Page 2 of 43 

### 1. Executive summary

The Environmental Fate and Effects Division (EFED) and the Antimicrobial s Division (AD)

have completed the preliminary problem formulation for the ecological risk and drinking water

exposure assessments to be conducted as part of the registration review of dazomet [ (tetrahydro

3,5

- dimethyl

- 2 H

- 1,3,5

- thiadiazine

- 2

- thione) (PC Code 035602)]

. T he pr eliminary risk

assessment will address the potential ecological risk from both dazomet and its primary degradate, methyl isothiocyanate (MIT C)

. The problem formulation describes the methods planned to be used during the completion of drinking water and ec ological r isk assessments and provide s an ove rview of the environmental fate, ecological effects , potential risks and

uncertainties associated with the use of dazomet . This document also identifies additional

studies that are needed for the conduct of an ecological risk assessment

, which would address

both conventional and antimicrobial uses

.

Based on the available information, the following effects studies are recommended to be

submitted in order to assess the environmental risks assoc iated with the conventional and

antimicrobial use of dazomet (and exposures to MITC) : an acute oral passerine study with dazomet, a honey bee acute vapor exposure toxicity study with MITC, a terrestrial plant seedling emergence study with MITC, and an ear ly life

- stage study with freshwater fish and MITC. Because MITC has a potential (high solubility and low sorption affinity to soil) for movement into surface water, aerobic aquatic metabolism data for MITC would be useful to assess competitive processes o f degradation and volatilization from water

. To assess potential residues of MITC that may be transported via wastewater attributed to various antimicrobial uses and

post

- processing effluent ( i.e. , down the drain), the submission of an Activated Sludge

Res piration or Modified Activated Sludge Respiration Inhibition study, as well as the Ready Biodegradability test or one of three Biodegradation in Activated Sludge Simulation tests, will be useful to assess the potential fate to industrial wastewater treatme nt plants. The justifications for recommending the request of these studies are provided below

.

2. Introduction

For the Problem Formulation (PF) , EFED and AD evaluated the most recent ecological risk

assessments for dazomet in association with any update d toxicity, exposure, and usage

information to determine if sufficient data are available and if further updates are needed to support registration review. Recent risk assessments in clude a 2008 ecological risk assessment
conducted for the Reregistration E ligibility Decision (RED) (USEPA 2008) . In addition, the latest Agency science policies and risk assessment methodologies were considered

. The

structure of dazomet , as well as the chemical names and other identifiers can be found in the chemical identity table attached to this document ( Attachment 1 )

.

Soil fumigants, such as dazomet, are used to kill weed seeds and underground plant parts

, as well

as nematodes and disease

- causing organisms before planting in areas where high

- value crops are to be grown. Dazomet exhibits nematicidal, herbicidal, fungicidal, insecticidal, and slimicidal activity. Dazomet is a dithiocarbamate that converts readily to the methyl isothiocyanate ( MITC ) degradate upon application to soil. MITC accounts for most of the fumigan t activity by diffusing, either as a gas or volatile liquid, upward through the interstitial spaces in the soil andPage 3 of 43 

### killing living organisms with which it comes in contact. MITC is highly toxic and results in the disruption of biological functions of soil organisms. For example, MITC is highly reactive with the nucleophilic centers such as thiol groups in vital enzymes of nematodes (Cremlyn, 1991). Other fumigants also trans form to MITC [ i.e ., metam sodium (PC Code: 039003) and metam potassium (PC Code: 039002)] and MITC (PC Code: 068103) is registered as an active ingredient in some antimicrobial pesticides; these active ingredients (a.i.) are going through Registration Revi ew concurrently with dazomet.

There is currently one registered dazomet end

- use product for conventional pesticide uses (Basamid ® 

### Granular, EPA Reg. No. 5481

- 9027 ; 99% a.i.) , and is a Restricted Use Pesticide that can only be applied by certified pesticid e applicators. This product i s registered for use on compost piles, soil heaps or piles, golf course greens/tees, potting soils, seed and propagating beds, renovating turf sites, ornamental sites, field nurseries (including forests), soils of nonbearing c rops , and soils prior to the planting of strawberries and tomatoes (California only)

. Application of dazomet can be made either as a preplant treatment or as fall preplant treatment for spring sowing and transplanting. Dazomet can be applied to soil at r ates of 259 to 52 0 lb

a

. i

. /acre ( dazomet must be incorporated either mechanically or with water; the higher rates are

allowed when mechanical ly incorporat ed; the lower rates are to be used when incorporati ng using water) (see Table 1 ). For both mechanical and water incorporation, the label directions state to apply the granules, and then apply overhead irrigation to activate and seal soil surface over 4 days (irrigate enough to move water 4

– 6 inches into soil profile

- ~0.75

– 1 inch o f water). Treated soil surfaces can also be tarped. The maximum number of applications and maximum application rate per year are not specified on the label . Additionally, there are some uses in which more than one application per year is possible ( e.g ., soil heaps, ornamentals, etc .). Therefore, multiple application s per year at a particular use site will be modeled in the risk

assessments

.

Table 1. Currently Registered Conventional Pesticide Uses for Dazomet.

Use Site Application Method Type Desc ription Maximum Single Application

Rate Max # Apps /

Year A. I.

Max App

Rate/

Year Minimum

Retreatment

Interval

ORNAMENTAL SITE ( e.g ., flowers, bulbs, bedding plants, ground cover, seed or propagating beds) Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) NS NS NS

FIELD NURSERIES ( e.g ., forest, nonbearing and ornamental trees, shrubs, or Christmas tree seedlings) Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) NS NS NS

HOOP HOUSES Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) NS NS NS

NONBEARING CROPS Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp .) NS NS NS

‘California only : STRAWBERRIES and

TOMATOES” Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) NS NS NS

TURF [ e.g ., golf course (tees, greens), athletic fields, sod farms, lawns] Drop

- type spreader; water incorporation

with overhead irrigation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) NS NS NS

TURF (golf course fairways) Mechanical or water incorporation 520 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp .) NS NS NSPage 4 of 43 Use Site Application Method Type Desc ription Maximum Single Application

Rate Max # Apps /

Year A. I.

Max App

Rate/

Year Minimum

Retreatment

Interval

GREENHOUSES (all doors, windows, vents need to be open to outdoors) Mechanical or water incorporation 417 lb a.i./ acre (mech. incorp.)

259 lb a.i./ acre (water incorp.) [max area treated is 50,000 ft 2 ] NS NS NS

SOIL MEDIA ( e.g ., potting soils, soil heaps, or compost piles) Mechanically incorporate 0.68 lb a.i./yard 3 NS NS NS

INTERPLANTING (in existing orchards, berry fields, or similar areas) Mechanical incorporation 417 lb a.i./ acre (mech. incorp.) NS NS NS

NS = not specified on the label.



### For agricultural uses, the only usage data available indicate that ~800 lb and 600 lb a.i. of dazomet were used on soils for plums in 2009 and 2010, respectively, in California. For non

agricultural uses, the available information indicate the following u sage of dazomet: golf

courses

- ~15,500 lb a.i. (2002) and ~6,000 lb a.i. (2006); lawn care

- ~3,500 lb a.i. (2006);

nursery

- 15,000 lb a.i. (2003); and rights

- of

- ways

– 55,511 lb a.i. (2010, data on rights

- of

- ways

are available for California only) (USE PA, 201 2)

.

A ntimicrobial uses involve three scenario s that are considered high exposure worker scenarios: paper/pulp, cooling towers, and oil field drilling muds (fracking process). The environmental risks associated with these applications are minim al, and are discussed in further detail in the Conceptual Model section

.

3. Conclusions from Previous Risk Assessments

During the RED process the potential ecological risks associated with conventional pesticide and

antimicrobial uses of dazomet were assessed separately. In t he environmental fate and effects

risk assessment conducted for conventional pesticidal uses of dazomet (USEPA, 2008) , risks from dazomet and the transformation product of concern (MITC), were discussed separately. For

dazome t, risk to all exposed plants and animals from acute exposure was presumed , since

dazomet is a broad

- spectrum fumigant. It was assumed that all living organisms in the treated

soil we re at high risk of mortality. Based on an LD 50 

### / ft 2 

### analysis, acute RQ values for dietary exposure (ingestion) of dazomet exceed ed levels of concern (LOC) for birds and mammals that potentially could be exposed to granules . There wa s a potential for adverse reproductive effects

in birds from dazomet, but a quantitative asses sment of risk could not be conducted with the data

available at the time of the RED

. Modeling indicated no aqua tic exposure to parent dazomet, however, t here wer e uncertainties in estimating aquati c ecological effects of MITC due to the

limitations of the exposure models and crop scenarios available at the time of the assessment

. Limitations in exposure modeling include accounting for the rate of volatilization of MITC in

runoff and surface water.

For MITC (a gas) formation resulting from dazomet applications , it was determined that the residues downwind from a single 40

- acre field would not likely reach exposure levels to exceed

acute levels of concern ( LOCs ) for inhalation (equivalent to the acute oral LOCs) in mammals. However, multiple fields may be treated at one time and over time, possibly posing a greaterPage 5 of 43 

### acute and/or longer

- term risk from air residues. I nhalation toxicity data were not available for

MITC and other taxa (including birds) at the time of the RED

. N o aquatic LOCs we re exceed ed

, based on exposure to MITC

, in the modeled pond. The estimated MITC sur face water concentrations may have represented upper bound values because the rate of volatilization of MITC was not accounted for in the modeling. No LOCs we re exceeded for aquatic plant exposure to MITC, based in part on supplemental data.

3 .1. Ecological Risk Assessments

The Reregistration Eligibility Decision (RED) science chapter s and a 2006 new use assessment

for tomatoes and strawberries serve as a basis for this problem formulation . T he major ecological conclusions presented in the RED for conventional uses were as follows ( Table 2) :

Table 2 . Summary of Risk Concerns Identified for Dazomet in Previous Assessments

Birds Mammals Terrestrial

Plants Terrestrial

Inverts Fish Aquatic

Inverts Aquatic

Plants Groundwater

Contamination Persistence Degrad at es of Concern √ √ √ a √

-- b

-- b

-- b √ No concern MITC
a No terrestrial plant data were available to allow for a plant risk assessment

b There we re uncertainties in estimating aquatic ecological effects of dazomet/MITC due to the limitations of the exposure models and crop scenarios.



### The 2007 ecological risk assessment for the RED serve as a basis for this problem

formulation on the antimicrobial uses of Dazomet and MITC. Registered high exposure antimicrobial uses include paper/pulp, cooling towers, and oil field drilling muds (fracking process). While the primary exposure and risk concern is the release of water containing the chemical into wast e water system s ( i.e. down the drain)

, the environmental risks associated with these applications are expected to be minimal

.

3 .2. Drinking Water Exposure Assessments

A drinking water exposure assessment has not been conducted for dazomet

, specifically

. However, since a drinking water assessment was previously conducted for MITC (degradate of concern for human health exposure) forming from metam sodium and metam potassium applications , those exposures and conclusions are discussed here

. ( DP Barcode D293341, dated September 16, 2003 ).

