UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

PCCodes:030501,030502,030516, 

030563,030564 

DP Barcode: D420780 

MEMORANDUM August 14, 2014 

Subject: 

To: 

From: 

Through: 

EFED Response to Public Comments on: Preliminary Problem Formulation for 

Environmental Fate and Ecological Risk, Endangered Species, and Drinking 

Water Assessments for MCPA 

Khue Nguyen, Chemical Review Manager 

Neil Anderson, ChiefRMIB I ./ 

Pesticide Re-Evaluation Division (7508P) '3{{'f{t'( 

Brian D. Kiernan, Biologist ~t::;;; ) IwonaMaher, Chemist ~I.JdjJ....A (~J. ~}a, Environmental Risk Branch VI 

Environmental Fate and Effects Division (7507P) 

Mark Corbin, Branch Chief 

Environmental Risk Branch VI 

Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) has reviewed three comments received on 

the preliminary problem formulation (D414986; 03/05/2014) for the environmental fate and 

ecological risk, endangered species and drinking water assessments to be conducted as part of 

the registration review of the herbicide active ingredient MCP A and its salts and ester (PC Codes 

030501, 030502, 030516, 030563 and 030564). Public comments related to the ecological risk 

assessment were submitted by the MCPA Task Force Three, Center for Biological Diversity, and 

the Central Valley Regional Water Quality Control Board (ofthe California Water Boards). 

Responses to the specific comments are provided in this memorandum. 

EFED Response to Comments Submitted by MCPA Task Force Three 

In general, the MCP A Task Force Three provided a number of comments regarding corrections 

of citations (e.g. MRID 42642204 was stated to be bluegill sunfish, but is actually rainbow trout) 
and other errata noted (e.g. an incorrect reference to a different chemical) will be corrected, as 

necessary, in the registration review risk assessment. Additionally, several studies were 

referenced in the Problem Formulation for which MCPA Task Force Three requested EPA's data 

evaluations records (DER). EFED will evaluate whether the studies in question were included in 

error and will provide copies ofDERs, as appropriate, under separate cover. 

MCP A Task Force Three comment (page 6): 

The Registration Review case is said to include PC Code 030563, the isooctyl ester ofMCPA 

that is generally considered an obsolete form. Early in Reregistration (ca 1990), registrants and 

EPA agreed that the specific C8 alcohol that would be prepared as an ester of MCP A would be 

2-ethylhexanol rather than a mixed C8 rich isooctyl alcohol or other single C8 alcohol. Today, 

only one product is identified in PPIS (sic) as containing PC Code 030563. 

EFED response: 

EFED will, in collaboration with the management divisions (Registration Division and Pesticide 

Reevaluation Division) to determine the appropriate forms to assess at the time of risk 

assessment. 

MCP A Task Force Three comment (page 6): 

Task Force Response: An oral acute toxicity study according to OECD 213 has been submitted 

to EPA (MRlD 47666601). The study was reviewed in 2009 and at that time was evaluated as 

" .. scientifically sound .. " but was " ... classified as Supplemental as it does not meet any current 

guideline requirements." A second study (MRlD 45897007) evaluating the contact and oral 

LD50 of MCP A acid was conducted according to EPPO Standard PP 11170(2) which is cited in 

the OECD 213 Guideline. 

EFED response: 

The Problem Formulation requested·two studies to evaluate the potential for MCPA to adversely 

affect pollinators: an acute oral toxicity study (following OECD 213) and a larval toxicity study 

(following OECD 237). However, EFED policy on pollinator protection has recently been 

updated (Guidance for Assessing Pesticide Risks to Bees, 06.23.2014; signed by Donald Brady, 

Director, EFED; http:/ /www2.epa.gov/sites/production/files/20 14-

06/documents/pollinator _risk_ assessment _guidance_ 06 _19 _14.pdf). Thus, the required studies 

for all pesticides that have use patterns which can result in exposure to pollinators have been 

changed, and now include the following Tier 1 studies: 

• Acute oral toxicity to adult honey bees 

• Acute oral toxicity to larval honey bees 

• Chronic oral toxicity to adult honey bees 

• Chronic oral toxicity to larval honey bees 
While the EFED Problem Formulation indicated that an acute oral study (OECD 213) was 

needed, provisional review of the study referenced above by MCPA Task Force Three (MRID 

45897007) suggests that additional adult acute oral data will not be needed for the risk 

assessment. Although the adult chronic oral toxicity study was not specified in the Problem 

Formulation, this additional study should be conducted to support the MCP A risk assessment. 

While the PF did indicate that an acute larval toxicity study (following OECD 237) would be 

necessary, the release of the new guidance also requires a repeat-dose (chronic) larval toxicity 

study be submitted. The OECD has a draft guideline for a chronic larval toxicity study that may 

be utilized. It is possible to conduct the repeat-dose study in such a way as to derive both an 

LDso (acute endpoint of interest) and a NOAEC (chronic endpoint of interest) from a single 

study. If the chronic larval toxicity study is conducted in such a way that it derives both an LDso 

and NOAEC, then a separate acute larval toxicity study is not needed. 

