The effect of sediment organic carbon content on bioavailability of hydrophobic compounds in aquatic ecosystems

The effect of sediment organic carbon content on bioavailability of hydrophobic compounds was investigated, using a numerical dynamic model capable of incorporating several major factors affecting bioconcentration. These included adsorption/desorption, metabolism, volatilization, and biochemical degradation. The model was validated against data obtained by exposing goldfish to two chlordane isomers in the presence of benthic sediments. Two sediments with differing organic matter content were used in the experiment: muck sediment with high organic matter and loam sediment with low organic matter. The bioconcentration factor was estimated from the water solubility and sediment partition coefficients (Kp) measured in exposure experiment. There was good agreement between the model predictions and the experimental data for both chlordane isomers in two different sediments. In order to incorporate the organic content into the adsorption capacity of the sediment, the partition coefficients were normalized to organic carbon (Koc) by percentage of organic carbon content (%OC). Given different values of the partition coefficients computed from Koc and %OC as input conditions, the effect of sediment organic carbon on bioavailability was examined from the model results. It was shown that sediment organic carbon can cause a significant impact on bioavailability of hydrophobic compounds, especially sediment containing low organic carbon content, where small changes in organic carbon content produced large variations of chlordane concentration in organisms.