The Estimated Drinking Water Concentrations (EDWCs) for metam sodium and its degradate MITC were calculated based on a maximum application rate of 320 lb. a.i./ a cre. Th is application rate is equivalent to a da zomet application rate of 772.9 lbs lbs./acre, which is higher than the maximum label dazomet application rate of 5 2 0 lb a.i. / a cre

. The models, Pesticide Root Zone Model and Exposure Modeling Analysis System (PRZM/EXAMS) and SCreen Index GROWater (SCIGROW )

, were used in estimating EDWCs in surface water and groundwater, respectively ( Table 3) . The acute concentrations in surface water are 0.03μg/L for metam sodium and 73.22 μg/L for MITC (Table 6) . The chronic ( cancer ) concentrations are 2.99 μg/L

for MITC and negligible (≤0.001 μg/L) for metam sodium using the Florida tomato scenario. These values represent the mean value over a 30

- year period. Of the various exposure scenarios (onion, strawberry, and turf) modeled, t he worst case scenario appears to be Florida tomatoes.Page 6 of 43 

### The SCIGROW generated EDWCs for tomato is 0.13μg/L for metam sodium and 0.72 μg/L for MITC, which are values for use to represent both acute and chronic exposures. The SCIGROW generated EDWC for groundwater did not account for the volatilization of MITC, hence, this value may be more conservative than it would be for a non

- volatile chemical.

Given the option for untarped application methods of dazomet, runoff of MITC to reservoirs after rain events may occur shortly after soil tre atments. In addition, leaching of MITC to ground water and wells nearby treated fields are possible due to MITC’s high water solubility. The relative importance of MITC drinking water dosing concentrations with MITC inhalation doses resulting from dazome t applications will be determined. As a result of this determination, drinking water assessments addressing dazomet applications will be conducted on an as needed basis. In case that a drinking water assessment is conducted, the PRZM

- GW model accounting for volatility from soil will be used to calculate the EDWCs.

Table 3 . Estimated Drinking Water Concentrations (EDWC’s) in surface water and Groundwater

Chemical Surface Water (μg/L) Groundwater (μg/L) Acute Non

- cancer chronic C ancer ( chronic )

Florida Tomato

Metam Sodium 0.03 0 0 0.13*

MITC 73.22 0.53 2.99 0.72 *

* Recommended EDWCs values for acute and chronic for groundwater



### Monitoring Data

Surface water and Groundwater Survey Data

Based on non

- targeted survey data, no MITC has been detected in 14864 ground water samples collected from 45 states over several years for Pesticides in Ground Water Data Base (PGWDB). At present time, MITC is not included in the National Water Quality Assessment Program (NAWQA) of United States Geological Survey (www.water.wr.usgs.gov), and it is also not included in the National Pesticide Survey

.

Monitoring Data Related to Incidents

Several water monitoring studies were conducted following the derailment of a railroad car north of Dunsmuir, California on July 4, 1991, when approximately 19,000 to 27,000 k g of metam sodium spilled into the Sacramento River. MITC concentrations in water samples collected following the spill, reach a maximum of 5500 ppb three days after the spill at the northern most

inlet o f Shasta Lake, and decreased to 8 ppb six days later. None of the degradates of metam sodium in water samples analyzed were detected 1 week after the spill (Segawa

, et a l , 1991).Page 7 of 43 

### 3 .3. Clean Water Act Programs

An Aquatic Life Ambient Water Quality Crite ria document has not been published for dazomet (or MITC) . Aquatic life benchmarks for MITC (but not dazomet) have been published and are

listed in T able 4

.

Table 4. OPP Aquatic Life Benchmarks (μg/L freshwater)

- MITC

Fish Invertebrates Nonvascular Plants Vascular Plants Acute Chronic Acute Chronic

25.6

-- 27.5 25 254 590



### Dazomet or MITC are not identified as a cause of impairment for any water bodies listed as impaired under section 303(d) of the Clean Water Act based on EPA’s WATERS Expert Query Tool ( http://iaspub.epa.gov/pls/waters/f?p=ASKWATERS:EXPERT:0 :::::)

. To our knowledge,

n o Total Maximum Daily Load (TMDL) criteria have been developed for either chemical

.

4. Environmental Fate and Transport

a. Physicochemical Properties

Dazomet is non

- volatile and readily soluble (3 g/L at 25 0 

### C) in water and degrades very rapidly to

MITC in soil and water . MITC has a high vapor pressure (19 mm Hg at 25 0 

### C) and a Henry’s

Law Constant of 1.79 x 10 - 4 

### atm

- m 3 

### /mol, which suggests that it will readily volatilize from

dazomet treated fields. MITC has a distinct pungent horseradish like odor. The important physicochemical and environmental fate properties of dazomet and its primary degradate MITC are provided in Table 5

.

Table 5. Physicochemical and Environmental Fate Properties of Dazomet and its Major Degradation Product Methyl isothiocyanate (MITC).

Property Value Reference (MRID)

Physicochemical Properties of Parent Dazomet

Chemical Name Tetrahydro

- 3,5

- dimethyl

- 2 H

- 1,3,5

- thiadiazine

- 2

- thione Tomlin, 1997 (ed.)

Chemical Group Dithiocarbamate Tomlin, 1997 (ed.)

CAS Number 533

- 74

- 4 Tomlin, 1997 (ed.)

SMILES String S=C1N(CN(CS1)C)C

Molecular Weight (g Mole - 1 ) 162.3 Tomlin, 1997 (ed.)

Molecular Formula C 5 H 10 N 2 S 2 Tomlin, 1997 (ed.)

Water solubility at 25°C 3000 mg L - 1 Tomlin, 1997 (ed.)

Melting point 104

- 105°C Tomlin, 1997 (ed.)Page 8 of 43 Property Value Reference (MRID)

Octanol/water partition coefficient (log K ow) 0.15 Tomlin, 1997 (ed.)

Vapor Pressure 2.8 x 10 - 6 mm Hg at 20°C Tomlin, 1997 (ed.)

Fate Properties of Parent Dazomet

Hydrolysis half

- lives 6.8 hrs. at pH 4, 4.4 hours at pH 7, and 2.4 hours at pH 9

6.6 h ours at pH 3, 5.8 h ours at pH 5, 4.0 h ours at pH 7, and

5.4 h ours at pH 9 Major Degradation products: MITC and carbon disulfide 459083

- 01,

414790

- 03 and

421114

- 01

Aqueous photolysis half

lives 4 .0 hours pH 7 buffer Major Degradation product: MITC 414799

- 01 and

421114

- 02

Soil photolysis half

- life 9

- 10 days Major Degradation product: MITC 431725

- 01

Aerobic soil metabolism

half

- life 17.2 hours Major Degradation product: MITC

5.4 and 7.0 days for loamy sand, and 20.2 days for sandy

loam 402119

- 01 and

421114

- 03

460847

- 01

Anaerobic aquatic half

- life (water/ sediment system) 3 hours Major Degradation product: MITC and methyl S

- [N

- formyl

N

- methylaminomethyl

- (N

- methyl)aminomethyl]

dithiocarbamate (MAM

- DCT) 435965

- 01

Terrestrial Field half

- lives 1.5 days (Germany, silt loam soil) 1.8 days (Spain, loamy sand soil) 1.9 days (Spain, loamy sand soil) Major Degradation product: MITC 460847

- 02

9.65 days for dazomet residue (dazomet and MITC)

(CA loamy sand soil) Major Degradation product: MITC 418748

- 01 and

418748

- 02

Physicochemical Properties of MITC

Chemical Name Methyl isothiocyanate

Chemical Group Isothiocyanate

CAS Number 556

- 61

- 6

Molecular Weight 73.1g Mole - 1 423656

- 03

Molecular Formula C 2 H 3 NS

Water solubility 8,610 mg/L at 25°C CDPR, 2002

Melting point 35

- 36°C Hartly (ed.) 1992Page 9 of 43 Property Value Reference (MRID)

Vapor pressure (VP) 16 mm of Hg at 25°C CALDPR, 2002

Octanol/water partition coefficient (log K ow) 0.98 MRID 435409

- 03

Henry’s law constant 1.79 x 10 - 4 (atm

- m 3 /mol) CALDPR, 2002

Fate Properties of MITC

Hydrolysis half

- life 3.5 days at pH 5, 20.4 days at pH 7, and 4.6 days at pH 9 00158162

Photodegradation half

- life in

water 51.6 days CDPR, 2002

Photodegradation half

- life in

air 1.21 to 1.60 days Geddes, et al., 1995

Aerobic soil metabolism

half

- life 3.3 days for Har Barquan, 4.1 days for Golan, 4.6 days for Belt Nir, 5.0 days for Gilat and Mivatachim, and 9.9 days for Malkiya. Gerstl et al., 1977

Anaerobic aquatic

metabolism half

- life 21 days MRID 435965

- 01

Soil water partition coefficient (K d ) 0.26 L Kg - 1 Gerstl et al., 1977



### The environmental fate of dazomet in aquatic and terrestrial environments is dependent on rapid hydrolytic degradation to form methyl isothiocyanate (MITC). The dissipation of MITC is predominately dependent on volatilization and to a lesser extent leachin g and degradation. Once MITC is volatilized into the atmosphere, it undergoes direct photolysis. MITC is also highly soluble in water and has a low adsorption in soil. Geddes et al. (1995) estimated the half

- li fe of MITC in the atmosphere to range from 29 to 39 hours. Alvarez and Moore (1994) calculated a photolysis half

- life of 39 hours f or noontime condition under mid

- summer at 40 ° 

### N latitude.

b. Degradation and Metabolism

Dazomet rapidly hydrolyzed (t 1/2 

### < 7 hours) in sterile, buffer solutions at 25°C (MRIDs 459083

- 01, 41479003 and 42111401). The major hydrolytic degradation product in pH 4, 5, 7, and 9

buffer solutions was MITC. Other hydrolysis degradation products were also identifie d methylamino(thioxo)methanesulfonic acid, methylamino(thioxo) methanesulfonic acid, [1,2,4]

dithioazolidine

- 3

- thione, N,N dimethylthiourea, and CO 2 

### . Formation of these degradation products was pH dependent. Similar dazomet degradation patterns and rates were observed in photodegradation in water studies (MRIDs 41479901 and 42111402). In an aerobic soil metabolism study (MRID 40211901, 42111403, and 46084701), dazomet degrades in soil with a

half

- life of less than 18 hours (Table 5 .). The majority of the residues had been volatilized: 92% of the applied as MITC; 3.02% as other volatiles (CO 2 

### , COS and CS 2 

### ) ; and other non

- volatile compounds including thiadiazolidine sulfur and thiadiazolidine sulphoxide

.Page 10 of 43 

### The chemical structures of dazomet and its primary degradation products (including MITC) are

shown in Appendix A

. Supplemental data from field dissipation studies indicate dazomet residues (dazomet and MITC) were rapidly dissipated (t 1/2 

### < 10 days) from a loamy sand soil in California (MRIDs 41874801 and 41874802). Field volatilization studies in Florida showed MITC and formaldehyde volatilization from watered

- in surface applications and soil incorporated applications of dazomet (MRID 48674301).

