### UNITED STA **TES ENVIRONMENTA L PROTECTION A**  **GENCY WA** **SHINGTON, D. C. 20460 OFFICE OF CHEMICA** **L SA FETY A**  **ND POLLUTION PREVENTION**

**ENVIRONMENTAL RISK BRANCH III ENVIRONMENTAL FATE & EFFECTS**  **DIVISION OFFICE OF PESTICIDE PROGRAMS**  

### PC CODE: 060101 DP BARCODE: 410836 **MEMORANDUM** DATE: April 10 , 201 4 

### SUBJECT: EFED Risk Assessment for the Proposed New Use s of Thiabendazole as a Seed

Treatment for Several Crop Groups, and an Increase d Application Rate for Soy bean Seed Treatment TO: Tony

Kish , Product Manager (RM 23 ) Rosemary

Ke arn s , Reviewer Fungicide Branch Registration Division (75 05P ) FROM: Nick Mastro ta, Ph.D
. , Wildlife Biologist

James K. Wolf, Ph.D., Environmental Scientist Environmental Risk Branch III Environmental Fate and Effects Division (7507P) THRU: Dana Spatz, Branch Chief

James Hetrick, Ph.D., Senior Science Advisor Melissa Panger, Ph.D., Senior Biologist Rosanna Louie
- Juzwiak, RAPL Environmental Risk Branch III Environmental Fate and Effects Division (7507P) EFED has completed an assessment of the ecological exposure and potential risks associated with the proposed additional seed treatment use s of thiabendazole on root vegetables (except sugar beet) (Subgroup1B); onion, bulb (Subgroup 3
- 07A); brassica, head and stem (Subgroup 5A); cucurbit (Group 9); alfalfa; spinach (including baby) , and small grains cereals (wheat, barley, oats, rye, and triticale), as well as an increase in the maximum seed treatment rate for soy bean
. The ecological risk assessment concluded that all of the proposed new use s could pose a risk to mammals because of potential chronic toxic effects resulting from consumption of treated seeds (ri sk quotients (RQ) of 1.1 to 44.2 ) . All of the proposed new uses except soybean and some root2



### vegetables (e.g. , radish) may also pose a risk to bird s because of chronic toxic effect s (RQs 1.43 to 11.5) , although these RQs may overestimate risk because they were based on NOAECs from chronic avian test s that were conducted at dietary residue levels less than those predicted on many of the treated seeds. These chronic avian studies set the NOAEC at the highest dietary concentration tested, but testing at higher levels could establish higher NOAECs, which would decrease the RQ values. A few cucurbit uses ( e.g. , cucumbers and muskmelons) also may pose an acute risk to birds. For many of the new uses, RQs for acute toxicity exceed the endangered species level of concern for birds , but not for mammals. These conclusions are based on exposure through direct consumption of treated seeds. S pecies that do not consume seeds would have much less exposure and may not be at risk
. The proposed seed treatment uses are expected to result in very little exposure to aquatic organisms and nontarget terrestrial plants. Risk to all aquatic organisms and all terrestrial plants is expected to be minimal. Available ecotoxicity

data were adequate to assess the ecological risks ass ociated with the proposed new seed treatment uses . However, it should be noted that information about avian acute oral toxicity to passerine s (850.2100) and effects on avian reproduction (850.2300) at dietary concentrations above 400 mg a.i./kg is not available from the current thiabendazole ecotoxicity

database
.3 

### E **COLOGICAL RISK ASSESSMENT FOR THE Registration of New Use**  **s for**  **Thiabendazole**

**PC Code: 060101**  **Proposed New Seed** 
**– Treatment**  **U se**  **:**
 **Root vegetables (except sugar beet), Subgroup1B**   **Onion, bulb; Subgroup 3 -**  **07A**  **Brassica, head and stem; Subgroup 5A**  **Cucurbit, Group 9**  **Alfalfa**  **Spinach (including baby)**  **Small grains cereals (wheat, barley, oats, rye, and triticale)**  **Soybean (increased application rate)**

**End Use Product**  : Mertect ® 

### 340
- F4



## Table	of	Contents I. Problem Formulation
................................ ................................ ................................ ................ 5 A. Nature of Chemical Stressor
................................ ................................ .............................. 5 B. Mode of Action
................................ ................................ ................................ .................. 5 C. Structure and Physical
- Chemical Characteristics
................................ .............................. 5 D. Overview of Pesticide Usage
................................ ................................ ............................. 6 E. Uncertainties
................................ ................................ ................................ ....................... 8 II. Environmental Fate and Transport
................................ ................................ ............................ 9 A. Transformation Products
................................ ................................ ................................ .. 10 B. Bioaccumulation
................................ ................................ ................................ ............... 11 III. Estimation of Exposure
................................ ................................ ................................ ........ 11 A. Aquatic Exposure Modeling
................................ ................................ ............................. 11 B. Water Monitoring Data
................................ ................................ ................................ .... 12 C. Terrestrial Exposure Modeling
................................ ................................ ......................... 12 1. Oral Exposure from Consumption of Treated Seed
................................ ..................... 12 2. LD 50 

### per Square Foot Analysis
................................ ................................ ..................... 13 3. Exposure Modeling for Non - Target Plants
................................ ................................ .. 14 IV . Ecological Effects Characterization
................................ ................................ ..................... 14 V. Risk Characterization
................................ ................................ ................................ .............. 17 A. Aquatic Organisms
................................ ................................ ................................ ........... 17 B. Terrestrial Organisms
................................ ................................ ................................ ....... 17 1. Oral Exposure from Consumption of Treated Seeds
................................ ................... 17 2. LD 50 

### per Square Foot Analysis
................................ ................................ ..................... 22 3. Terrestrial Plants
................................ ................................ ................................ ........... 22 VI . Risk Discussion and Conclusions
................................ ................................ ........................ 23 VII. References
................................ ................................ ................................ ............................ 26 Appendix A. Thiabendazole degradates identified in Environmental Fate Studies
...................... 27 Appendix B. Thiabendazole and Its Environmental Degradates
................................ ................... 28 Appendix C. GENEEC2 Model Outputs
................................ ................................ ....................... 30 Appendix D. Output from Terrestrial Exposure Model (T
- REX)
................................ ................. 31 Appendix E. Output from Terrestrial Plant Risk Model (TerrPlant)
................................ ............. 33 Appendix F. Ecotoxicity Data ................................ ................................ ................................ ........ 345



## I. **P roblem	Formulation** 

**A. Nature of Chemical Stressor**  Thiabendazole is a fungicide used to control fungal diseases in germinating seeds . It is currently registered for treatment of seeds of clover, corn, garbanzo (including chickpea), lentil, peas, and soy bean, and treatment of seed pieces of potato and sweet potato. This ecological risk a ssessment evaluates expanding the crop group uses registered for the product Merte ct ® 

### 340
- F Fungicide (EPA Reg. No. 100
- 889) to include the following crops and crop groups:

 Root vegetables (except sugar beet), Subgroup1B  Onion, bulb; Subgroup 3
- 07A  Brassica, head and stem; Subgroup 5A  Cucurbit, Group 9  Alfalfa  Spinach (including bab y)  Small grains cereals (wheat, barley , oats, rye, and triticale) In addition, the risk assessment evaluates the proposed increase of the maximum seed treatment application rate for soy

bean from 0.005 lb a.i./100 lb seed to 0.020 lb a.i./100 lb seed (or 0.00 87 lb a.i./A to 0.033 lb a.i./A)
.

**B. Mode of Action**  Thiabendazole is a s ys temic fungicide. The mode of action of thiabendazole inhibits the mitosis of plant pathogenic fungi species by preventing the poly

merization of beta
- tubulins . Because dimers of beta
- tubulin and alpha
- tubulin poly merize to form microtubule structures inside the cells, thiabendazole acts as an inhibitor of microtubuline poly merization, terminating cell division. **C. Structure**  **and Physi**  **cal -**  **Chemical Characteristics** The CAS name for thiabendazole is 2
- (4
- Thiazolyl)
- 1H
-benzimidazole , the CAS No. 148
- 79
- 8 . The IUPAC name is 4
- (1H
-benzimidazol
- 2
- yl )
- 1,3
- thiazole
. Figure 1 shows the chemical structure of thiabendazole
. Select physical
- chemical characteristics are provided for thiab endazole in Table 1 .6



### Figure 1 . Chemical Structure of Thiabendazole
Table 1 . Physical and Chemical Properties of Thiabendazole **Parameter Value**  **Description Source**  **(MRID #) Selected Physical/Chemical Parameters**  Molecular mass 201.1 g/mol
-- (Calculated) Molecular formula C 10 H 7N 3 S
-- Vapor pressure (25°C) 3.45 x 10 - 9 mm Hg 4.0 x 10 - 9 mm Hg -- 48354601 Thiabendazole RED (2002) Henry’s Law Constant (25°C) 3.26 x10 - 11 atm- m3 /mol
-- (Calculated) Dissociation Constants pKa1 = 4.5 pKa2 = 12.01 -- 48354604 40947302 Aqueous solubility Buffered solution (25  C) at pH 5: 30 mg/L pH 7: 28 mg/L pH 9: 28 mg/L Water: 22.74 mg/L Buffer solution (20  C) at: pH4: 79.82 mg/L pH7: 22.77 mg/L pH10: 23.75 mg/L -- 40947301

