The purpose of this report is to present the experimental and theoretical results that lead to the development model for the analysis of adsorption and desorption of hexachlorobiphenyl from suspended and sedimented particles. The reversibility of the adsorption reaction between dissolved organic chemicals and naturally occurring soils, sediments, and suspended particles is of fundamental importance in the understanding of the fate of these chemicals in the environment. The issue of reversibility becomes critical if the adsorption-desorption behavior of a chemical is to be expressed quantitatively within the framework of mass balance equations.

"PB83-261677." "EPA-600/3-83-088." "September 1983." "January 1982"--Bottom of title page. Includes bibliographical references (p. 134-137). Photocopy.

Part A -- I Summary and recommendations -- II Introduction and previous work -- III Experimental methodology and initial experimental results --- IV Kinetics -- V Effect of solution composition -- VI Sediment composition effects -- VII Sediment concentration effects -- VIII Reversibility of adsorption and desorption -- Part B -- I Exchangeable and nonexchangeable components model of adsorption and desorption -- II Effect of sediment concentration and composition -- III Resuspension and dilution: implications for fate of PCB The purpose of this report is to present the experimental and theoretical results that lead to the development model for the analysis of adsorption and desorption of hexachlorobiphenyl from suspended and sedimented particles. The reversibility of the adsorption reaction between dissolved organic chemicals and naturally occurring soils, sediments, and suspended particles is of fundamental importance in the understanding of the fate of these chemicals in the environment. The issue of revresibility becomes critical if the adsorptioin-desorption behavior of a chemical is to be expressed quantitatively within the fframework of mass balance equations. In the formulations used to date, with a notable exception to be discussed below, the furmulations used to express the adsorption and desorption reactions assume reversible behavior, that is, at equilibrium, the same isotherm applies for adsorption and desorption. The difficulty with this assumption is that for many organic chemicals and many naturally occuring adsorbents, laboratory adsoption and subsequent desorption experiments demonstrate only partially reversible behavior. In the experiment described in Part A, Section VIII, this nonsingular behavior was confirmed and, using various experimental procedures, it was found to persist. This suggests that it is necessary to account for this behavior in a quantitative and consistent way. It is the purpose of Part B of this report to present a framework within which this nonsingular behavior can be analyzed in a manner that can be easily incorporated into mass balance calculations.