The article by Smith et al. assesses the cancer risks associated with arsenic in drinking water, particularly focusing on liver, lung, kidney, and bladder cancers. The study draws on large population studies in Taiwan, where well water contains high levels of arsenic (170-800 μg/L), to establish dose-response relationships between cancer risks and arsenic concentrations. Key findings include: 1. **Skin Cancer**: Well-established link between inorganic arsenic and skin cancer, with high prevalence rates observed in areas with high arsenic levels. 2. **Liver Cancer**: Evidence suggests a causal relationship between arsenic ingestion and liver cancer, supported by case reports, studies in arsenic-poisoned winegrowers, and epidemiological studies in Taiwan. 3. **Lung Cancer**: Strong evidence of a link between lung cancer and arsenic ingestion, supported by case reports and epidemiological studies. 4. **Kidney and Bladder Cancer**: Evidence of a dose-response relationship between arsenic levels in water and cancer mortality rates for these sites, with significant increases in risk observed at higher arsenic concentrations. The study also examines the possibility of a threshold for arsenic carcinogenicity, concluding that there is no evidence to support a threshold, as methylation of inorganic arsenic does not appear to prevent cancer risks. The article estimates that for the current U.S. drinking water standard of 50 μg/L, the lifetime risk of dying from liver, lung, kidney, or bladder cancer due to arsenic in drinking water could be as high as 13 per 1000 persons. The authors recommend measures to reduce arsenic levels in water supplies, noting that about 350,000 people in the U.S. may drink water with levels above 50 μg/L, and over 2.5 million people may be supplied with water containing more than 25 μg/L. The article compares these risks to those from environmental tobacco smoke and radon, highlighting the serious environmental cancer risks posed by arsenic in drinking water. It also discusses the potential benefits of arsenic as a micronutrient, but concludes that the risks of cancer outweigh any potential health benefits.The article by Smith et al. assesses the cancer risks associated with arsenic in drinking water, particularly focusing on liver, lung, kidney, and bladder cancers. The study draws on large population studies in Taiwan, where well water contains high levels of arsenic (170-800 μg/L), to establish dose-response relationships between cancer risks and arsenic concentrations. Key findings include: 1. **Skin Cancer**: Well-established link between inorganic arsenic and skin cancer, with high prevalence rates observed in areas with high arsenic levels. 2. **Liver Cancer**: Evidence suggests a causal relationship between arsenic ingestion and liver cancer, supported by case reports, studies in arsenic-poisoned winegrowers, and epidemiological studies in Taiwan. 3. **Lung Cancer**: Strong evidence of a link between lung cancer and arsenic ingestion, supported by case reports and epidemiological studies. 4. **Kidney and Bladder Cancer**: Evidence of a dose-response relationship between arsenic levels in water and cancer mortality rates for these sites, with significant increases in risk observed at higher arsenic concentrations. The study also examines the possibility of a threshold for arsenic carcinogenicity, concluding that there is no evidence to support a threshold, as methylation of inorganic arsenic does not appear to prevent cancer risks. The article estimates that for the current U.S. drinking water standard of 50 μg/L, the lifetime risk of dying from liver, lung, kidney, or bladder cancer due to arsenic in drinking water could be as high as 13 per 1000 persons. The authors recommend measures to reduce arsenic levels in water supplies, noting that about 350,000 people in the U.S. may drink water with levels above 50 μg/L, and over 2.5 million people may be supplied with water containing more than 25 μg/L. The article compares these risks to those from environmental tobacco smoke and radon, highlighting the serious environmental cancer risks posed by arsenic in drinking water. It also discusses the potential benefits of arsenic as a micronutrient, but concludes that the risks of cancer outweigh any potential health benefits.