Equilibrium Model of Fate of Microcontaminants in Diverse Aquatic Food Chains

Abstract

Bioconcentration and bioaccumulation factors of PCB, 239Pu, and 137Cs are compiled from the literature as a function of organism size. The distribution of field-observed bioaccumulation factors varies markedly between each substance but similarly to order of magnitude within each substance across diverse food chains. It can be inferred from the literature that PCB levels in top predators are due primarily to food chain transfer. A steady state compartment food chain model is derived for estimation of the relative effect of uptake directly from water versus food chain transfer. The model food chain transfer number f, given by αC/K + G for α = chemical absorption efficiency, C = specific consumption, K = excretion rate, and G = net organism growth rate indicates the degree of food chain accumulation. For f > 1, food chain transfer is significant; for f < 1, uptake from water is more significant. Application of the model suggests that (a) PCB body burden in top predators is due almost entirely to consumption of contaminated prey, (b) for 239Pu all of the body burden is due to uptake from the water only, and (c) observed 137Cs concentration factors are due principally to food chain transfer with a high dependence on the salinity-dependent phytoplankton adsorption.Key words: food chain model, bioconcentration, bioaccumulation, PCB, 239Pu, 137Cs, water uptake, food chain transfer