48354601 48354604
Log octanol
- to - water partition coefficient (log KOW) 1.61 @ Room temperature = 16.6°C 48254601 48354604 a Transformation rates of thi abendazole: pH 5 (
- 0.0019 days - 1 ); p H 7 (
- 0.0035 days - 1 ); pH 9 (
- 0.0026 days - 1 )



### D. **Overview of Pesticide Usage** Mertect ® 

### 340
- F (42.3% thiabendazole) is applied to crop seeds as a water
- based slurry using standard seed treatment equipment. Treated seeds may be planted at any

time of the year. Onl y one application ( i.e ., one planting of treated seed) may be made per crop cycle; however, in some7



### regions, more than one may occur per year . The maximum seed treatment rates de fined on the label are given in **Table** 2 . Table 2 . Maximum Application Rates for Proposed New Seed Treatment Use s of Thiabendazole **Crop or Crop Group Crop Group ID**  **Max. Seed Treatment Rate mg a.i./seed**  **fl oz product per**

**100 lb seed lb a.i. per** 

**100 lb seed** Alfalfa NA 0.004 5.8 0.18578 Cereals, Small Graina Barley NA 0.03 2.6 0.08328 Oat NA 0.03 3.4 0.10891 Rye NA 0.03 3.2 0.1025 Triticale NA 0.03 2.6 0.08328 Wheat NA 0.03 3.1 0.09930 Brassica, head and stem Subgroup 5A 0.002 ND b ND Cucurbit Group 9 0.1 ND ND Onion, bulb Subgroup 3
- 07A 0.002 ND ND Root vegetables (except sugar beet) Subgroup 1B 0.002 ND ND Spinach NA 0.006 ND ND a “Small grains” is not designated as an EPA crop group. b “ND” designates that the value is not defined by the product label. 

### In addition to adding these new uses, the proposed label for Mertect ® 

### 340
- F Fungicide would increase the maximum seed treatment rate for so ybean (for control of Fusarium spp. fungal diseases) b y approximately four times. The maximum seed treatment rate for soy beans would increase from 0.0052 lb a.i./100 lb seed to 0.02 0 lb a.i. / 100 lb seed. Assuming a maximum seeding rate of 166.7 soy

bean seeds per acre (USEPA, 2011 ) , the maximum rate for so yb ean seed treatment would change from 0.008 7 lb a.i./A to 0.033 lb a.i./A. The seed treatment rates provided on the label define the m aximum amount of active ingredient that can be applied per seed. To convert this to rates in terms of pounds of active ingredient per acre, these seed treatment rates need to be multiplied by the seeding rates (number of seeds per acre). Maximum seeding rates for a variety of crops were defined by the Biological and Economical Anal ys is Division (USEPA , 2011 ) . These values are used in the conversion calculations and the resulting application rates (in lb a.i./A) are shown in Table 3 . It is EFED’s understanding that the registrant of Mertect ® 

### 340
- F (S yn genta Crop Protection) has agreed to put on the label a statement which would restrict the maximum allowable annual application rate for any seed treatment to 0.15 lb a.i./A per year . This is similar to the maximum single application rate on the current label for wheat (assuming the maximum seeding rate for wheat proposed b y Sy ngenta), whereas the maximum single rates for other seed treatment crops is expected to be less than thi s. Therefore, this risk assessment will use the calculated rates shown in Table 3 as the maximum single application rate , and 0.15 lb a.i./A as the maximum annual rate for all crops.8



### Table 3 . Conversion of Proposed Seed Tre atment Rates to Pounds of Active Ingredient per Acre **Crop Group Ma** **x. Seed Treat**  **me nt Rate**  **Representative Crop**  **s Seeding Rates**  **( # seeds/acre** **) b**  **Ma x.** **Appl. Rate**

**( lbs a.i./acre** **) c**  **fl. oz. product/ 100 lb seed**  **a mg a.i./seed**  **a** Al falfa 5.8 0.004 Al falfa 3,405,000 0.030 Cereals (small grains) 2. 6 0.03 Barley 1,222,000 to 1,300,000 0.086 3.4 0.03 Oats 1,305,000 0.0863 3.2 0.03 Rye 1,962,000 0.130 2.6 0.03 Triticale 1,744,00 0 0.115 3.1 0.03 Wheat Wheat, winter 2,250,000 d

600,000 to 1,350,000 0.149 0.089 Brassica , head and stem - 0.002 Broccoli 8,297 to 210,845 0.0009 3 Cabbage 7,260 to 98,010 0.00043 Bulb Vegetables
- 0.002 Onion 87,120 to 1,254,528 0.0055 Garlic 261,360
- 392,040 0.0017 Cucurbit Vegetables - 0.1 Cucumber 4,840 to 139,392 0.031 Muskmelon 2,420 to 34,848 0.0077 Pumpkin 908 to 7,260 0.0016 Squash, summer 1,452 to 15,374 0.0034 Squash, winter 2,723 to 7,260 0.0016 Watermelon 605 to 4,356 0.00096 Spinach
- 0.006 196,020 to 653,400 0.0086 Root Vegetables (except sugarbeet) - 0.002 Beet, garden 261,360 to 2,090,880 0.0092 Carrot 104,544 to 2,090,880 0.0092 Horseradish 9,680 to 10,249 0.00005 Radish 418,176 to 1,045,440 0.0046 Parsley 52,272 to 1,568,160 0.0069 Parsnip 87,120 to 435,600 0.0019 Turnip 29,040 to 261,360 0.0012 Soybeans 1.05 0.0302 Soybean 50,000 to 250,000 0.017 a Proposed label MERTEC 340
- F 889 MAS 0313 HILITE

–dt/df 3/15/13 (Density = 4.1 lb a.i./gallon of product; 42.3 % active ingredient (a.i.).[e
- submission #4085; MRID 4907800] b USEPA , 2011. c The maximum application rates were calculated based on the maximum expected seeding rates as follows: mg a.i./seed * seeds/acre * (1 lb/453.59 g) *1 g/1000 mg = lb a.i./acre. d Conservative maxim

um seeding rate proposed by Syngenta. 

### E. **Uncertainties** The assessment assumes that 100 percent of the a.i. comes off the seed and is available for runoff or leaching (EFED, 1999 1 

### ). Thus, the amount of “a.i.” in runoff and leachate are expected to be conservative
.

1 EFED, 1999. Standard Method of Determining the Leachability of pesticides from treated seeds. July 30, 1999, USEPA, OPP, EFED, Arlington, VA.9



### The avian acute toxicity

studies yielded non
- definitive “greater than” values for the acute oral LC 50 

### and the dietary

LC 50 

### . These data were adequate for concluding that the acute risk is below the LOC for risk to nonlisted species, but in some cases are not adequate for concluding that the acute risk is below the LOC for endangered species
. For chronic risk, the avian reproduction studies with the bobwhite (MRID 00123327) and the mallard (MRID 00 123328) tested only up to 400 mg/kg
- diet . No statistically significant effects were observed at the highest test concentration. The concentration s of thiabendazole on treated seeds of some crops are expected to be much greater than this amount, up to 4590 mg/kg
- diet for muskmelon seeds. Therefore, these results are not adequate for assessing chronic risk to seed
eating birds. Without additional testing at higher test levels, the assessment must calculate RQ’s based on the NOAEC equal to the highest concentration tested (400 mg a.i./kg
- diet), which yield chronic avian RQs that exceed the LOC. Tier 1 terrestrial plant toxicity data for thiabendazole failed to establish an NOAEL for some plant species. However, the data do show that thiabendazole has relatively low toxicity to terrestrial plants . Exposure to the relatively high rate of 0.23 lb a.i./A (which is higher than the maximum allowable seasonal application rate of 0.15 lb ai/A) resulted in growth inhibition of no more than 25% . Likewise, aquatic plant tests with thiabendazole are supplemental, but are adequate to show that it has low toxicity . Considering that seed treatment uses result in very little exposure to nontarget terrestrial and aquatic plants, additional testing with plants is not warranted. Toxicity data are not available for saltwater animals except for one acute test with the saltwater mysid. However, seed treatment use of thiabendazole is expected to result in little exposure to aquatic habitats, and based on toxicity data for freshwater species, risk to aquatic species is expected to be minimal. Furthermore, the mys id study indicates that the toxicity of thiabendazole to saltwater species is similar to that of freshwater species. Therefore, additional testing with saltwater species is not needed to assess these proposed uses
. 

