M2 AM Aquatic Ecotoxicology (Part 1)
Monday, 14 November 2005: 8:00 AM - 11:40 AM in Ballroom 2

(DIA-1116-617081) Sublethal effects of pulsed chemical exposures: implications for aquatic life criteria and wastewater permit limits.

Diamond, J¹, Klaine, S², Butcher, J³, ¹ Tetra Tech, Inc., Owings Mills, MD, USA² Clemson University, Pendleton, SC, USA³ Tetra Tech, Inc., Research Triangle Park, NC, USA

ABSTRACT- Water quality criteria and effluent permit limits, based on results of constant contaminant exposures, may not be relevant for assessing episodic or variable exposures typical in the environment. Over 300 different pulsed treatments of copper, zinc, ammonia, and chlorpyrifos were examined in this research, representing a range of magnitudes, durations, frequencies, and recovery times between pulses, using both 7 or 14-d Pimephales promelas and 21-d Daphnia magna tests. Most treatments did not affect fish growth or D. magna reproduction independent of effects on survival. Surviving organisms rebounded from pulses and often exceeded control responses in growth or reproduction. Significantly higher fish mortality was observed when pulses were spaced further apart in time while greater mortality effects on D. magna were observed with more closely-spaced pulses, reflecting different adaptation mechanisms for the two species. Organism responses were not predictable based on the average concentration over the test because pulse timing and recovery time between pulses were significant factors. Pulses well below the acute toxicity threshold had little effect on either survival or sublethal indicators for both species. These data suggest that brief exceedences of chronic discharge permit limits might have little or no measurable effects on aquatic populations. However, pulses near the acute threshold may result in effects on aquatic biota, even if the pulses are brief (24h), depending on the pulse frequency and recovery period between pulses. For some chemicals, use of only an acute criterion and a short averaging period (24h) may provide as much environmental protection against pulsed exposures as the current two-tiered system using acute and chronic criteria. Protection against sublethal effects of subacute pulsed exposures may not be ensured given the current averaging period for chronic criteria.

Key words: pulsed exposure, aquatic toxicity, metals, water quality criteria