Occupational diseases

STUDY UNIT NINE
LEARNING OBJECTIVES
After having worked through this study unit, students are expected to:

• Be knowledgeable on the classes of occupational diseases 
• Be able to identify and suggest measures to reduce occurrence of the diseases

 

OCCUPATIONAL DISEASES
Large companies may employ a number of specialists in the field of health, hygiene and safety who co-operate as a team and pool their particular expertise, but in small firms the safety adviser is often the only local source of advice on these matters, other expertise being brought in when considered necessary.
The task of safeguarding the health of persons at work is a formidable one especially during periods of rapid technological and organisational change. Thousands of chemical substances are used by industry and in commerce but only about 800 of those in common use have been recognised as presenting a risk to the health of workpeople.
This component introduces some of the more important diseases and materials that cause them. Conveniently, these fall into four major areas covering illnesses and diseases due to:

• chemical agents
• physical agents
• biological agents
• psycho-social causes

CHEMICAL AGENTS
Toxicology
There is no such state as absolute safety in the use of chemicals since all chemicals are toxic to a degree depending on the dose. The toxicity of a substance is its potential to cause harm on contact with body tissues.
Toxicology is the scientific study of the medical effects on living beings of poisons.

Portals of entry
Occupational poisons gain entry to the body via the lungs, skin and sometimes the gut. Absorption of a poison depends on its physical state, particle size and solubility. Of the substances entering the lung some may be exhaled, coughed up and swallowed, attacked by scavenger cells and remain in the lung or enter the lymphatics. Soluble particles may be absorbed into the blood stream. The skin is protective unless abraded when soluble substances can penetrate to the dermis, as they may also do via the hair follicles, sweat and sebaceous glands, and then be absorbed into the blood stream.
In pregnancy, harmful substances in the mother’s body may cross the placenta to affect the unborn baby.

 

Effects
Effects may be acute, i.e. of rapid onset and short duration; or chronic, i.e. of gradual onset and prolonged. They may be local, occurring at the site of contact only, or general following absorption. Toxic substances may disturb normal cell function, damage cell membranes, interfere with enzyme and immune systems, RNA and DNA activity. Pathological response may be irritant, corrosive, toxic, fibrotic, allergic, asphyxiant, narcotic, anaesthetic and neoplastic.

Metabolism
Most substances absorbed will be carried by the blood stream to the liver where they may be rendered less harmful by a change in their chemical composition. However, some may be made more toxic, e.g. naphthylamine which is responsible for bladder cancer and tetra-ethyl lead which is converted into the tri-ethyl form and is toxic to the central nervous system.

Excretion
The body eliminates harmful substances in the urine, lungs and less commonly the skin. Some are also excreted in the faeces and milk. The time taken to reduce the concentration of a substance in the blood by 50% is known as its biological half-life. Similarly, the time for a 50% fall in concentration of a substance or its metabolite in urine or breath, after cessation of exposure, is its half-life in that medium.

Factors influencing toxicity
A number of factors are important when considering the toxic effect of a substance on the body. These include:

1.  The inherent potential of a substance to cause harm.
2. Its ease of body contact and entry: work method, particle size and solubility.
3. Dose received (concentration and time of exposure).
4. Metabolism in the body (bio-transformation) and its half-life.
5. Susceptibility of the individual which depends on a number of factors:

(a) Body weight; the same dose of a substance is more damaging to the smaller person.
(b) The extremes of age in the working population are more prone to skin damage.
(c) Fair skinned persons are more liable than the dark skinned to chemically induced dermatitis, and to radiation induced skin cancer.
(d) Physical and physiological differences between the sexes may cause a variation in toxic response.
(e) Immunological, nutritional and genetic defects.
(f) Failure to reach a set health standard for work may expose the individual to greater risk.
(g) Inadequate level of training, information, supervision and protection.

 

Epidemiology
Epidemiology may be defined as the study and distribution of disease in human populations. The need for a study may be triggered by suspicions about an individual case, a complaint or the occurrence of a cluster of cases.
An initial descriptive study of a cross-section of the affected population is undertaken to determine:

• What is the disease
• Who is affected (sex, age, race, social class and occupation)
• Where does it occur (factory, workshop, room, laboratory, area of site)
• When does it occur (time, day, shift)
• How are persons infected (skin contact, airborne, body fluids)

From this study a hypothesis may be formed which needs to be tested by an analytical investigation involving a case-control study and a cohort study.
A case-control study compares persons who have the disease with those without to establish whether the suspect cause occurs more frequently among those with than those without the disease.
A cohort study compares those exposed to the suspect cause with those who are not to determine if more persons exposed to the cause develop the disease than those who are not.

DISEASES OF THE SKIN
Non-infective dermatitis
The term ‘dermatitis’ simply means an inflammation of the skin. When the condition is due to contact with a substance at work it is called ‘occupational’ or ‘industrial’ dermatitis. It is a common cause of occupational disease but the number of cases is declining owing to improved work conditions.
The skin has two layers, the outer layer is called the ‘epidermis’ and the inner the ‘dermis’. The epidermis has a protective function. It consists of densely packed flat cells, thicker in some areas, like the palms of the hands, which are more subject to injury. It is covered by a moist film known as an ‘acid mantle’, made up of secretions from sweat and sebaceous glands, that helps to protect from acids, alkalis, excessive water, heat and friction by preventing the skin from drying out. The natural grease of the skin can be removed by solvents. In the deeper layer of the epidermis are pigment cells which produce the ‘tan’ following exposure to sunlight and protect the body from ultraviolet radiation.

