Boron sources, speciation and its potential impact on health

Abstract

The behaviour of boron (B) and its fate in the environment remains in many respects obscure. The major B sources and fluxes seem to have been identified, although there are many uncertainties about the magnitude and importance of each; published evaluations vary greatly. Little is known about B speciation of living matter-bearing formations, i.e. soils, natural waters, and sediments. Many authors suppose that B in nature occurs only as oxocompounds, although, natural inorganic and organic B compounds and complexes have been described. Moreover, the most common approach to B biogeochemistry in terms of inorganic B compounds (as boric acid and borates) seems to oversimplify the matter. Data on the physiological functions of B are fragmentary and often contradictory. Some data exists on endemic symptoms and diseases among humans and grazing cattle that are supposedly triggered by B abundance in the natural environment. Unfortunately, the published data are scarce and vague. In this paper, we review the up-to date references on B sources, turnover, and speciation in the environment and the element potential impact on health.

Effect of Boron on Human Health

“…This element has one less valence electron than valence orbitals. Due to small size and high ionization energies, boron results in covalent bonding rather than metallic bonding [1]. B is a rare element in the Earth, representing only 0.001%.…”

Boron

“…The global abundance of B is extremely low: about 10 29 -fold less than that of hydrogen, and 10 26 -fold less than that of carbon, nitrogen or oxygen (Kot, 2009). …”

“…Both B and Si have a strong tendency to form covalently bonded molecular networks. However, B has one less electron than the number of valence orbitals, which makes its chemistry markedly different from that of Si, and this generates a dominant effect on the behaviour of B in chemical processes (Kot, 2009).…”

“…Therefore, B easily leaches out from soil with high rainfall, resulting in the limited B accessibility for plants. In contrast, arid and semiarid areas often have B concentrated surface horizon due to the less leaching and capillary action followed by water evaporation, leading to B toxicity in plants (Kot, 2009). In addition to natural B sources, anthropogenic B excretions caused through irrigation agriculture and over-fertilisation easily increase soil B levels as toxic (Nable et al, 1997).…”

“…In addition to natural B sources, anthropogenic B excretions caused through irrigation agriculture and over-fertilisation easily increase soil B levels as toxic (Nable et al, 1997). The other sources including waste from surface mining, fly ash and industrial chemicals are also important (Kot, 2009).…”