## II. **Environmental	Fate	and	Transport** There have been no additional environmental fate data submitted since the previous assessments. The environmental fate studies show that thiabendazole is persistent and immobile ( **Table 4**  ). Thiabendazole is stable to hydrol ys is and soil photolysis and degrades slowly in aerobic (half

- life ~ 700 days) and anaerobic soil environments (>200 days). Aquatic photol ysis, with a half life of 1.2 days in clear water, appears to be the onl y significant degradation pathway
. Under anaerobic aquatic conditions thiabendazole showed no evidence of abiotic or biotic degradation but moved rapidly from water phase to the sediment phase. Thiabendazole binds tightly to soil due to its high soil/water partitioning coefficients (Koc 

### s > 1,000 mL/g oc 

### ), thus limiting the amount available for leaching into ground water and for solution phase runoff into surface water. With the high sorption capacity, thiabendazole would be transported on eroded sediment. Sorption was weakl y correlated to organic carbon. Terrestrial field dissipation studies showed thiabendazole to be extremely persistent with no leaching. Vapor pressure and Henry ’s Constant indicate that there is a low potential for thiabendazole to volatiliz e from soil and water. These studies are discussed in more detail in the most recent Reregistration Eligibility Decision (RED) (DP B arcode D245780 ).10



### There are no degradation products that are expected to f orm at levels that are of ecological concern. Table 4 . Environmental Fate Parameters of Thiabendazole **Parameter Value**  **Description Source**  **(MRID #) Persistence**  Hydrolysis half

- life (22  C) Stable @ pHs 5, 7, 9 Rates a of transformation were extrapolated resulting in t 1⁄2 s (200 days) far beyond the length of the study (30 days) 41265301 (D245780; 02/04/99) Aqueous photolysis half

- life (22.5 to 23.2  C) 1.2 days 96 hour study @ pH5 43328305 Soil photolysis half

- life (25  C) Stable
-- 41297301 41397302 Aerobic soil metabolism half
- life (25°C) 688 days EFED Registration Document D245780 41791201 Anaerobic soil metabolism half
- life (25°C) 211 day Only degradate detected was benzimidazole in a 90 day study. (max 13.7 % AR;). 41559601 Anaerobic aquatic metabolism half
- life No evidence of biotic or abiotic degradation. Rapidly moved from water phase to the sediment phase. 122888 070753 Aerobic aquatic metabolism half
- life [dissipation half

- life A] (25  C) -- Study requirement waived 41559601 (D169687; 12/30/92) **Mobility** Freundlich soil
- water partition coefficients (KF); organic carbon
normalized Freundlich coefficients (KFOC ) KF ( mL/g) / Koc (m

L/goc): (soil textural class) 2.49 / 1,104: (sand) 15.97/3,992: (sandy loam) 21.75/1,812: (silt loam) 269.6/22,467: (clay) Mean = 7,343 mL/g oc Median = 2,902 mL/g oc 41170102

**Field Dissipation** Terrestrial field dissipation half
- life in upper 6 inch soil layer; (max. depth of observed leaching) 1100 days; (6 inches). 990 and 1444 days; (12 inches) 833 and 1093 days: (6 inches). Winter wheat/loamy sand/WA Soybean and bare ground/sandy loam/IL Soybean and bare ground/sandy loam/GA 43187201 43187202 43187201
Octanol/Water Partition Coefficient

(logP ow) 1.61
-- 48354604

a Transformation rates of thi abendazole: pH 5 (
- 0.0019 days - 1 ); p H 7 (
- 0.0035 days - 1 ); pH 9 (
- 0.0026 days - 1 ) 

### A. **Transformation Products** Three degradates were identified in the aqueous photolysis study (benzimidazole
- 2
- carboxamide as a major degradate; benzimidazole and benzimidazole
- 2
- carboxyl ic acid as minor degradates), two minor degradates were identified in the aerobic soil metabolism study (benzimidazole and 5
- hydroxythiabendazole), and one major degradate was identified in the anaerobic soil metab olism11



### study (benzimidazole) (Appendix A). The metabolite 5
- hydroxythiabendazle and benzimidazole are included in the tolerance dietary exposure for food (40 CFR 180.242 2 

### ), but not included in drinking water. The common name, chemical names, CAS No., molecular formula and mass, chemical structure, and maximum and final percent of applied radioactivity (AR) of the major degradates are summarized in Appendix B .

**B. Bioaccumulation**  A BCF study

with the rainbow trout measured a BCF value 86.5 (whole); 19.7 ( fillet), 747 (viscera) . Three
- day

depuration was 96% in viscera and 50% in edible tissue (MRID s 41631801 ; 42022701 ) . These results indicate that the potential of thiabendazole to bioconcentrate is low. 

## III. **Estimation	of Exposure** 

**A. Aquatic Exposure Modeling**  This exposure assessment was completed using the GENEEC model. Exposure was estimated for a seed treatment application at 0.15 lb ai/A, which is to be the maximum annual application rate allowed on the Mertect® 

### 340
- F label for any s eed treatment use. Model input parameters used are given in Table 4 . A description o f this model can be found on the EPA’s website at : http://www.epa.gov/pesticides/science/models_pg.htm Table 4 . Summary

of Input Parameter Values for Modeling Aquatic Exposure of Thiabendazole Using the GENEEC Model **Environmental Fate Param** **eter Value**  **a Justification**  **Source**

Solubility 28 ppm (mg/L)
- MRID 40947301 Adsorption Coefficient (Koc ) 7,343 mL/g oc Average Koc MRID 41170102 Aerobic Soil Metabolism (ASM) 2064 days 3 x single ASM half
- life MRID 41791201 Aerobic Aquatic Metabolism

(Days) Stable (0) No Data and Persistence observed in ASM No Data Aqueous Photolysis 1.2 days
- MRID 43328305 Hydrolysis (@pH7) Stable (0)
- MRID 41265301 GENEEC Management Options Wetted
- In No Not specified on label Label Method of Application Granular It is assumed there is no spray drift for treated seed and granular is the nondrift option in GENEEC -

2 http://www.gpo.gov/fdsys/pkg/CFR
- 2005
- title40
- vol23/xml/CFR
- 2005
- title40
- vol23
- sec180
- 242.xml12 **Environmental Fate**

**Param eter**  **Value a**  **Justification Source**  Incorporation Depth 1 and 2 inch Range of planting depths for a variety of crops b,c

. -
a http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm b http://www.channel.com/Agronomics/Pages/Plant
- Soybeans
- to - the
- Right
- Depth.aspx c htt p://www.omafra.gov.on.ca/english/crops/pub811/4planting.htm 

### Maximum generic estimated environmental concentrations (E ECs) for seed
- treatment use at 0.15 lb a.i./A are given in Table 5 . These values represent the upper bound of concentrations expected for the proposed new use on the label. This modeling indicates that peak EECs for all uses are expected to be less than 1.0 μg a.i./L (1 ppb)
. A representative GENEEC model output is listed in Appendix C. Table 5 . Generic aquatic e stimated environmental concentrations (EECs) of thiabendazole fo r proposed maximum annual application rate of 0.15 lb a
. i
. /A and two seeding depth s . **Crop Scenario**  **Aquatic EECs (μg a.i./L) Peak**  **21 -**  **Day Mean 60**  **- Day Mean**  All crops, 0.15 lb a.i./A Generic granular/seed

treatment scenario with 1
- inch soil incorporation 0.8 8 0.7 3 0. 53 Generic granular/seed treatment scenario with 2
- inch soil incorporation 0.44 0.37 0.27


### B. **Water Monitoring Data** There are no detections of thiabendazole reported in the California Department of Pesticide Regulation (CDPR) Surface Water 3 

### Monitoring Database available and it is not included in CDPR Groundwater Protection List4



### . Thiabendazole is not included in the surface water database collected in the USGS National Water Quality Assessment (NAWQA) 5 

### Program. There were no detections of thiabendazole reported in groundwater (49 samples from CA, DE, FL,MD, NJ) in USGS NAWQA 6 

### data warehouse with limits of detection <0.06 μg/L.

**C. Terrestrial**  **Exposure Modeling**  **1. Oral	Exposure	from**  **C onsumption	of	Treated	Seed**  Oral exposure from use of thiabendazole as seed treatment was estimated by modeling the dose to birds and mammals that feed directly on the treated seeds or seed pieces. EPA’s T
- REX program (version 5.1) was used to predict the dose of pesticide that would be ingested by birds and mammals of various sizes. A sample of the T
- REX model output is provided in Appendix D .

3 http://www.cdpr.ca.gov/docs/emon/surfwtr/index.htm ; searched January 27, 2014. 4 http://www.cdpr.ca.gov/docs/legbills/calcode/040101.htm#a6800 ; searched January 27, 2014 . 5 http://infotrek.er.usgs.gov/nawqa_queries/jsp/swmaster.jsp ; searched January 27, 2014. 6 http://infotrek.er.usgs.gov/nawqa_queries/jsp/gwmaster.jsp ; search January 27, 2014.13



### These predictions are calculated based on average daily food intake and the concentration of active ingredient on a treated seed. Th e model makes the assumption that 100% of the animal’s diet is comprised of treated seed. Maximum concentrations on seeds were calculated b y dividing the maximum seed treatment rate (mg a.i./seed) by the minimum seed weights (mg/seed). The minimum seed wei ghts were derived from the maximum seeds per pound counts reported by the Biological and Economical Anal ys is Division ( BEAD) (USEPA , 2011). Input values for this anal ys is are presented in Table 6 . Table 6 . Input values for the anal ys is of risk to terrestrial animals from consumption of thiabendazole
- treated seeds. **Crop Group Seed Treatment Rate**  **Representative Crops**  **Ma x.** **No. of Seeds** 

