| Arsenic Cancer Risk Confounder in Southwest Taiwan Data Set Steven H. Lamm,1,2,3 Arnold Engel,2 Cecilia A. Penn,1,2 Rusan Chen,4 and Manning Feinleib1 1Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA; 2Consultants in Epidemiology and Occupational Health LLC, Washington, DC, USA; 3Georgetown University School of Medicine, Washington, DC, USA; 4Georgetown University Graduate School, Washington, DC, USA Abstract
Quantitative analysis for the risk of human cancer from the ingestion of inorganic arsenic has been based on the reported cancer mortality experience in the blackfoot disease (BFD) –endemic area of southwest Taiwan. Linear regression analysis shows that arsenic as the sole etiologic factor accounts for only 21% of the variance in the village standardized mortality ratios for bladder and lung cancer. A previous study had reported the influence of confounders (township, BFD prevalence, and artesian well dependency) qualitatively, but they have not been introduced into a quantitative assessment. In this six-township study, only three townships (2, 4, and 6) showed a significant positive dose–response relationship with arsenic exposure. The other three townships (0, 3, and 5) demonstrated significant bladder and lung cancer risks that were independent of arsenic exposure. The data for bladder and lung cancer mortality for townships 2, 4, and 6 fit an inverse linear regression model (p < 0.001) with an estimated threshold at 151 µg/L (95% confidence interval, 42 to 229 µg/L) . Such a model is consistent with epidemiologic and toxicologic literature for bladder cancer. Exploration of the southwest Taiwan cancer mortality data set has clarified the dose–response relationship with arsenic exposure by separating out township as a confounding factor. Key words: arsenic, blackfoot disease, bladder cancer, cancer risk, confounder, dose–response relationship, southwest Taiwan, threshold model. Environ Health Perspect 114:1077–1082 (2006) . doi:10.1289/ehp.8704 available via http://dx.doi.org/ [Online 13 January 2006]
Address correspondence to S.H. Lamm, Consultants in Epidemiology and Occupational Health LLC, 3401 38th St. NW, Washington, DC 20016 USA. Telephone: (202) 333-2364. Fax: (202) 364-5266 (call first) . E-mail: Steve@CEOH.com Supplemental material is available online at http://www.ehponline.org/members/2006/8704/suppl.pdf We thank E. Crouch of Cambridge Environmental Inc. for careful and critical review, D. Klemm of Georgetown University for his graphic illustration, and J. Herson of Johns Hopkins University for analytic considerations, and K. Shelley for assistance in developing the final manuscript. Our arsenic research program has been funded in part by industrial, plaintiff, and governmental clients. Received 29 September 2005 ; accepted 12 January 2006.
Correction The following figures have been modified from the originally published article online: Figure 1: Now includes the horizontal regression line at SMR = 100 to indicate the level at which no increased risk is observed. Figure 3: Now includes township group 0, 3, 5 (Twn grp 0, 3, 5) . A vertical line has been added to separate the township-specific results within each township, and the 95% CI values have been added to the Twn 2 data point. Figure 7: 95% CI values have been corrected for female bladder and female lung cancers.
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