2000-04-20_PERMIT FILE - M2000002

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4l?D/CO 1'HU 18:15 FA% i-~ III IIIIIIIIIIIII III Colorado Department of Public Health and Environment 002 Rocky Moutain Arsenal Offpost Operable Unit ^`~ n Estimation of Fluman Health Noncancer Risks due to Ingestion of DIMP- - 4~-t" Contaminated Vegetables and Fruits April 2000 ~~pp ~'"~ Executive Summary T'he ingestion of homegrown vegetables and fruits, irrigated with diisopropyl methylphosphonate (DIMP)-contaminated groundwater, represents a complete DIMP exposure pathway. DIMP is classified as EPA Group D eazcinogen (i.e., not classifiable as to human carcinogenicity). To address the potential noncancer health risk associated with such a pathway, the Colorado Departrnent of Public Health and Environment (CDPHE} conducted a risk assessment. This assessment addresses a spectrum of potential exposure including variation in both the amounts of homegrown fruits and vegetables consumed and the concentration of D11v1P in gazden irrigation wells. The assessment examines child and adult exposure scenarios. Risk calculations for a variety of DIMP groundwater concentrations are provided. Environmental risk assessors evaluate chronic noncancer risks by comparing an exposure level over a specified time period with a reference dose derived for a similaz exposure period. This ratio is called a hazard quotient. If the hazard quotient (HQ) exceeds 1.0, there may be concern for potential noncancer effects. T}~e results of this risk assessment indicate that the hazard quotients for children and adults, at the 8 ppb State Water Quality Standard for DIMP, are below the EPA's benchmazk level of 1.0 and aze not likely to be associated with adverse health risks, based on the current knowledge of D1MP toxicity and biouptake by plena. Specifically, the adult hazard quotient estimates for central tendency (CTE) and reasonable maximum (ItME) exposure assumptions are 0.03 and 0.08, respectively. The child hazard quotient estimates are 0.04 (CTE) and 0.10 (RME). ~ 1n the event that a DIMP concentration exceeds the State Water Quality Standard of 8 ppb, the potential risk to children and adults will increase linearly (as discussed in Appendix A). For example; based on the highest DIMP concentration of 100 ppb (most recent data available) measured in a garden irrigation well, the child HQ = 0.52 (CTE) and 1.20 (RME), and the adult HQ = 0.43 (CTE) and 1.00 (RME). Tri-County Health Department maintains an ItMA'Offpost private well inventory, resident survey, and well sampling computer database. Based on the resident survey, we aze not aware of any current exposure to children at DIMP concentrations significantly higher than 8 ppb. The risk estimates for the reasonable maximum exposure assumptions aze at, or slightly above, the EPA benchmazk of 1.0. Risk estimates of this level may be of concern for potential adverse health effects. However, the survey indicates that homegrown gazden use does not occur at the household with 100 ppb DIIviP measured in its .