 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1969 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1970 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00

1971 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1972 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1973 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1974 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1975 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
98

Year Max 

Peak

4-day Max 14 

day

Max 21 

day

Max 30 

day

Max 60 

day

Max 90 

day

Annual

1976 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1977 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1978 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1979 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

1980 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1981 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00

1982 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.00

1983 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00

1984 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1985 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1986 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1987 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1988 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1989 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1990 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

90th %(ppm) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00

90th % (ppb) 12.46 12.41 12.15 11.44 10.30 7.40 6.98 3.90

Summary of Water Modeling of Terbufos and the USEPA Standard Pond

Estimated Environmental Concentrations for terbufos are presented in Table F-7 for the USEPA 

standard pond with the TXsorghumOP field scenario. A graphical presentation of the year-toyear peaks is presented in Figure F-1. These values were generated with the Surface Water 

Concentration Calculator (SWCC Version 1.106). 

Table F-7. Estimated Environmental Concentrations (ppb) for Terbufos

Peak (1-in-10 yr) 19.1

4-day Avg (1-in-10 yr) 7.64

21-day Avg (1-in-10 yr) 1.80

60-day Avg (1-in-10 yr) 0.662

365-day Avg (1-in-10 yr) 0.111

Entire Simulation Mean 0.426E-01
99

Figure F-1. Yearly Peak Concentrations
100

Appendix G: Representative T-REX Input and Output

Scenario: Corn, 7 inch band at planting, 1.3 lb ai/A (0.075 lb ia/1000 ft row), toxicity based on 

TGAI

Table G-1. Input

Application Rate 1.3 lb / acre

% AI 100.00%

Avian LD50 (20g) 20.60 mg/kg bw

(100g) 26.23

(1000g) 37.05

Mammalian LD50 (15g) 2.75 mg/kg bw

(35g) 2.22

(1000g) 0.96

Row Spacing 30 inches

Bandwidth 7 inches

Unincorporation 15%

Table G-2. Output and Calculations

# rows acre-1 83.48

row length (ft) 208.71

lb ai/1000 ft row 0.075

bandwidth (ft) 0.58

mg ai/ft2 58.02

exposed mg ai/ft2 8.70

wgt class (grams)

Acute RQ 

LD50/ft2

Avian 20 21.12

100 3.32

1000 0.23

Mammal 15 211.17

35 111.85

1000 9.05

Chronic RQs were calculated based on the ratio of exposed mg ai/ft2 to dose-based NOAEL (mg ai/kg 

bw). 

The avian dietary-based chronic toxicity value (NOAEC = 5 mg ai/kg diet; MRID 0161574) was 

converted to a dose equivalent toxicity value. mg ai/kg bw = (mg ai/kg diet * daily food intake)/kg bw. 

daily food intake = 0.0582 * bw^0.651 (source: SIP v 1.0 manual). bw = 1.136 kg (source: mean value 

from MRID 0161574). NOAEL= 0.278 mg ai/kg bw = (5 mg ai/kg diet * 0.632 kg/day)/1.136 kg bw
101

Appendix H: Representative KABAM Input

Scenario: Corn (1.3 lb ai/A), crop scenario: MScorn_STD

Table H-1. Chemical Characteristics of Terbufos

Characteristic Value Comments/Guidance1

Pesticide Name Terbufos

Log KOW 4.71 Enter value from acceptable or supplemental study submitted by 

registrant or available in scientific literature.

KOW 51286 No input necessary. This value is calculated automatically from 

the Log KOW value entered above.

KOC (L/kg OC) 17950

Input value used in PRZM/EXAMS to derive EECs. Follow 

input parameter guidance for deriving this parameter value 

(USEPA, 2009).

Time to steady state 

(TS; days) 16 No input necessary. This value is calculated automatically from the Log KOW value entered above.

Pore water EEC (μg/L) 8.74

Enter value generated by PRZM/EXAMS benthic file. 

PRZM/EXAMS EEC represents the freely dissolved 

concentration of the pesticide in the pore water of the sediment. 

The appropriate averaging period of the EEC is dependent on 

the specific pesticide being modeled and is based on the time it 

takes for the chemical to reach steady state. Select the EEC 

generated by PRZM/EXAMS which has an averaging period 

closest to the time to steady state calculated above. In cases 

where the time to steady state exceeds 365 days, the user should 

select the EEC representing the average of yearly averages. The 

peak EEC should not be used. 

Water Column EEC (μg/L) 2.44

Enter value generated by PRZM/EXAMS water column file. 

PRZM/EXAMS EEC represents the freely dissolved 

concentration of the pesticide in the water column. The 

appropriate averaging period of the EEC is dependent on the 

specific pesticide being modeled and is based on the time it 

takes for the chemical to reach steady state. The averaging 

period used for the water column EEC should be the same as the 

one selected for the pore water EEC (discussed above). 

