With a few exceptions, such as a short 2008 report from the Canadian Policy Research Networks, socioeconomic inequalities in exposure to environmental hazards have not been a central concern of Canadian population health research or public health practice. In the United States, on the other hand, the highly visible and persistent reality of racial segregation has generated a substantial stream of research and activism on environmental justice, including the establishment of units like the Environmental Justice Resource Centre in Atlanta. In 1994, an executive order issued by then-President Clinton required all federal agencies to consider environmental justice in their programs. Official interested waned (to put it politely) under subsequent Republican administrations, but the issues are now being revisited.
The December 2011 issue of the American Journal of Public Health – fortunately, available on an open-access basis – is based on a symposium on Strengthening Environmental Justice Research and Decision Making organized by the US Environmental Protection Agency in March 2010. The articles are a valuable resource for exploring both the strengths and the limitations of current US approaches to the issues, and amply support an editorial conclusion that the EPA's current approach "is not sufficient to end make progress toward ending environmental health disparities and environmental injustices," given its heavy reliance on toxicology and engineering.
Among the many important points raised in the collected articles:
- An overview of methodologies points out that most existing studies of the spatial distribution of environmental health hazards rely on census data, so effectively track only nighttime exposure. People's daytime locations and exposures are harder to track, and it's certainly plausible that people living in locations where their exposure to environmental hazards is high are also more likely than others to be working in similar environments.
- In assessing the overall distribution of inequalities in the chance to lead a health life, it is essential to consider the combined health effects of chemical exposures and stressors of other kinds, including psychological and social stressors. A companion article by Bruce McEwen, one of the world's leading researchers on the biology of stress, elaborates on the physiological pathways that are likely to be relevant. Since population health researchers often ignore the massive accumulation of human and non-human evidence on this topic, its recognition is especially important.
- Paula Braveman and colleagues elaborate on a now familiar definition of health equity by dealing explicitly with the issue of strength of evidence and standards of proof, arguing: "It must be plausible, but not necessarily proven, that policies could reduce [health] disparities, including not only policies affecting medical care but also social policies addressing important non-medical determinants of health and health disparities ..."
The symposium also (not always intentionally) underscores the limitations of the US approach. For a variety of reasons, many of which have to do with industry's use of the courts to resist environmental regulation, quantitative risk assessment is "the central paradigm of the Environmental Protection Agency". Especially in the case of cancer risk, it can be difficult to establish links with the spatial distribution of hazards: because of long induction and latency periods, "studies would need to include residential histories for as many as 15 to 30 years before a cancer diagnosis to capture pertinent environmental exposures," even before dealing with the problem of exposures when people are not at home – on the job, for instance. The effect is to build in a bias against regulation that requires "requires positive evidence of 'dead bodies' before acting," in the words of a classic 1978 article by environmental economist Talbot Page, unfortunately not available for open access. More generally, the emphasis on quantitative risk assessment focuses attention and resources on refining measurement techniques and building ever more elaborate models of causal pathways. An alternative, explicitly precautionary approach to environmental justice would focus instead on eliminating hazards once a much lower standard of proof is met. This tension is hardly unique to environmental justice; indeed, as Page pointed out, it is pervasive in the regulation of many kinds of health hazards.
As mentioned, environmental justice issues have had a relatively low profile in Canada. Three Canadian researchers recently argued (I think quite correctly) that institutional health promotion here has simply failed to address environmental health inequalities. Here's one of many areas related to social determinants of health in which even a modest commitment of additional research dollars is likely to generate valuable, if politically awkward, findings.