Comment: 

Response: 

Predicted exposure estimates from PRZM/EXAMS cannot be directly compared with the 

monitoring data because there are no monitoring data that specifically targeted phosmet use 

(application period and/or sites). NAWQA is a non-targeted monitoring study that includes 

analysis for a wide range of pesticides. Generally, targeted monitoring data are collected based 

on a sampling program designed to capture, both spatially and temporally, the maximum use of a 

particular pesticide. Typically, sampling frequencies employed in non-targeted monitoring 

studies are insufficient to document peak exposure values. The lack of targeted data coupled 

with the fact that these data are not temporally or spatially correlated with pesticide application 

times and/or areas limit the utility of these data in estimating exposure concentrations for risk 

assessment purposes. Therefore model-generated values are used for estimating acute and 

chronic exposure values, and the non-targeted monitoring data (such as NAWQA monitoring 

data) are used for qualitative characterization. Further, the drinking water assessment may be 

revised with the submission of an acceptable hydrolysis study (OPPTS 835.2120). At the writing 

of these responses, EFED has not yet received an acceptable hydrolysis study. The estimates 

assumed conservative values for input parameters based on core guideline studies which have 

not been fulfilled. 

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Comment: 

Response: 

EFED recognizes the qualitative use of the data presented by Kamel et al. These data were 

incorporated into the phosmet drinking water exposure assessment to highlight the uncertainty 

surrounding the formation of the potentially more toxic oxon degradate in drinking water 

sources. Further, NAWQA data reported six detections of phosmet oxon. These detections were 

not concurrent with detections of phosmet parent; however given the generally short half-lives of 

oxons in natural waters and the limitations of monitoring data (see response to Comment 3.1), 

monitoring detections are evidence of the potential for acute environmental exposure to oxons. 

Therefore, the data presented by Kamel et al. and the NAWQA monitoring data show that the 

phosmet oxon degradate may form in the environment and under oxidative chlorination 

treatment processes. Further, data show that oxon degradates of many organophosphate 

pesticides are stable in the presence of chlorine and do not degrade until the chlorine leaves the 

system. Thus oxons can persist while they are in the distribution system. The data presented in 

Kamel et al., 2008 indicate that this may not be the case for phosmet oxon; however, these data 

were used to show the formation of the oxon degradate under oxidative chlorination system, not 

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to quantitatively estimate the persistence of phosmet oxon in the distribution system. Additional 

information is needed to better quantify the exposure of the oxon under environmental conditions 

(e.g., additional targeted studies of finished and raw water). Without the additional information, 

the formation and persistence of phosmet oxon and the exposure of this potentially more toxic 

degradate remains an uncertainty and is thus qualitatively discussed and cannot be dismissed 

from the assessment. 

Comment: 

Response: 

EFED believes that a discussion of the validity of the use of Kenaga nomograph values, as 

modified by Fletcher et al. must recognize that the values are based on a robust set of actual field 

residue data. Hoerger and Kenaga (1972) state that the upper limit values from the nomograph, 

represent the 95th percentile of residue values from actual field measurements. The Fletcher et 

al. (1994) modifications to the Kenaga nomograph are also based on measured field residues 

from 249 published research papers, including information on 118 species of plants, 121 

pesticides, and 17 chemical classes. These modifications represent the 95th percentile of the 

expanded data set. 

EFED will consider chemical- and use-specific residue data, provided the data are sufficiently 

robust to account for intra- and inter-site variability as well as account for temporally variable 

environmental conditions. Gowan should cite the MRIDs it believes should be reviewed by 

EFED for the upcoming risk assessment. These data will be considered in the course of 

conducting the risk assessment. For example, for the phosmet risk assessment, the available 

foliar dissipation half-life of four days, the upper-bound on the mean of the available data points, 

will be used instead of EFED’s default value of 35 days. 

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