Dazomet_WSM_Documentation_SERA_TR-056-11-01-03a.pdf

SERA TR-056-11-01-03a

Dazomet Soil Incorporation:

WorksheetMaker Workbook Documentation

Final Report

Submitted to:

Dr. Harold Thistle

USDA Forest Service Forest Health Technology Enterprise Team

180 Canfield St.

Morgantown, WV 26505 Email: hthistle@fs.fed.us

USDA Forest Service Contract: AG-3187-C-12-0009 USDA Forest Order Number: AG-3187-D-14-0146

SERA Internal Task No. 56-11

Submitted by:

Patrick R. Durkin

Syracuse Environmental Research Associates, Inc.

8125 Solomon Seal

Manlius, New York 13104

E-Mail: SERA_INC@msn.com Home Page: www.sera-inc.com

November 19, 2014 mailto:hthistle@fs.fed.us http://www.sera-inc.com/ ii

Table of Contents

LIST OF TABLES ......................................................................................................................... iii ACRONYMS, ABBREVIATIONS, AND SYMBOLS ................................................................ iv

1. INTRODUCTION

1.1. General Information

1.2. Chemical Specific Information

2. CHEMICAL/PHYSICAL PROPERTIES

3. HUMAN HEALTH

3.1. Hazard Identification

3.2. Exposure Assessment

3.2.1. Workers

3.2.1.1. Applications (Dazomet)

3.2.1.2. Inhalation (Methyl Isothiocyanate)

3.2.2. General Public

3.2.2.1. Surface Water (Methyl Isothiocyanate)

3.2.2.1.1. Expected Concentrations

3.2.2.1.2. Accidental Spill

3.2.2.2. Inhalation

3.3. Dose-Response Assessment

3.3.1. Dazomet

3.3.2. Methyl Isothiocyanate (MITC)

3.3.2.1. Oral Toxicity Values

3.3.3.2. Inhalation Toxicity Values

3.4. Risk Characterization

3.4.1. Workers

3.4.1.1. Applications (Dazomet)

3.4.1.2. Inhalation (Methyl Isothiocyanate)

3.4.2. General Public

3.4.2.1. Surface Water

3.4.2.2. Inhalation

4. ECOLOGICAL EFFECTS

4.1. Hazard Identification

4.2. Exposure Assessment

4.2.1. Oral

4.2.1.1. Dazomet

4.2.1.1. Methyl Isothiocyanate

4.2.2 Inhalation

iii

4.3. Dose-Response Assessment

4.3.1. Terrestrial Organisms

4.3.1.1. Mammals

4.3.1.1.1. Dazomet

4.3.1.1.2. Methyl Isothiocyanate

4.3.1.2. Birds

4.3.1.2.1. Dazomet

4.3.1.2.2. Methyl Isothiocyanate

4.3.1.3. Other Terrestrial Organisms

4.3.2. Aquatic Organisms

4.3.2.1 Fish

4.3.2.2. Aquatic Invertebrates

4.3.2.3. Aquatic Plants

4.3.2.3.1. Algae

4.3.2.3.2. Aquatic Macrophytes

4.3.2.4. Other Aquatic Organisms

4.4. Risk Characterization

4.4.1. Terrestrial Organisms

4.4.1.1. Mammals

4.4.1.2. Birds

4.4.1.4. Other Organisms and Indirect Effects

4.4.2. Aquatic Organisms

5. REFERENCES

5.1. Chemical Specific References

5.2. Standard Reference

LIST OF TABLES

Table 1: Chemical and Physical Properties Table 2: Summary of toxicity values used in human health risk assessment Table 3: Summary of toxicity values used in ERA iv

ACRONYMS, ABBREVIATIONS, AND SYMBOLS

ACGIH American Conference of Governmental Industrial Hygienists ADI Acceptable Daily Intake AEL adverse-effect level a.e. acid equivalent a.i. active ingredient a.k.a. also known as a.s. active substance AOEL acceptable occupational exposure limit APHIS Animal and Plant Health Inspection Service ATSDR Agency for Toxic Substances and Disease Registry ASAE American Society of Agricultural Engineers BCF bioconcentration factor bw body weight calc calculated value CBI confidential business information CI confidence interval cm centimeter CNS central nervous system COC crop oil concentrates DAA days after application DAT days after treatment DER data evaluation record d.f. degrees of freedom EC emulsifiable concentrate ECx concentration causing X% inhibition of a process EC25 concentration causing 25% inhibition of a process EC50 concentration causing 50% inhibition of a process ECOTOX ECOTOXicology (database used by U.S. EPA/OPP) EFED Environmental Fate and Effects Division (U.S. EPA/OPP) ERA ecological risk assessment ExToxNet Extension Toxicology Network F female FH Forest Health FIFRA Federal Insecticide, Fungicide and Rodenticide Act FQPA Food Quality Protection Act g gram GLP Good Laboratory Practices ha hectare HED Health Effects Division (U.S. EPA/OPP) HHRA human health risk assessment HIARC Hazard Identification and Assessment Review Committee (part of U.S. EPA/OPP/HED) HQ hazard quotient HRAC Herbicide Resistance Action Committee IARC International Agency for Research on Cancer IRED Interim Reregistration Eligibility Decision v

IRIS Integrated Risk Information System ka absorption coefficient ke elimination coefficient kg kilogram Ko/c organic carbon partition coefficient Ko/w octanol-water partition coefficient Kp skin permeability coefficient L liter lb pound LC50 lethal concentration, 50% kill LD50 lethal dose, 50% kill LOAEL lowest-observed-adverse-effect level LOC level of concern LR50 50% lethal response [EFSA/European term] m meter M male mg milligram mg/kg/day milligrams of agent per kilogram of body weight per day mL milliliter mM millimole mPa millipascal, (0.001 Pa) MITC methyl isothiocyanate MOS margin of safety MRID Master Record Identification Number MSDS material safety data sheet MSO methylated seed oil MW molecular weight NOAEL no-observed-adverse-effect level NOEC no-observed-effect concentration NOEL no-observed-effect level NOS not otherwise specified N.R. not reported OPP Office of Pesticide Programs ppm parts per million RED re-registration eligibility decision RfD reference dose SERA Syracuse Environmental Research Associates T.G.I.A. Technical grade active ingredient UF uncertainty factor U.S. United States USDA U.S. Department of Agriculture U.S. EPA U.S. Environmental Protection Agency USGS U.S. Geological Survey WHO World Health Organization