1 SWCC is the current model.
102

Table H-2. Input Parameters for Rate Constants 

Trophic level

k1 

(L/kg*d)

k2 

(d-1)

kD 

(kgfood/kgorg/d)

kE 

(d-1)

kM* 

(d-1)

phytoplankton calculated calculated 0* 0* 0

zooplankton calculated calculated calculated calculated 0

benthic invertebrates calculated calculated calculated calculated 0

filter feeders calculated calculated calculated calculated 0

small fish calculated calculated calculated calculated 0

medium fish calculated calculated calculated calculated 0

large fish calculated calculated calculated calculated 0

* Default value is 0. 

k1 and k2 represent the uptake and elimination constants, respectively, through respiration.

kD and kE represent the uptake and elimination constants, respectively, through diet.

kM represents the metabolism rate constant. 

Table H-3. Mammalian and Avian Toxicity Data for Terbufos

Animal

Measure of 

effect 

(units) Value Comment

Avian LD50

(mg/kg bw)

28.6 Northern bobwhite quail

LC50 (mg/kgdiet) 143 Northern bobwhite quail

NOAEC 

(mg/kg-diet)

5 Mallard duck

Mineau Scaling 

Factor

1.15 Default value

Mammalian LD50

(mg/kg bw)

1.25 Laboratory rat

NOAEC

(mg/kg-diet)

1 Laboratory rat
103

Appendix I: STIR Input and Output

Scenario: Corn – use with the lowest maximum application rate (1.3 lb ai/A)

Table I-1. Inputs

Enter Chemical Use Outdoor

Is the Application a Spray? No

Enter Chemical Molecular Weight (g/mole) 288.4

Enter Chemical Vapor Pressure (mmHg) 3.16E-04

Enter Application Rate (lb ai/A) 1.3

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 28.6

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 1.25

Enter Lowest Rat Inhalation LC50 (mg/L) 0.0012

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Table I-2. Avian Results (0.020 kg)

Maximum Vapor Concentration in Air at 

Saturation (mg/m3) 4.90E+00

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 6.17E-01

Adjusted Inhalation LD50 1.53E-01

Ratio of Vapor Dose to Adjusted Inhalation LD50 4.03E+00

Table I-3. Mammalian Results (0.015 kg)

Maximum Vapor Concentration in Air at 

Saturation (mg/m3) 4.90E+00

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 7.75E-01

Adjusted Inhalation LD50 7.14E-02

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.08E+01
104

Appendix J: SIP Input and Output

SIP employs the following conservative assumptions to derive upper bound exposure estimates:

1) The chemical concentration in drinking water is at the solubility limit in water (at 25oC).

2) The assessed animals obtain 100% of their daily water needs through drinking water.

3) The daily water need is equivalent to the daily water flux rate as calculated by Nagy and 

Peterson (1988).

4) The body weight of the assessed bird is equivalent to the smallest generic bird modeled in TREX (i.e., 20 g). This assumption results in the highest ratio of exposure to toxicity for the 3 

assessed avian body weights of T-REX (i.e., 20, 100, 1000 g).

5) The body weight of the assessed mammal is equivalent to the largest generic mammal 

modeled in T-REX (i.e., 1000 g). This results in the highest ratio of exposure to toxicity for the 3 

assessed mammalian body weights of T-REX (i.e., 15, 35, 1000 g). 

Table J-1. Inputs

Parameter Value

Chemical name Terbufos

Solubility (in water at 25oC; mg/L) 5.4

Mammalian LD50 (mg/kg bw) 1.25

Mammalian test species Laboratory rat

Mammalian NOAEL (mg/kg bw) 0.07

Mammalian test species Laboratory rat

Avian LD50 (mg/kg bw) 28.6

Avian test species Northern bobwhite quail

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 5

Bobwhite quail NOAEC (mg/kg-diet) 30

Table J-2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg bw) 0.9288 0.9288

Adjusted toxicity value (mg/kg bw) 0.9615 0.0538

Ratio of exposure to toxicity 0.9660 17.2507

Conclusion

Exposure through drinking 

water alone is a potential 

concern for mammals

Exposure through drinking water 

alone is a potential concern for 

mammals

Table J-3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg bw) 4.3740 4.3740

Adjusted toxicity value (mg/kg bw) 20.6043 0.2481

Ratio of exposure to acute toxicity 0.2123 17.6326

Conclusion

Exposure through drinking 

water alone is a potential 

concern for birds

Exposure through drinking water 

alone is a potential concern for 

birds
105

APPENDIX K: TerrPlant Input and Output (NC use on corn)

Table K-1. Chemical Identity

Chemical Name Terbufos

PC code 105001

Use Corn (NC supplemental label)

Application Method Banded

Application Form Granular 

Solubility in Water (ppm) 5.4

Table K-2. Input Parameters Used to Derive EECs

Input Parameter Symbol Value Units

Application Rate A 2.6 lb ai/A

Incorporation I 1 none

Runoff Fraction R 0.01 none

Drift Fraction D 0 none

Table K-3. EECs for Terbufos (lb ai/A)

