2. Where is boron found?
- 2.1 What is the production and use of boron?
- 2.2 What are the sources of boron releases to the environment?
- 2.3 How does boron react in the environment?
2.1 What is the production and use of boron?
The primary source of both boron and borates is the mining of boron-containing minerals such as colemanite, ulexite, tincal, and kernite. Only certain deposits can be mined economically. These are located in arid regions of Turkey and the USA, and also in Argentina, Chile, Russia, China, and Peru.
The total world production of boron minerals was approximately 2 750 000 tonnes in 1994. About 250 000 tonnes of boron, corresponding to 800 000 tonnes of boron oxide (B2O3), was present in commercial borate products manufactured from these minerals.
Click here for information on measuring methods and units for boron
Commercial borate compounds are used in the manufacture of many different commercial products. These include insulation and textile-grade fibreglass, borosilicate glass, fire retardants, enamels, ceramic glazes, frits, laundry bleach (sodium perborate), agricultural fertilizers and herbicides as well as many other applications. More...
2.2 What are the sources of boron releases to the environment?
Boron enters the environment mainly through natural processes and, to a lesser extent, from human activities.
Natural processes lead to boron releases:
- from boron-containing rocks through weathering;
- from seawater, as boric acid vapour; and
- from volcanic activity and other geothermal releases such as geothermal steam.
Human activities mainly release boron through:
- agricultural use, mainly from the use of borate-containing fertilizers and herbicides;
- burning of domestic waste, crop residues and wood fuel, as boron is present in many plants being necessary for their growth;
- power generation using fossil fuels such as coal and oil;
- waste from borate mining and processing, including the manufacture of glass products. The use of glass products does not release boron, however, as the boron is tightly bound within the glass itself;
- the use of borates and perborates in the home and industry;
- leaching from treated wood or paper; and
- disposal of sewage and sewage sludge.
It is difficult to determine the exact amount of boron which enters the air, soil, or water from many of these sources.
Borates and boric acid are mainly released to air through evaporation from the sea and through volcanic activity in the form of vapour and small particles. To a lesser extent, they can be released to the atmosphere during mining operations, glass and ceramics manufacturing, the application of agricultural fertilizers and herbicides, and from coal-fired power plants. However, boron is not present in the atmosphere at significant levels. Borates do not remain for a long time in the atmosphere, as they generally return to the land or sea during rainfall.
Boron added to soils from agricultural products, including sewage sludge, is discussed further in section 5.
Boron can be released to fresh water such as rivers and also to the water contained within soils. This occurs through weathering processes and, to a much smaller extent, through human discharges such as sewage and treated effluent releases to rivers. More...
2.3 How does boron react in the environment?
Boron is present in the environment in boron-containing compounds called borates. Borates dissolved in water can adsorb onto, and desorb from, the many different surfaces found in rivers and streams. The amount of borate adsorption depends on the water’s pH and the concentration of borate in the water. Borates dissolved in water are very stable, and do not react with oxygen or other chemicals which may be present in the water, or undergo changes from one type of borate to another. Also, animals and plants are not able to convert borates from one form to another by biological processes.
Boron is also adsorbed onto soil particles. The type of soil determines the degree of adsorption and to what extent the adsorption is reversible or irreversible, i.e. whether boron can be removed again by water running through the soil or not. The soil characteristics which affect the amount and type of boron binding to soil include soil pH as well as the amount of salt, organic matter, iron and aluminium oxides and hydroxy-oxides, and clay present in the soil.
Boric acid, the main form in which boron is present in biological fluids in plants and animals, has only a low ability to move into fat. Laboratory experiments have confirmed that boric acid does not bioaccumulate in animals which live in water. Plants do accumulate boron depending on several factors including the pH of the soil, the temperature, the intensity of the available light, and the concentration of other elements in the soil (e.g. calcium and potassium). However, boron does not biomagnify along the aquatic food chain i.e. it does not accumulate to a greater extent in animals which eat the plants, or in predatory animals which eat these animals. More...