Cell-type specificity of lung cancer associated with low-dose soil heavy metal contamination in Taiwan: An ecological study

Background: Numerous studies have examined the association between heavy metal contamination (including arsenic [As], cadmium [Cd], chromium [Cr], copper [Cu], mercury [Hg], nickel [Ni], lead [Pb], and zinc [Zn]) and lung cancer. However, data from previous studies on pathological cell types are limited, particularly regarding exposure to low-dose soil heavy metal contamination. The purpose of this study was to explore the association between soil heavy metal contamination and lung cancer incidence by specific cell type in Taiwan. Methods: We conducted an ecological study and calculated the annual averages of eight soil heavy metals (i.e., As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) by using data from the Taiwan Environmental Protection Administration from 1982 to 1986. The age-standardized incidence rates of lung cancer according to two major pathological types (adenocarcinoma [AC] and squamous cell carcinoma [SCC]) were obtained from the National Cancer Registry Program conducted in Taiwan from 2001 to 2005. A geographical information system was used to plot the maps of soil heavy metal concentration and lung cancer incidence rates. Poisson regression models were used to obtain the adjusted relative ratios (RR) and 95% confidence intervals (CI) for the lung cancer incidence associated with soil heavy metals. Results: For males, the trend test for lung SCC incidence caused by exposure to Cr, Cu, Hg, Ni, and Zn showed a statistically significant dose-response relationship. However, for lung AC, only Cu and Ni had a significant dose-response relationship. As for females, those achieving a statistically significant dose-response relationship for the trend test were Cr (P = 0.02), Ni (P = 0.02), and Zn (P = 0.02) for lung SCC, and Cu (P < 0.01) and Zn (P = 0.02) for lung AC. Conclusion: The current study suggests that a dose-response relationship exists between low-dose soil heavy metal concentration and lung cancer occurrence by specific cell-type; however, the relevant mechanism should be explored further.