Until now, most studies into the siting of industrial facilities have looked at a single point in time, and tended to use a combination of census and postcode data to assess the pattern of residency around the facilities. This snapshot-type analysis can’t observe how the area has changed over time, and the postcode analysis can be misleading as postcode areas can be large, so that not all residents within a particular postcode will be adversely affected by the industry in question. What’s more, in cases where facilities are located near postcode boundaries, populations in nearby postcodes who are affected are not counted.

In order to overcome these hurdles, Paul Mohai from the University of Michigan and Robin Saha from the University of Montana studied a longitudinal dataset of commercial hazardous waste facilities sited in the US between 1966 and 1995. The researchers looked at the demographic composition of the neighbourhoods within a 3 km radius of these facilities and analyzed how the demographics changed over time.

The results showed that neighbourhoods tended to become poorer after hazardous waste facilities were located there. But Mohai and Saha also found that in most cases the neighbourhoods had already been becoming poorer a decade or two before the facilities were introduced.

"This means that the facilities did not cause the decline, as has been widely believed until now," said Mohai. "Instead, neighbourhoods in decline appear to be attracting the facilities. Thus, neighbourhoods where minorities and poor people are disproportionately present and are in decline appear to be the ones mostly likely targeted for new facilities."

Low-income and ethnic-minority neighbourhoods have fewer resources and less political clout than wealthier neighbourhoods. That and the transitory nature of the neighbourhoods make them more vulnerable to the siting of a polluting industry.

"The demographic changes may result in the weakening of social ties in the community generally, making mobilization more difficult," said Mohai. "The community may come to be seen as the 'path of least resistance' by industry." Counter examples, such as the African-American residents of Convent in Louisiana, who managed to mobilize and prevent the arrival of what would have been the world's largest polyvinyl chloride (PVC) manufacturing plant in the late 1990s, or the residents of Flint in Michigan, who kept a steel mill from being built in an already heavily polluted area, again in the late 1990s, add weight to the idea that stable communities, even if they are not wealthy, are better able to resist hazardous facilities being sited in their neighbourhood.

Understanding this dynamic should help to improve the way that hazardous facilities are sited in the future, by creating policies that prevent industry from taking advantage of declining communities. "Policies that require buffer zones around hazardous waste and other polluting industrial facilities and prohibitions against siting new facilities in environmentally over-burdened communities are a few steps that could be taken to mitigate the problem in the future," said Saha.

Meanwhile, in communities that are already affected by the proximity of hazardous industries, steps can be taken to improve lives, by involving citizens more, enabling independent monitoring of pollution in the neighbourhood, and working to reduce the amount of waste produced.

The team reported the findings in Environmental Research Letters (ERL).

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