Some persons are more susceptible to skin damage than others, particularly the young, those with soft, sweaty skin, the fair complexioned and those with poor personal hygiene. Occupational dermatitis can affect any part of the body, but the hands, wrists and forearms are most commonly involved. Damage to the skin may follow exposure to chemical and biological substances as well as physical agents. Dermatitis is of two kinds: irritative and sensitising – the former is four times more common. Chemicals which cause irritative dermatitis include acids, alkalis, cement, solvents, some metals and their salts. Their effect on the skin depends on the concentration and duration of exposure, and will affect most people in contact with them. At first the response may be minor, but it worsens with repeated contact.
Sensitisers, on the other hand, do not cause dermatitis until the individual has first become sensitised by them. This involves an allergic response in the tissues initially, dermatitis follows on subsequent exposure. Once sensitisation has occurred a small dose may be sufficient to cause a rash. Sensitisers include chrome-salts, nickel, cobalt, plastics made of epoxy, formaldehyde, urea or phenolic resins, rubber additives, some woods and plants. Some substances act as both irritant and sensitiser, e.g. chrome, nickel, turpentine and mercury compounds.

Symptoms
The onset of dermatitis may be unnoticed, especially as it usually clears up when away from work, i.e. at weekends and holidays. On return to work and further exposure the condition recurs, worsening with each subsequent contact. The skin, at first rough and raw, may itch, become cracked and sore, prompting the individual to seek medical advice. The rash may be diffuse, as with eczema, or pimple-like as with acne – the former following exposure to irritative and sensitising agents, and the latter from exposure to mineral oils, pitch and chlorinated hydrocarbons. Patch testing, in which a dilute quantity of chemical is applied to the skin under a plaster and left for several hours to see if a reaction develops, is useful only for determining allergic response to chemicals but requires specialist interpretation.

Protective measures
Persons with dermatitis or sensitive skin may need to be excluded from certain kinds of work. Good personal hygiene is essential and barrier creams may be helpful. Protective clothing should be considered.

Cancer of the scrotum
The first occupational skin cancer was reported by Percivall Pott in 1775, among chimney sweeps. In those days children were apprenticed to master sweeps to climb inside and clean chimneys; their skin became ingrained and their clothes impregnated with soot, and as they seldom washed or changed their clothes the skin was constantly irritated. From puberty onwards a ‘soot wart’ might appear on the scrotum and develop into a cancer. In 1820, Dr Paris wrote of the influence of arsenical fumes affecting those engaged in copper smelting in Cornwall and Wales, giving rise to a cancerous disease of the scrotum similar to that affecting
sweeps. From 1870 a number of substances in a variety of industries were found to cause scrotal cancer – shale oil in those engaged in oil refining and cotton mule spinning; pitch and tar in those making briquettes from pitch-containing coal dust; mineral oil used by engineers and gunsmiths, and paraffin in refinery workers. Others at risk include creosote-timber picklers and anthracene chemical workers, and also sheep-dippers using arsenic.
Workers’ clothes become begrimed with the offending substance, making close contact with the scrotum, the wrinkled skin of which favours the harbouring of the carcinogen.
The cancer begins as a wart, which enlarges and hardens, then breaks down into an ulcer with spread of malignant cells to neighbouring glands and other parts of the body.
Skin cancer is often due to polycyclic aromatic hydrocarbon of the benzpyrene or benzanthracene type. It has also been attributed to sunlight, ionising radiation and arsenic compounds.

Prevention
The use of non-carcinogen oils: carcinogens can be removed from mineral oil by washing with sulphuric acid or solvents. Workers should be educated to avoid contact as much as possible. The use of splash guards on machinery, protective clothing, avoidance of an oily rag placed in a pocket, which could spread oil through the clothes to the scrotum. To wash the hands before toilet and to have a daily bath. Clothes should be kept reasonably clean and a laundry service provided, so that overalls can be changed once or twice a week as need requires. Workers should not wear their dirty overalls after duty, but be encouraged to change into their home clothes. Workers also should be medically examined prior to employment and periodically to ensure that their skin is clear, and be encouraged to report to the doctor any doubtful ‘wart’ that might appear.

Coal tar and pitch
The destructive distillation of coal yields a variety of products, depending on the temperature at which distillation takes place, e.g.
GAS                                                    Temp°C           Product
↑                                                         200                  light oil
250      carbolic substances
Ammoniacal     ←         COA L              →         TAR      ←         300                  creosote
liquid                            ↓                                                         350                  anthracene
↓

COKE              Residue = pitch                       

Distillation at high temperatures results in aromatic polycyclic hydrocarbons retained in the pitch which are harmful to health. Pitch is used in many industries: briquetting of coal, roofing materials, waterproofing of wood, manufacture of electrodes, impermeable paper, optical lenses, dyestuffs and paints.

