Fate and Transport in the Environment

Distribution between environmental compartments (as predicted by EpiSuite M 4.11). 

Product Stewardship Life Cycle Analysis and the Environment 

The Organization for Economic Cooperation and Development (OECD) has developed another way to assess the potential for persistence and long-range transport. The OECD Poo and LRTP Screening Tool utilizes the Henry s law constant (also referred to as the air-water partition coefficient, K ), and half-lives in environmental media to calculate three factors [35,36]  

Modeled results above the benchmark values suggest—subject to the limitations of the model—the potential for a substance to be persistent and travel long distances. 

As to the consequences of exposure to this substance in the environment, let s briefly review the toxicological and (eco)toxicological data. 

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The toxicological or cumulative effect of illicit drugs on the ecosystems has not been studied yet. Moreover, their fate and transport in the environment is to a big extent still unknown. Due to their physical-chemical properties (octanol-water partition coefficient, solubility, etc.) some of them, such as cannabinoids, are likely to bioaccumulate in organisms or concentrate in sediments whereas the rest, much more polar compounds, will tend to stay in aqueous environmental matrices. However, continuous exposure of aquatic organisms to low aquatic concentrations of these substances, some of them still biologically active (e.g., cocaine (CO), morphine (MOR) and MDMA) may cause undesirable effects on the biota. 

H. F. Hemond and E. J. Fechner, Chemical Fate and Transport in the Environment. Academic Press, New York, 1994. 

Schnoor, J.L. (1992) Chemical fate and transport in the environment. In Fate of Pesticides and Chemicals in the Environment. Schnoor, J.L., Editor, pp. 1-24, John Wiley Sons, New York. 

Exposure assessment, however, is a highly complex process having different levels of uncertainties, with qualitative and quantitative consequences. Exposure assessors must consider many different types of sources of exposures, the physical, chemical and biological characteristics of substances that influence their fate and transport in the environment and their uptake, individual mobility and behaviours, and different exposure routes and pathways, among others. These complexities make it important to begin with a clear definition of the conceptual model and a focus on how uncertainty and variability play out as one builds from the conceptual model towards the mathematical/statistical model. 

Several factors and processes may lead to interactions between chemicals in the environment. Such interactions not only determine fate and transport in the environment, but may also play a role in determining uptake. More insight into such interactions is highly needed in order to enable a more accurate exposure assessment of mixtures. 

This textbook is expanded and extensively revised from the first edition of Chemical Fate and Transport in the Environment. It is intended for a one-semester course covering the basic principles of chemical behavior in the environment. The approach is designed to include students who are not necessarily pursuing a degree in environmental science, but whose work may require a basic literacy in environmental transport and fate processes. 

I. Basic Concepts of Chemical Fate and Transport in the Environment... 

I. BASIC CONCEPTS OF CHEMICAL FATE AND TRANSPORT IN THE ENVIRONMENT... 

Hemond, H. R, and Fechner-Levy, E. J. (2000). Chemical Fate and Transport in the Environment, Academic Press, San Diego, CA. Mackay, D. (2001). Multimedia Environmental Models— The Fugacity Approach, Lewis Publishers, Boca Raton, FL. 

Multiple processes can affect the fate and transport of a chemical substance, each of which can depend not only on the physicochemical properties of the substance but also on the environment around it. In general terms, the processes include changes in state, biodegradation and bioaccumulation, and chemical reactions advective transport can move a substance with wind or water within a localized area or even globally. We look at these processes individually before exploring through examining models and specific examples how the processes combine to determine a chemical s fate and transport in the environment. 

The preceding chapters used brief case studies to illustrate key points. This chapter examines the life cycle of four substances in greater detail. Three of these substances, orthonitrochlorobenzene, 1,4-dichlorobenzene, and hexa-chlorobenzene, share a basic chlorinated benzene structure. The degree of chlorination and the presence of other functional groups affect their properties, usage, fate and transport in the environment, and (eco)toxicity. These substances also differ in their uses, which influences the potential for exposure. The remaining case study examines microbeads, a product whose size determines in part its life cycle. 

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