1. INTRODUCTION 1

1.1. General Information 2

This document supports the development of a WorksheetMaker EXCEL workbook for the 3 subject pesticides. As detailed in SERA (2011a), WorksheetMaker is a utility that automates the 4 generation of EXCEL workbooks that accompany Forest Service risk assessments, and these 5 EXCEL workbooks are typically generated in the development of Forest Service risk 6 assessments (SERA 2014). 7 The development of full Forest Service risk assessments, however, is resource intensive. For 9 some pesticides that are used in only relatively small amounts and/or only in few locations, the 10 development of full Forest Service risk assessments is not feasible. Nonetheless, the Forest 11 Service may be required to develop risk analyses supported by WorksheetMaker EXCEL 12 workbooks. To meet this need, an MS Word utility was developed to facilitate the addition of 13 pesticides and pesticide formulations into the Microsoft Access database used by 14 WorksheetMaker (SERA 2011b). With this addition, WorksheetMaker can be used to generate 15 EXCEL workbooks typical of those that accompany Forest Service risk assessments. 16 The current document is designed to serve as documentation for the application of this general 18 method for the pesticide discussed in Section 1.2. The major difference between this approach to 19 using WorksheetMaker and the typical use of WorksheetMaker in the development of Forest 20 Service risk assessments involves the level of documentation and the sources used in developing 21 the documentation. While standard Forest Service risk assessments involve a relatively detailed 22 review and evaluation of the open literature and publically available documents from the U.S. 23 EPA, as discussed further in Section 1.2, the current assessment relies primarily on secondary 24 sources with minimal independent evaluation of the data. 25

1.2. Chemical Specific Information 26

The current document concerns dazomet. Most of the information on dazomet was identified at 27 the U.S. EPA’s Pesticide Chemical Search website 28 (http://iaspub.epa.gov/apex/pesticides/f?p=CHEMICALSEARCH:1:5025550978400::NO:1::) 29 using the search term “Dazomet”. Files cited in the current document were obtained from the 30 Regulatory Actions and Science Reviews tabs on this web site. Dazomet is not included in the 31 U.S. EPA’s Agency-wide IRIS (Integrated Risk Information System) database 32 (http://www.epa.gov/IRIS/). 33 Dazomet is a non-selective soil fumigant which can be used to kill fungi, vegetation, and soil 35 nematodes. As a soil fumigant, dazomet is somewhat atypical in that it is applied to soil as a dry 36 granular formulation then incorporated into soil. The current version of WorksheetMaker does 37 not accommodate soil fumigants and does not encompass inhalation exposures (SERA 2011a). 38 Consequently, rather than adding dazomet to the database for WorksheetMaker, this document 39 supports a highly customized EXCEL workbook that is consistent with the conventions used in 40 WorksheetMaker. 41 Also because soil fumigants are not explicitly covered in the methods document for preparing 43 Forest Service risk assessments (SERA 2014), the current document is somewhat more elaborate 44 than a simple documentation for WorksheetMaker inputs values. 45 http://iaspub.epa.gov/apex/pesticides/f?p=CHEMICALSEARCH:1:5025550978400::NO:1 http://www.epa.gov/IRIS/

2. CHEMICAL/PHYSICAL PROPERTIES 2

Dazomet was initially registered in the United States in 1967 and was reregistered in 2008 with 3 an amended registration in 2009 (U.S. EPA/OPP 2008a,b, 2009). The U.S. EPA registration 4 review program operates on a 15-year cycle. Dazomet is currently under registration review and 5 the EPA has identified several data needs for dazomet (U.S. EPA/OPP 2014). The data needs 6 are also discussed in the most recent EPA risk assessment of dazomet (U.S. EPA/OPP/EFED 7 2008, pp. 7-9). The registration review for dazomet is not scheduled for completion until 2019 8 (U.S. EPA/OPP 2014). Thus, the registration review process will not contribute to the current 9 summary of information on dazomet. 10 The Forest Service has specified the use of a single formulation, Basamid, presumably referring 12 to Basamid G. The Forest Service has also indicated that the application rate would be 350 13 lbs/acre (presumably as the formulation) and that up to 40 acres could be treated for a total 14 annual use of 14,000 lbs formulation. Applications would be made in September. Since 15 Basamid G consists of 99% dazomet (AMVAC Chemical Corporation 2011; Certis USA ND), 16 the distinction between application rates in units of formulation versus a.i. is incidental. 17 Based on an April 29, 2014 posting from AMCAC Chemical Corporation, Basamid G is 19 exclusively distributed by AMVAC Chemical Corporation, a subsidiary of American Vanguard 20 Corporation (http://www.amvac-chemical.com/News-Media/Press-Releases/2014-Press-21 Releases/April-29-2014-Press-Release). The product label (undated) at the AMVAC website, 22 however, indicates CERTIS USA as the distributer. The most recent product label (December 23 27, 2011) at the EPA label website (http://iaspub.epa.gov/apex/pesticides/f?p=PPLS:1) lists 24 AMVAC as the manufacturer (U.S. EPA/OPP 2011). The transfer information at the EPA label 25 website (http://iaspub.epa.gov/apex/pesticides/f?p=PPLS:8:17199968499318::NO::P8_PUID:19059) 26 indicates that registration for Basamid G was transferred to BASF on February 20, 2004 and then 27 transferred to CERTIS on December 21, 2010. The current registrant is listed as AMVAC 28 Chemical Corporation. The earliest label at the EPA website (April 11, 1991) identifies BASF 29 as the original registrant. Kegley et al. (2014) indicate that many additional formulations of 30 dazomet are available (i.e., 616 active formulations in the United States). Nevertheless, U.S. 31 EPA/OPP/EFED (2008a, p. 23) indicates that only 20 end-use formulations of dazomet are 32 currently registered. 33 Table 1 summarizes the chemical and physical properties of dazomet. In terms of potential risks 35 in the use of dazomet, the dominant factor is the rapid conversion of dazomet to methyl 36 isothiocyanate. As discussed in the most recent EPA risk assessment on dazomet (U.S. 37 EPA/OPP/EFED 2008a) and summarized in Table 1, dazomet is rapidly converted to methyl 38 isothiocyanate primarily by hydrolysis—i.e., hydrolysis half-lives of 3 to 9 hours in water and a 39 soil hydrolysis half-time of 17.2 hours. As discussed further in Section 3.2.1.1, soil 40 incorporation of dazomet must be followed by irrigation to facilitate the hydrolysis of dazomet to 41 methyl isothiocyanate. Methyl isothiocyanate forms a vapor which serves as the active soil 42 fumigant. Methyl isothiocyanate is much more persistent than dazomet—e.g., the dissipation 43 half-lives are about 1.5 to 2 days for dazomet and about 10 days for methyl isothiocyanate. In 44 addition, as discussed further in Section 3, methyl isothiocyanate is more toxic than dazomet. 45 http://www.amvac-chemical.com/News-Media/Press-Releases/2014-Press-Releases/April-29-2014-Press-Release http://www.amvac-chemical.com/News-Media/Press-Releases/2014-Press-Releases/April-29-2014-Press-Release http://iaspub.epa.gov/apex/pesticides/f?p=PPLS:1 http://iaspub.epa.gov/apex/pesticides/f?p=PPLS:8:17199968499318::NO::P8_PUID:19059

