Cancer risk assessment from exposure to trihalomethanes in tap water and swimming pool water

We investigated the concentration of trihalomethanes （THMs） in tap water and swimming pool water in the area of the Nakhon Path- om Municipality during the period April 2005-March 2006. The concentrations of total THMs, chloroform, bromodichloromethane, dibromochloromethane and bromoform in tap water were 12.70-41.74, 6.72-29.19, 1.12-11.75, 0.63-3.55 and 0.08-3.40 μg/L, respectively, whereas those in swimming pool water were 26.15-65.09, 9.50-36.97, 8.90-18.01, 5.19-22.78 and ND-6.56 μg/L, respectively. It implied that the concentration of THMs in swimming pool water was higher than those in tap water, particularly, brominated-THMs. Both tap water and swimming pool water contained concentrations of total THMs below the standards of the World Health Organization （WHO）, European Union （EU） and the United States Environmental Protection Agency （USEPA） phase Ⅰ, but 1 out of 60 tap water samples and 60 out of 72 swimming pool water samples contained those over the Standard of the USEPA phase Ⅱ. From the two cases of cancer risk assessment including Case Ⅰ Non-Swimmer and Case Ⅱ Swimmer, assessment of cancer risk of nonswimmers from exposure to THMs at the highest and the average concentrations was 4.43×10^-5 and 2.19×10^-5, respectively, which can be classified as acceptable risk according to the Standard of USEPA. Assessment of cancer risk of swimmers from exposure to THMs at the highest and the average concentrations was 1.47×10^-3 and 7.99×10^-4, respectively, which can be classified as unacceptable risk and needs to be improved. Risk of THMs exposure from swimming was 93.9%-94.2% of the total risk. Cancer risk of THMs concluded from various routes in descending order was： skin exposure while swimming, gastro-intestinal exposure from tap water intake, and skin exposure to tap water and gastro-intestinal exposure while swimming. Cancer risk from skin exposure while swimming was 94.18% of the total cancer risk.

Carcinogen-Macromolecular Adducts As Biomarkers in Human Cancer Risk Assessment

Substantial data have been generated during the past 5 years in both experimental systems and human populations which shed light on the potential role of carcinogen-macromolecular adducts in human cancer risk assessment. The use of DNA and protein adducts is based on the fundamental concept in chemical carcinogenesis that most genotoxins are metabolized to electrophilic 'ultimate' carcinogens that are capable of forming covalent adducts with cellular macromolecules. This report examines the relative usefulness and limitations of using DNA and protein adducts and related techniques for assessing human exposure to genotoxic carcinogens. Data discussed in this report clearly demonstrate that these biomarkers not only allow early detection of potential cancer hazard in humans, but they can also significantly increase the power of conventional cancer epidemiological studies in determining true causal relationships. In addition, such biomarkers can improve extrapolation of cancer risks from laboratory animals to humans or from one human population to another.

Seasonal variation effects on the formation of trihalomethane during chlorination of water from Yangtze River and associated cancer risk assessment

For the system of water samples collected from Yangtze River,the effects of seasonal variation and Fe（III） concentrations on the formation and distribution of trihalomethanes （THMs） during chlorination have been investigated.The corresponding lifetime cancer risk of the formed THMs to human beings was estimated using the parameters and procedure issued by the US EPA.The results indicated that the average concentration of THMs （100.81 μg/L） in spring was significantly higher than that in other seasons,which was related to the higher bromide ion concentration resulted from the intrusion of tidal saltwater.The total cancer risk in spring reached 8.23 × 10 ？5 and 8.86 × 10 ？5 for males and females,respectively,which were about two times of those in summer under the experimental conditions.Furthermore,it was found that the presence of Fe（III） resulted in the increased level of THMs and greater cancer risk from exposure to humans.Under weak basic conditions,about 10% of the increment of THMs from the water samples in spring was found in the presence of 0.5 mg/L Fe（III） compared with the situation without Fe（III）.More attention should be given to the effect of the coexistence of Fe（III） and bromide ions on the risk assessment of human intake of THMs from drinking water should be paid more attention,especially in the coastland and estuaries.