Oral Presentation Society of Environmental Toxicology and Chemistry Australasia 2023

DOM toxicity amelioration is a scam! Well… at least for some Australian DOM sources when microalgae are exposed to zinc. (#86)

Gwilym AV Price 1 2 , Jenny Stauber 2 , Dianne Jolley 2 , Darren Koppel 3 , Aleicia Holland 4
  1. School of Life Sciences, University of Technology, Sydney, Sydney, NSW, Australia
  2. Land and Water, CSIRO, Lucas Heights, NSW, Australia
  3. Australian Institute of Marine Science, Crawley, Western Australia, Australia
  4. School of Life Science, La Trobe University, Wodonga, Vic, Australia

Aim:

There has been increased interest in the development of bioavailability-based metal water quality guidelines (WQG) and to develop these, large amounts of high quality toxicity data examining how water chemistry influences bioavailability and toxicity is needed. Prior to this study, there was no literature available on the independent influence of natural dissolved organic matter (DOM) on chronic zinc toxicity to freshwater microalgae. This study assessed the influence of natural Australian DOM on the toxicity of zinc to an Australian freshwater microalga under different pH conditions.  

Methods:

Toxicity tests (72-h growth rate inhibition) were conducted using Chlorella sp. with test solutions prepared with each DOM source across five concentrations (0-15 mg C/L) under different pH conditions. Each treatment was exposed to a dissolved zinc concentration series (0-5,000 µg/L). A range of speciation methods, including diffusive gradients in thin-films and ultrafiltration (<3kDa) were used concurrently on matched test solutions.

Results:

The influence of DOM on zinc toxicity was dependent on both concentration and source. In the absence of DOM, the Zn EC50 was 112 µg/L. In the presence of DOM high in fulvic-like components, zinc toxicity was either slightly decreased (EC10 values) or unchanged (EC50 values). In the presence of DOM high in humic-like components zinc toxicity strongly increased, with  EC50 values decreasing to 17-25 µg/L. The influence of pH on zinc toxicity was dependent on the source of DOM. In the presence of DOM high in humic-like components, pH did not influence toxicity whereas in the presence of DOM high in fulvic-like components, pH had a significant effect on EC50 values.

Conclusion:

This study provides high quality data useful for incorporating DOM source and concentration into bioavailability-based WQGs and highlights the importance of assessing the influence of different DOM sources when considering bioavailability models.