Consequently, methyl isothiocyanate is the agent of concern for most exposure scenarios 1 following applications of dazomet. 2

3. HUMAN HEALTH 4

3.1. Hazard Identification 5

While full Forest Service risk assessments provide a detailed discussion of the available toxicity 6 data on the pesticide under consideration, this approach is not taken in the current document, in 7 the interest of economy. A reasonably complete discussion of the toxicity data on dazomet and 8 methyl isothiocyanate is provided in U.S. EPA/OPP/HED (2009a). As discussed in U.S. 9 EPA/OPP/HED (2009a, p. 13), the toxicity database on dazomet is reasonably complete; 10 however, the same is not true for methyl isothiocyanate, the major breakdown product of 11 dazomet. Furthermore, the mode of action of methyl isothiocyanate is not well characterized. 12 Additional details of the data needs for dazomet and methyl isothiocyanate are discussed in the 13 EPA’s final work plan for the registration review of dazomet (U.S. EPA/OPP 2014). 14

3.2. Exposure Assessment 15

3.2.1. Workers 16

3.2.1.1. Applications (Dazomet) 17

Dazomet, formulated as Basamid G, is applied by soil incorporation, as specified on the product 18 label. A description of the methods used to apply Basamid G at the Forest Service JH Stone 19 Nursery was provided by John Justin (Forest Service Nursery Manager): 20

Currently we are fumigating about 30 acres annually with Dazomet. If our 22 business grows like I hope this could increase to 40 acres annually. The annual 23 acreage would decrease by as much as 10 acres annually if we add some 24 additional herbicides for use in our grass crops through this NEPA effort. We 25 can fumigate a maximum of ten acres per 8 hour day. 26 Fumigation is a complicated process involving at least five staff members. One 28 person is applying the Dazomet with a drop spreader. A second staff member 29 immediately follows behind tilling the fumigant into the soil. A third staff 30 member follows immediately behind the tiller with a roller that compacts the soil 31 to seal the fumigant into the soil. Two or more staff members are irrigating the 32 fields as soon as the other work is done. The fumigated acres are irrigated 33 multiple times a day for at least five days after the chemical application. After 34 five days the fields are dried and then tilled again to release any remaining 35 fumigant gas. All these steps are outline in detail on the label and we follow the 36 label exactly. 37 Last year it took us a week to do 30 acres. All staff are wearing the full PPE 39 required by the label during all work activities and entries into the fields. We 40 also have the equipment to monitor fumigant gas levels in the air. This 41 monitoring allows us to determine safety levels for our staff. All fumigated areas, 42 including the appropriate buffer zones, are closed to all access except trained 1 handlers until the fields are tilled to release the fumigant. 2

Based on the above input and as detailed in Worksheet A01 of the EXCEL workbook that 4 accompanies the current document, the exposure assessment is based on a treatment rate of 10 5 acres per day, an application rate of 350 lbs/acre (Section 1.2), and a field size of 40 acres. 6 These three inputs can be modified in Worksheet A01. As with WorksheetMaker workbooks, 7 changes made in Worksheet A01 are then applied to all calculations in the workbook. 8 The occupation exposure rates for pesticides typically used in Forest Service risk assessments 10 (SERA 2013) do not include rates for soil incorporation of a granular formulation such as 11 Basamid G. As an alternative, the current assessment adopts the exposure assessment from U.S. 12 EPA/OPP/HED (2009a, pp. 75-76). This exposure assessment is based on exposure rates for 13 granular a formulation from the Pesticide Handlers Exposure Databased (PHED). As detailed in 14 SERA (2014, Section 3.2.2), PHED is a deposition based method for estimating occupational 15 exposures based on exposure rates in units of mg agent per lb a.i. handled. Somewhat atypically, 16 the EPA exposure assessment (U.S. EPA/OPP/HED 2009a) does not explicitly provide exposure 17 rates in terms of mg agent per lb a.i. handled. Instead, the EPA analysis presents Margins of 18 Exposure (MOE) associated with applications at different application rates and field sizes. By 19 definition, the MOE is the exposure divided by a NOAEL. Thus, the underlying exposure rate 20 (ER in units of mg/kg bw per lb handled) can be estimated as: 21 mg kg bw mg kg per lbhandled lbhandled

NOAEL

ER Amt

MOE

= ÷ (1) 23 where Tox is the toxicity value in units of mg/kg bw, MOE is the margin of exposure, and Amt 25 is the amount handled by the worker expressed in units of pounds. 26 The above method is implemented in Worksheet C01. For calculating the exposure rate, the 28 toxicity value is taken as 1.5 mg/kg bw, which is the animal NOAEL used for occupational 29 exposures to dazomet, as discussed in Section 3.3.17. The EPA analysis gives sets of four MOE 30 baseline exposures: no PPE, gloves, gloves and double layer clothing, and engineering controls. 31 While not explicitly noted in U.S. EPA/OPP/HED (2009a), the term engineering controls 32 appears to refer to NIOSH certified full facepiece air-purifying respirators which are required on 33 the product label (Certis USA ND) for workers handling Basamid G. For calculating the 34 exposure rate, the MOEs for applications to a 40-acre field and an application rate of 530 35 lbs/acre—i.e., at total of 21,200 lbs handled—are used to minimize rounding errors in calculating 36 the exposure rates. Note that the 530 lbs/acre is the application rate used by U.S. 37 EPA/OPP/HED (2009a, p. 75) to derive the MOEs. In Worksheet C01, this application rate is 38 adjusted to the application rate of 350 lbs/acre that will be used by the Forest Service. 39 As summarized in Worksheet C01, the worker exposures associated with an application rate of 41 350 lb/acre with 10 acres treated per day range from about 0.0004 mg/kg bw/day (engineering 42 controls) to 0.02 mg/kg bw/day (baseline). 43

