Validation trial of Japan's zinc water quality standard for aquatic life using field data

Abstract

This study sought to validate Japan's zinc water quality standard for aquatic life (algae and benthic invertebrates) based on field survey data. The effects of zinc on aquatic life, especially algae and benthic invertebrates, were investigated mainly in water areas with upstream basins that contain mines. Seven biological indicators (number of cells or individuals, number of taxa, number of EPT taxa, number of collector–gatherer taxa of benthic invertebrates, and Simpson index, Shannon–Weiner index, and Margalef index for algae and benthic invertebrates) were analyzed with respect to zinc concentrations and the zinc toxic equivalent quantity (Zn-TEQ), and additive contribution from other metals was assumed. The results showed that the number of taxa of algae and benthic invertebrates significantly decreased with increases in zinc concentration and Zn-TEQ. For benthic invertebrates, six of the metrics (all except the number of individuals) tended to decrease with increases in zinc concentration and Zn-TEQ. The effect level of biocenosis (ELB) was defined as the concentration at which the metrics decrease significantly with Wilcoxon's rank sum test. The ELB calculated for zinc was in the range of 16–54 μg/L for zinc concentration and 38–50 μg/L for Zn-TEQ; thus, Japan's environmental zinc standard for the protection of aquatic life, at 30 μg/L, was found to be a level consistent with these results.