Toxicity and Bioconcentration of 2,3,7,8-TCDD to fathead minnows ( [formula omitted])

Results are presented from toxicity tests showing that 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was highly toxic to fathead minnows (Pimephales promelas), was slow-acting, and could cause mortalities for several weeks after a single exposure for 1 day to concentrations as low as 7.1 ng per litre. The steady-state (maximal) wet-weight bioconcentration factor was estimated as 7900; time to 90 per cent of steady state was calculated to be 48 days. The whole-body residues of fish exposed to 0.9 ppt TCDD for 28 days were directly related to exposure concentration and period of exposure. In contrast to these results with fish, 2,3,7,8-TCDD had no effect on young or adult Daphnia magna at concentrations up to 1030 ppt during a 48-h exposure followed by observation for 1 week.