It should be noted that these occupational exposures apply to dazomet rather than methyl 1 isothiocyanate. As discussed in U.S. EPA/OPP/HED (2009a, p. 75), these exposures will be 2 predominantly dermal and will occur prior to the generation of significant amounts of methyl 3 isothiocyanate. 4

3.2.1.2. Inhalation (Methyl Isothiocyanate) 5

As discussed in Section 2, dazomet is rapidly converted to methyl isothiocyanate in soil, and 6 methyl isothiocyanate is primary toxic agent of concern. As summarized in Table 1 and 7 discussed in various U.S. EPA risk assessments, inhalation is the major route of exposure to 8 methyl isothiocyanate (U.S. EPA/OPP 2008a,b; U.S. EPA/OPP/EFED 2008a; U.S. 9 EPA/OPP/HED 2009a). 10 Workers as well as members of the general public could be exposed to methyl isothiocyanate as 12 this agent volatilizes from soil. The current screening level analysis adopts the exposure 13 assessments from U.S. EPA/OPP/EFED (2008a, p. 37 ff.) using the Industrial Source Complex 14 Short Term (ISCST3) model for a 40-acre field and an application rate of 530 lbs/acre at various 15 wind speeds, distances downwind, and levels of atmospheric stability. Note that the 530 lbs/acre 16 is the application rate used in the EPA modeling rather than the 350 lbs/acre that the Forest 17 Service proposed to use. While not explicitly discussed in U.S. EPA/OPP/EFED (2008a), the 18 atmospheric stability categories appear to be Pasquill Stability Classes which range from 19 extremely unstable (Class A) to moderately stable (Class F) (e.g., 20 https://ready.arl.noaa.gov/READYpgclass.php). As detailed in U.S. EPA/OAQPS (1995) the 21 Industrial Source Complex model is a deterministic dispersion model which can be used to 22 estimate peak/short term concentrations in air (using ISCST3) or longer-term concentrations in 23 air (using ISCLT3). U.S. EPA/OPP/EFED (2008a) estimates only short-term concentrations. 24 The estimated concentrations of methyl isothiocyanate in air from U.S. EPA/OPP/EFED (2008a, 26

p. 105-106) are summarized in the upper section of Worksheet C02. The lower section of 27 Worksheet C02 normalizes the concentrations based on the values entered in Worksheet A01 for 28 the application rate used by the Forest Service and the size of the treated field. For the current 29 analysis, these values are taken as 350 lb/acre to a 40-acre field. As summarized in Worksheet 30 C02, the modelled concentrations range from 6.83 to about 2770 µg/m3

. 31 For the sake of completeness, it is noted that U.S. EPA/OPP/HED (2010a) also uses the 33 Probabilistic Exposure and Risk model for FUMigants (PERFUM) (Reiss and Griffin 2008). As 34 the name indicates, this is a probabilistic rather than deterministic model. The application of the 35 probabilistic method is beyond the scope of the current limited assessment. 36 In addition to dispersion modelling, U.S. EPA/OPP/HED (2009, p. 69, Table 6.1.4.1) 38 summarizes concentrations of methyl isothiocyanate monitored in California from areas 39 characterized as “high use”. These monitoring data, as reported by EPA, are reproduced in 40 Worksheet B05, and statistics (mean, minimum, and maximum) are summarized in Worksheet 41 E02b of the EXCEL workbook that accompanies this document. As indicated in Worksheet 42 B05, the monitoring data are reported as both maximum and mean concentrations. 43 For risk characterization, U.S. EPA/OPP/HED (2009, p. 69, Table 6.1.4.1) uses the maximum 44 concentrations to characterize acute risks and the mean concentrations to characterize both short-45 https://ready.arl.noaa.gov/READYpgclass.php term and intermediate-term risks. As detailed further in Section 3.4, the same approach is used 1 in the current analysis. 2 As indicated in Worksheet B05, the EPA reports the monitoring data as ppm (v/v). As discussed 4 in Section 3.2.2.2, the toxicity data are expressed in units of µg/m3. For all of the analyses in the 5 current document, units of ppm (v/v) are converted to µg/m3 using the following equation: 6

3 24.1 // ( / ) 1000 /L moleg m ppm v v g mg

MW

m m= × × (2) 8

Details of this conversion are given in Drager Safety AG (2011). It should be noted that the 10 constant of 24.1 L/mole is the molar volume of an ideal gas at 20°C or about 68°F. Differing 11 temperatures will require the use of different constants for the molar volume; however, these 12 differences do not have a substantial impact on the conversions. Specifically, the molar volume 13 of a gas is defined (using the Ideal Gas Law) as: 14

KRTV

P

= (3) 16 where R is the universal gas constant (0.08207 L atm/K mol), TK is the temperature in Kelvin 18 units (0 °C = 273.15° K), and P is the barometric pressure in units of atmosphers (1 atm = 760 19 mm Hg). The above equation is simply a rearrangement of the Ideal Gas Law (PV=nRt) where 20 the number of moles (n) is set to 1 (e.g., http://authors.library.caltech.edu/25050/4/Chapter_03.pdf ). 21 As summarized in Worksheet E02b, the maximum peak concentrations are about 8.5 (0.19-45) 23 µg/m3 and the longer-term average concentrations are about 4.7 (0.03-23) µg/m3. These 24 concentrations are in the lower range of the concentrations modeled using ISCST3 (Worksheet 25 C02)—i.e., distances of about 500 feet or greater from the application site under moderate wind 26 speeds of about 2.5 m/s (≈4.5 mph) or greater, which seems intuitively reasonable given that the 27 monitoring data summarized in U.S. EPA/OPP/HED (2009, p. 69, Table 6.1.4.1) were not 28 sampled at application sites. 29 [Working Note: Worksheet E02b contains a shaded area near the 31 bottom of the worksheet that implements Equation 2 for 32 converting ppm to µg/m3 using the molecular weight of 73.11 for 33 methyl isothiocyanate and the molar gas volume of 24.1 L/mole. 34 This utility was used in making conversions not otherwise 35 detailed in the text of this document. 36 To the right of the ppm to µg/m3 conversion tool, the workbook 38 has another utility that implements Equation 3 for calculating 39 the molar volume of a gas at any temperature and barometric 40 pressure.] 41

