The Political Economy Research Institute (PERI) is an institute at the University of Massachusetts Amherst which, according to its mission statement, "...promotes human and ecological well-being through our original research.
PERI's Toxic 100 list includes one hundred United States companies ranked by the amount of air pollution produced and the relative toxicity of the pollutants, as determined by PERI at the University of Massachusetts Amherst. The top five companies from the adjusted 2016 index are Alcoa, E.I. du Pont de Nemours, General Electric, ExxonMobil and Berkshire Hathaway.
Toxic scores are calculated by the formula:
Emissions are measured in millions of pounds. Population exposure is based on the proximity of nearby residents, and factors such as prevailing winds and height of smokestacks. Toxicity is per the US EPA's Risk-Screening Environmental Indicators.