T he reported data indicate dazomet is not persistent in terrestrial and aquatic environments.

c. Transport and Mobility

Fate data indicate that MITC could potentially be transported via atmospheric, groun dwater, and surface water pathways; however, data suggest that MITC should not persist in terrestrial environments because of volatilization and degradation. Volatilization of MITC is likely the primary mechanism for transport as indicated in environmenta l fate laboratory studies. I ts high solubility in water and low adsorption in soil (K d 

### of 0.26 L Kg - 1 

### ) suggest that leaching to groundwater may be a potential transport pathway under flooded and saturated conditions ; h owever, under most field conditions, the potential for groundwater contamination of MITC is unlikely due to unsaturated soil conditions and its volatilization and degradation characteristics in soil (aerobic soil half

- lives of 3.3 to 20.2 days). Based on the available non

- targeted monitoring data, no MITC was detected in the groundwater samples within the U.S.A. MITC can also potentially move to surface water through runoff under a worst

- case scenario, such as an intense rainfall that occurs right after dazomet application. However, the Henry’ s Law Constant

f

or MITC suggests that it will volatilize rapidly from surface water. No monitoring data of MITC in surface water are available at the present time.

d. Field Studies

Field dissipation studies (MRID 41874801 and 46084702 ) conducted with dazomet in California and Europe were considered in this problem formulation . Dazomet residues (dazomet and MITC) had a field dissipation half

- life of 9.65 days (DT 50 

### < 3 days ) in a California loamy sand

, 1.5 days in silt loam soil in Germany, and 1.8 to 1.9 days in loamy sand soils in Spain

. In the California study, d azomet residues were predominately detected in the surface 6 inch soil layer; however, residues (dazomet or MITC) were detected at depths of 12 to 18 inches at 3, 5, 10, 12, and 21 days. No residues were detected in deeper soil samples except immediately post

treatmen t

. In the European studies, dazomet was rapidly degraded in the soil to the major transformation product MITC in all three study trials, with MITC reaching maximum concentrations in the soil within 3 days posttreatment. The dissipation rate of dazomet was comparable for each site, independent of the trial location, the weather conditions, and the type of soil sealing (with or without plasti c cover).

A dissipation study of [2

- 14 

### C]3,5

- dimethyl

- 1,3,5

- thiadiazinane

- 2

- thione(dazomet; BAS 002 N)

was also conducted in three outdoor lysimeter

- enclosed plots (1.2

- m diameter and 1.2

- m height) of loamy sandy

- sandy loam soil in Germany (MRID 44641601)

. Results indicate that the majority of the applied radioactivity, 93

- 96%, was lost to the atmosphere and not characterized

, 4

- 6% was present in the soil, 0.1

- 0.9% in the leachate, and <0.1% in the plants. Of thePage 11 of 43 

### radioactivity present in the soil, 3.62

- 4.9 1% was detected in the top three soil layers (0

- 10 cm,

10

- 20 cm, and 20

- 30 cm layers) and only 0.16

- 0.26% was detected in the soil layers below 30 cm. The highest concentrations of radioactivity in the 0

- 10 cm, 10

- 20 cm, 20

- 30 cm, and >30 cm soil layers we re 7.6 μ g/g, 7.0 μ g/g, 2.7 μ g/g, and 0.4 μ g/g, respectively, all from the lysimeter receiving the 600 kg/ha application rate. The majority of the radioactivity detected in the leachate was detected during the first year of the study. Total [ 14 

### C]

- CO 2 

### in the leachate ranged

from 0.03

- 0.53% of the applied, and total unidentified radioactivity ranged from 0.04

- 0.30% of the applied. Methyl isothiocyanate (MITC) was not detected in any leachate samples above 0.1

μ g/L.

Along with terrestrial field dissipat ion and lysimeter studies, there is one field volatility study available which was conducted in California sandy loam soil (MRID 46340401). Between 2.24 percent and 3.7 percent of the overall dazomet applied material volatilized in the form of MITC

over 7 days for mechanically soil incorp or ated (8 inch depth) and surface applications, respectively. Field volatilization studies in Florida showed MITC and formaldehyde

volatilization from watered

- in surface applications and soil incorporated applications of dazomet (MRID 48674301). Study author reported flux values of MITC and formaldehyde from

watered

- in surface application s ranged from 73

- 82 % and 13

- 14% of applied dazomet, respectively. Volatilization of MITC and formaldhyde from mechanically incorpo rated dazomet ranged 16

- 34% and 0.6

- 1.3% of applied dazomet, respectively.

4 .1. Transformation Products

The environmental fate of dazomet in aquatic and terrestrial environments is dependent on rapid hydrolytic degradation to form methyl isothiocyanate (MITC). The dissipation of MITC is predominately dependent on volatilization and to a lesser extent leaching and degradation. Once MITC is volatilized into the atmosphere, it undergoes direct photolysis. MITC is also highly

soluble in water and has a low adsorption in soil. Geddes et al. (1995) estimated the half

- li fe of MITC in the atmosphere to range from 29 to 39 hours. Alvarez and Moore (1994) calculated a photolysis half

- life of 39 hours f or noontime condition under mid

- summer at 40 ° 

### N l atitude.

The major degradation product and active ingredient of dazomet, MITC, has a vapor pressure of 19 mm Hg and water solubility of 7.6 g/L at 25°C (Table 5 ). The calculated Henry's Law

constant of MITC is 1.79 x 10 - 4 

### atm

- m 3 

### /mol. A Henry's Law const ant in the range of 10 - 5 

### to 10 - 3



### atm

- m 3 

### /mol indicates volatilization from water can be a significant route of dissipation for the compound; however, transport resistance in liquid and gas phases is expected to reduce the rate of volatilization for the comp ound (Lyman et al ., 1990). Volatilization of MITC was a major route of dissipation in environmental fate laboratory studies. Laboratory soil volatility data ranged from a maximum concentration of 1.02 x 10 5 

### μg/m 3 

### and volatility rate of 16.9 μg/cm 2 

### /hr

at 50 % field capacity ( FC ) and 100 ml/minute air flow to a concentration of 2.8 x 10 5 

### μg/m 3 

### and volatility of 24.9 μg/cm 2 

### /hr at 75% FC and 300 ml/minute air flow (MRID 42569202). A field volatility study in a California sandy loam soil (MRID No. 46340401) indic ate that between 2.24 percent and 3.7 percent of the overall dazomet applied material volatilized in the form of MITC over 7 days for mechanically incorporated (8 inch depth) and surface applications, respectively

.Page 12 of 43 

### Once MITC volatilize s into the atmosphere, it undergoes direct photolysis. Geddes et al. (1995)

estimated the half

- li fe of MITC in the atmosphere to range from 29 to 39 hours. Alvarez and Moore (1994) calculated a photolysis half

- life of 39 hours for noontime under mid

- summer conditions at 40 ° 

### N latitude. Several metabolites were identified that included methyl isocyanate (MIC), methyl isocyanide, sulfur dioxide, hydrogen sulfide, carbonyl sulfur, N

methylthioformamide, and methylamine (Geddes et al .,1995). They also reported that 80 % of MITC can potentially degrade to MIC. MIC is known to be very reactive and can be acutely

toxic to terrestrial animals. Although other degradation products have been identified from dazomet degradation (including MIC) , their toxicity and exposu re profile are not expected to

exceed those of MITC (see below)

.

The degradation rates of MITC in soils have been reported in a number of studies (MRID

46084701 and Gerstl et al , 1977). These studies generally found that MITC degradation in soil

was do minated by microbial processes and followed first

- order degradation kinetics. Gerstl et al

. (1977) calculated MITC degradation with half

- lives ranging from 3.3 to 9.9 days depending on soil composition. Since MITC is a volatile compound, very little inform ation is available on the metabolites of MITC degradation in soil. Dungan and Yates (2003) reported that the microorganisms responsible for enhanced degradation of MITC specifically target the isothiocyanate functional group, which may compromise the pesti cidal efficacy of MITC containing active ingredients like metam sodium and dazomet in soil.

Methyl isothiocyanate degradation in soil and water appears to be also dependent on hydrolysis

and microbial

- mediated degradation. A hydrolysis study indicates rad iolabeled MITC hydrolyzes
[t 1/2 

### < 21 days in buffer solutions (Accession No. 257305)]. The only hydrolytic product at pH 5 and pH 7 was CH 3 

### NH 3 

### OH. Hydrolytic products in pH 9 buffer solution were S=C(CH 3 

### NH) 2 

### (dimethylthiourea) and CH 3 

### NH 2 

### (methylamine). MIT C had a half

- life of 27 days in a non

- sterile,

anaerobic soil

- water test system under a static incubation system (MRID 43596501). A major degradation product was methyl S

- [N

- formyl

- N

- methylaminomethyl

- (N

- methyl) aminomethyl]dithiocarbamate (MAM

- DCT). Mino r degradation products were 1,3

- dimethyl

- 2

- thiourea and 1

- methyl

- 2

- thiourea (DMTU

- MMTU). The above data suggest that MITC should not persist in terrestrial environments and surface water because of volatilization and degradation.

5

. Receptors

Although other degradation products have been identified from dazomet degradation, their toxicity and exposure profile are not expected to exceed those of MITC. Therefore, the stressors

of concern are dazomet and MITC. Since dazomet rapidly hydrolyzes to MITC, p otential exposure to aquatic receptors is primarily to MITC via surface runoff; consequently, the toxicity data for MITC will be used to assess risk to fish, aquatic invertebrates, and aquatic plants.

Terrestria l exposure to birds, mammals, invertebrates can occur orally as dazomet granules (on the site of application only , since spray drift is not expected) and/or by inhalation of MITC (on and off the site of application)

. There is also a potential for exposure to MITC and non

- target
terrestrial animals via drinking water , however, this route of exposure will not be assessed since the primary route of exposure to terrestrial animals is expected to be via inhalation (see below)

.Page 13 of 43 

### Off

- site exposure to dazomet and terrestrial plants is not expected (since sp ray drift is not expected) ; however, terrestrial plants may be exposed off

- site to MITC as a vapor or via runoff

. Therefore, for terrestrial animal s, toxicity data for both dazomet and MITC will be considered. For terrestrial plants, toxicity data for MI TC [vegetative vigor (vapor exposure) and seedling emergence (water /vapor exposure)] will be u sed to assess risk

. Table 6 and 7 provide a summary of the aquatic toxicity data (MITC only) and terrestrial toxicity data (dazomet and MITC), respectively. The most sensitive species tested in each taxon is reported for each

chemical and will be used to characterize the potential acute a nd chronic ecological effects of dazomet (terrestrial organisms) and MITC (aquatic and terrestrial organisms)

.