The product label for Basamid G indicates that methyl isothiocyanate concentrations may range 43 from 0.6 to 6 ppm may after applications of dazomet. These concentrations correspond to about 44 http://authors.library.caltech.edu/25050/4/Chapter_03.pdf

1820 to 18,000 µg/m3 (using the above equation). The lower bound of this range is only 1 modestly below the highest concentration of 2770 µg/m3 estimated in Worksheet C02 for or the 2 Forest Service application rate of 350 lb/acre. This is not to suggest a validation of the EPA 3 modeling; however, these relationships do suggest that the modeled concentrations of 6.83 µg/m3 4 to about 2770 µg/m3 are not implausible. 5

3.2.2. General Public 6

3.2.2.1. Surface Water (Methyl Isothiocyanate) 7

3.2.2.1.1. Expected Concentrations 8

Full Forest Service risk assessments typically estimate concentrations of a pesticide in surface 9 water using GLEAMS-Driver (SERA 2014, Section 3.2.3.4.3). GLEAMS, however, does not 10 explicitly accommodate soil fumigation (Knisel and Davis 2000). While fumigation might be 11 approximated using soil injection, this type of custom modelling is beyond the scope of the 12 current effort. 13 As an alternative, the surface water modeling from U.S. EPA/OPP/EFED (2008a) using 15 PRZM/EXAMS is adapted to the current assessment. As with GLEAMS, PZMZ/EXAMS has 16 limitations in terms of handling highly volatile compounds in soil that are addressed in U.S. 17 EPA/OPP/EFED (2008a, p. 9) in a reasonably conservative manner. U.S. EPA/OPP/EFED 18 (2008a, p. 30-31) provides five application scenarios: two in California (tomatoes and 19 strawberries), two in Florida (both turf), and one in Oregon (Christmas trees). Because the 20 current assessment is focused on a Forest Service nursery in Oregon, the results from the Oregon 21 scenario are used in the current assessment (i.e., U.S. EPA/OPP/EFED 2008a, p. 103). The peak 22 (lower bound – upper bound) concentrations from the EPA analysis are 0.00033 (0.00001 to 23

0.00064 mg/L) and the 90-day average concentrations are 0.00002 (0.00001 to 0.00004) mg/L. 24 The central and upper bound estimates are based on the average and maximum concentrations 25 reported in U.S. EPA/OPP/EFED (2008a, p. 103). Many of the yearly concentrations reported 26 by EPA are zero, which is similar to many GLEAMS-Driver simulations in Forest Service risk 27 assessments. Consequently, the lower bounds are set at the lowest non-zero concentrations 28 reported. The EPA simulations were done at a maximum application rate of 530 lb/acre (U.S. 29 EPA/OPP/EFED 2008a, p. 32, Table III.b). 30 The concentrations reported by EPA were thus normalized to Water Contamination Rates 32 (WCRs, in units of mg/L per lb/acre) by dividing the values by the application rate of 530 33 lb/acre. Details of these calculations are given in Worksheet B04Rt of the EXCEL workbook 34 that accompanies this risk assessment. As discussed in SERA (2014, 3.2.3.4.6), the WRCs are 35 multiplied by the application rate of 350 lbs/acre in Worksheet A01 to estimate the expected 36 concentrations of methyl isothiocyanate in water, which are given in Worksheet B04a. 37 The estimated concentrations of methyl isothiocyanate in surface water are used to elaborate 39 exposure scenarios associated with acute exposure scenarios (Worksheets D05, D09a, D09b, and 40 D11), and longer-term exposure scenarios (D07, D-09a, and D09b). These are standard exposure 41 scenarios used in most Forest Service risk assessments as detailed in SERA (2014). As 42 discussed in Section 3.3.1, dietary exposures are not relevant given the application method and 43 properties of methyl isothiocyanate. 44

3.2.2.1.2. Accidental Spill 1

Accidental spill scenarios are considered in most Forest Service risk assessments and typically 2 model spills of 100 (20-200) gallons of a field solution. This type of scenario, however, is not 3 relevant to applications of dazomet. As an alternative, an accidental spill scenario is developed 4 in Worksheet B04b involving a dazomet spill in the amount used to treat 0.1 (0.01 to 1) acre. At 5 the application rate of 350 lb/acre used in the WorksheetMaker workbook that accompanies this 6 assessment, the spill is equivalent to 35 (3.5 to 350) lbs of dazomet. Because of the rapid 7 conversion of dazomet to methyl isothiocyanate, the expected concentrations are converted to 8 units of methyl isothiocyanate by multiplying the mass of dazomet by the ratio of the molecular 9 weight of methyl isothiocyanate (73.11 g/mole) to the molecular weight of dazomet (162.27 10 g/mole). The estimated concentrations of dazomet in surface water following an accidental spill 11 are detailed in Worksheet B04b. 12 The values for estimated concentrations of dazomet in surface water following an accidental spill 14 are simply intended to reflect central (lower bound to upper bound) spills that might reasonably 15 be viewed as moderate (small to large). The accidental spill scenarios are detailed in Worksheets 16 D05 (consumption of water by a small child), D08a (consumption of contaminated fish by a 17 member of the general population), and D08b (consumption of contaminated fish by a member 18 of a subsistence population). 19

3.2.2.2. Inhalation 20

The approach to handling inhalation exposures to methyl isothiocyanate by members of the 21 general public is identical to that used for workers (Section 3.2.1.2). The only difference is that 22 workers are likely to be closer than the general public to the treated field, as discussed in the risk 23 characterization for members of the general public (Section 3.4.2.2). 24

3.3. Dose-Response Assessment 25

The toxicity values for dazomet and methyl isothiocyanate relating to potential health effects in 26 humans are summarized in Table 2 and are discussed below. The toxicity values summarized in 27 Table 2 are based on the most recent EPA human health risk assessment (U.S. EPA/OPP/HED 28 2009a). 29