Description Equation EEC

Runoff to dry areas (A/I)*R 0.026

Runoff to semi-aquatic areas (A/I)*R*10 0.26

Spray drift A*D 0

Total for dry areas ((A/I)*R)+(A*D) 0.026

Total for semi-aquatic areas ((A/I)*R*10)+(A*D) 0.26

Table K-4. Plant Survival and Growth Data Used for RQ Derivation. Units are in lb ai/A

Plant type

Seedling Emergence Vegetative Vigor

EC25 NOAEC EC25 NOAEC 

Monocot ND 2 ND ND

Dicot ND 2 ND ND

Table K-5. RQ Values for Plants in Dry and Semi-Aquatic Areas Exposed to Terbufos 

Through Runoff.*

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed N/A N/A N/A

Monocot listed <0.1 0.13 N/A

Dicot non-listed N/A N/A N/A

Dicot listed <0.1 0.13 N/A

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

ND = no data

N/A = not applicable
106

Appendix L: Characterization of Avian and Mammal Risk from Consuming Terbufos Granules

Table L-1. Characterization of Avian Risk from Consuming Terbufos Granules1

Use Application 

Method (% 

incorporation)

lb 

ai/1000 

ft row

Product Band 

width 

(in)

Row 

Spacing 

(in)

Exposed 

mg 

ai/ft2

# 

Exposed 

Granules/

ft2 (2)

Toxicity 

(form)3

# granules to exceed acute LOC4

0.02 kg bird 0.1 kg bird 1 kg bird

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC = 

0.1

Corn Banded, 

at planting 

(85%)

0.15 15G 

(NC)

7 30 17.4 637-1758 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

0.075 CR 8.7 51 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 319-879 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 5 12.18 381 TGAI 6 1 41 8 579 116

4 15.23 476

In furrow, 

at planting

(99%)

0.15 15G 

(NC)

1 8.12 297-820 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

0.075 CR 4.06 24 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 149-410 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 127 TGAI 6 1 41 8 579 116

Banded, 

postemergence 

and at cultivation

(85%)

0.075 CR 7 8.7 51 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 319-879 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 272 TGAI 6 1 41 8 579 116
107

Use Application 

Method (% 

incorporation)

lb 

ai/1000 

ft row

Product Band 

width 

(in)

Row 

Spacing 

(in)

Exposed 

mg 

ai/ft2

# 

Exposed 

Granules/

ft2 (2)

Toxicity 

(form)3

# granules to exceed acute LOC4

0.02 kg bird 0.1 kg bird 1 kg bird

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC = 

0.1

Sorghum Knifed in,

at bedding and at 

planting

(99%)

0.065 CR 1 20 3.5 21 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

0.066 15G 3.53 129-357 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

0.065 20G 3.5 109 TGAI 6 1 41 8 579 116

Banded,

at planting

(85%)

0.065 CR 7 7.5 44 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

0.066 15G 7.56 277-764 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

0.065 20G 7.5 234 TGAI 6 1 41 8 579 116

0.066 15G 5 10.59 388-1070 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

0.065 20G 10.5 328 TGAI 6 1 41 8 579 116
108

Use Application 

Method (% 

incorporation)

lb 

ai/1000 

ft row

Product Band 

width 

(in)

Row 

Spacing 

(in)

Exposed 

mg 

ai/ft2

# 

Exposed 

Granules/

ft2 (2)

Toxicity 

(form)3

# granules to exceed acute LOC4

0.02 kg bird 0.1 kg bird 1 kg bird

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC = 

0.1

Sugar 

beet

Modified in 

furrow and 

knifed in,

at planting

(99%)

0.075 CR 1 20 4.08 24 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 149-412 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 128 TGAI 6 1 41 8 579 116

Banded,

at planting and 

postemergence

(85%)

CR 7 8.75 51 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 321-884 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 273 TGAI 6 1 41 8 579 116

CR 5 12.25 72 TGAI 1 <1 8 2 109 22

CR 1 <1 6 1 78 16

15G 449-1237 TGAI 8-21 2-4 48-

132

10-27 679-

1871

136-

374

15G 3-7 1-2 16-

44

3-9 226-

623

45-125

20G 383 TGAI 6 1 41 8 579 116 1 Product application methods (timing, lb ai/ft row, band width, and row width) were obtained from the most recent product labels. 2 Based on the following granule weights: CR = 0.85 mg/granule (source: American Cyanamid as reported in USEPA, 1999); 20G = 0.16 mg/granule (source: 

email from AMVAC dated 3/3/14); 15G = 0.066-0.182 mg/granule (source: Hill and Camardese, 1984 and MRID 41508803 & 41508805). # exposed 

granules/ft2 = exposed mg ai/ft2

/(granule weight as mg * % ai) 3 Toxicity based on TGAI, Bobwhite quail LD50 = 28.6 mg ai/kg/bw; 15G, Mallard duck LD50 = 13.21 mg ai/kg bw; CR, Cowbird LD50 = 16.9 mg ai/kg bw 4 Number of granules rounded to nearest whole number.
109

