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Physical and Monetary Methods for Estimating the Hidden Trade of Materials

1,2,3,*, 1,2,3, 4 and 5,6
Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
Xiamen Key Lab of Urban Metabolism, Xiamen 361021, China
University of Chinese Academy of Sciences, Beijing 100049, China
Industrial Ecology Group, Faculty of Environment and Natural Resources, University of Freiburg, Tennenbacher Strasse 4, D-79106 Freiburg, Germany
Institute for Advanced Study, Tongji University, Shanghai 200092, China
UNEP-Tongji Institute of Environment for Sustainable Development, Tongji University, Shanghai 200092, China
Author to whom correspondence should be addressed.
Resources 2019, 8(2), 89;
Received: 8 March 2019 / Revised: 15 April 2019 / Accepted: 3 May 2019 / Published: 6 May 2019
PDF [1857 KB, uploaded 6 May 2019]


The hidden trade of a material (e.g., aluminum) refers to the trade of that material embedded in final products (e.g., automobiles). There are two methods for estimating the hidden trade amount of materials: (1) the physical method relies on the physical trade data (measured by physical units) in which products are categorized according to the standard international trade classification codes or the harmonized system codes; and (2) the monetary method relies on the monetary trade data (measured by monetary units) in which products are categorized in accordance to the sectors of an input–output (IO) table. Information on material concentrations in products can be relatively quickly estimated by an IO-based model in the monetary method, but will have to be collected from various sources with intensive time cost in the physical method. Exemplified by the U.S. hidden trade of aluminum, iron, and copper in 2007, this study attempts to compare the two methods. We find that, despite the unavoidable but reasonable differences in the amounts of three metals trade, the results generated by the two methods are consistent with each other pretty well for final products at the level of end-use product groups (e.g., total transportation facilities). However, the comparison for specific products (e.g., automobiles) is challenging or does not generate consistent enough results. We suggest that similar estimations be done for more materials, more countries/territories, and different years, to gain experience, reduce estimation time and costs, and increase the knowledge base on metal flows in society. View Full-Text
Keywords: material flow analysis; hidden trade of materials; anthropogenic metal cycles; industrial ecology material flow analysis; hidden trade of materials; anthropogenic metal cycles; industrial ecology

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Chen, W.-Q.; Ma, Z.-J.; Pauliuk, S.; Wang, T. Physical and Monetary Methods for Estimating the Hidden Trade of Materials. Resources 2019, 8, 89.

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