5 .1. Effects to Aquatic Organisms

Table 6 . Summary of the M ost S ensitive E ndpoints from A quatic T oxicity S tudies for MITC (Transformation Product of Dazomet)

Taxonomic

Group Study Type Surrogate Species Toxicity Value MRID and

Classification Acute Toxicity

Classification

Freshwater fish 1 Acute Rainbow Trout ( Oncorhynchus mykiss ) LC 50 = 94 μg

a.i. /L ( slope = N/A ) 42058002 Acceptable Very highly

toxic

LC 50 = 53 μg

a.i. /L ( slope = N/A ) 45919420 Supplemental (due to (hydrolytic instability and

insufficient sampling of

the test chemical) Very highly

toxic

Chronic (Early

Life

Stage) No data available

Freshwater

invertebrates Acute Water Flea ( Daphnia magna ) EC 50 = 55 μg

a.i/L (slope not available) 41819302 Acceptable Very highly

toxic

Chronic Water Flea NO A EC = 25

μ g a.i. /L

LO A EC = 50

μ g a.i. /L (based on parental mortality and reproduction) 45634001 Supplemental (based on (mean

measured

concentrations

not determined, stability of

chemical not assessed,

terminal growth

measurements not obtained) N/APage 14 of 43 Taxonomic

Group Study Type Surrogate Species Toxicity Value MRID and

Classification Acute Toxicity

Classification

Estuarine/marine

fish Acute Sheepshead Minnow ( Cyprinodon variegat u s ) Study in review 48731101 Study in

review

Estuarine/marine

invertebrates Acute Eastern Oyster ( Crassostrea virginica ) Study in review 48985201 Study in

review

Saltwater mysid ( Americamysis

bahia ) Study in review 48649301 Study in

review

Aquatic plants and algae Vascular Duckweed ( Lemna gibba ) 7

- day EC 50 (frond number) = 0.59 mg a.i/L

NOAEC (frond

number and growth rate) = 0.09 mg a.i/L 45919421 Acceptable

Non

vascular 2 Freshwater Algae ( Scenedesmus subspicatus ) 96

- hour EC 50

( cell density) = 0.2 mg a.i/L

NOAEC = 0.13 mg a.i/L 44588903 Supplemental

(non

guideline species used)

1 Freshwater fish may be surrogates for aquatic

- phase amphibians.

2 Several additional aquatic non

- vascular plants studies have been submitted for MITC and are currently under review (MRIDs: 48733401, 48733501, 48733601, and 48733701).



### 5 .2. Effects to Terrestrial Organisms

Table 7

. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for D azomet (Oral Exposure) and I t s Transformation Product, MITC

- Inhalation Exposure ; (Animals ) ; Exposure Via Vapors or Via Runoff (Plants)]

.

Taxonomic

Group Study Type Surrogate Species Toxicity Value (all units in

terms of

measured active ingredient) MRID and

Classification Acute Toxicity

Classification

Birds 1 Dazomet

Acute Bobwhite quail ( Colinus virginianus ) LD 50 = 424 mg a.i. /kg

- bw 42365101 Acceptable

Sub

- acute dietary Bobwhite quail ( Colinus virginianus ) LC 50 = 1,832 mg a.i./kg

- diet 00131918 Acceptable

Chronic Bobwhite quail ( Colinus virginianus ) Study in review 48834701 Study in review

Mallard duck ( Anas platyrhynchos ) Study in review 48834702 Study in reviewPage 15 of 43 Taxonomic

Group Study Type Surrogate Species Toxicity Value (all units in

terms of

measured active ingredient) MRID and

Classification Acute Toxicity

Classification

MITC

Acute (Inhalation) Bobwhite quail ( Colinus virginianus ) Study in review 48788401 Study in review

Mammals Dazomet

Acute Oral Laboratory rat ( Rattus norvegicus ) LD 50 = 415 mg a.i. /kg

- bw 00132468 Acceptable

Chronic Laboratory rat ( Rattus norvegicus ) NOAE C = 5 mg a.i./kg

- diet

LOAEC = 30 mg a.i./kg

- diet (based on reduced parental body weight and reduced weight gain) 41865301 Acceptable

MITC

Acute (Inhalation) Laboratory rat ( Rattus norvegicus ) 4 hour LC 50 = 0.54 mg a.i/L 42365605 Acceptable

Insects Dazomet

Acute

contact Honey bee ( Apis mellifera

L. ) LD 50 = >24 μg a.i. /bee 00001999 Listed as ‘DMMT, Mylone®’ in the toxicity table;

based on a note on the DER, there was 6% mortality at 24 μg a.i./bee

MITC

Acute

contact Honey bee ( Apis mellifera

L. ) No data

available N/A

Terrestrial plants MITC

Vegetative Vigor (Tier II) Various species Study in review 49058001 Study in review

Seedling Emergence Various species No data

available N/A This study was previously waived (see USEPA, 2012 )

1 Birds represent surrogates for terrestrial

- phase amphibians and reptiles.Page 16 of 43 

### 5 .3. Ecological Incidents

A search of the available pesticide ecological incident databases on March 5, 2013

, resulted in

the following: the American Bird Conservancy’s Avian Incident Monitoring System ( AIMS ) identified no ecological incidents involving dazomet; the Environmental Incident Information System ( EIIS ) returned three aquatic animal incidents involving dazomet (see bel ow) ; there are four aggregate incidents reported for dazomet in IDS (see below). There are no reported ecological incidents associated with MITC in the AIMS, EIIS, or IDS databases.

For the three dazomet incidents reported in the EIIS, all of them involv ed aquatic animals ( i.e

., fish). One occurred in Bladen County

, North Carolina

, in 1993 and was the result of a misuse in an agricultural area that killed 50 fish ( I003654

- 002). Another fish kill (unknown magnitude)

resulted from a misuse of dazomet (use site not reported) in Mercer County, Pennsylvania, in 2004 (I014993

- 001). For both of these incidents, the certainty index was ‘highly probable’. The third incident occurred in Arlington County, Virginia, in 2001 and was the result of a registered

use o f dazomet on a golf course (I012014

- 003). It was unknown how many fish were killed in this incident and the certainty index was ‘possible’ for dazomet.

In IDS

, registrants reported four aggregate incidents involving dazomet [ all involving the product BAS AMID (EPA Reg. No.: 007969

- 00099) in 2001]

. Three involved unspecified wildlife and one involved an unspecified ‘other nontarget’. Unless additional information on these aggregated incidents becomes available, they will be assumed to be representative of registered uses of dazomet in the risk assessment.

6

. Conceptual Model

The environmental fate properties of dazomet indicate that potential exposure to the conventional

uses of dazomet is expected to be limited to the site of application; spray drift is not expected (since dazomet is applied as a granule and is soil incorpor ated) . Dazomet is expected to rapid ly degrade in aquatic and terrestrial environments to form MITC , whose dissipation is predominately dependent on volatilization

, and degradation

, to a lesser extent. A ny potential runoff, leaching or volatilization from the site of application is expected to be in the form of

MITC , as MITC is highly soluble in water and has a low adsorption in soil . Potential exposu re to MITC is expected both on the site of application (as a vapor) and off the site of application ( primarily via vapor transport and runoff).

With the exception of potential exposure to aquatic organisms resulting from down

- the

- drain

effluent containin g residues of dazomet and/or MITC from paper pulp processing or cooling

tower uses, exposure to non

- target organisms from the antimicrobial uses of parent dazomet is expected to be limited.Page 17 of 43 

### 7

. Analysis Plan

7 .1. Stressors of Concern

The stressors of ecologic al concern for terrestrial animal s are dazomet (via ingestion of granules )

and its main degradate MITC (via inhalation)

. As stated earlier, any exposure to dazomet is expected to be limited to the site of application. For terrestrial plants, the stressor of concern for

non

- targets (off the site of application) is expected to be MITC (via vapor transport and/or runoff). For aquatic organisms (plants and animals), the stressor of concern is expected to be MITC (via vapor transport and/or runoff)

. Although other degradation products have been identified from dazomet degradation, their toxicity and exposure profile are not expected to

exceed those of MITC.

Although exposure via ingestion of contaminated drinking water and/or contaminated terrestr ial

invertebrates is possible for terrestrial animals, the main route of exposure to terrestrial animals to MITC is expected to be through inhalat ion. For birds, based on MITC’s vapor pressure and calculations using STIR, the maximum 1

- hour vapor inhalati on dose for birds is 7914 mg/kg. By contrast, based on MITC ’ s solubility limit and calculations using SIP , the upper bound daily drinking water intake dose for a bird is 6974 mg/kg bw. Multiplying the STIR estimate of one hour by 12 (to match the daily e xposure duration of the SIP estimate) yields 94

, 968 mg/kg which is 2 orders of magnitude more than the potential drinking water dose (see Appendices B and C)

. For MITC, t his suggests that the potential daily inhalation exposure of a bird is substantially greater than the potential daily drinking water exposure for a bird indicating that inhalation exposure may be of more concern. Additionally, based on an earthworm fugacity model (see Appendix D), mammals and birds that ingest subterranean invertebrates ( i.e ., earthworms) from sites treated with dazomet are expected to receive MITC doses of 0.14 mg a.i./kg

- bw and 0.16 mg a.i./kg

- bw, respectively. These are well below the predicted one

- hr inhalation dose s for mammals and birds predicted from STIR ( i.e ., ~9 ,950 and 7,910 mg a.i./kg

- bw, respectively) (again, see Appendices B and D)

.

Additionally , acute oral and acute inhalation toxicity data are available for the laboratory rat (MRIDs 00162331 and 42365605, respectively). While the acute inhalation study di d not

achieve a definitive toxic ity endpoint, the data indicate that for mammals, MITC is at least 2 orders of magnitude more toxic on an inhalation basis than on an oral basis [ oral LD 50 

### of 55 mg a.i/kg bw vs

. acute inhalation LD 50 

### = 0.80 mg/L (converted from an LC 50 

### of <0.0296 mg/L) ]

. Therefore, a ny risks associated with terrestrial animals and exposure to MITC via inhalation are expected to be protective of other potential routes of exposure (including via drinking water and the ingestion of contaminate d terrestrial invertebrates ). Therefore, for terrestrial animals (including terrestrial invertebrates) and MITC, the risk assessment will focus on risks associated

with inhalation.Page 18 of 43 

### 7 .2. Measures of Exposure

Dazomet:

Exposure to dazomet ( but not its transformation product, MITC) is expected to be limited to the site of application since it is applied as a granular formulation and i t hydrolizes rapidly to MITC

. The primary route of exposure to non

- target terr estrial animal species is expected to be via direct ingestion of dazomet granules.

