Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

partition in sediment between acid-volatile sulfide, pore water, benthic organisms, and other
sediment phases such as organic carbon. When the sum of the molar concentrations of
simultaneously extracted metal (∑SEM) minus the molar concentration of AVS is less than zero,
it can accurately be predicted that sediments are not toxic because of these metals. Note that this
approach can be used to predict the lack of toxicity, but not the presence of toxicity. It is
important to emphasize that metals must be evaluated as a mixture using this approach.
If individual metals, or just two or three metals, are measured in sediment, ∑SEM would be
misleadingly small and it may inaccurately appear that ∑SEM / AVS is less than 1.0.
If ∑SEM / AVS is normalized to the organic carbon fraction (i.e., (∑SEM / AVS)/fOC),
mortality can be more reliably predicted by accounting for both the site-specific organic carbon
and AVS concentrations. When evaluating a metal mixture containing cadmium, copper, Pb,
nickel, silver, and zinc, the following predictions can be made (U.S. Environmental Protection
Agency, 2005c):
• A sediment with (SEM / AVS)/fOC < 130 µmol/gOC should pose low risk of adverse
biological effects due to these metals.
• A sediment with 130 µmol/gOC < (SEM / AVS)/fOC < 3000 µmol/gOC may have adverse
biological effects due to these metals.
• In a sediment with (SEM / AVS)/fOC > 3000 µmol/gOC, adverse biological effects may
be expected.
A third approach is to measure pore water concentrations of cadmium, copper, Pb, nickel,
and zinc and then divide the concentrations by their respective FCVs. If the sum of these
quotients is