Table L-2. Characterization of Mammalian Risk from Consuming Terbufos Granules1

Use Application 

Method (% 

incorporation)

lb ai/

1000 ft 

row

Product Band 

width 

(in)

Row 

Spacing 

(in)

Exposed 

mg ai/ft2

# Exposed 

Granules/ 

ft2 (2)

Toxicity

(form)3

# granules to exceed acute LOC4

0.015 kg5 0.035 kg5 1 kg5

LOC 

= 0.5

LOC

= 0.1

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC 

= 0.1

Corn Banded, 

at planting 

(85%)

0.15 15G 

(NC)

7 30 17.4 637-1758 TGAI <1-2 <1 1-4 <1 18-49 4-10

0.075 CR 8.7 51 TGAI <1 <1 <1 <1 3 <1

15G 319-879 <1-2 <1 1-4 <1 18-49 4-10

20G 5 12.18 381 TGAI <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

4 15.23 476 TGAI <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

In furrow, 

at planting

(99%)

0.15 15G 

(NC)

1 8.12 297-820 TGAI <1-2 <1 1-4 <1 18-49 4-10

0.075 CR 4.06 24 TGAI <1 <1 <1 <1 3 <1

15G 149-410 <1-2 <1 1-4 <1 18-49 4-10

20G 127 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

Banded, 

postemergence 

and at cultivation

(85%)

0.075 CR 7 8.7 51 TGAI <1 <1 <1 <1 3 <1

15G 319-879 <1-2 <1 1-4 <1 18-49 4-10

20G 272 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

Sorghum Knifed in,

at bedding and at 

planting

(99%)

0.065 CR 1 20 3.5 21 TGAI <1 <1 <1 <1 3 <1

0.066 15G 3.53 129-357 <1-2 <1 1-4 <1 18-49 4-10

0.065 20G 3.5 109 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

Banded,

at planting

(85%)

0.065 CR 7 7.5 44 TGAI <1 <1 <1 <1 3 <1

0.066 15G 7.56 277-764 <1-2 <1 1-4 <1 18-49 4-10

0.065 20G 7.5 234 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

0.066 15G 5 10.59 388-1070 TGAI <1-2 <1 1-4 <1 18-49 4-10

0.065 20G 10.5 328 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2
110

Use Application 

Method (% 

incorporation)

lb ai/

1000 ft 

row

Product Band 

width 

(in)

Row 

Spacing 

(in)

Exposed 

mg ai/ft2

# Exposed 

Granules/ 

ft2 (2)

Toxicity

(form)3

# granules to exceed acute LOC4

0.015 kg5 0.035 kg5 1 kg5

LOC 

= 0.5

LOC

= 0.1

LOC 

= 0.5

LOC 

= 0.1

LOC 

= 0.5

LOC 

= 0.1

Sugar 

beet

Modified in 

furrow and 

knifed in,

at planting

(99%)

0.075 CR 1 20 4.08 24 TGAI <1 <1 <1 <1 3 <1

15G 149-412 <1-2 <1 1-4 <1 18-49 4-10

20G 128 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

Banded,

at planting and 

postemergence

(85%)

CR 7 8.75 51 TGAI <1 <1 <1 <1 3 <1

15G 321-884 <1-2 <1 1-4 <1 18-49 4-10

20G 273 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2

CR 5 12.25 72 TGAI <1 <1 <1 <1 3 <1

15G 449-1237 <1-2 <1 1-4 <1 18-49 4-10

20G 383 <1 <1 1 <1 15 3

20G <1 <1 <1 <1 10 2 1 Product application methods (timing, lb ai/ft row, band width, and row width) were obtained from the most recent product labels. 2 Based on the following granule weights: CR = 0.85 mg/granule (source: American Cyanamid as reported in USEPA 1999); 20G = 0.16 mg/granule (source: 

email from AMVAC dated 3/3/14); 15G = 0.066-0.182 mg/granule (source: Hill and Camardese, 1984 and MRID 41508803 & 41508805). # exposed 

granules/ft2 = exposed mg ai/ft2

/(granule weight as mg * % ai) 3 Toxicity based on TGAI, Rat LD50 = 1.25 mg ai/kg/bw; 20G, rat LD50 = 0.836 mg ai/kg bw 4 Number of granules rounded to nearest whole number.

5 Mammal body weight
111

Appendix M: ECOTOXicology Database References

Terbufos Refresh Acceptable Bibliography 2012

1. Ayers, A. R.; Duncan, H. E.; Barker, K. R., and Beute, M. K. Effects of Crop Rotation and Nonfumigant 

Nematicides on Peanut and Corn Yields in Fields Infested with Criconemella Species. 1989; 21, (2): 

268-275. EcoReference No.: 87066

2. Barillas-Argueta, J. R. The Influence of Root-Knot Nematode (Meloidogyne incognita (Kofoid and White) 

Chitwood 1949) on Growth and Development of Kenaf (Hibiscus cannabinus L.) and Its Control. 

