# Department of Pesticide Regulation

Mary-Ann Warmerdam

Director 

### M E M O R A N D U M Arnold Schwarzenegger

Governor

1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov

A Department of the California Environmental Protection Agency

Printed on recycled paper, 100% post-consumer--processed chlorine-free. TO: Randy Segawa Environmental Program Manager I Environmental Monitoring Branch (916) 324-4137

FROM: Terri Barry Original signed by

Research Scientist III Environmental Monitoring Branch (916) 324-4140

DATE: January 29, 2010

SUBJECT: Response to public comments on the Met hyl Iodide Risk Char acterization Document

Background

The Department of Pesticide Re gulation (DPR) received comments on the Methyl Iodide (MeI) Risk Characterization Document (RCD) from several outside parties. This memorandum provides responses to comments on the air disp ersion modeling and the environmental fate

sections.

Comments were received from the following parties: Arysta, Worksafe, National Resource Defense Council (NRDC), Pesticide Action Netw ork North America (PANNA), and K. Collins. Each set of comments will be discussed separately below.

Responses to Comments

Arysta –

Arysta’s comments are centered on the idea th at DPR has used “outdated methods” for the exposure assessment. DPR is using screening methods for the RCD. Screening methods are acceptable and appropriate to produc e air concentration estimates. DPR has used this approach since 1992 when mitigation measures in the form of buffer zones were developed for methyl bromide. Because of the long history of use, sc reening methods used at DPR are well understood and characterized. In fact, the document “Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Revised (EPA -454/R-92-019)” is currently on the U.S. EPA Support Center for Regulatory Atmos pheric Modeling internet website (http://www.epa.gov/scram001/guidance_permit.ht m). This document includes methods for estimating screening level air concentrations for area sources and has an u pdate that specifically applied to screening estimates for area source s which can be found at the following website: http://www.epa.gov/scram001/guidance/guide/scr upd.pdf. Thus, it is still a U.S. EPA accepted method. Screening methods are r easonable worst-cas e estimates.Randy Segawa January 29, 2010 Page 2

The U.S. EPA Screening Procedures document stat es: “The simple screening procedure (Phase 1) is applied to determine if the source poses a po tential threat to air qual ity. The purpose of first applying a simple screening procedure is to c onserve resources by eliminating from further analysis those sources that clear ly will not cause or contribute to ambient concentrations in

excess of short-term air quality standards or allowable concen tration increments. A relatively large degree of "conservatism" is incorporated in that screening procedur e to provide reasonable

assurance that maximum concentrations will not be underestimated.”

Arysta states: “The assumption of a constant wind dir ection over 24 hours, or for that matter 8 hours, is particularly unrealistic. Furthermor e, the wind speed assumption is at the extreme low-end of the distribution of wind speeds in th e environment. In fact, the dispersion model used by DPR will not even accept a smaller wind speed than 1 m/sec.”

Air concentration produced using screening methods are not “incorrect.” As discussed above, the document “Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Revised (EPA-454/R-92-019)” is currently on th e U.S. EPA Support Center for Regulatory Atmospheric Modeling website. The meteorolog ical conditions used to product the air

concentrations are not “a rtificial.” They are screening mete orological scenarios that can, and do,

occur.

Arysta states: “ The illogical nature of DPR’s calcula tions can be observed by comparing the concentration estimates averaged over 8-hour and 24-hours in Table 13.”

There are several inte racting and confounding factors that make the Arysta comparisons inappropriate: 1) the maximum 8-hr flux was c hosen using a rolling average. This highest average flux was then paired with the reasonabl e worst-case meteorological conditions for the 8- hr scenario. This estimate is totally independent of the 24-hr scenario and should be interpreted as such. 2) The meteorological s cenarios are different for the 8- hr versus the 24-hr averaging

times. The 8-hr case uses D stabil ity, the 24-hr case uses C stabili ty. Even if all other factors were held constant (which they are not since the flux estimates are specific to the averaging time), the difference in stability class pr oduces significant nonlinear changes in air concentrations between averaging times. Thus, the 8-hr air concentration is expected to be substantially higher than the 24-hr air concentration because it was derived independently using maximum 8-hr flux and more stable atmospheri c conditions. The example calculation Arysta presents, “ Even if the concentration were zero fo r the other 16 hours of the day, given a concentration of 9.5 μg/L for the first 8 hours, the “maximum” 24-hour c oncentration would be 3.2 μg/L,” is not valid because of this diffe rence in atmospheric stability.Randy Segawa January 29, 2010 Page 3

