Forms of polycyclic aromatic hydrocarbon in the formation of sewage sludge toxicity to Heterocypris incongruens

The aimof the present studywas to evaluate to what degree polycyclic aromatic hydrocarbon (PAH) determines sewage sludge toxicity in relation to Heterocypris incongruens. Six differing sewage sludges with increasing contents of polycyclic aromatic hydrocarbons were selected for the present study. As well as total PAH content, the content of the potentially bioavailable fraction was also determined in the sewage sludges using amethod ofmild-solvent extraction (with n-butanol). The PAH content was also calculated in the sewage sludge pore water by the equilibrium partitioningmethod. The total PAH content in the sewage sludges studied were in the range 3.60 to 27.95 mg kg−1. The contribution of the n-butanol extracted fractionwas in the range 38.7 to 75.4%. In the group of individual PAHs, 4- and 5-ring compounds had the highest content in the potentially bioavailable group. H. incongruens mortality in the range 6.7 to 100%, depending both on the sewage sludge and the dose applied. An increase of the sewage sludge dose usually resulted in an increase in toxicity. At the highest dose, a 100%mortality of H. incongruens was found in half of the sludges. The lowest dose, irrespective of the sludge type, caused over 40% growth inhibition. However, the results obtained did not allowfor the establishing of an unambiguous relationship between various sludge toxicity levels and the content of potentially bio-available PAHs. In some cases only, the extraction using n-butanol explained the high difference in toxicity despite a slight differentiation in the PAH content.