History and current status of dioxin contamination in the Tama River (1990s to 2020s)

History and current status of dioxin contamination in the Tama River (1990s to 2020s)

1990s: Discovery of contamination
In the 1990s, highly toxic dioxin contamination was confirmed in the entire Tama River area, attracting significant attention as an environmental problem. According to a survey conducted by the National Institute of Public Health and Welfare, 0.05 to 2.8 picograms per gram of 2378-tetrachlorodioxin, the most toxic dioxin, were detected in bottom sediment, with higher concentrations found in the lower reaches of the river. The main sources of contamination were estimated to be industrial effluent and bleaching processes in the upstream areas and waste incineration plants around Kawasaki City and Ota Ward, Tokyo, in the downstream areas. This raised concerns about the impact on the river ecosystem and residents, and local residents and environmental groups formed the "Association to Protect the Tama River" and launched a cleanup campaign.

2010s: Improvement Efforts
In the 2010s, technological improvements to waste incineration facilities and tighter regulations on industrial wastewater were implemented in response to the pollution problem. During this period, dioxin concentrations in the bottom sediment of the Tama River dropped to an average of 10 picogram TEQ/g, although high concentrations of 50 picogram TEQ/g or higher were observed in some areas. Exhaust gas treatment technology has been introduced at incineration facilities in Kawasaki City and Ota Ward, Tokyo, reducing dioxin emissions. In addition, local residents and non-profit organizations regularly conducted cleanup activities, contributing to the improvement of the Tama River environment.

Improved recycling rates also attracted attention during this period, and the Tokyo Metropolitan Government and Kawasaki City strengthened the separate collection of waste plastics. This further reduced the generation of waste-derived dioxin.

2020s: Further Progress
In the 2020s, the Tama River environment is undergoing further improvement. According to a survey conducted by the Bureau of Environment of the Tokyo Metropolitan Government, the average concentration of dioxin in the water in FY2020 was 0.18 picogram TEQ/L, and in the sediment, 6.5 picogram TEQ/g, a significant decrease compared to the past. However, some high concentration detection sites remain a challenge.

Kawasaki City and Ota Ward in Tokyo have introduced the latest exhaust gas treatment technology, and dioxin emissions for the entire Tokyo metropolitan area have been reduced to approximately 5 grams TEQ/year. Efficient combustion technology using alternative fuels produced in Tomakomai has also contributed to this reduction. Furthermore, companies and local governments are cooperating to promote environmental conservation, with the Tokyo Tama Wide-area Resource Recycling Association continuing its research at the Futatsuzuka disposal site, and Sumitomo Chemical and Sumitomo Mitsui Construction working to develop alternative technologies for chlorine compounds.

Summary: Purification of the Tama River and Challenges
Dioxin contamination of the Tama River, which was first discovered in the 1990s, has shown signs of improvement as a result of 30 years of efforts. The river environment has gradually recovered thanks to the introduction of the latest technology, stricter laws and regulations, and the active participation of local residents. However, improvement of some high concentration points in the bottom sediment and efforts for sustainable water quality management continue to be important issues. The case of the Tama River has become a remarkable model case for improving the water environment in Japan as a whole.