Safety in the Use of ChemicalsChapter 1Chemicals and the Human Body |
Our bodies are composed of chemicals. Our skins, bones, blood, teeth, hair and nails are all made of chemicals. We eat proteins, carbohydrates, fats, vitamins, minerals, all of which are chemicals. We drink water, sodas or soft drinks and juices when we are thirsty, all in essence chemicals or mixtures of chemicals. The air we breathe is 78 per cent nitrogen, 21 per cent oxygen and contains traces of other gases. We take chemicals in medicine when we are sick. Our daily soap, shampoo, tooth paste and other cosmetics are all made up of chemicals. They help to make our lives more comfortable. But sometimes they can also threaten our health, our well-being and our safety. Many of the chemicals we encounter daily can cause damage to our own health and that of others.
How chemicals enter the body
We can be exposed to chemicals when:
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There are three main ways that chemicals can enter our bodies: breathing, skin contact and swallowing. They may also be injected into the body or enter through the eyes.
Breathing
Most chemicals enter our bodies when we breathe. During a normal day we breathe in about 8.3 m3 of air. Sometimes we breathe in air containing chemicals in the form of dust, vapours, gases or mists. Air comes into our bodies through the nose, passes through the larynx, then enters the trachea, a long tube connected at its end to two other tubes, called bronchi. These supply air to the lungs (Fig. 1.1).
Fig. 1.1 The human respiratory system
Breathing in chemicals
Depending on their make-up, gases and vapours may be absorbed in the blood.
A worker spraying paint without adequate protection may be heavily exposed to organic vapours by breathing.
| The smaller the size of the particles we breathe, the more deeply they are likely to penetrate into the respiratory system. |
How deeply the aerosols (dust, mist, fog, smoke, or other kinds of particles suspended in air) penetrate the respiratory system depends upon the particle size, physical shape and properties of the chemical. Some particles are attacked by the body's defence cells, called macrophages, and may be either destroyed or converted into more harmful substances. The more the amount of chemicals we breathe and the longer we are exposed to them, the more serious are the health effects likely to be. Some individuals are more prone to the effects of chemicals than others. Similarly, children, the elderly, pregnant women and those weakened by illness are more at risk from the unhealthy effects of chemicals.
Where we breathe them
Chemicals enter and leave our bodies all the time. Tiny spores, pollen and bacteria by the thousands enter the lungs with each breath. Most of these are breathed out, others are removed or destroyed by the defence mechanisms of our body. While some chemicals announce their presence by their smell (or sometimes colour), most often we breathe them without being aware of it. Our sense of smell is not always infallible. If we are suffering from flu or have been inhaling too much of a chemical (perfume, for example), we may not be able to notice the presence of chemicals.
But there are a large number of chemicals which have no smell. A deadly example is carbon monoxide gas. Every year hundreds of people die from breathing carbon monoxide when they sleep in a room with little or no source of air, heated by a burning fuel (wood, coal, oil or gas, etc.) Carbon monoxide is produced when a fuel burns where there is a lack of oxygen, and it has no smell.
Table 1.1 lists some day-to-day situations or activities in which we may be exposed to chemicals through inhalation.
Table 1.1 Some activities and situations where exposure to chemicals by breathing is possible
| Type of chemicals |
Chemical nature of the contaminant |
Activities, situations, processes or products |
| Gases | Carbon monoxide (CO)
Hydrogen sulphide (H2S)
Ammonia (NH3)
Sulphur dioxide
Nitrogen oxides (Nox)
Chlorine (Cl2) |
- Sleeping in a room with burning fuel and insufficient air
- Working in coke-oven or steel-furnace plants - Automobile engine exhausts
- Working in confined spaces, where organic matter is putrefying - Working in sewers or wells - Working in refineries - Working in leather tanneries - Chemical laboratories
- Fertilizer plants - Ice factories/cold storage - Detergents
- Coal burning in homes and factories - Sugar refining - Petroleum refineries
- From automobile engine exhaust - Fertilizer plants
- Bleach - Textile finishing - Disinfectants - Water treatment plants |
| Vapours | Volatile organic compounds (VOCs) in general
Benzene
Formaldehyde
Acetone |
- Spray painting
- Auto repair garages - Filling stations - Nail polish removers - Furniture making/polishing - Printing presses
- Gasoline (when used as solvent) - Rubber industry - Paint removers - Varnish
- Glues - Leather tanning - Hospital mortuaries
- Paint, varnish, nail polish removers |
| Aerosols
- Dusts - Mists - Fumes |
Grain/flour dust
Silica dust
Cement dust
Cotton dust
Asbestos dust
Sulphuric acid mist
Organic solvents mist
Metal fumes
Lead fumes
Zinc fumes
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- Farming - Flour mills - Bakeries
- Foundries - Glass/ceramic factories - Quarries - Granite cutting/polishing
- Construction - Cement factories
- Textile mills
- Heating insulation - Brake linings of vehicles - Asbestos mines
- Battery manufacture - Dyestuff manufacture - Textile dyeing - Food processing factories - Electroplating
- Spray painting - Degreasing
- Welding operations - Furnaces/foundries
- Vehicle exhaust - Soldering - Battery repair/manufacture - Manufacture/use of some paints
- Zinc smelters - Galvanizing operations |
Through the skin
The skin forms a barrier between the organs of the body and the outside world. It is composed of a number of layers (Fig. 1.2) which can protect us from biological, physical and chemical hazards encountered in the natural environment. But a number of chemicals corrode or burn the skin, others dissolve the outer layer. Once chemicals enter through the skin, they may be carried away in the blood stream, causing harm to the organs or to bodily functions related to breathing, the nervous system, and so on.
