Levels of dioxin-like compounds in sewage sludge determined with a bioassay based on EROD induction in chicken embryo liver cultures

A bioassay for the detection of dioxin-like compounds was used to estimate levels in sewage sludge from Swedish sewage treatment plants (STPs). The sl udge extracts were HPLC-separated into three fractions containing a) monoar omatic/aliphatic, b) diaromatic (e.g. polychlorinated biphenyls [PCBs], pol ychlorinated dibenzodioxins and polychlorinated dibenzofurans [PCDDs/Fs]), and c) polyaromatic compounds (e.g. polycyclic aromatic hydrocarbons [PAHs] ). The bioassay, which is based on EROD (7-ethoxyresorufin O-deethylase) in duction in cultured chicken embryo livers detected dioxin-like activity in all unfractionated extracts and in the di- and polyaromatic fractions of al l sludge extracts, but not in the monoatomatic/aliphatic fractions. The lev els ranged between 6 and 109 pg bio-TEQ/g sludge (d.w.). In sediment sample s from rural lakes in Sweden, levels of about 5 pg bio-TEQ/g (d.w.) have be en found. The polyaromatic fractions of the sludge samples were potent in t he bioassay, probably due to various PAHs and other polyaromatics in the sl udge. The levels of six PAHs that are screened for in the sludge at Swedish STPs accounted for only 3-10% of the observed EROD-induction by the polyar omatic fractions. Consequently, many other polyaromatic EROD-inducing compo unds were present in the sludge. Inclusion of a biological test like the ch icken embryo liver bioassay in the screening of sludge would improve the ab ility to detect the presence of bioactive dioxin-like compounds. A theoreti cal estimation of bio-TEQ concentrations in farm-soil following long-term a pplication of sludge with bio-TEQ concentrations similar to those observed in this investigation indicated that the bio-TEQ levels in soil would incre ase very slowly over time. The chicken embryo liver bioassay proved useful in assessing levels of dioxin-like compounds in sewage sludge and it gives valuable complementary information to chemical analysis data. (C) 1994 Else vier Science Ltd. All rights reserved.