Environmental chemistry, physiological homeostasis, toxicology, and environmental regulation of copper, an essential element in freshwater fish

Exploitation of natural mineral deposits and subsequent re-deposition in aquatic environments at levels potentially harmful to biota necessitate regulation of environmental discharge of metals. Proper environmental regulation of metals requires adequate knowledge on the bioavailability and effects of metals on aquatic organisms. Moreover, the need to better understand biological effects of metals has given impetus for studies on the homeostatic physiology of metals because the root cause of toxicity is the breakdown of homeostasis. In this paper we review recent advances in the understanding of the environmental chemistry, toxicology, and physiological homeostasis of copper (Cu) in freshwater systems. Present water quality criteria do not adequately consider bioavailability and metal homeostasis. We show that consideration and incorporation of recent knowledge on bioavailability, homeostatic physiology, and acute and chronic toxic effects of Cu greatly improve the predictive precision of models, such as the Biotic Ligand Model, for ecological risk assessment and environmental regulation of Cu, and reduces the need for reliance on the Precautionary Principle. Furthermore, we highlight present gaps in knowledge of environmental physiology, homeostasis, and toxicology of Cu and suggest directions for future research.