Improving the Assessment and Monitoring of Risks of Adverse Toxicological Effects from Short-Term Episodic Contaminant Exposures within Aquatic Environments

To determine the risk of toxic effects to aquatic organisms due to chemicals or discharges of stormwater and other effluents, toxicity assessment methods typically employ continuous exposure to the effluent (end of pipe or mixed receiving waters) for the duration of the standardized toxicity test procedure. Toxicity test exposure periods typically range from multiple days to a week, depending on the species and test endpoint. However, in many environments, the intermittent (episodic, fluctuating or pulsed) release of contaminated waters results in aquatic organisms receiving only short exposures (e.g. hours) to contaminants at concentrations that exceed water quality criteria (WQC) or other criteria determined by whole effluent toxicity (WET) methods. Such variable contaminant exposures are common for many effluent discharges, including stormwater. Thus, often assessment methodologies do not adequately replicate the dynamic nature of the contaminant-stressor exposure at either the point of compliance, or as it mixes with the receiving environment. While the application of assessment methods that assume continuous exposure may provide conservative assessment outcomes, this may result in highly over-conservative assessments of short-term discharges that lead to unnecessarily high costs for management (by regulators and industry), treatment, or remedial actions. A proposed pulsed exposure methodology will be showcased with data examples from both laboratory spiked studies and stormwater samples collected in southern California. A 4-year program funded by ESTCP that includes the development of an expert advisory panel, a series of laboratory and field validation demonstration projects, and a nation-wide intercalibration laboratory study following the proposed methodologies will also be highlighted in the presentation. An important objective of the program is to discuss barriers to end-users adopting new monitoring approaches and provide suggestions on how these may be overcome.