Symptoms
Exposure of a worker to pitch dust or vapour may harm the skin by causing irritation, tumour or dermatitis. Benign tumours or warts occur on exposed areas of skin, primarily the face, eyelids, behind the ears, the neck, arms and, occasionally, on the scrotum and thighs. Their recurrence is related to duration and degree of exposure to pitch. Many regress spontaneously, especially those appearing early, but some undergo malignant change, particularly those appearing in the older age groups. They need to be removed and examined under the microscope, i.e. biopsied, to check for any malignant change. A variety of other skin conditions may occur such as darkening and thickening of the skin, acne, blackheads, cysts and boils, pitch burns and scarring. There is also a risk of damage to the cornea.

Prevention
Pitch dust and vapour must be avoided by transporting the raw material in a liquid or granular state and enclosing the process as far as possible. Workers require clean protective clothing for head, neck and forearms and eye protection should be worn. Employees ought to be warned of the risk, and advised to report any skin disease which develops. Good personal hygiene is essential and adequate wash and shower facilities need to be provided. Barrier creams applied before work are helpful. Those susceptible to warts should be excluded from further exposure, and each worker needs to be medically examined regularly to detect possible skin disorders.

DISEASES OF THE RESPIRATORY SYSTEM
Pneumoconiosis
The term pneumoconiosis means ‘dust in the lung’, but medically refers to the reaction of the lung to the presence of dust.

Respirable dust is that dust in the air which on inhalation may be retained by the lungs. The amount of dust retained depends on the duration of exposure, the concentration of dust in the respired air, the volume of air inhaled per minute and the nature of the breathing. Slow, deep respirations are likely to deposit more dust than rapid, shallow breathing. Dust in the lung causes a tissue reaction, which varies in nature and site according to the type of dust. Coal and silica dust involve the upper lungs whereas asbestos involves the lower lungs.

Beryllium dust causes acute and chronic symptoms. Early features are breathlessness, cough with bloody sputum and chest pain. Recovery follows removal from exposure, but a chronic state can develop insidiously with cough, breathlessness and loss of weight.

Organic dusts, such as mouldy hay, when inhaled cause a disease known as extrinsic allergic alveolitis with ‘flu-like symptoms; cough and difficulty in breathing occur within a few hours of exposure. Repeated exposure leads to further lung damage and chronic breathlessness.

Talc is a white powder consisting of hydrous magnesium silicate. Although some talc presents little risk to health, commercial grades may contain asbestos and quartz and provoke pneumoconiosis and lung cancer.
Cobalt combined with tungsten carbide forms a hard metal used for the cutting tips of machine tools and drills. Inhalation of the dust may give rise to fibrosis of the lungs causing cough, wheezing and shortness of breath.

Man-made mineral fibres irritate the skin, eyes and upper respiratory tract. A maximum exposure limit has been set based on the risk of lung cancer because a ‘no-adverse-effect’ level cannot be established with reasonable certainty.

 

Silicosis
Silicosis: the commonest form of pneumoconiosis is due to the inhalation of free silica. Free silica (SiO2) or crystalline silica occurs in three common forms in industry: quartz, tridymite and cristobalite.

Industrial exposure occurs in mining, quarrying, stone cutting, sand blasting, some foundries, boiler scaling, in the manufacture of glass and ceramics and, for diatomite, in the manufacture of fluid filters.

Silicosis is the one form of pneumoconiosis which predisposes to tuberculosis, when additional symptoms of fever, loss of weight and bloody sputum may occur.

Medical surveillance
Where exposure to free silica is a recognised hazard, a pre-employment medical is advised, which should enquire into previous history of dust exposure, of respiratory symptoms, with examination of the chest, lung function testing and a chest X-ray. The medical should be repeated periodically as circumstances demand.

Prevention
Reduction of the dust to the lowest level practicable and where necessary by the provision of personal respiratory protective equipment.

Asbestosis
There are three important types of asbestos, blue (crocidolite), brown (amosite) and white (chrysotile). Asbestosis is a reaction of the lung to the presence of asbestos fibres which, having reached the bronchioles and air sacs, cause a fibrous thickening in a network distribution, mainly in the lower parts of the lung. There follows a loss of elasticity in the lung tissue (relative to the concentration of fibres inhaled and the duration of exposure), resulting in breathing difficulty.
Among those at risk are persons engaged in milling the ore, the manufacture of asbestos products, lagging, asbestos spraying, building, demolition, and laundering of asbestos workers’ overalls.
Symptoms develop slowly after a period of exposure which varies from a few to many years. In some cases exposure may have begun so long ago that it cannot be recalled. Breathlessness occurs first and progresses as the lung loses its elasticity. There may be little or no cough and chest pain seldom occurs. The individual becomes weak and distressed on effort and, eventually, even at rest. Unless periodic medicals are introduced the diagnosis will not be made until symptoms appear.
Early diagnosis is essential in order to prevent further exposure and an exacerbation of the condition. Asbestosis predisposes to cancer of the bronchus, a risk increased by cigarette smoking. The chest should be X-rayed every two years and special lung function tests are helpful. Diagnosis depends on history of exposure, chest X-ray, lung function testing, symptoms and physical signs.