1993: 155 p. (UMI# 9400469). EcoReference No.: 157921

3. Belluck, D. and Felsot, A. Bioconcentration of Pesticides by Egg Masses of the Caddisfly, Triaenodes tardus 

Milne. 1981; 26, 299-306. EcoReference No.: 2340

4. Bessin, R. T. and Townsend, L. H. Japanese Beetle Larval Control in Field Corn, 1994. 1995; 20, 160-161 

(20F). EcoReference No.: 110864

5. Biales, A. D.; Bencic, D. C.; Flick, R. L.; Blocksom, K. A.; Lazorchak, J. M., and Lattier, D. L. Proteomic 

Analysis of a Model Fish Species Exposed to Individual Pesticides and a Binary Mixture. 2011; 101, 

(1): 196-206. EcoReference No.: 156142

6. Boetel, M. A. and Fuller, B. W. Planting-Time and Post-Emergence Insecticide Treatments for Controlling 

Corn Rootworms in South Dakota, 1998. 1999; 24, 209-210 (F21). EcoReference No.: 88058

7. Bogatko, W. and Labanowski, G. Chemical Control of the Black Vine Weevil (Otiorrhynchus sulcatus F.) on 

Ornamental Crops. 1993; 1, (3): 93-101. EcoReference No.: 153283

8. Cabrera, J. A.; Pocasangre, L. E.; Pattison, A. B., and Sikora, R. A. Terbufos Biodegradability and Efficacy 

Against Radopholus similis in Soils from Banana Cultivation Having Different Histories of 

Nematicide Use, and the Effect of Terbufos on Plant Growth of In Vitro-Propagated Musa AAA cv. 

Grande Naine. 2010; 56, (1): 61-67. EcoReference No.: 157846

9. Call, D. J. and Geiger, D. L. Subchronic Toxicities of Industrial and Agricultural Chemicals to Fathead 

Minnows (Pimephales promelas). Volume I. 1992: 318 p. EcoReference No.: 150898

10. Call, D. J.; Poirier, S. H.; Lindberg, C. A.; Harting, S. L.; Markee, T. P.; Brooke, L. T.; Zarvan, N., and 

Northcott, C. E. Toxicity of Selected Uncoupling and Acetylcholinesterase-Inhibiting Pesticides to 

the Fathead Minnow (Pimephales promelas). 1989: 317-336. EcoReference No.: 14097

11. Calvin, D. D. and Losey, J. E. Evaluation of Black Cutworm Insecticide Efficacy, 1989. 1991; 16, 147-(34F). 

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12. Campbell, C. D. and Hutchison, W. D. Timing of Insecticides for SRA Management in Southern Minnesota, 

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13. Castro-Escobar, A. The Interaction of Acetolactate Synthase Inhibiting Herbicides with Graminicides and 

Insecticides. 1995: 79 p. (UMI# 1376283)//Publ in part as Ecoref 101249. EcoReference No.: 

157919

14. Charlet, L. D.; Oseto, C. Y., and Gulya, T. J. Application of Systemic Insecticides at Planting: Effects on 

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Yield in North Dakota. 1985; 78, (6): 1347-1349. EcoReference No.: 112148
112

 15. Chaves, N. P.; Pocasangre, L. E.; Elango, F.; Rosales, F. E., and Sikora, R. Combining Endophytic Fungi and 

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Insecticides. 1978; 71, (3): 389-393. EcoReference No.: 63297

17. Choung, C. B.; Hyne, R. V.; Mann, R. M.; Stevens, M. M., and Hose, G. C. Developmental Toxicity of Two 

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Mixtures to Ceriodaphnia cf dubia. Department of Biological Sciences, Macquarie University, 

Balaclava Road, Macquarie University, NSW 2109, Australia. 

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2011b

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(Homoptera: Aphididae) on Grain Sorghum. 1987; 80, (2): 490-493. EcoReference No.: 113373

21. Diehl, K. E.; Taylor, S. L.; Simpson, D. M., and Stoller, E. W. Effect of Soil Organic Matter on the 

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EcoReference No.: 101802

22. Downard, R. W.; Morishita, D. W.; Dexter, A. G.; Wilson, R., and Hein, G. L. Interaction Between 

Triflusulfuron and Organophosphate or Carbamate Insecticides in Sugarbeet. 1999; 36, (4): 47-81. 

