Table 1. Comments from DuPont Cr op Protection and EFED Responses
DuPont Comment EFED Response Reference Section 3, page 7: The structure of the metabolite G is incorrect as presented. Acknowledged. The structure will be corrected
when the Problem Formulation is revised. The degradation pathway for hexazinone in soil has been previously described in existing laboratory and field studies, and is well understood. The weight of evidence indicates that the degradation of hexazinone in soil is not predominantly pH dependent. Therefore requiring additional anaerobic and aerobic studies conducted in soils, differentiated by pH, is not warranted. As indicated in the Problem Formulation, according to current OCSPP guidelines, four aerobic, and four anaerobic soil metabolism studies are required for chemicals with outdoor uses. Only one aerobic soil metabolism study
has been identified and no anaerobic soil
metabolism studies are av ailable. Thus, new studies are required. In ge neral, the soils should be typical of the use sites and cover a range of physical and chemical properties.

In a registrant’s letter (from C.S. Baer to A. Ertman, dated May 7, 1991), it described the dependence of the degradation pattern of hexazinone with pH. It is indicated that in acidic soils, A, B, C, G and D are the transformation products mostly formed, while
in neutral to alkaline soil s, A, B, 1 and D are the transformation products mostly formed. Clarification is required. The degradation pathway for hexazinone is
well understood in the anaerobic environment based on an existing an aerobic aquatic study (MRIDs 41807402, 42657301). Anaerobic aquatic studies have historically been preferred and accepted by EPA to fulfill the requirement of an anaerobic soil metabolism study. It is unlikely that additional substantive information will be gained by conducting an anaerobic soil metabolism study. Even though in the pa st, anaerobic aquatic
metabolism studies were used in lieu of anaerobic soil metabolism studies, the data requirement is being imposed to all chemicals with outdoors uses undergoing registration
review. The anaerobic soil metabolism studies may provide information about potential processes occurring in anaerobic soils, as opposed to anaerobic sediments. The EFED
searched and did not find a DER for the MRID 42657301. The study appears to be a supplement to MRID 41807402. The study will be evaluated to verify if it meets requirements for a new anaerobic aquatic metabolism; however, the status of the data requirement remains unfulfilled until the study is evaluated and found acceptable.

2Table 1. Comments from DuPont Cr op Protection and EFED Responses
DuPont Comment EFED Response In the context of the aerobic aquatic metabolism data requireme nt, DuPont indicates
that it does not understand the basis for the statement that hexazinone is susceptible to pH and therefore another sediment study is required with a test system having a near neutral or slightly acidic pH. According to the current OCSPP guidelines, at least two aerobic aquatic metabolism studies are required for chemicals undergoing registration review, with outdoor uses. It was observed that the single available aerobic aquatic metabolism study was conducted for only 56 days, while hexazinone generally presents persistence to biodegradation. The period of time may not have been sufficient. With respect to the dependence of the degrad ation pattern with pH, please, refer to response to a similar comment above. In the problem formulation it is indicated that an aerobic aquatic metabolism study is available in only one sediment system (a sandy loam, pH 7.8). Thus a study with sediment with a neutral to acidic pH is required.
DuPont does not believe that another anaerobic aquatic study is warranted. According to OCSPP current guidelines, at least two anaerobic aquatic metabolism studies are required for chemicals with outdoor uses. The
EFED would like to obtain information on the
behavior of hexazinone in various water/ sediment systems. Thus, the study is required. DuPont indicates that environmental chemistry methods (ECMs) and independent laboratory validations (ILVs) for soils and water were submitted to the Agency (MRIDs 45132801, 45132802 and 45132803). As indicated in the problem formulation, these ECMs and ILVs have not been evaluated. They
will be verified for their suitability according to the Agency requirements. The EFED considers that the data requirement remains unfulfilled
until the studies are evaluated. DuPont does not agree that hexazinone will biomagnify in terrestrial food chains based on the low log K OW= 1.85 The EFED agrees with Dupont’s comment. The statement in the problem formulation reads as follows: “it appear s that hexazinone may biomagnify, but possibly not substantially , in terrestrial food chains” (emphasis added). With
a K OW~ 70, it appears that hexazinone is not likely to bioconcentrate or to biomagnify substantially. When the problem formulation is revised, the statement will be modified accordingly. DuPont will provide an acute oral passerine toxicity study under the DCI. EFED agrees with this comment.

Maximum use rate is 8 lb/A not the 10 and 12 lb/A reported in the problem formulation. EFED agrees that the us e rate should reflect the mitigation recommended in the RED. The use
rate will be based on labels active at the time of the registration review assessment.

