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In parts of the western United States groundwater used for drinking water contains high concentrations of metals, including arsenic. In a rural county in Nevada, USA, we measured concentrations of arsenic and tungsten and the proportion of arsenic occurring in trivalent form (As(III)) in tap water samples from private domestic wells in 307 households. The proportion of arsenic occurring as As(III) ranged from 0 to 100% (ave. 21%, median 1%). Tungsten concentrations ranged from 0 to 610 μmg l-1 (ave. 26 μmg l-1, median 2 μmg l-1). Among 253 respondents who consumed water: (a) 177/253 (70%) of tap water samples contained more than 10 μmg l-1 total inorganic arsenic (ave. 66 μmg l-1, median 20 μmg l-1); (b) As(III) occurred as a small proportion of total arsenic in most samples (ave. 22%, median 3%); and (c) tungsten occurred in concentrations ranging from below the detection limit (3 μmg l-1) to a maximum of 610 μmg l-1 (ave. 30 μmg l-1, median 3 μmg l-1). Log10 concentrations of tungsten and total arsenic in consumed water were positively correlated (log10[W] = 20.400 + 0.703(log10[AsT]), p = 0.000+, adj. r² = 0.53). This suggests that householders in this area were likely to be exposed to both metals simultaneously, given that 253/307 of the respondents (82%) reported consuming tap water. [ABSTRACT FROM AUTHOR]

In many rural areas domestic drinking water needs are met by a mixture of public water supplies and private water supplies. Private supplies are not subject to the regulations and management requirements of the Safe Drinking Water Act (SDWA). Amendments to the SDWA recently lowered the standard for arsenic from 50 to 10 ppb in public water supplies (effective in 2006). Churchill County, Nevada, has approximately 25,000 residents. Slightly more than half (13,500) rely on private domestic wells for water supply. Ample data and media publicity about high arsenic concentrations in water supplies and a federally led investigation of a Ieukaemia cluster suggested that residents of the county would be aware that arsenic concentrations in private wells were highly likely to exceed the 10 ppb standard. A survey carried out in 2002 showed that a majority of respondents (72%) consumed water from private wells and among them a minority (38%) applied treatment. Maximum, median and minimum concentrations of arsenic from all samples (n = 351) were 2,100, 26 and <3 ppb, respectively. Seventy-four per cent of all samples exceeded 10 ppb. A majority (87%) of those who applied treatment consumed tap water. The relatively low rate of application of treatment suggested that these rural residents did not recognize that consumption could have associated health risks. However, those who applied treatment were ∼0.3 times as likely to be consuming water with > 10 ppb arsenic than those who consumed water that was not treated. in areas where concentrations of arsenic have been demonstrated to be high, it may be important to conduct a focused educational effort for private well owners to ensure that they take the steps needed to assess and reduce risks associated with contaminants found in tap water, including arsenic. An educational effort could include promoting sampling efforts to determine the magnitude of arsenic concentrations, explaining the risk associated with arsenic consumption and providing information about choices for home treatment systems that are likely to be effective in removing arsenic. This may be especially important in rural areas where adverse health effects are not evident to local populations. [ABSTRACT FROM AUTHOR]