The influence of hardness at varying pH on zinc toxicity and lability to a freshwater microalga, Chlorella sp.

Abstract

Zinc is an essential element for aquatic organisms, however, activities such as mining and refining, as well as zinc’s ubiquitous role in modern society can contribute to elevated environmental concentrations...

Development and Validation of Multiple Linear Regression Models for Predicting Chronic Zinc Toxicity to Freshwater Microalgae

“…The chronic toxicity of zinc has been tested over a wide range of water chemistries for the freshwater microalga Chlorella sp. These data were sourced from Price et al (2021, 2023) and Price, Stauber, Holland et al (2022), with each source providing a detailed description of the tests carried out. All tests were conducted using laboratory‐prepared synthetic freshwaters with pH levels ranging from 6.7 to 8.3, hardness concentrations from 5 to 400 mg CaCO 3 L –1 , and DOC concentrations of 0–15 mg C L –1 .…”

“…All tests were conducted using laboratory‐prepared synthetic freshwaters with pH levels ranging from 6.7 to 8.3, hardness concentrations from 5 to 400 mg CaCO 3 L –1 , and DOC concentrations of 0–15 mg C L –1 . Tests were performed at a constant alkalinity (~40 mg L –1 ) and calcium to magnesium ratio (~0.7) as described in Price, Stauber, Holland et al (2022). The toxicity data used met the acceptability criteria outlined by Warne et al (2018) for use in development of Australian water quality guidelines.…”

“…Currently, the Australian and New Zealand water quality guidelines for zinc only account for the influence of hardness on bioavailability via a hardness algorithm (Australian and New Zealand Governments, 2018). This algorithm is largely based on acute toxicity data derived from North American fish species and has recently been shown to not be appropriate for freshwater microalgae (Price, Stauber, Holland et al, 2022). Increased attention has focused on bioavailability‐based water quality guidelines with the development of the biotic ligand model (BLM), which predicts the toxicity of a metal to a species based on water quality parameters.…”

“…The objective of the present study was to use recently published zinc toxicity data under varying pH, hardness, and DOC conditions for the microalga Chlorella sp. (Price, Stauber, Holland et al, 2022; Price et al, 2021, 2023) to develop empirical models that predict zinc toxicity as a function of these parameters. Models were independently validated using six different zinc‐spiked Australian natural waters with a range of water chemistries.…”

Does toxicity test variability support bioavailability model predictions being within a factor of 2?

“…There were seven datasets based on EC10 values, which is much less than the 22 datasets based on EC50 values reflecting that EC50 values are more common acceptability criteria in reference toxicant testing (see examples in Stone et al (2022) and Price et al (2022)). The seven available EC10 datasets were comprised of 92 toxicity tests across four species (two invertebrates and two microalgae) and two contaminants (copper and nickel) with both acute and chronic data (Supplementary Table S1).…”