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 μg l⁻¹ (ave. 26 μg l⁻¹, median 2 μg l⁻¹). Among 253 respondents who consumed water: (a) 177/253 (70%) of tap water samples contained more than 10 μg l⁻¹ total inorganic arsenic (ave. 66 μg l⁻¹, median 20 μg 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 μg l⁻¹) to a maximum of 610 μg l⁻¹ (ave. 30 μg l⁻¹, median 3 μg l⁻¹). Log₁₀ concentrations of tungsten and total arsenic in consumed water were positively correlated (log₁₀[W]=−0.400 + 0.703(log₁₀[As^T]), 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.