01_principles_of_toxicology_and_epidemiology_20140117152955

Question 1

There are several pieces of legislation that control the supply and use of hazardous substances in the UK. These are: 6

Answer 1

European Regulations  Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) Regulation EC 1907/2008  Classification, Labelling and Packaging of Substances, and Mixtures (CLP) Regulation EC1272/2008 UK Regulations  Chemical (Hazard, Information and Packaging for Supply) Regulations 2009 CHIP4  Control of Substances Hazardous to Health Regulations 2002, as amended CoSHH  Control of Lead at Work Regulations 2002 CLAW  Control of Asbestos Regulations 2012 CAR

Question 2

Countries in the United Nations, including those in the European Union, have been working together with industry representatives and others to agree a classification and labelling system that can be used worldwide. The outcome is

Answer 2

the Globally Harmonised System of Classification and Labelling of Chemicals, known as the ‘GHS’. The GHS provides a single system to identify hazards and to communicate them in transporting and supplying chemicals across the world i.e. labels and safety data sheets.

Question 3

European Union (EU) Member States agreed to adopt the GHS across the EU through a direct acting Regulation:

Answer 3

the Classification, Labelling and Packaging of Substances and Mixtures. This is also known as the ‘CLP Regulation’ or just ‘CLP’.

Question 4

In addition to CLP The European Commission presented a proposal for a new EU regulatory system for chemicals:

Answer 4

REACH, which stands for:  Registration  Evaluation  Authorisation of CHemicals.

Question 5

All Chemicals will require EU authorisation by _________ before the materials are allowed to sold or imported within the EU. Their use may also be restricted.

Answer 5

the European Chemical Agency (ECHA)

Question 6

REACH is an EU Regulation that covers all chemicals (with a few exceptions) if they are manufactured or imported into the EU in quantities of ________________

Answer 6

1 tonne or above.

Question 7

REACH is designed to: 7

Answer 7

 Improve information in the supply chain - many substances are data poor and this can lead to inadequate risk assessments.  Promote better risk management measures.  Facilitate compliance with CoSHH.  Encourage the use of safer alternatives for CMR substances.  Allow the free movement of substances on the EU market.  Question the need for animal testing.  Lead to improvements in occupational health.

Question 8

Under REACH, each producer and importer of chemicals in volumes of 1 tonne or more per year and will have to register each chemical with the EU Chemicals Agency (the ECHA), submitting information on:

Answer 8

 properties  uses  safe ways of handling them.

Question 9

Through REACH evaluation, public authorities will look in more detail at registration dossiers and at substances of concern. 4

Answer 9

 Completeness check.  Compliance check.  Dossier evaluation.  Substance evaluation.

Question 10

Under REACH, Use-specific authorisation will be required for chemicals that cause: 4

Answer 10

 Cancer  Mutations  Problems with reproduction. It is also required for those that accumulate in human bodies and the environment.

Question 11

A comparison between the approach of REACH and CoSHH 4

Answer 11

REACH CoSHH Main obligations on manufacturer / importer (though also on supplier and downstream user) All obligations on individual employer Covers manufacture of a substance and all identified uses across the EU >10 tonnes / year Covers all work activities with all hazardous substances at that site, including process derived substances (dust, fume etc.) Substance driven Tends to be task/process driven Risk management measures more likely to be broadly based Risk management measures more likely to be site specific

Question 12

The intention of the CLP Regulation is:

Answer 12

very similar to CHIP – substances and mixtures that are placed on the market should be classified, labelled and packaged appropriately. But because CLP adopts the GHS, in time, the same classifications and labelling will be used throughout the world.

Question 13

CHIP 4 is a set of UK Regulations that

Answer 13

sets out the transitional arrangements for the implementation of CLP within the UK,

Question 14

Classification Classification is the process of: 2

Answer 14

 Deciding what kind of hazard the chemical has.  Explaining the hazard by assigning a simple sentence that describes it (known as a 
‘risk phrase’ or ‘R-phrase’ for short).

