Wood preservation facilities, inorganic boron (borate): chapter I-4

4. Human Health Concerns

Boron is a naturally ubiquitous element to which humans are commonly exposed (15). However, in industrial settings, appropriate safeguards (see section 6) need to be implemented to avoid overexposure.

Table 4 presents the estimated daily intake of boron by Canadians. Even at the maximum levels measured in marine air, intake of boron through inhalation is likely to be negligible compared with that ingested in food and water. In the past, boron was considered to be non-essential for animals. However, one study indicating a narrow range of levels in human blood, as well as deprivation studies in rats, suggests that boron might indeed be an essential element (6).

Boron has been classified in Group IVC--probably not carcinogenic to humans.

Boron does not accumulate in normal tissues but may concentrate in malignant brain tumors. Boron is eliminated from the body mainly by the kidney (urine), with minor amounts being excreted in feces, sweat and saliva. About half of the boron absorbed by humans is excreted during the first 24 hours after intravenous administration of 562 to 611 mg of boric acid; more than 92% elimination has been reported to occur within 96 hours of ingestion of 750 mg of boric acid in water or up to 50 mg in a water-emulsifying ointment by human volunteers (6).

A number of acute poisonings in humans from boric acid or borax have been reported following ingestion; parenteral injection; scrubbing of serous cavities; enemas; and application of dressings, powders or ointments to large areas of burned or abraded skin. Symptoms of acute boron poisoning include nausea, vomiting, diarrhea, headache, skin rashes, desquamation and evidence of central nervous system stimulation followed by depression. In severe cases, death usually results in five days as a result of circulatory collapse and shock. The acute lethal dose of boric acid has been estimated to be 15 to 20 g for adults, 5 to 6 g for infants and 1 to 3 g for newborns. Children, the elderly and individuals with kidney problems are most susceptible to the acute toxic effects of boron (6).

Researchers at the University of California in Los Angeles conducted a NIOSH-funded study of over 1000 boron-exposed workers in China. Preliminary results indicate that 9.6% of boron-exposed workers reported a history of infertility, compared with 4.8% of unexposed workers. No significant correlations were found between blood or urine boron and adverse semen parameters. Exposures did not reach those causing adverse male reproductive effects, as published in animal toxicology work, but exceeded those previously published for boron occupational groups. Laboratory measurements of semen quality, blood hormones and boron levels revealed that high exposure levels changed the ratio of Y- to X-bearing sperm, potentially influencing the gender of the workers’ offspring--and suggesting a need for further study (16).