Systemic effects

Dusts

Some dusts e.g. lead of its salts can be absorbed into the body after inhalation or skin contact. They can then have harmful effects on other organs e.g. the nerves or the blood forming organs. Ultrafine particles might travel through the alveoli to produce harmful effects elsewhere.

Systemically toxic gases and vapours

Examples: Methylene chloride, various chloroethanes and chloroethylenes. The effect of methylene chloride is similar to the effect of vapours given off by organic solvents (e.g. trichlorethylene). Initially they might cause a feeling of well being similar to that produced by alcohol. At higher concentrations they cause unconsciousness. Repeated exposure can lead to permanent brain damage.

Simple asphyxiant gases

Life depends on an adequate supply of oxygen reaching the tissues of the body. Oxygen present in the air breathed into the lungs passes into the blood and is carried to the tissues. Simple asphyxiants may interfere with this process either by displacing oxygen from the air breathed in.

Examples: Methane, Nitrogen. This happens usually in enclosed, poorly ventilated spaces particularly underground where methane can be produced by naturally occurring processes or where natural oxygen has been depleted. Symptoms include breathlessness due to lack of oxygen. Carbon dioxide also causes rapid breathing, headache and sweating. Eventually, loss of consciousness and death can result.

Chemical asphyxiants gases

These cause asphyxia by interfering with oxygen transport.

Examples: Carbon monoxide, Hydrogen cyanide, Hydrogen sulphide (Agius website) 
See: Toxicology: toxicodynamics (Agius website)