Page 2 of 43

1. Executive summary

The Environmental Fate and Effects Division (EFED) and the Antimicrobials 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 [(tetrahydro3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione) (PC Code 035602)]. The preliminary risk 

assessment will address the potential ecological risk from both dazomet and its primary 

degradate, methyl isothiocyanate (MITC). The problem formulation describes the methods

planned to be used during the completion of drinking water and ecological risk assessments and 

provides an overview 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 associated 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 early 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 of 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 

Respiration 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 treatment 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 updated 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 include a 2008 ecological risk assessment

conducted for the Reregistration Eligibility 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 fumigant activity by 

diffusing, either as a gas or volatile liquid, upward through the interstitial spaces in the soil and 
Page 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 transform 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 Review 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 pesticide applicators. This product is 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 crops, 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 rates of 259 to 520 lb 

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

allowed when mechanically incorporated; the lower rates are to be used when incorporating

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 of 

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 applications 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 Description

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 NS
Page 4 of 43

Use Site Application Method 

Type Description

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 ft2]

NS NS NS

SOIL MEDIA (e.g., potting soils, soil 

heaps, or compost piles)

Mechanically 

incorporate 0.68 lb a.i./yard3 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 nonagricultural uses, the available information indicate the following usage 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) (USEPA, 2012).

Antimicrobial uses involve three scenarios 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 minimal, 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 the 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 

dazomet, 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 were at high risk of mortality. Based on an LD50/ ft2 analysis, acute RQ values for dietary 

exposure (ingestion) of dazomet exceeded levels of concern (LOC) for birds and mammals that 

potentially could be exposed to granules. There was a potential for adverse reproductive effects 

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

available at the time of the RED. Modeling indicated no aquatic exposure to parent dazomet, 

however, there were uncertainties in estimating aquatic 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 greater 
Page 5 of 43

acute and/or longer-term risk from air residues. Inhalation toxicity data were not available for 

MITC and other taxa (including birds) at the time of the RED. No aquatic LOCs were exceeded, 

based on exposure to MITC, in the modeled pond. The estimated MITC surface water 

concentrations may have represented upper bound values because the rate of volatilization of 

MITC was not accounted for in the modeling. No LOCs were exceeded for aquatic plant 

exposure to MITC, based in part on supplemental data. 

3.1. Ecological Risk Assessments

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

for tomatoes and strawberries serve as a basis for this problem formulation. The 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 Degradates 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 were 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 waste water systems (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./acre. This application 

rate is equivalent to a dazomet application rate of 772.9 lbs lbs./acre, which is higher than the 

maximum label dazomet application rate of 520 lb a.i./acre. 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, the 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 treatments. 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 dazomet 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 Cancer (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 kg 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 of 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 al, 1991).
Page 7 of 43

3.3. Clean Water Act Programs

An Aquatic Life Ambient Water Quality Criteria document has not been published for dazomet 

(or MITC). Aquatic life benchmarks for MITC (but not dazomet) have been published and are 

listed in Table 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, 

no 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 250

C) in water and degrades very rapidly to 

MITC in soil and water. MITC has a high vapor pressure (19 mm Hg at 250

C) and a Henry’s 

Law Constant of 1.79 x 10-4 atm-m3

/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-2H-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 C5H10N2S2 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 Kow)

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 hours at pH 3, 5.8 hours at pH 5, 4.0 hours at pH 7, and 

5.4 hours at pH 9

Major Degradation products: MITC and carbon disulfide

459083-01,

414790-03 and 

421114-01

Aqueous photolysis halflives4.0 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-formylN-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 C2H3NS

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

Melting point 35 - 36°C Hartly (ed.) 1992
Page 9 of 43

Property Value Reference (MRID)

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

Octanol/water partition 

coefficient (log Kow) 0.98 MRID 435409-03

Henry’s law constant 1.79 x 10-4 (atm-m3

/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 (Kd) 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 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-life 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 condition under mid-summer at 40° N latitude. 

b. Degradation and Metabolism

Dazomet rapidly hydrolyzed (t1/2 < 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 identified 

methylamino(thioxo)methanesulfonic acid, methylamino(thioxo) methanesulfonic acid, [1,2,4] 

dithioazolidine-3-thione, N,N dimethylthiourea, and CO2. 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 (CO2, COS and CS2); 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 (t1/2 < 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). 