MITC:

Given that fumigants (such as MITC) possess volatile characteristics and that they are applied to soil, there is a unique situation where there can be exposure of concern in air, soil, and water resulting from multiple dissipation pathways such as volatilization, runoff, and leaching from

soil as shown in Figure 1 below. Although air and inhalation exposure are the domina n t exposure pathways for fumigants, the fumi gant gas can become dissolved in runoff or leaching water without a tarp covering the entire field. Volatilization of the fumigant may occur from the soil for some time after the application. Dry gas

- phase deposition may also add to exposures in plant, w ater, and soil media for all fumigant uses. Given the highly volatile and highly mobile nature of the fumigants, such as MITC, spray drift (especially in the case of dazomet, which is applied as a granular) , sorpt ion to erodible soil particles , and plant uptake from crop planted later are not expected to be of concern for risk in ecosystems adjacent to fumigant applications.

Figure 1. Dissipation and degradation pathways for soil fumigants.

Applied

Pesticide Volatilization

Transformations

microbial

chemical Sorption /

Retention

Leaching Surface Runoff

Lateral

Flow

Tile DrainagePage 19 of 43 

### Aquatic Exposures

Surface Water Exposure Modeling

Aquatic EECs will be estimated for the conventional uses of dazomet ( and MITC ) using PRZM

/EXAMS with the volatilization algorithm. The maximum application rate for dazomet w ill be

used in the PRZM/EXAMS modeling

. Environmental fate data for dazomet will be used in the modeling ( Table 8 ).

Table 8 . PRZM/EXAMS Input Parameters for Dazomet

Parameters Values Sources

Molecular Weight 162.3 g Mole - 1

Vapor Pressure 20 o C 2.8 X 10 - 6 mm Hg

Water Solubility @ pH 7.0 and 25 o C 3000 mg L - 1

Hydrolysis Half

- Life (pH 7) 0.18 Days (0.17 and 0.18 days) (Calculated 90 th Percentile)

MRID#s 4211140

- 01 and

459083

- 01

Aerobic Soil Metabolism t 1⁄2 , 2.13 ( 0.71 x 3 ) Days MRID#s 40211901, 42111403

Aerobic Aquatic metabolism: 4.16 ( 2.13 x 2 ) Days EFED Guideline

Anaerobic Aquatic metabolism: for entire sediment/water system 0.39 ( 0.13 x 3 ) Days MRID 43596501

Aqueous Photolysis 0.17 Day MRID#s 41479901, 42111402

Soil Water Partition Coefficient (K

oc ) 13.64 L Kg - 1 Model estimated value

Pesticide is Wetted

- In Yes Product Label



### Because dazomet degrades rapidly to form MITC, PRZM/EXAMS modeling will also be

conducted on MITC. The application rate of MITC w ill be calculated according to molar ratio of

MITC to dazomet. O ne mole of dazomet 162.3 g/mole can produce one mole of MITC ( 73.1 g/mole); therefore, the molar ratio is 0.45 (73.1 g/mole/ 162.3 g/mole). The aerobic soil metabolism study suggests that the maximum conversion rate of dazomet to MITC was 92%. Therefore, the maximum MITC

- equivalent ‘ application rate ’ would be (0.92)(0.45)(530) = 219.4

lbs/ a cre at 530 lbs/ a cre application rate for dazomet. Env ironmental fate data specific to MITC will be used in the modeling ( Table 9 ).

Table 9 . PRZM/EXAMS Input Parameters for MITC

Parameters Values Sources

Molecular Weight 73.12g Mole - 1 Product Chemistry

Vapor Pressure @ 25 o C 19 mm Hg CDPR, 2002

Water Solubility @ pH 7.0 and 25 o C 7600 mg L - 1 Product ChemistryPage 20 of 43 Parameters Values Sources

Vapor Phase Diffusion Coefficient (DAIR) 8227 cm 2 day - 1 Fuller et al., 1966

Enthalpy of Vaporization 8.91 kcal mole - 1 Chickos and Acree, 2003

Hydrolysis Half

- Life (pH 7) 20.4 MRID 001581

- 62

Aerobic Soil Metabolism t 1⁄2 , 9.61 Days

(5.4

- 20.2 days) (3.3

- 9.9 days) (Calculated 90 th Percentile)

MRID 460847

- 01 Gerstl et al, 1977

Aerobic Aquatic metabolism: for entire sediment/water system 19.2 EFED Guideline

Anaerobic aquatic metabolism Stable MRID 439084

- 26

Aqueous Photolysis 51.6 Day s CDPR, 2002

Soil Water Partition Coefficient 0.26 L Kg - 1 (Mean K d ) Gerstl et al., 1977



### Down The Drain Assessment for Antimicrobial Uses

Cooling Towers The cooling tower use involves the removal of heat in a circulating system along with the use of dazomet (highest application rate: 6.5 fluid oz/1000 gallons water) and i s expected to degrad e faster at high er temperature s, having a shorte r half life (3.5 days at room temperature). The major degradate of dazomet is MITC ; it will also have shorter half life at high temperature (its half life is 4.5 days at room temperature)

. W ith a higher volatilization rate from the cooling water system

and the amounts of dazomet and or MITC

, reaching a wastewater stream would be low.

Treatmen t of Paper and Pulp

A p ossibility of MITC residues on paper and pulp exists. However the fact that in the paper/pulp process mixing of the pesticide (highest application rate: 1 lb/8000 gallons of pulp) takes place at high temperature, and in a closed system, paper as an end product will likely not have any appreciable residues of MITC, as its half life is 4.5 days at room temperature and at pH 7, around which the paper making process takes place. The spe nt water from the paper making process might contain some residual MITC, but with a high vapor pressure, and half life of less than five days, MITC will likely enter into wastewater streams with much reduced quantity.

Oil field recovery application

It is a process that can take many weeks to complete and so oil field application of dazomet (highest application rate is 182 lbs/1000 bbl) presents a unique scenario from a fate perspective;

its primary exposure dissipation routes are hydrolysis, aquatic photol ysis, aerobic soil metabolism, and anaerobic aquatic metabolism. Its terrestrial field half life is 1.5 day in European soils. MITC also appear to have multiple degradation pathways. It hydrolyzes in abiotic conditions in less than 4 days, and photodegrade s in air in 1.6 days. Its half life in soil under aerobic condition is less than 4 days. It metabolizes in aquatic medium within 21 days, under anaerobic conditions. It is mobile in soils. Thus any residual dazomet or MITC is expectedPage 21 of 43 

### to be quite low in wa stewater streams and may not pose any risks to nontarget aquatic organisms (t his document does not address any workers exposure for the field workers)

.

The Industrial Releases Module of the E

- FAST (Exposure and Fate Assessment Screening Tool)

will be use d to determine the potential for aquatic organisms downstream of the industrial wastewater treatment plants that receive discharges from the antimicrobial use s of d azomet and its major degradate MITC. Dazomet is used in industrial water systems such as

co mmercial/industrial cooling water, industrial wast ewater, pulp/paper mills, etc. Antimicrobial uses will eventually be released to industrial wastewater treatment plants whose effluents are expected to reach surface water

, and potentially be exposed to aq uatic organisms. The primary and major ( > 10 % of applied parent compound) degradate include MITC. Chemicals that are

released down

- the

- drain can typically take from a few to several hours to reach wastewater treatment plant intakes following their dischar ge and from several hours to roughly a day following their discharge down

- the

- drain to subsequently be discharged from industrial wastewater treatment plants to surface water. MITC is highly soluble in water and can be discharged to surface waters.

Terrestrial Exposures

For dazomet, the predominant exposure to terrestrial organisms is expected to be attributed to the

conventional uses. T he primary route of exposure to non

- target terrestrial vertebrates is expected to be via direct ingestion of granules. To assess potential dietary exposure to birds (used as a surrogate for reptiles and terrestrial

- phase amphibians) and mammals, the LD 50 

### /ft 2 

### analysis in the

T

- REX model will be used (for details, see: http://www.epa.gov/oppefed1/models/terrestrial/index.htm#trex ). I n the absence of available data to inform on the potential exposure concentrations to terrestrial organisms, i t will be assumed that 100% of the applied dazomet will be bioavailable before o ff

- gassing.

For MITC and terrestrial animals (including terrestrial invertebrates)

, the main route of exposure is expected to be via inhalation. For terrestrial plants, exposure to vapor phase MITC is also expected. To estimate exposures to MITC vapor, a tiered approach will be used. Both

AERSCREEN [the screening version of AERMOD (the American Meteorological Society/EPA Regulatory Model Improvement Committee) (AERMIC Model)] and PERFUM (Probabilistic Exposure and Risk Model for Fumigants) can predict the upper bound air EEC at a point nearby the edge of the treated field directly downwind from the application site. In addition, both models can predict fumigant air concentrations at specified points downwind from the treated

field. AERSCREEN , which co nsiders worst

- case meteorological conditions coupled with a peak flux rate, will be used as a screen. If LOCs are exceeded using AERSCREEN , PERFUM, which has the capability of producing a distribution of air EECs from a range of different meteorological c onditions, will be used to refine the potential exposure values for animals and plants (vegetative vigor).

For exposure to plants via runoff (seedling eme rgence), TerrPlant will be used . T he application

rate of MITC w ill be calculated according to molar ratio of MITC to dazomet (as discussed above).Page 22 of 43 

### 7 .3. Measures of Effect

Toxicity data presented in Section 5 of this problem formulation will be used to calculate risk quotients. Any additional information submitted by the registrant or found in the open literature prior to conduct of the risk assessment will also be considered. The open literature studies are identified using EPA’s ECOTOXicology database ( ECOTOX) ( USEPA, 2007 c ), which employs a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants,

and wildlife. The evaluation of both sources of data can also provid e insight into the direct and

indirect effects of pesticides on biotic communities from loss of species that are sensitive to the

chemical s and from changes in structure and functional characteristic s of the affected

communities.

7 .4. Endangered Species A ssessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate risks to federally listed threatened and/or endangered (listed) species from registered uses of pesticides in registration review . The se assessment s will be conducted in

accordance with standard EPA procedures and good scientific judgment

.

7 .5. Endocrine Disruptor Screening Program

Dazomet was not included in the first group of 67 chemicals issued an order to conduct Tier 1

EDSP testing. For additional information the EDSP program, visit http://www.epa.gov/endo/

.

8

. Preliminary Identification of Data Gaps

8 .1. Environ mental Fate

Table 10 and Table 11 

### identify environmental fate studies that offer data for each guideline

re quirement, as well as study classifications and whether or not further data are needed in order to support risk assessment.Page 23 of 43 Table 10 . Submitted Environmental Fate Data for Dazomet

OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed to

conduct risk

assessment? Comments

835.2120 Hydrolysis 45908301

42111401

41479903 Acceptable Supplemental Supplemental No

835.2240 Aqueous photolysis 41479901

42111402 Acceptable Acceptable No

835.2370 Air photolysis N/A N/A No

835.2410 Soil photolysis 43172501 A cceptable No

835.4100 Aerobic soil

metabolism 40211901

42111403

46084701 Acceptable Acceptable Supplemental No

835.4200 Anaerobic soil

metabolism N/A N /A No Anaerobic soil metabolism data are not needed due to rapid hydrolysis of

dazomet

835.4300 Aerobic aquatic

metabolism N/A N/A No Aerobic aquatic metabolism data are

not needed because dazomet is not expected to reach aquatic environments due to rapid hydrolysis

835.4400 Anaerobic aquatic

metabolism 43 596201 Acceptable No

835.1230

835.1240 Adsorption/ desorption and leaching 42569201 A cceptable No

835.1410 Volatility

– laboratory 42569202 Acceptable No Volatility study was conducted for

dazomet.

