UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460



### MEMORANDUM

SUBJECT:

FROM:

THRU:

TO: September 18, 2012 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 038904 DP Barcode: 404321 De.c-tsroN:**4b4Z4~** Drinking Water Exposure Assessment for ProposedNewUse of Endothall Dipotassium on Apple Trees for Thinning ofBlossoms James Lin, Environmental Engineer

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# - Environmental Risk Branch II En-vironmental Fate and**Eff~cts Di:fJ/~07P~**  . BnanAnderson, Branch Chief // (

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## l)vvJ/**/t--;7'~** Environmental Risk Branch II (.__ Environmental Fate and Effects Division (7507P) Kathryn Montague, Risk Manager Grant Rowland, Risk Manager Reviewer Registration Division (7505P) This memo presents the drinking water exposure assessment ofThinRite blossom thinner (5.37% ofendothall dipotassium) use on apples. The proposed annual maximum applicationrate is 12 pints (0.846 lbs ai or 0.60 acid equivalent). This is a terrestrial food use. Considering the possible exposure ofdrinking water, the greatestpotential will come from the direct applicationto drinking waterreservoirs. In a previous drinking water assessment, EFED has concludedthe use ofendothall-treated irrigation water represents the most conservative estimates for drinking water assessment (DP 356316, dated September 9, 2009, see attachment). Therefore, the drinking water exposure estimates (shownbelow) based onthe direct water applications should continue to be used for the humanhealthrisk assessment.

Media MaxConcentration Source (ppb, J.lg/L) Surface water (acute) 100 Maximum Contaminant Level (MCL) Surface water (chronic) 31 Calculated Annual Average

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# 1111111111 2087954Attachment

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF PREVENTION, PESTICIDES, AND TOXIC SUBSTANCES

PC Code: 038901,038903,038904,038905 DP Barcode: 356316 September 9, 2009 MEMORANDUM

SUBJECT: Drinking Water Assessment for the IR-4 Tolerance Petition for the Use of Endothall-treated Irrigation Water on a Variety ofCrops TO: Sidney Jackson, Risk Manager BarbaraMadden, Risk Manager Registration Division (7505P) FROM: Nelson Thurman, Senior Environmental Scientist Environmental Risk Branch 2 Environmental Fate and Effects Division (7507P) THROUGH: Tom Bailey, Branch Chief Environmental Risk Branch II Environmental Fate and Effects Division (7507P)
Summary A drinking water exposure assessment has been conductedto support the humanhealthrisk assessment for the proposed use ofendothall-treated irrigation water on a variety ofcrops. The maximumpotential exposure ofendothall in drinking water sources is expectedto result from the direct application ofendothall to drinking waterreservoirs to control aquatic weeds. EFED assumed that the entire reservoir would be treated at the maximum rates, with no more than 1 0% ofthe reservoir treated at one time as stated onthe label, so that 1 0 treatments were applied 7 days apart to getthe entire reservoir. Since the label specified thatthe community water system (CWS) could not supply treated drinking water unless the residues were below 0.1 2ppm (100 11g/L), EFED assumed 100 

