University of California Water Resources Center

A technique has recently been proposed to assess the bioavailability of sediment-associated contaminants by in vitro incubation of the sediments in digestive fluids of a deposit-feeding organism. This procedure mimics the chemical environment to which a contaminated particle would be exposed as it passes through the gut, and is based on the presumption that the bioavailable contaminant fraction is that which is desorbable under these conditions. This study was intended to further explore some key assumptions and limitations of this procedure. With regards to use of the technique to measure trace metal bioavailability, it was found that the procedure does allow oxygenation of the gut fluid in comparison to the in vivo gut environment which is near anoxic. This oxygenation did influence solubilization of about half the trace metals tested, though the effect was usually too small to have an appreciable impact on risk assessment decisions. With regards to assessment of bioavailability of organic contaminants, there was an excellent correlation between the proportion of contaminant solubilized in vitro, and that judged to be bioavailable by other in vivo techniques using two deposit-feeding polychaetes. This relationship held not only for polycyclic aromatic hydrocarbons which had been previously studied, but for several other pesticides and chlorinated organic compounds. Moreover, one traditional measure of bioavailability (absorption efficiency as measured by a dual label technique) was shown to underestimate bioavailability due to complications caused by selective feeding. The digestive fluid technique showed considerable promise across a broader range of contaminants and substrate types than had been previously tested, and appears to be a simple and rapid means to assess bioavailability, and obtain information otherwise available only by using live animals and more lengthy and logistically difficult procedures.