**per Pound Ma** **x Seed** 

**Concentration (m** **g a.i./seed) fl. oz.**  **product/100 lb seed**  **mg a.i./seed** Al falfa 5.8 0.004 Al falfa 227,000 2,002 Cereals (small grains) 2. 6 0.03 Barley 14,000 926 3.4 0.03 Oats 18,144 1,200 3.2 0.03 Rye 18,000 1,190 2.6 0.03 Triticale 22,680 1,500 3.1 0.03 Wheat 18,000 1,190 Brassica , head and stem - 0.002 Broccoli 150,000 661 Cabbage 165,000 728 Bulb Vegetables
- 0.002 Onion 130,000 573 Cucurbit Vegetables
- 0.1 Cucumber 18144 4,000 Muskmelon 20,800 4,586 Pumpkin 6,400 1,411 Squash, summer 6,400 1,411 Squash, winter 6,400 1,411 Watermelon 9,600 2,116 Spinach
- 0.006 Spinach 45,360 600 Root Vegetables (except sugarbeet) - 0.002 Carrot 400,000 1 , 764 Radish 50,000 220 Parsley 296,500 1 , 307 Turnip 167,000 736 Soybeans 0.624 0.0302 Soybean 3 , 600 240



### 2. **LD 50**  

### per	Square	Foot	Analysis In addition to exposure through a dietary route, risk to terrestrial animals was assessed using the LD 50 

### -per- square - foot risk index. This analysis does not assume any explicit exposure route, but rather relates the amount of active ingredient available to an animal within one square foot of treated habitat to the acute oral LD 50 

### . The LD 50 

### -per- square - foot is considered a proxy for an RQ
. For seed treatment uses of thiabendazole, the maximum application rate in terms of lb a.i./A were calculated b y multiplying the maximum allowable seed treatment rate (i.e., amount of a.i. per seed) b y the maximum expected seeding rates (seeds per acre) expected for each crop ( Table 3 ).14



### Seeding rates were assumed to be at the maximum of the range of seeding rates provided b y the BEAD (USEPA , 2011). As a con servative screen, this analysis assumed no soil incorporation of the seed. It is recognize, however, that most seeds will be soil incorporated , which would reduce the exposure to terrestrial animals. The amount of AI available on one square foot of ground planted with treated seeds were then divided b y the body
- weight adjusted LD 50 

### for small, medium, and large birds and mammals . Equations for these calculations are given in the User Manual for the T
- REX Mode (USEP A , 2012).

**3. Exposure	Modeling	for**  **Non -**  **Target Plants**  Exposure to terrestrial and semi
- aquatic plant s was estimated using the OPP’s TerrP lant model (version 1.2.2)
. Sample output from the TerrPlant model is provided in Appendix E . The application rate was assumed to be 0.15 lb a.i./A, the maximum annual application rate allowed on the proposed Mertect ® 

### 340
- F label. Seeds were assumed to be planted at a depth of 1 inch. Because the new uses are seed treatments , the spray drift fraction was set at zero
. The predicted terrestrial plant EECs for the new se ed treatment uses are summarized in Table 7 . Table 7 . EECs for Thiabendazole S eed Treatment Uses with an Application Rate of 0.15 lb a.i./A **Exposure Description**  **EEC (lb a.i./A)**  Runoff to dry areas 0.0075 Runoff to semi
- aquatic areas 0.075 Spray drift 0 Total for dry areas 0.0075 Total for semi
- aquatic areas 0.075 

## IV. **Ecological Effects Characterization** Table **8** provides a summary of the toxicity

of thiabendazole to aquatic organisms. Thiabendazole is highly toxic to fish and aquatic invertebrates on an acute bas i s (LC 50 

### s 0.1
- 1.0 mg a.i./L). With chronic exposure, the Daphnia magna was the most sensitive species, with chronic effects observed at concentrations as low as 87 μg a.i./L(NOAEL: 42 μga.i./L). Table 9 provides a summary of the toxic ity

of thiabendazole to terrestrial animals
. On an acute bas i s, thiabendazole is classified as practically nontoxic to birds, mammals, and the honey bee. While the avian acute oral tests with the bobwhite and mallard determined the LD 50 

### s were greater than the highest test dose of 4640 mg ai/kg
-bw, one mortality and some sublethal toxic effects were observed in the test with the mallard. One duck died on day 2 at 4640 mg ai/kg
-bw, and lethargy, lower limb we akness, and loss of coordination was observed in ducks at this level during the first 5 days after exposure (MRID 00123313). In the avian dietary tests with the bobwhite and mallard , no mortality was observed at any

test level, but reduced food consumption and reduced body weight gain were observed in the bobwhite test at 5620 mg ai/kg
-bw (MRID 41025 0 03) and in the mallard test at 3160
- 5620 mg ai/kg
-bw (MRID 41025004)
. No reproductive or developmental effects were observed in chronic toxicity studies with b irds at a concentration of 400 mg a.i./kg
diet
. For chronic toxicity to mammals , a two - generation rat reproductive study established the NOAE L at 10 mg a.i./kg/day based on reduction in body weight gain and food consumption at the15



### next higher concentration of 30 mg a.i./kg/day (MRID 43190301). This NOAEL is roughly equivalent to a dietary

dose of approximately

200 mg a.i./kg
- diet. Previous ecological risk assessments used a higher NOAEC of 1800 mg ai/kg
- diet, but that was ba sed only on the lack of reproductive effects observed in this study
. Other studies also have noted sublethal toxic effects at dietary exposures at or near 600 mg a.i./kg
- diet, including liver hy pertrophy (MRID 43593201) and histopathological changes in bon e marrow, liver, and thyroid (MRID 42942802). In a developmental rat study, a growth effect was also observed in developing young (decreased fetal body weight) at the slightly

higher dietary

concentration of 800 mg ai/kg
- diet (MRID 42942803). Table 8 . Toxicity

of Thiabendazole to Aquatic Organisms **Taxonomic Group**  **Test Species Principal Acute Toxicity**  **Endpoint Acute Toxicity** 

**Categories Principal Chronic Toxicity**  **Endpoint** Freshwater Fish Rainbow Trout

( Oncorhynchus mykiss ) 96
-hr LC 50 = 0.56 ppm

a.i. Highly toxic NOAEC : 0.11 ppm a.i.

LOAEC: 0.23 ppm a.i. ( Reduced weight) Freshwater Invertebrates Water Flea

( Daphnia magna ) 48
-hr EC 50 = 0.31 ppm a.i. Highly toxic NOAEL: 0.042 pp m a.i. LOAEL: 0.087 pp m a.i. (Reduced survival and num ber of young per female) Marine/ Estuarine Invertebrates Mysid

( Americamysis bahia ) 96
-hr EC 50 = 0.34 ppm a.i.

(acceptable) Highly toxic No Data Available Aquatic nonvascular plants Duckweed

( Lemna gibba ) 7 - day EC 50 = 2.32 ppm a.i. NOAEC : 0.26 ppm a.i. (supplemental) NA 1 NA 2
Aquatic vascular plants Freshwater Green

Algae (Pseudokirchneriella subcapitata ) EC 50 = 3.06 ppm a.i. NOAEC : 0.532 ppm a.i. (supplemental) NA 1 NA 2

1 . This item is not applicable (NA) because the EPA does not assign acute toxicity characterizations to aquatic plant toxicity endpoints. 2. This item is not applicable (NA) because the EPA does not characterize aquatic plant toxicity tests as being “acute” or “chronic.” 

### Table 9 . Toxicity

of Thiabendazole to Terrestrial Animals **Taxonomic Group**  **Test Species Principal Acute Toxicity**  **Endpoint Acute**  **Toxicity Categories**  **Principal Chronic Toxicity Endpoint**  Birds Bobwhite

( Colinus virginianus ) and mallard (

Anas platyrhynchos ) Ac ute oral LD 50 > 4 , 460 mg a.i. /kg
-bw (One mortality and sublethal effects, see text) Ac ute dietary LC 50 > 5,620 mg a.i. /kg
- diet (No mortality but sublethal effects, see text) Practically nontoxic NOAEC : 400 ppm a.i.

LOAEC : >400 ppm a.i. (No observed toxic effects )16

Mammals Laboratory rat

( Mus musculus ) LD 50 = 5,070 mg a.i. /kg (M) LD 50 = 4,734 mg a.i. /kg (F) Practically nontoxic NOAEC =

10 mg a.i./kg/day LOAEL = 30 mg a.i./kg/day (Reduced bodyweight gain and food consumption) Honey Bee Honey bee

( Apis mellifera ) Ac ute Contact LD 50 > 34 μg a.i. /bee Practically nontoxic NA 1. This item is not applicable (NA) because the Agency does not assign toxicity characterizations to terrestrial plant toxicity endpoints. 2. This item is not applicable (NA) because there no guideline terrestrial plant chronic toxicity studies. 

