Implications of Pulsed Chemical Exposures for Aquatic Life Criteria and Wastewater Permit Limits

Abstract

Subacute effects of pulsed copper, zinc, or ammonia exposures were examined, including a range of pulse concentrations, durations, frequencies, and recovery times between pulses, using short-term chronic Pimephales promelas and 21-d Daphnia magna tests. Sublethal effects were rarely observed independent of mortality. Effects were observed only at concentrations near the species continuous exposure 48 h LC50 for each chemical. Daphnia often rebounded from temporary reproduction effects, meeting or exceeding control responses by the end of the test. Effects of 24 h ammonia or copper pulses were diminished soon after the pulse was removed, while 24 h zinc pulses caused continued effects for several days following removal of the pulse, indicating a slower uptake and/or depuration rate for zinc. D. magna exhibited less mortality as copper pulses were spaced further apart, while fish were equally or more affected with longer recovery times between copper pulses, indicative of different adaptation mechanisms between the two species. Responses were not predictable based on either average concentration or a combination of duration and concentration. Chronic water quality criteria and effluent permit limits, expressed as a 4- or 30-d average concentration, respectively, may not be appropriate for protecting against effects of pulsed exposures, depending on the frequency, magnitude, and duration of pulses, as well as the recovery period between events.

Toxicity to Melita plumulosa from intermittent and continuous exposures to dissolved copper

“…This trend is supported by studies in which similar toxicity was the result of different exposure scenarios with equivalent metal TACs for D. magna exposure to Se [20] and P. promelas exposure to Cd [25]. The results of the current study indicated that continuous exposure bioassays with M. plumulosa are likely to accurately predict the acute-lethality effects of pulsed exposures with similar TACs, and supports the use of TAC-effect data to predict the risk of acute toxicity [2,6]. Results of the current study suggest that in cases in which single time-point sampling is used to assess water quality, overestimations of the risk of toxicity may occur if the high concentration is not sustained over a significant duration of the life cycle of the organism.…”

“…However, latent mortality was not observed in P. promelas exposed to Cu and Cd, D. magna exposed to pulses of copper or ammonia, or for C. dubia, H. azteca, and P. promelas exposed to pulses of phenol [4][5][6]25]. The degree of latent toxicity that occurs for different toxicants and organisms may be attributed to different mechanisms of action [10].…”

Time-averaged copper concentrations from continuous exposures predicts pulsed exposure toxicity to the marine diatom, Phaeodactylum tricornutum: Importance of uptake and elimination

“…A few studies have found that for different exposure scenarios with an equivalent contaminant dose, longer exposure durations resulted in greater toxicity. This was observed for survival of Pimephales promelas exposed to cadmium and copper (Diamond et al, 2005), survival and reproduction of Daphnia magna exposed to zinc (Diamond et al, 2006), reproduction of D. magna exposed to fenoxycarb (Hosmer et al, 1998) …”

Bioaccumulation kinetics of organic xenobiotic pollutants in the freshwater invertebrateGammarus pulexmodeled with prediction intervals

“…Individual G. pulex were sampled after 2,4,7,12,24,26,28,31,36,48,72,96, and 168 h, and internal concentrations of the test compounds were quantified as total 14 C radioactivity. Organisms were removed from the beaker, blotted dry, placed in preweighed scintillation vials, weighed, and frozen at À208C until analysis.…”

“…The time course of internal concentrations (toxicokinetics) under conditions of time-variable exposure is the first step to solving the former problem [21,[27][28][29][30], whereas the latter two questions become more accessible when internal concentrations serve as the biologically relevant dose [1,7]. In particular, toxicokinetic-toxicodynamic models describe toxicity quantitatively in two steps [21,31] which may be linked to different properties of the chemical [31][32][33][34] or different species traits [25,26].…”