Identifying body residues of HCBP associated with 10-d mortality and partial life cycle effects in the midge, Chironomus riparius

The relationship between the body residue of 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) and its effects, including 10-d mortality and chronic sublethal effects on the midge, Chironomus riparius, are examined in a partial life cycle assessment. The alga, Chlorella vulgaris, was loaded with 14C-labeled HCBP and fed to midges as the method for delivery of the toxicant. In a 10-d bioassay, median lethal body residue (LR50) was 0.57 (95% CI: 0.49-0.66) mmol/kg. In the partial life cycle test, midges were fed a mixture of 12C- and 14C-HCBP-laden algae and exposed in four separate tests to assess the different developmental stages representing 2nd to 3rd instar, 2nd to 4th, 2nd to pupa, and 2nd to adult stages. A variety of sublethal endpoints were monitored, including developmental time within a stadium, body concentration at the end of each stadium, body weight, and fecundity (the number of ova) for the female pupae and adults. Overall, midge body concentrations of HCBP increased with increasing exposure concentration. Body weight was not significantly affected by HCBP except during the 4th instar. Body residue also increased with each successive stadium. Developmental time increased significantly with increasing body concentration in 2nd to 4th, 2nd to pupa, and 2nd to adult tests, while there was no statistical significance in developmental time for the 2nd to 3rd instar test. The number of ova decreased significantly in adults with increasing body concentration of HCBP, with an average of 345 ova in controls, 289 ova at 0.028 mmol/kg of HCBP, and 258 ova at 0.250 mmol/kg. These data, which relate chronic endpoints to body residues, suggest that sublethal endpoints in invertebrates are useful for defining sublethal hazards of PCBs. These data also suggest that ecological consequences may result from relatively low body burdens of PCBs.