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


                                                               PC Code:  104601
                                                             DP Barcode: 456087
                                                            Date: June 18, 2020
MEMORANDUM

SUBJECT:	Response to Public Comment on the Draft Risk Ecological Risk Assessment of Fenbutatin- Oxide

FROM:		Karen Milians, Ph.D., Chemist
		Thomas Steeger, Ph.D., Senior Science Advisor
      Environmental Risk Branch IV
		Environmental Fate and Effects Division (7507P)
REVIEWED 
BY:		Ideliz Negron-Encarnacion, Ph.D., Risk Assessment Process Leader
		Cheryl Sutton, Ph.D., Environmental Scientist
		Environmental Risk Branch IV
		Environmental Fate and Effects Division (7507P)

THROUGH:	Jean Holmes, D.V.M., Branch Chief
		Environmental Risk Branch IV
		Environmental Fate and Effects Division (7507P)

TO:	Lauren Weissenborn, Chemical Review Manager
Melanie Biscoe, Team Leader
Cathryn Britton, Branch Chief
Risk Management and Implementation Branch V
Pesticide Re-evaluation Division (7508P)


The Environmental Fate and Effects Division (EFED) completed its review of public comments received on the Draft Ecological Risk Assessment (DRA; USEPA 2019) for the acaracide fenbutatin-oxide (PC Code 104601; CAS No: 13356-08-6) as part of Registration Review. The fenbutatin-oxide DRA was published in the docket on September 30, 2019 (Docket Number:  EPA-HQ-OPP-2009-0841). Below is a summary of the comments received and EFED's responses.  

Comment: 

Writing on behalf of the  U.S. Department of Agriculture Office of Pest Management Policy, Dr. Sheryl Kunickis (EPA-HQ-OPP-2009-0814-0032) noted that while fenbutatin-oxide is no longer a primary mite control tool for most crops, "significant usage is still reported on citrus" for which there are registered uses in Arizona, California, Florida and Texas. Dr. Kunickis indicated that fenbutatin-oxide kills by contact only and that the compound has no systemic activity; therefore, adequate foliar coverage is "critically important for efficacy." USDA also noted that based on EPA's screening-level usage analysis (SLUA), strawberries, and caneberries are also important agricultural uses.  According to USDA, although raspberries in Washington and Oregon are the only caneberries with labeled uses for fenbutatin-oxide, overall use estimates for caneberries may misrepresent (underestimate) actual usage as the acaracide continues to be important for mite control in raspberries in the Pacific Northwest.  USDA also noted that although additional mite control products have become available for other crops, fenbutatin-oxide remains an important component of integrated pest management (e.g., Christmas trees; strawberries) and resistance management (e.g., apples) efforts.

With respect to the ecological risk assessment, USDA agreed with EPA's conclusions regarding potential risks of concern for aquatic taxa and believes that the restricted use classification of the compound in combination with application setbacks/buffers from water bodies have historically addressed such risks.  USDA encouraged EPA to focus on practical and feasible measures to minimize off-site movement while retaining the efficacy/utility of the compound. Given that fenbutatin-oxide acts through contact, USDA stressed the importance of uniform coverage on treated plants and expressed concern regarding the implementation of overly stringent restrictions on spray droplet sizes to reduce risk, in that it may lead to the use of "increased application rates...to compensate for decreased efficacy."  USDA encouraged EPA to "explore the potential for prohibiting aerial applications" given that the registered uses for which fenbutatin-oxide remains important typically rely on ground equipment to maximize foliar coverage.  Similar to their comments regarding risks of concern for aquatic taxa, USDA indicated that risks of concern for terrestrial taxa are addressed through the restricted use classification; however, USDA noted that EPA default assumptions used in modeling terrestrial animal exposure (e.g., 100% of the diet treated) may "significantly over-estimate" foraging activity and subsequent exposure. It was noted that the use of rate reductions as a mitigation option "may pose significant challenges for both efficacy and resistance management, as sub-lethal/non-effective doses can exacerbate selection pressure for miticide resistance." With respect to terrestrial invertebrates, USDA recognized the uncertainty from data gaps but noted that since fenbutatin-oxide is not systemic in plants, exposure is likely limited to contact and direct contamination of pollen/nectar from spraying the blooms themselves.  USDA noted that although that growers/applicators attempt to be "judicious about avoiding applications to bee-pollinated crops during bloom," as spider mite outbreaks that occur rapidly could require applications during bloom, particularly in crops (e.g., citrus, berries) with indeterminant bloom periods.

