The Coastal Resource Coordinator's Bioassessment Manual

HAZMAT 93-1 Role of Bioassessment
of contaminated media from the site in the laboratory with clean media, or by collecting a
number of samples of contaminated media from different spatial areas that are known to
have different chemical concentrations. The samples representing the range of chemical
concentrations obtained by either approach are tested using one or more bioassessment
techniques to determine which concentrations are toxic and which are not. The lowest
contaminant concentration found to be toxic (induce the designated biological endpoint) is
determined to be the target level for cleanup.
One example of this approach is the apparent effects threshold (AET), which uses field
chemistry data (concentrations of toxic substances in sediments) and at least one biological
indicator of injury (sediment toxicity tests, altered benthic infaunal abundance,
bioaccumulation, histopathology, etc.) to determine the concentration of a given
contaminant above which statistically significant biological effects would always be
expected (Tetra Tech, 1986). The AET approach was developed in Puget Sound,
Washington to establish chemical criteria for disposal of dredged material, and is being
considered by U.S. Environmental Protection Agency (EPA) Region 10 for use in
establishing cleanup target levels in that area. As currently developed, the AET approach
should be used on a site-specific basis and can require extensive data collection. However,
by carefully selecting one or a few appropriate bioassessment procedures, the approach can
be cost effective at many sites. Further, if similar data are collected at different sites within a
region that have similar habitat characteristics, the data may be suitable to combine into a
regional database that might be used to develop standards with broad application.
A second approach that is particularly useful where the suite of chemicals is complex (e.g.,
landfills and hazardous waste recycling sites) is to use the biological responses measured by
one or more of the bioassessment techniques directly to determine which areas of a waste
site need to be cleaned up. For example, it might be agreed that all sediments in a stream
that were significantly toxic in the applicable toxicity test (irrespective of any chemical
measurement) would be treated to eliminate the toxicity. No remedy would be applied to
sediments that were not significantly toxic. This approach was suggested by investigators
at the Rocky Mountain Arsenal waste site where toxicity tests results showing toxicity above
a pre-selected level were used with a statistical mapping technique (kriging) to define
contaminated areas for potential cleanup. (Thomas et al., 1986).
In both approaches discussed above, it is important to note that there are currently no
guidelines for selecting appropriate tests to determine target levels or to select the endpoint
of those tests that have more than one possible endpoint. To use bioassessment procedures
2-5 July 2003