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
• 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
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
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
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
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
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
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)
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
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
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
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
Classification of carcinogens
• International Agency for Research on Cancer
(IARC)
• Classifies substances into 5 groups depending on strength
of evidence for causing cancer
•
•
•
•
Group 1
Group 2A
Group 2B
Group 3
• Group 4
Carcinogenic to humans
Probably carcinogenic to humans
Possibly carcinogenic to humans
Not classifiable as to carcinogenicity
to humans
Probably not carcinogenic to humans
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 A1
• Group A2
• Group A3
• Group A4
• Group A5
Confirmed human carcinogen
Suspected human carcinogen
Confirmed animal carcinogen with
unknown relevance to humans
Not classifiable as a human carcinogen
Not suspected as a human carcinogen
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
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
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)
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
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, rosincored solder fumes, animal proteins, some wood dusts and
detergent and bakery enzymes
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
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?