Mesothelioma
Mesothelioma is a malignant tumour of the lining of the lung (pleura) or abdomen (peritoneum). The abdominal form is less common. The disease is significantly related to exposure to asbestos, especially the blue and brown varieties. However, in some 10–15% of cases there is no such history of exposure13. Those at risk are miners, manufacturers of asbestos, builders and demolition workers, and even residents in the neighbourhood of blue asbestos working. While the exposure time may have been minimal, there is no safe threshold of dose below which there is no risk of asbestos-related disease. The onset of the disease is delayed by some 20 to 50 years.

Bronchial asthma
Bronchial asthma is defined as breathlessness due to narrowing of the small airways and it is reversible, either spontaneously or as a result of treatment. It may follow inhalation of a respiratory sensitiser or an irritant toxic substance. Symptoms due to sensitisation may be delayed for weeks, months or even years; symptoms due to a toxic substance occur within hours of inhalation, resolve spontaneously but can persist indefinitely. Most cases of occupational asthma are due to sensitization by substances including:

• Isocyanates.
• Flour and grain dust.
• Antibiotic manufacture.
• Hard wood dusts of cedar, oak and mahogany.
• Caster bean dust.
• Azodicarbonamide used in plastics.
• Glutaraldehyde, a cold disinfectant used in the health service.
• Persulphate salts or henna used in hair dressing.
• Crustaceans or fish products used in the food processing industry.
• Reactive dyes.
• Soya bean.
• Tea dust.
• Green coffee bean dust.
• Fumes from stainless steel welding.

 

STUDY UNIT TEN
LEARNING OBJECTIVES
After having worked through this study unit, students are expected to:

• Be knowledgeable on the classes of occupational diseases 
• Be able to identify and suggest measures to reduce occurrence of the diseases

DISEASES FROM METALS
Lead
Lead (Pb) is a relatively common metal, mined chiefly as the sulphide (galena) in many countries – USA, Australia, USSR, Canada and Mexico. Lead has a great variety of uses, e.g. (percentages approximated from annual production figures issued by World Bureau of Metal Statistics, London):

• Electric batteries 27%
• Electric cables 17%
• Sheet, pipe, tubes 16%
• Anti-knock in petrol 11%
• Solder and alloys 9%
• Pottery, plastics, glass, paint 4%
• Miscellaneous 15%

Lead, as a fume or dust hazard, is therefore met in many industries. The pure metal melts at 327°C and begins to fume at 500°C, but the presence of impurities alters these properties and may form a slag on its surface and thereby reduce fuming, except at higher temperatures. Particle size and solubility are important factors governing the absorption of lead via the lungs. In the gut, however, solubility differences of ingested compounds are of less significance. Among lead
miners lead poisoning does not occur due to the insolubility of the sulphide ore.

Inorganic lead can enter the body by inhalation or ingestion. Up to about 50% of that inhaled is absorbed and only about 10% of that ingested. It is then transported in the blood stream and deposited in all tissues, but about 90% of it is stored in the bone. It is a cumulative poison; excretion is slow and occurs mainly in the urine and faeces. Because of the excretion of lead in the urine, kidney damage is a likely long-term effect

Mercury
Mercury (Hg) occurs naturally as the sulphide in the ore known as cinnabar, and also in the metallic form quicksilver. It is mined chiefly in Spain, but also in Italy, Russia, USA and elsewhere. The ore is not particularly hazardous to miners, as the sulphide is insoluble. Risk is greater in other industries, such as in the manufacture of sodium hydroxide and chlorine, electrical and scientific instruments, fungicides, explosives, paints and in dentistry.

Acute mercury poisoning is rare but can occur following the inhalation of quicksilver – it being very volatile at room temperature. There is particular risk should spillage occur in an enclosed space. About 80% of that inhaled can be absorbed17, and a few hours later there occurs cough, tight chest, breathlessness and fever. Symptoms last a week or so, dependent upon degree of exposure, but its effects are reversible.

Chromium
Chromium (Cr) is a silvery hard metal used in alloys and refractories. Chrome salts are used in dyeing, photography, pigment manufacture and cements. Electroplating tanks contain solutions of chromic acid which forms a mist during the electrolysis process.
Chromates and dichromates used in cement manufacture and chromium plating may cause skin irritation or ulceration and chrome ulcers in the skin of the hands or in the inside of the nose where the ulcer may penetrate the cartilage of the nasal septum.

Arsenic (As)
Inorganic arsenic compounds cause irritation of the skin and may produce skin cancer. It is used in alloys to increase hardness of metals, especially with copper and lead.

Manganese (Mn) and compounds
This is used to make manganese alloy steels, dry batteries and potassium permanganate which is an oxidising agent and a disinfectant. Poisoning is rare and follows inhalation of the dust causing acute irritation of the lungs and affects the brain leading to impaired control of the limbs rather like Parkinson’s disease.

PESTICIDES
Insecticides
Various organo-phosphorus compounds are used; two of the commonest are demeton-S-methyl and chlorpyrifos. Poisoning causes headaches, nausea and blurred vision. Further symptoms include muscle twitching, cramps in the belly muscles, severe sweating and respiratory difficulties. Extreme exposure may lead to death.

All these effects are due to interference with a chemical enzyme called cholinesterase which is concerned with the passage of nerve impulses. The level of this enzyme in the worker’s blood can be measured and if it falls below a certain value the worker must be removed from contact with the chemical until his blood returns to normal. The appropriate protective clothing must be worn at all times when working with these materials.

