Great Lakes Environmental Center (GLEC) conducted flow-through acute and early life stage toxicity tests and associated chemical analysis in support of ambient water quality criteria development for the U.S. Environmental Protection Agency (EPA). The objective of the work was to supply EPA with acute and early life-stage dieldrin toxicity data for fathead minnows to update the toxicity database in support or ambient water quality criteria and sediment criteria development. Fathead minnows of two age groups (<24-hour old larvae, and 30-day old juveniles) were exposed under flow-through conditions to measured concentrations of dieldrin in a flow-through system for 96 hours to determine the acute toxicity of dieldrin to each age group of fish. Secondly, the embryo larval toxicity of dieldrin was determined by exposing fathead minnow embryos and hatched larvae for 32-days to measured concentrations of dieldrin in a flow-through system. Ultimately, the median lethal toxicant concentration (LC50) was estimated from the 96-hour acute toxicity tests, and no-observed-effect-concentration (NOEC), lowest-observed-effect-concentration (LOEC), and the maximum-allowable toxicant-concentration (MATC) was estimated for dieldrin from the 32-day early life stage toxicity test. Toxicity test results were used to calculated acute:chronic ratios for dieldrin based on the toxicity to larval and juvenile fathead minnow. Results indicated that there was significant differences between the acute:chronic ratio when the two ages of fathead minnow were used to calculate the acute toxicity endpoint.
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