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

Abstract

Two bioassays, a fish hepatoma cell line (PLHC-1) and a midge ( Chironomus riparius), were used to monitor surficial sediments from Lake Võrtsjärv and River Narva, Estonia. L. Võrtsjärv is polluted with mainly polycyclic aromatic 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 which the cytotoxicity (total protein content) and cytochrome P4501A (CYP1A) inducibility (7-ethoxyresorufin O-deethylase activity (EROD) and CYP1A protein content) were measured. The midges were grown in whole sediments after which the midge growth (larval growth and survival as endpoints) or the emergence (larval survival and adult emergence) were tested. Contents of selected 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 toxic and caused higher EROD activities at lower doses than the sediments from L. Võrtsjärv. The most polluted sediment in R. Narva (total PAH content 744 ng g −1 dry weight sediment) gave 15 mg dry sediment ml −1 as the ED 50 for induction of EROD activity in the cells exposed for 3 days. In the midge growth test, larvae seemed to grow better in the sediments from L. Võrtsjärv than from R. Narva and the mortality was somewhat higher in two areas in R. Narva than in other study areas. Adult emergence did not show such clear trends between these two watersheds, though emergence was accelerated in some sediments. A sediment from a point source of pollution (accidental release of asphalt) from R. Narva was also studied and found to be the most toxic for the PLHC-1 cells and the most potent inducer of CYP1A (ED 50s 0.59 and 0.56 mg dry sediment ml −1). None of the midge larvae survived in this 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 cases where catalytic EROD activity was decreased at higher doses of PAH fraction. Overall, the PLHC-1 bioassays were shown to be sensitive methods for detecting PAH pollution. The midge bioassays reflected better the bioavailability and the in situ effects of the complex mixture of compounds in the sediments.