Boron has two forms of stable isotopes (10B, 11B) as well as 13 forms of radioactive isotopes (ranging from 7B through to 21B, not including the stable forms). Stable forms of boron are the only naturally occurring isotopes with 10B making up 20% of natural boron and 11B making up 80%.
Given the extensive use of boron in many different products, it is released to the environment on a regular basis. Based on data provided by the US Environmental Protection Agency (EPA, 1976), in 1972 alone, a total of 35.5 kilotons of boron was released into the environment, 73% of which was directly introduced to the water. The release of boron is particularly problematic as boron cannot be destroyed in the environment, but rather it can change its form by separating and becoming attached to other particles in soils, sediments, and water. This boron can eventually make its way into food (vegetables and fruit) given its an essential nutrient for plant growth.
Natural denitrification and mixing processes may extensively alter the isotopic values of nitrate contamination (δ15N and δ18O), making the differentiation of urban and agricultural origins of nitrate is very challenging. As δ11B is not affected by fractionation, the isotopic ratio of boron combined with O- and N-isotopic ratios of nitrate prove to be a very powerful tool for tracing contaminant sources.
Read more on using boron isotopes to enhance nitrate source tracking.
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