Abstract
The effect of sublethal concentrations of heavy metals on cladoceran growth and reproduction is a cornerstone of modern ecotoxicology. However, the literature contains assays across numerous concentrations, on numerous species and genotypes, and conditions are far from consistent. We undertook a systematic review of the sublethal effects of copper and cadmium concentrations on Cladocera spp. life history (reproduction, maturation age, and somatic growth rate). Using meta-analysis, we tested the hypothesis that the effects of increasing Cu and Cd concentrations on traits may vary by species. We also evaluated where possible whether the effect of metal concentrations on traits vary by water hardness, exposure duration, or whether the metals were delivered in aqueous solution or via food. We surveyed > 200 papers, resulting in a set of 32 experimental studies representing 446 trials where the results were presented compared with Daphnia magna—the most commonly assayed species. We found qualitatively similar effects of Cu and Cd on life history traits that included reduction in reproduction and somatic growth rate and delay of maturation. Cladocera species showed marked variations in their susceptibility to metals, and D. magna was found to be the least sensitive species to sublethal changes in reproduction. The effects were largely consistent for aqueous vs. dietary food. Water hardness, where data were available, had no detectable effect. Available data indicate that exposure duration had no effect on the toxicity of Cu but did for D. magna reproductive response to Cd. Our study highlights the importance of including species identity when considering toxicological testing and regulation development.
Highlights
Anthropogenic and natural processes introduce a great deal of pollutants and stress into natural ecosystems (Mountouris et al 2002; Demirak et al 2006; Dedourge-Geffard et al 2009; Martins et al 2017)
We report on the experimental factors of water hardness and exposure duration
Overall, increasing Cu concentration led to a decrease in the mean number of neonates produced per female per day and the effects of copper on reproduction varied by species (Fig. 2; likelihood ratio test (LRT) = 19.76, p = 0.0002)
Summary
Anthropogenic and natural processes introduce a great deal of pollutants and stress into natural ecosystems (Mountouris et al 2002; Demirak et al 2006; Dedourge-Geffard et al 2009; Martins et al 2017). Over the past few decades, trace levels of metals have received much attention (Jing et al 2006), because they generate negative biological effects on aquatic organisms, such as algae grazers and subsequently alter water quality. Such “sublethal” effects include changes in reproduction (Bodar et al 1988a; Wang et al 2009; Kim et al 2017), somatic growth rate (Chandini 1989; Koivisto et al 1992; De Schamphelaere and Janssen 2004a), feeding rate The concentrations associated with sublethal effects for Cu range from 0.2 to 30 μg/L (Al-Reasi et al 2012), whereas it is lower than 0.1 μg/L for Cd (Tan and Wang 2011)
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