Resin Acids and Retene in Sediments Adjacent to Pulp and Paper Industries (8 pp)

Aim and Background In order to identify potential risks of sediments contaminated by pulp and paper mill effluents, two boreal lake areas were investigated from core samples. Resin acids (RA) and their aromatized derivative retene were measured, suggesting that these aquatic toxicants can be long-lasting sources to expose benthic biota. On the other hand, dredging or other human actions can liberate toxicants, even from deep sediments, to an aqueous phase with harmful consequences to aquatic species. Since no historical sediment profiles were available, we investigated the toxic potential of sediment-water elutriates by way of the bioluminescent bacteria Vibrio fischeri. In this investigation, we therefore analyzed both the concentrations of toxic chemicals and the toxicity as profiles in two contaminated lake sediments in Finland. Methods Freeze-dried sediment samples were purified with the liquid-liquid extraction and column separation methods. RA and retene were further analyzed by GC/MS and GC/FID techniques. The toxicity assessment by microbial tests from sediment-water elutriates represents an approximation of the ecotoxic potency of sediment layers containing wood-derived extractives. Elutriates were produced by mixing sediment and water in standardized volume ratio (sediment/water; 1:4, v/v), and, after 15 min of incubation, EC50 values were measured. Results and Discussion In samples from the pre-industrial time and in a reference site of an uncontaminated lake, the concentrations of RA varied from 0.3 to 20 mg g–1 dw. Due to the wood-processing industry, the abundance of RA was dramatically increased at downstream sites. The most contaminated sediment layer contained 1070 mg g–1 of RA, dated back to the 1970s, representing the time of chlorine gas bleaching and before the secondary wastewater treatment technology. Retene occurred as a similar kind of concentration profile as RA, the highest concentrations being found from the deepest layers of industrial history. Besides trapping, this suggests a time-consuming process of retene formation under anaerobic conditions. For comparison, the detection limit of retene (0.1 mg g–1) was not exceeded in samples from pre-industrial time or in the reference site. - RA and retene correlated with toxicity in some sediment-water elutriates, but it was obvious that other chemical and also physical factors were behind the strong toxicity observed in another investigated lake area. Conclusion and Outlook Results showed that historically massive concentrations of wood extractives have been buried in the industrial sediments. It is well detectable that the emissions and the toxicity have significantly decreased in accordance with the modernization of mills. According to our investigation, serious consideration of the potential ecotoxicological risks should be made when planning any dredging or remediation actions at areas contaminated in this manner.