Herbicides
Commonly used as a weedkiller (e.g. paraquat). Ingestion may result in damage to the liver, kidneys and lung. There is no antidote and death occurs in about half the cases.

 

SOLVENTS
A solvent is a liquid that has the power to dissolve a substance: water is a common example. In industry organic liquids are often used as solvents, and these are mainly hydrocarbons used as degreasing agents and in the manufacture of paints and plastics.
Examples of solvents

1. Hydrocarbons

(i)        Aromatic Benzene; toluene; styrene
(ii)       Aliphatic Paraffin; white spirit
Aliphatic alcohols Methyl alcohol; ethyl alcohol
Aliphatic ketones Methyl-ethyl-ketone
Aliphatic ethers Diethyl ether
Aliphatic esters Ethyl acetate
Aliphatic chlorinated Trichloroethylene; carbon tetrachloride

2. Non-hydrocarbons Carbon disulphide

 

All organic solvents are volatile and have a vapour density greater than one, i.e. their vapours are heavier than air and will therefore settle at floor level; this is important to note when considering ventilation. With the exception of the chlorinated hydrocarbons they tend to be flammable and explosive and in the liquid form most have specific gravities of less than one so will float on water. In the event of a fire, attempt should not be made to extinguish with water, as the solvent will float away and the fire will spread. The chlorinated solvents, being neither flammable nor explosive but heavier than water, have been used as fire
extinguishants.

Solvents vary widely in their toxicological properties. In common they cause dermatitis by removing the natural grease from the skin, and narcosis by acting on the central nervous system; additionally some can damage the peripheral nerves, the liver and kidneys and interfere with blood formation and cardiac rhythm. Chlorinated solvents can decompose if exposed to a naked flame to produce acidic fumes (hydrochloric acid and small amounts of phosgene) which are harmful to the lungs. Any harmful effect is related to the amount of solvent absorbed.

Carbon tetrachloride
Its main use is in the manufacture of chlorofluorocarbons, also aerosols and refrigerants. It has been used in fire extinguishers and grain fumigation. Its use in dry cleaning has declined because of its toxicity. Carbon tetrachloride is absorbed into the blood mainly via the lungs, but also via the skin and gut.

In common with other solvents it has a narcotic effect, with features varying from headache and drowsiness to coma and death.
Carbon tetrachloride can also cause damage to the kidneys and liver.

GASSING
In the UK those gassing accidents that are reported annually occur in the following approximate order of frequency:
1 Carbon monoxide
2 Chlorine*
3 Hydrochloric acid*
4 Trichloroethylene
5 Sulphur dioxide*
6 Ammonia*
7 Hydrogen sulphide*
8 Phosgene
9 Carbon dioxide
10 Nitrous fumes
11 Phosphorus oxychloride*
12 Carbon tetrachloride
*Highly soluble gases which will irritate the eyes and upper respiratory tract while the less soluble components pass further down the tract to irritate the lung tissue.

Asphyxia caused by gassing falls into two broad categories:

Simple:           in which oxygen in the lungs is replaced by another gas such as carbon dioxide, nitrogen or methane.
Toxic:             in which there is a metabolic interference with the oxygen taken up by the body. This occurs with gases such as carbon monoxide, hydrogen sulphide and hydrogen cyanide.

Oxygen deficiency
Normal respiration requires:

1. An adequate concentration and partial pressure of oxygen in the inspired air.
2. A clear airway to the lungs.
3. Transfer of oxygen in the air sacs to the blood.
4. The transport of oxygen by the red cells to the tissues.

Normal oxygen requirements depend on body size, activity and fitness, and interruption of the supply can occur through failure at any of the above indicated levels. Fresh air contains approximately 21% oxygen, 79% nitrogen, 0.03% carbon dioxide. Although inspired air contains 21% oxygen, that in the air sacs has only 14% which at sea level exerts sufficient partial pressure to cross the lung–blood barrier.
At altitudes above sea level the percentage of oxygen in air is unaltered, but because the barometric pressure is less, the partial pressure of oxygen drops accordingly and makes breathing more difficult.

In confined spaces the oxygen concentration can fall by several means. It can be displaced by another gas, e.g. a simple asphyxiant such as carbon dioxide. In a disused and ill-ventilated coal mine the oxygen present could be used up in oxidising the coal, resulting in a condition known as ‘black damp’. Combustion requires oxygen, so that in a confined space a flame will burn up the oxygen present.
Similarly, oxygen can be ‘combusted’ by ordinary respiration of persons working in the space. Canister type respirators should not be worn in a confined space, because of the danger of a depletion of oxygen in the atmosphere; instead full breathing apparatus should be used.

OCCUPATIONAL CANCER
Cancer is a disorder of cell growth. It begins as a rapid proliferation of cells to form the primary tumour (neoplasm) which is either benign or malignant. If benign it remains localised, but may produce effects by pressure on neighbouring tissue. A malignant tumour invades and destroys surrounding tissue and spreads via lymph and blood streams to distant body parts (metastasis) such as the lung, liver, bone or kidney (secondary tumours).

