FIGURE 5-3 The microbial biotransformation of hexachlorocyclohexane [α-HCH] in soil systems ranges greatly from the laboratory scale to the field scale. The rate of biotransformation is greatest in laboratory studies and is enhanced by mixing in the field. SOURCE: Courtesy of Alexander Zehnder, EAWAG.

results in the decision not to excavate or dredge, as the resulting exposure to receptors would be greater than that which would occur without intervention.

Examples of how treatment and containment technologies impact bioavailability processes (intentionally or unintentionally) are summarized in Table 5-1.


Explicit consideration of bioavailability processes in site-specific risk assessment can be technically difficult, time consuming, and costly. As the preceding discussion indicates, uncertainties associated with data and models pertaining to bioavailability processes must be confronted and dealt with. Experience shows that decisions to consider bioavailability processes occur on case- or topic-specific bases. An important dimension for the risk manager to consider is the value

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