### J.lg/L (0.1 ppm) as the acute (peak) exposure and the constant exposure during the treatmentperiod andthen modeled residue decline by degradation afterthe final treatment. This resulted in a chronic (annual average) concentration of31 J,lg!L (0.031 ppm) for endothall. This represents the likelyhigh-end chronic exposure from endothall from the use most likelyto generatethe highest exposures (treatment ofa reservoir). Nature ofAction Endothall is anherbicide withbothterrestrial and aquatic uses. Interregional ResearchProject No.4 (IR-4) submitted field trial datato supportthe use ofendothall as an algaecide and aquatic herbicide inirrigation and drainage canals. The irrigation waterwould subsequently be applied to a variety ofvegetables, berries, grains, nuts, grapes, and feed crops. With no geographic limitations, potentially all irrigated crops could be subjectto endothall residues from treated irrigation waters. Endothallmaybe applied to irrigation canals at a maximum single rate of5 ppm (as endothall acid), with a maximum of30 ppm during the growing season, with a minimum 7-day application interval (based onboththe Hydrothol191 and Aquathol® K labels). Based on the maximum seasonal rate, EFED assumed a maximum exposure from 6 applications at 5 ppm with 7-day intervals between applications or 10 applications at 3 ppmfor the 3 ppmmaximum on one label. Endothall may also be appliedto lakes, ponds, and impoundments, including drinking water reservoirs, atrates ofup to 3 ppm (Hydrothol) to 5 ppm (Aquathol). For submerged aquatics in lakes orponds, no more than 1110 ofthe impounded watermaybetreated at one time. The labels state that consumption ofwaterbythe public is allowed only whenthe concentration of endothall in water is less thanthe Maximum ContaminantLevel (MCL) of 100 11g/L (0.1 ppm). Previous DrinkingWater Exposure Assessment In May, 2004, EFED conducted a drinking water assessment for endothall uses onterrestrial crops inthe western US (potatoes, cotton, clover, alfalfa for seed, hops) and direct aquatic applications1. The estimated maximum 1-in-10-year exposures from terrestrial uses were: 7.1 11g /L for the 1in 10 year annual peak concentration (acute) 2.5 11g /L for the 1in 10 year annual mean concentration (non-cancer chronic) and 2.4 11g /L for the 36 year annual mean concentration (cancer chronic). Maximum ground water concentrations were less than 0.1 !lg /L. The greatestpotential exposures from endothall use, however, come from direct applicationto drinking waterreservoirs. Assuming 1 00% ofthe reservoir is treated at the maximumrate, the maximum peak (single-day) exposure couldbe as high as 5000 !lg/1 (5 ppm), based onthe maximum application rate to the reservoir. However, Endothall has a Maximum Contaminant Level (MCL) of 100 11g/L (0.1 ppm); therefore, EPAused the MCL as the maximum exposure

1 "Drinking Water Assessment for Endothall for both Terrestrial and Aquatic Uses". Memorandum from James Breithaupt, EFED, to Susan Lewis and Pat Dobak, SRRD, May 5, 2004. 3level expected from direct application ofendothall to reservoirs. Although the MCL is likely to overestimate average (i.e., chronic) residues ofendothall indrinking water, EPA believes it provides a reasonable high-end estimate ofpotential acute drinking water concentrations from the aquatic uses ofendothall. For a screening approach, EFED used the MCL of 100 f..lg/L (0.1 ppm) for boththe acute and chronic exposures in the dietary risk assessments. The 2005 Revised Human Health Risk Assessmentfor the RED indicated that chronic dietary exposure assuming an average 100 ppb concentration for endothall accounted for 99% ofthe cPAD for infants <1 yr old and 45% ofthe cPAD for children 1-22. 

### Summary ofEnvironmentalFateProperties ofEndothall The environmental fate andtransport properties ofendothall are described in the 2005 EFED environmental fate and ecological risk assessment3. This section briefly summarizes the RED characterization. Endothall exists inthree forms in the environment: endothall dipotassium, endothall potassium cation, and endothall acid. These chemical forms are highly soluble and mobile in the environment. Exposure is expressed interms ofendothall acid equivalents. Endothall degrades bybiotic processes such as aerobic metabolism. Single laboratory studies measured first-order degradation half-lives of 14.5 days for aerobic soil metabolism, 10 days for aerobic aquatic metabolism, and 9 days for anaerobic soil metabolism. Terrestrial dissipation studies measured dissipation half-lives from the soil surface of 13 to 19 days. Dissipation/disappearance half-lives in aquatic dissipation studies ranged from 4 to 30 days (median 8.5 days) in lab studies, and 0.5 to 20 days (median 4 days) in ponds and lakes. As noted in Table 1, EFED multiplied the single half-life measurement by 3 to reflect the uncertainty in the range ofpotential half-life values in the field. The resultant 3X value for aquatic metabolism is within the range ofdissipation half-lives reported for the aquatic dissipation studies while the single value is closer to the median dissipation half-lives from the studies.
Table 1. Endothall Inputs Used for DrinkingWaterExposure Modeling.