835.6100 Terrestrial field dissipation 46084702

41874801

41874802 Supplemental Supplemental Supplemental Yes

An ECM/ILV in soil for dazomet and

MITC are needed to support the field dissipation studies. 850.6100 Analytical

method in soil No N/A

835.6200 Aquatic field dissipation N/A N/A N/A

Analytical

method in water

165

- 4 (850.1730) Fish

bioconcentration N/A N/A N/A

835.7100 Ground Water

Small Scale Prospective 44641601 Supplemental NoPage 24 of 43 Table 11 . Submitted Environmental Fate Data for the MITC

OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed to

conduct risk

assessment? Comments

835.2120 Hydrolysis 00158162 Acceptable No

835.2240 Aqueous photolysis 41517701 N /A No Because metam sodium dissociates to form MITC, the degradate of concern,

the available photolysis data for metam sodium provides photodegradation

information on MITC generation from

dazomet.

835.2410 Soil photolysis (None) N /A No

835.2370 Air photolysis (None) N/A No Open literature data will be used to address this data gap.

835.4100 Aerobic soil

metabolism 460847 01 Supplemental No

835.4200 Anaerobic soil

metabolism (None) N /A No

835.4300 Aerobic aquatic

metabolism (None) N /A Yes There is a potential for MITC to become dissolved in runoff , with the potential for exposure to aquatic organisms. A laboratory aquatic study is needed to

determine MITC’s residence time in

water.

835.4400 Anaerobic aquatic

metabolism 43596501 Supplemental No

835.1230

835.1240 Adsorption/ desorption and leaching (None) N /A Yes Given its high solubility in water and low adsorption affinity to soil, these suggest the potential for leaching to groundwater under flooded and

saturated conditions. An adsorption/desorption study on MITC would help to inform on the potential mobility in soi l.

835.1410 Volatility

– laboratory (None) N/A No

835.6100 Terrestrial field dissipation (None) N/A No

Analytical

method in soil (None) N/A

835.8 100

860.6100 Volatility

- Field 46340401 Pending No

Analytical

method in air (None) N/A Yes Environmental chemistry methods (ECMs) and independent laboratory validation (ILVs) are needed to support

all methods used in each MITC field volatility study.Page 25 of 43 OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed to

conduct risk

assessment? Comments

835.6200

850.6100 Aquatic field dissipation (None) N/A No Although dazomet has no aquatic uses and MITC is volatile from water, an

ILV/ECM in water is needed because of MITC’s high acute aquatic toxicity and its potential to reach surface water Analytical

method in water (None) N/A Yes

850.1730 Fish

bioconcentration (None) N/A No

OECD 209

or 850.6800 3 Activated Sludge Respiration

Inhibition or

Modified Activated Sludge Respiration

Inhibition (antimicrobial) None N/A

Yes Transport to Industrial wastewater treatment plant

835.3110

835.3220

835.3280

835.3240 Ready biodegradability

test or one of

three biodegradation in activated sludge

simulation tests (antimicrobial) None Yes Transport to Industrial wastewater treatment plant

1. For studies with finalized classification pending, cursory review found studies adequate for risk assessments. Finalized review with formal DER pending.

2. Field volatility stu dies were conducted with dazomet as the test substance. MITC flux is measured in all field volatility studies.



### 8 .2. Effects

Tables 12 and 1 3 identif y ecological effects studies that offer data for each guideline requirement, as well as study classifications and whether or not further data are needed in order

to support the risk assessment for dazomet

. Rationale s for the additional data requested are

p resented below the tables.

Table 7 summarizes the available toxicity data and data needs for dazomet and terrestrial organisms (aquatic toxicity data for dazomet are not needed based on the expected routes of

exposure to non

- target species discussed previ ously). Table s 12 and 1 3 summarize the available toxicity data and data needs for the primary dazomet transformation product, MITC, and terrestrial and aquatic species, respectively.

The adequacy of the current toxicity data submitted to assess dazomet ( and, thus, MITC) will largely depend on the review of recently submitted data that were submitted in response to aPage 26 of 43 

### RED data call

- in (DCI). These studies are listed as ‘under review’ in the following tables. If

these studies are found to be in adequate for use in risk assessment, EFED recommends requesting the following studies to assess the environmental risks associated with the use of dazomet: an acute oral passerine study with dazomet, and an avian reproduction study with

dazomet. For environmental ris ks associated with MITC, the following studies are requested: an avian inhalation study with MITC, a honey bee acute vapor exposure study with MITC, a terrestrial plant seedling emergence study with MITC, an early life

- stage study with freshwater

fish and MITC , a saltwater invertebrate acute toxicity with MITC , a saltwater fish acute toxicity study with MITC, and an aquatic plant growth Tier II study with MITC . The justifications for recommending the request of these studies are provided below. If any of the studies listed as under review are not found to be acceptable for use in risk assessment, additional data may be

needed.

Table 12

. Submitted Terrestrial E cological E ffects D ata for Dazomet.

OCSPP

Guideline Data Requirement Submitted

Studies (MRID ) Study

Classifications Are data

needed for

risk

assessment ? Current Additional Data Need

850.2100 Avian oral toxicity 42365101 Acceptable Yes Data are currently only available on the bobwhite quail. Given the toxicity of dazomet and the likelihood of exposure, there is uncertainty if the bobwhite quail is the most sensitive avian species. Acute oral toxicity data are

necessary for a passerine sp ecies.

850.2200 Avian dietary toxicity 00131918 Acceptable No

--

850.2300 Avian reproduction 48834701 Under review Yes Depending on the results of the review of the recently submitted

studies. 48834702 Under review

850.3020 Honey bee

acute contact toxicity 00001999 Acceptable No

--

850.3030 Honey bee

residue on foliage None Not applicable (N/A) No Not needed be cause the chemical is applied as a granular

formulation.

850.3040 Field testing for pollinators None (N/A) No

--

850.4100 Terrestrial plant toxicity:

Tier II seedling

emergence None Not applicable (N/A) No Due to the fate properties and pesticide formulation (i.e., granular), off

- site exposure to terrestrial plants and dazomet is not expected.Page 27 of 43 OCSPP

Guideline Data Requirement Submitted

Studies (MRID ) Study

Classifications Are data

needed for

risk

assessment ? Current Additional Data Need

850.4150 Terrestrial plant toxicity:

Tier II vegetative vigor None N/A No Due to the fate properties and pesticide formulation (i.e., granular), off

- site exposure to terrestrial plants and dazomet is not expected.

Table 13

. Submitted Terrestrial E cological E ffects D ata for MITC.

OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed for

risk

assessment ? Current Additional Data Need

850.2100 Avian oral toxicity None N/A No Due to the fate properties of MITC, the exposure route of

concern is inhalation (not dietary)

850.2200 Avian dietary toxicity None N/A No Due to the fate properties of MITC, the exposure route of concern is inhalation (not dietary)

850.2300 Avian reproduction None N/A No Due to the fate properties of MITC, the exposure route of concern is inhalation (not dietary)

Non

guideline Avian

inhalation 48788401 Under review Yes Depending on the results of the review of the recently submitted study.

Non

guideline Honey bee

acute vapor

exposure None N/A Yes Because the primary route of exposure to MITC and terrestrial invertebrates is likely through inhalation, a special vapor

exposure study with honey bees is

recommended.

850.3020 Honey bee

acute contact toxicity None N/A No

--

850.3030 Honey bee

residue on foliage None (N/A) No

--

850.3040 Field testing for pollinators None (N/A) No

--

850.4100 Terrestrial plant toxicity:

Tier II seedling

emergence None N/A Yes The requirement was previously

waived (see USEPA 2012,

D395875 ); however, upon further evaluation, it was determined that exposure to MITC via runoff is a potential risk concern.Page 28 of 43 OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed for

risk

assessment ? Current Additional Data Need

850.4150 Terrestrial

p lant toxicity:

Tier II vegetative vigor 49058001 Under review Yes Depending on the results of the review of the recently submitted study.

Table 14

. Submitted A quatic E cological E ffects D ata for MITC.

OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed to

conduct risk

assessment? Current Additional Data Need

850.1010 Freshwater

invertebrate acute toxicity 41819302 Acceptable No

--

850.1025

850.1035

850.1045

850.1055 Saltwater

invertebrate acute toxicity 48985201 Under review Yes Depending on the results of the review of the recently submitted study.
48649301 Under review

850.1075 Freshwater

fish acute toxicity 42058002

45919420 Acceptable Supplemental No

--

850.1075 Saltwater fish acute toxicity 48731101 Under review Yes Depending on the results of the review of the recently submitted study.

850.1300 Freshwater

invertebrate life cycle 45634001 Supplemental No

--

850.1350 Saltwater

invertebrates life cycle None (N/A) No

--

850.1400 Freshwater

fish early

- life stage None (N/A) Yes There is a potential for sublethal effects from exposure to MITC that

c an not be adequately assessed using the available acute toxicity

data for fish.

850.1400 Saltwater fish early

- life stage None (N/A) No

--

850.1500 Fish life cycle None (N/A) No

--

850.4400 Aquatic plant

g rowth:

Tier II vascular plants 45919421 Acceptable No

--

850.5400 Aquatic Plant

Growth: 44588903 Supplemental Yes Depending on the results of the review of the recently submitted 48733401 Under reviewPage 29 of 43 OCSPP

Guideline Data Requirement Submitted

Studies (MRID) Study

Classifications Are data

needed to

conduct risk

assessment? Current Additional Data Need

Tier II algae 48733401 Under review study.

48733401 Under review

48733401 Under review



### For all of the studies that are listed as ‘under review’ in Tables 12

, 13 , and 1 4 , the data are

needed to fully assess dazomet. Upon review, if an y of the se studies are found to be scientifically invalid or supplemental (and not adequate for use in risk a ssessment), additional data may be needed to adequately assess the potential risks of dazomet (including its primary degradate, MITC).

Dazomet :

850.2100 Avian Acute Oral Toxicity

- Passerine

For dazomet, acute oral toxicity data are currently not available for a passerine species. Because dazomet is considered moderately toxic to bobwhite quail (MRID 42365101), and there is a potential for passerines to be more sensitive than either bobwhite quail or mallard duck on an acute exposure basis, EFED r ecommends requesting an acute oral study with a passerine species

and dazomet.

