What is Materials Accounting and why is it important to pollution prevention?

Materials accounting consists of determining the quantity of a chemical or hazardous substance at key junctures in its progression through a production process at an industrial facility. This requires data on the quantity of each listed chemical brought on site, produced on site, chemically consumed within a production process, shipped off site as or in product, and generated as nonproduct output. Materials accounting is an engineering approach that estimates the pounds of chemical at various stages in its flow through a manufacturing facility, thus the term "throughput data" is often used synonymously with materials accounting data. Materials accounting data generates direct pollution prevention information, thereby expanding public, industry and government understanding of a facility's environmental performance.

Materials accounting data is different than complex chemical mass balance analysis. A mass balance identifies and precisely quantifies all inputs and outputs of chemicals into each step of a production process and requires closure in analysis. As such, a mass balance analysis often must rely on direct measurement techniques for all incoming and outgoing points. In contrast, materials accounting relies upon best engineering judgement or estimation to determine inputs and outputs. Materials accounting or throughput data is readily derived from accounting and production records, such as invoices for raw material purchases, inventory figures, product composition, and sales records. Many facilities use their materials accounting data to derive environmental release data such as that required by the federal Toxics Release Inventory (TRI).

Materials accounting quantitatively tracks chemicals through the facility's production processes where pollution prevention practices are most likely to occur. This is in contrast to TRI's end-of-pipe focus where pollution treatment or control could cause reductions in releases to the environment. Several valuable pollution prevention measurements can be computed from materials accounting data. One of the most useful calculations is determining chemical throughput or use for a given year, i.e., calculating the quantity of chemical used at the facility in its manufacturing operations. Yearly use comparisons can provide insight into the magnitude of chemical use and the relationship of this use to releases and production, and can be a quantitative indicator of actual toxics use reduction.

The two primary pollution prevention measures are use per unit of product and nonproduct output per unit of product. Chemical use per unit of product is a simple measure of process efficiency: how much chemical did it take to make a unit of product? Nonproduct output per unit of product is a measure of process inefficiency: how much waste (or nonproduct output) was produced to make a unit of product? Reductions in use per unit of product and nonproduct output per unit of product are both considered to be pollution prevention.