Toxicity and exposure to chemicals

1 Hazard and toxicity. Any material is a poison if the dose is large enough and the study of the effects of substances on the human body through, dose-response relationships, known as toxicology, is an advanced discipline. It is at the centre of occupational health activities in industry. Exposure can result in a number of effects depending on the levels of substance  

The major hazards are carcinogenicity, cancer causing or incidence increasing teratogenicity, the induction of non-heriditable birth defects in 

Exposure pathways, in particular their relative significance for different substances, are varied In an industrial context, these are by swallowing, by absorption through the skin and by breathing. Once in the bloodstream, toxins may attack one or more organs, causing harm. 

Dermal (skin) absorption is a significant hazard for a number of volatile substances. These include aromatic compounds such as benzene and toluene nitro-compounds such as nitrobenzene, trinitrotoluene and nitro-propane several insecticides and herbicides hydrogen cyanide and organo phosphates. Protective clothing can minimize risks except where splashing and adsoprtion into cloth concentrates exposure to the skin. 

The inhalation pathway is the major route for chemicals into the body. Gases and vapours can penetrate deep into the lungs where, as the penetration of particles is strongly dependent on size, the general rule being the finer (smaller) the further they penetrate. Deposition in the lungs of very fine (1-2/xm) particles is of greatest concern. The action of asbestos is well known.  

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