Research - Category III: Water Quality

Enhancing the Utility of In Vitro Digestive Fluid Extraction as a Management Tool for Contaminated Aquatic Sediments
(Funded 1999-2000)

Principal Investigator: Donald P. Weston
Integrative Biology
UC Berkeley
(510)231-5626
dweston@uclink4.berkeley.edu

Executive Summary:
It is well known that many pollutants in aquatic systems are highly sediment associated and that a substantial fraction (often >50%) of any given contaminant is associated with particles in such a way that it is not available to biota. Ideally, environmental management decisions pertaining to contaminated sediments should include consideration of the bioavailable fraction rather than merely the total contaminant concentration. However, existing chemical methods of analysis extract the total contaminant and do not differentiate the bioavailable fraction.

A new approach to assessment of the bioavailability of particle-associated contaminants has recently been proposed that employs the digestive fluid of deposit feeders to solubilize contaminants. Digestive fluid of a deposit-feeding organism is removed from the digestive tract and the sediments of concern are then incubated with that fluid in vitro. The fraction of the total contaminant that is solubilized in those fluids is considered a measure of bioavailability, and an estimate of the maximum amount of contaminant that is potentially absorbable during gut passage. The approach has the simplicity of a chemical extraction, but by using digestive fluid rather than an exotic solvent, the approach provides more environmental realism than is achieved by conventional chemical methods.

Our work to date on in vitro digestive fluid extraction has focused on polycyclic aromatic hydrocarbons in coarse sediments, and this proposal is intended to extend potential applications of the technique to other contaminants and other sediment types through three research tasks. The first task will extend the approach to trace metals, and specifically, will determine the effect of oxic vs. anoxic conditions on metal extractability. Preliminary work has been done under oxic conditions, but resulting measures of bioavailability may not be meaningful given the anoxic conditions that prevail in many deposit feeder guts. The second task will validate the technique in

fine-grained, organic-rich sediments, a substrate type more typical of most pollution problem areasthan the coarse sediments employed in work to date. Finally, the third task will determine for which contaminant classes the approach provides useful information. Estimates of bioavailability by digestive fluid solubilization will be compared to more traditional measures for several pesticides, industrial chemicals, a plasticizer, and several trace metals.

There are many instances when it is necessary to determine the ecological risk posed by contaminated sediments including dredged material management, source control decisions, and Superfund clean-up efforts. The proposed work will improve our ability to make these risk evaluations by including consideration of contaminant bioavailability. Our past work has shown the in vitro digestive fluid extraction method to be an extremely valuable tool in understanding the mechanisms of aromatic hydrocarbon bioaccumulation from sediments. The proposed research will provide the data needed to expand the sediment management applications of the approach and incorporate many more types of pollutants. Results should be of value to a wide variety of state and federal agencies responsible for ecological risk assessment.