We Knew That
I just picked up an abstract from the open access journal Environmental Health which presents a review of cancer epidemiology studies at hazardous waste sites. Epidemiology is the science and art that attempts to identify the relationships between disease and environmental factors. Some of the most painstaking investigative work in science occurs in epidemiological investigations. A classic example is the investigation of occurrence of cholera in London, conducted by John Snow As a part of this investigation, Snow mapped the locations where cholera cases occurred along with the locations of the local water pumps, thus creating the story of “the pump handle”.
The conclusion from this study was that epidemiological investigations generally did not provide a lot of information about whether communities near hazardous waste sites experienced an increased cancer risk or not. Limitations in the study design and limited information regarding levels of exposure were cited as support for this conclusion.
This study was funded by the City of New York. Why the City of New York is interested in drawing attention to the limitations of hazardous waste epidemiology isn’t made clear. However, it isn’t really news that hazardous waste epidemiology is grossly imperfect. We knew that already back as 1991. What is surprising is how little appears to have changed in the intervening years.
Most of the studies reviewed in this recent paper were identified as ecological studies, which examine rates of diseases between different groups (i.e. a community using contaminated groundwater compared with a community using an uncontaminated supply). Detailed information on the health status of individuals or detailed exposure information generally is not part of an ecological study. An ecological study is most useful for generating hypotheses and scoping more detailed epidemiological studies. Limited modeling or sampling data were incorporated into these studies, particularly measurements at the locations where individuals were most likely to come into contact with hazardous waste contaminants.
There’s a whole litany of things that could be done better here. We’ve known about these for a long time, but haven’t bestirred ourselves to deal with them.
The exposure data for assessing hazardous waste site contaminants is very limited, but we can’t all be tobacco epidemiologists who get to work with human populations who dose themselves like they were laboratory animals. There hasn’t been enough emphasis on community-based participatory methods for increasing community cooperation with exposure studies, as well as not enough emphasis on risk communication to help explain that simply looking for exposure doesn’t necessarily mean there’s a significant risk. From personal experience, I am aware that residents get understandably edgy when you want to come in to collect air samples from inside their homes or soil samples from their yards. They naturally run to the conclusion that there must be a problem (if there wasn’t, we wouldn't be looking, right?). However, because risk assessors are unable to discuss exposure and health risk in simple English, decision makers really don’t have a clue about what’s really going on, and everyone is afraid to speak up without a bunch of hedging and qualifying when the lawyers are in earshot, the people who have the biggest need to understand what’s going on – the neighbors to a hazardous waste site – routinely don’t get a straight story.
There’s the two-part problem of the lack of conclusiveness of epidemiology, coupled with the extremely sensitive perceptions of risks, both of which contribute to the sense of anxiety and uncertainty in the neighbors of hazardous waste sites. Both parts, the relative risk of 2.0 as evidence of causation, and the excess lifetime cancer risk of 1 in 1,000,000 as a threshold of acceptable risk, do not appear to be grounded in any sort of public health reality. It’s an obscure point, which is the topic for another post (because this one’s getting too long. . .).
We don’t seem to have learned anything from epidemiology to better inform hazardous waste decision making. Therefore, we fall back on making cleanup decisions using the crudest of risk assessment methods, which either don’t address real and significant health risks, or are a wasteful expenditure of resources in relation to the amount of risk reduction that occurs.
Labels: environmental health policy, epidemiology, hazardous waste sites, risk assessment