Assessing bioavailability of particle-associated pollutants by mimicry of digestive processes

Donald Weston, Ph.D.
University of California, Berkeley

Friday, April 23, 1999
12:00 Noon—Pacific Forum (Video Conference from UC Berkeley)

Particle-associated contaminants are accumulated by deposit-feeding organisms via ingestion and digestion, but often only a small fraction of the contaminant in sediment is bioavailable. The bioavailability of contaminants can be measured by a new approach that employs the digestive fluid of deposit-feeders to solubilize contaminants in vitro. The sediment of concern is incubated in digestive fluid obtained from the polychaete, Arenicola brasiliensis, and the ability of the fluid to desorb contaminants from the sediment is quantified. Digestive fluids are far more efficient pollutant solubilizers than is seawater, yet typically less than half of the chemically quantifiable contaminant is available to an organism via digestion. The new approach shows good agreement with more traditional measures of bioavailability. We have extended the approach with digestive fluids from 19 species of invertebrates representing 7 phyla. Digestive solubilization of both zinc and benzo(a)pyrene from sediment varied by about 10-fold, depending on the species from which the digestive fluid was obtained. Echinoderms tended to have digestive fluids that were very poor at solubilizing contaminants and, in general, were comparable in extraction efficiency to seawater. Fluids from echiurans and priapulids tended to be among the most effective extractants. These relationships are interpretable based on fluid characteristics including enzyme activity and surfactant properties. These data clearly indicate that the concept of "the bioavailable contaminant fraction" is highly species-specific, and dependent upon phylogenetically based differences in gut fluid characteristics.

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