CALIBRATING THE UPTAKE KINETICS OF SEMIPERMEABLE-MEMBRANE DEVICES USING EXPOSURE STANDARDS

Organic contaminant exchange kinetics between semipermeable membrane d evices (SPMDs) and water were studied in two suspensions of estuarine and marine sediments under conditions of high and low turbulence over a period of 56 d. Prior to exposure, the SPMDs were spiked with a numb er of exposure standards not occurring in the environment, The release rate of these compounds was used as an independent measure of the exc hange kinetics between the SPMD and water. The uptake rates of chlorob enzenes, polychlorinated biphenyls, (PCBs) and polycyclic aromatic hyd rocarbons (PAHs) were lower by a factor of three under conditions of l ow turbulence. For compounds with a log octanol-water partition coeffi cient (K-ow) > 5.5 the uptake rate was constant during the entire peri od. Within each compound class, uptake rate constants correlated well with log K-ow, The uptake rate constants of PAHs were lower than those of PCBs and chlorobenzenes by a factor of 10, but these estimates pro bably are artificially low due to an overestimation of the aqueous PAH concentrations. Release rate constants of the exposure standards fell within the range of the uptake rate constants of chlorobenzenes and P CBs, although with poor precision. Suggestions for improving the measu rement of exchange rate constants of exposure standards are presented. The role of triolein in the exchange kinetics is shown to be minor.