The 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, groundwater, 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 environmental fate laboratory studies. Its high 

solubility in water and low adsorption in soil (Kd of 0.26 L Kg-1) suggest that leaching to 

groundwater may be a potential transport pathway under flooded and saturated conditions;

however, 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 

for 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 (DT50 < 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, dazomet 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 posttreatment. 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 plastic cover).

A dissipation study of [2-

14C]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 the 
Page 11 of 43

radioactivity present in the soil, 3.62-4.91% 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 were 7.6 μg/g, 7.0 μg/g, 2.7 μg/g, and 0.4 μg/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 [14C]-CO2 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 

μg/L.

Along with terrestrial field dissipation 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 incorporated (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 applications ranged from 73-82% and 13-14% of applied dazomet, 

respectively. Volatilization of MITC and formaldhyde from mechanically incorporated 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-life 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 condition under mid-summer at 40° N latitude. 

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 (Table5). The calculated Henry's Law 

constant of MITC is 1.79 x 10-4 atm-m3

/mol. A Henry's Law constant in the range of 10-5 to 10-3

atm-m3/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 compound (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 105 μg/m3 and volatility rate of 16.9 μg/cm2/hr 

at 50% field capacity (FC) and 100 ml/minute air flow to a concentration of 2.8 x 105 μg/m3 and 

volatility of 24.9 μg/cm2/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) indicate 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 volatilizes into the atmosphere, it undergoes direct photolysis. Geddes et al. (1995) 

estimated the half-life 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, Nmethylthioformamide, 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 exposure 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 dominated 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 information 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 pesticidal 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 radiolabeled MITC hydrolyzes 

[t1/2 < 21 days in buffer solutions (Accession No. 257305)]. The only hydrolytic product at pH 5 

and pH 7 was CH3NH3OH. Hydrolytic products in pH 9 buffer solution were S=C(CH3NH)2

(dimethylthiourea) and CH3NH2 (methylamine). MITC 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). Minor 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, potential 

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. 

Terrestrial 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 spray drift is not 

expected); however, terrestrial plants may be exposed off-site to MITC as a vapor or via runoff. 

Therefore, for terrestrial animals, toxicity data for both dazomet and MITC will be considered. 

For terrestrial plants, toxicity data for MITC [vegetative vigor (vapor exposure) and seedling 

emergence (water/vapor exposure)] will be used 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 and chronic ecological effects of 

dazomet (terrestrial organisms) and MITC (aquatic and terrestrial organisms). 

5.1. Effects to Aquatic Organisms

Table 6. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for MITC

(Transformation Product of Dazomet)

Taxonomic 

Group

Study 

Type Surrogate Species Toxicity Value MRID and Classification

Acute 

Toxicity 

Classification

Freshwater fish1

Acute

Rainbow Trout

(Oncorhynchus 

mykiss)

LC50 = 94 μg 

a.i./L

(slope = N/A)

42058002 

Acceptable

Very highly 

toxic

LC50 = 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 

LifeStage)

No data available

Freshwater 

invertebrates

Acute Water Flea 

(Daphnia magna)

EC50 = 55 μg 

a.i/L 

(slope not 

available)

41819302

Acceptable

Very highly 

toxic

Chronic Water Flea 

NOAEC = 25 

μg a.i./L

LOAEC = 50 

μg 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/A
Page 14 of 43

Taxonomic 

Group

Study 

Type Surrogate Species Toxicity Value MRID and Classification

Acute 

Toxicity 

Classification

Estuarine/marine 

fish Acute

Sheepshead Minnow 

(Cyprinodon 

variegatus)