EFED response: 

EFED appreciates the comments provided by Dr. Kunickis and the acknowledgement that the ecological risk assessment bracketed risk estimates by examining variability in toxicity as well as exposure estimates and that the assessment provided helpful risk characterization information. EPA also appreciates the willingness of USDA to provide additional information on usage and assessing the benefits of fenbutatin-oxide.  EFED concurs with USDA comments that the restricted use classification of fenbutatin-oxide in combination with buffers/setbacks help to mitigate exposure; however, the aquatic exposure assessment took setbacks/buffers into consideration when assessing risk. As noted in the "Risk Conclusions Summary" of the assessment, "Buffers stipulated for use in aerial (125-ft) and ground applications (25-ft) to citrus reduce EECs; however, the EECs as a result of the buffers are not reduced sufficiently to drop RQ values below acute or chronic risk LOC [Level of Concern] for aquatic organisms."  Additionally, the monitoring data provide evidence that even with such restrictions in place, the compound can move off-site and potentially pose risk to aquatic communities. 

EFED also appreciates USDA comments with respect to restricting aerial applications. Based on EFED's analysis of labeled use patterns, citrus and Christmas trees were the only uses for which aerial applications were identified.  However, in follow-up discussion with the Biological and Economic Analysis Division (BEAD) of the Office of Pesticide Programs, aerial applications are conducted for other uses (e.g. almonds).  Therefore, the ecological risk assessment does not fully and accurately reflect potential risks to aquatic communities from such applications.

Comment: 

The National Agricultural Aviation Association (NAAA) provided comments regarding default assumptions in the Tier 1 AgDrift(TM) model used to assess risk from spraydrift as a result of aerial applications.  According to NAAA, aerial applicators routinely use large droplet sizes and the NAAA recommends medium droplet size as a default (vs. EFED's default of fine to medium) when modeling drift as this size is the most commonly observed at clinics where aerial applicators have their spray systems tested for droplet efficiency and drift prevention.  Surveys conducted by the National Agricultural Aviation Research and Education Foundation's (NAAREF) Professional Aerial Application Support System (PAASS) indicated that 49% of the respondents primarily used flat fan nozzles which typically produce medium droplet sizes, whereas 17% utilize straight stream nozzles that provide coarse droplet sizes, and 22% used deflector-type nozzles which can produce medium or coarse droplets.  

The NAAA indicated that the Tier 1 default assumptions do not account for the effect of lowered spray boom and nozzles in reducing off-target deposition. NAAA also noted that the default conditions regarding swath displacements and standard 10 mile per hour crosswind conditions improperly bias spray drift estimates and do not account for aviator standard practices.  According to NAAA, surveys of aerial applicators indicated that >90% of the aerial operators account for swath offset during applications.

The NAAA also noted that the Tier 1 model assumes neutral air stability and that this assumption can include negative stability ratios which can occur during atmospheric inversions; however, training provided by NAAREF and the pesticide label itself prohibit applications during inversions.  Therefore, NAAA recommended changes to some of the AgDrift(TM) input values used by EFED in assessing spray drift along with modifications to label language regarding temperature inversions (i.e., "to not apply
product if an inversion is present at or near the ground level.") 

Response:

EFED appreciates the information provided by NAAA on standard practices used by aerial applicators, along with the published articles that NAAA cited, to support their comments/recommendations.  The 
AgDRIFT(TM) model, a modified version of the Agricultural DISPersal (AGDISP(TM)) model, was developed as a collaborative effort between EPA, the USDA Forest Service and the Spray Drift Task Force.  The model is used to estimate downwind deposition of spray drift from aerial, ground and airblast applications.  NAAA is correct in noting that at Tier 1, EPA relies on conservative assumptions which are intended to be protective, i.e., representative of worst-case scenarios.  While applicator standard practice may include more conservative practices in terms of spray droplet sizes, swath off-sets, and applications during atmospheric inversions, the survey data provided by NAAA indicate that those measures are not ubiquitously practiced; therefore, it would be inappropriate for EFED to utilize less conservative assumptions when modeling spray drift.  However, based on the information provided by NAAA, it is clear that the organization and its affiliates are attempting to promote methods to reduce spray drift, and risk managers can consider these efforts along with the other reference materials provided by NAAA. The concerns raised by NAAA are consistent with those expressed by USDA regarding potential restrictions on droplet size leading to increases in application rate to retain the same level of efficacy given the need to ensure that foliar surfaces are properly treated.  EFED will consider the information provided by NAAA in future risk assessments; however, risk assessments will continue to rely on conservative assumptions to ensure that such assessments are protective for a broad range of application practices.
