Draft for Comment Version – March 1, 2014

Human Health Bystander Screening Level 

Analysis: Volatilization of Conventional 

Pesticides

Office of Pesticide Programs

Office of Chemical Safety and Pollution Prevention

U.S. Environmental Protection Agency

Washington, DC

March 1, 2014
Draft for Comment Version – March 1, 2014

2

1 Table of Contents

2

3 Section 1.0: Introduction................................................................................................................. 2

4 Section 2.0: Volatilization Screening Tool Development .............................................................. 4

5 Section 3.0: Volatilization Screening Tool Inputs.......................................................................... 8

6 Section 4.0: Registration Review Chemical Volatilization Screen Results.................................. 11

7 Section 5.0: Registration Review Chemical Volatilization Screen Characterization................... 17

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26
Draft for Comment Version – March 1, 2014

3

27 Section 1.0: Introduction

28

29 Over many years, the Environmental Protection Agency (the Agency) has been actively engaged 

30 in evaluating possible exposures associated with air borne, off-target movement of pesticides. 

31 This has included developing and refining its methodologies for assessing bystander exposures 

resulting from volatilization of fumigants as well as exposure to spray drift1 32 from the application 

33 of conventional pesticides in agricultural settings. More recently, the Agency has been adapting

34 the approaches developed for conducting risk assessments for the fumigants for use in assessing

35 potential bystander inhalation risk resulting from the volatilization of other conventional 

36 pesticides (i.e., non-fumigants). Notable milestones in this effort include the 2009 FIFRA 

Scientific Advisory Panel (SAP) 2 37 review of issues related to volatilization of conventional 

pesticides and the 2013 chlorpyrifos volatility assessment3 38 .

39

40 The Agency has recently developed a Volatilization Screening Tool that provides a consistent 

41 and health protective framework to assess the potential inhalation bystander risks resulting from 

42 volatilization of conventional pesticides. In addition, a Volatilization Screening Tool Guidance 

43 Document (see Appendix A) was produced to support the screening tool. The screening tool 

44 utilizes a number of physical and chemical properties to predict flux (i.e., the rate at which a 

chemical volatilizes off of a treated field); the AERSCREEN4 45 model to estimate air 

46 concentrations at different distances from a treated field; and chemical-specific human health 

47 toxicological data to estimate potential bystander inhalation risks. This document provides 

48 details on the volatilization screening methodology including the development of the screening 

49 tool, the guiding principles behind the screening tool, and the various inputs utilized in the 

50 screening tool. It also presents the results of the screening analysis that the Agency has recently 

51 completed using this methodology which examined all of the conventional pesticides being 

evaluated in the Registration Review5 52 process. The Agency plans to use the results of the 

53 screening analysis to determine when volatilization data (i.e., flux studies) and/or route-specific 

54 inhalation toxicological data (if not already available) should be required for a chemical.

55

56 Section 2: Volatilization Screening Tool Development provides a brief discussion of the 

57 development of the volatilization screening tool as well as a discussion of the guiding principles 

58 behind the screening tool. Section 3: Volatilization Screening Tool Inputs outlines the inputs 

59 used to populate the volatilization screening tool. Section 4: Registration Review Chemical 

60 Volatilization Screen Results discusses the results of the Agency’s volatilization analysis for the 

61 conventional Registration Review chemicals. Section 5: Registration Review Chemical

62 Volatilization Screen Characterization discusses issues that should be considered when 

63 interpreting the volatilization analysis for the Registration Review chemicals.

64

 1 Reference Spray Drift Doc once final

2 2009 Volatilization SAP: http://www.regulations.gov/ (EPA-HQ-OPP-2009-0687) 3 2013 Chlorpyrifos Volatility Assessment: http://www.regulations.gov/ (EPA-HQ-OPP-2008-0850) 4 http://www.epa.gov/ttn/scram/dispersion_prefrec.htm

5 http://www.epa.gov/oppsrrd1/registration_review/
Draft for Comment Version – March 1, 2014

4

65 Section 2.0: Volatilization Screening Tool Development

66

67 In order to assess the potential inhalation bystander risks resulting from volatilization of 

68 conventional pesticides in a consistent and health protective manner, a volatilization screening 

69 tool has been developed. This screening tool can be used to estimate upper bound, health 

70 protective air concentrations at various distances from a treated field resulting from the 

71 volatilization of conventional pesticides. Prior to development of this screening tool, the Agency

72 typically used the Probabilistic Exposure and Risk model for FUMigants (PERFUM) for 

conducting bystander inhalation screening assessments. Use of PERFUM6 73 is resource intensive 

74 and requires the input of emission rate profiles (gathered from field volatility studies) that are not 

75 typically available for conventional pesticides.

76

77 Given these issues, a need was identified for a tool that was less resource and data intensive but

78 still resulted in health protective risk estimates. The volatilization screening tool utilizes three 

79 main inputs in assessing the potential inhalation bystander risks from conventional pesticides. 