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 EC50

(frond number) 

= 0.59 mg a.i/L 

NOAEC (frond 

number and 

growth rate) = 

0.09 mg a.i/L

45919421 Acceptable

Nonvascular2

Freshwater Algae 

(Scenedesmus 

subspicatus)

96-hour EC50 

(cell density) = 

0.2 mg a.i/L 

NOAEC = 0.13 

mg a.i/L

44588903

Supplemental 

(nonguideline 

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 Dazomet 

(Oral Exposure) and Its 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

Birds1

Dazomet

Acute

Bobwhite quail

(Colinus 

virginianus)

LD50 = 424 mg

a.i./kg-bw 42365101 Acceptable

Sub-acute 

dietary

Bobwhite quail

(Colinus 

virginianus)

LC50 = 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 review
Page 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)

LD50 = 415 mg

a.i./kg-bw 00132468 Acceptable

Chronic

Laboratory rat 

(Rattus 

norvegicus)

NOAEC = 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 LC50 = 

0.54 mg a.i/L 42365605 Acceptable

Insects

Dazomet

Acute 

contact

Honey bee 

(Apis mellifera 

L.)

LD50 = >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 below); 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 involved 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 of 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 BASAMID (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 incorporated). Dazomet is expected to rapidly 

degrade in aquatic and terrestrial environments to form MITC, whose dissipation is 

predominately dependent on volatilization, and degradation, to a lesser extent. Any 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 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). 

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

effluent containing 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 ecological concern for terrestrial animals 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 terrestrial 

invertebrates is possible for terrestrial animals, the main route of exposure to terrestrial animals 

to MITC is expected to be through inhalation. For birds, based on MITC’s vapor pressure and 

calculations using STIR, the maximum 1-hour vapor inhalation 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 exposure 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, this 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 doses 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 did not 

achieve a definitive toxicity 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 LD50 of 55 mg 

a.i/kg bw vs. acute inhalation LD50 = 0.80 mg/L (converted from an LC50 of <0.0296 mg/L)]. 

Therefore, any 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 contaminated 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 it hydrolizes rapidly to MITC. 

The primary route of exposure to non-target terrestrial 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 dominant 

exposure pathways for fumigants, the fumigant 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, water, 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), sorption 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 

Drainage
Page 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 will 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 20oC 2.8 X 10-6 mm Hg

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

Hydrolysis Half-Life (pH 7) 0.18 Days

(0.17 and 0.18 days)

(Calculated 90th Percentile)

MRID#s 4211140-01 and 

459083-01 

Aerobic Soil Metabolism t1⁄2, 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 (Koc) 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 will be calculated according to molar ratio of 

MITC to dazomet. One 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/acre at 530 lbs/acre application rate for dazomet. Environmental 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 @ 25oC 19 mm Hg CDPR, 2002

Water Solubility @ pH 7.0 and 25oC 7600 mg L-1 Product Chemistry
Page 20 of 43

Parameters Values Sources

Vapor Phase Diffusion Coefficient (DAIR) 8227 cm2 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 t1⁄2, 9.61 Days

(5.4 - 20.2 days)

(3.3-9.9 days)

(Calculated 90th 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 Days CDPR, 2002

Soil Water Partition Coefficient 0.26 L Kg-1 (Mean Kd) 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 is expected to degrade

faster at higher temperatures, having a shorter 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). With a higher volatilization rate from the cooling water system 

and the amounts of dazomet and or MITC, reaching a wastewater stream would be low.