3.3.1. Dazomet 30

RfDs or comparable values for dazomet have been proposed by the European Food Safety 31 Authority (ESFA 2010) and the U.S. EPA/OPP’s Health Effects Division (U.S. EPA/OPP/HED 32 2009a). It should be noted that both sets of toxicity values are consistent with each other and 33 appear to be based on the same studies. The major difference between the two sets of values is 34 that the U.S. EPA did not perceive a need for any chronic oral toxicity values for dazomet 35 because it is rapidly converted to methyl isothiocyanate. The current assessment agrees with the 36 EPA position. The chronic RfD is noted for the sake of completeness but is not used 37 quantitatively in the EXCEL workbook that accompanies this risk assessment. 38 The toxicity values from U.S. EPA/OPP/HED (2009a) are presented solely for the risk 40 assessment of workers by dermal exposures: 41

Based on the currently registered use pattern of dazomet, dietary exposure 42 is not expected. Acute and chronic reference doses are not necessary at 43 this time. 44

U.S. EPA/OPP/HED (2009a, p. 16). 1 Again, this approach is sensible. Given the rapid conversion of dazomet to methyl 3 isothiocyanate, exposures of members of the general public to dazomet should be minimal and 4 insignificant, relative to exposures to methyl isothiocyanate. 5 Note that most of the exposure assessments (Section 3.2) involve methyl isothiocyanate. The 7 only exception involves workers applying dazomet. Consistent with the approach used in U.S. 8 EPA/OPP/HED (2009), the assumption is made that workers applying dazomet will be exposed 9 primarily to dazomet rather than methyl isothiocyanate. Thus, the only toxicity value for 10 dazomet used quantitatively in the EXCEL workbook is 0.015 mg/kg bw/day which is adopted 11 from U.S. EPA/OPP/HED (2009a, p. 28) and consistent with the occupational exposure limit 12 recommended by ESFA (2010, p. 7) and the European Union (2012, p. 3). 13

3.3.2. Methyl Isothiocyanate (MITC) 14

Both oral RfDs (or their equivalents such as Acceptable Daily Intakes [ADIs] and Acceptable 15 Occupational Exposure Limits [AOELs]) as well as RfCs (Reference Concentrations) or 16 analogous values are available on methyl isothiocyanate. 17

3.3.2.1. Oral Toxicity Values 18

The oral acute RfD and chronic ADI are given in the risk assessment by European Food Safety 19 Authority (ESFA 2010). The U.S. EPA/OPP assessments on dazomet and methyl isothiocyanate 20 do not derive oral or dermal toxicity values for methyl isothiocyanate, because significant oral or 21 dermal exposures were not anticipated in the EPA assessments (e.g., U.S. EPA/OPP/HED 2009a, 22

p. 22). 23 As discussed in Section 3.2.2.1, however, the EPA’s most recent ecological risk assessment on 25 dazomet does estimate concentrations of methyl isothiocyanate in surface water (U.S. 26 EPA/OPP/EFED 2008a). When concentrations of a compound in surface water can be 27 estimated, Forest Service risk assessments will use these estimates for risk characterization so 28 long as adequate toxicity data are available. The European Food Safety Authority is a credible 29 organization, and the acute and chronic oral toxicity values from EFSA (2010) are accepted 30 without modification. These toxicity values, specified in Table 2, are used to characterize risks 31 associated with the acute and longer-term consumption of surface water contaminated with 32 methyl isothiocyanate. 33

3.3.3.2. Inhalation Toxicity Values 34

The EPA derived inhalation toxicity values for acute exposures to methyl isothiocyanate (U.S. 35 EPA/OPP/HED 2009a, pp. 18-20). Somewhat atypically, the EPA derived two sets of acute 36 toxicity values, one for eye irritation in humans and the other for systemic toxicity. 37 The toxicity value for eye irritation is based on a human study on eye irritation and odor 39 threshold over exposure periods of 4 minutes to 8 hours (U.S. EPA/OPP/HED (2009a, pp. 17-19, 40 MRID 44400401). For exposure periods of 1 to 8 hours, the NOAEL was designated as 0.22 41 ppm (U.S. EPA/OPP/HED 2009a, Table 4.4e, p. 29). Because this study is based on human data, 42 the EPA used an uncertainty factor of 10 to account for potential variability within the human 43 population. Thus, the acute toxicity value—i.e., a functional acute RfD—is 0.022 ppm or 44 approximately 66.7 µg/m3. In the EXCEL workbook that accompanies this document, a utility 1 included at the bottom of Worksheet E02b may be used for converting ppm to µg/m3. 2 For short- and intermediate-exposures (1 day to 6 months), the toxicity value is 0.166 mg/m3 4 (166 µg/m3). The concentration of 0.166 mg/m3 is based on the NOAEL of 5 mg/m3 from a 28-5 day inhalation study in rats exposed to methyl isothiocyanate nominal concentrations 0, 5, 20, or 6 100 mg/m3 (U.S. EPA/OPP/HED 2009a, pp. 82-83, MRID 45314802). At 20 mg/m3, adverse 7 effects included an increase in a type of white blood cell (i.e., neutrophilic polymorphonuclear 8 granulocytes) as well as clinical signs consistent with irritation. The EPA did not specifically 9 derive an RfC but used the NOAEL of 5 mg/m3 with a margin of exposure of 30, which is 10 equivalent to setting the subchronic RfC at 0.166 mg/m3 [5 mg/m3 ÷ 30 ≈ 0.166 mg/m3] (U.S. 11 EPA/OPP/HED 2009a, Table 4.4e, p. 29). 12

3.4. Risk Characterization 13

3.4.1. Workers 14

3.4.1.1. Applications (Dazomet) 15

The HQs for workers are given in Worksheet E01 of the EXCEL workbook. These HQs range 16 from 1.3 (i.e., baseline or no PPE) to 0.03 (i.e., full PPE/engineering controls). Given the 17 detailed description of worker PPE provided by the Forest Service and the requirements 18 specified on the product label (Section 3.2.1.1), the HQ of 0.03 is clearly the only HQ relevant to 19 the current assessment. This HQ is below the level of concern (HQ=1) by a factor of over 30. 20 Thus, there is no basis for asserting that workers will be at risk of adverse effects associated with 21 applications of dazomet. 22