3) The effect of scaling on averaging times is not proportional. For example, the maximum continuous 8-hr concentration during a conti nuous 24-hr monitoring period will be in the neighborhood of twice the 24-hr conc entration. This effect is docum ented in air dispersion theory

literature.

Thus, it is inappropriate to make the direct comparison and calcul ations such as those made by Arysta. With respect to the DPR air concentratio n estimates, it is not possible to make simple

statements such as “ For a given “maximum” 8-hour aver age concentratio n, the corresponding “maximum” 24-hour average concentr ation should not be less t han one-third of the “maximum” 8-hour average concentration.”

This is exactly the stage that DPR is at with Iodomethane. DPR chose to use the screening method at this stage of evaluation.

Arysta states: “ DPR’s methodology for estimating the 2- week average concentration is based on something DPR calls “peak-to-mean” theory. The peak-to-mean theory is based on measurements made in the 1950-1960s of the va riability in air pollutio n at sampling points downwind of contiuously- emitting smoke stacks...”

The technique is commonly used in the air pollution regulatory community. The memorandum cited (Barry, 2000) is available for refe rence at the following internet website: http://www.cdpr.ca.gov/docs/emon/pubs/ehapr eps/analysis_memos/2000_segawa.pdf. The theoretical foundation of “peak-to-mean” methods dates back to 1921 in the work of G.I. Taylor’s concepts of diffusion by continuous mo tion. The first major paper addressing the peakto-mean concept was published in 1959 by Giff ord. The method was further developed by Hino in 1968 and is referenced specifically by Tu rner in his 1994 text entitled “Workbook of atmospheric dispersion estimates. Furthermore, th e peak-to-mean adjustment concept is used by U.S.EPA in the 1992 document Screening Procedur es for Estimating the Air Quality Impact of Stationary Sources, Revised (EPA-454/R-92-019) in the same manner as applied by DPR. This method has been used routinely to obtain long-te rm averages from shorter averaging time air

concentrations.

Arysta states; “...emission rates for iodometh ane dramatically decl ine after the first 24- hours after the application, as evidenced in all of the flux studies. Therefore, the primary reason for lower concentrations over a 2-week period is the reduction in emission rate. Peak-to-mean theory is used to estimate th e impact of variability due to changes in the wind direction and the looping of the plume. Therefore, it was misapplied to estimate season exposures by DPR.Randy Segawa January 29, 2010 Page 4

DPR staff is aware, and agrees that methyl iodide flux declines steeply after the first 24 hours. That is why the effective flux used to estimate th e 2 week average air conc entration is the 2 week average 24 hr flux. This flux estimate incorporates the form of the flux profile over 2 weeks and is effectively a uniform flux for that period, t hus satisfying the continuously emitting assumption of the peak-to-mean theory (see the Arysta comm ent above). It should be noted that the peak-tomean theory does not incorporate the looping of an elevated plume. The theory is derived by characterizing the lateral displ acement of the plume centerline over one averaging period relative to the averaging period of interest. P.J. Ba rry in Boundary-Layer Meteorology Vol 2(1971): 122- 126 indicates that the basic peak-to-mean ratio holds for any s hort-period to long-period ratio within the bounds given in his paper. The short period bounds ar e 5 s to 24 hrs; long period bounds are 6 min and 5 yrs. The ratio can be app lied to obtain long to s hort or short to long adjustments, as discussed in Turner. Peak-to-mean adjustments are routinely used on area sources (e.g. manure piles, sewage tr eatment plants) in odor abatement.

Worksafe – This set of comments pertai ns only to farm workers. No air dispersion modeling or environmental fate comments were included. Thus, no response is required.

