Biodynamic Model is Unraveling the Complexities of Metal Bioaccumulation from Contaminated Sediments
Three scenarios of potential selenium discharges and bioaccumulation that could result from a proposed extension of the San Luis Drain, California. The DYMBAM model was used as part of a larger model to develop the scenarios of effects in the San Francisco Bay, California (figure taken from USGS Fact Sheet 2004-3091)
(Click on photo for larger version)
Water resource managers use various ecological risk assessment methodologies to assess
- options for restoring ecosystems contaminated with toxic metals,
- remediation of sediments contaminated with heavy metals, and/or
- water management programs that regulate the amount of metals in wastewater discharges.
A key factor controlling the outcome of these risk assessments is the rate that metals are bioaccumulated by affected organisms. The only problem is that metal bioaccumulation is highly variable due to differences among species, the environmental chemistry or bioavailability of metals, and the complexities of the cycling of metals in aquatic ecosystems. USGS scientists and their colleagues have developed a biodynamic model of bioaccumulation (DYMBAM) that can be used to predict the bioaccumulation of metal contaminants in affected organisms, such as clams and ducks. The model is "biodynamic" in the sense that
- A kinetic approach is used rather than an equilibrium-based approach to simulate the accumulation of metals by aquatic animals. The kinetic approach takes into account the rates of reactions, and allows the model to be flexible and predictive under changing conditions. In contrast, a model based on an equilibrium approach assumes all components of reactions are constant.
- DYMBAM uses experimentally derived species-specific rate constants that take into account differences in how aquatic animals react internally to metals rather than theoretical equations of bioaccumulation.
In short, it’s a biodynamic model because a biological approach is used rather than a strictly chemical approach.
Biodynamics can be viewed as a unifying concept that can explain why species differ in magnitude and patterns of metal bioaccumulation and why bioaccumulation differs widely among metals. The biodynamic approach has been used to help water resource managers make decisions involving contaminated sediments in the San Francisco Bay, California, area. For example:
- The DYMBAM model was used as part of a larger model that forecast selenium discharges and ecological effects of a proposed extension of the San Luis Drain.
- The model is being used to assist the U.S. Environmental Protection Agency to forecast the implication of different ambient water-quality standards for selenium.
- The model was used to help provide the scientific basis for the San Francisco Bay area's Regional Water Quality Control Board to regulate selenium discharges from refineries.
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