Cancer mortality in a Texas county with prior uranium mining and millingactivities, 1950–2001

Abstract

Uranium was discovered in Karnes County, Texas, in 1954 and the first uraniummill began operating in 1961 near Falls City. Uranium milling and surface and insitu mining continued in Karnes County until the early 1990s. Remediation ofuranium tailings ponds was completed in the 1990s. There were threemills and over 40 mines operating in Karnes County over these years andpotential exposure to the population was from possible environmentalreleases into the air and ground water. From time to time concerns havebeen raised in Karnes County about potential increased cancer risk fromthese uranium mining and milling activities. To evaluate the possibilityof increased cancer deaths associated with these uranium operations, amortality survey was conducted. The numbers and rates of cancer deaths weredetermined for Karnes County and for comparison for four ‘control’ counties inthe same region with similar age, race, urbanisation and socioeconomicdistributions reported in the 1990 US Census. Comparisons were also made withUS and Texas general population rates. Following similar methods tothose used by the National Cancer Institute, standardised mortality ratios(SMRs) were computed as the ratio of observed numbers of cancers in thestudy and control counties compared to the expected number derived fromgeneral population rates for the United States. Relative risks (RRs) werecomputed as the ratios of the SMRs for the study and the control counties.Overall, 1223 cancer deaths occurred in the population residing in KarnesCounty from 1950 to 2001 compared with 1392 expected based on generalpopulation rates for the US. There were 3857 cancer deaths in the fourcontrol counties during the same 52 year period compared with 4389expected. There was no difference between the total cancer mortality ratesin Karnes County and those in the control counties (RR = 1.0;95% confidence interval 0.9–1.1). There were no significant increases in KarnesCounty for any cancer when comparisons were made with either the USpopulation, the State of Texas or the control counties. In particular, deaths due tocancers of the lung, bone, liver and kidney were not more frequent in KarnesCounty than in the control counties. These are the cancers of a priori interestgiven that uranium might be expected to concentrate more in these tissues thanin others. Further, any radium intake would deposit primarily in the bone andradon progeny primarily in the lung. Deaths from all cancers combined alsowere not increased in Karnes County and the RRs of cancer mortality inKarnes County before and in the early years of operations (1950–64),shortly after the uranium activities began (1965–79) and in two latertime periods (1980–89, 1990–2001) were similar, 1.0, 0.9, 1.1 and 1.0,respectively. No unusual patterns of cancer mortality could be seen in KarnesCounty over a period of 50 years, suggesting that the uranium miningand milling operations had not increased cancer rates among residents.