Question 15

Labelling If a dangerous chemical is supplied in a package, the package must be labelled. The aim of the label is to: 2

Answer 15

 Inform anyone handling the package or using the chemicals about its hazards.  Give brief advice on what precautions are needed.


Question 16

Packaging CHIP requires that the packaging used for a chemical must be suitable. CHIP sets out special requirements for the packaging of certain chemicals that are sold to the public: 2

Answer 16

 Some have to be fitted with a child-resistant closure (meeting a certain standard) to prevent young children swallowing the contents.  Some must have a tactile danger warning (normally a small, raised triangle) to alert the blind and partially sighted that they are handling a dangerous product.

Question 17

CoSHH defines a ‘substance hazardous to health’ as one which: 5

Answer 17

1) Is listed in the approved supply list (ASL) as dangerous for supply within the meaning of the CHIP Regulations and for which an indication of danger specified for the substance is very toxic, toxic, harmful, corrosive or irritant. 2) The Health and Safety Executive has approved a workplace exposure limit (WEL). 3) Is a biological agent. 4) Is dust (other than those covered in (a) or (b) above) present at a concentration in air equal to or greater than:  10 mg/m3, as a time-weighted average over an 8-hour period, of inhalable dust  4 mg/m3, as a time-weighted average over an 8-hour period, of respirable dust 5) Because of its chemical or toxicological properties and the way it is used or is present at the workplace creates a risk to health.

Question 18

A summary of the CoSHH duties

Answer 18

6 Risk assessment 7 Prevention or control of exposure 8 Use of control measures 9 maintenance, examination and test of control measures 10 Monitoring exposure at workplace 11 Health surveillance 12 Information, training 13 Arrangements to deal with accidents, incidents and emergencies

Question 19

Monitoring exposure (Regulation 10) Where the risk assessment indicates it is necessary, workplace (environmental) monitoring of exposure must be undertaken unless it is possible to demonstrate another means of preventing or controlling exposure. Monitoring must be at regular intervals in addition to when a change occurs that may affect exposure. There is mandatory monitoring for:

Answer 19

Vinyl chloride monomer (VCM) Spray given off from vessels at which an electrolytic chromium process is carried on, except trivalent chromium

Question 20

Health surveillance (Regulation 11) Health surveillance of employees should be carried out where:

Answer 20

 An identifiable disease or adverse health effect may be related to the exposure.  There is a ‘reasonable likelihood’ that the disease or health effect may occur under the particular conditions of work.  Valid techniques exist for detecting indications of the disease of health effect.  The technique presents a low risk to the employee.

Question 21

Information, instruction and training (Regulation 12) This regulation demands that all employees are liable to be exposed to hazardous substances, they are provided with suitable and sufficient information, instruction and training, including: 6

Answer 21

 Details of the hazardous substances including: - Names of substances and the risk that they present to health - Any relevant occupational exposure standard, maximum exposure limit or similar occupational exposure limit - Access to any relevant safety data sheet.  Other legislative provisions which concern the hazardous properties of those substances.  Significant findings of risk assessment.  Appropriate precautions and actions to be taken by the employee in order to safeguard himself and other employees at the workplace.  Results of any monitoring of exposure and, in particular, in the case of a substance hazardous to health for which a maximum exposure limit has been approved, the employee or his representatives shall be informed forthwith, if the results of such monitoring show that the maximum exposure limit has been exceeded.  Collective results of any health surveillance undertaken in a form calculated to prevent those results from being identified as relating to a particular person.

Question 22

Accidents, incidents and emergencies (Regulation 13) Regulation 13 requires that employers prepare for possible accidents, incidents and emergencies involving hazardous substances by: 3

Answer 22

 Preparing emergency procedures, including provision of first aid.  Making available technical information on possible accidents and hazards and bringing it to the attention of the emergency services.  Installing alarms and other warnings and communication systems.

Question 23

An employee’s exposure to lead is significant if one of the following three conditions is satisfied:

Answer 23

1) Exposure exceeds half the occupational exposure limit for lead. 2) There is a substantial risk of the employee ingesting lead. 3) If there is a risk of an employee’s skin coming into contact with lead alkyls or any other substance containing lead in a form, for example: lead naphthenate, which can also be absorbed through the skin.

