What can we learn from epidemiological studies on chronic boron exposure?

Boric acid and sodium borates are classified as toxic to reproduction and development under category 1B, with the hazard statement of H360FD (May damage fertility. May damage the unborn child) in the EU-CLP regulation. This classification triggered environmental and occupational epidemiology studies on boron in China, Türkiye, and Argentina. The highest mean total daily boron exposure (DBE) levels in mining areas or processing plants in China and Türkiye were 41.2 and 47.17 mg/day, respectively. These DBE levels are higher than the proposed reference doses (RfDs) for the developmental (9.6 mg B/day) and reproductive effects (20.3 mg B/day) of boron in females and males. Despite these high exposure levels in occupational settings, boron-mediated reproductive and developmental effects have not been reported. Blood (or serum) boron concentrations were also reported in these studies. The highest mean blood-boron concentration reported for the boron-exposed male workers in Türkiye is 570.6 ng B/g (ppb). This blood-boron concentration is still much lower than the blood boron concentrations corresponding to the no observed adverse effect level (NOAEL) for both developmental and reproductive effects in rats. Given the blood boron concentrations reported in current epidemiological studies, the lack of reproductive and developmental effects in humans is not surprising. Recent epidemiological studies have proven that it will not be possible to reach the critical blood boron concentrations in humans for the reproductive and developmental effects, especially in daily life.

Environmental boron exposure does not induce DNA damage in lymphocytes and buccal cells of females: DNA damage in lymphocytes and buccal cells of boron exposed females

Boron (B) compounds are essential for plants and animals and beneficial for humans in nutritional amounts. I animals and humans increasing evidence have shown beneficial effects on B compounds on nutrition and on antioxidant status. The genotoxic effects of environmental B exposure in women living in boron-rich and boron-poor areas was examined in this study. For this purpose, the DNA damage in the lymphocytes and buccal cells of females were assessed by Comet and micronucleus (MN) assays respectively. No significant difference was observed in the DNA damage of the lymphocytes of B exposed groups of female volunteers in Comet assay. Even buccal micronucleus (MN) frequency observed in the high exposure group was significantly lower than the low exposure group (p < 0.05). The results of this study came to the same conclusions of the previous studies that boron does not induce DNA damage even under extreme exposure conditions.

Pre- and postnatal environmental boron exposure and infant growth: Results from a mother-child cohort in northern Argentina

BACKGROUND

Experimental studies show developmental toxicity of boron and we recently found impaired weight and length in newborns of mothers exposed to boron through drinking water during pregnancy.

OBJECTIVES

To evaluate potential impact of pre- and postnatal boron exposure on infant anthropometry.

METHODS

In our mother-child cohort (n = 177) in Argentinean Andes, where drinking water concentrations of boron, lithium and arsenic have been found to vary considerably, we collected maternal blood and urine during and after pregnancy, placenta, breast milk, as well as infant urine and blood during the first 6 months of life. In all samples, boron and other potentially toxic elements were measured by ICP-MS. Infant weight (g), length (cm) and head circumference (cm) were measured at birth, 0-3 (n = 120) and/or 3-6 months (n = 120; 79 overlap) of age.

RESULTS

Boron concentrations in breast milk (range: 46-786 µg/L) correlated strongly with those in maternal serum (range: 47-624 µg/L; r^s = 0.94) 0-3 months post-partum. In multivariable-adjusted linear regression, urinary boron (log₂-transformed; range 60-9200 µg/L) in the youngest infants, but not maternal serum boron during pregnancy, was inversely associated with body weight at both 0-3 months (B: -141, 95% CI: -240; -42, p = 0.006) and 3-6 months (B: -200, 95% CI: -377; -23, p = 0.027). Infant urinary boron was also inversely associated with head circumference at 0-3 months (B: -0.39, 95% CI: -0.74; -0.04, p = 0.028), as well as length (B: -0.57, 95% CI: -1.1; -0.03, p = 0.040) and head circumference (B: -0.30, 95% CI: -0.64; 0.04, p = 0.083) at 3-6 months.

CONCLUSIONS

The observed first evidence that elevated environmental boron exposure in early infancy may adversely affect growth supports previous findings of boron-related impaired fetal growth. More research is needed to verify the findings at older age and in other populations.

Is There an Association Between Extreme Levels of Boron Exposure and Decrease in Y:X Sperm Ratio in Men? Results of an Epidemiological Study

Objectives

A negative association between Y:X sperm ratio and high levels of boron exposure was suggested in an epidemiological study conducted in boron mining areas of China. That study, however, was criticized by many authors due to some weaknesses in the study design. The present epidemiological study was designed to corroborate or refute the above-mentioned negative association between boron exposure and Y:X sperm ratio in men.

Materials and Methods

The study was conducted in a boric acid production zone in Bandırma. One hundred sixty-three male workers voluntarily participated in our study. The workers employed in the boric acid production facilities were assigned as the exposed workers (n=86). The control group was composed of workers employed in the steam power plant, energy supply unit, demineralized water plant, mechanical workshop, etc. (n=77). Blood and semen samples were sampled from the participating workers at the end of the work shift. Y:X sperm ratio in semen samples was determined by fluorescence in situ hybridization. Boron concentrations in semen and blood samples were determined using inductively coupled plasma-mass spectrometry.

Results

Boron-mediated adverse effect on the Y:X sperm ratio was not determined in workers in our study even under extreme occupational exposure conditions. The results of our study refute the negative association between Y:X sperm ratio and high levels of boron exposure that was suggested in a previously published epidemiological study conducted in boron mining areas of China.

Conclusion

The results of our study indicate that boron-mediated adverse effects on the Y:X sperm ratio do not seem possible even under occupational boron exposure conditions.