MODEL INPUT VARIABLE Molecular Weight, g/Mol Vapor pressure (Torr at 24.3 °C) Solubility (mg/L) Kd (mUg) Aerobic Soil Metabolic Half-life INPUT VALUE

186.2

100,000

2.4 43.5 COMMENTS 2005 RED 2005 RED 2005 RED Average ofvalues in MRID 41616404 3X 14.5 day half-life based on extractable residues in
2 "Endothall: Revised Human Health Risk Assessment. HED Chapter of the Reregistration Eligibility Decision Document (RED)". Memorandum from Zendzian et al, HED, to Mika Hunter, SRRD, 09/30/05. 3 "Environmental Fate and Ecological Risk Assessment of Endothall- Revised". Memorandum from Embry et al, EFED, to Mika Hunter, SRRD, April 22, 2005. 4MODEL INPUT VARIABLE (days) Aerobic Aquatic Metabolic Half-life (days) Anaerobic Aquatic Metabolism halflife (days) INPUT VALUE

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27 COMMENTS MRID 44949401 3X I0 day half-life based on extractable residues in MRID 42618901 3X 9 day half-life based on extractable residues in MRID 42903901 DrinkingWaterExposureAssessment for the Proposed Use For chronic drinking water exposures, the 100 11g/L (0.1 ppm) MCL is the presumable maximum threshold for surface water sources ofdrinking water. Thatthreshold assumes that the CWS downstream ofthe agricultural areas that are releasing treated irrigation canal water into the larger waterbodies are aware ofthe applications so they can ensure that endothalllevels stay belowthat threshold inthe waterthey release to the public. In the event that the CWS is not aware ofwhat's going on upstream, it is possible that short-term exposures from endothall may exceed the MCL because ofthe high rates used intreating the waters. For flowing water bodies, the endothall residues would quickly dissipate downstream so that elevated exposures would only be expected for shortperiods after endothall-treated irrigation water is released to the water body. Application ofendothall-treated irrigation water to crops would result in lower exposure concentrations released to surface water sources ofdrinking water due to (a) filtration of irrigation water through the crops and soil and (b) increasedtime for degradation from the time oftreatment. Estimated 1-in-10-yearpeak and average annual concentrations from irrigation applications ofendothall are expected to be in the same range as those estimated for endothall applications to terrestrial crops inthe 2005 RED (up to 39 11g /L peak and 10 11g /L annual). The maximumpotential drinking water exposures are expected to result from the direct application ofendothall as an aquatic herbicide in a drinking water reservoir. In a maximum potential exposure scenario, the entire reservoir is treated at maximum rates (3 to 5ppm, depending onthe label), with no more than 10% ofthe reservoir treated at one time. This would result in 10 treatments of3 ppm applied 7 days apart to get the entire reservoir (assuming a 30 ppm maximum seasonal rate). The labels state that consumption ofwaterbythe public is allowed only whenthe concentration ofendothall in water is less than the MCL of 100 11g/L (0.1 ppm). At the maximum rates, even with a 600-foot setback from the drinking water intake, endothall residues may exceed the MCL for one or a few days after application. However, based on the label specifications, the water cannot be released for public consumption until the concentration is less than the MCL. Thus, the maximum peakconcentration ofendothall residues would be 100 f.lg/L (0.1 ppm). Given the degradation/dissipation rates ofendothall, the concentrations will likely decline fairly quickly once treatments have ended, even in the most static ofreservoirs. So longer-term
5average exposures will likely be well belowthe MCL. For chronic exposures, EFED usedthe following estimates: (1) an assumed 100 f..LgiL (0.1 ppm) concentration during the 70-day treatment window (2) first-order degradation, based on a 30-day aquatic metabolism half-life (3Xthe single measured value provided bythe registrant), using the Ct = Coe-kt where Co= initial concentration, k = first-order degradationrate (hr- 1), and t =time. The calculated daily concentrations were averaged overthe yearto generate a chronic (annual average) concentration of31 J.lg /L (0.031 ppm) for endothall. This would represent the likely high-end chronic exposure from endothall from the use that is most likely to generate the highest exposures (treatment ofa drinking waterreservoir). To characterize the range inpotential exposures, EFED variedthe degradation/ dissipationhalflife (30 days vs 10 days) and included an estimate ofreservoir flow-through rates, similarto the approach inthe 2004 EFED drinking water assessment. These are summarized inTable 2. The FLreservoir hadthe greatest flow-through rates (see the 2004 EFED drinking water assessment for details). Table 2: Range in estimated annual average concentrations ofendothall residues based on
· d d" d 

