Transport and Fate of Toxicants in the Environment

Toxicants are released into the environment in many ways, and they can travel along many pathways during their lifetime. A toxicant present in the environment at a given point in time and space can experience three possible outcomes it can be stationary and add to the toxicant inventory and exposure at that location, it can be transported to another location, or it can be transformed into another chemical species. Environmental contamination and exposure resulting from the use of a chemical is modified by the transport and transformation of the chemical in the environment. Dilution and degradation can attenuate the source emission, while processes that focus and accumulate the chemical can magnify the source emission. The actual fate of a chemical depends on the chemical s use pattern and physical-chemical properties, combined with the characteristics of the environment to which it is released. 

A Textbook of Modern Toxicology, Third Edition, edited by Ernest Hodgson ISBN 0-471-26508-X Copyright 2004 John Wiley Sons, Inc. 

Transport and fate model Environmental factors that modify exposure 

In fact, physiologically based pharmacokinetic models are similar to environmental fate models. In both cases we divide a complicated system into simpler compartments, estimate the rate of transfer between the compartments, and estimate the rate of transformation within each compartment. The obvious difference is that environmental systems are inherently much more complex because they have more routes of entry, more compartments, more variables (each with a greater range of values), and a lack of control over these variables for systematic study. The discussion that follows is a general overview of the transport and transformation of toxicants in the environment in the context of developing qualitative and quantitative models of these processes. 

The rate (units of g/h) at which a toxicant is emitted by a source (mass emission rate) can be estimated from the product of the toxicant concentration in the medium (g/m3) and the flow rate of the medium (m3/h). This would appear to be relatively simple for point sources, particularly ones that are routinely monitored to meet environmental 

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Haque, R. (ed.), Proc. of the Workshop on Transport and Fate of Toxic Chemicals in the Environment, 1981. 

Birge, W.J. and J.A. Zuiderveen. 1995. The comparative toxicity of silver to aquatic biota, in A.W. Andren and T.W. Bober (organizers). Transport, Fate and Effects of Silver in the Environment. 3rd International Conference. August 6-9, 1995, Washington, D.C. Univ. Wisconsin Sea Grant Inst., Madison, WI. 

Di Toro DM, Paquin PR, Santore R, Wu KB. 1997. Chemistry of silver bioavailability a model of acute silver toxicity to fish. 5th International Argentum Conference on Transport, Fate and Effects of Silver in the Environment, Hamilton, Ontario, Canada, p 191-204. 

Allan, R. J. (1994). Transport and Fate of Persistent Toxic Organic Chemicals in Aquatic Ecosystems the Niagara River to St. Lawrence River Estuary Example. In Hydrological, Chemical a. Biological Processes of Transformation a. Transport of Contaminants in Aquatic Environments, Proc. of the Rostov-on-Don symposium. May 1993, IAHS Publication, 219, pp. 21-32. 

The presence of humic and fulvic acids in surface waters and groundwaters will have a significant influence on the transport and fate of metals, radionuclides, and organic contaminants in the environment. These natural organic acids can either transport or immobilize contaminants, depending on the environmental conditions. Humic and fulvic substances can also retard or enhance the photochemical decomposition of pesticides or toxic organics. Therefore, to be sucessfiil any remediation strategies must consider the effects of humic materials. If properly understood, this behavior can be used to manipulate pollutant solubilization and facilitate containment or cleanup of contaminated sites. 

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