The harmful effects of chemical substances depend on the toxicity and the exposure to that chemical. Toxicity is a property of the chemical substance, while the exposure depends on the way the chemical is used. The level of exposure depends on the concentration of the hazardous chemical and on the period of contact time. Many substances do not give any warning by odour, even though they may be present at dangerous concentrations in the workplace air.
Acute effects - Chronic effects
The effects may be acute: after a short exposure an immediate effect may be experienced. Chronic effects usually require repeated exposure and involve a delay between the first exposure and appearance of adverse health effects.
A substance may have acute and chronic effects. Both acute and chronic conditions can result in permanent injury.
Injury from exposure to a chemical substance can be temporary, i.e. reversible. It will disappear when exposure to that chemical stops.
Exposure to solvents may cause contact dermatitis, headache or nausea. These effects could be both acute and temporary. Solvents can also cause chronic effects and result in an irreversible, permanent injury to the nervous system.
Local effects - Systemic effects
Hazardous substances may cause local effects. Acute local effects may include corrosive injuries from acids and bases or lung injuries from inhaled gases such as ozone, phosgene and nitrogen oxides.
Many other gases cause adverse effects only after they have been inhaled repeatedly over a long time period. Low concentrations of a gas may also be effective in this way. A persistent irritation of the respiratory system can arise from exposure to gases such as sulphur oxides, hydrogen fluoride and hydrogen chloride.
Once the hazardous substance has entered the blood circulation, it may be distributed to all parts of the body. It will reach the liver, which is the most important detoxication organ of the body. The liver attempts to convert the toxic agents to a less toxic ones or to the ones useful to the body. This process is called metabolism. Some substances such as alcohol and carbon tetrachloride can damage the liver. The body excretes unwanted chemicals. The kidneys filter them from blood circulation, which is the main way that the body excretes poisons, but in doing this, they can be damaged by toxic substances such as carbon tetrachloride, ethylene glycol and carbon disulphide. Cadmium causes permanent damages to kidneys.
Other means of excretion are via faeces, sweat and through lung exhalation.
The nervous system is sensitive to chemicals. The adverse effects may be on the central nervous system or on the nerves that transport impulses to other parts of the body. Organic solvents are commonly used at work and are known to be able to affect the nervous system. Many other substances may behave in the same way such as carbon disulphide, mercury, lead, manganese and arsenic.
Our body has a considerable capacity to excrete, to render dangerous substances harmless, and to protect us. However, our defense system can be overloaded by repeated heavy exposure so that it no longer fulfills its function. The body stores the harmful substance which may consequently result in health problems.
Lead is an example of a substance for which removal from the body takes a long time. Cadmium is an example of a substance that is not processed by the body at all, and once it has entered it will stay there.
What all we get from raw oil! This is a description of the product coming from fractional distillation of raw oil.
