Boron occurs in soils at concentrations ranging from 10 to 300 mg/kg (average 30 mg/kg), depending on the type of soil, amount of organic matter, and amount of rainfall. Concentrations of boron in surface water are dependent on such factors as the geochemical nature of the drainage area, proximity to marine coastal regions, and inputs from industrial and municipal effluent discharges. Concentrations of boron in surface water range widely, from 0.001 to as much as 360 mg/litre. However, mean boron concentrations for waters of Europe, Pakistan, Russia, and Turkey are typically well below 0.6 mg/litre. Concentrations of boron in water in Japan, South Africa, and South America are generally below 0.3 mg/litre. Typical boron concentrations in North American waters are below 0.1 mg/litre, with about 90% at or below 0.4 mg/litre.
Boron accumulates in aquatic and terrestrial plants but does not magnify through the food-chain. Concentrations of boron have been shown to range between 26 and 382 mg/kg in submerged aquatic freshwater plants, from 11.3 to 57 mg/kg in freshwater emergent vegetation, and from 2.3 to 94.7 mg/kg dry weight in terrestrial plants. Based on wet weights, boron concentrations in marine invertebrates and fish are similar to the levels found in the exposure media, between 0.5 and 4 mg/kg. The bioconcentration factor for two freshwater fish species was found to be 0.3.
Boron concentrations in ambient air range from <0.5 to approximately 80 ng/m3, with an average over the continents of 20 ng/m3.