3Table 1. Comments from DuPont Cr op Protection and EFED Responses
DuPont Comment EFED Response The use rate is especially critical when conducting endangered species assessments. The 8 lb/A use is only for non-agricultural

uses, The endangered species assessment will be based on signed labels at the time of the assessment. All uses are evaluated by individually to provide risk estimations for the ES assessment. Therefore, the non-agricultural uses will be identified and a separate ES risk
determination will be calculated for those uses. DuPont requests that the California Red Legged Frog (CRLF) assessment be
reconsidered. The CRLF risk determination was based on using the bird as a surrogate in the T-Herps model. This model is a screening model which assumes 100% of dietary exposure is from 100% hexazinone use rate.
The model does not consider issues such as the low accumulation in tissue, hexazinone dissipation over time, and time spent in the area of potential exposure to hexazinone. The CRLF assessment uses the bird as asurrogate for the terrestrial-phase CRLF. TRex, based on bird weights and diets, is used as a screening model. T-Herps is a refinement based on diet and weight of the CRLF. Direct dietary effects are conservatively estimated from the T-Herps model, which assumes 100% of the use rate. T-Herps provides an estimate of risk determined from a conservative assumption based on the maximum rate (100%). The CRLF assessment also included a spatial assessment that provided an overlap action area based on
the hexazinone use area and CRLF habitat. THerps will not be used in the registration review

assessment. Dupont recommends using similar taxa (Ranids) for ESA. Open literature and submitted studies on Ranids will be reviewed for use in the registration
review or other assessmen ts if available and if the study provided acceptable information for use in a qualitative or quantitative assessment. DuPont recommends using the USDA Forest Service hexazinone risk assessment reporting that based on limited data available, amphibians appears to be less sensitive to
hexazinone than fish or aquatic invertebrates. This assessment may be reviewed under open literature guidelines. This assessment was reported to be based on limited available data, which increases the uncertainty.

DuPont recommends that the CRLF assessment be based on frog, fish and aquatic toxicity data. The diet for the juvenile CRLF includes aquatic and terrestrial invertebrates. The diet for the adult CRLF aquatic and
terrestrial invertebrates as well as vertebrates such as mice, frogs and fish. The aquatic-phase CRLF assessment was based on fish and aquatic inverteb rate toxicity studies. However, the terrestrial-phase CRLF inhabits
terrestrial environments and the diet includes
mammals which are based on the rat as a surrogate. Therefore, direct effects for the terrestrial-phase CRLF are based on terrestrial surrogates (bird) and indi rect dietary effects for mammals are based on terrestrial surrogates,
mammals.

4Table 1. Comments from DuPont Cr op Protection and EFED Responses
DuPont Comment EFED Response DuPont notes that the quail NOAEC =1000 mg/kg for reproduction, not 300 mg/kg for feed consumption. No reproductive effects were observed at the 1000 mg/kg treatment
level. The reported reproductive endpoint is for surviving adult weight. Although there was a significant increase in feed consumption, there was no significant reducti on in adult weight at
test termination. The st udy reported no effect on juveniles at the highest test concentration. The
value will be corrected when the Problem
Formulation is revised. DuPont recommends using the acute oral rat study (MRID 41235004) rather than the open literature acute oral rat study. The assessment will use the latest acceptable oral study reviewed by HED.

DuPont states that the most relevant chronic daphnid test is MRID 41406002, rather than
MRID 00078041. Both studies were classified as supplemental. The most sensitive endpoint is for MRID 00078041. The RQ using either value will be compared to a chronic LOC = 1.Both studies
will be reviewed for the assessment.
The EC 25 for tomato should be 0.0063 lb/A, 0.0205 lb/A for sorghum, 0.01 lb/A for rape
and 0.0193 lb/A for wheat. The values were reported from the RED and DERs. The values reported from the DERs for tomato (0.00064), rape (0.011), sorghum (0.019), and wheat (0.020) will be reviewed for
the assessment. The detection level will be considered for rounding purposes.
The EC 50 for Lemna (MRID 43225101) should be 0.0383 mg/L. The Lemna frond EC50=37.4 ppb was taken from the RED. The study used weighted least squares to statistically analyze the data, while the DER used probit analysis. The study will be reviewed during the assessment. The duration of the green algae, blue-green algae, freshwater diat om and marine diatom
was 120 hrs. Acknowledged. The duration will be corrected
when the Problem Formulation is revised.

DuPont requests that th e review indicate how
the conclusion was made as to cause for incident data. The registrant notes that it is impossible to unequivocally assert cause
without additional information such as residue analysis of tissue, water or sediment. Incident data reported in the database will be
summarized at the time of the risk assessment. Although there is no statement reflecting cause for this specific incident, there is a statement indicating the certainty classification, based on reported information such as location of incident, application rate, method, time of application, and species . If tissue analysis results are reported in the incident data, that
information will be included in the assessment. DuPont requests that criteria for accepting open literature endpoints is referenced in the
PF. Acknowledged. The criteria for accepting endpoints from the open literature in the PF will
be referenced when the Problem Formulation is
revised.

5Table 1. Comments from DuPont Cr op Protection and EFED Responses
DuPont Comment EFED Response DuPont does not feel that new vegetative vigor and seedling emergence toxicity test are needed, based on MRID 43605001, which
addresses the use of thiram. The studies were requested in the RED. Per the 2000 SAP, it was agreed th at the use of thiram is acceptable to treat the seeds. Therefore these studies do not have to be repeated. DuPont does not think seedling emergence studies for onion and peas are needed based on the phytotoxicity endpoint. The visual injury data indicate that pea is less
sensitive than tomato. It also indicates that onion is more sensitive than sorghum. Since no data was available to statistically analyze the weight for onion and pea, the visual injury data
will be used.

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