Boron is widely distributed in surface water and groundwater. Average surface water concentration in the United States is about 0.1 mg boron/L (Butterwick et al. 1989; EPA 1986b), but concentrations vary greatly, depending on boron content of local geologic formations and anthropogenic sources of boron (Butterwick et al. 1989). A survey of U.S. surface waters detected boron in 98% of 1,577 samples at concentrations ranging from 0.001 to 5 mg boron/L. Mean concentrations calculated for the 15 drainage basins in the continental United States ranged from 0.019 mg boron/L in the Western Great Lakes Basin to 0.289 mg boron/L in the Western Gulf Basin (Butterwick et al. 1989). The concentration of boron in sea water is about 4.5 mg/L (Butterwick et al. 1989; EPA 1986b).

Several studies have measured boron concentrations in water in those areas of California with boron-rich deposits. Reported high boron concentrations in surface waters ranged from 15 mg boron/L in coastal drainage waters to 360 mg boron/L in a boron-rich lake (Butterwick et al. 1989; Deverel and Millard 1988). Mean boron concentration in a California river ranged from 0.30 to 0.50 mg boron/L over a 20-year period (Butterwick et al. 1989). Reported boron concentrations in groundwater in the San Joaquin Valley ranged from 0.14 to 120 mg boron/L with a median concentration of about 4 mg boron/L (Butterwick et al. 1989; Deverel and Millard 1988). Waggott (1969) reports that groundwater boron concentrations greater than 100 mg/L are common in California.

Drinking water surveys generally do not report boron concentration. However, concentrations of boron in tap water have been reported in a range of 0.007-0.2 mg/L in the United States and England (Choi and Chen 1979; Waggott 1969), and the National Inorganics and Radionuclides Survey completed in 1987 reported relatively widespread occurrence of boron in 989 public water supplies (NIRS 1987). Boron concentrations ranged from less than 0.005 to greater than 2 mg/L, with concentrations of up to 0.4 mg/L in 90% of systems (NIRS 1987). A survey of 969 public water supply systems showed 99% contained boron at less than 1 mg/L. The maximum level measured was 3.28 mg/L (McCabe et al. 1970).

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