1 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENC Y WASHINGTON, D.C. 20460

MEMORANDUM

DATE: July 10, 2014

SUBJECT: Response to Public Comments on th e EFED Registration Review Problem Formulation for Aminopyralid (PC Code No. 005100, 005209, 005219 ; DP Barcode D421326)

TO: Veronica Dutch, Chemical Review Manager Jill Bloom, Team Leader Linda Arrington, Branch Chief Risk Management and Implementation Branch V Pesticide Re-evalu ation Division (7508P)

FROM: Edward Scollon, Ph.D., Toxicologist Katrina White, Ph.D., Biologist Environmental Risk Branch IV Environmental Fate and Effects Division (7507P)

THROUGH: James N. Carleton, Ph.D., Senior Fate Scientist Thomas Steeger, Ph.D., Senior Advisor Sarah Winfield, Acting Branch Chief Environmental Risk Branch IV Environmental Fate and Effects Division (7507P)

The Environmental Fate and Effects Division’s (E FED) reviewed comments from the technical registrant (Dow AgroSciences) on the “Registration Review: Prelim inary Problem Formulation for Environmental Fate, Ecological Risk, E ndangered Species, and Human Health Drinking Water Exposure Assessments for Aminopyra lid, Potassium salt of Aminopyralid, and Triisopropanolamine Salt of Aminopyralid” (Document ID EPA-HQ-O PP- 2013

- 0749 -0011) in www.regulations.gov , referred to as Problem Formulation in this document). The purpose of this memorandum is to respond to these comments. EFED appreciates the comments and has considered them carefully; res ponses are provided below each se t of paraphrased comments.2 1. Aerobic Aquatic Metabolism Study (OCSPP Guideline 835.4300 1 )

Stated in the Problem Formulation: “ Aerobic conditions were not maintained throughout the aerobic aquatic studies. In the absence of an ac ceptable study, the model half-life input for aerobic aquatic metabolism will be assumed to be twice the aerobic soil metabolism half-life, per EFED's input parameter guidance (USEPA, 2009b). ”

Dow AgroSciences Comment: “Dow AgroSciences disagrees with the Agency recommendation for the following reasons:

Three sediments were evaluated in the aer obic aquatic study (MRID 46235731) which used a continuous flow of CO 2 -scrubbed, moist air. The two EU a queous layers were measured as aerobic (>2 ppm oxygen) throughout the study period. The amount of oxygen in the US sediment samples started with lower oxygen content (<1 pp m) but the amount of oxygen steadily increased over the study to ca 3-4 ppm. Furthermore, for all thr ee aqueous layers the redox potential suggested aerobic conditions, with generally positive or small negative values. The redox potential of the sediment suggests mildly anaer obic to anaerobic conditions, with values in the negative range. This is completely expected, especially as the sediment measurements are obtained from the bottom of the sediment (the pr obe rests on the container, for consistency in measurement). Furthermore, this is in full ag reement with current guidance OECD 308, which states in paragraph 2, "The aerobic test simu lates an aerobic water column over an aerobic sediment layer that is underlai n with an aerobic gradient.''

EFED Response: OCSPP Guideline 835.4300 states, “ The aerobic system desc ribed in this test guideline consists of an aerobic water layer (typ ical oxygen concentratio ns range from 7 to 10 mg/L) and a sediment layer, aerobic at the su rface and anaerobic below the surface (typical average redox potentials (E h ) in the anaerobic zone of the sedime nt range from -80 to -190 mV). Moistened air is passed over the surface of th e water in each incubation unit to maintain sufficient oxygen in the head space. ” Moistened air was used in the test systems. In the U.S. test systems, the initial and final dissolved oxygen concentrations were 0.2 and 3.3 mg/L. In the Italian test system, the initial and final disso lved oxygen concentrations were 3.0 and 4.6 mg/L. In the French test system, the initial and fina l dissolved oxygen concentrations were 4.2 and 7.3 mg/L, respectively. All but one of these disso lved oxygen concentrations are below the range recommended in the OCSPP guideline. Additionally, electron activity (pe) plus pH values at the initial and final measurements in water were all less than 12, indicati ng redox potentials where aerobic microorganisms that utilize oxygen to oxidize organic matter do not function 2 . The boundary between oxic and suboxic c onditions can be seen in Spos ito, 1989 Figure 6.1 to be near a pe + pH of 12. Also, ferric iron (Fe 3+ ) is eliminated as an elec tron acceptor near pe + pH <12. This methodology of determining anaerobic versus aerobic conditions takes into account that both oxidation -reduction potential (E h ) and pH must be considered when determining which microbial populations may be active. Add itionally, the observed aerob ic aquatic metabolism

