Background Colorectal cancer has increased in Middle Eastern countries and exposure to environmental pollutants such as heavy metals has been implicated. However, data linking them to this disease are generally lacking. This study aimed to explore the spatial pattern of age-standardized incidence rate (ASR) of colon cancer and its potential association with the exposure level of the amount of heavy metals existing in rice produced in north-eastern Iran. Methods Cancer data were drawn from the Iranian population-based cancer registry of Golestan Province, north-eastern Iran. Samples of 69 rice milling factories were analysed for the concentration levels of cadmium, nickel, cobalt, copper, selenium, lead and zinc. The inverse distance weighting (IDW) algorithm was used to interpolate the concentration of this kind of heavy metals on the surface of the study area. Exploratory regression analysis was conducted to build ordinary least squares (OLS) models including every possible combination of the candidate explanatory variables and chose the most useful ones to show the association between heavy metals and the ASR of colon cancer. Results The highest concentrations of heavy metals were found in the central part of the province and particularly counties with higher amount of cobalt were shown to be associated with higher ASR of men with colon cancer. In contrast, selenium concentrations were higher in areas with lower ASR of colon cancer in men. A significant regression equation for men with colon cancer was found (F(4,137) = 38.304, P < .000) with an adjusted R2 of 0.77. The predicted ASR of men colon cancer was − 58.36 with the coefficients for cobalt = 120.33; cadmium = 80.60; selenium = − 6.07; nickel = − 3.09; and zinc = − 0.41. The association of copper and lead with colon cancer in men was not significant. We did not find a significant outcome for colon cancer in women. Conclusion Increased amounts of heavy metals in consumed rice may impact colon cancer incidence, both positively and negatively. While there were indications of an association between high cobalt concentrations and an increased risk for colon cancer, we found that high selenium concentrations might instead decrease the risk. Further investigations are needed to clarify if there are ecological or other reasons for these discrepancies. Regular monitoring of the amount of heavy metals in consumed rice is recommended.

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Background: Nowadays, the heavy metals pollution is increasing and the accumulation of these metals in food has posed adverse effects on humans such as inducing various kinds of cancer and non-cancer diseases. The Northeast of Iran, especially Torkman Sahra, has the maximum number of patients with esophageal cancer. Objectives: We investigated the levels of four heavy metals (Zn, Cd, Pb, and Cu) in cucumber and tomato samples in Golestan province, an endemic esophageal cancer region. We evaluated the levels and potential health risks of heavy metals in vegetable samples of Northeastern Iran. Methods: The heavy metal content of the samples was determined by polarography methods. All sample preparation and digestion procedures were carried out according to the Standard Methods for the Examination of Water and Wastewater, 20th Edition. Results:The results showed that Cd and Pb concentrations in cucumber and tomato were estimated to be respectively 2.4 to 14.4 and 1.6 to 7 folds higher whereas Zn and Cu levels were lower than the maximum permissible limit for vegetables. The amounts of Pb intake through the consumption of these vegetables were determined more than the provisional tolerable daily intake. The total non-cancer and cancer risk results indicated that the investigated region was relatively unsuitable for growing the vegetables in the view of the risk of the elevated intakes of heavy metals adversely affecting food safety for consumers. Pb was the heavy metal posing non-cancer risks while Cd caused the greatest cancer risk. Conclusions: It was concluded that due to the toxic effects of cadmium and lead, we should be more serious to reduce pollution levels in this region.

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