Dissertation

A toxicokinetic model for the determination and prediction of a biota-sediment accumulation factor for PCB-52

Feldhaus, Jane Marie Heslop

1996

Overview

In aquatic ecosystems, sediments serve as a reservoir for neutral organic chemicals such as PCB-52 which partition primarily to the lipids of the biota and the organic carbon of the sediment. The bioaccumulation potential predicts adverse chronic effects which result from the uptake and retention of a persistant chemical by the aquatic biota. The biota-sediment accumulation factor (BSAF) is a measure of bioaccumulation potential used in hazard assessment. Mathematically, the BSAF is the ratio of an organism's concentration of a particular chemical to the sediment concentration of the same chemical, normalized to biota lipid and sediment organic carbon. If an aquatic ecosystem is considered as a series of compartments reversibly connected with each other, then chemicals can move dynamically in and out of these compartments at different rates. Toxicokinetic modeling using the intercompartmental transfer rate constants of closed compartmental models can be used to express this movement. In this study, two- and three-compartment closed models were developed to describe the phase distribution of PCB-52 among fish, sediment, and water. Integration of the simultaneous differential rate equations of each model provided a set of predictive time-course equations. Fish and suspended sediment were simultaneously and separately exposed to an aqueous solution of PCB-52. Intercompartmental transfer rate constants were generated by fitting differential equations to the experimental data. Coefficients and hybrid rate constants of the integrated equations were obtained indirectly from the transfer rate constants and directly from fitting the experimental data to the integrated equations. Uptake of PCB-52 by fish (Compartment 3), adsorption of PCB-52 by sediment (Compartment 2), and decline of PCB-52 in water (compartment 1) were rapid. For simultaneous exposures, an initial rapid adsorption of PCB-52 by sediment was followed by a gradual desorption which was reflected in a gradual uptake by fish. Intercompartmental transfer rate constants ranged from 0.0023 h$\\sp{-1}$ (Japanese medakas to water) to 0.5381 h$\\sp{-1}$ (water to Barataria Bay sediment). Generally, for all exposure systems, k$\\sb{12} \\ge$ k$\\sb{21} >$ k$\\sb{13} \\gg$ k$\\sb{31}$. No significant difference (p $>$ 0.05) was found between indirectly and directly generated coefficients and hybrid rate constants. BSAFs calculated from the intercompartmental transfer rate constants of the separate and simultaneous exposures ranged from 1.03 to 4.35 and were within the reported range of literature values for PCB-52. Analysis of variance of BSAF values obtained from simultaneous exposures indicated that no significant difference existed between BSAFs according to sediment type. Differences in TOC of the sediments appeared to account for differential adsorption and desorption of PCB-52 by the sediments. A significant difference (p $<$ 0.05) which appeared to correlate with differences in ventilation volume, was found between the BSAFs of the fish species. Differences in lipid content of the fish species did not completely explain differences in uptake and elimination of PCB-52 by fish. Short-term kinetic studies offer a simple, more accurate, and more economical means of predicting BSAFs than long-term equilibrium partitioning studies. The three-compartment closed model developed in this project was able to successfully predict reliable BSAFs. These novel methods of predicting the bioaccumulation potential provide a new tool for use in the hazard assessment of polluted sediments.

• Publisher: ProQuest Dissertations & Theses
• Subject: Environmental engineering / Environmental science / Toxicology
• ISBN: 0591144417, 9780591144413