1 USEPA. 2008. Fate, Transport, and Transformation Guidelines . OPPTS 835.4300 Aerobic Aquatic Metabolism; OPPTS 835.4400 Anaerobic Aquatic Metabolism . EPA 712-C-08-018 & E. 712-C-08-019. October 2008. Office of Prevention, Pesticides, and Toxic Su bstances. United States Environmental Protection Agency. Available at http://www.epa.gov/ocspp/pubs /frs/publications/Test_Guidelines/ser ies835.htm (Accessed May 17, 2012).

2 Sposito, G. 1989. The Chemistry of Soils. Oxford Univ. Press, New York.3 half-life values (462 to 990 days) are much long er than the observed aerobic soil metabolism half-life values (26.4 to 408 days). These resu lts together with the data indicating reducing conditions and low oxygen concentrations in the aerobic aquatic test systems suggest that the available values underestimate aerobic aquatic degradation ( e.g ., result in a high half-life), and their use in modeling could resu lt in very conservative estimated environmental concentrations (EECs). Having additional data will reduce uncerta inty in the potential for risk to terrestrial plants from residues in irrigation water for terrestrial uses. For a pplications directly to water, this study will reduce the uncertainty for the risk a ssessment for aquatic and te rrestrial plants. In the absence of additional data, the available aerobic aquatic metabolism study results will be used in the risk assessment or a value of 2x the aerobic soil metabolism value will be used.

2. Dissipation study in co mpost (Non-Guideline)

Stated in the Problem Formulation: “ Aminopyralid applied to vegetative matter used as animal feed, from which manure is produced that is subsequently composted, has been found to remain present in sufficient quantity to damage non-target pl ants (see Section 6c Ecological Incidents). A study is requested to quantify rate s of aminopyralid degrada tion with in composted material. ”

Dow AgroSciences Comment: Dow AgroSciences has conducted a benc h scale manure/straw composting study. Aminopyralid residues did not decline appreciabl y during the thermophilic or mesophilic phases of the composting process. These results indicate that composting process is not likely to be a useful technique to mitigate aminopyralid residue in compost inputs. Upon request by EPA, "Depuration and Composting of Aminopyralid in Ruminant Manure Systems" (study ID 081082, 2008) would be submitted.

EFED Response: EFED recommends the study be submitted for review and subsequent determination of how those data will be used. In the absence of information submitted to better understand the rate of degradation in compost, aminopyralid will be assumed to be stable in composted materials.

3. Prospective Groundwater Monitoring Study (OCSPP 835.7100 3 )

Stated in the Problem Formulation: “ Residues of aminopyralid have been detected in groundwater and other picolinic acids have incide nts where residues of picolinic acids in groundwater used for irrigation resulted in damage to terrestrial plants. Additionally, risk assessments for aminopyralid have identified this pathway as a pot ential concern for damage to terrestrial plants. Additional data are recomme nded to better understand the potential for risk due to residues of aminopyralid in groundwat er. Studies that would be useful include a prospective groundwater monitoring study or st udies to refine groundwat er modeling inputs for the Pesticide Root Zone Mode l for Groundwater (PRZM-GW) mode l. A prospective groundwater