## ·o h h varymg egra at10n rates an reservOir ow-t rougl rates. Exposure Scenario Annual average Endothall Flow-through Effective dissipation (chronic) degradation halflife (m3/hr) I equiv rate (da-1) concentration (da) Irate (da-1) turnover rate (da-1) (J.lg /L) Static reservoir (no water flow-through) 30 da I 0.0231 0 0.0231 31 (0.031 ppm) 10 da I 0.0693 0 0.0693 23 (0.023 ppm) FL reservoir (FL su_g_arcane scenario) 30 da I 0.0231 121 mjlhr I 0.0201 0.0432 25 (0.025 ppm) 10 da I 0.0693 121 mjlhr I 0.0201 0.0894 22 (0.022 ppm)

LivestockDrinking Water Exposure Assessment To evaluate potential endothall residues inmilk/dairy products, HED asked EFED for an estimate ofpotential endothall residues in livestock/animal drinking water. The highest exposures would come from a static pond withno water flow-through. Endothall would soon be diluted outofany water bodywith flow init (canals, etc) and, even with multiple applications, thehigher concentrations would soonbe moving away from the source. The labels have certainwaiting periods before treated water could be used for animal consumptiondepending onthe application rate: 6Applied 0.3 ppm- 7 days after application Applied 3.0 ppm- 14 days after application Applied 5.0 ppm- 25 days after application The estimated concentrations use the simple first-order degradation model, assuming either static (no flow) or varying waterturnover rates in the farm waterbody. Endothall concentrations degraded with a first-order model starting immediately after application. No water was consumed during the specified waiting periods; annual average concentrations reflect daily concentrations beginning after the waiting period. The uncertainty in the estimates is boundby the range in potential degradationrates ofendothall and the potential waterturnoverrates for the water body. At the high end ofthe half-life range in water (30 days), average annual water exposures in static water bodies are 0.26 and 0.35 ppm, for the 3 and 5ppmtreatments respectively; at the low-end (10 days) ofthe half-life range, average water exposures are below 0.1 ppm. Table 3: Range in estimated annual average concentrations ofendothall residues in 

## r k d b d · d d · 

### t d fl 

### th h t 1vestoc waterpon s ase onvarymg egra ation ra es an ow- roug1 ra es. Exposure Scenario Annual average concentration, mg/L (ppm) Endothall Pond turnover Effective 0.3 ppm 3ppm Sppm degradation rate (% daily dissipation rate applied applied applied halflife (da) turnover) (da-1) Single application 30 da 0% 0.0231 0.03 0.26 0.35 1% 0.0331 0.02 0.16 0.19 5% 0.0731 0.007 0.04 0.03 10 da 0% 0.0693 0.007 0.04 0.04 1% 0.0793 0.006 0.03 0.02 5% 0.1193 0.003 0.01 0.006 3 applications spread throughouttheyear (1, 123, 245 days) 30 da 0% 0.0231 0.09 0.82 0.78 1% 0.0331 0.06 0.51 0.44 5% 0.0731 0.02 0.13 0.07 10 da 0% 0.0693 0.02 0.15 0.08 1% 0.0793 0.02 0.11 0.06 5% 0.1193 0.009 0.04 0.01 6 applications at 7-day treatmentintervalsw/no consumption duringtreatment 30 da 0% 0.0231 0.12 1.06 1.42 10% 0.1231 0.002 0.01 0.004 10 da 0% 0.0693 0.01 0.08 0.06 10% 0.1693 0.001 0.002 0.001 In most instances, some waterturnover/exchange (replenishment withrain and/or runoff) occurs 7in a farm pond overtime. Ranges of 1to 5% turnover on a daily basis is not uncommon. At a 5% water exchange rate for a pond, the year-long average concentrations for the 3 rate/waiting period combinations were below 0.2 ppm. Table 3 also provides average annual concentration estimates for a variety ofmultiple application scenarios. Each ofthe scenarios assume that the waiting period is enforced betweentreatments.

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