The patient becomes weak, anaemic and loses weight (cachexia). Pneumonia is the commonest form of death. The incidence of cancer increases with age and is responsible for 24% of all deaths.

Cancer is caused either by the inheritance of an abnormal gene, or exposure to an environmental agent acting either directly or indirectly on the cell genes.
Of all cancers, less than 8% are occupational and due to chemical and physical agents (see Table 3.2.1). Occupational cancers tend to occur after a long latent period of some 10–40 years and at an earlier age than spontaneous cancers.
Some carcinogens act together (synergistically); an example is found in asbestos workers who smoke and are much more likely to develop cancer of the bronchus than those who do not.

Table 3.2.1 Table of some causes of occupational cancer in man

Agent	Body site affected	Typical occupation
Sunlight	Skin	Farmers and seamen
Asbestos	Lung, pleura, peritoneum	Demolition workers, miners
2-naphthylamine	Bladder	Dye manufacture, rubber workers
Polycyclic aromatic hydrocarbons	Skin, lung	Coal gas manufacture, workers exposed to tar
Hard wood dust	Nasal sinuses	Furniture manufacture
Leather dust	Nasal sinuses	Leather workers
Vinyl chloride monomer	Liver	PVC manufacture
Chromium fume	Lung	Chromate manufacture
Ionising radiations	Skin and bone marrow	Radiologists and radiographers

The classification of carcinogens is based on internationally agreed epidemiological and animal studies and are:
Group 1         Carcinogenic to humans.
Group 2a       Probably carcinogenic to humans with sufficient evidence from animal studies.
Group 2b       Possibly carcinogenic to humans but absence of sufficient evidence from animal tests.
Group 3         Not classifiable as to its carcinogenicity to humans.
Group 4         No evidence of carcinogenicity in humans or animals.

Although the total number of deaths from cancer has risen there is no evidence that the increase is due to the effect of industrial chemicals. The two most important factors leading to this increase appear to be the ever increasing number of lung cancer deaths due to smoking and fewer deaths from other causes such as infection thus putting more people at risk of developing cancer who otherwise would have died from other causes.

 

PHYSICAL AGENTS
In recent years there has been an increasing recognition of the harm that physical agents can do to the health of people at work. Injuries from this source now account for two-thirds of the new successful claims for industrial disease compensation.

Hand–arm vibration syndrome (HAVS)
HAVS follows from exposure to vibrations in the range 2–1500 Hz which causes narrowing in the blood vessels of the hand, damage to the nerves and muscle fibres and to bones and joint31 evidenced by pain and stiffness in the joints of the upper arm. The impaired circulation of blood to the fingers leads to a condition known as vibration white finger (VWF). The most damaging frequency range is 5–350 Hz.

Ionising radiations
Ionising radiations are so called because they produce ‘ions’ in irradiated body tissue. They also produce ‘free radicals’ which are parts of the molecule, electrically neutral but very active. The biological consequences of radiation depend on several factors:

1. The nature of the radiation – some radiations being more damaging than others. Alpha particles are not harmful until they enter the body by inhalation, ingestion or via a wound. Beta particles can penetrate the skin to about 1 cm and cause a burn. X-rays, gamma rays and neutrons can pass right through the body and cause damage on the way.
2. The dose and duration of exposure.
3. The sensitivity of the tissue.
4. The extent of the radiation.
5. Whether it is external or internal.

Principles of control
The following simple precautions should be adopted to reduce to a minimum hazards from the use of radioactive materials:

1. Employ the smallest possible source of radiation.
2. Ensure the greatest distance between source and person.
3. Provide adequate shielding between source and person.
4. Reduce exposure time to a minimum.
5. Practice good personal hygiene where there is risk of absorption of radioactive material.
6. Personal sampling by use of (a) film badge and/or (b) thermal luminescent dose meter.
7. A dose of 15 mSv whole body in a year requires investigation of work exposure and control procedures. A cumulative dose of 75 mSv within five years requires further investigation of work, personal circumstances, dose history and advice regarding further exposure to ionizing radiations.

Noise-induced hearing loss
Noise is commonly defined as unwanted sound. The definition is dependent on individual interpretation and may or may not include the recognition that some sounds produce harmful effects. Some ‘sounds’ cause annoyance, fright, or stress; others may interfere with communication. Loud sounds can cause deafness. ‘Noise’-induced deafness is of two kinds: temporary and permanent.
Temporary deafness
Exposure to noise levels of about 90 dBA for even a few minutes may induce a temporary threshold shift (change of the threshold at which sound can just be heard), lasting from seconds to hours, and which can be detected by audiometry. Temporary threshold shift (TTS) may be accompanied by ‘noises’ in the ears (tinnitus) and may be a warning sign of susceptibility to permanent threshold shift (PTS) which is an irreversible deafness.
Permanent deafness
The onset of permanent deafness may be sudden, as with very loud explosive noises, or it may be gradual. A gradual onset of deafness is more usual in industry and may be imperceptible until familiar sounds are lost, or there is difficulty in comprehending speech. There is a risk too that a person exposed to excessive noise may believe himself to be adjusting to it when, in fact, partial deafness has already developed.