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1995; 32, (2/3): 79-88. EcoReference No.: 157890

24. Foster, R. E. and Brust, G. E. Effects of Insecticides Applied to Control Cucumber Beetles (Coleoptera: 

Chrysomelidae) on Watermelon Yields. 1995; 14, (8): 619-624. EcoReference No.: 92727

25. Frazier, T. L. and Nissen, S. J. Influence of Crop Safeners on the Interaction of Primisulfuron and Terbufos in 

Corn (Zea mays). 1994; 42, (2): 168-171. EcoReference No.: 101798

26. Gable, R. H.; Emfinger, K. D.; Leonard, B. R., and Temple, J. Evaluation of Selected Insecticides Against 

Sugarcane Beetle and Cutworms in Field Corn, 2004. 2005; 30, 2 p. (F21). EcoReference No.: 

110034

27. Green, J. M. and Ulrich, J. F. Response of Maize (Zea mays) Inbreds and Hybrids to Rimsulfuron. 1994; 40, 

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28. Greenlee, A. R.; Ellis, T. M., and Berg, R. L. Low-Dose Agrochemicals and Lawn-Care Pesticides Induce 

Developmental Toxicity in Murine Preimplantation Embryos. 2004; 112, (6): 703-709. 

EcoReference No.: 82041
113

29. Haas, M. J. and Landis, D. A. 1st Generation European Corn Borer Larvicide Trial, 1995. 1996; 21, 219-

(36F). EcoReference No.: 95501

30. Hammond, R. B. Phytotoxicity of Soybean Caused by the Interaction of Insecticide-Nematicides and 

Metribuzin. Dep. Entomol.,Ohio Agric. Res. Dev. Cent.,Wooster,OH//:1983; 76, (1): 17-19. 

EcoReference No.: 103910

31. Henzell, R. F.; Skinner, R. A., and Clements, R. O. Insecticides for Control of Adult Grass Grub, Costelytra 

zealandica (White) V. Screening and Behaviour of Insecticides in Soil Bioassays. 1983; 26, (1): 129-

133. EcoReference No.: 79045

32. Hoffmann, M. P.; Kirkwyland, J. J., and Gardner, J. Impact of Western Corn Rootworm (Coleoptera: 

Chrysomelidae) on Sweet Corn and Evaluation of Insecticidal and Cultural Control Options. 2000; 

93, (3): 805-812. EcoReference No.: 58574

33. Johnson, D. R.; Studebaker, G., and Kimbrough, J. Control of Thrips in Cotton with In-Furrow Insecticides, 

1991. 1993; 18, 230-(55F). EcoReference No.: 150470

34. Kappelman, A. J. Jr. Effect of Fungicides, Insecticides, and Their Combinations on Stand Establishment and 

Yield of Cotton. 1980; 64, (12): 1076-1078. EcoReference No.: 96622

35. Kwon, C. S.; Kells, J. J., and Penner, D. Combined Effects of Acetolactate Synthase-Inhibiting Herbicides 

with Terbufos and Piperonyl Butoxide on Corn (Zea mays) and Soybean (Glycine max). 1995; 9, 

(4): 696-702. EcoReference No.: 75595

36. Lentz, G. L.; Hayes, R. M., and Chambers, A. Y. Interactions of Insecticide-Nematicides, Metribuzin, and 

Environment on Soybean Injury and Yield. 1985; 78, (6): 1217-1221. EcoReference No.: 101285

37. Mize, T.; Wilde, G., and Smith, M. T. Chemical Control of Chinch Bug and Greenbug on Seedling Sorghum 

with Seed, Soil, and Foliar Treatments. 1980; 73, (4): 544-547. EcoReference No.: 113402

38. Morton, C. A. Selectivity and Efficacy of Sulfonylurea Herbicides and Wild-Proso Millet Competition in 

Field and Sweet Corn. 1993: 173 p. (UMI# 9318633), Publ in Part as Ecoref 101253, Ecoref 62641. 

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39. Nendza, M. and Wenzel, A. Discriminating Toxicant Classes by Mode of Action 1. Ecotoxicity Profiles. 

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40. Nielsen, D. G. and Boggs, J. F. Topical Toxicity of Insecticides to First-Instar Black Vine Weevil 

(Coleoptera: Curculionidae). 1985; 78, (5): 1114-1117. EcoReference No.: 112759

41. Noetzel, D. and Kellesvig, C. Comparison of Seed Coating and Granular Systemics for Flea Beetle Control, 

1992. 1993; 18, 194-(12F). EcoReference No.: 105630

42. Noetzel, D. and Nyegaard, C. Flea Beetle Control in Canola, 1987. 1988; 13, 196-(30F). EcoReference No.: 

88850

43. Noetzel, D. and Putnam, D. Seed Coating for Flea Beetle Control, 1992. 1993; 18, 193-194 (11F). 

EcoReference No.: 105631

44. Noetzel, D. M. Flea Beetle Control in Canola, Roseau, MN, 1994. 1996; 21, 207-(20F). EcoReference No.: 

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45. Oleson, J. D.; McNutt, J. J.; Pruisner, R. D., and Tollefson, J. J. Corn Rootworm Larval Control, 1994. 1995; 