Although appreciable effects are not expected, the need for higher Tier studies will be 

determined after review of these Tier 1 studies. 

MCP A Task Force Three comment (page 7): 

EPA Comment: "Since that time the MCPA task force has voluntarily cancelled the use on 

rice and sorghum in response to the RED (2004)." 

Task Force Response: Although the outcome is the same, it would be more accurate to state that 

the MCPA Task Force Three did not support uses on rice and sorghum and that all registrants 

voluntarily cancelled rice and sorgh1,1m uses in response to the RED (2004). 

EFED response: 

This Task Force comment; and several other comments suggesting more accurate wording, are 

noted and will, to the extent possible and necessary, be incorporated into the risk assessment. 

MCP A Task Force Three comment (page 7): 

EPA Comment: "MCPA is usually applied in combination with other phenoxy class 

chemicals, such as 2,4-D, 2,4DB, MCPP-p, and MCPB (2004). According to product labels, 

MCPA can be applied any time of year, but for best efficacy application is recommended in 

early spring and early fall. " 

Task Force Response: MCPA is not usually applied in combination with 2,4-D and 2,4-DB. In 

fact, each ofthese three products is most often used to the exclusion ofthe others. MCPA and 

MCPB are both registered for use on peas and there are occasions when a grower may use a very 

low rate ofMCPA with a reduced rate ofMCPB to lower the treatment cost versus a full rate of 

MCPB alone. For example, an indicative product registered in several countries contains 1 part 

MCPA to 15 parts MCPB. For turf and nonagricultural crop use sites, there are many EPA 

registered multiple active ingredient products containing combinations ofMCPA, MCPP-p, 

2,4-DP-p and other non-phenoxy actives. 
EFED response: 

We appreciate the comment regarding the paragraph and will incorporate it, as appropriate, at the 

time of the risk assessment. 

MCP A Task Force Three comment (page 8): 

EPA Comment: Therefore, the Agency requests any additional information on the presence of 

dioxins/furans impurities in MCPAformulated products that may be available based on 

currently achievable LOQs. 

Task Force Response: Technical phenoxy herbicide registrants have provided dioxin/furan data 

at intervals for several decades in response to Data Call-Ins and product chemistry requirements 

applicable to impurities of potential toxicological concern in technical MCPA. Relevant product 

specific studies have MRID numbers associated with the individual technical registrations. These 

results have demonstrated non-detectable or extremely low detections while the LOQs for many 

dioxins/furans have steadily declined over the period with analytical advances. As discussed in a 

separate telephone conference call between EPA and representatives ofthe MCPA Task Force 

Three, EPA should make a specific request to technical registrants for additional data. The 

MCPA Task Force Three believes that the Holt et al. paper cited by EPA is superseded by 

specific information available on EPA registered technical MCPA products. 

EFED response: 

A more detailed and accurate accounting for the amounts of the dioxins/furans congeners in 

formulations ofMCPA would allow comparison to concentrations previously determined to be 

sufficient to be of environmental concern. If the concentrations of dioxins/furans in an MCP A 

product fall below these identified thresholds, those formulations will be cleared as a dioxin 

source of concern. If they are not cleared, more effort will need to be applied regarding dioxin 

contribution from these sources. 

MCPA Task Force Three comment (page 10): 

EPA Comment: "It is likely that some unknown percentage of the MCPA detected in surface 

water and groundwater monitoring data may result from degradation of MCPB to MCPA. 

Therefore, in the event of uncertainties regarding MCPA and MCPB use pattern overlap, 

EFED will assess an impact the degradation of MCPB to MCPA on monitoring data, EDWCs, 

and aquatic EECs, in a conservative manner." 

Task Force Response: The overlap in use patterns ofMCPA and MCPB is application to peas. 

Due to the cost of the herbicides and the potential for crop injury, it is extremely unlikely that 

full rates ofboth MCPA (0.375lb ae/A) and MCPB (1.5lb ae/A) would be applied. Labeling 

clarifying this situation would likely be agreeable to registrants. As described in a previous 

comment, there are occasions when a grower may use a very low rate of MCP A with a reduced 

rate ofMCPB to lower the treatment cost versus a full rate ofMCPB alone. For example, an 

indicative product registered in several countries contains 1 part MCPA to 15 parts MCPB. 

EFED response: 
We appreciate the comment on the overlap of MCP A and MCPB use and will incorporate it, as 

appropriate, at the time of the risk assessment. 

MCP A Task Force Three comment (page 10): 

Page 15, Table 5 - Dissociation 

Task Force Response: A comment is absent in the "Sufficient for EFED?" column. What is the 

answer? 

EFED response: 

The data are sufficient. 

MCPA Task Force Three comment (page 11): 

Page 16, Table 5- Volatility-laboratory and Page 17, paragraph 1 

EPA Comment: " ... dry soil, with sufficient-moisture to still maintain microbial activity, and 

most soil in a higher temperature are recommended to be tested. 

Task Force Response: A clarification on the Rationale for Additional Data Need is requested. 

