Boron

Boron is a chemical element with symbol B and atomic number 5. [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1]

It is a non-metallic element and the only non-metal of the group 13 of the periodic table. Boron is electron-deficient, possessing a vacant p-orbital. It has several forms, the most common of which is amorphous boron, a dark powder, unreactive to oxygen, water, acids and alkalis. It reacts with metals to form borides. At standard temperatures boron is a poor electrical conductor but is a good conductor at high temperatures. [2] Boron is found in the environment primarily combined with oxygen in compounds called borates. Common borate compounds include boric acid, sodium tetraborates (also referred to as borax) and boron oxide. [3]

 

Uses [4]

 

Boron is used in special-purpose alloys, in cementation of iron, as oxygen scavenger for copper and other metals, as fibres and filaments in composites with metals or ceramics, as semiconductor, for nuclear reactors, as a shield for nuclear radiation and in instruments used for detecting neutrons. Boron is used in pyrotechnic flares (distinctive green colour), for rockets (as an igniter), in boron-coated tungsten wires and in high temperature brazing alloys.

 

Borates are used mostly to produce glass. They are also used in fire retardants, leather tanning industries, cosmetics, photographic materials, soaps and cleaners, adhesives and for high-energy fuel. Some pesticides used for cockroach control and some wood preservatives also contain borates.

 

Borax is used in soldering metals, as a cleansing flux in welding, in the manufacture of glazes and enamels (e.g. for covering steel of refrigerators and washing machines), in tanning, in cleaning compounds, to artificially age wood, as a preservative against wood fungus (either alone or with other antiseptics), and in fireproofing fabrics. It is also used for curing and preserving skins, in cockroach control and as a water softener in washing powders.

 

Boric acid is used for weatherproofing and fireproofing fabrics, as a preservative, in the manufacture of cements, crockery, porcelain, enamels, glass, borates, leather, carpets, hats, soaps, and artificial gems, and in nickel-plating baths. It is also used in the manufacture of cosmetics, in ointments and eye washes, as a mild antiseptic, in printing and dyeing, in photography, for impregnating wicks, for hardening steel, in welding flux, copper brazing, as an insecticide for cockroaches and carpet beetles, and in fungus control for citrus fruits.

 

Boron oxide is used in metallurgy, in the analysis of silicon dioxide in silicates, in blowpipe analysis, for the production of boron, in heat-resistant glassware, as a fire-resistant additive for paints, in electronics and as an herbicide.

 

Boron carbide is used as an abrasive, in the manufacture of hard and chemical-resistant ceramics or wear-resistant tools, in the refractory industry, in light weight cermets, in armour tiles, in radiation protection and shielding, in the nuclear industry in control rods in nuclear reactors (high capture cross-section to absorb thermal neutrons), as raw material for producing other boron containing materials (e.g. titanium boride), and in solid fuel (propellant for ducted rockets).

 

Boron nitride is used as a refractory material, laboratory reagent, and abrasive. Boron trichloride is used in the manufacture and purification of metal alloys, in bonding of iron and steel, in soldering fluxes, and in the manufacture of electrical resistors. It is also used to extinguish magnesium fires in heat resisting furnaces.

 

Boron trifluoride is widely used to promote various organic reactions. Boron filaments are high-strength, lightweight materials that are used in fibre optics research and for advanced aerospace structures.

 

Sources of Emission & Routes of Exposure

 

Sources of Emission [4]

 

  • Industry sources: Boron can be released from industries that use boron and boron compounds, e.g. leather tanning, cement works, and glass works.
  • Diffuse sources: Boron can be released from household use of consumer products containing borates such as cosmetics, washing powders, or pesticides, and sub-threshold facilities.
  • Natural sources: Boron is not an abundant element. The element boron does not occur in nature and boron is mostly found combined with oxygen in compounds called borates. Common borate compounds include boric acid, salts of borates and boron oxide. Natural deposits of borates are borax and kernite. Tourmaline contains about 10 % boron. Boron is released to the environment from natural sources such as volcanoes and geothermal steam. Traces are present in rocks, soil, water and some food.
  • Transport sources: Mobile sources are normally not associated with the emission of boron.
  • Consumer products: Heat-resistant household glassware (Pyrex), laboratory glassware, some soap, some pesticides, some cosmetics and laundry products, some leather products and some cement products.

 

Routes of Exposure [5]

 

  • Inhalation – Minor route of exposure for the general population. Predominant route of exposure for boron workers.
  • Oral – Predominant route of exposure for the general population via ingestion of boron in food and drinking water.
  • Dermal – Minor route of exposure.

 

Health Effects [4]

 

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.

 

The International Agency for Research on Cancer (IARC), and the United States Environmental Protection Agency (EPA) have not classified boron for human carcinogenicity.

 

Safety [6]

 

First Aid Measures

 

  • Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical attention if irritation occurs.
  • Skin Contact: Wash with soap and water. Cover the irritated skin with an emollient. Get medical attention if irritation develops.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention.
  • Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt or waistband. Seek medical attention.
  • Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen tight clothing such as a collar, tie, belt or waistband.

 

Exposure Controls & Personal Protection

 

Engineering Controls

 

Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits. If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.

 

Personal Protective Equipment

 

The following personal protective equipment is recommended when handling boron:

  • Safety glasses;
  • Lab coat;
  • Dust respirator (Be sure to use an approved/certified respirator or equivalent);
  • Gloves.

 

Personal protective equipment recommended for large spills:

  • Splash goggles;
  • Full suit;
  • Dust respirator;
  • Boots;
  • Gloves;
  • A self-contained breathing apparatus should be used to avoid inhalation of the product. Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.

 

Regulation

United States [3]

 

OSHA: The Occupational Health and Safety Administration has limited workers’ exposure to an average of 15 mg/m3 for boron oxide in air for an 8-hour workday, 40-hour workweek.

 

EPA: The Environmental Protection Agency has determined that exposure to boron in drinking water at concentrations of 4 mg/L for 1 day or 0.9 mg/L for 10 days is not expected to cause any adverse effects in a child. In addition, the agency has determined that lifetime exposure to 1 mg/L boron is not expected to cause any adverse effects.

 

Australia [4]

 

Safe Work Australia: Safe Work 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).

 

Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 2004):

Maximum of 4 mg/L (i.e. 0.004 g/L)

 

References

 

  1. http://en.wikipedia.org/wiki/Boron
  2. http://www.lenntech.com/periodic/elements/b.htm
  3. http://www.atsdr.cdc.gov/phs/phs.asp?id=451&tid=80
  4. http://www.npi.gov.au/resource/boron-and-compounds
  5. http://www.atsdr.cdc.gov/toxguides/toxguide-26.pdf
  6. http://www.sciencelab.com/msds.php?msdsId=9923126

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