Bioavailability and bioaccumulation of sediment-associated, desorption-resistant fraction of polycyclic aromatic hydrocarbon contaminants

This study is directed toward identifying and characterizing the bioavailability of both reversibly sorbed and desorption-resistant fraction of hydrophobic organic contaminants in natural biologically active sediments and the corresponding consequences to prediction, control and regulation of these contaminants. The focus is on polycyclic aromatic hydrocarbons (PAHs) with particular emphasis on phenanthrene and benzo[a]pyrene. A quantity of well-characterized and extensively desorbed sediments was prepared by desorbing the lab-inoculated sediment with an isopropanol and electrolyte solution. This procedure was proved to be a very effective method to prepare sediments containing contaminants largely limited to a desorption-resistant compartment. Accumulation of contaminants in the tubificid, Ilyodrilus templetoni, was measured after exposure to the prepared sediments. The uptake route of sediment-associated phenanthrene and benzo[a]pyrene and the effect of sediment ingestion and digestion by deposit feeders on the release of the contaminants from ingested sediment particles was also investigated.; Desorption-resistant or sequestered fraction of phenanthrene was available to Ilyodrilus templetoni but with reduced availability compared to reversibly sorbed phenanthrene. The reduction in bioavailability was approximately proportional to the increase in sediment-water partition coefficient. Strong correlation of bioavailability with effective partition coefficient was also observed for benzo[a]pyrene. The results of this study demonstrated that sediment pore water concentration defines steady state accumulation of PAHs in the deposit-feeding oligochaete, regardless of the route of uptake (via sediment ingestion or absorption from water). Therefore, bioavailability of desorption-resistant fraction of contaminant is reduced in direct proportion to the reduction in pore water concentration as measured by physico-chemical means (i.e. abiotic). Since steady state accumulation for these compounds in the deposit feeders is controlled by pore water concentration, extraction by gut fluids as proposed by some authors does not indicate bioavailability for the contaminants and organisms employed in this study. These conclusions would be complicated by metabolic processes that might occur with other compounds or in other organisms that would introduce fate processes other than simple partitioning.