### Table 10 provides a summary of the toxic ity

of thiabendazole to terrestrial plants
. In formation on the phy totoxicity of thiabendazole is limited because only tier
- 1 terrestrial plant toxicity tests are available. Based on these studies, the EC 25 

### values were determined to be equal to or greater than the tested rate of 0.23 lb a.i./A, which is greater than the maximum annual application rate allowed on the label (0.23 lb a.i./A). However, statistically s ignificant adverse effects were observed at this test level in both the seedling emergence study and the vegetative vigor study
. In the seedling emergence study, cucumber exhibited significant reduction in emergence and survival (22% reduction compared to the control) at 0.23 lb a.i./A (MRID 48996306). In the vegetative vigor study, significant inhibition was observed in growth, as measured b y shoot length, in ryegrass (9% inhibition), tomato (11% inhibition), and soy bean (13% inhibition). Therefore, these studies did not determine NOAEL values for toxicity of thiabendazole to terrestrial plants. The toxicity

data given in these tables represent the most sensitive toxicity endpoints available from acceptable studies
. A complete listing of all available toxicity data for thiabendazole can be found in Appendix F Table 10 . Toxicity

of Thiabendazole to Terrestrial Plants **Taxonomic Group**  **Study Type Surrogate**  **Species Toxicity Value** 

**(all units in terms of measured**  **active ingredient) Source** 

Terrestrial plants Seedling

Emergence Monocot* NOAE L = 0.23 lb/A EC 25 > 0.23 lb/A 48996306 (Acceptable, except Supplemental for bean and soybean) Dicot

– cucumber NOAE L < 0.23 lb/A

EC 25 ≥ 0.23 lb/A Endpoint: emergence and survival Vegetative Vigor Monocot

–

Ryegrass NOAE L < 0.23 lb/A

EC 25 > 0.23 lb/A Endpoint: shoot length 48996307 (Acceptable) Dicot* NOAE L = 0.23 lb/A

EC 25 > 0.23 lb/A * Because no significant inhibition was observed in any test species, the most sensitive species was not determined in this study.17



## V. **R isk	Characterization** 

**A. Aquatic Organisms**  For aquatic risk, a screening
- level assessment was conducted b y cal culating risk quotients for the maximum annual application rate for all proposed seed treatment crops, which the label restricts to 0.15 lb ai/A. At this application rate, none of the acute or chronic RQs exceed the acute or chronic LOC ( Table 11 ). While data are not available to assess acute or chronic risk to saltwater fish, or chronic risk to saltwater invertebrates, the very low aquatic RQs for freshwater species suggest that risk to saltwater species is unlikely . Therefore, all of the proposed new seed treatment uses of thiabendazole are presumed to pose minimal risk to all aquatic plants and animals. Table 11 . RQs for Aquatic Organisms Exposed to Thiabendazole f rom the Proposed New Seed Treatment Uses **Risk Type Taxa**  **EEC a**  **(μg a. i**  **./L) Toxicity** 

**(μg a. i**  **./L) RQ**  **Aquatic Animals** Ac ute Freshwater Fish 0.8 8 560 <0.01

Freshwater Invertebrate 0.8 8 310 <0.01 Saltwater Invertebrate 0.8 8 340 <0.01 Chronic Freshwater Fish 0. 53 110 <0.01

Freshwater Invertebrate 0.7 3 42 0.0 17 Saltwater Invertebrate 0.7 3 No Data -- **Aquatic Plants** Non- listed Species Vascular Plants 0.8 8 2,320 <0.01

Non- vascular Plants 0.8 8 3,060 <0.01 Listed Species Vascular Plants 0.8 8 260 <0.01

Non- vascular Plants 0.8 8 532 <0.01 a From Table 5 . 

### B. **Terrestrial Organisms 1.**  **Oral	Exposure	from Consumption	of	Treated	Seeds**  **a) Birds**  Acute RQs for risk to birds are given in18



### Table **13** . The values shown were calculated using the nondefinitive “greater than” toxicity values ( i.e. , the highest level tested in the acute studies). These RQs are conservative because if the actual toxicity

levels were determined, the RQs would be less than the values shown. For all crops except two cucurbit crops, cucumbers and muskmelons, the conservative RQs indicate that the acute risk is below the LOC for nonendangered species. For cucumber and muskmelons , the acute risk to nonendangered species is uncertain because the conservative RQs slightly exceed the acute risk LOC of 0.5 None of the acute dose
-based RQ s for non
- endangered species exceed th e LOC. Most of the uses had one or more conservative RQ that exceed the LOC for threatened and endangered species (0.10). Again, however, acute risk for listed species is uncertain since the actual RQs would be less than the values shown. Only radish, and soy bean had RQs which were all below the endangered species LOC. Table 12 . Avian Acute RQs for the Proposed New Uses of Thiabendazole
**Crop Group Seed Treatment Rate**  **Representative Crops**  **Ma x**  **Seed**

**Concentration (m** **g a.i./seed) Dietary** ****

**Based RQ**  **Dose -**  **Based Acute RQ fl. oz.**  **p roduct/**  **100 lb seed**  **a mg** 

**a.i./seed a**  **Sm all**  **Med. Large**  Al falfa 5.8 0.004 Al falfa 2,002 0.36 * 0.15* 0.07 0.02 Cereals (small grains) 2. 6 0.03 Barley 926 0.16 * 0.07 0.03 0.01

3.4 0.03 Oats 1,200 0.21 * 0.09 0.04 0.01 3.2 0.03 Rye 1,190 0.21 * 0.09 0.04 0.01 2.6 0.03 Triticale 1,500 0.27 * 0.11* 0.05 0.02 3.1 0.03 Wheat 1,190 0.21 * 0.09 0.04 0.01 Brassica , head and stem - 0.002 Broccoli 661 0.12 * 0.05 0.02 0.01 Cabbage 728 0.13 * 0.06 0.02 0.01 Bulb Vegetables - 0.002 Onion 573 0.10 * 0.04 0.02 0.01 Cucurbit Vegetables - 0.1 Cucumber 4,000 0.71 * * 0.30* 0.14* 0.04 Muskmelon 4,586 0.82 ** 0.35* 0.16* 0.05 Pumpkin 1,411 0.25 * 0.11* 0.05 0.02 Squash, summer 1,411 0.25 * 0.11* 0.05 0.02 Squash, winter 1,411 0.25 * 0.11* 0.05 0.02 Watermelon 2,116 0.38 * 0.16* 0.07 0.02 Spinach
- 0.006 Spinach 600 0.11 * 0.05 0.02 0.01 Root Vegetables (except sugarbeet) - 0.002 Carrot 1 , 764 0.31* 0.13* 0.06 0.02 Radish 220 0.04 0.02 0.01 <0.01 Parsley 1 , 307 0.23* 0.10* 0.04 0.01 Turnip 736 0.13* 0.06 0.02 0.01 Soybeans 0.624 0.0302 Soybean 240 0.04 0.02 0.01 <0.01 * RQ exceeds the LOC for presumption of acute risk to threatened and endangered species
. ** RQ exceeds the LOC for presumption of acute risk to non - endangered species
. 

### RQs for chronic risk to birds (19



### Table **13** ) are considerably higher than the acute RQs . The chronic RQ exceeds the LOC (1.0) for chronic risk for all crops evaluated except for radish and soy bean. For crops which exceeded the LOC, chronic RQs generally ranged from approximately 1.5 to 5.0, but were 10 or more for cucumber and muskmelons.20



### Table 13 . Avian Chronic RQs for the Proposed New Uses of Thiabendazole **Crop Group Seed Treatment Rate**  **Representative Crops**  **Ma x**  **Seed**

**Concentration (m** **g a.i./seed) Chronic RQ**  **fl. oz. p**  **roduct/ 100 lb seed**  **a mg** 

**a.i./seed a**  Al falfa 5.8 0.004 Al falfa 2,002 5.00 * Cereals (small grains) 2. 6 0.03 Barley 926 2.31 * 3.4 0.03 Oats 1,200 3.00 * 3.2 0.03 Rye 1,190 2.98 * 2.6 0.03 Triticale 1,500 3.75 * 3.1 0.03 Wheat 1,190 2.98 * Brassica , head and stem - 0.002 Broccoli 661 1.65 * Cabbage 728 1.82 * Bulb Vegetables
- 0.002 Onion 573 1.43 * Cucurbit Vegetables - 0.1 Cucumber 4,000 10.00 * Muskmelon 4,586 11.46 * Pumpkin 1,411 3.53 * Squash, summer 1,411 3.53 * Squash, winter 1,411 3.53 * Watermelon 2,116 5.29 * Spinach
- 0.006 Spinach 600 1.50 * Root Vegetables (except sugarbeet) - 0.002 Carrot 1 , 764 4.41 * Radish 220 0.55 Parsley 1 , 307 3.27 * Turnip 736 1.84* Soybeans 0.624 0.0302 Soybean 240 0.60 * RQ exceeds the LOC for presumption of chronic risk to endangered and non
- endangered species.