3.4.1.2. Inhalation (Methyl Isothiocyanate) 23

The HQs for acute eye irritation for exposure to air concentrations of methyl isothiocyanate are 24 given in Worksheet E02a. The HQs in Worksheet E02a would not apply to workers during the 25 application of dazomet, due to the use of protective clothing, including respirators. After 26 applications, however, workers could be in the area of the treated soil and exposed to methyl 27 isothiocyanate vapors. 28 As summarized in Worksheet E02a, the HQs are highly variable ranging from about 0.1 to 42. 30 These HQs are based on a concentration of 66.7 µg/m3 for eye irritation (Section 3.3.3.2) and air 31 concentrations estimated by the EPA under a variety of winds speeds, atmospheric stability, and 32 distances downwind (U.S. EPA/OPP/EFED 2008a), as discussed in Section 3.2.1.2. As 33 summarized in Table 2, the concentration of 66.7 µg/m3 is based on an uncertainty factor of 10, a 34 human NOAEL of 66.7 µg/m3 associated with a human LOAEL of 2392 µg/m3 for eye irritation. 35 Thus, an HQ of 10 would correspond to the reported human NOAEL and an HQ of about 36 36 would correspond to the observed human LOAEL [2392 µg/m3 ÷ 66.7 µg/m3 ≈ 35.86]. 37 For workers on or very close to the application site, HQs in the range of 10 to 40 could be 39 applicable at low wind speeds and under relatively stable atmospheric conditions on the 40 application site (i.e., no buffer). Eye irritation could not be ruled out in some workers who are 41 sensitive to methyl isothiocyanate. Conversely, under less extreme conditions, it is plausible that 42 no signs of eye irritation would be noted in workers or other individuals in the area of the 1 application site. 2 The duration of potential risks due to vapor release cannot be determined based on the modeling 4 done by EPA. As discussed further in Section 3.4.2.2, the product label for Basamid G specifies 5 a 48-hour period in which a buffer zone must be in effect, which suggests that vapor release after 6 48 hours may be negligible. U.S. EPA/OPP/HED (2009a), however, does not explicitly discuss 7 the rationale for the 48-hour buffer period specified on the Certis product label. 8

3.4.2. General Public 9

3.4.2.1. Surface Water 10

The risk characterization associated with exposures to methyl isothiocyanate in surface water is 11 given in Worksheet E04. Based on the estimated concentrations of methyl isothiocyanate in 12 surface water (Section 3.2.2.1.1), none of the HQs approach a level of concern (HQ=1). The 13 highest HQ is 0.002, the upper bound for the short-term consumption of contaminated water by a 14 small child. This HQ is below the level of concern by a factor of 500. 15 In the event of an accidental spill (Section 3.2.2.1.2), all of the central and upper estimates of the 17 HQs exceed the level of concern ranging from 1.7 to 269. As discussed in Section 3.2.2.1.2, this 18 exposure scenario is based on variable assumptions involving the amount spilled—i.e., 35 (3.5 to 19

350) lbs of dazomet. The HQs for this exposure scenario simply suggest that mitigation 20 measures would be appropriate in the event of an accidental spill of dazomet into a relatively 21 small body of water. This risk characterization is similar to that of many accidental spill 22 scenarios considered in full Forest Service risk assessments. 23

3.4.2.2. Inhalation 24

The risk characterization for inhalation exposures for members of the general public can be 25 based on the modeling from U.S. EPA/OPP/EFED (2008a) and the monitoring data reported in 26 U.S. EPA/OPP/HED (2009a). 27 The product label for Basamid G (Certis USA, ND) specifies buffer zones for different types of 29 applications of dazomet and specifies that the buffer zone must remain in effect for 48 hours. 30 Based on Table 1 of the product label, the buffer zone for an application rate of about 350 lb/acre 31 to a 40-acre field is about 680 feet. The Forest Service has indicated, however, that only 10 32 acres would be treated in a given day and that the typical buffer would be about 220 feet (Justin 33 2014). This buffer is consistent with the product label for Basamid G (Certis USA, ND) for field 34 size of 10 acres and an application rate of about 350 lb/acre. 35 Thus, the HQs in Worksheet E02a for 0 to 200 feet downwind would not be applicable to 37 members of the general public. Excluding these HQs results in HQs for the general public that 38 range from 0.1 to 10. The HQs that exceed the level of concern by a factor of 2 or more are 39 those for low wind speeds (≈1 m/s or about 2.2 mph) and relatively stable atmospheric 40 conditions (stability categories F and D). These HQs range from 2 to 10 and. These HQs might 41 be associated with eye irritation in some sensitive members of the population. 42

In addition to the modeled estimates of methyl isothiocyanate in air from U.S. EPA/OPP/EFED 1 (2008a), risks to both workers and members of the general public can be estimated from the 2 monitoring provided in U.S. EPA/OPP/HED (2009a). These data are summarized in Worksheet 3 B02b. As with the analysis in U.S. EPA/OPP/HED (2009a, Table 6.1.4.1, p. 69), risks 4 associated with the maximum concentrations are characterized using the concentration of 66.7 5 µg/m3 based on eye irritation, and risks associated with the mean concentrations are 6 characterized using the concentration of 167 µg/m3 based on systemic effects (i.e., an increase in 7 white blood cells). As summarized in Worksheet E02b, none of the HQs exceed the level of 8 concern (HQ=1) with the acute HQs ranging up to 0.7 and the intermediate-term HQs (i.e., for 1 9 day to 6 months) ranging up to 0.1. 10

4. ECOLOGICAL EFFECTS 12

4.1. Hazard Identification 13

As with the hazard identification for human health (Section 3.2), the hazard identification for 14 ecological effects is highly abbreviated in the current document. The overall database for 15 ecological effects is discussed in detail in U.S. EPA/OPP/EFED (2008a), the most recent risk 16 assessment on dazomet as well as the EPA’s final work plan for the registration review of 17 dazomet (U.S. EPA/OPP 2014). The current assessment relies heavily on U.S. EPA/OPP/EFED 18 (2008a) for the derivation of HQs. As detailed in these EPA documents, there are several 19 important data gaps for methyl isothiocyanate. These data gaps have an impact on the risk 20 characterization for methyl isothiocyanate as discussed further in Section 4.4. 21

