Introduction

DIMP IS A GROUNDWATER contaminant at and near the Army's Rocky Mountain Arsenal in Adams County, Colorado. It was released into the environment as a result of the manufacturing process and neutralization of GB (Sarin), which was manufactured at the arsenal between 1953 and 1957. There has been a long-standing controversy between the Army and the State of Colorado regarding the appropriate drinking-water guideline for DIMP. EPA recommends a guideline (lifetime health advisory) of 600 µg/L, whereas the State of Colorado has promulgated a lower guideline of 8 µg/L. The reason for the difference is that different studies were used to calculate the drinking-water guidelines. Colorado used a one-generation reproductive toxicity study in mink (Aulerich et al. 1979) that reported increased mortality in female mink. EPA did not use that study, citing natural high mortality in captive mink and uncertainties about the relevance of mink to human health assessment. Instead, EPA used a 90-day toxicity study in dogs (Hart et al. 1980).

In 1990, the NRC Committee on Toxicology (COT) evaluated the scientific basis for the two drinking-water guidelines for DIMP. COT found the data from the one-generation mink study to be compromised because of inadequate testing and reporting procedures, and it concluded that EPA's drinking-water guideline for DIMP was an appropriate interim drinking-water guideline until additional research was



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RE-EVALUATION OF DRINKING-WATER GUIDELINES FOR DIISOPROPYL METHYLPHOSPHONATE Introduction DIMP IS A GROUNDWATER contaminant at and near the Army's Rocky Mountain Arsenal in Adams County, Colorado. It was released into the environment as a result of the manufacturing process and neutralization of GB (Sarin), which was manufactured at the arsenal between 1953 and 1957. There has been a long-standing controversy between the Army and the State of Colorado regarding the appropriate drinking-water guideline for DIMP. EPA recommends a guideline (lifetime health advisory) of 600 µg/L, whereas the State of Colorado has promulgated a lower guideline of 8 µg/L. The reason for the difference is that different studies were used to calculate the drinking-water guidelines. Colorado used a one-generation reproductive toxicity study in mink (Aulerich et al. 1979) that reported increased mortality in female mink. EPA did not use that study, citing natural high mortality in captive mink and uncertainties about the relevance of mink to human health assessment. Instead, EPA used a 90-day toxicity study in dogs (Hart et al. 1980). In 1990, the NRC Committee on Toxicology (COT) evaluated the scientific basis for the two drinking-water guidelines for DIMP. COT found the data from the one-generation mink study to be compromised because of inadequate testing and reporting procedures, and it concluded that EPA's drinking-water guideline for DIMP was an appropriate interim drinking-water guideline until additional research was

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RE-EVALUATION OF DRINKING-WATER GUIDELINES FOR DIISOPROPYL METHYLPHOSPHONATE done. COT recommended that another reproductive toxicity study in mink be conducted. In 1997, a two-generation reproductive toxicity study (Bucci et al. 1997) in mink was completed, and the Army requested that NRC independently review the study and other recent publications on DIMP to determine whether the interim drinking-water guideline supported by NRC in 1990 is still valid. If it is not, the subcommittee was asked to make scientific recommendations for developing an appropriate guidance level.