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W507 – Types of health effects. Types of health effects. Asphyxiation Irritation Narcosis Systemic toxicity Genotoxicity and carcinogenicity Sensitisation (allergic reaction) Reproductive effects. Asphyxiation. Asphyxiants can reduce the level of oxygen in the body to dangerous levels

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W507 – Types of health effects

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W507 – Types of health effects


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Types of health effects

  • Asphyxiation

  • Irritation

  • Narcosis

  • Systemic toxicity

  • Genotoxicity and carcinogenicity

  • Sensitisation (allergic reaction)

  • Reproductive effects


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Asphyxiation

  • Asphyxiants can reduce the level of oxygen in the body to dangerous levels

    • Two types – simple asphyxiants and chemical asphyxiants

  • Simple asphyxiants

    • Chemically inert – they reduce the amount of oxygen in the air by displacing it in an enclosed environment

      • Air normally contains 21% oxygen

      • If reduced below about 16% it can result in unconsciousness

      • At lower levels can lead to death

    • Examples include nitrogen, argon, helium, methane


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Chemical asphyxiation

  • Prevent normal uptake or use of oxygen in the body

  • Haemoglobin in red blood cells, transports oxygen around the body as oxyhaemoglobin.

    • Carbon monoxide binds strongly with haemoglobin forming carboxyhaemoglobin. This reduces the amount of haemoglobin available to transport oxygen.

    • Hydrogen cyanide – fast acting asphyxiant that prevents normal uptake of oxygen into the cells


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Irritation

  • An irritant can cause inflammation on contact with the skin or mucous membranes

  • Acute effects include

    • Skin – redness

    • Eyes – itchy, red or watery

    • Upper respiratory tract – coughing, sneezing (in severe cases lungs may produce excess fluid causing breathing difficulties

  • Examples include ammonia, chlorine, oxides of nitrogen etc


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Irritation

  • Chronic exposure can also lead to other effects

    • Chronic exposure to respiratory irritant can cause bronchitis

    • Chronic exposure to skin irritants can lead to dermatitis – symptoms include dry flaking skin, itchy, redness, inflammation

  • Extreme form of irritation is from contact with corrosive substances that can cause tissue damage from which the tissues generally do not recover

    • e.g. concentrated acids, alkalis


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Narcosis

  • A narcotic substance depresses the normal function of the central nervous system (CNS)

  • Symptoms may include

    • fatigue, headaches, light headedness and euphoria

    • at higher exposures dizziness, nausea, unconsciousness and death

  • A common group of substances found in industry that can cause narcosis are organic solvents


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Systemic toxicity

  • Systemic toxicity - effects caused by a substance at organs remote from the point of contact

    • Effects may be caused by the substance or by its metabolites (breakdown products)

    • Due to metabolic processes liver and kidney particularly susceptible to damage by toxic substances


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Carcinogenicity

  • Carcinogenicity – the ability of a substance (a carcinogen) to induce cancer

  • Cancer is a disorder of cells characterised by abnormal cell division and growth

    • It begins when one or more cells fails to respond to the normal control mechanisms and divide in an uncontrolled manner

  • Two main mechanisms by which cancer may be caused

    • Genotoxic mechanism

    • Irritant (non-genotoxic mechanism)


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Genotoxicity and carcinogenicity

  • Genotoxicity – ability of a substance to induce damage to the genetic material in a cell

    • Such substances termed genotoxic or mutagenic

  • Can damage the genetic material in the cell and lead to irreversible changes called mutations

    • If mutations occur in germ cells they can be passed on to offspring where effects may be seen

    • If mutations occur in non-germ (somatic) cells, they may change the way that normal cell division is regulated so that it becomes uncontrolled and may lead to cancer


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Genotoxicity and carcinogenicity

  • Non-genotoxic mechanism

    • Not all carcinogens are genotoxic (e.g. asbestos) therefore there must be another mechanism

    • Repeated damage to tissues may cause increased rate of cell division

      • Tissues are constantly being damaged and repaired - any increase in cell division may lead to a greater chance of mutations becoming permanent rather than be repaired


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Genotoxicity and carcinogenicity

