means of pollution prevention, for example, but not have the information they need to identify opportunities and make good decisions. Todd explains that the information needed to make good environmental decisions may be either lacking entirely or unreliable. She proposes a set of guidelines for developing an effective information and measurement system to support environmental decision making.

Plant-Based or Organization-Based Measurements
Raw Flux Measurements

Perhaps the most important raw flux measurement system in operation is the Toxic Release Inventory (TRI). TRI was mandated by the 1986 Emergency Planning and Community Right-to-Know Act. The law requires companies to publicly report releases of each of more than 300 chemicals. Many people believe that the TRI has been remarkably effective in reducing environmental impacts. When companies and people living near them have learned of the quantities of emissions from plants, those companies have often chosen to voluntarily reduce their emissions. The beauty of TRI is that no one is required to act in response to the TRI data, but many have done so anyway. Critics have emphasized that the TRI does not distinguish chemicals on the basis of their relative toxicity and have questioned the accuracy of emissions reports.

3M's Waste Ratio

3M calculates a simple ''waste ratio" to assess the environmental performance of their operations (Zosel, this volume):

(waste)/(waste + products + by products).

The waste ratio uses mass as a common currency that can be followed over time. The advantages of the waste ratio include its simplicity and its limited data requirements. Using mass balances, the waste ratio can be calculated from information on the mass of products, by-products, and wastes. Most of these data are already collected for other purposes, or can be calculated from existing data and process engineering relationships.

The major disadvantage of the waste ratio is that it characterizes waste purely on the basis of mass. A kilogram of nontoxic waste has the same effect on the waste ratio as a kilogram of highly toxic waste. Nevertheless, initial results suggest that the waste ratio can be a valuable tool for improving environmental performance. From the time 3M Corp. introduced the ratio in 1990 through 1995, it reduced wastes 32.5 percent worldwide.

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