80 First, physical and chemical properties are used to predict flux based on the work by Woodrow et 

al. (1997)7 and Woodrow et al. (2001)8 81 . Second, the screening tool uses the estimated flux along 

with the AERSCREEN9 82 model to estimate air concentrations at different distances from the

83 treated field. [Note: AERSCREEN is used routinely for regulatory air permitting and has 

84 undergone extensive review as described in the associated background materials.] Finally, the air 

85 concentrations are compared to chemical-specific human health toxicological data to estimate 

86 potential bystander inhalation risks. All of these components are combined into a simple to use 

87 Excel workbook. Users must have Microsoft Excel 2007 or higher in order to use the screening 

88 tool. In addition, the tool also uses Visual Basic functions, so users must enable macros in order 

89 to use the tool. Figure 1 provides a screen shot of the Volatilization Screening Tool.

90

 6 http://www.exponent.com/ProjectDetail.aspx?project=450

7 Woodrow, J., Seiber, J., Baker, L. 1997. Correlation Techniques for Estimating Pesticide Volatilization Flux and 

Downwind Concentrations. Environ. Sci. Technol., 31:523-529

8 Woodrow, J., Seiber, J., Dary, C. 2001. Predicting Pesticide Emissions and Downwind concentrations Using 

Correlations with Estimated Vapor Pressures. J. Agric. Food Chem. 49:3841-3846 9 http://www.epa.gov/ttn/scram/dispersion_prefrec.htm
Draft for Comment Version – March 1, 2014

5

91

92 Figure 1. Input Screen for Volatilization Screening Tool

93

94 More specific details on the use of a modified Woodrow equation and the AERSCREEN model 

95 in the Volatilization Screening Tool are presented below. Specific details on the physical and 

96 chemical properties and toxicological inputs used in the Volatilization Screening Tool are 

97 presented in Section 3.0.

98

99 Modified Woodrow Equation

At the 2009 FIFRA Scientific Advisory Panel (SAP) 10 100 related to volatilization of conventional 

101 pesticides, the Agency presented multiple methods for estimating emissions released from a 

102 pesticide-treated field. The approach defined in Woodrow et al (1997) and Woodrow et al

103 (2001) was one of the methods presented to the Panel. The Panel commented that the Woodrow 

104 approach would be a good starting point for a Tier I, screening level approach. In these two 

105 papers, the study authors developed a linear relationship between the natural logarithm of a 

106 chemical’s physical and chemical properties to the natural logarithm of the amount of chemical 

107 emitted from soil or a plant surface. However, like all linear relationships, half of the emissions 

108 were underestimated when compared to the measured values used to derive the relationship. In 

109 order to be conservative and health protective, the Agency used the data provided in the 

110 Woodrow et al (1997) to construct an alternative linear model using the 90% lower confidence 

111 limit of the slope and 90% upper confidence limit of the intercept as the model parameters. The 

112 results of the regressions are presented in the Volatilization Screening Tool Guidance Document

113 (see Appendix A).

114

 10 2009 Volatilization SAP: http://www.regulations.gov/ (EPA-HQ-OPP-2009-0687)
Draft for Comment Version – March 1, 2014

6

115 For soil applied pesticides, the following equation can be used to derive a flux rate:

116

117

118

119

120

121 Where:

flux = flux rate (μg/m2 122 -s),

123 VP = vapor pressure (Pa),

124 AR = application rate (lb/A),

125 Sol = solubility (mg/L), and

126 Koc = organic carbon sorption coefficient (ml/g).

127

128 For foliar applied pesticides, the following equation can be used to derive a flux rate

129

130

131

132 Where:

flux = flux rate (μg/m2 133 -s), and

134 VP = vapor pressure (Pa). 135

136 Note: In Woodrow et al (1997), pesticide residues on plant surfaces were assumed to be 

137 volatilizing from a non-interactive surface in the period just after application and a very good 

138 correlation between flux and vapor pressure was obtained for a dozen compounds. An attempt 

139 was made to develop an equation that incorporates application rate for foliar applied pesticides 

140 however the Agency was unable to obtain a good correlation for this equation.

141

142
Draft for Comment Version – March 1, 2014

7

143 AERSCREEN Model

AERSCREEN is a screening air model based on AERMOD11 144 , which is an air quality model that 

145 incorporates air dispersion based on planetary boundary layer turbulence structure and scaling 

146 concepts, including treatment of both surface and elevated sources, and both simple and complex 

147 terrain. AERMOD was developed as a joint effort between the American Meteorological 

Society and the EPA. In 1998, a formal peer review of the model was performed12 148 . An 

independent model evaluation was also completed in 199813,14 149 . AERMOD is currently a 

recommended EPA air model as per Appendix W15 150 of 40 CFR Part 51.

