Toxic boron concentrations

Maternal blood boron concentrations were elevated in all boron groups in a dose-dependent manner. On gestational day 20, blood B concentrations of 1.3 mg/kg FW were associated with the no-observed-adverse-effect level (NOAEL) and 1.53 mg/kg FW with the lowest-observed-adverse effect level (LOAEL), equivalent to dietary intakes of 10 and 13 mg B/kg BW daily, respectively, for developmental toxicity. Developmental toxicity persisted postnatally only at 25 mg B/kg BW daily, a dose associated with more than a 10-fold increase in maternal blood B (2.8 mg B/kg FW) vs. 0.23 mg/kg FW in controls (34)... 

Boron concentration in brines can vary from 10 to 100 mg L 1. In the soil solution, a boron concentration as low as 4 mg L-1 is toxic to some crops. 

Table II. Toxic Boron Concentrations of Saturation Extracts for Sensitive, Semitolerant, and Tolerant Crop Species ...

The fact that boron is essential to plants is firmly established. However, when boron concentrations in irrigation waters exceed 2.0 mg/L, extensive plant toxicity should be... 

A number of carboranyl porphyrins have been obtained on the basis of the natural porphyrin derivatives, such as deuteroporphyrin IX and hematoporphyrin IX, and two of than, VCDP and BOPP (Figure 9.12), have been extensively studied in animals. BOPP was reported to have a tumor-normal brain ratio from 13 1 to 400 1 for different glioma models [117,118]. High boron levels in tumor (>60 pg °B/g tumor) were achieved in these animal studies. However, data obtained from a human Phase I clinical trial showed that under intravenous injection BOPP does not deliver therapeutic concentrations of boron to the tumors of glioblastoma patients, and dose escalation is prevented by the toxicity of this compound. Nevertheless, BOPP has shown some promise as an effective PDT photosensitizer [119-121]. More recently, it was demonstrated that convection-enhanced delivery of BOPP significantly enhances the boron concentration in tumors and produces very favorable tumor-brain and tumor-blood ratios [122]. 

Health and Safety Factors. Boron trifluoride is primarily a pulmonary irritant. The toxicity of the gas to humans has not been reported (58), but laboratory tests on animals gave results ranging from an increased pneumonitis to death. The TLV is 1 ppm (59,60). Inhalation toxicity studies in rats have shown that exposure to BF at 17 mg/m resulted in renal toxicity, whereas exposure at 6 mg/m did not result in a toxic response (61). Prolonged inhalation produced dental fluorosis (62). High concentrations bum the skin similarly to acids such as HBF and, if the skin is subject to prolonged exposure, the treatment should be the same as for fluoride exposure and hypocalcemia. No chronic effects have been observed in workers exposed to small quantities of the gas at frequent intervals over a period of years. 

For all natural waters, boron is one of their constituents with varying concentrations from minute traces to several ppm (parts per million). It is essential for plant growth but is exceedingly toxic at concentration slightly above optimum. Boron tolerances vary depending upon climate, and crop varieties. Relative boron tolerances of agricultural crops are presented in Table 3 [12]. 

Finally, the most popular extractant for boron is boiling water (eg, McGeehan et al., 1989) and it is agreed in many countries that concentrations below 1 mg B kg-1 soil imply the likelihood of deficiencies in susceptible crops. In England and Wales, the National Agricultural Advisory Service classifies boron levels as follows 0-0.5 mg L 1 indicates severe deficiency, 0.6-1.0 mg L 1 implies a likelihood of deficiency and values >4.1 mgL 1 indicate the possibility of boron toxicity. 

Li 2.5 Tolerated by most crops up to 5 mg L-1 mobile in soil. Toxic to citms at low concentrations (<0.075 mg L 1). Acts similarly to boron... 

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