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. 2023 Feb 1:318:120797.
doi: 10.1016/j.envpol.2022.120797. Epub 2022 Dec 7.

Natural organic matter source, concentration, and pH influences the toxicity of zinc to a freshwater microalga

Gwilym A V Price  1 , Jenny L Stauber  2 , Dianne F Jolley  3 , Darren J Koppel  4 , Eric J Van Genderen  5 , Adam C Ryan  5 , Aleicia Holland  2
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Free article

Natural organic matter source, concentration, and pH influences the toxicity of zinc to a freshwater microalga

Gwilym A V Price et al. Environ Pollut. .
Free article

Abstract

Zinc is a contaminant of concern in aquatic environments and is a known toxicant to many aquatic organisms. Dissolved organic matter (DOM) is a toxicity modifying factor for zinc and is an important water chemistry parameter. This study investigated the influence of DOM concentration, source, and water pH on the chronic toxicity of zinc to a freshwater microalga, Chlorella sp. The influence of DOM on zinc toxicity was dependent on both concentration and source. In the absence of DOM, the 72-h EC50 was 112 μg Zn.L-1. In the presence of a DOM high in fulvic-like components, zinc toxicity was either slightly decreased (<4-fold increase in EC10s across 15 mg C.L-1 range) or unchanged (minimal difference in EC50s). In the presence of a DOM high in humic-like (aromatic and high molecular weight) components, zinc toxicity was slightly decreased at the EC10 level and strongly increased at the EC50 level. The influence of pH on zinc toxicity was dependent on the source of DOM present in the water. In the presence of DOM high in humic-like components pH did not influence toxicity. In the presence of DOM high in fulvic-like components, pH had a significant effect on EC50 values. Labile zinc (measured by diffusive gradients in thin-films) followed linear relationships with dissolved zinc but could not explain the changes in observed toxicity, with similar DGT-labile zinc relationships shown for the two DOMs despite each DOM influencing toxicity differently. This indicates changes in toxicity may be unrelated to changes in zinc lability. The results suggest that increased toxicity of zinc in the presence of DOM may be due to direct uptake of Zn-DOM complexes. This study highlights the importance of considering DOM source and characteristics when incorporating DOM into water quality guidelines through bioavailability models.

Keywords: Bioavailability; Dissolved organic carbon; Metal toxicity; Water quality guidelines.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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