Environment. Overall Environmental Fate

Environmental Fate. Zinc partitions to the air, water, and soil (Callahan et al. 1979 Guy and Chakrabarti 1976 Houba et al. 1983 Pita and Hyne 1975). Zinc occurs in the environment mainly in the +2 oxidation state (Lindsey 1979). Adsorption is the dominant fate of zinc, resulting in enrichment of zinc in suspended and bed sediments (Callahan et al. 1979). The mobility of zinc in soil has been characterized (Base and Sharp 1983 Bergkvist et al. 1989 EPA 1980d Hermann and Neumann-Mahikau 1985 Kalbasi et al. 1978 Saeed and Fox 1977 Tyler and McBride 1982). No estimate for the atmospheric lifetime of zinc is available. Development of pertinent data on the atmospheric processes important for zinc speciation in the atmosphere would be helpful. Development of this information would permit construction of a comprehensive model for the transport and interaction of zinc not only in air but in other media as well. Transformation in air and water can occur as a result of changes in chemical speciation (Anderson et al. 1988 Callahan et al. 1979 EPA 1980d Stokinger 1981). Data that describe the transformation processes for zinc in soil or the fate of zinc in soil are needed. A model of zinc flux from all environmental compartments would be useful for providing information on the overall environmental fate of zinc. 

An important consideration that affects the transport and partitioning of ammonia in the environment is that ammonia is a base. As a base, the physical and chemical properties of ammonia are pH-dependent, and thus, environmental fate processes that influence the transport and partitioning of NH3 will also be those that are pH-dependent. For some environmental fate processes, a change in pH may only affect the relative rate of a process, while for others, it could change the direction or overall result of that process. The influence of pH on the environmental fate of ammonia will be discussed where appropriate. Temperature is also an important consideration in the environmental fate of ammonia. Temperature, although to a lesser extent than pH, affects the ammonia-ammonium equilibrium. 

Fate studies identify the type of compounds and their exposure concentration at different points in the ecosystem and the organism(s) at greatest risk of exposure. The toxicant released into the environment can reach humans through a number of pathways (Figure 11.10). Although greatest immediate attention should be paid to human health, ultimate human welfare may depend on the overall quality of the ecosystem. Future environmental hazard assessment should be based on comparative toxicology. 

Studies aimed at understanding the sources, fate and effects of environmental contaminants, such as those described in this book, have provided much of the information used by managers and regulators to limit and regulate inputs to the environment as a result of human activities. These inputs include direct discharge to air, soil and water from point sources and more diffuse inputs, from so-called non-point sources, such as agricultural and urban runoff and atmospheric inputs to aquatic systems. Overall, much has been... 

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