Fig. 1.2 A cross-sectional view of the skin showing different protective layers
Heavy exposure to potentially harmful chemicals may occur during such activities as wood polishing if no protective measures are adopted
Most alkaline and acids have corrosive action on the skin and can cause burns and boils. Most organic solvents can penetrate through the protective layer of the skin. If the skin is damaged by cuts, burns or other injuries, it is more likely to be penetrated by chemicals. Many pesticides also cause skin and other health problems.
Contact dermatitis is caused when the skin becomes tender, reddens and cracks through acids, alkalis, solvents, detergents and cutting liquids. Once the source of exposure is removed, the skin heals itself. The healing process may take several months. Allergic contact dermatitis is similar to contact dermatitis except that the skin becomes sensitized to certain chemicals and the allergy usually persists throughout the life of the affected person. Once someone comes in contact with the substance again, the symptoms return. Some people are more likely to develop allergy from chemicals than others. Table 1.2 lists some important activities and situations in which one is likely to be exposed to chemicals through the skin.
Table 1.2 Activities and occupations associated with skin exposure to chemicals
| Activities, occupations and situations | Chemicals associated with skin exposure |
| Households (washing, repair jobs, painting, etc.) | - Detergents (chlorine or enzymes)
- Glues (epoxy and wood bonding containing formaldehyde) - Solvents from paints, paint and nail polish removers - Nickel from jewellery, watches, etc. |
| Woodworking and furniture making | - Wood dust
- Enamels - Solvents from spray mists - Varnishes - Formaldehyde and epoxy compounds from resins |
| Farming and agriculture | Pesticides |
| Auto repair garages | - Gasoline
- Kerosene - Paints and thinners - Epoxy resins - Grease and lubricants |
| Engineering workshops | - Cutting oils
- Paints and thinners - Abrasives - Alkalis - Acids |
Chemicals in food and drink
Chemicals can be consumed accidentally or even deliberately (in the case of suicide). Normally they are taken in through eating, drinking or smoking. Small children are more at risk as they sometimes try to eat anything they can lay their hands on. Inadvertent exposure to chemicals through the food we eat is a very serious problem. Even nail biting can result in exposure to chemicals.
| Eating and drinking can sometimes lead to exposure to chemicals, with serious implications for our health |
Contamination of food
The food we eat can become contaminated during processing, storage or transportation. The over-use of pesticides on vegetable and fruit crops may leave residues which can cause poisoning. Some toxic chemicals are taken in by fish, which may cause poisoning when contaminated fish products are consumed.
Water
Normally chemicals in water produce a taste, colour or smell which make it undrinkable. Problems begin when low levels of chemicals enter the water supply and result in long-term effects on the health of those who drink it. Some chemicals which occur in nature, such as arsenic, may enter the water supply and cause serious health problems. Many other heavy metals, like lead from pipes and fittings, or chromium from tannery effluents, have been detected in drinking water supplies in different parts of the world.
Other ways of exposure
The human eye is also highly susceptible to damage by chemicals. Many processes in industry emit acids, alkalis, organic solvents and other corrosive chemicals which can cause severe eye damage and sometimes blindness. Bad personal hygiene and not using protective equipment can also have serious health implications.
The injection of chemicals through the skin is also a potential means of exposure to chemicals, but is not normally found in ordinary occupations and day-to-day activities, unless of course you are a bee keeper or milk venom from snakes!
Chemicals may cause harm to the eyes if good personal hygiene practices and protective equipment are not used while working with them
Exercise
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