WORKING IN HEAT
Normally the human body maintains its core temperature within the range 36–37.4°C by balancing its heat gains and losses. Maintaining an employee’s health in a hot environment requires the control of air temperature and humidity, body activities, type of clothing, exposure time and ability to sweat. To sweat freely the individual must be fit, acclimatised to the heat with sufficient water intake to ensure a urine output of about 2 1⁄2 pints per day. When the air temperature reaches 35°C plus, the loss of body heat is by sweating only, but this may be difficult when humidity reaches 80% or more.
Body reactions to overheating are:

• An increase in pulse rate. The rate should fall by 10 beats/minute on cessation of exposure.
• Muscle cramp due to insufficient salt intake. Exhaustion with the individual feeling unwell and perhaps confused.
• Fainting and dizziness with pallor and sweating.
• Heat stroke is the most serious with the body temperature very high, the skin dry and flushed.
• Dehydration due to insufficient fluid intake. Prolonged dehydration may lead to the formation of stones in the kidney.

Following first aid care, the patient needs to be referred to a doctor.

 

STUDY UNIT ELEVEN
LEARNING OBJECTIVES
After having worked through this study unit, students are expected to:

• Be knowledgeable on the classes of occupational diseases 
• Be able to identify and suggest measures to reduce occurrence of the diseases

 

WORKPLACE BIOHAZARDS
The assessment of biohazards in the workplace has been concentrated on agricultural workers, health-care workers and laboratory personnel, who are at considerable risk of adverse health effects. The compilation of biohazards below shows how widespread the risks can be to workers in many other occupations as well.  
 
Table:  Occupational settings with potential exposure of workers to biological agents

Sector	Examples
Agriculture	Cultivating and harvesting Breeding and tending animals Forestry Fishing
Agricultural products	Abattoirs, food packaging plants Storage facilities: grain silos, tobacco and other processing Processing animal hair and leather Textile plants Wood processing: sawmills, papermills, cork factories
Laboratory animal care
Health care	Patient care: medical, dental
Pharmaceutical and herbal products
Personal care	Hairdressing, chiropody
Clinical and research laboratories
Biotechnology	Production facilities
Day-care centres
Building maintenance	“Sick” buildings
Sewage and compost facilities
Industrial waste disposal systems

 
Source: Dutkiewicz et al. 1988.

 

Micro-organisms
Micro-organisms are a large and diverse group of organisms that exist as single cells or cell clusters. Microbial cells are thus distinct from the cells of animals and plants, which are unable to live alone in nature but can exist only as parts of multicellular organisms.
 
Four broad classes of micro-organisms that can interact with humans are bacteria, fungi, viruses and protozoa. They are hazardous to workers due to their wide distribution in the working environment. There are three major sources of such microbes:
 
1. those arising from microbial decomposition of various substrates associated with particular occupations (e.g., mouldy hay leading to hypersensitivity pneumonitis)
2. those associated with certain types of environments (e.g., bacteria in water supplies)
3. those stemming from infective individuals harbouring a particular pathogen (e.g., tuberculosis).
 
Some Occupational Settings with Biohazards
Medical and laboratory staff and other health-care workers, including related professions, are exposed to infection by micro-organisms if the appropriate preventive measures are not taken. Hospital workers are exposed to many biological hazards, including human immunodeficiency virus (HIV), hepatitis B, herpes viruses, rubella and tuberculosis.
 
Work in the agricultural sector is associated with a wide variety of occupational hazards. Exposure to organic dust, and to airborne micro-organisms and their toxins, may lead to respiratory disorders. These include chronic bronchitis, asthma, hypersensitivity pneumonitis, organic dust toxic syndrome and chronic obstructive pulmonary disease. Dutkiewicz and his colleagues (1988) studied samples of silage for the identification of potential agents causing symptoms of organic and toxic syndrome. Very high levels of total aerobic bacteria and fungi were found. Aspergillus fumigatus predominated among the fungi, whereas bacillus and gram-negative organisms (Pseudomonas, Alcaligenes, Citrobacter and Klebsiella species) and actinomycetes prevailed among the bacteria. These results show that contact with aerosolized silage carries the risk of exposure to high concentrations of micro-organisms, of which A. fumigatus and endotoxin-producing bacteria are the most probable disease agents.
 
Short-term exposures to certain wood dusts may result in asthma, conjunctivitis, rhinitis or allergic dermatitis. Some thermophilic micro-organisms found in wood are human pathogens, and inhalation of ascomycete spores from stored wood chips has been implicated in human illnesses.
 
Examples illustrative of specific working conditions follow:
 
1. The fungus Penicillium camemberti var. candidum is used in the production of some types of cheese. The high frequency of precipitating antibodies of this fungus in the workers’ blood samples, together with the clinical causes of the airway symptoms, indicate an aetiological relationship between airway symptoms and heavy exposure to this fungus (Dahl et al. 1994).
2. Micro-organisms (bacteria and fungi) and endotoxins are potential agents of occupational hazard in a potato processing plant (Dutkiewicz 1994). The presence of precipitins to microbial antigens was significantly correlated with the occurrence of the work-related respiratory and general symptoms that were found in 45.9% of the examined workers.
3. Museum and library personnel are exposed to moulds (e.g., Aspergillus, Penicillium) which, under certain conditions, contaminate books (Kolmodin-Hedman et al. 1986). Symptoms experienced are attacks of fever, chill, nausea and cough.
4. Ocular infections can result from the use of industrial microscope eyepieces on multiple shifts. Staphylococcus aureus has been identified among the micro-organism cultures (Olcerst 1987).
 