The previously submitted study MRID 47075203 was conducted at 25 ± 2 °C in soils at 40-60% 

of the 0.33 bar moisture capacity at flow rates of 100 and 300 mL/minute. This study was 

classified as acceptable. The request is for a dry soil, with sufficient moisture to still maintain 

microbial activity, and most (moist?) soil in a higher temperature are recommended to be tested. 

Soils at 40% of the 0.33 bar moisture capacity are normally considered dry soils for agricultural 

purposes. Testing for volatility in soils dryer than this would normally be considered to be 

testing in soils that were too dry for agricultural purposes and therefore an environment not 

intended for use of the pesticide. It may be possible to conduct the study at a higher temperature 

but since no volatility other than carbon dioxide was observed at_25 ± 2 °C after a period of 15 

days at a flow rate of300 mL/minute it is unlikely that a doubling ofthe temperature in the study 

would result in any appreciable volatilization which was observed to be at the LOD (<0.02%) in 

the trapping solutions. 

EFED response: 

EFED believes the volatility data for MCP A EHE at low moisture content and high temperature 

are still needed. However, EFED will consider any citable sources of information that support 

the registrant's general statement that low soil moisture and I or high temperature would not be 

occurring at an agricultural field where MCP A is applied. 

EFED Response to Comments Submitted by the Center for Biological Diversity 

(CBD) (EPA-HQ-OPP-2014-0180-0020) 

While three specific comments were received from CBD regarding the reregistration ofMCPA, 

all three addressed EPA's responsibilities under the Endangered Species Act (ESA). For·clarity, 

the general comments are included below, but a general response is provided to address all three. 
CBD comments: 

I. EPA Has an Independent Duty Under the Endangered Species Act to Consult with the U.S. Fish 

and Wildlife Service and National Marine Fisheries Service on the Reregistration ofMPCA. 

II. The EPA Must Make Defensible "Not Likely to Adversely Affect" and "Likely to Adversely 

Affect" Determinations as a Prerequisite for Defensible "Jeopardy" and "No Jeopardy" 

Determinations. 

III. EPA and the Services Must Assess the Adverse Impacts ofMPCA in Critical Habitat. 

EFED response: 

Regarding CBD's request for EPA to begin informal consultation with the Services immediately 

after the workplan for MCP A is finalized, EPA plans to follow the March 2013 stakeholder 

engagement paper ("Enhancing Stakeholder Input in the Pesticide Registration Review and ESA 

Consultation Processes and Development of Economically and Technologically Feasible 

Reasonable and Prudent Alternatives") to identify the appropriate time for initiation of 

consultation, either formal or informal, with the Services. The stakeholder engagement paper, 

jointly developed by the EPA, USDA, and the Services and available at 

http://www.regulations.gov/#!docun1entDetaii:D=EPA-HQ-OPP-2012-0442-0038, allows for 

early interaction with the -Services under informal consultation. EPA and the Services 

acknowledge that early interaction as part of informal consultation may result in refinements to 

EPA's effects determinations that can improve the efficiency ofthe ESA compliance process. 

For example, EPA may involve the Services at the earliest stages of registration review. In 

general, EPA plans to initiate formal ESA consultation, if necessary, at the final decision stage in 

the registration review process. Consulting later in the process allows the EPA to develop more 

refined ecological risk assessments and to engage stakeholders in discussions that should result 

in more focused consultation packages that may include risk mitigation for listed species. 

EFED Response to Comments Submitted by Central Valley Regional Water Quality 

Control Board (EP A-HQ-OPP-2014-0180-0021) 

Central Valley Regional Water Quality Control Board comment: 

In order to prevent water quality impairments caused by MCP A we are requesting the following 

action in registration review: 

• Consider the cumulative risk of additive toxicities between MCPA and other phenoxy 

herbicides. 

EFED response: 
EPA appreciates the need to address cumulative risk from mixtures of pesticides both within and 

across modes of action. EPA, FWS, and NMFS collectively engaged the National Academy of 

Sciences (NAS) on the issue of mixtures as part of the broader approach to conduct ESA 

compliant pesticide risk assessments. As noted by the NAS report, the ability to quantitatively 

assess risk from mixtures (tank, formulated product, and environmental) is perhaps the most 

daunting challenge facing EPA and the Services. EPA currently considers cumulative mixture 

toxicity where data are available on combined effects from one or more compounds. EPA 

acknowledges that mixtures represent a consideration that may influence the toxicity of the 

active ingredient; however, there are many uncertainties and limitations to quantitatively 

assessing the impact of mixtures on the overall risk picture. As the NAS noted, there are 

significant challenges to incorporation of mixtures analyses into the risk assessment process 

including the lack of a generic peer-reviewed method to assess the risks from mixtures, 

uncertainty on the temporal aspects of exposure to mixture constituents (e.g. each constituent 

behaves differently once in the environment), lack of knowledge about mechanism of action in 

non-targets, and uncertainty on the portability of observed interactions across taxa. EPA and the 

Services have made the issue of developing an approach for assessing mixtures toxicity a priority 

for future risk assessments.