The concentration of mild-extracted polycyclic aromatic hydrocarbons in sewage sludges

The present study evaluates the content of the mild-solvent extracted fraction of the polycyclic aromatic hydrocarbons. Ten compounds from the US EPA list (phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chryzene, benzo[b]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene oraz indeno[1,2,3-cd]pyrene) were chosen. The compounds were extracted with n-butanol from 11 sewage sludges that differed both in the total PAH content and in their physicochemical properties. On the basis of the results obtained, the influence of the properties of the PAH and some properties of selected sludge on the content of the mild-solvent extracted fractions of these compounds was determined. The content of the fraction extracted with n-butanol within the total of 10 PAHs ranged from 12.5 to 83.2% (mean 40.1%) depending on the type of sludge. Similarly, as in the case of the total of the 10 PAHs, significant differences in the content of PAHs extracted with n-butanol were also noted for the individual compounds studied. In the case of most individual PAHs their mean share did not differ statistically in relation to the PAH type and was close to 40%. An evaluation of the relation between the share of the fraction extracted with n-butanol from the different types of sludge and the properties of the PAHs showed that statistically, there existed significant (P < 0.05) correlations between log Koc (in the case of one sewage sludge) and between the nitrogen content, the ratio of C/N, cations Mg2+ and K+ (in the case of a few PAHs). A clear and significant relation was found between the content of and the share of the fraction of n-butanol extracted and the PAH fraction present in the sewage sludge pore water (determined on the basis of an equilibrium partition model).