Minority and low-income communities often lack economic and political clout, making them the path of least resistance for companies looking to dump their hazardous waste. That’s among several conclusions of a new environmental justice study conducted by researchers at the University of Michigan and the University of Montana.

Paul Mohai, professor in Michigan’s School of Natural Resources and Environment, and Robin Saha, associate professor of environmental studies at the University of Montana, analyzed 30 years of demographic data about the placement of U.S. hazardous waste facilities and published those findings in two articles in the November and December issues of Environmental Research Letters.

While the disparate placement of environmental hazards in poor and minority communities has been aptly demonstrated in numerous studies, questions remain as to the cause: is it a pattern of disproportionately siting hazardous waste facilities among the poor and people of color or is it demographic changes that lead to a disproportionate concentration of such populations around such facilities after siting?

To answer the question, Mohai and Saha analyzed demographic conditions before and after the siting of 319 commercial hazardous waste treatment, storage and disposal facilities in the United States from 1966 to 1995.

They found “a consistent pattern over a 30-year period of placing hazardous waste facilities in neighborhoods where poor people and people of color live,” according to the article, “Which Came First, People or Pollution? A Review of Theory and Evidence From Longitudinal Environmental Justice Studies.”

That pattern may have been influenced by companies targeting “weaker” communities with less ability to successfully protest the siting of hazardous waste facilities in their neighborhoods, and also by racial discrimination in policies such as housing and zoning, the researchers concluded.

“NIMBYism (objection to the placement of something unpleasant or toxic in one’s neighborhood) in more affluent, white communities…resulted in industry taking the ‘path of least resistance’ and targeting communities with fewer resources and political clout,” the study read. “These communities are where the poor and people of color live.”

Demographic change before the establishment of hazardous waste sites, resulting in “the weakening of social ties, the loss of community leaders, and weakening of civic organizations” likely has an influence on siting decisions. Surprisingly, the researchers concluded, demographic changes after the fact are often just a continuation of earlier changes.

“Contrary to earlier beliefs about post-siting demographic change, neighborhood transition may serve to attract noxious facilities, rather than the facilities themselves attracting people of color and low-income populations,” Mohai said in a statement. “Ours is the first national study to demonstrate this pattern.”

He added, “We hope our papers help resolve confusion and arrive at a clearer understanding of the processes and contributory factors by which present-day racial and socioeconomic disparities in the distribution of environmental hazards have come about.”