Japan Releases New Implementation Manual for Biodegradability Assessment Under CSCL 
Japan’s Ministry of Economy, Trade and Industry (METI) has developed and published a new implementation manual for the comprehensive biodegradability assessment method known as Weight of Evidence under the Chemical Substances Control Law (CSCL). Released in May 2025, the manual aims to improve transparency in the assessment process by providing valuable information sources, tools, standard evaluation methods, and key considerations. Moving forward, the manual will guide biodegradability assessments for general chemical substances and priority evaluation chemical substances using the Weight of Evidence approach. The results will be reviewed by the Chemical Substances Council’s Safety Measures Subcommittee and incorporated into screening and risk assessments of chemicals under CSCL. METI also urges businesses to voluntarily provide relevant biodegradability data for general and priority evaluation chemical substances—even if they are not subject to the reporting obligation under Article 41 of CSCL—if they possess environmental degradation data.
Background and Purpose of Weight of Evidence
Traditionally, biodegradability assessments under CSCL primarily adopted ready biodegradability tests equivalent to OECD Test Guidelines 301C and 301F, and based on their results, substances were classified as readily or poorly biodegradable. These tests helped determine whether a substance was readily or poorly biodegradable. However, for poorly water-soluble substances, the standard 100 mg/L test concentration may not have been sufficient to accurately assess their degradability in natural environments. With the introduction of Weight of Evidence, biodegradability evaluations now incorporate multiple sources of information, including:
- Biodegradation test data
- Existing knowledge on similar substances
- Predictive results from (Q)SAR models (Quantitative Structure-Activity Relationship)
This integrated approach provides a more comprehensive and rational assessment of whether a chemical substance remains persistent in natural environments after its release.
Related Links
METI Information: Implementation of Weight of Evidence for Biodegradability Assessment in Screening and Risk Evaluations (May 2025)
https://www.meti.go.jp/policy/chemical_management/kasinhou/information/woe_biodegradation.html
