Introduction
Material flow accounting provides economy-wide data on material use. Through international standardization, this data has become reliable and comparable across countries. Increasingly, the data are also being made available in medium- to long-term time series allowing for the analysis of past trends as well as potential future developments. Material flow accounts provide information on the material inputs into, the changes in material stock within, and the material outputs in the form of exports to other economies or discharges to the environment of an economy. Material flow accounting can be used in national planning, especially for scarce resources, and also allows for forecasting. The method can be used to assess environmental burdens associated with the economic activities of a nation and to determine how material intensive an economy is.The principle concept underlying MFA is a simple model of this interrelation between the economy and the environment, in which the economy is an embedded subsystem of the environment. Similar to living beings, this subsystem is dependent on a constant throughput of materials and energy. Raw materials, water and air are extracted from the natural system as inputs, transformed into products and finally re-transferred to the natural system as outputs (waste and emissions). In order to highlight the similarity to natural metabolic processes, the terms "industrial" or "societal" metabolism have been introduced.In MFA studies for a region or on a national level the flows of materials between the natural environment and the economy are analyzed and quantified on a physical level. The focus may be on individual substances (e.g. Cadmium flows), specific materials, or bulk material flows (e.g. steel and steel scrap flows within an economy). Researchers in this field are organized in the Socio-Economic Metabolism (SEM) section of the International Society for Industrial Ecology (ISIE). Statistics related to material flow accounting are usually compiled by national statistical offices, using economic, agricultural and trade statistics measuring the exchange of material between different products available in an economy.
Scope and indicators
Aside from calculating the ''net additions to stock'' (NAS) as a balancing item, flows within the economy are not considered (advances are currently being made in the field of