Copper contamination and rising atmospheric CO2, which lowers pH through acidification. Because copper becomes more toxic at lower pH, acidification may make copper more harmful than current water quality guidelines predict. Northern Clearwater crayfish (Faxonius propinquus) and zebrafish (Danio rerio) were exposed to a range of copper concentration under current atmospheric CO2 to identify the No Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC) for chemosensory impairment, measured as the ability to detect a food odour. These NOEC concentrations were then combined with elevated pCO2 levels projected for the end of this century under a high-emission scenario, and Visual MINTEQ was used to model copper speciation across treatments. Under ambient CO2, crayfish were impaired at 30μg/L copper but not 20μg/L, while zebrafish were roughly six times more sensitive, impaired at 5μg/L but not 2.5μg/L. Elevated pCO2 alone did not impair crayfish, but did impair zebrafish at 1000μatm. Critically, when the previously safe copper concentration (NOEC) was paired with elevated pCO2 that caused no impairment on its own, both species lost the ability to detect food odours. MINTEQ modelling confirmed that lower pH under elevated pCO2 increased bioavailable free Cu2+ by 1.9- to 3.8 fold, offering a likely mechanism for this combined effect. These results show that freshwater acidification can lower copper toxicity thresholds, with direct consequences for how aquatic animals are protected from metal contamination under climate change. Current water quality guidelines do not account for this pH-driven increase in toxicity, representing a significant and largely overlooked gap in the literature.
Shaikh N., 2026. Effect of increased carbon dioxide on copper-induced olfactory dysfunction in aquatic animals. MSc thesis, Algoma University, 79 p. Thesis (restricted access).
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