Abstract
Report prepared for Environment Southland.
This report comprises a preamble, three main sections, and a concluding section outlining future research needs. Section 1 summarises the key findings of two surveys of the metal concentrations in 22 rivers in Southland, New Zealand, carried out by Environment Southland in 2023 and 2024. Section 2 provides an overview of the known ecotoxicological effects on freshwater organisms for aluminium, copper and zinc, focusing on these metals’ effects on ecologically relevant responses of freshwater fish, invertebrates and algae or (in a few cases) other plants. The combined evidence presented here indicates that the aluminium, copper and zinc concentrations detected in Southland rivers are all high enough to raise concerns regarding potential detrimental effects on the freshwater biota in these rivers – with a few cautionary notes regarding this overall assessment. Section 3 outlines the chemistry of aluminium in natural waters, the speciated forms that co-exist in response to pH, and importantly, identifies the individual labile inorganic species that collectively constitute the more highly toxic forms of aluminium (AlMono). This section focuses on aluminium, but the methods and techniques discussed are similarly applicable to copper, zinc and other heavy metals whose toxicity similarly derives from labile inorganic mononuclear cationic molecules. The final section of the entire report points out several key knowledge gaps and future research needs on the topic.