Schlebusch CM, Gattepaille LM, Engström K, Vahter M, Jakobsson M, Broberg K. Human Adaptation to Arsenic-Rich Environments. Molecular Biology and Evolution. 2015 Mar 3. pii: msv046.
Adaptation drives genomic changes; however, evidence of specific adaptations in humans remains limited. We found that inhabitants of the northern Argentinean Andes, an arid region where elevated arsenic concentrations in available drinking water is common, have unique arsenic metabolism, with efficient methylation and excretion of the major metabolite dimethylated arsenic and a less excretion of the highly toxic monomethylated metabolite. We genotyped women from this population for 4,301,332 single nucleotide polymorphisms (SNPs) and found a strong association between the AS3MT (arsenic [+3 oxidation state] methyltransferase) gene and mono- and dimethylated arsenic in urine, suggesting that AS3MT functions as the major gene for arsenic metabolism in humans. We found strong genetic differentiation around AS3MT in the Argentinean Andes population, compared with a highly related Peruvian population (FST = 0.014) from a region with much less environmental arsenic. Also, 13 of the 100 SNPs with the highest genome-wide Locus-Specific Branch Length occurred near AS3MT. In addition, our examination of extended haplotype homozygosity indicated a selective sweep of the Argentinean Andes population, in contrast to Peruvian and Colombian populations. Our data show that adaptation to tolerate the environmental stressor arsenic has likely driven an increase in the frequencies of protective variants of AS3MT, providing the first evidence of human adaptation to a toxic chemical.
Paper is here (Open Access).
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Grellier J, Rushton L, Briggs DJ, Nieuwenhuijsen MJ. Assessing the human health impacts of exposure to disinfection by-products – A critical review of concepts and methods. Environment International. 2015 Mar 9;78:61-81. doi: 10.1016/j.envint.2015.02.003.
Understanding the public health implications of chemical contamination of drinking water is important for societies and their decision-makers. The possible population health impacts associated with exposure to disinfection by-products (DBPs) are of particular interest due to their potential carcinogenicity and their widespread occurrence as a result of treatments employed to control waterborne infectious disease. We searched the literature for studies that have attempted quantitatively to assess population health impacts and health risks associated with exposure to DBPs in drinking water. We summarised and evaluated these assessments in terms of their objectives, methods, treatment of uncertainties, and interpretation and communication of results. In total we identified 40 studies matching our search criteria. The vast majority of studies presented estimates of generic cancer and non-cancer risks based on toxicological data and methods that were designed with regulatory, health-protective purposes in mind, and therefore presented imprecise and biased estimates of health impacts. Many studies insufficiently addressed the numerous challenges to DBP risk assessment, failing to evaluate the evidence for a causal relationship, not appropriately addressing the complex nature of DBP occurrence as a mixture of chemicals, not adequately characterising exposure in space and time, not defining specific health outcomes, not accounting for characteristics of target populations, and not balancing potential risks of DBPs against the health benefits related with drinking water disinfection. Uncertainties were often poorly explained or insufficiently accounted for, and important limitations of data and methods frequently not discussed. Grave conceptual and methodological limitations in study design, as well as erroneous use of available dose-response data, seriously impede the extent to which many of these assessments contribute to understanding the public health implications of exposure to DBPs. In some cases, assessment results may cause unwarranted alarm among the public and potentially lead to poor decisions being made in sourcing, treatment, and provision of drinking water. We recommend that the assessment of public health impacts of DBPs should be viewed as a means of answering real world policy questions relating to drinking water quality, including microbial contaminants; that they should be conducted using the most appropriate and up-to-date data and methods, and that associated uncertainties and limitations should be accounted for using quantitative methods where appropriate.
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