Question 24

Also, lead can be easily absorbed through ingestion. To avoid this risk, it is important to

Answer 24

make sure that employees do not eat, drink or smoke in any place which is liable to be contaminated by lead.

Question 25

If there is significant exposure to lead, the monitoring of employees’ exposure should be carried out by both:

Answer 25

 Air sampling.  Measuring the concentration of lead in their blood or their urine (for work with lead alkyls). These two approaches have complementary roles.

Question 26

Action levels are concentrations of lead in blood set below the appropriate suspension limit. If these are reached or exceeded, the employer must: 3

Answer 26

 Carry out an urgent investigation to find out why  Review control measures  Take steps to reduce the employee’s blood-lead concentration below 
the action level, so far as is reasonably practicable.

Question 27

Asbestos is classified as

Answer 27

a category 1 carcinogen

Question 28

Since the 2006 Control of Asbestos Regulations there has been a single Control Limit of

Answer 28

0.1f/cm3 (equivalent to 0.1f/ml) The Action Levels have been withdrawn. The Short Term Exposure Limit of 0.6f/cm3 over 10 minutes is maintained, but is an ACoP standard instead of being in the regulations because there is no requirement for a STEL in the EU Directive on Asbestos.

Question 29

The duty holder has to take reasonable steps to find out if there are asbestos containing materials (ACMs) in the premises and, if so, how much, where they are and what condition they are in. This can, but does not have to, involve a survey. A survey can be: 2

Answer 29

 Management survey: This is to locate all materials that are likely to contain asbestos. It will usually involve the taking of samples to confirm the presence of asbestos. If no samples have been taken then it is assumed that all materials contain asbestos.  Refurbishment/demolition surveys: These involve getting access full access to all parts of the building using destructive inspection if necessary and will involve the taking of samples which are analysed to confirm whether asbestos is present. This type is usually used before major refurbishment or just before demolition.

Question 30

No employer can carry out demolition, maintenance or any other work which exposes, or may expose, their employees to asbestos in any premises unless they have found out: 4

Answer 30

 whether asbestos is, or may be, present  what type of asbestos it is  what material it is in  what condition it is in  if there is any doubt about whether asbestos is present, the employer has assumed that it is present and that it is not only white asbestos.

Question 31

An employer must hold a licence before undertaking any licensable work with asbestos. ‘Licensable work with asbestos’ is defined as work: 4

Answer 31

 Where the exposure to asbestos of employees is not sporadic and of low intensity.  In relation to which the risk assessment cannot clearly demonstrate that the control limit will not be exceeded.  On asbestos coating  On asbestos insulating board (AIB) or asbestos insulation for which the risk assessment: - demonstrates that the work is not sporadic and of low intensity - cannot clearly demonstrate that the control limit will not be exceeded - demonstrates that the work is not short duration work.

Question 32

Every employer must give adequate training (which includes information and instruction) to employees who are, or may be, exposed to asbestos, their supervisors and those who do work to help the employer comply with these Regulations. This should make them aware of: 6

Answer 32

 The properties of asbestos, its health effects and the interaction of asbestos and smoking.  The type of materials likely to contain asbestos.  What work could cause asbestos exposure and the importance of preventing exposure.  How work can be done safely and what equipment is needed.  Emergency procedures.  Hygiene facilities and decontamination. 


Question 33

Apart from a few exceptions (where exposure is very low), for each employee who is exposed to asbestos, employers have to: 5

Answer 33

 Keep a health record.  Keep the record (or a copy) for at least 40 years.  Ensure the employees are under adequate medical surveillance by a relevant doctor (appointed doctor or employment medical advisor).  Provide a medical examination not more than two years before such exposure and one at least every two years while such exposure continues (certificates of examination need to be kept for four years).  Tell the employee if the medical shows any disease or ill-health effect from the exposure. 


