Boron is one of the micronutrients essential for plant growth. It may be present naturally in water, or find its way into a watercourse through industrial waste effluents. Boron in excess of 2.0 mg/L in irrigation water can be detrimental to plant growth,  some plants may even be adversely affected by concentrations lower than 1.0 mg/L (ppm). The United States Department of Agriculture (USDA) reports the following classification:

Boron (ppm)Effect on crops
< 0.5 goodexcept for very sensitive crops
0.5 to 2.0 some risksmany crops must be excluded
> 2.0 dangerousmay only be used for very tolerant crops

The average abundance of boron in soils is 18 to 63 ppm, in streams it is 10 μg/L, and in groundwaters it is 0.01 to 10 mg/L. The most common form of boron in natural waters is H3BO3. The most important mineral is borax, which is used in the preparation of heat-resistant glasses, detergents, porcelain enamels, fertilizers, and fiberglass.

Drinking water rarely contains more than 1 mg B/L and generally less than 0.1 mg/L, concentrations considered safe for human consumption. The ingestion of large amounts of boron can affect the central nervous system, with protracted ingestion resulting in a syndrome known as borism.

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