The severity of health effects will depend on how much boron a person has been exposed to, for how long, and current state of health. Once different borates are dissolved in the acid of gastric juices, they cannot be distinguished from each other on chemical or toxicological grounds. Both boric acid and borax may enter the body by absorption from the gastrointestinal tract or through mucous membranes. Although absorption can occur through undamaged skin, it is slow and toxic effects are less likely. However, absorption through damaged skin can be rapid and complete.
Ingestion of large borate quantities is unlikely, but may be harmful if it occurs. Ingestion or absorption through the skin can cause nausea, abdominal pain, diarrhoea and persistent vomiting (vomitus and faeces may sometimes contain blood), which may be accompanied by headache and weakness, lethargy, restlessness, tremors, intermittent convulsions, and characteristic erythematous (abnormally red) lesions on the skin. In severe cases, shock with fall in arterial pressure, tachycardia (increase in heart rate) and cyanosis (blue skin colour) may occur. Central nervous system stimulation followed by depression, gastrointestinal disturbance (haemorrhagic gastroenteritis) and erythematous skin eruptions (giving rise to a boiled lobster appearance) may be present. The kidneys (producing oliguria (small volume of urine), albuminuria (presence of albumin in the urine), anuria (absence of or defective excretion of urine)) and, rarely, the liver (jaundice) may also be involved. Excretion occurs mainly through the kidneys with about half excreted in the first 12 hours and the remainder over 5-12 days. Toxic symptoms may be delayed for several hours. The mean lethal dose of sodium borate or boric acid probably exceeds 30 grams in adults and death occurs due to vascular collapse in the early stages or to central nervous system depression in later stages. Children are thought to be more susceptible to the effects of borate intoxication.
Breathing moderate levels of boron dust or fume can result in irritation of the nose, throat, and eyes.
There is little information on the health effects of long-term exposure to boron. Most of the studies are on short-term exposures. Chronic intoxication with boric acid may give rise to anorexia, loss of strength, confusion and loss of hair (alopecia). Reproductive effects, such as low sperm count, were seen in men exposed to boron over the long-term.
Entering the body
Boron can be ingested or inhaled. Absorption through intact skin is unlikely but it can be readily absorbed through areas of damaged, abraded or burned skin as well as areas of active dermatitis.
Low levels of boron can be found naturally in air, water and some food. Hence, drinking water and eating food can contribute to some normal boron intake. Certain consumer products such as cosmetics and laundry products are also likely sources of exposure. Boron is unlikely to leach from borosilicate glasses. Occupational exposure to boron and boron compounds can occur in industries that produce special glass, washing powder, soap and cosmetics, leather, cement etc. The nuclear industry (e.g. ANSTO) also uses boron.
Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 2004):
Maximum of 4 mg/L (i.e. 0.004 g/L)
Worksafe Australia defines boron oxide as hazardous and has set its exposure standard to 10 milligram/m3 (TWA). Boron halides are also classified as hazardous with an exposure standard of 1 ppm (TWA). The exposure standard for the non-hazardous borax is 5 milligram/m3 (TWA).
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