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Approaches for Evaluation of Episodic Discharges: A Review and Recommendations for Toxicity Testing Compliance Monitoring

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Technical Report

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Naval Information Warfare Center Pacific San Diego

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Included herein is a discussion of the advantages of pulsed toxicity methodologies, and various considerations for designing pulsed exposure testing protocols. In addition, there is a brief discussion of potential options to incorporate pulsed exposure testing methods into regulatory frameworks. This review ends with implications for the current pulsed exposure work at Naval Information Warfare Center NIWC Pacific. Industrial and municipal discharges are required to comply with increasingly stringent water quality requirements for stormwater runoff and other intermittent discharges. These requirements generally include end-of-pipe monitoring, enforced by National Pollutant Discharge Elimination System NPDES permits, prior to mixing in the receiving water. As a result, the existing EPA whole effluent toxicity WET test methods developed to assess continuous point source discharges are now also being applied to episodic discharges, such as stormwater, dry dock discharges, and ballast water. These procedures have been criticized by the science community for failing to use exposures relevant to the intermittent, or episodic, nature of these events, instead using continuous static exposures. Using WET testing procedures with continuous exposures for intermittent discharges likely overestimates potential toxicological effects in receiving systems. However, in some cases, short-term pulsed exposures to elevated chemical concentrations may also be more toxic than continuous exposure to an averaged exposure concentration. Several lab studies primarily in freshwater systems and using agrochemicals have explored the effects of several factors of pulsed exposures these include pulse concentration, pulse duration, pulse frequency, latent effects, and age of exposed organisms.

Subject Categories:

  • Manufacturing and Industrial Engineering and Control of Production Systems
  • Toxicology

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