Sediments collected near an aluminum plant on the St. Lawrence River have been found to be lethal to the larvae of the aquatic insect, Chironomus tentans. Initial studies suggest that the concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlodibenzodioxins (PCDDs)/polychlorodibenzofurans (PCDFs) in the sediment cannot account for the toxicity of the sediment. The major objective of this project is to determine the complete range of toxic compounds in the sediment by coupling separation schemes with direct bioassays. This novel approach, termed bioassay-directed chemical analysis, can greatly simplify the identification of toxic compounds in complex environmental samples.
In the first phase of the project, the sediment is being sequentially extracted with two solvents of increasing polarity (toluene and methanol) followed by extraction with water. The extracts are being subjected to a battery of one in vivo and four in vitro bioassays to determine acute toxicity, genotoxicity estrogenicity/antiestrogenicity and neurotoxicity. For the acute toxicity measurements, we are using the Chironomus tentans larvae procedure and a rapid bacterial assay based on the ability of a toxicant to reduce light output from a luminescent bacterium. Genotoxicity will be assessed with a non-luminescent variant of the bacterium to which luminescence can be restored by a mutation. Estrogenicity/antiestrogenicity will be evaluated by mammalian cell systems based on the growth of MCF-7 human breast cancer cells. Finally, neurotoxicity will be evaluated by catecholamine metabolism in rat brain slices. The selected bioassays are simple, rapid and cover a range of important biological responses.
In the second phase extracts will be subjected to chemical fractionation, with each fraction being evaluated by the bioassays described in the first phase. Fractions showing an increase or decrease in toxicity relative to the original extract will be analyzed by high and low resolution mass spectrometry and Fourier Transfer Infrared Spectroscopy.
The final phase will examine bioaccumulation and metabolism of toxic compounds in fish exposed to sediment in the laboratory.
