Desorption resistance of polycyclic aromatic hydrocarbons and duration of exposure

The desorption-resistant fraction of laboratory-spiked phenanthrene in two Louisiana (USA) sediments was not observed to be significantly different, but the two sediments exhibited different condensed-phase organic carbon contents, as defined operationally by the organic carbon remaining after combustion of the sediment at 375 degrees C. Only 3% of the original saturated phenanthrene in the sediments was not readily removed by exposure to a nonpolar polymeric resin and sorbent XAD-2. Allowing the laboratory-spiked contaminants to age for periods of up to three years yielded little difference in the desorption-resistant characteristics of the sediments. Field-contaminated sediments from Utica Harbor (Utica, NY, U.S.A.) and Rouge River (Detroit, MI, USA) that had a lengthy (decades to a century) period of contamination, however, exhibited significantly different desorption-resistant contaminant fractions, consistent with the fractions of condensed-phase organic carbon in the sediments. Measurements of the fraction that could be rapidly desorbed using the XAD-2 sorbent also accounted for essentially all desorption to pore water and, thus, provided a good prediction of effective bulk partition coefficients. It was concluded that the condensed-phase organic carbon was a good indicator of the potential for desorption resistance in field-contaminated sediments and that the rapidly desorbing fraction provided a quantitative indicator of its significance.