151

152 AERSCREEN produces estimates of "worst-case" 1-hour concentrations for a single source

153 without the need for site specific hourly meteorological data. The Volatilization Screening Tool 

154 was developed using a limited number of AERSCREEN model runs, at a standard flux rate of 

1x10-6 g/m2 155 -s, for various field sizes, crop scenarios, seasons of application, and meteorological 

156 conditions. The results of these AERSCREEN model runs were then imported into the Excel 

157 screening tool. The Volatilization Screening Tool Guidance Document details the input 

158 parameters used in the AERSCREEN model runs (see Appendix A).

159

160 EPA air screening guidance from 1992 does not recommend calculation of air concentrations 

161 beyond 1 hour periods to different exposure periods for field source emissions (e.g., 8-hour time 

weighted air concentration)16 162 . However, a peak-to-mean scaling factor has been developed, 

163 based on runs done in PERFUM, to allow estimation of concentrations for averaging periods 

164 longer than one hour, but less than 24 hours in order to match the duration of the potential 

165 exposure period to a period similar to that used for defining the toxicological level of concern 

166 (e.g., 6 hour inhalation dose administration in a rodent study is typical). The Agency notes that 

PERFUM received a favorable review by the FIFRA SAP in 200417 167 and since that time the 

168 Agency has consistently used it in the assessment of the fumigants. The Volatilization Screening 

169 Tool Guidance Document details the specifics of the peak-to-mean scaling factor (see Appendix 

170 A).

171

172 In AERSCREEN, air concentrations are directly related to the emission rate from a field. The

173 Volatilization Screening Tool scales the results from the AERSCREEN runs, using the 

174 application rate and physical and chemical properties of the pesticide to estimate flux, to estimate 

175 off-field air concentrations for a variety of crop scenarios and meteorological conditions. The 

176 Volatilization Screening Tool provides estimates of the distance from the edge of the field where 

177 air concentrations fall below the concentration of concern for a chemical. In this way, the 

 11 http://www.epa.gov/ttn/scram/dispersion_prefrec.htm#aermod 12 United States Environmental Protection Agency. Compendium of

http://www.epa.gov/scram001/7thconf/aermod/dockrpt.pdf. Accessed March 2002. 13 Paine, R.J, R.F. Lee, R. Brode, R.B. Wilson, A.J. Cimorelli, S.G. Perry, J.C. Weil, A.Venkatram, and W. Peters. 

Model Evaluation Results for AERMOD. 14 Paine. R., R. Lee, R. Brode, R. Wilson, A. Cimorelli, S. Perry, J.Weil, A. Venkatram, W.

Peters. AERMOD: Model Formulation and Evaluation Results. Preprints, 92th Annual Meeting of Air and Waste 

Management Association, Air and Waste Management Association, Pittsburgh, PA. (1999) 15 http://www.epa.gov/ttn/scram/guidance/guide/appw_05.pdf 16 U.S. EPA, 1992: Screening Procedures for Estimating the Air Quality Impact of Stationary Sources. EPA-454/R92-019. U.S. Environmental Protection Agency, Research Triangle Park, NC 27711. 17 http://www.epa.gov/scipoly/sap/meetings/2004/082404_mtg.htm
Draft for Comment Version – March 1, 2014

8

178 Volatilization Screening Tool can be used to easily eliminate the inhalation pathway for 

179 pesticides not posing a risk of concern to bystanders following applications. 

180

181 Section 3.0: Volatilization Screening Tool Inputs

182

183 As described in Section 2, the Volatilization Screening Tool consists of three major components, 

184 the modified Woodrow Equation, AERSCREEN, and chemical-specific human health 

185 toxicological data. In order to run the screen, a number of input parameters must be utilized (see 

186 Figure 1 above). These parameters include a number of physical/chemical properties,

187 application scenarios, application rate, application timing, and human-health toxicological data. 

188 These inputs were obtained or derived from a number of sources. In many cases, 

189 physical/chemical properties and toxicological information for individual chemicals were

190 publicly available in Agency exposure and risk assessment documents and were defined based 

191 on guideline studies intended for this purpose. However, in some cases, it was necessary to find

192 or verify the physical/chemical properties of a chemical via other reliable internet resources. In 

193 addition, application scenarios, application rate, and application timing were obtained from 

194 pesticide labels. The following sections will discuss the details of each specific input parameter 

195 for the Volatilization Screening Tool.

196

197 Vapor Pressure (Pa)

198 Vapor pressure is the pressure exerted by a vapor in equilibrium with its solid or liquid state. 

199 Chemicals with higher vapor pressures are more likely to transform to the gaseous stage and 

200 volatilize off of treated fields. The modified Woodrow equation utilizes vapor pressure for both 

201 the soil and foliar surface flux equations (see Section 2).

202

203 Solubility (mg/L)

204 Solubility is the ability of a substance to dissolve in solution. Chemicals with higher solubility 

205 have a greater likelihood to remain in solution and not volatilize. The modified Woodrow 

206 equation utilizes solubility only in the soil surface flux equation (see Section 2).

