Substitution and Application of Toxicity Reference Substance for Evaluating the Ecological Safety of Leather by Luminescent Bacteria

HgCl₂ was commonly used as toxicity reference substance in the luminescent bacteria test. In this paper, low toxic zinc salts were used as a substitution by studying the effects of SO₄^2- and Cl^- on the species distribution, stability and toxicity of Zn²⁺. The results showed that in aqueous solution, inorganic anions had little effect on the species of zinc. In 3% NaCl medium of the toxicity test, more Zn²⁺ species in zinc sulfate was observed. Nevertheless, the content remained constant mainly 65% Zn²⁺ and 25% ZnCl⁺ in the pH range of 1-8. Zinc sulfate had better storage stability, while zinc chloride was easy to absorb moisture. The EC₅₀ value of zinc sulfate was 1.23 mg/L greater than 0.92 mg/L of zinc chloride. Finally, using zinc sulfate as a reference, the ecological safety of leather tanned by common tanning agents was evaluated. The results showed that all leather samples satisfied the comprehensive toxicity threshold as common waste. However, chromium affected the ecological safety of tanned leather to some extent compared with organic tanning agents.