Variation in cancer incidence in northeastern Belgium and southeastern Netherlands seems unrelated to cadmium emission of zinc smelters
Exposure to cadmium has been established to be carcinogenic for humans by the International Agency for Research on Cancer, but this is mainly based on studies with occupational exposures. The substantial 100 year long emission of cadmium by three zinc smelters in the Kempen area across the Dutch-Belgian border might have affected the incidence of cancer in this region. Following a study of increased risks of lung cancer due to cadmium emission (hazard ratio was 4.2 for high vs. low cadmium exposure areas in that study), we used data from the three regional population-based cancer registries, covering an area with 2.9 million inhabitants. Analyses of observed incidence were carried out for all cancers and cancer of the lung, kidney, bladder, prostate, testis, and breast separately. At the municipality level standardized incidence ratios were calculated and smoothed using a Poisson-gamma or a conditional autoregressive model. To detect clusters and to calculate an observed/expected ratio (O/E ratio) for each cluster a spatial scan statistic was applied. Significantly increased cancer incidence rates were found at a multimunicipality level for female lung cancer (O/E ratio=1.2), male and female bladder cancer (O/E ratio male=1.8, O/E ratio female=1.7), and prostate cancer (O/E ratio=1.3), none of these clusters being located specifically around the area of the zinc smelters. Therefore, the long term emission of cadmium by the zinc smelters in the Kempen area did not seem to lead to an increase in the incidence of all cancers, and lung, kidney, bladder, prostate, testicular, or breast cancer.