Chain of custody （CoC） models certify traceability of the claim made on materials or products with a set of specified characteristics. Initially, a CoC model was applied to certify the sustainability of agricultural products. Recently, mass balance （MB） model, one of the CoC models, has been applied to the environmental claims of engineering materials. However, there are many challenges when implementing MB model in engineering materials. MB model allows flexibility in determining the ratio of specific feedstocks within materials, raising concerns about deceptive environmental claims. Credible claims with MB model need to establish requirements for applying the model. Defining system boundaries and identifying inputs and outputs are essential for CoC models. However, current MB model lacks consistency in determining system and allocation method of the specific characteristics. In addition, for most engineering materials other than chemicals, claiming methods depend on individual entities. Establishing a uniform evaluation method and certification scheme is desirable. Moreover, under conventional definitions, distinction between MB and book and claim models is vague in terms of relationship between input and output. Differentiation of these models requires further discussions. Establishing requirements and eligibility for MB model applied to engineering materials is necessary, which leads to a unified methodology.

This study examines the possibility of registration carbon credits in Japan for the reduction of greenhouse gas emissions from a project to plug natural gas from the abandoned Kurokawa Mine （oil field） in Akita Prefecture, Japan, with reference to a project to plug an abandoned oil well by a carbon credit certifier in the United States. As a result, the effectiveness of the project has not been confirmed in the Japanese Greenhouse Gas Inventory Report, which is a requirement for registration of J-credits, due to insufficient measurement and research of greenhouse gas emissions from decommissioned oil wells in Japan, and there are various issues such as the long monitoring period after sealing and the marketability of the credits. However, attempting to issue credits will greatly contribute to the visualization of the effects of GHG reductions among stakeholders, and will improve the quality of the project by sharing information and preventing leakage. Furthermore, the promotion of a decarbonized society through the purchase and carbon offsetting of carbon credits generated in the region by local companies is expected to be a game changer as a tool for the formation of a regional recycling symbiosis zone.

This article provides a summay of research supported by Environment Research and Technology Development Fund (JPMEERF20193002). First, the study proposed a group of material flow and stock indicators based on six cross-sections of material life cycle: resource input from the environment, raw material input to production processes, raw material utilization in production processes, product use, end-of-life product treatment, and waste emissions to the environment. After material flow database were developed for major materials, the proposed indicators were applied to demonstrate their usefulness. Second, the study developed methodologies to evaluate integrated efforts for the environment, economy, and society. As for a methodology based on input-output analysis, it was applied to major resource recycling efforts to demonstrate its usefulness. As for an indicator "market size of business for a Sound Material-cycle Society," the study proposed the new target business and its classification with the trial estimations. Third, the circular economy indicators used in the major European countries were reviewed to provide a database of indicators and discuss improvement in international comparability. The indicator database includes definitions, calculation methods, and necessary data. Differences in the definitions of major indicators in Japan and Europe were examined and necessary measures to improve comparability were proposed.