3 USEPA. 2008. Fate, Transport, and Transformation Guidelines. OPPTS 835.7100: Guidanc e for Prospective Ground-Water Monitoring Studies . EPA 712-B-10-001. August 25, 2008. Office of Preven tion, Pesticides, and To xic Substances. U.S. Environmental Protectin Agency. Available at http:// www.regulations.gov/#!documentD etail;D=EPA-HQ-OPPT-2009-0152- 0044 (Accessed July 8, 2014).4 monitoring study could be used to determine wh ere groundwater concerns were likely to occur and whether what we predict based on laboratory data, is observed in th e field. Additionally, it could be used to determine vulnerability of di fferent areas. Data to refine inputs to PRZM-GW may be used to refine modeling estimates of groundwater concentrati ons. Studies may involve understanding sorption or degradation in subsurfa ce environments. It is recommended that a protocol be submitted, prior to conducting any of these studies. In the absence of more suitable inputs or scenarios, estimated environmental concentrations (EECs) generated from PRZM-GW in the same fashion as estimat ed drinking water concentrations (EDWCs) for groundwater used as drinking water, will be used to characterize risks to terrestrial plants from residues in irrigation water obtained from groundwater sources. ”

Dow AgroSciences Comment:

“ The agency intends to use the PRZM-GW mode l to estimate water concentrations in groundwater, for use as inputs into drinking wate r and non-target plant risk assessments. Recent presentations (e.g., Negley et. al.) have shown that proper parameteri zation of PRZM-GW is critical to yield representative estimates of pred icted concentrations. The characterization of soil sorption has been found to be especially crit ical and it has been f ound that including a time dependent formulation of the so rption greatly improves the pred ictive power of the model (as compared to field data). The current impl ementation of PRZM-GW, however, does not support this representation, but various groups have shown that this can be accomplished quite readily. In keeping with EPA's statements that “additi onal data are recommended to better understand the potential for risk due to resi dues of aminopyralid (2) or clopyralid (3), Dow AgroSciences proposes to parameterize PRZM-GW assessments using best available information and methodology. DAS will undertake further field studi es or monitoring efforts if refined modeling efforts do not yield sufficie nt refinements of exposure .”

EFED Response: EFED agrees in principle that a tier ed study approach can be useful for refining risk estimates. EFED co mpleted some sensitivity analys is on incorporation of nonlinear sorption and degradation in subsurface soil laye rs using the PRZM-GW model, to determine how useful conducting additional studie s in refining risk estimates. The analysis is shown in Appendix B . EFED is currently exploring the issu e of time-dependent sorption and how it may be used in PRZM-GW modeling; however, EFED recommends against pursuing the timedependent residue study at this time.

EFED explored the potential for considering nonlinear sorpti on and a degradation rate in subsurface layers. When PRZM-GW was run usi ng the highest and lowest measured sorption coefficient (K d ) at a single equilibrium con centration in water in all of the sorption studies, it was found that aminopyralid concentrations in groun dwater still had the pot ential to result in exposure levels that could exceed levels of concern for terrestrial plants (see Appendix B ). EFED also evaluated aminopyralid concentrations assuming a subsurface degradation rate of 100 days. Currently, aminopyralid has been shown to be stable to hydrolysis (based on data evaluating hydrolysis over 31 days), which is ty pically the only dissip ation pathway currently considered in PRZM-GW modeling below 1 meter. It was shown that assuming a subsurface degradation rate of 100 days c ould significantly reduce estimated exposure. EFED recommends if any additional analyses are performe d, that these analyses focus on better understanding/quantifying the potential for degrada tion in subsurface layers (either via longer term hydrolysis studies or degradation in soils from subsurface layers).5 Based on currently available data, aminopyralid is considered persistent and mobile. The surface layer degradation half-lives for parent plus une xtracted residues are near 100 days, and it is unlikely that subsurface degradation rates will be faster than this. It is likely that whether inputs to PRZM-GW can be refined or not, the compound ha s the potential in vulnerable areas to reach groundwater at concentrations that could result in a risk concern if the wa ter is used to irrigate sensitive terrestrial plants. A prospective groundwater (PGW) mon itoring study could be used to determine where groundwater concerns are likely to occur, and whether m odeled concentrations estimated based on laboratory data, are obser ved under actual field conditions. It is recommended that protocols be submitted for review and approval prior to initiating any additional studies. Finally, in the absence of additional data, EFED will use PRZM-GW to estimate the potential exposure to terrestrial plan ts from residues in irrigation water obtained from groundwater sources.