20, 174-176 (37F). EcoReference No.: 106400
114

46. Oleson, J. D.; McNutt, J. J.; Tollefson, J. J., and Wang, X. Seedcorn Maggot Control, 1996. 1997; 22, 224. 

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47. Oleson, J. D.; McNutt, J. J.; Warshaw, J. A., and Tollefson, J. J. Corn Rootworm Larval Control in Iowa, 

1993. 1994; 19, 200-203 (37F). EcoReference No.: 106407

48. Oleson, J. D.; Nowatzki, T. M., and Tollefson, J. J. Field Corn, Wireworm Larval Control, 1998. 1999; 24, 

217-218 (F30). EcoReference No.: 88098

49. Peairs, F. B. and Pilcher, S. D. Second Generation European Corn Borer, Handplots, Wray, CO, 1985. 1986; 

11, 242-243 (316). EcoReference No.: 88670

50. Rogers, D. J. and Brier, H. B. Application Methods for Granular Insecticides to Control Heteronyx piceus 

Blanchard (Coleoptera: Scarabaeidae) Larvae in Peanuts in Queensland. 1992; 7, (2): 48-50. 

EcoReference No.: 154187

51. Ruppel, R. F. and Laughlin, C. W. Toxicity of Some Soil Pesticides to Earthworms. 1977; 50, (1): 113-118. 

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52. Seymour, R. C.; Campbell, J. B., and Wright, R. J. Control of European Corn Borer on Whorl Stage Corn in 

West Central Nebraska, 1992. 1994; 19, 207-208 (43F). EcoReference No.: 121354

53. Shapiro, C. A.; Echtenkamp, G. W.; Witkowski, J. F., and Hunt, T. E. Effects of Manure, Hybrid Root 

Strength, and Reduced Rates of Insecticide on Corn Rootworm (Coleoptera: Chrysomelidae) Injury 

to Corn. 2002; 21, (2): 95-107. EcoReference No.: 157858

54. Smart, J. R. and Bradford, J. M. CGA-152005 and Terbufos in Corn and Grain Sorghum. 1995; 48, 77-81. 

EcoReference No.: 157860

55. Tasistro, A. and Mihm, J. A. Control of Fall Armyworm in Field Corn, 1985. 1987; 12, 223-224 (260). 

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56. Tetreault, G. E. Metabolism of Carbaryl, Chlorpyrifos, DDT, and Parathion in the European Corn Borer: 

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Against Soil Insects in Field Corn, 2004. 2005; 30, 2 p. (F31). EcoReference No.: 102135

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Population to Soil Insecticides: Laboratory Bioassays, Assays of Detoxification Enzymes, and Field 

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Terbufos Refresh Acceptable Bibliography April 2008

1. Barrett, G. W.; Haviland, C. S., and Taylor, D. H. Perturbation Effects on Deer Mouse Populations in Corn 

Agroecosystems. 1990; 90, (4): 125-129. Rec #: 80. EcoReference No.: 101173

2. Belluck, D. and Felsot, A. Bioconcentration of Pesticides by Egg Masses of the Caddisfly, Triaenodes tardus 

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3. Block, E. K.; Lacher, T. E. Jr.; Brewer, L. W.; Cobb III, G. P., and Kendall, R. J. Population Responses of 

Peromyscus Resident in Iowa Cornfields Treated with the Organophosphorus Pesticide COUNTER. 

MOR,POP,ACC,BCM,REP. Department of Wildlife and Fisheries Sciences, 210 Nagle Hall, Texas 

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320. EcoReference No.: 67171

4. Block, E. K.; Lacher, T. E. Jr., and Kendall, R. J. Effects of the Organophosphate Pesticide Counter on 

Laboratory Deer Mice (Peromyscus maniculatus). 1993; 12, 377-383. Rec #: 260. EcoReference 

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5. Brecken-Folse, J. A.; Mayer, F. L.; Pedigo, L. E., and Marking, L. L. Acute Toxicity of 4-Nitrophenol, 2,4-

Dinitrophenol, Terbufos and Trichlorfon to Grass Shrimp (Palaemonetes spp.) and Sheepshead 

Minnows (Cyprinodon variegatus) as Affected by Salinity and Temperature. 1994; 13, (1): 67-77. 

Rec #: 110. EcoReference No.: 13273

6. Brewer, R. A.; Carlock, L. L.; Hooper, M. J.; Brewer, L. W.; Cobb III, G. P., and Kendall, R. J. Toxicity, 

Survivability, and Activity Patterns of Northern Bobwhite Quail Dosed with the Insecticide 

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7. Call, D. J.; Poirier, S. H.; Lindberg, C. A.; Harting, S. L.; Markee, T. P.; Brooke, L. T.; Zarvan, N., and 

Northcott, C. E. Toxicity of Selected Uncoupling and Acetylcholinesterase-Inhibiting Pesticides to 

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Imported Fire Ant in Grain Sorghum, 1994. 1995; 20, 232-233 (110F). Rec #: 60. EcoReference 