MITC:

850.3020 Honey Bee Acute Contact Toxicity Study

Amvac Chemical Corporation (AMVAC), a registrant for dazomet, has previously requested a waiver for the honey be e acut e contact study using MITC. The initial waiver request argued that a valid contact study could not be performed due to the volatility of the test substance. In a response by EFED (see USEPA, 2011), EFED recommended that the honey bee study be

conducted u sing MITC as a liquid ( i.e ., via a topical drop and not a dusting). The hydrolysis

half

- life for MITC ranges from 3.5 to 20.4 days (depending on pH) (MRID 00158162 ); its photodegradation half

- life in water is 51.6 days (CDPR, 2002); its photodegradation h alf

- life in air is 1.2 to 1.6 days (Geddes, et al ., 1995); and its aerobic soil metabolism half

- life ranges from 5.4 to 20.2 days (depending on soil type) (MRID 460847

- 01). Therefore, MITC applied as a topical drop to the bees is expected to persist suffi ciently for a 48

- hr acute contact study and could be informative for understanding risks to subterranean invertebrates, such as ground

nesting bees, for which the honey bee would be a surrogate

.

AMVAC recently requested further consideration for waiving t he bee contact study (Habig 2012). AMVAC concluded:Page 30 of 43 

### “...(A) n y e x pos u re of p o l l inato r s or other te r r e strial inve r te b r a tes to M I TC wi l l be to

M I TC i n the f o rm of a g a s. The OP P TS hon e y b e e ac ute to x ici t y testing g uideline ( OP P TS 850.3020) ind i ca tes th a t hon e y b e e ac ute c onta c t t o x ici t y test i n g is g e n e r a l l y not

r e quir e d f o r substan c e s that a re a g a s, a h i g h l y volati l e l i quid, r e ac t i ve solid, or a

c o rrosive mat e ri a l. M I T C c le a r l y me e ts t h e s e c ri t e ria f or w a iv e r; it is a hi g h l y volati l e if

p re s e nt as a l i qui d

, a nd a ll potential e x posure to M I TC u n d e r norm a l use c ondi t ions
would be to M I TC g a s ). M I TC i s also c o r rosive in m a m m a l ia n e y e a nd skin ir r i t a t i on testin g
, a nd b a s e d on i t s prop e rties a nd mode o f a c t i on, would be e x p ec ted to be c o r rosive
to b ee s.” (Harbig, 2012, p. 6).

Although EFED disagrees that the only exposure to pollinators or other terrestrial invertebrates to MITC will be in the form of a gas (exposure via drinking water and via contact in soils is also possible), EFED does agree that the primary route of exposure to terrestrial invertebrates is likely

via exposure to MITC vapor . Therefore, any risks based on the exposure to vapor phase MITC are likely to be protective of the other potential routes of exposure. EFED recommends that an acute honey be e contact study be waived for MITC. However, because an understanding of potential risks to terrestrial invertebrates, including honey bees, will be important for understanding th e environmental risks of the use of dazomet (and, thus, also MITC), EFED recommends requesting a special, non

- guideline acute honey bee vapor exposure toxicity study

for MITC (see Appendix E ) . Because this is a non

- guideline study, EFED recommends that th e registrant work with the Agency to develop a study protocol. At a minimum, EFED recommends that a study protocol be submitted to EFED for review before the study is

conducted.

850.4100 Terrestrial Plant Toxicity: Tier II Seedling Emergence

EFED previ ously recommended waiving a terrestrial pla nt study for seedling emergence (see USEPA 2012, D395875 ). U pon further evaluation, however, it was determined that exposure to

MITC via runoff (and, thus, to vapors in soil) is a potential risk concern. MITC is highly soluble in water and has a low adsorption in soil. Potential exposure to MITC is expected both on the site of application (as a vapor) and off the site of application (primarily via vapor transport and runoff). Therefore, exposure relevant to the seedling emergence is possible. Therefore, to fully assess the potential risks associated with dazomet use, EFED recommends requesting a seedling emergence study with MITC.

850:1400 Freshwater Fish Early Life

- Stage Toxicity Study

There are currently no acceptable chronic toxicity data available for fish. Although MITC is not expected to be persistent i n aquatic systems, preliminary aquatic exposure modeling (using PRZM/EXAMS) indicates that MITC may remain at concentrations of toxicity concern for

seve ral days. There is also a possibility of pulsed exposures to MITC from some of the uses of dazomet, since there may be multiple applications per year at the same use site for some uses ( e.g ., dirt piles). Additionally, the available acute fish data are n ot adequate for assessing potential sublethal effects associated with MITC exposure. Sublethal exposures of MITC at certain points of the life cycle of a fish may elicit effects on the growth and reproduction as is

shown in available freshwater invertebra te data Therefore, EFED recommends requesting an early life

- stage study with freshwater fish. In the absence of data to indicate otherwise, it will bePage 31 of 43 

### assumed that MITC is similarly toxic to freshwater fish and estuarine/marine fish , and EFED

does not r ecommend requesting chronic toxicity data for est uarine/marine fish at this time

.

9 . References

ARB, 1997. Ambient air monitoring for MIC and MITC after a soil injection application of metam sodium in Kern County during August 1995. Test Report No. C94

- 046, May 20, 1997. Air Resources Board, Sacramento, CA.

Alvarez, R. and C.B. Moore. 1994. Quantum yield for production of CH 3 

### NC in the photolysis of

CH 3 

### NCS. Science263: 205

- 207.

Cremlyn, R.J. 1991. Agrochemicals: Preparation and Mode of Action. p. 2 83

- 307. John Wiley and Sons. New York, NY.

CDPR (California Dept. of Pesticide Regulation). 2002. Evaluation of Methyl Isothiocyanate as a Toxic Air Contaminant, Part A

- Environmental Fate. California Environmental Protection Agency, Sacramento, CA.

Dunga n, R.S. and S.R. Yates. Degradation of fumigant Pesticides. 2003. 1,3

- Dichloropropane, methyl isothiocyanate, and methyl bromide. Vodose Zone Jour. 2: 279

- 286.

EPISUITE. The EPI (Estimation Program Interface) SuiteTM is a Windows® based suite of physical/ chemical property and environmental fate estimation models developed by the EPA’s Office of Pollution Prevention Toxics and Syracuse Research Corporation SRC. http://www.epa.gov/opptintr/exposure/docs/updates_episuite_v3.11.htm

Geddes, J.D., G.C. Miller, and G. E. Taylor Jr. 1995. Gas phase photolysis of methyl isothiocyanate. Environ. Sci. Technol. 29:2590

- 2594.

Gerstl, Z., U. Mingelgrin, B. Yaron. 1977. Behavior of Vapam and Methylisothiocyanate in

soils. Soil Sci. Soc. Am. J. 41: 545

- 548.

Hartley, D. 1992. Agricultural Handbook. Royal Society of Chemistry Information Service. Nottingham NG7 2RD, England.

Lyman, W.J., Reehl, W.F. and Rosenblatt, D.H. 1990. Handbook of Chemical property estimation methods. Environmental behavior of organic compounds. Amer. Chem. Soc. Washington, D.C.

OECD (Organization for Economic Co

- Operation and Development). 2004. Emission Scenario

Document on Water Treatment Chemicals. OECD Environmental Health and Safety Publications. ENVJM/MONO (2004)9. http://www.oecd.org/env/ehs/risk

- assessment/emissionscenariodocuments.htmPage 32 of 43 

### Tomlin, C.D.S. (ed.) 1997. The Pesticide Manual. Eleventh Ed. p 335

- 339. British Crop Protection Council. Surrey, GU9 7PH, UK.

U.S. EPA (United States Environmental Protection Agency). 2005. Overview of the use and usage of soil fumigants. http://www.epa.gov/oppsrrd1/rere gistration/soil_fumigants/soil_fumigant_use.pdf

U.S. EPA (United States Environmental Protection Agency). 2004a. Pe4 Shell. 2004. Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency, Washington, D.C. Information downloaded from the website http://www.epa.gov/oppefe d1/models/water/

U.S. EPA (United States Environmental Protection Agency). 2004b. Health Effects Division’s Draft Standard Operating Procedures (SOPs) for Estimating Bystander Risk from Inhalation Exposure to Soil Fumigant.

U.S. EPA. (United States Envi ronmental Protection Agency). 1995. User’s Guide for the Industrial Source complex Dispersion Models. Volume 1. User Instructions. USEPA Office of Air Quality Planning and Standards; Emissions, Monitoring and Analysis Division, Research Triangle Park, Nort h Carolina.

Habig, C. 2012. Dazomet/MITC: Request for Reconsideration of Request for a Waiver from Honey Bee Acute Contact Toxicity Testing. Submitted by AMVAC Chemical Corporation, Commerce, CA 90040. September 12, 2012.

Segawa, R.T., S.J. Marade, N .K. Miller, and P.Y. Lee. 1991. Monitoring of the Cantara metam

sodium spill. Environmental Hazards Assessment Program, Report Number EH 91

- 09. Department of Pesticide Regulation. Sacramento, CA

USEPA, 2011. EFED Review of the Data Waiver Request for the Dazomet Degradate Methyl Isothiocyanate (MITC) and Honey Bee Acute Contact Toxicity Data Requirements. Environmental Fate and effects Division, Office of Pesticide Programs, United States Environmental Protection Agency. Washington, DC. September 1, 2011

.

USEPA, 2012. Review of Test Protocol for MITC : Seedling Emergence and Vegetative Vigor

Terrestrial Plant Toxicity Stud ies. Environmental Fate and effects Division, Office of Pesticide Programs, United States Environmental Protection Agency. Washingt on, DC. February 29,

2012.

USEPA, 2012. BEAD Chemical Profile for Registration Review: Dazomet (035602). Biological and Economic Analysis Division, Office of Pesticide Programs, United States Environmental Protection Agency. Washington, DC. May 14, 201 2.Page 33 of 43 

### Appendix A

- Chemical Structures of Dazomet and Its Hydrolysis Degradation Products

Dazomet (BAS 002 N) IUPAC name: 3,5

- Dimethyl

- 1,3,5

- thiadiazinane

- 2

- thione CAS name: Tetrahydro

- 3,5

- dimethyl

- 2 H

- 1,3,5

- thiadiazine

- 2

- thione

CAS No: 533

- 74

- 4

Unlabeled

[2

- 14 

### C] thiadizine label

* Position of the radiolabel. N N S S

C H 3 C H 3

N N S S

C H 3 C H 3 *Page 34 of 43 

### N,N’

- Dimethylurea IUPAC name: N,N’

- Dimethylurea

CAS name: NA

CAS No: NA

N,N’

- Dimethylthiourea

IUPAC name: N,N’

- Dimethylthiourea

CAS name: NA

CAS No: NA

S

n 

### - homologues of N,N’

- Dimethylthiourea

IUPAC name: N,N’

- Dimethylthiourea

CAS name: NA

CAS No: NA N H N H

O

N H N H

S

S

n N H N C H 3

HPage 35 of 43 

### (Methylamino)(thioxo)methanesulfenic acid

IUPAC name: (Methylamino )(thioxo)methanesulfenic acid

CAS name: NA

CAS No: NA

Hydroxymethyl dithiocarbamic acid (isomer)

IUPAC name: Hydroxymethyl dithiocarbamic acid

CAS name: NA

CAS No: NA

(Methylamino)(thioxo)methanethiosulfenic acid

IUPAC name: ( Methylamino)(thioxo)methanethiosulfenic acid

CAS name: NA

CAS No: NA N H S O H

S

N H S H O H

S

N H S S H

SPage 36 of 43 S S C 

### MITC IUPAC name: Methylisothiocyanate

CAS name: NA

CAS No: NA

Carbon disulfide

IUPAC name: Carbon disulfide

CAS name: NA

CAS No: NA

Dithiazolidine

- 3

- thione IUPAC name: [1,2,4]dithiazolidine

- 3

- thione

CAS name: NA

CAS No: NA N

C H 3 S C

S S C

S N H S SPage 37 of 43 

### Methyl amine IUPAC name: Methyl amine

CAS name: NA

CAS No: NA

Formaldehyde

IUPAC name: Formaldehyde

CAS name: NA

CAS No: NA

Carbon dioxide

IUPAC name: Carbon dioxide

CAS name: NA

CAS No: NA C H 3 N H 2

C H 2 O

C 14 C O 2Page 38 of 43 

### APPENDIX B

– STIR Model Run to Establish Drinking Water Exposure Conceptual

Model for Birds and Mammals (MITC).Page 39 of 43 

### APPENDIX C

– SIP Model Run to Establish Drinking Water Exposure Conceptual Model

for Birds and Mammals (MITC).