4. Missing citations

Dow indicated that citations to aerobic so il metabolism studies MRID numbers 47925801 and 47911201 were omitted.

MRID 47925801 is listed under 835.4100 on page 36. MRID 47911201 was omitted and is listed below. EFED will be sure to include this citation in future documents, as appropriate.

Yoder, R.; Smith, K. (2009) Aerobic Soil Degr adation of XDE-750 in Four European Soils: Amended Report. Project Number: 020054. Unpublis hed study prepared by Dow AgroSciences, LLC. 72 p. MRID 47911201.6 Appendix A. Summary of pe plus pH results for the aerobic aquatic metabolism study MRID 46235731

French System – Aqueous Phase

Day Measured E h Measured pH pE pE+pH pE+pH < 12?
0 180 5.37 3.0 8.4 Yes
0 178 6.00 3.0 9.0 Yes
3 62 6.63 1.0 7.7 Yes
3 142 7.90 2.4 10.3 Yes
7 34 7.67 0.6 8.2 Yes
7 20 7.47 0.3 7.8 Yes
14 263 6.66 4.4 11.1 Yes
14 111 6.26 1.9 8.1 Yes
21 76 5.27 1.3 6.6 Yes
21 64 6.53 1.1 7.6 Yes
30 196 6.78 3.3 10.1 Yes
30 168 6.56 2.8 9.4 Yes
62 -56 6.51 -0.9 5.6 Yes
62 212 5.94 3.6 9.5 Yes
101 203 5.76 3.4 9.2 Yes
101 205 5.91 3.5 9.4 Yes Data from Table 8 page 50 of study report.

Italian System – Aqueous phase

Day Measured E h Measured pH pE pE+pH pE+pH < 12?
0 122 7.88 2.1 9.9 Yes
0 78 7.98 1.3 9.3 Yes
3 7 7.91 0.1 8.0 Yes
3 -12 8.33 -0.2 8.1 Yes
7 65 8.22 1.1 9.3 Yes
7 94 8.10 1.6 9.7 Yes
14 82 7.76 1.4 9.1 Yes
14 41 7.98 0.7 8.7 Yes
21 -97 7.39 -1.6 5.7 Yes
21 -168 7.49 -2.8 4.7 Yes
30 98 7.99 1.7 9.6 Yes
30 99 8.19 1.7 9.9 Yes
62 91 7.80 1.5 9.3 Yes
62 -65 7.67 -1.1 6.6 Yes
101 127 7.06 2.2 9.2 Yes
101 110 7.56 1.9 9.4 Yes Data from Table 9 page 51 of study report.7 U.S. System – Aqueous Phase

Day Measured E h Measured pH pE pE+pH pE+pH < 12?
0 -39 7.35 -0.7 6.7 Yes
0 -90 8.00 -1.5 6.5 Yes
3 -67 8.73 -1.1 7.6 Yes
3 -155 8.49 -2.6 5.9 Yes
7 -32 8.59 -0.5 8.1 Yes
7 -31 8.53 -0.5 8.0 Yes
14 -35 8.42 -0.6 7.8 Yes
14 -188 8.32 -3.2 5.1 Yes
21 -308 7.44 -5.2 2.2 Yes
21 -310 7.92 -5.2 2.7 Yes
30 35 8.67 0.6 9.3 Yes
30 -151 8.54 -2.5 6.0 Yes
62 16 8.54 0.3 8.8 Yes
62 -229 7.70 -3.9 3.8 Yes
101 37 8.59 0.6 9.2 Yes
101 2 7.71 0.0 7.7 Yes Data from Table 10 page 52 of study report.8 Appendix B. Summary of PRZM-GW Modeling and Sensitivity Analysis

