Acute toxicity of heavy metals to aerobic digestion of waste cheese whey

Effects of the acidity and of metal ions on metabolic activity of activated sludge from waste cheese whey biological treatment have been determined. The 10% and 50% inhibitory concentrations (IC₁₀ and IC₅₀) were evaluated for each ion. In a decreasing order of toxicity two groups were found: Hg²⁺ > Cd²⁺ > CrO₄²⁻ > Cr³⁺ > Cu²⁺ and Pb⁴⁺ > Zn²⁺. The discrepancy in results of other toxicity stufies reveals the impossibility of defining on an absolute scale an order of toxicity for these ions.

A very strong synergistic effect was noted in the mixed Cu and Zn studies, thus pointing out the difficulty of setting a water-quality standard based on single toxic chemicals.