Deconvoluting Thermodynamics from Biology in the Aquatic Food Web Model

Bioaccumulation of hydrophobic pollutants in an aquatic food web is governed by exposure concentrations in sediment and water phases and by complex trophic interactions among the various species. We demonstrate that biological interactions and exposure from the chemical environment can be deconvoluted for aquatic food webs to allow clearer assessments of the role of thermodynamic drivers from the sediment and surface water phases. We first demonstrate the feasibility of this deconvolution mathematically for hypothetical food webs with 3 and 4 interacting species and for more realistic real-world food webs with >10 species of aquatic organisms (i.e., the freshwater lake food web in Western Lake Erie [ON, Canada] and the marine food web in New Bedford Harbor [MA, USA]). Our results show both mathematically (for the simple food webs) and computationally (for the more complex food webs) that a deconvoluted food web model parameterized for site-specific conditions can predict the bioaccumulation of polychlorinated biphenyls in aquatic organisms same as existing complex food web models. The merit of this approach is that once the thermodynamic and biological contributions to food web bioaccumulation are computed for an ecosystem, the deconvoluted model provides a relatively simple approach for calculating concentrations of chemicals in organisms for a range of possible surface water and sedimentary concentrations. This approach is especially useful for calculating bioaccumulation of pollutants from freely dissolved concentrations measured using passive sampling devices or predicted by fate and transport models. The deconvoluted approach makes it possible to develop regulatory guidelines for a set of surface water and sediment (or porewater) concentration combinations for a water body that is able to achieve a risk-based target for fish concentration. Environ Toxicol Chem 2021;40:2145-2155. © 2021 SETAC.