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 good||except for very sensitive crops|
|0.5 to 2.0 some risks||many crops must be excluded|
|> 2.0 dangerous||may 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.