Treatment of Paper and Pulp

A possibility 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 spent 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 photolysis, 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 photodegrades 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 expected
Page 21 of 43

to be quite low in wastewater streams and may not pose any risks to nontarget aquatic organisms

(this 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 used to determine the potential for aquatic organisms downstream of the industrial 

wastewater treatment plants that receive discharges from the antimicrobial uses of dazomet and

its major degradate MITC. Dazomet is used in industrial water systems such as 

commercial/industrial cooling water, industrial wastewater, 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 aquatic 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 discharge 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. The 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 LD50/ft2 analysis in the 

T-REX model will be used (for details, see: 

http://www.epa.gov/oppefed1/models/terrestrial/index.htm#trex). In the absence of available 

data to inform on the potential exposure concentrations to terrestrial organisms, it will be 

assumed that 100% of the applied dazomet will be bioavailable before off-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 considers 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 conditions, will be used to refine the potential exposure values for animals and 

plants (vegetative vigor). 

For exposure to plants via runoff (seedling emergence), TerrPlant will be used. The application 

rate of MITC will 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, 2007c), 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 provide insight into the direct and 

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

chemicals and from changes in structure and functional characteristics of the affected 

communities.

7.4. Endangered Species Assessments

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. These assessments 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. Environmental Fate

Table 10 and Table 11 identify environmental fate 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 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 Acceptable 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

43596201 Acceptable No

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

42569201 Acceptable 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 WaterSmall Scale 

Prospective 

44641601 Supplemental No
Page 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

46084701 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 soil.

835.1410 Volatility –

laboratory

(None) N/A No

835.6100 Terrestrial field 

dissipation

(None) N/A No

Analytical 

method in soil

(None) N/A

835.8100

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 studies were conducted with dazomet as the test substance. MITC flux is measured in all 

field volatility studies.

8.2. Effects

Tables 12 and 13 identify 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. Rationales for the additional data requested are

presented 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 previously). Tables 12 and 13 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 a 
Page 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 inadequate 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 risks 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 Ecological Effects Data 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 species. 

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 because 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 Ecological Effects Data 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)

NonguidelineAvian 

inhalation

48788401 Under review Yes Depending on the results of the 

review of the recently submitted 

study.

NonguidelineHoney 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 

plant toxicity:

Tier II 

vegetative 

vigor

49058001 Under review Yes Depending on the results of the 

review of the recently submitted 

study.

Table 14. Submitted Aquatic Ecological Effects Data 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 

cannot 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 

growth:

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 review
Page 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 14, the data are 

needed to fully assess dazomet. Upon review, if any of these studies are found to be 

scientifically invalid or supplemental (and not adequate for use in risk assessment), 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 recommends 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 bee acute 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 using 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 half-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 sufficiently for a 48-hr acute contact study and 

could be informative for understanding risks to subterranean invertebrates, such as groundnesting bees, for which the honey bee would be a surrogate.

AMVAC recently requested further consideration for waiving the bee contact study (Habig 

2012). AMVAC concluded:
Page 30 of 43

“...(A)ny exposure of pollinators or other terrestrial invertebrates to MITC will be to 

MITC in the form of a gas. The OPPTS honeybee acute toxicity testing guideline 

(OPPTS 850.3020) indicates that honeybee acute contact toxicity testing is generally not 

required for substances that are a gas, a highly volatile liquid, reactive solid, or a

corrosive material. MITC clearly meets these criteria for waiver; it is a highly volatile if 

present as a liquid, and all potential exposure to MITC under normal use conditions 

would be to MITC gas). MITC is also corrosive in mammalian eye and skin irritation 

testing, and based on its properties and mode of action, would be expected to be corrosive

to bees.” (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 bee contact study be waived for MITC. However, because an understanding of 

potential risks to terrestrial invertebrates, including honey bees, will be important for 

understanding the 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 the 

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 previously recommended waiving a terrestrial plant study for seedling emergence (see 

USEPA 2012, D395875). Upon 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 in aquatic systems, preliminary aquatic exposure modeling (using 

PRZM/EXAMS) indicates that MITC may remain at concentrations of toxicity concern for 

several 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 not 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 invertebrate data Therefore, EFED recommends requesting an 

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

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

does not recommend requesting chronic toxicity data for estuarine/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 CH3NC in the photolysis of 

CH3NCS. Science263: 205-207.