  • Benign tumours - e.g. warts, polyps and fibroids

    • May grow large enough to cause pain

    • Do not spread to other parts of the body

    • Usually not life-threatening, can generally be surgically removed

  • Malignant tumours

    • Can spread (metastasise) throughout body with development of secondary tumours

    • Tend to respond poorly to medical treatment

    • Usually life-threatening


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Genotoxicity and carcinogenicity

  • Difficulties in identifying carcinogens

    • Many potential causes of cancer

    • Often difficult to prove a causal link between exposure to a substance and cancer

    • Often a long latent period between exposure and development of cancer

  • There is, however, significant evidence that cancer may develop after occupational exposure to a number of different chemicals


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Classification of carcinogens

  • International Agency for Research on Cancer (IARC)

    • Classifies substances into 5 groups depending on strength of evidence for causing cancer

    • Group 1Carcinogenic to humans

    • Group 2AProbably carcinogenic to humans

    • Group 2BPossibly carcinogenic to humans

    • Group 3Not classifiable as to carcinogenicity to humans

    • Group 4Probably not carcinogenic to humans


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Classification of carcinogens

  • American Conference of Governmental and Industrial Hygienists (ACGIH)

    • Classifies substances into 5 groups depending on strength of evidence for causing cancer

    • Group A1Confirmed human carcinogen

    • Group A2Suspected human carcinogen

    • Group A3Confirmed animal carcinogen with unknown relevance to humans

    • Group A4Not classifiable as a human carcinogen

    • Group A5Not suspected as a human carcinogen


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Classification of carcinogens

  • Globally Harmonised System (GHS) of Classification of Labelling of Chemicals (see Section 11)

    • Beginning to be implemented in many countries

    • Includes regulatory requirements to identify carcinogens on labels


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Sensitisation – (Allergic reaction)

  • The body’s immune system reacts as if the substance is an invading micro-organism, producing an adverse reaction

    • e.g. hay fever caused by pollen

  • White blood cells and antibodies play important roles in the body’s defence and immune systems

    • One type of antibody, Immunoglobulin E (IgE) is involved in many allergic responses

  • On first contact with an allergen, an allergy prone person makes large amounts of specific IgE antibodies

    • After first exposure these antibodies remain in the blood plasma for many years and respond rapidly to further exposure to that substance


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Sensitisation – (Allergic reaction)

  • In industrial hygiene there are two main types of sensitisers - respiratory sensitisers and skin sensitisers

    • Sensitisation normally develops over a period of time following repeated exposure

    • Once sensitised, the immune system of a person is likely to respond adversely to subsequent exposure (even at very low levels)


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Sensitisation – (Allergic reaction)

  • Skin sensitisers

    • Immune reaction results in release of histamine that causes inflammation of the skin (allergic contact dermatitis)

      • Symptoms include red, itchy, scaly rash

      • Usually occurs 6 – 48 hours after exposure

      • May also manifest as an itchy rash – pale raised areas surrounded by red skin – similar to nettle rash

    • Examples include chromium, nickel, latex and epoxy resins


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Sensitisation – (Allergic reaction)

  • Respiratory sensitisers

    • Immune reaction results in histamine release causing a range of effects including narrowing and inflammation of airways and difficulty in breathing

      • Symptoms in many cases are characteristic of asthma

      • Term ‘occupational asthma’ often used instead of respiratory sensitisation

      • In extreme cases reaction can be particularly severe leading to heart stopping (anaphylactic shock)

    • Examples include isocyanates, grain and flour dusts, rosin-cored solder fumes, animal proteins, some wood dusts and detergent and bakery enzymes


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Reproductive effects

  • Reproductive toxicants

    • Substance that may affect an individual by reducing their fertility

      • e.g. glycol ethers, lead

  • Developmental toxicants (teratogens)

    • Substances that may affect the developing foetus

    • May result in abnormalities of the child or affect its development after birth

      • e.g. lead, methyl mercury, thalidomide


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Group work

  • In your allocated groups list 5 hazardous substances that people are exposed to at your workplaces. For each identified substance identify the following

    • What are the likely health effects of the substance?

      • e.g. irritant, asphyxiant, narcotic, carcinogenic etc

    • In what physical form are the substances present?

      • e.g. gas, vapour, fume, dust etc

    • Are the effects acute or chronic?

    • Are the effects local or systemic?


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