### b) **Mammals** Acute RQs for risk to mammals are given in Table 14 . Acute RQs were all below the LOC for risk to non
- endangered species (0.5), as well as the LOC for possible direct effects to listed species (0.05)
. Therefore, all of the proposed new seed
- treatment uses of thiabendazole is presumed to pose minimal acute risk to mammals. Table 14 . Mammalian Acute RQs for the Proposed New Uses of Thiabendazole **Crop Group Seed Treatment Rate**  **Re presentative**  **Crops Ma** **x Seed** 

**Concentration (m** **g a.i./seed) Dose**  **- Based Acute RQ**  **fl. oz. p**  **roduct/ 100 lb seed**  **a mg** 

**a.i./seed a**  **Sm all**  **Med. Large**  Al falfa 5.8 0.004 Al falfa 2,002 0.04 0.03 0.02 Cereals (small grains) 2. 6 0.03 Barley 926 0.01 <0.01 <0.01 3.4 0.03 Oats 1,200 0.02 <0.01 <0.01 3.2 0.03 Rye 1,190 0.02 <0.01 <0.01 2.6 0.03 Triticale 1,500 0.02 <0.01 <0.01 3.1 0.03 Wheat 1,190 0.01 <0.01 <0.01 Brassica , head and stem - 0.002 Broccoli 661 <0.01 <0.01 <0.01 Cabbage 728 <0.01 <0.01 <0.0121

**Crop Group Seed Treatment Rate**  **Re presentative**  **Crops Ma** **x Seed** 

**Concentration (m** **g a.i./seed) Dose**  **- Based Acute RQ**  **fl. oz. p**  **roduct/ 100 lb seed**  **a mg** 

**a.i./seed a**  **Sm all**  **Med. Large**  Bulb Vegetables
- 0.002 Onion 573 <0.01 <0.01 <0.01 Cucurbit Vegetables - 0.1 Cucumber 4,000 0.05 0.02 0.04 Muskmelon 4,586 0.07 0.03 0.04 Pumpkin 1,411 <0.01 <0.01 <0.01 Squash, summer 1,411 <0.01 <0.01 <0.01 Squash, winter 1,411 <0.01 <0.01 <0.01 Watermelon 2,116 0.02 0.01 0.02 Spinach
- 0.006 Spinach 600 0.01 <0.01 <0.01 Root Vegetables (except sugarbeet) - 0.002 Carrot 1 , 764 0.02 0.01 0.02 Radish 220 <0.01 <0.01 <0.01 Parsley 1 , 307 0.01 <0.01 0.01 Turnip 736 0.02 < 0.01 <0.01 Soybeans 0.624 0.0302 Soybean 240 <0.01 <0.01 <0.01 

### Chronic RQs are given in **Table 15**  . Dose -based c hronic RQ s range from 0.88 for turnip to 44.2 for muskmelon. All dose
-based chronic RQs exceeds the LOC (1.0) except for those for large mammals for use on turnips
. Thus, the risk assessment concludes chronic risk to mammals from all of the proposed seed treatment uses. Table 15 . Mammalian Chronic RQs for the Proposed New Uses of Thiabendazole **Crop Group Seed Treatment Rate**  **Representative C**  **rops Ma** **x Seed** 

**Concentration (m** **g a.i./seed) Dose**  **- Based Chronic RQ**  **fl. oz. p**  **roduct/ 100 lb seed**  **a mg** 

**a.i./seed a**  **Sm all**  **Med. Large**  Al falfa 5.8 0.004 Al falfa 2,002 19.3 * 16.5 * 8.8 * Cereals (small grains) 2. 6 0.03 Barley 926 8.9 * 7.6 * 4.1 *

3.4 0.03 Oats 1,200 11.6 * 9.9 * 5.3 * 3.2 0.03 Rye 1,190 11.5 * 9.8 * 5.3 * 2.6 0.03 Triticale 1,500 14.5 * 12.4 * 6.6 * 3.1 0.03 Wheat 1,190 11.5 * 9.8 * 5.3 * Brassica , head and stem - 0.002 Broccoli 661 6.4 * 5.4 * 2.9 * Cabbage 728 7.0 * 6.0 * 3.2 * Bulb Vegetables - 0.002 Onion 573 5.5 * 4.7 * 2.5 * Cucurbit Vegetables - 0.1 Cucumber 4,000 38.6 * 32.9 * 17.7 * Muskmelon 4,586 44.2 * 37.8 * 20.2 * Pumpkin 1,411 13.6 * 11.6 * 6.2 * Squash, summer 1,411 13.6 * 11.6 * 6.2 * Squash, winter 1,411 13.6 * 11.6 * 6.2 * Watermelon 2,116 20.4 * 17.4 * 9.3 * Spinach
- 0.006 Spinach 600 5.8 * 4.9 * 7.8 * Root - 0.002 Carrot 1 , 764 17.0 * 14.5 * 1.0 *22

Vegetables (except sugarbeet) Radish 220 2.1 * 1.8 * 5.8 * Parsley 1 , 307 12.6 * 10.8 * 3.3 * Turnip 736 7.1 * 6.1 * 0. 88 Soybeans 0.624 0.0302 Soybean 240 2.3 * 2.0 * 1.1 * * RQ exceeds the LOC for presumption of chronic risk to endangered and non
- endangered species.



### 2. **LD 50**  

### per	Square	Foot	Analysis To further evaluate the potential risk posed the proposed new seed tre atment uses of thiabendazole, the LD 50 

### -per- square - foot index was calculated to compare the amount of active ingredient expected in one square foot of ground to the acute oral toxicity of thiabendazole for birds and mammals . This index was calculated for all crops shown in Table 3 based on the maximum application rates (lb a.i./A) given in that table. For all of the crops, the LD 50 

### -persquare - foot index was less than 0.01. Thus, for all proposed seed treatment crops, the index was well below all levels of concern.

**3. Terrestrial	Plants**  RQ s for risk to nontarget terrestrial plants are given in Table 16 . In tier
- 1 phy totoxicity tests, plants were exposed to an appli cation rate (0.23 lb a.i./A) which was greater than the maximum annual application rate allowed by the proposed product label for Mertect 340
- F (0.15 lb a.i./A). At this rate, the observed inhibition of emergence and plant growth was less than 25% for all monocot and dicot plants. Results from the TerrPlant model indicates that the RQs for nonendangered species are well less than 1, and thus less the LOC. For threatened and endangered species, however, the conclusions are less certain. Statistically signifi cant effects were observed in test some species in the seedling emergence and the vegetative vigor studies. As the percent inhibition was no greater than 22 % with exposure at 0.23 lb a.i./A (see Section IV) , and the proposed new seed
- treatment uses are expected to result in nontarget plant exposure at no more than 0.0 7 5 lb a.i./A ( Table **16** Table 7 ) , direct adverse effects to nontarget plants are expected to be small. Additional factors that suggest little risk to nontarget plants are that 1. Seed treatment uses would result in no spray drift, and thus there would be minimal foliar exposure 2. Thiabendazole is immobile in soil, and therefore off
- site movement from planted fields would be minimal 3. The widespread use of thiabendazole as a fungicidal seed treatment and lack of plant incidents suggest that it d oes not have significant phy totoxicity at the application rates used. Therefore, while limitations of the phy totoxicity data results in some uncertainty, the EPA does not expect the proposed seed treatment uses of thiabendazole to result in effects to ter restrial plants.23



### Table 16 . RQs for Terrestrial Plants Exposed to Thiabendazole from the Proposed Seed
Treatment Uses

**Taxa EECs** 

**(lb a.i./A) Non**  **- listed** 

**Species Endpoint**  **(EC 25**  **in lb**  **a.i./ A** **) Listed Species** 

**Endpoint (NOAEC in**  **lb a.i./** **A )**  **Non -**  **Listed**

**Species RQ Listed** 

**Species RQ** Monocots Uplands 0.0015 >0.23 <0.23 <0.07 >0.007 Wetlands 0.015 >0.23 <0.23 <0.07 >0.007 Dicots Uplands 0.0015 >0.23 0.23 <0.07 <0.007 Wetlands 0.015 >0.23 0.23 <0.07 <0.07


## VI. **R isk**  **Discussion	and Conclusions**  The proposed seed treatment uses are expected to result in very little exposure to aquatic organisms and nontarget terrestrial plants. The application rates of the new uses in terms of pounds of active ingredient per acre is small ( 0.00004 to 0.15 lb a.i./A). These application rates are not higher than those of previousl y registered seed treatment uses . N o spray drift would occur with seed treatment uses, which reduces off
- site transport of the pesticide. Furthermore, because the seeds generall y are buried and because thiabendazole has very little mobility

in soil, off

- site movement of thiabendazole in runoff is expected to be very limited. As a result, exposure to aquatic organisms and to nontarget terrestrial plants is expected to be very limited, and is not expected to reach levels which may be toxic. The acute oral honey

bee test classifies thiabendazole as practically nontoxic to the honey

bee (LD 50 

### > 34 μg a.i./bee). Therefore, no warning statement is needed on the product labels to protect bees. In contrast, wildlife that feed on the treated seeds in fields planted with treated seeds may have significant exposure to thiabendazole. Based on an assumption of a diet comprised entirel y of treated seeds, the ecological risk assessment concluded that all of the proposed new use s pose a risk to mammals due to chronic toxic ity (RQs of 1.1 to 44.2). All of the proposed new uses except soy bean and some root vegetables ( e.g . , radish) also pose a risk to bird s due to chronic toxic ity (RQs 1.43 to 11.5) . A few cucurbit uses (e.g., cucumbers and muskmelons) also may pose a risk to birds because of acute toxicity, although this conclusion is uncertain because the avian acute toxicity endpoints are non
- definitive ( i.e. , “greater than” values) . For many of the new uses, RQ values also indicate that the endangered species acute toxicity level of concern is exceeded for birds , but not for mammals. The potential for acute effects to birds is uncertain because the assessment is based on non
definitive “greater than” estimates of acute toxicity endpoints. The conclusions for chronic risk are also uncertain because the available avian reproduction studie s only tested up to 400 mg a.i./kg
- diet , which is lower than some of the estimated exposure value s . Since the chronic avian toxicity of thiabendazole is above 400 mg a.i./kg
- diet, the level of risk is uncertain for all crops24



