Toxicity vs. deficiency

This lecture explores the concepts of bioavailability and bioaccessibility, absorption at physiological membranes, and the Free Ion Activity Model in the context of water quality and biogeochemistry. It delves into the relative toxicity of cations in various organisms, the Hard and Soft Acid and Base Principle, and toxicity target examples focusing on enzymes. The instructor emphasizes that the total concentration of an element does not determine its toxicological risk, highlighting the importance of speciation and the role of softness in toxicity. The lecture concludes by discussing how even ultra-traces of certain elements can substitute within enzymes, affecting their function.