Table 1. Comments from DuPont Crop 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 available. Thus, new 

studies are required. In general, 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 soils, 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 anaerobic 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 past, 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. 

2
Table 1. Comments from DuPont Crop Protection and EFED Responses 

DuPont Comment EFED Response 

In the context of the aerobic aquatic 

metabolism data requirement, 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 degradation 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 KOW = 1.85 

The EFED agrees with Dupont’s comment. 

The statement in the problem formulation reads 

as follows: “it appears that hexazinone may 

biomagnify, but possibly not substantially, in 

terrestrial food chains” (emphasis added). With 

a KOW ~ 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 use 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. 

3
Table 1. Comments from DuPont Crop 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 a 

surrogate 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 assessments 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 invertebrate 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 indirect dietary effects for 

mammals are based on terrestrial surrogates, 

mammals. 

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Table 1. Comments from DuPont Crop 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 reduction in adult weight at 

test termination. The study 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 EC25 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 EC50 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 diatom and marine diatom 

was 120 hrs. 

Acknowledged. The duration will be corrected 

when the Problem Formulation is revised. 

DuPont requests that the 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. 

5
Table 1. Comments from DuPont Crop 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 that 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. 

6