### for which the seed concentration exceeds this amount. The chronic risk conclusions for mammals are more certain as they

are base d on studies in which toxic effects were observed and thus both NOAEC and LOAEC values were established. The conclusions of risk to terrestrial wildlife are based on exposure through direct consumption of treated seeds. Exposure would be much less for sp ecies that do not consume seed s, or for which seeds comprise onl y a small portion of their diet
. Some thiabendazole may be absorbed b y the plant and translocated to emerged portions of the plant, and thus may result in some exposure to herbivorous animals which feed on the crop soon after it emerges. Likewise, some thiabendazole c ould leach into the upper soil and expose soil arthropods, and thereby would expose insectivorous animals which feed on them. However, these routes of exposure are expected to be much less significant than direct consumption of treated seeds. Therefore, risk to herbivorous and insectivorous animals is uncertain. A cute RQs fo r birds and mammals derived from the LD50
- per- square - foot anal ys is were very low (<0.01), which indicates that acute risk to wildlife that do not feed on seeds might be low. Since birds serve as a surrogate for reptiles and terrestrial phases of amphibians, the conclusion that the proposed uses of thiabendazole pose risk to birds also apply to terrestrial rep tiles and amphibians with terrestrial phases. However, reptiles and amphibians are generall y insectivorous or herbivorous, and therefore risks to these taxa are uncertain. To further characterize the chronic risk to seed eating mammals, an anal ys is was do ne to determine the number of seeds that small mammals of various sizes would need to eat for the chronic RQ to reach 1, the LOC for concluding chronic risk ( Table 17 )
. Since most seed
- eating mammals are small rodents, the results for small to medium mammals are most relevant. The number of seeds required for mammals of these sizes range from 3.3 to 311. None of the numbers for these weight sizes appear to be so large to be considered impossible, although the numbers for Brassica, bulb vegetable, and root crops appear unlikely . The numbers for small grains, so ybeans, and cucurbits would be easy for small mammals to reach. This anal ys is agree s with that o f the previous RQ anal ys is in indicating that chronic mammalian risk is highest for cucurbit vegetable crops (See Table 15 ) . This is because the seed treatment rate is higher for this crop group than for other crops and crop groups. Table 17 . Number of Seeds that Must Be Eaten for Oral Exposure to Reach a Mammalian Chronic LOC **Crop Group Seed Treatment**  **Rate (**  **mg a.i./seed** **) Size**  **BW (g) Weight** **** **Adjusted NOAEL**  **Number of Seeds** Al falfa 0.004 Small 15 21.978 82 Medium 35 17.783 156 Large 1000 7.6916 192 3 Cereals (small grains) 0.03 Small 15 21.978 11 Medium 35 17.783 2 1 Large 1000 7.6916 256 Brassica , head and stem 0.002 Small 15 21.978 16 5 Medium 35 17.783 311 Large 1000 7.6916 384 625

**Crop Group Seed Treatment**  **Rate (**  **mg a.i./seed** **) Size**  **BW (g) Weight** **** **Adjusted NOAEL**  **Number of Seeds** Bulb Vegetables 0.002 Small 15 21.978 16 5 Medium 35 17.783 311 Large 1000 7.6916 384 6 Cucurbit Vegetables 0.1 Small 15 21.978 3 Medium 35 17.783 6 Large 1000 7.6916 7 7 Spinach 0.006 Small 15 21.978 5 5 Medium 35 17.783 10 4 Large 1000 7.6916 128 2 Root Vegetables (except sugarbeet) 0.002 Small 15 21.978 16 5 Medium 35 17.783 312 Large 1000 7.6916 384 6 Soybeans 0.0302 Small 15 21.978 1 1 Medium 35 17.783 20 Large 1000 7.6916 25 5 

### The chronic mammalian RQ analysis was based on an NOAEC of 200 mg/kg
- diet, which was established by

observations of reduced weight gain in adult rats and reduced food consumption in the next highe st treatment level of 600 mg a.i./kg ( MRID 43190301). Previous ecological risk assessments used the NOAEC obtained in this study for reproductive endpoints only, which was 1800 mg ai/kg
- diet. However, consistent with current EFED policy, the NOAEC used in this assessment is based on the most sensitive endpoint affecting the reproduction, survival, or growth, and effects on weights of the adults is considered a growth effect. Other studies have also noted toxic effects at dietary

exposures at or near 600 mg a. i./kg
- diet based on organ - level effects, such as liver hypertrophy (MRID 43593201) and histopathological changes in bone marrow, liver, and thy roid (MRID 42942802). In a developmental rat study , a growth effect was also observed in developing young (decrea sed fetal body weight) at the slightly

higher dietary concentration of 800 mg ai/kg
- diet (MRID 42942803). Taken together, these results support use of 200 mg/kg
- diet as the appropriate NOAEC for chronic effects to mammals. The primary

ecological risk fro m the proposed thiabendazole seed
- treatment uses (as well as existing uses) is to birds and small mammals which could feed directl y on the treated seeds. Exposure, and thus risk, to these animals depend on two factors, the maximum seed treatment rate (i.e. , the maximum amount of active ingredient that can applied to a seed) and the size of the seed. Greater risk is associated with crops for which the seed treatment rate is higher and the seed size is smaller. The maximum seed treatment rate for cucurbit veg etables (0.1 mg a.i./seed) is far greater than for any other crop or crop group, making the risk to seed
- eating animals greatest for this crop groups. Among the crops within this group, ones with relativel y s mall seeds, such as cucumbers and melons, have the highest risk. Risk to seed
- eating animals is also high for alfalfa and for certain root vegetables, such as carrots. While the seed treatment rates for these crops are fairl y low, the seeds are extremely small, making the concentration on these seeds fairl y high. RQs are also fairl y high for small grains (barley, oat, rye, triticale, and wheat) , which have the second highest seed treatment rate (0.03 mg a.i./seed) and moderatel y small seeds.26



## VII. **References** USEPA, 2011. Acres Planted per Day and Seeding Rates of Crops Grown in the United States
. Memorandum from the Biological and Economic Analysis Division to the Environmental Fate and Effects Division. Office of Pesticide Programs. U.S. Environmental Protection Agency . Washington, DC. March 17, 2011.27



## Appendix **A .**  **Thiabendazole	degradates	identifie d	in	Environmental	Fate**  **Studies Degradates**  **Hydrolysis Photolysis**  **(water) Photolysis** 

**(soil) Aerobic** 

**Soil Anaerobic** 

**Soil Terrestria** 

**l Field** Benzimidazole X X X a 5 -hydroxy thiabendazole X Benzimidazole
- 2
- carboxamide X a Benzimidazole
- 2
- carboxylic acid X Unidentified [ 14 C] X X Unknown 1 X 14 CO 2 X a
- major degradates (>10%)28 

## Appendix **B .		Thiabendazole	and	Its**  **Environmental	Degradates**

**Nam e**  **Chemical Name CAS No.**  **Form ula**  **Molecular Mass Chemical Structure**  **Study Type Maximum %AR**  **(day) Final %AR** 

**(study length) PARENT**  Thiabendazole 2
- (4
- thiazolyl )
- 1H
benzimidazole CAS No.: 148
- 79
- 8 Formula: C 10 H 7N 3 S MW **:** 201.25 g/mol Aerobic Soil Metabolism Anaerobic Soil Metabolism 56.8% 78% (@ day 90)
**TRANSFORMATION PRODUCTS** Thiabendazole
- 5 -hydroxy 5 - hydroxythiabendazole; 2
- (4
- Thiazolyl)
- 5 - benzimidazolol CAS No.: 948
- 71
- 0 Formula: C 10 H 7N 3 S MW: 217.25g/mol Aerobic Soil Metabolism29 **Nam e**  **Chemical Name CAS No.**  **Form ula**  **Molecular Mass Chemical Structure**  **Study Type Maximum %AR**  **(day) Final %AR** 

**(study length)** Benzimidazole 1H
- Benzimidazole CAS No.: 962
- 28
- 7 Formula: C 7 H 6N2 MW: 118.05 g/mol Aq . Photolys is (minor) Aerobic Soil Metabolism Anaerobic Soil Metabolism Terrestrial Field Dissipation - 2.2% 13.7%

- 6.49% (avg.)

