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5. What are the effects of boron on organisms in the environment?

    The effect of boron has been determined for several types of organisms in the environment, but more information is available for some types of organism than for others. Some of the information covers the effects of short-term exposure to boron, while other information focuses on long-term or chronic exposure. The information may be available for several types of organism within a group – for example, for several types of invertebrates – or it may be available for only one type. The amounts and types of information available for different species are important in the overall judgement of the relative sensitivity of environmental organisms to boron in the environment.

    The table below shows the information available for different organisms, and the types of tests and the approximate number of different species for which these tests were carried out.

    Table: "Reported critical boron levels for several types of environmental organism"

    Type of organism Type of effect(s) reported Boron concentration in the water
    Bacteria Mixture of acute and chronic effects, for several types of bacteria 8 - 340 mg/litre (mainly above 18 mg/litre)
    Protozoa First very small effects, for 2 types of protozoa 0.3 - 18 mg/litre
    Freshwater green algae Highest concentration with no effect (NOEC), for several types of algae 10 - 24 mg/litre
    Blue-green algae First very small effect for 1 type of blue-green algae 20 mg/litre
    Invertebrates Acute effects for several types of invertebrates 95 to 1376 mg/litre (mainly 100-200 mg/litre)
    Water flea (Daphnia magna) Highest concentration with no effect (NOEC), found in many chronic tests for this one invertebrate type 6 - 10 mg/litre
    Fish Acute effects in several types of fish 10 to nearly 300 mg/litre
    Rainbow trout Chronic tests with standard laboratory water (NOEC) 0.009 - 0.103 mg/litre
    Rainbow trout Chronic tests in several natural waters (NOEC) 0.75 - > 18 mg/litre

    The data in the table show that bacteria are much less sensitive to boron, compared to other chemicals. Protozoa are somewhat more sensitive. Algae, for which boron is an essential nutrient, also have low sensitivity to boron. Invertebrates also have a low boron sensitivity, as determined from many long-term studies. Fish are the most sensitive species to boron.

    The experts assembled by the World Health Organization (WHO) to write the IPCS document decided, based on the sensitivity of the various tests and the numbers of tests for the different types of organisms, that a boron level of 1 mg/litre water would cause no adverse effect on the environment. As well as information on the toxicity of boron in the aquatic environment, information is also available for one predator which eats aquatic species. In mallard, a water fowl species, boron can affect duckling growth at dietary intake levels of 30 - 300 mg/kg weight of animal, and can reduce survival at 1000 mg/kg weight of animal.

    Boron is an essential micronutrient for plants, but different plant species require different boron levels for optimum growth. Boron plays several roles within the plant cell: in cell division, in the metabolism, and in the cell membrane. As a result, boron (in the form of borates) occurs naturally in fruits, nuts, and vegetables (see table on Boron content of some common foods in question 3.2).

    In plants, there is only a narrow margin between boron deficiency and excess boron uptake leading to toxicity. Boron deficiencies in terrestrial plants have been reported in many countries. Boron deficiency occurs when boron leaches out of the soil, particularly in humid regions with light-textured, acid soils. Boron excesses usually occur in soil solution, i.e. the water found in the soil containing soluble material, from geologically young deposits, arid soils and soils derived from marine sediments. It also occurs in soils contaminated by human activities, such as releases from coal-fired power plants and mining operations. Irrigation water containing boron is one of the main sources of high boron levels leading to toxicity on agricultural land. More...

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