Direct and Delayed Mortality of Ceriodaphnia dubia and Rainbow Trout Following Time‐Varying Acute Exposures to Zinc

Abstract

The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans (Ceriodaphnia dubia) and rainbow trout (Oncorhynchus mykiss) to zinc (Zn) in various 1-to 48-h and 1-to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia, 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia. With C. dubia, the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate (C. dubia) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances.

Characterization of Metal Pulsed Exposure to Aquatic Organisms with Post‐Exposure Monitoring: Implications for Stormwater Exposure Assessment

“…Latent effects of metals to aquatic organisms have been reported in previous pulsed exposure studies (Angel et al, 2010;Brent & Herricks, 1998;Bucher et al, 2006;Colvin et al, 2021;Hoang, Gallagher, Tomasso et al, 2007;Hoang & Klaine, 2008;Mebane et al, 2021;Zahner et al, 2006;Zhao & Newman, 2006). After a pulsed exposure ends, it is highly suggested that heavy metals continue to exert their toxic effects post-exposure, which is exemplified by the observation of latent effects.…”

“…Brent and Herricks (1998) also found greater proportions of the total mortality of both organisms after exposures ended for Zn than for Cd. Mebane et al (2021), however, studied Zn only and found strong latent effects of Zn on the mortality of <24‐h‐old C. dubia at an exposure time of <24 h and at Zn concentrations of µg/L. In general, lower treatment concentrations required a longer period before total cumulative mortality was achieved, suggesting that lower metal concentrations might take longer to exert visible latent effects as metals need to enter and accumulate in the organism to a level that exceeds the organism's tolerance to exert effects.…”

“…In addition, WET methods lack post-exposure monitoring following exposure to test solutions, thus ignoring the potential for post-exposure effects that can occur following stormwater runoff exposure. Latent (delayed) effects and/or increased tolerance have been reported previously in post-contaminant exposures (Angel et al, 2010;Butcher et al, 2006;Brent & Herricks, 1998;Colvin et al, 2021;Hoang, Gallagher, Tomasso et al, 2007;Hoang & Klaine, 2008;Mebane et al, 2021;Zahner et al, 2006;Zhao & Newman, 2006), therefore it is relevant to monitor the organism's post-pulsed exposure when conducting toxicity tests to characterize the toxicity of pulsed discharges.…”

Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses

“…2 ). In general, during post-exposure periods, animals exposed to metals show an increase of mortality (Pascoe and Shazili 1986 ; Handy 1994 ; Schill et al 2003 ; Zhao and Newman 2004 , 2006 ; Hoang et al 2007 ; Mebane et al 2021 ). In our study this was especially marked in the highest concentrations.…”

The Capacity of Freshwater Ecosystems to Recover from Exceedences of Aquatic Life Criteria

“…In practice, the true mechanisms of toxicity may be known, even for well‐studied substances and organisms, such as the chronic toxicity of metals to fish (Wood, 2012). Complicating this surrogacy in exposures are lag times between exposure and effects (Diamond et al, 2006; Mebane et al, 2021). In some case studies with organic chemicals, these depuration and recovery times were in the range of 5–30 days (Landrum et al, 2004; Landrum et al, 2013).…”