The Coastal Resource Coordinator's Bioassessment Manual

HAZMAT 93-1 Role of Bioassessment
identified. If the compounds such as PCBs or dioxin are present that are known to
bioaccumulate and are not acutely toxic to most organisms, bioaccumulation studies may be
the best approach.
Bioassessment procedures such as toxicity tests or benthic community studies provide a
direct evaluation of the spatial distribution of toxic areas and an indication of the degree to
which toxicity is associated with the distribution of one or more toxic substances. In the
simplest case, the bioassessment acts as an adjunct to the chemical analyses. The chemical
measurements provide the link between the spatial areas and the source(s) of
contamination, while the bioassessment measurements determine the zones where the
chemical contamination is sufficient to be toxic. In other situations, toxicity detected in the
bioassessment may not vary spatially in the same manner as the majority of the chemicals
measured; possibly because the biological test is responding to substances that are not
detected in the standard chemical tests. In both cases, synoptic surveys of bioassessment
and chemical measurements should be made. (Note that the spatial heterogeneity at
hazardous waste sites is often very high, both horizontally and vertically. As a result, the
bioassessment and chemical samples must, if possible, be taken as aliquots from the same
homogenized sample.)
Toxicity tests have been used effectively to determine the extent of contamination at the
Rocky Mountain Arsenal waste site in Colorado (Thomas et al., 1986). Using the results
from a lettuce seed soil toxicity test and a statistical mapping technique called kriging, the
extent of contamination at the site was determined solely by mapping the levels of toxicity.
In summary, the selection of the numbers of samples and the types of tests to perform must
be considered on a case-by-case basis, weighing the trade off between collecting greater
numbers of samples to improve spatial coverage and conducting more tests at each station
to broaden the types of toxicity that will be detected. In general, a minimum of two toxicity
tests should be performed. Additional toxicity tests should be included if the available data
indicate the possible presence of organism-specific toxins or complex suites of substances.
As resources allow, in situ bioassessments (e.g., benthic community assessments, incidence
of disease, bioaccumulation) may be included in the site characterization. Although these
types of tests tend to be less precise in their ability to define the spatial extent of problem
areas, they are important in demonstrating impact to natural resources and supporting the
results of the toxicity tests.
The data needed for the characterization of ecological effects from a site differ from those
needed for the earlier phases of the remedial process. Impact evaluation should be based on
2-3 July 2003