Question 34

The upper respiratory tract consists of

Answer 34

Mouth, nose and nasal cavityPharynxLarynx

Question 35

The lower respiratory tract consists of

Answer 35

TracheaBronchiBronchiolesAlveoliDiaphragm

Question 36

Most body organs are supplied by two separate sets of motor neurone nerves; one from the sympathetic system and one from the parasympathetic system. These neurones have opposite (or antagonistic) effects. In general the sympathetic system

Answer 36

stimulates the ‘fight or flight’ responses to threatening situations

Question 37

Most body organs are supplied by two separate sets of motor neurone nerves; one from the sympathetic system and one from the parasympathetic system. These neurones have opposite (or antagonistic) effects. In general the

Answer 37

parasympathetic system relaxes the body

Question 38

The skin is the body’s largest organ, covering the entire outside of the body and weighing approximately 3 kilos. In addition to serving as a protective shield against heat, light, injury, and infection, the skin also: 3

Answer 38

 regulates body temperature  stores water, fat, and vitamin D  can sense painful and pleasant stimulation.

Question 39

The skin is made up of the following layers, with each layer performing specific functions: 3

Answer 39

 Epidermis  Dermis  Subcutaneous (fat) layer.

Question 40

The epidermis is the thin outer layer of the skin. The epidermis itself is made up of three sub-layers:

Answer 40

 Stratum corneum (horny layer) Keratinocytes Basal layer

Question 41

The dermis is the middle layer of the skin. The dermis is made up of the following: 4

Answer 41

 Blood vessels  Lymph vessels  Hair follicles  Sweat glands

Question 42

Pneumoconiosis is

Answer 42

When dust particles of a certain size of some substances are inhaled the lungs are unable to remove them. The particles become embedded in the lungs

Question 43

The safety data sheet should be dated and contain the following headings: 19

Answer 43

 Identification of the substance/mixture and of the company/undertaking  Hazards identification  Composition/information on ingredients  First-aid measures  Fire-fighting measures  Accidental release measures  Handling and storage  Exposure controls/personal protection  Physical and chemical properties  Stability and reactivity  Toxicological information  Ecological information  Disposal considerations  Transport information  Regulatory information  Other information.

Question 44

Very Toxic

Answer 44

Substances and preparations which, at very low levels, may cause death, acute or chronic damage to health when inhaled, swallowed or absorbed via the skin.

Question 45

Toxic

Answer 45

Substances and preparations which, at low levels, may cause death, acute or chronic damage to health when inhaled, swallowed or absorbed via the skin.

Question 46

Harmful

Answer 46

Substances and preparations which may cause death, acute or chronic damage to health when inhaled, swallowed or absorbed via the skin.

Question 47

Corrosive

Answer 47

Substances and preparations which may, on contact with living tissues, destroy them.

Question 48

Irritant

Answer 48

Substances and preparations which, through immediate and prolonged or repeated contact with the skin or mucous membrane, may cause inflammation.

Question 49

Sensitising

Answer 49

Substances and preparations which, if they are inhaled or if they penetrate the skin, are capable of eliciting a reaction by hypersensitisation such that on further exposure to the substance or preparation, characteristic adverse effects are produced.

Question 50

Carcinogenic

Answer 50

Substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce cancer or increase its incidence.

Question 51

Carcinogens are placed into one of three categories: Category 1

Answer 51

Proven human carcinogens, for example: benzene, arsenic, chromium VI, asbestos

Question 52

Carcinogens are placed into one of three categories: Category 2

Answer 52

Suspected carcinogens, for example: cadmium compounds, beryllium compounds, sodium dichromate

Question 53

Carcinogens are placed into one of three categories: Category 3

Answer 53

Animal studies indicate a link, but there is no proven human link

Question 54

Mutagenic

Answer 54

Substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce heritable genetic defects or increase their incidence.

Question 55

Toxic for reproduction

Answer 55

Substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may produce or increase the incidence of non-heritable adverse effects in the progeny and/or of male or female reproductive functions or capacity.

Question 56

Asbestos is a naturally occurring mineral (fibrous silicate) which, because of its various useful properties (thermal insulation, fire resistance, electrical insulation and high tensile strength), has been in large scale use for about 150 years. Three main types have been used in Great Britain:

Answer 56

 Crocidolite (blue)  Amosite (brown)  Chrysotile (white).