4.2. Exposure Assessment 22

4.2.1. Oral 23

4.2.1.1. Dazomet 24

Given the application method for dazomet—i.e., soil incorporation—most of the standard oral 25 exposure scenarios (e.g., consumption of contaminated vegetation) used in both EPA and Forest 26 Service risk assessments are not applicable to dazomet. In addition and as discussed in 27 Section 2, dazomet is rapidly converted to methyl isothiocyanate. Some relevant oral exposure 28 scenarios for methyl isothiocyanate are discussed in Section 4.2.1.2. 29 U.S. EPA/OPP/EFED (2008a) uses an LD50/square foot method as a screening tool. As the name 31 implies, this method involves calculating the amount of the pesticide applied to a square foot and 32 comparing this to a relevant LD50. This is a convention developed by the U.S. EPA as a 33 screening tool and is not directly used in the current risk assessment. 34 As noted in Section 1.2, the application rate anticipated by the Forest Service is 350 lbs/acre, 36 which corresponds to approximately 3600 mg/ft2 [350 lbs/acre x 453,592 mg/lb ÷ 43,560 ft2/acre 37 ≈ 3,644.5638 mg/ft2]. As discussed further in Section 4.3.1, the LD50 values for mammals and 38 birds are somewhat greater than 400 mg/kg bw. For a small (200 g) mammal, this value 39 corresponds to a dose of 80 mg. Thus, an application rate of 350 lbs/acre would involve about 40 45 LD50 values per square foot [3600 mg/ft2 ÷ 80 mg/LD50]. 41

The above relationships are noted solely in the interest of transparency. While these types of 1 relationships may be useful to the EPA as a screening tool, they are not relevant to assessing 2 risks associated with soil incorporation. As detailed in Section 3.2.1.1, the manner in which 3 dazomet is applied in Forest Service programs—i.e., soil application followed immediately by 4 tilling and watering in—will greatly limit any exposure of mammals or birds to dazomet. 5 Consequently, no oral exposure scenarios for dazomet are developed in the EXCEL workbook 6 that accompanies this risk assessment. 7

4.2.1.1. Methyl Isothiocyanate 8

As with standard Forest Service risk assessments, exposure assessments associated with both 9 expected concentrations of methyl isothiocyanate in surface water and concentrations in surface 10 water following an accidental spill are identical to those used in the assessment of potential 11 effects in humans (Section 3.2.2.1). The only differences involve the amount of water consumed 12 by different groups of vertebrates. The specific assumptions used for estimating doses associated 13 with the consumption of contaminated surface water are detailed in Table 17 of SERA (2014). 14 The estimated doses for mammals and birds are summarized in Worksheet G01a (mammals) and 15 G01b (birds) of the EXCEL workbook that accompanies this document. These summary 16 worksheets reference the worksheets in which each exposure scenario is detailed. 17

4.2.2 Inhalation 18

Wildlife may be exposed to methyl isothiocyanate in the air. The estimated concentrations of 19 methyl isothiocyanate in air used to assess effects in wildlife are identical to those used to assess 20 exposures in workers. As detailed in the exposure assessment for workers (Section 3.2.1.2), 21 these concentrations are adopted from the EPA ecological risk assessment for dazomet (U.S. 22 EPA/OPP/EFED 2008a). The specific concentrations are summarized in Worksheet C02. 23 Furthermore, like the assessment of inhalation exposures to humans, inhalation risks to wildlife 25 are assessed based on monitoring data from U.S. EPA/OPP/HED (2009a, Table 6.1.4.1). These 26 monitoring data are summarized in Worksheet B05. 27

4.3. Dose-Response Assessment 28

The dose response assessment for nontarget organisms is summarized in Table 3 and is discussed 29 in the following subsections on different groups of receptors. 30

4.3.1. Terrestrial Organisms 31

4.3.1.1. Mammals 32

4.3.1.1.1. Dazomet 33

As discussed in Section 4.2.1.1, substantial exposures of mammalian wildlife to dazomet are 34 unlikely, given the manner in which dazomet is applied. As discussed in Section 4.2.1.1, U.S. 35 EPA/OPP/EFED (2008a) uses an LD50/square foot method as a screening approach. This 36 approach is based on a standard LD50 of 415 mg/kg bw in rats. In the interest of transparency, it 37 is noted that this method triggers concern for all risk categories used by the U.S. EPA, as detailed 38 in Table IV.i. in U.S. EPA/OPP/EFED (2008a, p. 49). As noted in Section 4.2.1.1, however, the 39 LD50 per square foot approach is a screening tool developed by the U.S. EPA/OPP and is not 40 directly relevant to the current assessment. 41

4.3.1.1.2. Methyl Isothiocyanate 1

While exposures of mammalian wildlife to dazomet are unlikely, potential oral and inhalation 2 exposures to methyl isothiocyanate are plausible. 3 As discussed in Section 3.3.2.1 and summarized in Table 2, the acute oral RfD is based on an 5 NOAEL of 3 mg/kg bw from a reproduction study in rats. Following standard practice in Forest 6 Service risk assessments (SERA 2014), the basis for the human health risk assessment is used as 7 the basis for assessing effects in mammalian wildlife. Thus, the NOAEL of 3 mg/kg bw is used 8 to characterize risks to mammals following short-term oral exposures to methyl isothiocyanate. 9 Similarly, the NOAEL of 0.4 mg/kg bw/day in dogs (which is the basis for the chronic oral RfD) 10 is used to assess the consequences of longer-term oral exposures of mammalian wildlife to 11 methyl isothiocyanate. 12 For inhalation exposures, the intermediate NOAEL of 5 mg/m3 from the 28-day study in rats 14 (U.S. EPA/OPP/HED 2009a, pp. 82-83, MRID 45314802) is used to assess intermediate 15 inhalation exposures. While this study is used by U.S. EPA/OPP/HED (2009a) to assess both 16 acute and intermediate exposures in humans, the use of the 5 mg/m3 28-day NOAEL is not 17 appropriate for assessing short-term exposures in mammalian wildlife. As an alternative, the 18 acute LC50 of 540 mg/m3 in rats (MRID 45919410 as summarized in U.S. EPA/OPP/EFED 19 2008a, p. 110) is divided by a factor of 10 to approximate an acute NOAEL of 54 mg/m3. The 20 rationale for the estimation of a NOAEL from an LD50 is discussed in SERA (2014, 21 Section 4.3.2) and is a modification of the methods used by U.S. EPA/OPP for defining variable 22 levels of concern. 23

4.3.1.2. Birds 24

4.3.1.2.1. Dazomet 25

As with mammals (Section 4.2.1.1), substantial exposures of avian wildlife to dazomet are 26 unlikely, given the manner in which dazomet is applied. Also, as with mammals, U.S.