Table 1. Inputs

Parameter Value

Chemical name MITC
Solubility (in water at 25 o C; mg/L) 8610

Mammalian LD 50 (mg/kg

- bw) 55 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg

- bw)

Mammalian test species Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg

- bw) 0
Avian test species northern bobwhite quail Body weight (g) of "other" avian species Mineau scaling factor

Mallard NOAEC (mg/kg

- diet) Bobwhite quail NOAEC (mg/kg

- diet) NOAEC (mg/kg

- diet) for other bird species Body weight (g) of other avian species NOAEC (mg/kg

- diet) for 2nd other bird species Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 1480.9200 1480.9200 Adjusted toxicity value (mg/kg

- bw) 42.3038 0.0000 Ratio of exposure to toxicity 35.0068 0.0000

Conclusion* Exposure through drinking water alone is

a potential concern for

mammals Due to insufficient data, risk cannot be precluded

Table 3. Avian Results

Parameter Acute Chronic Upper bound exposure (mg/kg

- bw) 6974.1000 6974.1000 Adjusted toxicity value (mg/kg

- bw) 0.0000 0.0000

Ratio of exposure to acute toxicity 0.0000 0.0000

Conclusion* Due to insufficient data, risk cannot be precluded Due to insufficient data, risk cannot be precludedPage 40 of 43 

### APPENDIX D

– Potential Exposure Values for the Ingestion of Contaminated Earthworms

By Birds and Mammals for Several Fumigants (Including MITC); Earthworm Fugacity Analysis

Use of fugacity approach to estimate exposures to small mammals and birds consuming earthworms contaminated with pesticides

.

Fugacity is most often regarded as the "es caping tendency" of a chemical from a particular phase. Fugacity (F) has units of pressure, generally pascals (Pa), and can be related to phase concentrations. For any particular environmental phase ( e.g., water, soil, air, or biota) there is a corresponding "fugacity capacity" with units of mol/m 3



### - Pa and is denoted by Z. The relationship between fugacity, fugacity capacity and chemical concentration (C) is defined by Equation 1.

Fugacity capacities for a given chemical are calculated for the phases of interest as part of the exposure point estimation methodology (Mackay and Paterson 1981). The following calculations of fugacity capacities for soil (Z S 

### ) and earthworms (Z E 

### ) (Equations 2 and 3, respectively) require several chemical

- specific parameters and assumptions of system temperature (25 o 

### C) and steady state equilibrium. Parameter values relevant to Equations 2 and 3

are defined in Table 1.

Fugacity capacities for a given chemical are calculated for the phases of interest as part of the exposure point concentration esti mation methodology. By definition, the ratio between Z values of different phases (compartments) equals the partitioning coefficient ( e.g., Equation 4).

In this approach, it is assumed that a pesticide partitions between the soil, the (pore) water and the air contained within the soil of the treatment site. It is assumed that earthworms dwelling within the soil are exposed to a pesticide via ingestion of contaminated soil. The concentration of a pesticide in earthworm tissues can be calculated according to Equation 5 (see Table 1 for parameter definitions).

Table 1. Summary of parameters relevant to earthworm fugacity model. 

### F Z C Equation *

. 1 =

H K Z Equation S d

S 

### ρ *

. 2 =

H K L Z Equation OW

E 

### *

. 3 =

OW

water ol oc 

### K Z Z Equation = tan



### . 4

       

=

S E

S E 

### Z Z C C Equation *

. 5Page 41 of 43 Symbol Definition Units

C E Chemical concentration in earthworm tissue mol/m 3

C E ' Chemical concentration in earthworm tissue g/kg

C S Chemical concentration in soil mol/m 3

H Henry’s Law constant m 3

- Pa/mol

K d Soil partitioning coefficient cm 3 /g

K OW Octanol to water partition coefficient none

L Lipid fraction of earthworm none

MW molecular weight of chemical g/mol

Z E Fugacity capacity of pesticide in earthworms mol/m 3

- Pa

Z S Fugacity capacity of pesticide in soil mol/m 3

- Pa

ρ E density of earthworm kg/m 3

ρ S Bulk density of soil g/cm 3



### Equation 5 can be redefined using equations 2 and 3 as follows in Equation 6. Equation 6 is used to calculate the concentration of a pesticide in earthworms inhabiting the soil of treatment sites.

C S 

### is intended to be representative of the steady

- state concentrations of the pesticide of interest in soil. This value is calculated using PRZM. Kd and Kow are chemical

- specific parameters. Kd

should be consiste nt with the value input into PRZM. ρ S 

### is dependant upon the soil properties of

the selected PRZM scenario used to derive C S 

### . L is based on the lipid content of earthworms, which was assumed to be 0.01 (Cobb et al. 1995). The resulting C E 

### value is in unit s of mol/m 3



### . This value is converted to units of g/kg using equation 7. The density of the earthworm (ρ E 

### ) is assumed to be 1000 kg/m 3 

### (equivalent to density of water). s d ow S

E 

### K K L C C Equation ρ *

* *

. 6 =

E E

E 

### MW C C Equation ρ *

. 7 '



### =Page 42 of 43 

### Comparison of STIR and Earthworm Fugacity Modeling Results for a Variety of Fumigants and Mammals and B irds.

Parameter Telone Methyl

Bromide DMDS MITC Chloropicrin

Application Rate (lbs. a.i./A) 628.49 400 455 219.4 1 350

Molecular Weight (g/mol) 110.97 94.94 94.2 73.12 164.38

Vapor Pressure (torr) 34.3 1,620 22.5 16 23.8

Kd (L/kg) 0.721 2 0.182 3 0.641 0.260 0.361 2

Log Kow 2.0 1.18 1.77 1.30 2.38

Earthworm Conc (g/kg) 0.001 0.0002226 0.00284 0.00014 0.001580

Mammal Diet Dose (mg/kg) 0.71 0.27 0.34 0.14 1.88

Avian Diet Dose (mg/kg) 0.84 0.32 0.40 0.16 2.55

STIR Air conc. (mg/m 3 ) 2.05 x 10 5 8.28 x 10 6 1.14 x 10 5 6.3 x 10 4 2.11 x 10 5

STIR Mammal Inhaled Dose (mg/kg) 3.24 x 10 4 1.31 x 10 6 1.80 x 10 4 9.95 x 10 3 3.33 x 10 4

STIR Avian Inhaled Dose (mg/kg) 2.57 x 10 4 1.04 x 10 6 1.43 x 10 4 7.91 x 10 3 2.65 x 10 4

15 g mammal, 20g bird STIR model and Earthworm Fugacity Model.

Depth 10 cm for earthworm exposure zone

1 Dazomet maximum application rate results in highest MITC equivalent application rate of MITC generators (from Metam Sodium = 150.31 lbs. a.i./A, from Metam Potassium = 150.38 lbs. a.i./A).

2 Based on EPISUITE estimated KOC and assumption of 1 percent soil organic carbon content.

3 Based on average of measured KOC values and assumption of 1 percent soil organic carbon content.

4 Shaded rows depict highest exposure dose.



### References:

Cobb, G.P., E.H. Hol, P.W. Allen, J.A Gagne, R.J. Kendall. 1995. Uptake, metabolism, and toxicity of terbufos in the earthworm ( Lumbricus terrestris ) exposed to COUNTER

- 15G in artificial soils. Environ. Toxicol. Chem. 14(2):279

- 285.

Mackay, D. and S. Paterson. 1981. Calculating fugacity. Environ. Sci. Technol. 15: 1006

- 1014.

U

. S

. EPA. 2008. User’s Guide: T

- REX Version 1.4.1 (Terrestrial Residue Exposure model). United States Environmental Protection Agency. Environmental Fate and Effects

Division. http://www.epa.gov/oppefed1/models/terrestrial/index.htm#trexPage 43 of 43 

### APPENDIX E

– Justification Table for the Acute Honey Bee Vapor Exposure Study (MITC).

Guideline Number: N/A (Non

- Guideline Study) Study Title: Acute Honey Bee Vapor Exposure Study

Rationale for Requiring the Data Due to the fate properties of fumigants, in particular their high volatility, it is expected that honey bees and other insect pollinators will be exposed to fumigants in the vapor phase. Neither of the standard Tier I toxicity studies with honey bees ( i.e., acute contact or acute oral toxicity study for honey bees) account for exposure to vapor phase pesticides. Therefore, to assess risks of MITC (as a transformation product of dazomet) to bees, EFED recommends

the submission of a non

- guideline acute honey bee vapor exposure study for MITC, to be conducted in lieu of the normally required acute honey bee contact study that would fulfill guideline 850.3020 and the newly proposed requirements for oral toxicity tests including adult and larval honey bees. Practical Utility of the Data

How will the data be used? Data from an acute honey bee vapor exposure study will be used to determine the potential for MITC to affect non

target terrestrial invertebrates in the terrestrial environment. Of particular interest is quantification of a toxicity endpoint, i.e., a 4

- hou r LC 50 , that can be used to derive risk quotients. In the absence of vapor exposure data specific for honey bees, risk to terrestrial invertebrates, including listed species, will be assumed.

How could the data impact the Agency’s future decision

- making? If future ecological risk assessments are performed without these data, the Agency would have to presume risk to

non

- target terrestrial invertebrates, including honey bees, from use of dazomet. Therefore, use of dazomet and its formulated products may need to be restricted in areas where terrestrial invertebrates, including honey bees, could be exposed. The lack of these data will limit the flexibility the Agency and registrants have in mitigating potential

risks and could result in use restrictions for daz omet that are unnecessarily severe.