NRDC – This set of comments has no comments pe rtaining to air disper sion modeling and one comment pertaining to environmental fate.

Comment 9: “MeI is likely to contaminate groundwater resources, which could pose a significant health hazard through contamination of drinking water.”

The assessment by NRDC is that the ground water i odide estimate should be refined and that the issue should be thoroughly studied and resolved before MeI is granted a California registration.

Response: DPR’s evaluation indicates that met hyl iodide is very un likely to contaminate groundwater. The potential for the iodide anion breakdown product to contaminate groundwater

is unknown. DPR’s assessment includes a worst-case estimate of potential groundwater contamination by iodide. In addition, DPR a dded an alternative estimate of ground water concentrations to its assessment, using bromide ion as a surrogate. The U.S. Geological Survey

detected bromide in 246 of 256 wells in Californi a, with concentrations ranging from 0.01 mg/L to 13.3 mg/L, and a mean of 0.30 mg/L. They also detected iodide in 234 of the same 256 wells, with concentrations rangi ng from 0.001 to 2.4 mg/L, and a mean of 0.08 mg/L. These groundwater concentration estimates are adequate to estimate the health risk of iodide in water.

A. Wise – This set of comments references DPR air dispersion modeling and environmental fate analysis but does not suggest changes in either. Thus, no response is required.

K. Collins – This set of comments pe rtains only to toxicology. Thus, no response is required.Randy Segawa January 29, 2010 Page 5

PANNA – Two documents are included in the P ANNA submission: Review of the DPR RCD

and Comments submitted to U.S.EPA.

Page 8. Suggestion that DPR should use AERMOD rather than ISCST3. Response: The new algorithms in AERMOD are not implemented for area sources. For similar inputs, similar results will be obtained with both ISCST3 and AERMOD. All previous modeling at DPR has been conducted using ISCST3. For c onsistency, ISCST3 will continue to be used since switching to AERMOD for area sources has no benefit.

Page 8. comment on modeling poisoning incidents.

Response: DPR staff has published fi ve peer reviewed articles on modeling incidents. All four California incidents shown on Page 6, Table 2 of the PANNA comments are subjects of those published peer review articles. Shown below are those articles:

1: Oriel M, Edmiston S, Beauvais S, Barry T, O'Malley M. Illnesses associated with chloropicrin use in California agriculture, 1992-2003. Rev Environ Contam Toxicol. 2009;200:1-31.

2: O'Malley M, Barry T, Ibarra M, Verder-C arlos M, Mehler L. Illnesses related to shank application of metam-sodium, Arvin, California, July 2002. J Agromedicine. 2005;10(4):27-42. Erratum in: J Agromedicine. 2006;11(2):91.

3: Centers for Disease Control and Prev ention (CDC). Illness associated with drift of chloropicrin soil fumigant into a residentia l area--Kern County, California, 2003. MMWR Morb Mortal Wkly Rep. 2004 Aug 20;53(32):740-2.

4: O'Malley M, Barry T, Verder-Carlo s M, Rubin A. Modeling of methyl isothiocyanate air concentra tions associated with community illnesses following a metam-sodium sprinkler application. Am J Ind Med. 2004 Jul;46(1):1-15.

5: Barry T, Oriel M, Verder-Carlos M, Me hler L, Edmiston S, O’Malley M. Community Exposure Following a Drip-Application of Chlo ropicrin. Journal of Agromedicine, 15:1–14,

2010Randy Segawa January 29, 2010 Page 6

Pages 8-9. Request that DPR include the detail of field studies...clarify how differences in soil temperature are accounted for by the model.

Response: DPR staff agrees in concept that te mperature should have some effect on flux. However, other factors also influence flux, su ch as method of application, soil type, soil moisture, and field preparation procedures. These other factors confound the effect of temperature on flux, so no relationship can be esta blished with existing data. In addition, it’s likely that soil temperature at the depth of injection has a greater influence on flux than air temperature. Since most fumigant applicati ons are made at a dept h of 12-24 inches, the temperature effect is dampened because the soil te mperature varies less than the air temperature.

