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For the past four years, residents of Flower Mound—a suburb of Dallas-Fort Worth, Texas—have been concerned about what they see as an unexplained rise in cancer diagnoses in their community. They wonder if pollution from the many new oil and gas operations nearby could be to blame. Unfortunately, the most recent update to the Texas Department of State Health Services’ investigation still fails to adequately evaluate residents’ concerns and they are left with many unanswered questions.
Flower Mound, population 65,000, sits atop the Barnett Shale, one of the largest and most heavily drilled onshore reserves of unconventional natural gas in the U.S. with more than 12,000 gas wells. Most of these wells have been horizontally drilled and hydraulically fractured (fracked) to stimulate gas flow since 2004. Residents asked for an investigation into what they thought to be an unusually high number of diagnoses for cancer including leukemia, brain and breast cancer. After initial investigations in 2010 and 2011, the Texas Department of State Health Services (DSHS) concluded that although the breast cancer rate among women was elevated, there was no reason for concern and not enough evidence of a cancer cluster. But residents were not convinced, arguing that the cancers in their community included rare types and affected children and young adults—demographic groups in which most cancers are typically rare.
In response to questions about the adequacy of its investigation, the DSHS has now released a new, updated report, which concluded that “female breast cancer was the only type of cancer … where the observed number of cases was higher than expected and the result was statistically significant; this result is consistent with previous findings.”
Yet, it is not only the breast cancer rate that is worrisome: a closer look at the numbers shows that certain types of leukemia and brain and nervous system cancers (reported only for children) also occurred at higher numbers than expected. However, due to the small population size it was not possible to say with very high certainty that they were not due to chance. Leukemia is a type of cancer that has been linked to chemical exposure, in particular the pollutant benzene, which has been detected in air samples at and near oil and gas production sites.
The DSHS simply says that it “plans to continue to monitor cancer incidence in the Flower Mound area.” As a statistician, and a parent, I can say that neither the analysis nor the DSHS’s response go far enough to address the legitimate concerns of Flower Mound residents. A real response would be to conduct a more detailed analysis of the patterns of breast, leukemia and brain and nervous system cancers in the community. The statistician’s toolbox contains a number of robust methods for working with small sample sizes in addition to the Standardized Incidence Ratios (SIR) used by the DSHS, which can be too easily dismissed for lack of statistical significance. Instead, an analysis of the number and location of diagnoses over time could show if there are increasing trends in diagnoses and their spatial patterns (i.e. proximity to pollution sources). The choice of study period is also an important component in the search for potential environmental risk factors. The DSHS based its investigation on the time period 2000-2011. However, gas production in the Barnett Shale started to increase substantially around 2001 and the boom in horizontal drilling and fracking began in 2004. Since gas drilling and fracking is seen by residents as a potential cause for the perceived cancer cluster, the investigation should have compared cancer incidences before and after 2001 and also before and after 2004.
The residents of Flower Mound deserve to have their concerns taken seriously by their state’s health department. A more detailed and rigorous analysis is an important first step and will go a long way towards providing this community with some real, and evidence-based, answers.
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