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A SMALL FISH MULTI-ENDPOINT BIOASSAY FOR ASSESSING THE EFFECTS OF WATER CONTAMINANTS PRESENT IN LOW CONCENTRATIONS: MEDAKA AND DICHLOROACETIC ACID
Citation:
Johnson, R. D., D B. Lothenbach, K. M. Flynn, D. F. Hammermeister, F W. Whiteman, P N. Fitzsimmons, P. K. Schmieder, A Deangelo, D C. Wolf, J W. Fournie, W W. Walker, R. N. Winn, AND M. J. Wolfe. A SMALL FISH MULTI-ENDPOINT BIOASSAY FOR ASSESSING THE EFFECTS OF WATER CONTAMINANTS PRESENT IN LOW CONCENTRATIONS: MEDAKA AND DICHLOROACETIC ACID. Presented at USEPA Science Forum 2002: Meeting the Challenges, Washington, DC, May 1, 2002.
Description:
In regulating the safety of water under SDWA and the CWA, the EPA makes decisions on what chemical contaminants to regulate and at what levels. To make these decisions the EPA needs hazard identification and dose-response information. Current methods that rely on rodent models for generating required information have several limitations for determining the risks of long-term exposure to low chemical concentrations found in drinking waters, ground waters, or surface waters. Limitations include: a) difficulty in delivering an effective toxicant dose through drinking water; b) exposure times of up to two years required for some effects endpoints such as cancer; c) sample sized needed to determine low frequency events (i.e., cancer or developmental anomalies) are costly; and d) assessing the effects of "naturally" occurring chemical mixtures requires the preparation of water concentrates which are costly and difficult to to with fidelity. Several divisions of the NHEERL laboratory are working together to a) develop a small fish bioassay to measure reproductive, developmental and carcinogenic effects of chemicals in water; and b) evaluate comparability of risk assessment endpoints across rodent and fish species on a dose-dependent basis. The goal is to use shorter-term, direct exposure fish bioassays to enable more efficient collection and use of data from multiple species to reduce uncertainties and improve efficiency of current risk assessments. Results of a nine-month continuous exposure of medaka to dichloroacetic acid at concentrations as much as 10 times lower than used in rodent assays are presented, including dose- and time-dependent increases in mutation frequencies (recorded in transgenic medaka), and detectable liver tumors (wild-type medaka). Comparisons between adverse effects noted in rats and mice and those seen in medaka support the need to consider these data for assessing the effects of long-term exposures to low water concentrations, for which efficient, effective models are currently not available. This abstract does not necessarily reflect EPA policy.