The relationship between air temperature and flux is not clear. Analysis of MeI flux from 11 field studies by Reiss and Griffin (2007) found no detectable re lationship between temperature

and flux.

A second example of the lack of demonstrated relationship between air temperature and flux is found for chloropicrin (Beard, 1996). A 33.8% ma ss loss for chloropicrin was found in a Washington field study. A 36.5% ma ss loss was found in a Florida field study. These were both broadcast tarp chloropicrin applications. The air temperatures during th e Florida study were 15 to 20 degrees F warmer yet the mass loss resu lts are similar to the Washington study.

DPR’s work with methyl bromide applications th roughout the year found that winter applications can show high flux, high emission ratios (flux expr essed as the fraction of amount applied), and high air concentrations. In fact, an alysis of the relationship between Julian date of the application (as a surrogate for temperature) and the emissi on ratio shows no significant relationship between emission ratio and day of application. The regr ession equations for each application of emission

ratio as a function of Julian da te had R-square values of 3%, 7%, and 12% for nontarp deep, tarp broadcast, and tarp bed applic ation methods respectively. A m easurable temperature effect should be clearly discernable in the regression results. Thus, a si mple, clear relationship between temperature and flux is not supported by the DPR methyl bromide database. More likely many factors act together.

A plot of the methyl bromide emi ssion ratios is shown below. Note the complete lack of trend for the tarp broadcast data. In pa rticular, the February 13, 1997 applic ation has an emission ratio of 9.8%. This could be argued to support the low te mperature, low flux theory. However, the July 25, 1998 application shows an emissi on ratio of 6.8%. It is also cl ear the tarp bed application method shows a high emission ratio no matter when the application is made. In fact, the tarp bed applications in December show a 100% emission ra tio, similar to those applications made in June and October. The methyl bromide database is the largest available and likely reflects broad

trends in flux and emission ratios for othe r fumigants. Thus, the relationship between temperature and total mass lost is not clear.Randy Segawa January 29, 2010 Page 7

jul dateem ratio

400 300 200 100 0 100

80

60

40

20

0 nontarp deep

tarp broadcast

tarp bed method Scatterplot of em ratio vs jul date

Page 9. Request that DPR provide clarification of which field studies were used to develop the flux profile and how soil temperatures may differ in those in the study from which the flux profile was determined

Response:

DPR used 7 flux profiles from the 7 studies av ailable at the time the exposure appraisal was developed. The flux profile that resulted in the highest air concentrations was used from among those 7 flux profiles. See Barry (2008a) for details of how the air concentrations were developed.

Page 9. Comment 3. Documentation of the exposu re model should be explicitly described...

See Barry(2008a) for details of the exposure modeling.

Page 12. Comment 5. Subchronic exposure...

See Barry (2008b) for details of the subc hronic air concentration development.Randy Segawa January 29, 2010 Page 8

References

Barry, T. 2008a. Screening level air concentration estimates fo r Worker Health and Safety Exposure Appraisals. Memorandum to Randy Segawa dated August 21, 2008. Environmental Monitoring Branch, Departme nt of Pesticide Regulation, California Environmental Protection Agency, Sacramento, CA. http://www.cdpr.ca.gov/docs/emon/pubs/eha preps/analysis_memos/2071_segawa.pdf

Barry, T. 2008b. Development of sub-chronic air concentration estimates associated with a single fumigant application. Memorandu m to Randy Segawa dated September 5, 2008Environmental Monitoring, Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, CA. http://www.cdpr.ca.gov/docs/emon/pubs/eha preps/analysis_memos/2077_segawa.pdf

Beard, K.K., P.G. Murphy, D.D. Fontaine, J.T. Weinberg. 1996. Monitoring of potential worker exposure, field flux and off-site air concentratio n during chloropicrin fi eld application. HEH 160. Chloropicrin Manufacturers Task Force. DPR Registration Data Volume199-072.

Reiss, R. and J. Griffin. 2007. A review of the flux rate data collected for Iodomethane and Midas® 50:50. DPR Registration Data Volume No. 52875-0140.