Accumulation of and hepatic monooxygenase induction by 2,3,4,7,8‐pentachlorodibenzofuran (PnCDF) were studied in juvenile rainbow trout (Onchorhynchus mykiss) by feeding treated food for 31 d followed by a 180 d depuration period. Efficiency of assimilation was 44 and 41% at exposure concentrations of 9.0 and 0.82 ng g−1 PnCDF, respectively. Depuration of PnCDF followed first‐order kinetics with half‐lives (based on toluene extraction of 14C‐radiolabel corrected for growth dilution) of 61 and 69 d at the low and high exposure concentrations, respectively. Monooxygenase enzyme induction measured by ethoxyresorufin‐O‐deethylase (EROD) activity in individual trout livers was 84‐ and four‐fold higher after 31 d of exposure to 9.0 and 0.82 ng g−1, respectively, than in livers of unexposed fish. Sustained EROD activity at the high treatment concentrations was observed during the 180 d depuration phase. Ethoxyresorufin‐O‐deethylase activity declined at approximately half the rate of elimination of PnCDF. No significant differences between growth rates of treated and control fish were found.

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Accumulation of four 14C‐labeled polychlorinated dibenzo‐p‐dioxins (PCDDs), 1,2,3,7‐T4CDD, 1,2,3,4,7‐P5CDD, 1,2,3,4,7,8‐H6CDD, and 1,2,3,4,6,7,8‐H7CDD, by juvenile rainbow trout (Salmo gairdneri) and fathead minnows (Pimephales promelas) was studied by feeding the fish treated food for 30 d followed by a 30‐ to 75‐d depuration period. Assimilation efficiencies (based on total 14C) of the isomers were low, ranging from 13% for H7CDD to 37% for H6CDD in trout, as compared with 64% for 4,4′‐DDT under the same conditions. Bioaccumulation factors, assimilation efficiencies and elimination rate constants for each PCDD congener were lower in fathead minnows than in rainbow trout. Half‐lives for total 14C ranged from 9 to 13 d for T4CDD and P5CDD in trout and minnows, respectively, and from 46 to 112 d for H6CDD and H7CDD in the same fish. Toluene‐extractable radioactivity for T4CDD and P5CDD was less than 30% during the clearance phase, indicating extensive transformation to polar products in both species. A four‐compartment model was used to estimate the accumulation of H6CDD and H7CDD in Great Lakes food chains (from detritus/phytoplankton to lake trout). The model predicted decreasing concentrations of the PCDDs at higher trophic levels, with accumulation primarily from food, assuming freely dissolved water concentrations of less than 2 × 10−5 ng L−1.

Emerging insects are a potential biotic transport route for export of contaminants sequestered in lake sediments to surrounding aquatic and terrestrial ecosystems Emerging insects (mainly Diptera) were collected from four lake mesocosms treated with 10 pg of sediment-sorbed 2,3,7,8tetrachlorodibenzofuran Insects emerging from the mesocosms had a mean contaminant concentration of 228 pg/g wet weight Contaminant export by emerging insects was from 0 2 to 2 1% of the total sediment contaminant content annually

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