A healthy workplace requires attention to numerous aspects, including exposure to chemicals and products. Inhalation of dusts, or small solid particles, is one of the leading paths for worker exposure to chemicals and products. Despite the fact that Borax dedicates one-third of its energy use to limiting worker exposure, dust can be generated by crushing, drilling, blasting and grinding materials or from mixing or handling products - standard practices at Borax.
Determining safe concentrations of dust can be a complicated process; some dust particles are too small to see. Government, academic and industry scientists have developed guidelines for dust concentrations based on predicted effects. Obviously, guidelines for products that contain highly poisonous chemicals are set much more strictly than for products that may simply be irritating.
Guidelines for occupational exposure to borate dusts were adopted by the California Occupational Safety and Health Administration (Cal-OSHA) in the early 1980s. At that time, following the recommendation of ACGIH they believed that two products - boric oxide and Neobor® (sodium tetraborate pentahydrate) - were more irritating than borax decahydrate. Permissible exposure limits (PELs) were set at one milligram per cubic meter of air for the former and five milligrams per cubic meter for the latter. Following review of a study showing the equivalency of all three products2, Cal-OSHA raised their PEL in the early 1990s to five milligrams per cubic meter.
Studies in the late 1980s and early 1990s evaluated workers at Boron Operations through questionnaire and real-time exposure measurements. A report of this investigation1 concluded that there were associations between levels of borate exposure and symptoms of acute respiratory irritation. However, experts found no evidence of long-term or chronic effects on lung function over a seven-year interval, nor did they find differences among the three different borate products. They concluded that "the totality of the evidence suggests that the current levels of sodium borate exposures in this plant are generally associated with no more than moderate irritant responses." One limitation of this study was that the symptoms and the severity of symptoms were not measured by any standard scale or criteria - what one person reported as "noticeable" another may have classified as more irritating.
To objectively address this limitation, Dr. William Cain of the University of California, San Diego, has developed a method to quantify dust irritation in a way that meets the highest international standards for occupational health and industrial hygiene. With support from Borax, Dr. Cain and his colleagues have investigated several dusts, including calcium sulfate (a dust that may cause no or minimal irritation), calcium oxide (which does cause moderate to severe irritation), and sodium borate. Based on these studies, Borax believes that a strong case can be made that an occupational exposure to 10 milligrams per cubic meter of air or less of sodium borate dust will protect against unacceptable irritation.
Animal tests have shown that adding relatively large amounts of boron to their food over a long period of time can result in mild or reversible effects on development and male fertility23. These animal data have led Borax to self-classify borates as reproductive toxicants under the strict criteria of the United Nations’ Globally Harmonized System for Classification and Labeling of chemicals (GHS)4. These animal studies also led the European Commission to classify borates as reproductive toxins in 2009.
The hazards are associated with animals being exposed to large amounts of borates in their feed over long periods of time – exposures that are not relevant to people, even those who work with borates every day. The diet of laboratory animals such as rodents naturally contains high levels of boron, about 45 times the typical boron concentration in human diets. Humans are likely to vomit if they consume a fraction of the high concentrations tested in animals, so it is not likely that any humans would experience long-term exposures to borates.
Borates have a long track record of being safe when used as directed. The study at Boron operations mentioned above found no significant problems with reproduction and fertility of the mine workers. Since then, studies in China and Turkey among highly exposed mine workers have used advanced approaches to look for reproductive health effects. An extensive study of Chinese mine workers found that they did experience high exposures. One sub-group which had been drinking from contaminated wells actually had a mean boron intake almost 10 times the WHO-recommended upper safe limit, and over 100 times the average exposure of the general population. However, the studies of their reproductive health, including evaluations of sperm quality, showed no adverse effects associated with boron exposure56. Another study has just been released looking at the reproductive health of Turkish mine workers and those living in areas naturally high in boron7. No adverse reproductive health effects were found.
1 Wegman, DH, EA Eisen, X Hu, SR Woskie, RG Smith, and DH Garabrant, 1994. "Acute and chronic respiratory effects of sodium borate particular exposures." Environmental Health Perspectives, Vol 102, Supplement 7, pages 119-128.
2 Price CJ, Strong PL, Marr MC, Myers CB, & Murray FJ (1996a) Developmental toxicity NOAEL and postnatal recovery in rats fed boric acid during gestation. Fundam Appl Toxicol, 32: 179-193.
3 Weir RJ & Fisher RS (1972). Toxicologic studies on borax and boric acid. Toxicology and Applied Pharmacology 23: 351 - 364.
4 The requirements are found at http://unece.org/trans/danger/publi/ghs_welcom_e.html.
5 Scialli AR, Bonde JP, Brüske-Hohlfeld, Culver DB, Li Y & Sullivan FM. (2010). An overview of male reproductive studies of boron with an emphasis on studies of highly exposed Chinese workers. Reproductive Toxicology 29: 10 - 24.
6 Robbins WA, Xun L, Jia J, Kennedy N, Elashoff DA & Ping L. (2010). Chronic boron exposure and human semen parameters. Reproductive Toxicology 29: 184 - 190.
7 Duydu Y, Başaran N, Ustündağ A, Aydın S, Undeğer U, Ataman OY, Aydos K, Düker Y, Ickstadt K, Waltrup BS, Golka K, Bolt HM. (2011). Reproductive toxicity parameters and biological monitoring in occupationally and environmentally boron-exposed persons in Bandırma, Turkey. Arch Toxicol. 2011 Jun;85(6):589-600. PMID:21424392.