207

208 Koc (ml/g)

209 Koc refers to the soil organic carbon-water partitioning coefficient. It is the ratio of the mass of a 

210 chemical that is absorbed in the soil per unit mass of organic carbon in the soil per the 

211 equilibrium chemical concentration in the solution. Koc is useful when predicting the mobility of 

212 organic soil contaminants; higher Koc values correlate to less mobile organic chemicals and lower 

213 Koc values correlate to more mobile organic chemicals. All other parameters being equal, 

214 chemicals with lower Koc values have a greater likelihood to volatilize from soil since they have 

215 less of an affinity to adsorb to the soil. The modified Woodrow equation utilizes Koc only in the 

216 soil surface flux equation (see Section 2).

217
Draft for Comment Version – March 1, 2014

9

218 Maximum Single Application Rate (lb ai/A)

219 The modified Woodrow equation utilizes application rate only in the soil surface flux equation 

220 (see Section 2). As a result, maximum application rate in the screening tool refers to the

221 maximum labeled application rate for broadcast soil directed applications. The maximum 

222 application rate is chosen in order to be protective of all labeled broadcast soil directed 

223 application rates. 

224

225 Application Timing

226 Application timing refers to when the pesticide is applied during the year. The screening tool 

227 allows for selection of winter, spring, summer, or fall for the timing of application. The 

228 application timing impacts the outputs of the AERSCREEN model runs that the Volatilization 

229 Screening Tool utilizes. The model runs are impacted by application timing via a variety of 

230 factors such as temperature, albedo, Bowen ratios, surface roughness, and release height. These 

231 are discussed in more detail in the Volatilization Screening Tool Guidance Document (see 

232 Appendix A). For the screening analysis, the Agency chose to use spring as the default 

233 application timing because it represents the most likely season of application.

234

235 Crop Scenario

236 The screening tool generates results for four different crop height scenarios that are labeled as

bare soil, cole, row, and orchards18 237 . The crop scenarios included in the screening tool are not a 

238 true input, but rather a built-in feature of the screening tool. These scenarios are designed to 

239 cover the range of potential release heights (i.e., crop canopy heights) that are most commonly 

240 associated with semi-volatile applications. Results for bare soil represent applications to soil 

241 prior to or at planting crops. Results for cole crops represent foliar applications to low growing

242 crops (i.e., about 3 feet or less) such as soybeans, strawberries, cabbage, and some vegetables. 

243 Results for row crops represent foliar applications to medium growing crops (i.e., 6 to < 18 feet)

244 such as corn and tomatoes. Results for orchard crops represent foliar applications to orchard 

245 crops (i.e., > 18 feet) such as apples or oranges. Crop scenario also impacts the potential size of 

246 the source field as acres treated can be impacted by the type of crop or application equipment 

247 used to treat that crop.

248

249 Averaging time for concentration (hours)

250 The averaging time for concentration input is defined based on the toxicological data for a 

251 chemical, and refers to the length of time the study animal was exposed in the study used to 

252 select the inhalation endpoint. In all cases, the Agency attempts to match the duration over 

253 which the estimated air concentrations (i.e., exposures) are averaged with the duration the animal 

254 was exposed in the toxicological study. For example, if a rat inhalation study is used where the 

255 rat was exposed for 4 hours a day, 4 hours would be input for the exposure concentration 

256 averaging time in the screening tool. As a default, 6 hours (i.e., the typical duration of exposure 

257 in many route-specific toxicological studies as described in Agency guidelines) was used as the 

258 averaging time in all cases where an oral study was used as the basis for the inhalation endpoint. 

259 Due to the importance of averaging time, a peak-to-mean scaling factor was developed (as 

260 discussed in Section 2 above) to allow estimation of concentrations for averaging periods longer 

261 than the one hour AERSCREEN outputs (Appendix A). 

 18 Air flow through an orchard is complex and AERSCREEN does not take this complexity into account. Orchard 

values should be characterized appropriately.
Draft for Comment Version – March 1, 2014

10

262

Inhalation Point of Departure (POD) (μg/m3 263 )

264 Inhalation POD refers to the chemical-specific human-health point of departure selected for the 

265 inhalation route of exposure in a chemical’s most recent human health exposure or risk 

266 assessment. For this input, there are three options and all three of these were used in the 

267 Registration Review chemical volatilization screening analysis:

268 • If, in the most recent, relevant risk assessment, a route-specific inhalation toxicological 

269 study was used as the basis for the inhalation endpoint and a human equivalent 

270 concentration (HEC) was calculated via use of the Agency’s reference concentration 

(RfC) methodology,

19 271 the Agency used the HEC for the inhalation POD.

272 • If, in the most recent, relevant risk assessment, a route-specific inhalation toxicological 

273 study was used as the basis for the inhalation endpoint, but an HEC was not calculated, 

274 the Agency used the no observed adverse effect level (NOAEL) for the inhalation POD. 

275 [Note: In the future, HECs could be calculated for these chemicals.]

