Comparison of two bioassays, a fish liver cell line (PLHC-1) and a midge (Chironomus riparius), in monitoring freshwater sediments

Two bioassays, a fish hepatoma cell line (PLHC-1) and a midge (chironomus r iparius), were used to monitor surficial sediments from Lake Vortsjarv and River Narva, Estonia. L. Vortsjarv is polluted with mainly polycyclic aroma tic hydrocarbons (PAHs) but R. Narva possesses complex contamination (PAHs, heavy metals, sulphates, chlorides). The PLHC-1 cells were exposed to the extracted lipid soluble compounds (PAH fraction) of the sediments, after wh ich the cytotoxicity (total protein content) and cytochrome P4501A (CYP1A) inducibility (7-ethoxyresorufin O-deethylase activity (EROD) and CYP1A prot ein content) were measured. The midges were grown in whole sediments after which the midge growth (larval growth and survival as endpoints) or the eme rgence (larval survival and adult emergence) were tested. Contents of selec ted PAHs and heavy metals in the sediments were also evaluated. In the PLHC -1 screening experiments, most of the sediments from R. Narva were more tox ic and caused higher EROD activities at lower doses than the sediments from L. Vortsjarv. The most polluted sediment in R. Narva (total PAH content 74 4 ng g(-1) dry weight sediment) gave 15 mg dry sediment ml(-1) as the ED50 for induction of EROD activity in the cells exposed for 3 days. In the midg e growth test, larvae seemed to grow better in the sediments from L. Vortsj arv than from R. Narva and the mortality was somewhat higher in two areas i n R. Narva than in other study areas. Adult emergence did not show such cle ar trends between these two watersheds, though emergence was accelerated in some sediments. A sediment from a point source of pollution (accidental re lease of asphalt) from R. Narva was also studied and found to be the most t oxic for the PLHC-1 cells and the most potent inducer of CYP1A (ED(50)s 0.5 9 and 0.56 mg dry sediment ml(-1)). None of the midge larvae survived in th is sediment. In a time-course study, the highest EROD activity in the PLHC- 1 cells was reached at lower doses of PAH fraction after 24-h exposure than after 48 or 72 h, suggesting metabolism of PAHs in the cultures. Further, CYP1A induction was still seen as elevated amounts of CYP1A protein in case s where catalytic EROD activity was decreased at higher doses of PAH fracti on. Overall, the PLHC-1 bioassays were shown to be sensitive methods for de tecting PAH pollution. The midge bioassays reflected better the bioavailabi lity and the in situ effects of the complex mixture of compounds in the sed iments. (C) 1998 Elsevier Science B.V. All rights reserved.