Occupational toxicology

Occupational exposures involve situations ranging، for example from a secretary using typewriter correction fluid to the loading and off-loading of tanker trucks with thousands of gallons of gasoline.

Early writings by Ulrich Ellenbog (1435–1499), Agricola (1494–1555), and Paracelsus (1492–1541) revealed the toxic nature of exposures in mining, smelting, and metallurgy. A systematic treatise by Ramazzini (1633–1714) described the hazards as they applied to miners, chemists, metal workers, tanners, pharmacists, grain sifters, stonecutters, sewage workers, and even corpse bearers.[1]

The measurement of a chemical, its metabolite, or a biochemical effect in a biologic specimen for the purpose of assessing exposure. Biologic monitoring is an important tool to identify the nature and amount of chemical exposures in occupational and environmental situations.[5]

Metals with a density of more than 5 g/cm3 and toxic effects. Including arsenic, cobalt, lead, lithium, mercury, and thorium, have documented ototoxic potential. The metals represent a different aspect of toxicology in that they do not undergo breakdown to other metals (to do so would be transmutation of the elements, an old alchemical principle still not possible without huge sources of energy, and a particle accelerator!). The absorption, disposition and excretion of metals are largely dependent on physical factors, such as solubility, ionisation, particle size and chemical species (for metal salts). About 70–80 elements in the periodic table are considered metals. Groups Ia and IIa, the's block’ metals, form monovalent and divalent cations respectively. Groups IIIb to VIb constitute the ‘p block’ elements, which include metals that can have ions of different valencies. These are called the transition elements. Of the metal elements, about 40 are considered to be ‘common’ metals. However, less than 30 have compounds that have been reported to produce toxicity. Metals are probably some of the oldest toxicants known to humans. Health effects such as colic were reported following exposure to lead, arsenic and mercury over 2000 years ago. On the other hand, metals such as cadmium, chromium and nickel belong to the modern era. The importance of some of the rarer metals may become apparent with emerging changes in technology, such as microelectronics and superconductors. The toxicity of a metal is only partially related to its position in the periodic table. Toxicity decreases with the stability of the configuration of electrons in the atomic nuclei. This produces a number of properties that can affect toxicity.[6]

The term solvent refers to a class of organic chemicals of variable lipophilicity and volatility. These properties, coupled with small molecular size and lack of charge, make inhalation the major route of exposure and provide for ready absorption across membranes of the lung, gastrointestinal (GI) tract, and skin. In general, the lipophilicity of solvents increases with increasing numbers of carbon and/or halogen atoms, while volatility decreases. Organic solvents are frequently used to dissolve, dilute, or disperse materials that are insoluble in water. As such they are widely employed as degreasers and as constituents of paints, varnishes, lacquers, inks, aerosol spray products, dyes, and adhesives. Other uses are as intermediates in chemical synthesis, and as fuels and fuel additives. Most organic solvents are refi ned from petroleum. Occupational solvent exposures involve situations ranging from a secretary using typewriter correction fl uid to the loading and off-loading of tanker trucks with thousands of gallons of gasoline. The greatest industrial use of solvents is as metal degreasers. This work environment is typically where the highest exposures occur, mainly via inhalation and secondarily via dermal contact. An estimated 10 million people are potentially exposed to organic solvents in the workplace.[7]

Asbestos is a term given to a group of fibrous silicates most of which contain magnesium. The health effects of asbestos are related to the fact that asbestos fibres can be small enough to be inhaled. Asbestos fibre bundles can break into smaller and smaller fibres until dust particles in the respirable size range are produced. Particles in the respirable range (2–10μm) can reach the lower regions of the lung (the alveolar region) which is beyond the reach of the normal mucous clearing system. Fibres retained in lung tissue may be up to 200μm long and 3μm or less in diameter. Some of the longer fibres get coated with an iron protein complex, producing drumstickshaped ‘asbestos bodies’. These are considered indicative of occupational exposure.[8]

• Toxipedia
• Information Toxicology International
• Society of Toxicology