Hexane is a simple organic chemical, a volatile liquid used industrially as a solvent. Once absorbed into the body, it is changed by metabolism into other products. One of these products, in which the hexane has been oxidized, is able to react with proteins in the nerves, and this is what underlies its toxic effects. Similar solvents that do not form this product are not toxic to the nerves, while those that do, predictably cause the same type of toxic effects.
That hexane is soluble in fat allows it to distribute to most tissues in the body, including nerves. The destruction of motor nerves leads to both loss of feeling and weakness in the fingers and toes.
some chlorinated hydrocarbons, such as trichloroethane, cause adverse effects on the heart after acute exposure, leading to arrhythmias. Tri-chloroethane also causes toxic effects in the heart after chronic exposure.
Another solvent widely studied and known to be the cause of serious effects is benzene, which is found in petrol and is also used in the shoe-making industry. Extensive studies have been carried out in Turkey, for example, where it has been used in shoemaking. The use of benzene has now been phased out in many countries but it continues to be used in others. It has been extensively used as a starting point for the production of other chemicals and as a solvent in the manufacture of rubber, paint, and plastics, and in printing. It has been added to petrol as an alternative anti-knock additive to lead compounds.
The main hazardous effects of benzene are to the blood system. Workers chronically exposed suffer from anaemia, due to damage to and sometimes complete destruction of the cells in the bone marrow, where the cells found in the blood are formed. Benzene exposure can lead to low levels of both red and white blood cells. A more serious effect is leukaemia, which is cancer of the blood system. Because of the hazards it poses, the use of benzene has been dramatically curtailed.
The solvents most commonly used in paints are glycol ethers, which are known to cause damage to the male reproductive system by destroying the cells that produce sperm in the testes.
Finally, another halogenated solvent that causes toxic effects after acute exposure is dichloromethane or methylene chloride. It is used for degreas-ing engines and metalwork, and is the main constituent of paint stripper. If it is used in confined, enclosed spaces, such as rooms without adequate ventilation, it can lead to serious, unexpected toxic effects. As the solvent is breathed in by the worker it becomes localized in body fat. Later the dichloromethane emerges from the stores in the fat into the bloodstream and liver, where the solvent is metabolized. The product is carbon monoxide, which is highly poisonous and can cause death from interference with the availability of oxygen (see, further, pp. 185-7). The victim may collapse some time after the exposure has ended, not from the effects of the solvent, but from the effects of the carbon monoxide produced from it.
It should be mentioned here that pesticides are significant in terms of the risks of chemical exposure for workers both in their production and their use. There is a large variety of these, ranging from organo-phosphates to organochlorines, and including paraquat, for example. The organophosphates probably cause the most problems for workers after acute exposure, from the point of view of skin irritation and of more serious adverse effects on the nervous system. There has been much debate as to whether agricultural workers exposed over time suffer permanent damage to the nervous system, and this is still unclear. For more detailed discussion of pesticides, see Chapter 4.
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