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

To develop chronic AWQC, acceptable chronic toxicity studies should encompass the full
life cycle of the test organism, although for fish, early life stage or partial life cycle toxicity
studies are considered acceptable. Acceptable endpoints include reproduction, growth and
development, and survival, with the effect levels expressed as the chronic value, which is the
geometric mean of the no-observed-effect concentration (NOEC) 1 and the lowest-observed-
effect concentration (LOEC) 2 . Although a chronic criterion could be calculated as the 5th
percentile of genus mean chronic values (GMCVs), sufficient chronic toxicity data are generally
lacking, as is the case for Pb. Consequently, an acute-chronic ratio (ACR) is typically applied to
the FAV to derive the chronic criterion. As the name implies, the ACR is the ratio of the acute
LC50 to the chronic value, based on studies with the same species and in the same dilution water.
For Pb, the final ACR is 51.29, which results in a final chronic value (FCV) of 1.317 µg/L (at a
hardness of 50 mg/L). The U.S. EPA guidelines for developing AWQC (Stephan et al., 1985) are
now more than 20 years old and thus are not reflective of scientific advances in aquatic
toxicology and risk assessment that have developed since the 1980s. For example, the
toxicological importance of dietary metals has been increasingly recognized and approaches for
incorporating dietary metals into regulatory criteria are being evaluated (Meyer et al., 2005).
Other issues include consideration of certain sublethal endpoints that are currently not directly
incorporated into AWQC development (e.g., endocrine toxicity, behavioral responses) and
protection of threatened and endangered (T&E) species (U.S. Environmental Protection Agency,
2003). In deriving appropriate and scientifically defensible air quality criteria for Pb, it will be
important that the state-of-the-science for metals toxicity in aquatic systems be incorporated into
the development process.
Subsequent sections summarize some of the toxicity studies that meet the AWQC
development guidelines, with an emphasis on key studies published since the last Pb AWQC
were derived in 1984.
1
The NOEC is the highest concentration tested that did not result in statistically significant effects relative
to the control.
2
The LOEC is the lowest concentration tested that resulted in statistically significant effects relative to
the control.
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