Cremlyn, R.J. 1991. Agrochemicals: Preparation and Mode of Action. p. 283-307. 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.

Dungan, 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.htm
Page 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/reregistration/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/oppefed1/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 Environmental 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, North 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 metamsodium 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 Studies. Environmental Fate and effects Division, Office of Pesticide 

Programs, United States Environmental Protection Agency. Washington, 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, 2012.
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-2H-1,3,5-thiadiazine-2-thione

CAS No: 533-74-4

Unlabeled 

[2-

14C] thiadizine label

* Position of the radiolabel.

N N

S S

H3C CH3

N N

S S

H3C CH3

*
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

Sn-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

NCH3

H
Page 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

OH

S

N

H

HO SH

S

N

H

S

SH

S
Page 36 of 43

S C S

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

H3C

C S

S C S

S

S NH

S
Page 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

H3C NH2

H2C O

C14 CO2
Page 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 25oC; mg/L) 8610

Mammalian LD50 (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 LD50 (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 

precluded
Page 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 "escaping 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/m3

-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 (ZS) and earthworms (ZE) (Equations 2 and 3, 

respectively) require several chemical-specific parameters and assumptions of system 

temperature (25oC) 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 estimation 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.

Equation 1. C = Z *F

H

K

Equation Z d S

S

* ρ 2. =

H

L K

Equation Z OW

E

*

3. =

OW

water

oc ol K

Z

Z

Equation = tan 4.















 =

S

E

E S Z

Z

Equation 5. C C *
Page 41 of 43

Symbol Definition Units

CE Chemical concentration in earthworm tissue mol/m3

CE' Chemical concentration in earthworm tissue g/kg

CS Chemical concentration in soil mol/m3

H Henry’s Law constant m3-Pa/mol

Kd Soil partitioning coefficient cm3/g

KOW Octanol to water partition coefficient none

L Lipid fraction of earthworm none

MW molecular weight of chemical g/mol

ZE Fugacity capacity of pesticide in earthworms mol/m3-Pa

ZS Fugacity capacity of pesticide in soil mol/m3-Pa

ρE density of earthworm kg/m3

ρS Bulk density of soil g/cm3

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.

CS 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 consistent with the value input into PRZM. ρS is dependant upon the soil properties of 

the selected PRZM scenario used to derive CS. L is based on the lipid content of earthworms, 

which was assumed to be 0.01 (Cobb et al. 1995). The resulting CE value is in units of mol/m3

. 

This value is converted to units of g/kg using equation 7. The density of the earthworm (ρE) is 

assumed to be 1000 kg/m3 (equivalent to density of water). 

d s

S ow

E K

C L K

Equation C

* ρ

* *

6. =

E

E

E

C MW Equation C

ρ

*

7. ' =
Page 42 of 43

Comparison of STIR and Earthworm Fugacity Modeling Results for a Variety of 

Fumigants and Mammals and Birds.

Parameter Telone Methyl 

Bromide

DMDS MITC Chloropicrin

Application Rate (lbs. a.i./A) 628.49 400 455 219.41 350

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) 0.7212 0.1823 0.641 0.260 0.3612

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/m3) 2.05 x 105 8.28 x 106 1.14 x 105 6.3 x 104 2.11 x 105

STIR Mammal Inhaled Dose (mg/kg) 3.24 x 104 1.31 x 106 1.80 x 104 9.95 x 103 3.33 x 104

STIR Avian Inhaled Dose (mg/kg) 2.57 x 104 1.04 x 106 1.43 x 104 7.91 x 103 2.65 x 104

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#trex
Page 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 nontarget terrestrial invertebrates in the terrestrial environment. Of particular interest is quantification of a toxicity 

endpoint, i.e., a 4-hour LC50, 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 dazomet that are unnecessarily severe.