Effect of Dissolved Organic Matter Concentration and Source on the Chronic Toxicity of Copper and Nickel Mixtures to Chlorella sp

• Published in: Environmental toxicology and chemistry 2021-07, Vol.40 (7), p.1908-1918
• Main Authors: Macoustra, Gabriella K., Koppel, Darren J., Jolley, Dianne F., Stauber, Jenny L., Holland, Aleicia
• Format: Article
• Language: English
• Subjects: Algae; Algal growth; Antagonism; Aquatic animals; Aquatic biota; Binary mixtures; Bioassays; Biota; Chlorella; Chronic toxicity; Copper; Copper - analysis; Copper - toxicity; Diffusive gradients in thin films; Dissolved Organic Matter; Factorial design; Growth rate; Heavy metals; Metal bioavailability; Metal concentrations; Metal ions; Metal speciation; Microorganisms; Mixture toxicology; Nickel; Nickel - analysis; Nickel - toxicity; Passive sampler; Predictions; Speciation; Synergism; Thin films; Toxicity; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - toxicity; Windermere Humic Aqueous Model
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1002/etc.5038

There have been limited studies on the effects of toxicity‐modifying factors, such as dissolved organic matter (DOM), on the toxicity of metal mixtures to aquatic biota. The present study investigated the effects of DOM concentration (low, 2.8 ± 0.1 mg C/L; high, 11 ± 1.0 mg C/L) and DOM source (predominantly terrestrial or microbial) on the chronic toxicity of copper (Cu) and nickel (Ni) binary mixtures to the green freshwater microalga Chlorella sp. This was assessed by using a full factorial design of 72‐h growth inhibition bioassays. Measured algal growth rate was compared with growth predicted by the concentration addition and independent action reference models. Model predictions were based on concentrations of dissolved metals, labile metals (measured by diffusive gradients in thin films [DGT]), and calculated free metal ions (determined by the Windermere Humic Aqueous Model). Copper/Ni mixture toxicity was synergistic to Chlorella sp. in the absence of added DOM, with evidence of metal concentration‐dependent toxicity at low effect concentrations. As DOM concentration increased, the mixture interaction changed from synergism to noninteraction or antagonism depending on the metal speciation method used. The DOM source had no significant effect on mixture interaction when based on dissolved and free metal ion concentrations but was significantly different when based on DGT‐labile metal concentrations. Ratio‐dependent mixture interaction was observed in all treatments, with increased deviation from the reference model predictions as the mixture changed from Ni‐ to Cu‐dominated. The present study demonstrated that both DOM concentration and source can significantly change metal mixture toxicity interactions and that these interactions can be interpreted differently depending on the metal speciation method used. Environ Toxicol Chem 2021;40:1908–1918. © 2021 SETAC Relationship between increasing dissolved organic matter (DOM) concentration and the interaction term a for mixture model predictions based on dissolved, diffusive gradients in thin films–labile, or free ion metal concentrations in the presence of 2 distinct DOM isolates. Where a positive interaction term (a > 0) indicates antagonism, a negative interaction term (a