The California Department of Public Health has found no evidence that a group of birth defects in Kettleman City, California is statistically unusual, but the epidemiological examination seems really to only be a half-measure.
… no evidence of a single cause for a series of birth defects in a central California farming town that is adjacent to the largest hazardous waste landfill in the West.
One major problem with the approach taken (besides the fact that 2009 data are not included) is that, as I read it, no separate environmental monitoring (of air, water, and soil) has been performed as a part of the investigation.
For example, the study report (pdf here), says the California Department of Public Health
… reviewed drinking water testing data for the Kettleman City public water system
This statement is an example of careful wordsmithing. Clearly, one can infer, with a high probability of being correct, that all available data on water quality were not examined. Further, there’s no mention of whether any thought had been given to testing the Kettleman City drinking water for the full panoply of chemicals that thorough testing would include.
Some might argue that the current epidemiological approach suggesting that there is no evidence of a cluster of birth defects at Kettleman City demonstrates lack of need for chemical testing. But that conclusion is incorrect, for a number of reasons.
First, people deserve to have as full an examination of potential exposures as possible, given the obvious interest in Kettleman City and its proximity to a hazardous waste facility. It would not be an expensive proposition to do in-depth water, soil and air testing. Compositing (mixing many samples to produce a single one) is often used as a screening measure, for example.
Further, as pointed out in the study, Kettleman City itself has such a low number of people and births that it is impossible to draw statistical inferences from the data for the town alone. Hence the need for bringing in other expertise, besides the health department.
Institutional myopia is one result of the current state of affairs: balkanization of environmental regulatory agencies. An epidemiological examination in a case like Kettleman City just does not go far enough. Other agencies (and especially their analytical chemists) need to be brought in as part of a thorough examination.