Table B1. PRZM-GW Input Parameters Parameter (units) Input Value Data Source Application Rate (kg a.e./hectare) 0.247 Maximum application rate of all the uses. Number of Applications 1 Label Application Dates (month/day) 14 day since emergence
Application Method 2 Above canopy application Annual Application Retreatme nt Once every year Label Hydrolysis Half-life (days) See Table B2 MRID: 46235726

Soil Metabolism Half-life (days) 98.8 Represents the 90 th percentile upper confidence bound on the

mean (109) of eight half-life values (aminopyralid + unextracted residues). Values were adjusted to 25 o C. average of K oc (mL/g oc ) See Table B2 See text.

Table B2

. PRZM-GW version 1.07: Modeling Results for Aminopyralid and Sensitivity Analysis of the K oc/ K d input and Hydrolysis input. Results are shown for the Wisconsin sand scenario. The simulation was run for 30 years for the mean and lowest single K d and 100 years for the highest single K d

.

K d /K oc input, hydrolysis input Highest Daily value (μg/L) Post Breakthrough Average (μg/L) Average Simulation Breakthrough

Time (days) Mean K oc of 8.96, stable 55.5 49 2491 Lowest single K d (0.0042 mL/g) 1 , stable 56.8 50.3 2440 Highest single K d (0.93 mL/g) 2 , stable 11 9.84 17674 Highest single K d (0.93 mL/g) 2 , DT 50 of 100 days 0.103 0.0861 17674 Mean K oc of 8.96, DT 50 of 100 days 1.31 0.509 2490 Bolded value represents the highest EDWC for aminopyralid acid.

1 Measured in M549 soil at aminopyralid equilibri um concentration in so lution of 0.949 μg/mL.

2 Measured in M616 soil at aminopyralid equilibri um concentration in so lution of 0.028 μg/mL.

To estimate exposure to plants when groundwater contaminated by aminopyralid is applied to crops and to determine whether changing input pa rameters would influenc e risk conclusions, the following method was used.

Assume a field is irrigated w ith one inch of water contai ning an estimated aminopyralid concentration in water in μg/L using the following equation.

EEC lb a.i./Acre = ( EEC in water in mg a.i./L ) × (102,790 L water/ Acre-in) × (1 inch) × (1 lb/ 453,592 mg) = 9.84 μg a.e./L ×1000 μg/mg × 0.226613 = 0.00223 lbs a.e./A9 For evaluating the potential for nonl inear sorption to influence risk conclusions, an aminopyralid concentration in water of 9.84 μg/L was assumed and resulted in an estimated application rate of 0.00223 lbs a.i./A. The lowest no observed adverse effect concentration (NOAEC) available for terrestrial plants ( i.e ., 0.0004 lb a.e./A, MRID 462358-25) is well below this estimated level of exposure. Therefore, considering the impact of nonlinear sorption on th e estimated exposure is unlikely to reduce the exposure estimat e to below levels of concern.

Assuming a 100-day half-life for hydrolysis and the highest K d , results in an estimated exposure level (EEC in groundwater = 0.0861 μg/L; EEC for 1 inch of irrigation water =1.95 ×10 -5 lbs a.e./A) that reduce risk estimates below le vels of concern. However, the highest K d is not expected to be conservative for all soil types and more than an inch of water may be used to irrigate.

Assuming a 100-day half-life for hydrolysis and the mean K d , results in an estimated exposure level (EEC in groundwater = 1.31μg/L; EEC for 1 in ch of irrigation water =0.0003 lbs a.e./A) that would in turn reduce risk estimates to just below levels of concern; however, it is expected that many areas will receive more than an inch of irrigation water.