The role of traditional and novel toxicity test methods in assessing stormwater and sediment contamination

Traditional effluent and ambient water column toxicity tests have been used widely for evaluating the contamination of stormwaters and sediments. Thes e assays consist of a routine bioassay exposure design of 1 to 9 days using freshwater and marine/estuarine species known to be sensitive to a wide ra nge of toxicants. While effluent toxicity may be indicative of sediment or stormwater toxicity in the receiving system, the exposure is different, and therefore toxicity cannot be readily predicted. Traditional, standardized, whole effluent toxicity (WET) test methods have been used effectively and also misused in evaluations of whole sediments, pore (interstitial) water, elutriates (extracts), and stormwaters. Results show these methods to be ve ry sensitive to sediment and stormwater toxicity. These traditional toxicit y tests are predictive of instream sediment or stormwater effects where sig nificant contamination exists or where exposure concentrations are similar. Modifications of these standardized test methods to include sediments or p ore waters have been shown to be as sensitive as short-term, whole sediment toxicity tests using benthic species. However, the added complexity of sed iments and stormwaters (e.g., partitioning, high Kow compound bioavailabili ty, suspended solids, sporadic exposures, multiple exposure pathways) dicta tes that traditional toxicity test applications be integrated into a more c omprehensive assessment of ecologically significant stressors. The limitati ons of the WET testing approach and optimized sample collection and exposur e alternatives are frequently ignored when implemented. Exposure to sporadi c pulses of contaminants (such as in stormwaters) often produce greater tox icity than exposure to constant concentrations. Lethality from short-term p ulse exposures may not occur for weeks after the high flow event due to upt ake dynamics. Pore water and elutriate exposures remove sediment ingestion routes of exposure and alter natural sorption/desorption dynamics. Traditio nal toxicity tests may not produce reliable conclusions when used to detect the adverse effects of: fluctuating stressor exposures, nutrients, suspend ed solids, temperature, UV light, flow, mutagenicity, carcinogenicity, tera togenicity, endocrine disruption, or other important subcellular responses. This reality and the fact that ecologically significant levels of high K-o w compounds may not produce short-term responses in exposures dictates that additional and novel assessment tools be utilized in order to protect aqua tic ecosystems. This inablilty to predict effects is largely a result of th e complex biological response patterns that result from various combination s of stressor magnitudes, duration, and frequency between exposures and als o the interactions of stressor mixtures, such as syngergistic effects of ce rtain pesticides, metals, and temperature. In watersheds receiving multiple sources of stressors, accurate assessments should define spatial-temporal profiles of exposure and effects using a range of laboratory (such as WET t ests) and novel in sine toxicity and bioaccumulation assays, with simultane ous characterizations of physicochemical conditions and indigenous communit ies.