Chemodynamics and Multicontaminant Joint Toxicity Modeling of Organic Leachates from Recycled Solid Wastes

Abstract

Chemodynamics (the fate and transport) of leachates from recycled solid waste materials (SWMs) of complex organic mixtures (COMs) is a basic need in environmental planning, restoration and engineering management. Sorption/desorption, an important chemodynamic behavior of leachates, can greatly influence the mobility and bioavailability of compounds from recycled wastes in the multimedia environment. Similar to all interphase mass-transfers, the sorption/desorption process can be defined by the final-phase equilibrium of the contaminant at the aqueous-solid phase interface and the time required to approach final equilibrium. Accordingly, aqueous-solid phase interfaces are significant in determining: (1) the route and rates by which organic contaminants can transfer to and/or from these interfaces, (2) the chemodynamics of contaminants, and (3) their toxicity, genotoxicity and bioavailability to the ambient microorganisms. When the rates of such processes are known, environmental fate modeling can provide an educated estimate and prediction of the accessibility and bioavailability of a target contaminant leached from SWMs to a specific transport mechanism in the environment. Therefore, the present chapter is an attempt to assess fate (in terms of contaminant mobility using predictive sorption or desorption coefficients), as well as effects (in terms of bioavailability) of various contaminants, and to correlate these observations for development of predictive relationships.

To fulfill this general objective, the following interdisciplinary approaches are covered in the present chapter: (1) a review of the most widely used models analyzing sorption/desorption data generated for leachates from recycled SWMs, discussion of their chemical kinetics, and estimates of their transport parameters from laboratory studies; (2) a discussion of the fundamentals of both quantitative structure-activity and structure-property relationships (QSARs and QSPRs, respectively), with special emphasis on using molecular connectivity indices as useful properties to predict contaminant mobility and bioavailability, and (3) a review of the multicomponent (multicontaminant) joint toxic/genotoxic effect models (additivity, synergism, antagonism) used to predict the bioavailable fraction and action of organic contaminants at aqueous-solid phase interfaces. The applicability of these interdisciplinary approaches is discussed and evaluated using a group of toxic and carcinogenic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), which are frequently characterized in most recycled solid wastes of complex organic mixtures.