The Coastal Resource Coordinator's Bioassessment Manual

HAZMAT 93-1–Toxicity Tests
contaminants. The Microtox ® test was determined to be the most cost effective. The use of
two amphipod species (Rhepoxynius and Eohaustorius) and the measurement of
developmental abnormalities in echinoderms (Dendraster) were determined to be
moderately cost effective. Tests using polychaetes (Neanthes) and geoduck clams (Panope)
were determined to be the least cost effective.
Although cost can be an important factor in the selection of toxicity tests, it should not be
the primary criterion. Ideal tests should have high discriminatory power, low withinsample
variability, and strong positive correlation with measured concentrations of
contaminants (Long et al., 1990). Although the Microtox ® test is relatively inexpensive and
may be very sensitive to some contaminants, this does not necessarily make it the test of
choice for all situations.
SAMPLING DESIGN CONSIDERATIONS
Designing a sampling plan for toxicity testing should be done in conjunction with a
chemical analysis sampling plan. Ideally the samples to be used for chemical analysis
should be split (subsampled) with one portion being chemically analyzed and the other
portion being used for toxicity testing. At the very least samples for chemical analysis and
toxicity testing must be taken at the same time and location. Without this conjunctive
sampling it would be impossible to correlate toxicity to contaminant concentrations.
Another consideration when designing a sampling plan is the holding time for samples; for
example, the time between sample collection and the beginning of the toxicity test. Many
chemical and toxicity test protocols specify maximum holding times for environmental test
samples in order to insure that the properties of the sample do not significantly change
between sampling and analysis. For example, the prolonged storage or exposure to air of
sediment samples will volatilize acid volatile sulfides (AVS) thus increasing the availability
and toxicity of metals which are normally bound to AVS. However, the exact implications
of exceedances of holding times are unknown for most chemicals. Resident infauna in
sediments will eventually die, decay, and may produce lethal levels of ammonia. Bacteria
present in the sample may continue to alter contaminants such as PAHs. Mercury for
example, is thought to change more quickly than other metals. Since the different forms of
many metals vary in toxicity, the response to test samples might change if holding times are
exceeded. A basic rule of thumb is not to exceed holding times of two weeks for sediment
toxicity tests when the samples are maintained at 4 degrees Celsius. While sediments for
3-11 August 1997