The effect of sorption on phenanthrene bioavailability

Critical parameters that need to be considered in a bioavailability study are reviewed and applied to a study on the sorption (binding) of phenanthrene to dissolved humic acid (HA). Sorption coefficients values (K(oc)) of phenanthrene to HA were measured for HA from several sources. These values were used to calculate the amount of HA that was needed to bind different fractions of solution-phase phenanthrene. Sorption linearity and complete reversibility were assumed. A mixed culture of phenanthrene degraders, dominated by Pseudomonas sp. was sensitive to changes in dissolved phenanthrene concentrations in the range that was used in this study. Therefore, it was expected that if bound phenanthrene was not available, as is commonly stated in the literature, sorption would affect mineralization rate by reducing the concentration of free phenanthrene. However, it was found that mineralization of phenanthrene was not affected by sorption even when 90% of the phenanthrene was in the bound phase. It was concluded that the organisms were able to use the phenanthrene directly from the bound phase and at the same rate as from the free phase.