Recent heavy metal concentrations in Watarase basin around Ashio Mine

Pollution in the Watarase River caused by mineral wastewater containing high levels of copper discharged during the development of the Ashio Copper Mine is one of the most well-known environmental pollution problems in Japan, and has been called the "Starting line of environmental pollution problems in Japan." In this study, we conducted follow-up investigations on the conditions of pollution in the Watarase River since 1991, and measured the heavy-metal levels in water in other rivers near the Watarase River and in soils around them. In addition, we compared the results in this study with previous results, i.e. pollution conditions in the Watarase River, other rivers and soils. Six points in upstream sites of the Watarase were chosen for sampling. Six samples from river water, five samples from soils around the respective points, and three samples from tap water distributed there were collected for the analysis. Heavy metal levels in rivers and soils around the Ashio Copper Mine were significantly lower than the environmental standards for them. When compared with our previous investigations, the levels of polluting heavy metals around the closed refinery at the Ashio Mine were gradually but clearly reduced. In conclusion, the environment around the Watarase River has been steadily improved so that safety in the living environment is assured.