276 • If, in the most recent, relevant risk assessment, a route-specific inhalation toxicological 

277 study is not available and, thus, an oral toxicological study was used as the basis for the 

278 inhalation endpoint, the Agency used the NOAEL from the oral study, converted to an 

279 inhalation equivalent concentration (IEC) via the following equation.

280

281

282

283

284

285 Where:

IEC = inhalation equivalent concentration (μg/m3 286 ),

287 NOAEL = NOAEL from oral study (mg/kg/day),

288 CF1 = conversion factor to convert mg to μg,

289 A = absorption (unitless),

290 CF2 = conversion factor to account for species specific respiratory

volume and body weight (m3 291 /hr/kg),

292 D = duration (hrs/day), and

293 AF = activity factor (unitless).

294

295 Subsequently, the IECs were used for the inhalation POD in the screening tool. The IECs 

296 used in the Registration Review chemical screen can be found in Appendix B.

297

298 Uncertainty Factor (UF) (unitless)

299 Uncertainty factor refers to the total uncertainty factors applied to an individual chemical. 

300 Uncertainty factors can be applied for a variety of reasons including, but not limited to, 

301 interspecies factor, intraspecies factor, FQPA (Food Quality Protection Act) factor, LOAEL to 

302 NOAEL factor, database uncertainty factor, etc. 

303

 19 U.S. EPA. Methods for Derivation of Inhalation Reference Concentrations (RfCs) and Application of Inhalation 

Dosimetry. U.S. Environmental Protection Agency, Office of Research and Development, Office of Health and 

Environmental Assessment, Washington, DC, EPA/600/8-90/066F.
Draft for Comment Version – March 1, 2014

11

304 For the Registration Review chemical screening analysis, the following uncertainty factors were 

305 used:

306 • Route-specific inhalation study; HEC calculated:

307 o UF for interspecies extrapolation may be reduced to 3X per the RfC methodology;

308 o UF for intraspecies variation was retained at 10X; and

309 o Additional UFs were applied consistent with the most recent, relevant risk 

310 assessment for each chemical (e.g., FQPA, LOAEL to NAOEL, etc.).

311 • Route-specific inhalation study; HEC not calculated:

312 o UF for interspecies extrapolation was retained at 10X;

313 o UF for intraspecies variation was retained at 10X; and

314 o Additional UFs were applied consistent with the most recent, relevant risk 

315 assessment for each chemical (e.g., FQPA, LOAEL to NAOEL, etc.).

316 • Oral study; IEC calculated:

317 o UF for interspecies extrapolation was retained at 10X;

318 o UF for intraspecies variation was retained at 10X; 

319 o FQPA UF of 10X to address database uncertainty due to lack of an inhalation 

320 study was applied consistent with current Hazard and Science Policy Council 

321 (HASPOC) policies; and

322 o Additional UFs were applied consistent with the most recent, relevant risk 

323 assessment for each chemical (e.g., FQPA, LOAEL to NAOEL, etc.).

324

325 Section 4.0: Registration Review Chemical Volatilization Screen 

326 Results

327

328 All pesticides distributed and sold in the United States must be registered by the Agency, based 

329 on scientific data showing that they will not cause unreasonable risks to human health, workers, 

330 or the environment when used as directed on product labeling. Registration Review is a process 

331 that makes sure that, as the ability to assess risk evolves and as policies and practices change, all 

registered pesticides continue to meet the statutory standard of no unreasonable adverse effects.20 332 

333 To ensure that the potential for exposure via volatilization from all impacted pesticides are 

334 considered under this process, the tools described above were used to perform a bystander 

335 inhalation screening analysis for all of the conventional Registration Review chemicals. 

336 Appendix C contains the input sheets for the Volatilization Screening Tool for every chemical

337 screened. The Agency plans to use the results of this screening analysis to determine when 

338 volatilization data (i.e., flux studies) and/or route-specific inhalation toxicological data (if not 

339 already available) should be required for a chemical.

340

341 The analysis consisted of screening 427 chemicals. There were three basic outcomes of the 

342 screen: no quantitative screen, pass the quantitative screen, and fail the quantitative screen. 

343 These outcomes are described in further detail below.

344

345

 20 http://www.epa.gov/oppsrrd1/registration_review/index.htm
Draft for Comment Version – March 1, 2014

12

346 • A quantitative screen was not performed for 174 chemicals. In all cases, these chemicals 

347 have no wide-scale, agricultural uses. For pesticides that did not receive a quantitative 

348 screen, the Agency has high confidence that use of the pesticide will not result in any 

349 meaningful bystander risk due to volatilization of residues based on a variety of specific 

350 reasons which are provided in Appendix D. In general, the categories of reasons for not 

351 performing a quantitative screen include the following:

352 o 22 of these chemicals will have qualitative risk assessments during Registration 

353 Review;

354 o 21 of these chemicals either have no currently registered products or have been 

355 voluntarily cancelled as part of Registration Review;

356 o 12 of these chemicals have inhalation toxicity studies that show no effects;

