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6. Conclusions

    Boron is a naturally occurring element that is found in nature in compounds called borates. Borates are found in the oceans, sedimentary rocks, coal, shale, and some soils. Borates are naturally released into the environment from the oceans, volcanic activity and other geothermal releases such as geothermal steam, and weathering of clay-rich sedimentary rocks. Boron is also released, to a lesser extent, from sources due to human activity.

    Boron is an essential micronutrient for plants, with levels of boron required for optimum growth depending on the plant species. Boron deficiency in terrestrial plants has also been observed in many parts of the world. In some plants, there is but a narrow range between boron deficiency and toxicity.

    The risk of adverse effects of boron on the aquatic ecosystem is low, because general levels of boron in the environment are below the no-effect concentration (1 mg/litre water). In a few boron-rich environments, natural levels will be higher. However, it is reasonable to assume that aquatic organisms in such habitats are adapted to the local conditions.

    Humans are primarily exposed to boron through food and drinking-water. The mean daily intake of boron via the diet is about 1.2 mg per person per day and the estimated mean boron concentration in drinking-water is between 0.1 and 0.3 mg/litre. In humans and animals, most of the boric acid and borate are absorbed from the gastrointestinal and respiratory tracts and rapidly excreted in the urine.

    Animal experiments have shown that boron in the form of both boric acid and borate can harm reproduction and development at levels that are approximately 100 to 1000 times greater than normal exposure levels. There is insufficient toxicity data on humans. The Tolerable Intake (TI) of boron was set at 0.4 mg/kg body weight per day.

    These conclusions have led to the formulation of a series of recommendations. More...

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