Health Stream Literature Summary - Issue 28 December 2002

Community cancer assessment in response to long-time exposure to perchlorate and trichloroethylene in drinking water.
Morgan J W, Cassady R E. J Occup Environ Med (2002) 44(7) p616-21.

Concerns about contamination of ground and drinking water with trichloroethylene (TCE) and ammonium perchlorate prompted a request for an assessment of the observed and expected numbers of new invasive cancer cases. The assessment was undertaken within a collection of 13 contiguous census tracts encompassing the city of Redlands, San Bernardino County, California. Studies have suggested that perchlorate contamination of some Redlands wells may have occurred as early as 1980 and TCE contamination as much as ten years earlier.

New invasive cancer cases diagnosed between January 1, 1988 and December 31, 1998 were included in the assessment. A total of 16 types of cancers were included. The number of cancer cases expected to occur among residents of the 13 census tracts during 1990 was estimated taking into account the age, race/ethnicity and gender distribution of the population. The number of new invasive cancer cases observed among residents of the 13 census tracts from 1988 through 1998 was obtained from the Desert Sierra Cancer Surveillance Program database. Standardised incidence ratios (SIRs) were calculated for each of the cancer sites by dividing the observed number of new invasive cancer cases by the growth-adjusted expected number of cases aggregated for the 13 census tracts over the 11 years studied.

The observed numbers of new cancer cases with origins in the lung and bronchus (SIR, 0.71; 99% CI, 0.61 - 0.81) and the colon and rectum (SIR, 0.86; 99% CI, 0.74 - 0.99) were statistically significantly lower than the numbers expected. These findings are consistent with what might be expected for a population having lower than average tobacco use and receiving better than average cancer screening. The number of melanomas of the skin (SIR, 1.42; 99% CI, 1.13 - 1.77) and malignancies with origins in the corpus uterus (SIR, 1.35; 99% CI, 1.06 - 1.70) were significantly higher than the number expected. These findings are consistent with the relatively high socio-economic status of this population. The increased access to health care means that low-grade melanoma lesions are detected and reported. The use of oestrogen replacement therapy is also more common among women receiving better access to health care and has been linked to elevated risk of uterine cancer. For childhood cancer, none of the finding showed any significant differences from observed numbers of new cancer cases than from the numbers of expected cases. This was also true for all cancers combined (SIR, 0.97; 99% CI, 0.93 - 1.02), thyroid cancer (SIR, 1.00; 99% CI, 0.63 - 1.47) and all other cancer types studied. The authors conclude that the observed pattern of cancer occurrence is consistent with the sociodemographic and lifestyle characteristics of the population, and did not indicate any generalised increase in cancer or specific increase in thyroid cancer (suggested as a possible effect of perchlorate exposure).