357 o 18 of these chemicals are classified as fumigants and thus volatilization is the 

358 major route of exposure and is already assessed or will be assessed during 

359 Registration Review;

360 o 12 of these chemicals have uses that will result in separate post-application 

361 inhalation assessments (e.g., indoor, mosquito adulticide uses);

362 o 65 of these chemicals are registered for uses that are not expected to have any 

363 significant potential for volatilization:

364  8 only registered for direct aquatic application uses;

365  18 are only registered as baits;

366  6 are only registered for greenhouse use;

367  5 are only registered for direct animal application uses (e.g., pet, livestock 

368 uses);

369  5 are only registered for seed treatment uses;

370  6 are only registered for repellent uses;

371  10 of these chemicals have import tolerances only and thus have no 

372 registered uses in the U.S.;

373  7 are only registered for other unique uses (e.g., post-harvest treatments, 

374 food handling establishments, tree injection, etc.)

375 o 24 of these chemicals have registered uses (e.g., residential turf, ornamentals) 

376 that cannot be screened with the Volatilization Screening Tool. The potential for 

377 these chemicals to volatilize will be dealt with on an individual chemical basis 

378 throughout Registration Review.

379

380 • 185 chemicals passed the quantitative screen. Passing the quantitative screen means that 

381 the concentration of concern (i.e., the point of departure divided by the total uncertainty 

382 factors or COC) was not exceeded for any crop scenario at any distance downwind from 

383 any size field. For a pesticide that passed the screening analysis, the Agency has high 

384 confidence that use of the pesticide will not result in any meaningful bystander risk due 

385 to volatilization of residues and further data would generally not be required.

386

387 • 68 chemicals failed the quantitative screen. Failing the quantitative screen means that the 

388 COC was exceeded for at least one crop scenario at some distance downwind from the 

389 field for at least one field size. Of the chemicals that failed the quantitative screen, 24

390 have route-specific inhalation toxicological data, while 44 do not. There are 53

391 occurrences of a foliar application failing the screen and 24 occurrences of a soil 
Draft for Comment Version – March 1, 2014

13

392 application failing the screen (i.e., some chemicals have multiple crop scenarios that 

393 fail). If a pesticide fails the screening analysis, the Agency would examine whether data 

394 are available to refine the analysis and whether additional data should be required. 

395 Failing the screening analysis does not necessarily mean that the pesticide poses a risk 

396 of concern due to volatilization. Rather, due to the purposely conservative nature of the 

397 screening analysis (see Section 5.0), failing the screen is merely a trigger for the Agency 

398 to further investigate the question of exposure from volatilization of the pesticide. 

399 Potential additional data that could help to refine a failing screen include the following:

400 o volatilization data (i.e., flux studies);

401 o route-specific inhalation toxicological data if none are available; and/or

402 o vapor-phase dose administration inhalation toxicological data if only aerosol dose 

403 administration inhalation toxicological data are available.

404

405 Table 1 presents the details of the 68 chemicals that failed the quantitative screen. In addition, 

406 Appendix D provides details on the screen for the entire 427 chemicals.
Draft for Comment Version – March 1, 2014

14

407

Table 1: Registration Review Chemicals that Fail the Quantitative Volatilization Screen Analysis

Chemical

Inhalation 

Tox Study 

Available?

Comments

Acephate Yes Cole and row scenarios exceed COC at 20 acre and larger fields.

Acibenzolar No Cole scenario exceeds COC at 60 acre and larger fields.

Atrazine No Soil scenario exceeds COC at all field sizes.

Bromoxynil and esters No Cole and row scenarios exceed COC at 60 acre and larger fields.

Buprofezin No Cole and orchard scenarios exceed at all field sizes.

Butylate No Soil scenario exceeds COC at all field sizes. All applications soil incorporated, likely conservative.

Captan Yes Cole, row, and orchard scenarios exceed COC at all field sizes.

Chlorethoxyfos Yes Row scenario exceeds COC at all field sizes.

Chlorothalonil Yes Cole, row, and orchard scenarios exceed COC at all field sizes.

Chlorpropham No Cole scenario exceeds COC at all field sizes. Only “agricultural” use is Easter lilies which are only grown in 

Norther CA and Southern OR.

Chlorpyrifos Yes Cole, row, orchard scenarios exceed COC at all field sizes.

Daminozide (Alar) No Row scenario exceeds COC at all field sizes.

DCNA No Cole and row scenarios exceed COC at 20 acre field sizes and larger.

Diazinon Yes Cole, row, orchard scenarios exceed COC at all field sizes.

Dicamba No Cole and row scenarios exceed COC at 40 acre field sizes and larger.

Dichlobenil Yes Row and orchard scenarios exceed COC at all field sizes.

Dicrotophos Yes Cole scenario exceeds COC at all field sizes.

Dimethenamid No Cole and soil scenarios exceed COC at all field sizes.

