The Role of Traditional and Novel Toxicity Test Methods in Assessing Stormwater and Sediment Contamination

Abstract

Traditional effluent and ambient water column toxicity tests have been used widely for evaluating the contamination of stormwaters and sediments. These 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 range 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 very sensitive to sediment and stormwater toxicity. These traditional toxicity tests are predictive of instream sediment or stormwater effects where significant contamination exists or where exposure concentrations are similar. Modifications of these standardized test methods to include sediments or pore waters have been shown to be as sensitive as short-term, whole sediment toxicity tests using benthic species. However, the added complexity of sediments and stormwaters (e.g., partitioning, high K_ow compound bioavailability, suspended solids, sporadic exposures, multiple exposure pathways) dictates that traditional toxicity test applications be integrated into a more comprehensive assessment of ecologically significant stressors. The limitations of the WET testing approach and optimized sample collection and exposure alternatives are frequently ignored when implemented. Exposure to sporadic pulses of contaminants (such as in stormwaters) often produce greater toxicity than exposure to constant concentrations. Lethality from short-term pulse exposures may not occur for weeks after the high flow event due to uptake dynamics. Pore water and elutriate exposures remove sediment ingestion routes of exposure and alter natural sorption/desorption dynamics. Traditional toxicity tests may not produce reliable conclusions when used to detect the adverse effects of: fluctuating stressor exposures, nutrients, suspended solids, temperature, UV light, flow, mutagenicity, carcinogenicity, teratogenicity, endocrine disruption, or other important subcellular responses. This reality and the fact that ecologically significant levels of high K_ow compounds may not produce short-term responses in exposures dictates that additional and novel assessment tools be utilized in order to protect aquatic ecosystems. This inablilty to predict effects is largely a result of the complex biological response patterns that result from various combinations of stressor magnitudes, duration, and frequency between exposures and also the interactions of stressor mixtures, such as syngergistic effects of certain 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 tests) and novel in situ toxicity and bioaccumulation assays, with simultaneous characterizations of physicochemical conditions and indigenous communities.

Keywords:

• stressors
• indigenous communities
• in situ
• bioassays.