No.: 101148

9. Clements, R. O.; Bentley, B. R., and Jackson, C. A. The Impact of Granular Formulations of Phorate, 

Terbufos, Carbofuran, Carbosulfan and Thiofanox on Newly Sown Italian Ryegrass (Lolium 

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10. Cobb, G. P.; Hol, E. H.; Allen, P. W.; Gagne, J. A., and Kendall, R. J. Uptake, Metabolism and Toxicity of 

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1990; 153, (4): 219-223. Rec #: 70. EcoReference No.: 101172

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17. Greenlee, A. R.; Ellis, T. M., and Berg, R. L. Low-Dose Agrochemicals and Lawn-Care Pesticides Induce 

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21. Howe, G. E.; Marking, L. L.; Bills, T. D.; Rach, J. J., and Mayer, F. L. Jr. Effects of Water Temperature and 

pH on Toxicity of Terbufos, Trichlorfon, 4-Nitrophenol and 2,4-Dinitrophenol to the Amphipod 

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22. Kataria, H. R. and Verma, P. R. Interactions of Fungicide and Insecticide Combinations Against Rhizoctonia 

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26. Labisky, R. F. Responses of Pheasants to Simulated Field Applications of Counter, An Organophosphate 

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28. Langton, S. J. Field Corn Tolerance to Acetolactate Synthase Inhibiting Herbicides and Weed Control in 

Sethoxydim Resistant Field Corn. 1997: 209 p. Rec #: 470. EcoReference No.: 99110

29. Matocha, J. E. and Hopper, F. L. Influence of Terbufos and Nicosulfuron on Iron Chlorosis and Growth of 

Corn. 2001; 24, (9): 1445-1455. Rec #: 50. EcoReference No.: 101099
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Exposure to Atrazine, Terbufos, and Their Mixtures. 2000; 64, (5): 748-754. Rec #: 220

Notes: EcoReference No.: 52188

31. Morton, C. A.; Harvey, R. G.; Kells, J. J.; Landis, D. A.; Lueschen, W. E., and Fritz, V. A. In-Furrow 

Terbufos Reduces Field and Sweet Corn (Zea mays) Tolerance to Nicosulfuron. 1993; 7, (4): 934-

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32. Morton, C. A.; Harvey, R. G.; Wedberg, J. L.; Kells, J. J.; Landis, D. A., and Lueschen, W. E. Influence of 

Corn Rootworm Insecticides on the Response of Field Corn (Zea mays) to Nicosulfuron. 1994; 8, 

(2): 289-295. Rec #: 250. EcoReference No.: 62641

33. Radford, B. J. and Allsopp, P. G. Use of Insecticides and a Press Wheel to Control Soil Insects Affecting 

Sorghum and Sunflower Establishment in Southern Queensland. 1987; 26, (2): 161-167. Rec #: 270

Notes: EcoReference No.: 64369

34. Reed, J. P.; Keaster, A. J.; Kremer, R. J., and Kerr, H. D. Activities and Degradation of Several Insecticides 

and Herbicides in Soils Poised for Enhanced Carbamate and Thiocarbamate Degradation. 1989; 24, 

(1): 23-35. Rec #: 40. EcoReference No.: 100901

35. Simpson, D. M.; Diehl, K. E., and Stoller, E. W. 2,4-D Safening of Nicosulfuron and Terbufos Interaction in 

Corn (Zea mays). 1994; 8, (3): 547-552. Rec #: 100. EcoReference No.: 101254

36. Sinclair, P. J.; Neeson, R. J., and Williams, P. A. Phytotoxicity of Some Organophosphate Insecticides to 

Onions and Carrots During Germination and Emergence. P.J.Sinclair, Hortic. Res. Advisory Stn., 

New South Wales Agric., Griffith, 2680, Australia. 1992; 7, (1): 23-25. Rec #: 410. EcoReference 

No.: 93323

37. Singh, B. D.; Singh, R. B.; Singh, R. M.; Singh, Y., and Singh, J. Effect of Insecticides on Germination, Early 

Growth and Cytogenetic Behavior of Barley (Hordeum vulgare). 1979; 19, (3): 127-132. Rec #: 240

Notes: EcoReference No.: 59664

38. Singh, B. D.; Singh, Y.; Singh, R. B.; Singh, R. M.; Sarma, N. D. R. K., and Singh, J. Cytogenetic 

Aberrations & Morphological Changes Induced by Insecticide Treatments of Barley Seeds. Dept. 

Genetics Plant Breeding, Fac. Agric., Banaras Hindu Univ., Varanasi, India. 1977; 15, (8): 688-691. 

Rec #: 480. EcoReference No.: 99386

39. Smith, C. R.; Funke, B. R., and Schulz, J. T. Effects of Insecticides on Acetylene Reduction by Alfalfa, Red 

Clover and Sweetclover. 1978; 10, (6): 463-466. Rec #: 290. EcoReference No.: 64478

40. Stall, W. M. and Bewick, T. A. Sweet Corn Cultivars Respond Differentially to the Herbicide Nicosulfuron. 

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