Determining stressor presence in streams receiving urban and agricultural runoff: development of a benthic in situ toxicity identification evaluation method.

Determining toxicity in streams during storm-water runoff can be highly problematic because of the fluctuating exposures of a multitude of stressors and the difficulty of linking these dynamic exposures with biological effects. An underlying problem with assessing storm-water quality is determining if toxicity exists and then which contaminant is causing the toxicity. The goal of this research is to provide an alternative to standard toxicity testing methods by incorporating an in situ toxicity identification evaluation (TIE) approach. A benthic in situ TIE bioassay (BiTIE) was developed for separating key chemical classes of stressors in streams during both low- and high-flow events to help discern between point and nonpoint sources of pollution. This BiTIE method allows for chemical class fractionation through the use of resins, and these resins are relatively specific for removing nonpolar organics (Dowex Optipore), ammonia (zeolite), and polywool (control). Three indigenous aquatic insects, a mayfly (Isonychia spp.), a caddisfly (Hydropsyche spp.), and a water beetle (Psephenus herricki), were placed in BiTIE chambers that were filled with natural substrates. Acute 96-h exposures were conducted at Honey Creek, New Carlisle, Ohio, USA (reference site), and Little Beavercreek, Beavercreek, Ohio, USA (impaired site). At both sites, significant (p < 0.025) stressor responses were observed using multiple species with polywool or no resin (control) treatments exhibiting < 80% survival and resin treatments with >80% survival. The BiTIE method showed stressor-response relationships in both runoff and base flow events during 96-h exposures. The method appears useful for discerning stressors with indigenous species in situ.