This review describes the findings from human and animal studies indicating that B is a dynamic trace element which, in physiological amounts, can affect the metabolism or utilisation of numerous other substances involved in life processes including macrominerals, energy substrates such as triglycerides and glucose, nitrogen containing substances such as amino acids and proteins, reactive oxygen species, and estrogen. Through these effects, B can affect the function or composition of several body systems, including the brain, skeleton and immune system, generally in a beneficial fashion. Moreover, homeostatic mechanisms apparently exist for B because it is rapidly excreted in the urine, does not accumulate in tissues, and is maintained in a relatively narrow range of concentrations in blood of healthy individuals. Thus, even though B has not been conclusively established as essential because a biochemical function for it has not been identified, its beneficial actions suggest that an intake of over 1 mg day-1 (but probably not more than 13 mg day-1) is desirable; diets low in fruits, vegetables, legumes and nuts may not provide this amount of B. Boron may be of more practical nutritional importance than currently acknowledged.

Boron in human and animal nutrition

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 oxo-compounds, 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.

Boron sources, speciation and its potential impact on health.

This paper reviews techniques for determining B concentration and isotopic ratio and their application to soil and plant samples. Boron concentration has been determined utilising spectrophotometry, potentiometry, chromatography, flame atomic emission and absorption spectrometry, inductively coupled plasma (ICP) optical emission (OES) and mass spectrometry (MS), and neutron activation analysis using neutron radiography and prompt-γ activation analysis. Isotopic ratios of B have been measured by ICP–MS, thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS). For isotopic measurements, TIMS and SIMS are more sensitive and provide higher degrees of accuracy and resolution than ICP–MS, however, extensive sample preparation and purification, and time-consuming measurements limit their usefulness for routine analyses.

Techniques for boron determination and their application to the analysis of plant and soil samples

Alkali dilution of blood samples for high throughput ICP-MS analysis—comparison with acid digestion

We report an approach for the accurate and reproducible measurement of boron isotope ratios in natural waters using an MC-ICP-MS (Neptune) after wet chemistry sample purification. The sample matrix can induce a drastic shift in the isotopic ratio by changing the mass bias. It is shown that, if no purification is carried out, the direct measurement of a seawater diluted one hundred times will induce an offset of −7‰ in the isotopic ratio, and that, for the same concentration, the greater the atomic mass of the matrix element, the greater the bias induced. Whatever the sample, it is thus necessary to remove the matrix. We propose a method adapted to water samples allowing purification of 100 ng of boron with a direct recovery of boron in 2 ml of 3% v/v HNO3, which was our working solution. Boron from the International Atomic Energy Agency IAEA-B1 seawater reference material and from the two groundwater reference materials IAEA-B2 and IAEA-B3, was chemically purified, as well as boron from the certified reference material NIST SRM 951 as a test. The reproducibility of the whole procedure (wet chemistry and MC-ICP-MS measurement) was ± 0.4‰ (2s). Accuracy was verified by comparison with positive-TIMS values and with recommended values. Seawater, being homogeneous for boron isotope ratios, is presently the only natural water material that is commonly analysed for testing accuracy worldwide. We propose that the three IAEA natural waters could be used as reference samples for boron isotopes, allowing a better knowledge of their isotopic ratios, thus contributing to the certification of methods and improving the quality of the boron isotopic ratio measurements for all laboratories.

Accurate and High‐Precision Determination of Boron Isotopic Ratios at Low Concentration by MC‐ICP‐MS (Neptune)

The commercial availability of inductively coupled plasma-mass spectrometry technology (ICP-MS) has presented the opportunity to measure the boron concentrations and isotope ratios in a large number of samples with minimal sample preparation. A typical analytical sequence for fecal samples consists of 25 acid blanks, 1 digestion blank, 5 calibration solutions, 4 standard reference material solutions, 10 samples, and 4 natural abundance bias standards. Boron detection limits (3 x 1 sigma) for acid blanks are 0.11 ppb for 10B, and 0.40 ppb for 11B. Isotope ratios were measured in fecal samples with 20 to 50 ppb boron with < 2% relative standard deviation. Rapid washout and minimal memory effects were observed for a 50 ppb beryllium internal standard, but a 200 ppb boron biological sample had a 1.0 ppb boron memory after a 6-min washout. Boron isotope ratios in geological materials are highly variable; apparently this variability is reflected in plants of a fixed natural abundance value for boron requires that a natural abundance ratio be determined for each sample or related data set. The natural abundance variability also prevents quantitation and calculation of isotope dilution by instrument-supplied software. To measure boron transport in animal systems, 20 micrograms of 10B were fed to a fasted rat. During the 3 days after a 10B oral dose, 95% of the 10B was recovered from the urine and 4% from the feces. Urinary isotope ratios, 11B/10B, changed from a natural abundance of 4.1140 to an enriched value of 0.95077, a 77% change.(ABSTRACT TRUNCATED AT 250 WORDS)

Deb Hoff

Papers

Use of inductively coupled plasma-mass spectrometry in boron-10 stable isotope experiments with plants, rats, and humans.