Dimethoate Yes Cole, row and orchard scenarios exceed COC at all field sizes.

Diquat Dibromide Yes Cole and row scenarios exceed COC at all field sizes. Orchard scenario exceeds COC at 80 acre field sizes and 

larger.

Emamectin Benzoate No Cole scenario exceeds COC at 60 acre field sizes and larger.

Endothall, and salts No Cole and row scenarios exceed COC at all field sizes.

EPTC Yes Cole and row scenarios exceed COC at all field sizes.
Draft for Comment Version – March 1, 2014

15

Table 1: Registration Review Chemicals that Fail the Quantitative Volatilization Screen Analysis

Chemical

Inhalation 

Tox Study 

Available?

Comments

Esfenvalerate No Row scenario exceeds COC at 60 acre field sizes and larger.

Ethalfluralin No Soil, cole, and row scenarios exceed COC at all field sizes.

Ethofumesate No Soil scenarios exceed COC at all field sizes.

Ethoprop No Soil scenario exceeds COC at all field sizes. All applications soil incorporated, likely conservative.

Fenpropathrin No Row scenario exceeds COC at 120 acre field size only.

Ferbam No Cole scenario exceeds COC at 20 acre field sizes and larger.

Flumetsulam No Soil scenario exceeds COC at 20 acres and larger.

Flumioxazin No Soil, cole, and row scenarios exceed COC at all field sizes.

Fomesafen No Soil scenarios exceed COC at all field sizes.

Formetanate HCl No Row and orchard scenarios exceed COC at all field sizes.

Fosthiazate Yes Row scenarios exceed COC at all field sizes.

Linuron No Soil, cole, and row scenarios exceed COC at all field sizes.

MCPA No Soil and cole scenarios exceed COC at most field sizes.

Metalaxyl No Cole and row scenarios exceed COC at 60 acre field sizes and larger.

Methamidophos Yes Cole and row scenarios exceed COC at all field sizes.

Metolachlor & 

s-Metolachlor No Cole and row scenarios exceed COC at 60 acre field sizes and larger.

Metsulfuron No Row scenario exceeds COC at 40 acre field sizes and larger.

Naled Yes Cole, row, and orchard scenarios exceed COC at all field sizes.

Nitrapyrin No Row scenarios exceed COC at all field sizes.

Paraquat dichloride Yes Cole and row scenarios exceed COC at all field sizes.

PCNB No Cole, row, orchard, and soil scenarios exceed COC at all field sizes.

Pendimethalin No Soil, cole, row, and orchard scenarios exceed COC at all field sizes.

Phorate No Soil scenario exceeds COC at all field sizes. Note: Granular products only. All applications soil incorporated, 

likely conservative.

Phosmet No Cole and row scenarios exceed COC at all field sizes.
Draft for Comment Version – March 1, 2014

16

Table 1: Registration Review Chemicals that Fail the Quantitative Volatilization Screen Analysis

Chemical

Inhalation 

Tox Study 

Available?

Comments

Pronamide No Soil, cole, and row scenarios exceed COC at all field sizes.

Propachlor No Soil scenarios exceed COC at all field sizes.

Propazine No Soil scenario exceed COC at 60 acre field sizes and larger.

Pyrethrin and derivatives Yes Cole and row scenarios exceed COC at 40 acre field sizes and larger.

Pyridaben Yes Cole scenario exceeds COC at 40 acre field sizes and larger.

Pyrimethanil No Cole scenario exceeds COC at 40 acre field sizes and larger.

Simazine No Soil scenario exceeds COC at 40 acre field sizes and larger.

Tebupirimiphos Yes Soil and row scenarios exceed COC at all field sizes.

Tefluthrin Yes Soil scenario exceeds COC at all field sizes. 

Terbacil No Row scenario exceeds COC at 120 acre field size only.

Terbufos Yes Soil scenario exceeds COC at all field sizes. Note: Granular products only. All applications soil incorporated, 

likely conservative.

Tetraconazole Yes Cole, row, and orchard scenarios exceed COC at all field sizes.

Thiazopyr No Soil scenario exceeds COC at all field sizes.

Thiobencarb No Soil scenario exceeds COC at all field sizes.

Thiodicarb Yes Cole and row scenarios exceed COC at all field sizes. Note: Inhalation study is on dust formulation.

Thiophanate-methyl No Cole and row scenarios exceed COC at 40 acre field sizes and larger.

TPTH (Triphenyltin hydroxide) Yes Cole and row scenarios exceed COC at all field sizes. Orchard exceed COC at 40 acre field sizes and larger.

Triadimefon No Orchard scenario exceeds COC at 80 acre field size only.

Triallate No Soil scenario exceeds COC at all field sizes.

Triclopyr, salts and esters No Row scenario exceeds COC at 80 acre field sizes and larger.

Triflumizole No Cole scenario exceeds COC at 40 acre field sizes and larger.

