Dynamics of Chlordane Under Nonconstant Exposure Conditions: A Numerical Bioaccumulation Model

Abstract

Much attention has been paid to the bioaccumulation of toxicants in aquatic organisms during the last several years. In order to accurately predict and assess toxicant fate in natural ecosystems, most efforts have employed mathematical models to determine the relationship between aqueous concentrations and organism accumulation (Barron et al 1990;Landrum et al. 1992;Newman, 1995). In most cases, bioaccumulation models are based on the assumption that the concentration in water remains constant over the exposure time period. Thus, many exposure experiments are designed to achieve constant aqueous concentration of chemicals using dynamic flow-through systems (Bruggeman, 1981).Constant exposure regimes greatly simplify the estimation of bioconcentration factor (BCF) as well as the model kinetics. In natural systems, however, the aqueous concentration may significantly and continuously change over time through dynamic processes of volatilization, sedimentation, and biochemical degradation, such that the steady-state equilibrium conditions are rarely established (Newman and Jogue, 1996). Even in dynamic exposure experiments, it is a constraint to maintain constant aqueous concentrations of chemicals in these systems (Karara and McFarland, 1992). Bioaccumulation itself can also cause significant changes of aqueous concentrations not accounted for in constant concentration models. In order to describe the bioaccumulation processes in the laboratory as well as in natural systems more accurately, these models should incorporate the changes of concentrations in both the water phase, as well as in aquatic organisms. This paper presents a bioaccumulation model where the concentrations of toxicants continuously change over time both in organisms and in water while incorporating volatilization, biochemical degradation, or sediment interaction terms. This model was developed based on a mass balance numerical approach and validated against data obtained from the bioaccumulation of trans-and cischlordane into goldfish (Carassius auratus).