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

Abstract

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.

Keywords:

• Boron exposure
• biomonitoring
• biomarkers
• environmental exposure
• occupational exposure
• reproductive toxicity
• developmental toxicity
• sex ratio at birth
• Y:X sperm ratio

Acknowledgements

The authors gratefully acknowledge the external reviewers selected by the editor and anonymous to the authors whose comments were very valuable in revising and refining the manuscript. The authors have no further acknowledgments to declare. The manuscript was prepared solely by the authors.

Declaration of interest

The epidemiological studies conducted by the authors of this review were initiated in 2008. Prof. Hermann M. Bolt was involved in this international project as chief consultant. These studies were extended with a second project in 2017. Prof. Hermann M. Bolt was the principal consultant also in this second international project. Turkish scientists involved in these international epidemiological studies are thankful to Prof. Hermann M. Bolt as the owner of both projects. Prof. Hermann M. Bolt is a member of the Editorial Advisory Board for CRT; however, he was not involved in any communications with the Editor or staff during the review of the paper. The epidemiological studies conducted by the authors of this review were supported by BOREN and Eti Mine General Management, Türkiye.