Trifluralin Yes Soil scenario exceeds COC at 20 acres and larger.
Draft for Comment Version – March 1, 2014

17

408 Section 5.0: Registration Review Chemical Volatilization Screen 

409 Characterization

410

411 There are a number of considerations and uncertainties that should be taken into account in the 

412 interpretation of the results of the Registration Review chemical volatilization screening analysis

413 presented in Section 4. The Agency acknowledges that there are uncertainties associated with 

414 the current knowledge base relating to the processes that govern volatilization of conventional 

415 pesticides from soil and foliar surfaces. However, the Agency is confident that the screening 

416 analysis uses data and methodologies that results in a consistent and health protective framework 

417 to assess whether a pesticide does not pose potential inhalation bystander risks resulting from 

418 volatilization of conventional pesticides.

419

420 Some of the considerations and uncertainties that should be considered in the interpretation of 

421 the screening analysis results include the following:

422

423 Modified Woodrow Equation Characterization

424 • Use of the modified Woodrow equation to predict flux from soil and foliar surfaces is 

425 consistent with the recommendations of the December 2009 Federal Insecticide, 

426 Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP) meeting 

427 entitled “Scientific Issues Associated with Field Volatilization of Conventional 

Pesticides”21 428 . In order to be more health protective, the Agency used the data provided in 

429 the Woodrow paper to estimate the 90% upper confidence limit around the slope and 

430 intercept so that 90% of the estimated flux rates would exceed the measured values. In 

431 addition, as more volatilization data for other chemicals become available it may be 

432 possible to update this equation.

433 • It is important to note that the Agency used physical/chemical properties for the active 

434 ingredient, or technical chemical, and these may not reflect the physical/chemical 

435 properties of the end-use product(s). Most pesticides are mixed or diluted with water, 

436 solvents, and inerts. The addition of these components can impact these 

437 physical/chemical properties relative to the active ingredient in its technical form. 

438

439 AERSCREEN Characterization

440 • AERSCREEN generates a maximum one-hour air concentration assuming air flow 

441 remains constant and in a single direction. The values reported in the tool are worst case 

442 values and should be characterized as such (Appendix A).

443 • AERSCREEN models air flow for simple, uniform terrain. Because of the complex 

444 topography and air flow patterns in an orchard, use of the results generated for orchards 

should be characterized appropriately.

22 445 While the topography for cole or row crops is 

446 not completely uniform, it is believed that the differences are not significant enough to 

447 impact the air flow regime and concentrations outside the treated field. 

 21 http://www.regulations.gov/ (EPA-HQ-OPP-2009-0687) 22 Unlike AERSCREEN, (interactive mode), the refined model AERMOD considers flow around or above complex 

mountainous terrain. However, neither AERSCREEN nor AERMOD considers complex flow patterns through 

highly localized non-homogeneous surfaces such as orchard groves.
Draft for Comment Version – March 1, 2014

18

448 • For simplicity, the fields in AERSCREEN were modeled as squares and the modeled 

449 field sizes were limited. While this may not necessarily reflect all real-world agricultural

450 scenarios, it is consistent with current Agency fumigant assessment methodology.

451 • In most cases, the maximum AERSCREEN concentration at any distance corresponded 

452 to the minimum wind speed of 0.5 m/s. In the case of many, but not all, conventional 

453 pesticides, the maximum flux rate is likely to occur during the middle of the day when 

454 temperatures are highest and air turbulence and wind speed have increased. As a result, 

455 for conventional pesticides, matching the maximum flux rate with the minimum wind 

456 speed will result in conservative, health protective air concentrations around a treated 

457 field.

458 • Users need appropriate justification for selecting field sizes and crop scenarios used in 

459 the modeling runs. Any differences between what was modeled and what is expected to 

460 occur in the real world should be characterized.

461 • Although the Agency chose to use spring as the default application timing for the 

462 Registration Review chemical screening analysis, if a particular pesticide has a very 

463 specific application timing requirement on the label, use of another season may be more 

464 appropriate and result in a different outcome.

465

466 Hazard Characterization

467 • The Volatilization Screening Tool provides risk estimates for exposure to chemicals in 

468 the vapor phase; however, even for those chemicals that have route-specific inhalation 

469 toxicological data, these studies are typically not performed under vapor phase

470 conditions. The majority of these data are performed with aerosols, and following 

471 Agency guidelines, the particles are typically 2-4 μm in size. Vapors and particles have 

472 the potential to be different in terms of the site of deposition, absorption, dose, and 

473 toxicity. At the 2009 Volatilization SAP, one of the questions asked by the Agency of 

474 the Panel related to the difference in toxicity between vapors and aerosols; however, the 

475 Panel knew of no studies that have investigated the health impact of exposure to a single 

476 chemical using different phases (e.g., vapors and aerosols). Since that time, data 

477 conducted using chlorpyrifos indicate that aerosols may be more toxic than vapors, at 

478 least for this specific chemical. More inhalation toxicological data, including direct 

479 comparison vapor/aerosol studies, are needed to further elucidate this issue.