Friday, December 03, 2010

John Snow and Medical Geography

The discipline of geography overlaps with many others -- even medicine and public health. The field known as medical geography includes such questions as how to deploy ambulance services and locate hospitals, but it is most commonly associated with the use of maps to understand diseases. Credit for originating this type of research generally goes to Dr. John Snow, a London physician who suggested in 1849 that cholera was transmitted by water, but had no technique for proving it. When cholera struck London in 1854, he found the right tool to validate his suggestion: a map of cholera deaths and water pumps. Scott Crosier describes John Snow's innovation (and provides a bibliography) for the Center for Spatially Integrated Social Science.

Maps have been used in similar ways in the second half of the twentieth century, as researchers use them to understand connections that were as elusive in recent history as cholera had been a century earlier. The effects of acute exposure to hazardous chemicals are often quite obvious -- a large dose in a short period of time leading to injuries, illness, or death that is tragic but not mysterious. For chronic exposure -- often very low doses over extended periods of years or decades -- the link between exposure and medical consequences is often quite obscure. (See my PPM page to get an idea of what a lethal dose of DDT looks like, for example.)

Geographic researchers have used maps of cancer deaths, birth defects, and other pathologies to find patterns  that might reveal sources of chronic chemical exposures. The most famous such case is Love Canal, New York, where Hooker Chemical Company had buried 80,000 drums of toxic waste on land that was eventually sold for the construction of houses and a school. Some children were killed by acute exposure to chemicals shortly after construction; many more were made ill by long-term exposures that were not understood until mapping that was done almost two decades later. Similar investigations were involved in the cases that were featured in the films A Civil Action and Erin Brockovich.

I teach about these cases in my introductory environmental geography class as well as an upper-level class I teach on environmental regulations. The case of Woburn, Massachusetts, which is the basis of A Civil Action, has been on my mind all week, since today's EarthView visit is to a school nearly within sight of the contaminated wells that led to so many leukemia cases in the neighborhood. A kind of mapping was involved in that case, when a mother on her back porch realized that many of the leukemia cases she knew about were clustered within her range of vision. Her doctor thought this was an illusion (or even a delusion), but her impression of the spatial pattern eventually proved to be correct.

A sad irony is that the history of Woburn as told on the city's web site extols the inventiveness of local industry -- including the development of chrome tanning -- but does not mention the dire consequences that are now so well known. Fortunately, the town library includes a "toxic waste" section near the bottom of its Local Links page.

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