0.17% 5. 5 % (@ day 90

-


### Benzimidazole carbox yl ic acid 1H
- Benzimidazole
- 2
- carboxylic acid CAS No.: Formula: C 8 H 6N2 O 2 MW: 162.15 g/mol Aq. Photolysis (minor) 9.98% @ 96 hrs

Benzimidazole
- 2
- carboxamide 1H
- Benzimidazole
- 2
- carboxamide CAS NO. 5805
- 52
- 7 Formula: C8H7N3O MW: 161.16 g/mol Aq. Photolysis (major) 10.2% @ 96 hrs30



## Appendix **C .**  **GENEEC2 Model Outputs**
RUN No. 1 FOR thiabendazole ON seed treat *INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO
- SPRAY INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

-------------------------------------------------------------------- .150( .150) 1 1 7343.0 28.0 GRANUL( .0) .0 1.0 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

---------------------------- ---------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND
- EFF) (POND) (POND)

-------------------------------------------------------------------- 2064.00 2 N/A 1.20
- 148.80 .00 148.80 GENERIC EECs (IN NANOGRAMS/LITER (PPTr)) Version 2.0 Aug 1, 2001

-------------------------------------------------------------------- PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

-------------------------------------------------------------------- 885.85 860.43 734.13 530.42 427.70 RUN No. 2 FOR thiabendazole ON seed treat *INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO
- SPRAY INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

-------------------------------------------------------------------- .150( .150) 1 1 7343.0 28.0 GRANUL( .0) .0 2.0 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND
- EFF) (POND) (POND)

------------------------------------- ------------------------------- 2064.00 2 N/A 1.20
- 148.80 .00 148.80 GENERIC EECs (IN NANOGRAMS/LITER (PPTr)) Version 2.0 Aug 1, 2001

-------------------------------------------------------------------- PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

-------------------------------------------------------------------- 442.93 430.22 367.07 265.21 213.8531



## Appendix **D. Output	from	Terrestrial	Exposure	Model	(T**  **- REX)** 
Chemical: Thiabendazole Name of seed treatment formulation: Mertect 340 - F Percent AI in formulation: 42% 0 Density of product (lbs/gal): 9.692670395 Endpoints Reported Tested Body Adjusted LD50 Size class for adjusted LD50 We ight (g) Avian LD50: 4640.00 178 3342.79 Sm all (20g) Avian repro. NOAEC: 400.00 4255.54 Medium (100g) 6011.11 Large (1000g) Mammalian LD50: 4734.00 350 10404.53 Sm all (15g) Mammalian NOAEL: 200.00 8418.37 Medium (35g) 3641.21 Large (1000g) Adjusted NOAEL for Mammals Sm all (15g) 21.98 Medium (35g) 17.78 Large (1000g) 7.69

Anim al Size Crop Maximum Application Rate Maximum

Seed Application Rate Avian Nagy

Dose Mammalian

Nagy Dose Available

AI (lbs ai/A) (m g ai/kg

seed) (m g ai/kg bw/day) (m g ai/kg bw/day) (m g ai ft- 2) Sm all cucumber 0.031 2645.55 669.56 560.52 0.32 Medium 381.81 387.39 Large 170.94 89.82
Crop Risk Quotients† Avian (20 g) Mammalian (15 g) Acute (# 1) Acute (# 2) Chronic Acute (# 1) Acute (# 2) Chronic32 cucumber 0.2003 0.00480 6.61 0.0539 0.00205 25.50 Avian (100 g) Mammalian (35 g) Acute (# 1) Acute (# 2) Chronic Acute (# 1) Acute (# 2) Chronic cucumber 0.0897 0.00075 6.61 0.0460 0.00109 21.78 Avian (1000 g) Mammalian (1000 g) Acute (# 1) Acute (# 2) Chronic Acute (# 1) Acute (# 2) Chronic cucumber 0.0284 0.00005 6.61 0.0247 0.00009 11.68

† Acute RQ #1 = (m g ai /kg - bw/day ) / LD50 Acute RQ #2 = mg ai ft- 2 /(LD50*bw) Avian Chronic RQ = mg k g - 1 seed / NOAEL Mammalian Chronic RQ = mg a.i./kg - bw/da y / adjusted NOAEL

**An imal**  **Nagy allometry**  **Food ingestion value g/day**  20 g Bird 5.061777181 15 g Mammal 3.178078065 100 g Bird 14.4321986 35 g Mammal 5.125113265 1000 g Bird 64.6148732 1000 g Mammal 33.9507279633



## Appendix	E. **Output	from	Terrestrial	Plant	Risk	Model	(TerrPlant) TerrPlant v. 1.2.2** 

**Table 1. Chemical Identity.**  **Chemical Name Thiabendazole**  **PC code 60101**  **Use Seed treatments**  **Ap plication Method**  **Ground Ap**  **plication Form Seed treatments**  **Solubility in Water (ppm)**  **22.74 Table 2. Input parameters used to derive EECs.**  **Input Parameter Symbol**  **Value Units**  Application Rate A **0.15 lb ai.A**  Incorporation I **1** none Runoff Fraction R **0.05** none Drift Fraction D **0** none **Table 3. EECs for Thiabendazole. Units in lb ai.A .** 

**Description Equation**  **EEC** Runoff to dry areas (A/I)*R 0.0075 Runoff to semi - aquatic areas (A/I)*R*10 0.075 **Spray drift** **A*D** **0 Total for dry areas**  **((A** **/I)*R)+(** **A*D)** **0.0075 Total for semi**  **- aquatic areas**  **((A** **/I)*R*10)+(** **A*D)** **0.075**34



## Appendix **F .**  **Ecotoxicity	Data Table**  **F .1. Aquatic Toxicity Profile for**  **Thiabendazole Taxon**  **Exposure**

**Duration Most Sensitive** 

**Species Tested Toxicity Value**  **Toxicity Category**  **MRID /**

**Classification Fish**  Freshwater Fish Acute Rainbow trout Oncorhynchus mykiss 96
-hr LC 50 = 0.56 mg/L Highly toxic 41025005 (Acceptable) Chronic Rainbow trout NOAEC = 0.11 mg/L LOAEC = 0.23 mg/L Endpoint: Reduced weight -- 42508901 (Acceptable) Estuarine/ Marine Fish Acute Sheepshead minnow Cyprinodon variegatus LC 50 > 10 mg/L 3 Slightly toxic 41192003 (Supplemental) Chronic No data No data
-- -- **Aquatic Invertebrates**  Freshwater Invertebrates Acute Water Flea Daphnia magna 48
-hr EC 50 = 0.31 mg/L2 Highly toxic 00123326 (Acceptable) Chronic Water Flea NOAEC = 0.042 mg/L LOAEC = 0.087 mg/L Endpoint: survival, offspring production -- 00094645 (Acceptable)

Estuarine/ Marine Invertebrates Acute Mysid shrimp ( Americamysis bahia ) 96
-hr LC 50 = 0.34 mg/L Highly toxic 41192002 (Acceptable) Eastern Oyster ( Crassostrea virginica ) IC 50 > 0.26 mg/L (22% inhibition at 0.26 mg/L) Endpoint: shell growth Not determined 41192004 (Supplemental) Chronic No data No data
-- -- Freshwater Benthic Invertebrates Acute No data

Chronic No data **Aquatic Plants** Vascular plant Acute Duckweed Lemna gibba 7 - day EC 50 = 2.32 mg/L

NOAEC = 0.26 mg/L Not defined 48996308 (Supplemental) Non - vascular plant Acute Green algae Selenastrum capricornutum 96
-hr EC 50 = 3.06 mg/L

NOAEC = 0.532 mg/L Not defined 49146601 (Supplemental)35



### Table **F .2. Terrestrial Toxicity Profile for**  **Thiabendazole Taxon**  **Exposure**

**Duration Most**  **Sensitive**

**Species Tested Toxicity Value**  **Toxicity Category**  **MRID**

**Reference Terrestrial Vertebrates** 
Mammals Acute Laboratory Rat Rattus norvegicus LD 50 = 5,070 mg ai/kg bw (M) LD 50 = 4,734 mg ai/kg bw (F) Practically nontoxic 41258201

(acceptable) Chronic Laboratory Rat NOAEL = 10 mg ai/kg diet LOAEL = 30 mg ai/kg diet (Reduced bodyweight gain and food consumption) Not applicable 4 3190301 (acceptable)

Non Passerine Birds Acute Oral Bobwhite Colinus virginianus LD 50 > 2250 mg ai/kg bw Practically nontoxic 410250
- 02

(acceptable) Bobwhite LD 50 > 4640 mg ai/kg bw Practically nontoxic 00123313

(acceptable) Mallard Anas platyrhynchos LD 50 > 4640 mg ai/kg bw Practically nontoxic 00137948

(acceptable) Acute Dietary Bobwhite and

Mallard LC 50 > 5 620 mg ai/kg diet Practically nontoxic 41 025003

41025004 (acceptable) Chronic Bobwhite and

Mallard NOAEC = 4 00 mg ai/kg diet

LOAEC >4 00 mg ai/kg diet Not applicable 00123327 00123328 (acceptable) Passerine Birds Acute No data **Terrestrial Arthropods**  Terrestrial Insects Acute Honey Bee Apis mellifera LD 50 > 34 μg a.i./bee Practically nontoxic 48996305

(acceptable) **Terrestrial Plants**  Terrestrial Pla nts - Seedling Emergence Survival

and growth Monocots NOAEL = 0.23 lb/A EC 25 > 0.23 lb/A NA 48996306 (Acceptable, except Supplemental for bean and soybean) Dicots NOAEL < 0.23 lb/A

EC 25 ≥ 0.23 lb/A Endpoint: emergence and survival NA Terrestrial Pla nts - Vegetative Vigor Survival

and growth Monocots NOAEL < 0.23 lb/A EC 25 > 0.23 lb/A Endpoint: shoot length NA 48996307 (Acceptable) Dicots NOAEL = 0.23 lb/A

EC 25 > 0.23 lb/A NA