Restricted substances: Antimony

What is antimony? Antimony is a silvery-white metal that is found in the earth's crust. It can exist in two forms: the metallic form is bright, silvery, hard and brittle; the non metallic form is a grey powder. Antimony is a poor conductor of heat and electricity; it is stable in dry air and is not attacked by dilute acids or alkalis. Antimony ores are mined and then mixed with other metals to form antimony alloys or combined with oxygen to form antimony oxide. Antimony compounds in the form of oxides, sulfides, sodium antimonite and antimony trichloride are used in the making of flame-proofing compounds, ceramic enamels, glass, paints and pottery. Antimony trioxide is the most important of the antimony compounds and is primarily used in flame retardant formulations. These flame retardant applications include such markets as children's clothing, toys, aircraft and automobile seat covers. Also, antimony sulfide is one of the ingredients of safety matches. The natural sulfide of antimony, stibnite, was known and used in biblical times as medicine and as a cosmetic. Stibnite is still used in some developing countries as medicine. Antimony has been used for the treatment of schistosomiasis (tropical parasitic disease of Africa and South America). Antimony attaches itself to sulphur atoms in certain enzymes, which are used by both the parasite and human host. Small doses can kill the parasite without causing damage to the patient. Antimony and its compounds are used in several veterinary preparations, which are used as a skin conditioner in ruminants. Antimony has a nourishing or conditioning effect on keratinised tissues, at least in animals. Tartar emetic is another antimony preparation which is used as an anti-schistosomal drug. Treatments chiefly involving antimony have been called antimonials. Antimony is sometimes found free in nature, but is usually obtained from the ores stibnite (Sb2S3) and valentinite (Sb2O3). Nicolas Lémery, a French chemist, was the first person to scientifically study antimony and its compounds. He published his findings in 1707. Antimony makes up about 0.00002% of the earth's crust. Very pure antimony is used to make certain types of semiconductor devices, such as diodes and infra red detectors. Antimony is alloyed with lead to increase lead's durability. Antimony compounds are used to make flame-proofing materials. What happens to antimony when it enters the environment? Antimony is released to the environment from natural sources and from industry. In the air, antimony is attached to very small particles that may stay in the air for many days. Most antimony ends up in soil, where it adheres strongly to particles that contain iron, manganese or aluminium. Antimony is found at low levels in some rivers, lakes and streams. How might I be exposed to antimony? Because antimony is found naturally in the environment, the general population is exposed to low levels of it every day, primarily in food, drinking water and air. It may be found in air near industries that process or release it, such as smelters, coal-fired plants and refuse incinerators. In polluted areas containing high levels of antimony, it may be found in the air, water and soil. Workers in industries that process it or use antimony ore may be exposed to higher levels. How can antimony affect my health? Antimony is a non-essential element in humans, animals and plants. Its toxicity highly depends upon chemical form and oxidation state with 3+ compounds exerting greater toxicity than 5+ compounds. Antimony compounds show toxic properties similar to those of arsenic. This depends on how much antimony a person has been exposed to, for how long, and current state of health. Exposure to high levels of antimony can result in a variety of adverse health effects. Breathing high levels for a long time can irritate eyes and lungs and can cause heart and lung problems, stomach pain, diarrhoea, vomiting and stomach ulcers. Ingesting large doses of antimony can cause vomiting. Antimony can irritate the skin on prolonged contact. Antimony can have beneficial effects when used for medical reasons. It has been used as a medicine to treat people infected with tropical parasites. It is not known whether elemental antimony will cause cancer in people. Human studies are inconclusive as to its human carcinogenicity; hence antimony has not been classified. Antimony in flame retardants Antimony trioxide is not a flame retardant per se but it is used as a synergist. It is utilised in the plastics, rubber, textiles, leather, paper and paint industries, typically 2-10% by weight, with organochlorine and organobromine compounds to diminish the flammability of a wide range of plastics and textiles. Antimony oxides and antimonates must be converted to volatile species. This is usually accomplished by the release of halogen acids at fire temperature. The halogen acids react with the antimony-containing materials to form antimony trihalide and/or antimony halide oxide. These materials act both in the substrate and in the flame to suppress spread of flame. In the condensed phase, they promote char formation, which acts as a physical barrier to flame and inhibits the volatilisation of flammable materials. In the flame, the antimony halides and halide oxides, generated in sufficient volume, provide an inert gas blanket over the substrate, thus excluding oxygen and preventing flame spread. These compounds alter the chemical reactions occurring at fire temperatures in the flame, thus reducing the ease with which oxygen can combine with the volatile products. It is also suggested that antimony oxychloride or trichloride reduces the rate at which the halogen leaves the flame zone, thus increasing the probability of reaction with the reactive species. Antimony trichloride probably evolves heavy vapours which form a layer over the condensed phase, stop oxygen attack and thus choke the flame. It is also assumed that the liquid and solid antimony trichloride particles contained in the gas phase reduce the energy content of the flames by wall or surface effects. Other antimony compounds include antimony pentoxide, available primarily as a stable colloid or as a redispersible powder. It is designed primarily for highly specialised applications, although manufacturers suggest it has potential use in fibre and fabric treatment. Toy Standards The legislation concerned with the safety of children's toys is EU Council Directive 88/378/EEC (metals listed in Annex II). They are tested as per BS EN 71.There are many different parts to this standard; however, it is Part 3 that deals with antimony (BS EN 71-3). The limit stated in the standard is 60ppm. Though this standard is directly related to toys, it is important to remember that any item that may be deemed child-appealing, such as children's footwear, should be tested for antimony along with other restricted substances. Conclusion Many brands and retailers with an interest in leather are now placing antimony on their restricted substance lists. It is mentioned by various environmental pressure groups as a chemical that should be avoided due to its toxicity. Its main use is as a component of flame retardants in the manufacture of a range of materials. BLC is able to offer advice and testing for the presence of antimony. For more information contact BLC Leather Technology Centre Ltd on info@blcleathertech.com