Toyosu - The Necessity of Brownfield Measures - From November 2007 to the 2020s

Toyosu - The Necessity of Brownfield Measures - From November 2007 to the 2020s

### Historical Background
In Toyosu, Koto Ward, Tokyo, including the former Tokyo Gas factory site, there are approximately 28000 hectares of brownfields nationwide, with an estimated asset scale of about 108 trillion yen. Among these, Toyosu has significantly exceeded the environmental standard for benzene (0.01 mg/L), specifically with concentrations of 10 mg/L or more detected, and remediation costs are estimated at approximately 67 billion yen.

In particular, when contamination is discovered before land sales, remediation costs exceed 20–40% of land prices, leading to stalled transactions in many cases. The Ministry of the Environment has been advancing the development of the Soil Contamination Countermeasures Act, supporting risk mitigation and land reuse through services such as simplified risk assessment provided by Kokusai Kogyo. On the other hand, countermeasures in regional cities have been delayed, with economically struggling areas facing more pronounced challenges.

### Developments in the 2010s
In the 2010s, the dissemination of low-cost technologies for the remediation of heavy metal-contaminated soils progressed, and on-site technologies developed by companies such as Ebara and DOWA Eco-System gained attention. Ebara's technology enabled cost-effective treatment of lead and arsenic-contaminated soils, reducing costs by 50%, saving approximately 1500 yen per square meter.

Additionally, in the contamination caused by radioactive materials from the Fukushima Daiichi Nuclear Power Plant accident, about 12 million cubic meters of contaminated soil had been processed in special decontamination zones by 2019. The government allocated approximately 2 trillion yen to promote the return of residents. In the real estate industry, third-party risk assessment became standardized, improving transparency in land transactions.

Urban redevelopment expanded brownfield utilization in the late 2010s, with concepts such as eco-cities and zero-emission towns gaining attention. For instance, in Osaka, the "Yumeshima Redevelopment Project" is underway, utilizing former factory sites with a total investment of approximately 200 billion yen.

### Current Status in the 2020s
In the 2020s, the number of investigations into contaminated land is increasing. In 2022, 1576 soil contamination surveys were conducted, and 982 cases were found to exceed environmental standards. In Toyosu, soil contamination by hazardous substances such as benzene and cyanides remains a challenge, and the total cost of remediation is expected to increase further.

Enbio Holdings is promoting projects to remediate contaminated land at a cost of approximately 20 million yen per project. In addition, in regional municipalities, remediation costs have reached 30–50% of land prices, and redevelopment is often difficult. Meanwhile, new remediation technologies, such as nanoparticle-based methods for decomposing hazardous substances, are in the research phase, with expectations for cost reductions.

**Summary**
The brownfield problem, including Toyosu, is a critical issue that balances land use and environmental conservation. Since the 2010s, technological innovation and institutional development have advanced, while in the 2020s, further development of remediation technologies and economic support is required. Continued efforts to promote sustainable urban development through the reuse of contaminated land are essential.