An understanding of the principles of epidemiology and the spread of infectious disease is essential in the methods used in the control of the causing organism.
 
Preliminary and periodic medical examinations of workers should be carried out in order to detect biological occupational diseases.

Vertebrates: Snakes and Lizards
In hot and temperate zones, snakebites may constitute a definite hazard for certain categories of workers: agricultural workers, woodcutters, building and civil engineering workers, fishermen, mushroom gatherers, snake charmers, zoo attendants and laboratory workers employed in the preparation of antivenom serums. The vast majority of snakes are harmless to humans, although a number are capable of inflicting serious injury with their venomous bites; dangerous species are found among both the terrestrial snakes (Colubridae and Viperidae) and aquatic snakes (Hydrophiidae).
 
According to the World Health Organization (WHO 1995), snakebites are estimated to cause 30,000 deaths per year in Asia and about 1,000 deaths each in Africa and South America. More detailed statistics are available from certain countries. Over 63,000 snakebites and scorpion stings with over 300 deaths are reported yearly in Mexico. In Brazil, about 20,000 snakebites and 7,000 to 8,000 scorpion stings occur annually, with a case-fatality rate of 1.5% for snake bites and between 0.3% and 1% for scorpion stings. A study in Ouagadougou, Burkina Faso, showed 7.5 snakebites per 100,000 population in peri-urban areas and up to over 69 per 100,000 in more remote areas, where case-fatality rates reached 3%.
 
Snakebites are a problem also in developed parts of the world. Each year about 45,000 snakebites are reported in the United States, where the availability of health care has reduced the number of deaths to 9-15 per year. In Australia, where some of the world’s most venomous snakes exist, the annual number of snakebites is estimated at between 300 and 500, with an average of two deaths.
should wear foot and leg protection and be provided with monovalent or polyvalent antivenom serum. It is recommended that persons working in a danger area at a distance of over half-an-hour’s travel from the nearest first-aid post should carry an antivenom kit containing a sterilized syringe. However, it should be explained to workers that bites even from the most venomous snakes are seldom fatal, since the amount of venom injected is usually small. Certain snake charmers achieve immunization by repeated injections of venom, but no scientific method of human immunization has yet been developed.

Many national occupational standards include biological hazards in their definition of harmful or toxic substances. However, in most regulatory frameworks, biological hazards are chiefly restricted to micro-organisms or infectious agents. Several US Occupational Safety and Health Administration (OSHA) regulations include provisions on biological hazards. The most specific are those concerning hepatitis B vaccine vaccination and blood-borne pathogens; biological hazards are also covered in regulations with a broader scope (e.g., those on hazard communication, the specifications for accident prevention signs and tags, and the regulation on training curriculum guidelines).
 
Although not the subject of specific regulations, the recognition and avoidance of hazards relating to animal, insect or plant life is addressed in other OSHA regulations concerning specific work settings-for example, the regulation on telecommunications, the one on temporary labour camps and the one on pulpwood logging (the latter including guidelines concerning snake-bite first-aid kits).

 

PSYCHO-SOCIAL DISORDERS
This group is probably the largest group of occupational diseases. It stems from the complex interaction of individual, social and work factors and is responsible for a great amount of sickness absence.
Stress
Stress is a reaction of the body to external stimuli ranging from the apparently normal to the overtly ill health. It varies with the individual personality but is one of the commonest occupational diseases.
The initial response is physiological and shows as an increase in pulse, blood pressure and respiratory rates. Although the body adjusts, persisting stimuli cause fatigue and the display of signs of ‘overstress’ with sweating, anxiety, tremors and dry mouth. There is difficulty in relaxing, a loss of concentration, appetite is impaired and sleep disturbed. Some may eventually become depressed, aggressive and try to avoid the cause through absenteeism or the use of alcohol or drugs. Other diseases may appear affecting the skin, peptic ulcer and coronary heart disease. Studies have identified two personality groups: type A people who are competitive, impatient achievers and who are at greatest risk from the severe effects of stress, whereas type B people are easy-going, patient and less susceptible to pressure. Causes of stress may be considered under a number of headings:
The person-              lack of physical and mental fitness to do the job; inadequate training or skill for the particular job; poor reward and prospects; financial difficulties; fear of redundancy; lack of security in the job; home and family problems; long commuting distances.
Work demand-          long hours; shift work; too fast or too slow a pace; boring repetitive work; isolation; no scope for initiative or responsibility.
Environment –          noise; heat; humidity; fumes; dust; poor ventilation; diminished oxygen; confined space; heights; poor house-keeping; bad ergonomic design.
Organisation –          poor industrial relations, welfare services and communications; inconsiderate supervision; remote management.
Common occupational causes of stress are sustained uncertainty, frustration and conflict. Stress has been given a ‘social rating scale’
death of a spouse               100
divorce                                  73
marital separation               65
injury/disease                      53
dismissal                               47
financial difficulties             38
work responsibilities           29
[adopted from Holmes, T.H. and Rahe, R.H., Journal of Psychosomatic Research, 213–218 (1967)]