TOXIC POTENCIES OF EXTRACTS OF SEDIMENT AND SETTLING PARTICULATE MATTER COLLECTED IN THE RECIPIENT OF A BLEACHED PULP-MILL EFFLUENT BEFORE AND AFTER ABANDONING CHLORINE BLEACHING

Extracts of bottom sediment and settling particulate matter (SPM) samp les collected in the recipient water body of a bleached pulp mill effl uent were separated into three fractions: monoaromatic/aliphatic compo unds, diaromatic compounds (e.g., polychlorinated biphenyls, polychlor inated dibenzo-p-dioxins, and polychlorinated dibenzofurans), and poly aromatic compounds assessment of dioxinlike potency were an in vitro a ssay, based on the induction of 7-ethoxyresorufin-O-deethylase (EROD) in chicken embryo livers, a test for EROD induction in ovo using chick en embryos, and an immunotoxicity test measuring inhibition of lymphoi d cell development in cultured fetal mouse thymuses. The samples colle cted closest to the mill were the most potent. There was a time-depend ent decrease in dioxinlike potency in the SPM samples collected near t he mill, which coincided with the cessation of chlorine gas bleaching at the mill. The bioassays in general, and the in vitro chicken embryo liver bioassay in particular, proved useful in the assessment of diox inlike compounds in the sediment and SPM samples. The polyaromatic fra ctions of the samples were generally more potent than the diaromatic f ractions. Only a small part of the effects caused by the polyaromatic fractions could be explained by 15 analyzed PAHs, indicating the prese nce of unquantified polyaromatic compounds with dioxinlike effects. Th is investigation indicates that the cessation of chlorine bleaching in the pulp mill resulted in a reduced load of diaromatic dioxinlike com pounds in the recipient water body.