Arsenic, As((III)), and tungsten in Nevada County's private water supplies

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 microg l(-1) (ave. 26 microg l(-1), median 2 microg l(-1)). Among 253 respondents who consumed water: (a) 177/253 (70%) of tap water samples contained more than 10 microg l(-1) total inorganic arsenic (ave. 66 microg l(-1), median 20 microg 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 microg l(-1)) to a maximum of 610 microg l(-1) (ave. 30 microg l(-1), median 3 microg l(-1)). Log(10) concentrations of tungsten and total arsenic in consumed water were positively correlated (log(10)[W] = -0.400 + 0.703(log(10)[As(T)]), p = 0.000+, adj. r(2) = 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.