Assessing ecological risk of zinc in Japan using organism- and population-level species sensitivity distributions

In Japan, the Environmental Quality Standard for zinc, established in 2003, was the first standard for the protection of aquatic species. To achieve this environmental criterion, the National Effluent Standard was lowered from 5 mg L–1 to 2 mg L–1 in 2006. However, some industries were permitted to apply a provisional effluent standard until 2011, when the provisional standard will revert to the national standard. Therefore, discussion about the environmental management of and countermeasures for the risk of zinc continues in Japan. The aim of this paper is to present the current status of the risk of zinc. Using long-term monitoring data for zinc from more than 3000 monitoring sites in Japan, both freshwater and marine, we found that the geometric mean concentration of zinc at freshwater sites was about 10.8 μg L–1 and that the annual mean concentrations have been generally decreasing. We identified sites where zinc concentrations were high, and we also identified the most likely sources of zinc responsible for the high concentrations. The ecological risk of zinc was estimated at the conventional individual level and at the population level. Individual-level risk was detected at about 20% of freshwater sites, and population-level risk at about 2%. The risks were lower in more recent years; however, they remain at unacceptable levels. Our results show the necessity of risk reduction strategies. We propose a new approach for risk management and countermeasures that consider both individual- and population-level risks.