Question 57

Asbestos was extensively used as a building material in the UK from the 1950’s through to the mid1980’s. The most common uses of asbestos in buildings were: 5

Answer 57

 Loose packing between floors and in partition walls.  Sprayed (‘limpet’) fire insulation on structural beams and girders.  Lagging on pipe-work, boilers, calorifiers, heat exchangers etc.  Asbestos insulation board (AIB) in ceiling tiles, partition walls, soffits, service duct covers, fire breaks, heater cupboards, door panels, lift shaft linings, fire surrounds.  Asbestos cement (AC) in roof sheeting, wall cladding, walls and ceilings, bath panels, boiler and incinerator flues, fire surrounds, gutters, rainwater pipes and water tanks.

Question 58

Chronic health effects of asbestos 4

Answer 58

 Diffuse pleural thickening (not fatal)  Asbestosis (not always fatal, but very debilitating)  Mesothelioma (always fatal)  Lung cancer (almost always fatal).

Question 59

Acute health effects of chromium: 3

Answer 59

 Irritation and inflammation of the nose and upper respiratory tract  Burns to the skin possibly leading to ulcers  Eye damage from splashes.

Question 60

Chronic health effects of chromium: 5

Answer 60

 Damage to the nose, including ulcers and holes in the flap of tissue separating the nostrils  Irritation of the lungs  Kidney damage  Allergic reactions in the skin and respiratory tract  Risk of cancer of the lung and nose from certain processes.

Question 61

Acute health effects isocyanates 6

Answer 61

 Recurring blocked or runny nose  Recurring sore or watering eyes  Chest tightness, often occurring outside working hours  Persistent cough  Wheezing  Breathlessness.

Question 62

Chronic health effects isocyanates

Answer 62

Exposure to isocyanates may lead to permanent and severe occupational asthma. There is no cure. Breathing in the smallest amount of isocyanate could then trigger an attack. Almost certainly, the sufferer would have to give up their current job. 


Question 63

Chronic health effects (inorganic lead) Continued uncontrolled exposure could cause more serious symptoms such as: 4

Answer 63

 Kidney damage  Nerve and brain damage  Infertility  Damage to an unborn baby, especially in the early weeks before a pregnancy becomes known.

Question 64

If employees could be exposed to lead, lead compounds, dust, fume or vapour at work employers must assess the risks to health to decide whether or not exposure is ‘significant’ 3

Answer 64

 Where any employee is or is liable to be exposed to a concentration of lead in the atmosphere exceeding half the occupational exposure limit for lead.  Where there is a substantial risk of any employee ingesting lead.  If there is a risk of an employee’s skin coming into contact with lead alkyls, or any other substance containing lead in a form which can also be absorbed through the skin.

Question 65

Action levels and Suspension levels for leadGeneral employee Young person under 18 Woman of child bearing age

Answer 65

50 μg/100ml 60 μg/100ml 40 μg/100ml 50 μg/100ml 25 μg/100ml 30 μg/100ml

Question 66

Control measures for RCS: 5

Answer 66

 Elimination by substituting non silicate materials, for example: using non-silica grits for blasting.  Eliminating or reducing dust levels by designing out the need for dust generating activities, for example: cutting or drilling concrete.  Controlling exposure to silica dust by dust suppression techniques (wet working) and local exhaust ventilated tools to remove the dust at source.  Respiratory protective equipment requires careful selection. For the dustiest processes, positive pressure or airline breathing apparatus will probably be necessary.  Good hygiene controls – washing facilities and laundry arrangements.

Question 67

Routes of entry Sodium hydroxide 3

Answer 67

 Breathing in mists or droplets.  Breathing in vapours due to exothermic reactions which ‘boil’ solutions.  Contact with skin and eyes.

Question 68

Chronic health effects sulphuric acid 3

Answer 68

 Inflammation (pulmonary oedema) of the lungs.  Dental decay.  Sulphuric acid mists are carcinogenic to humans. (Note: Sulphuric acid or its solutions are not considered to be carcinogenic).

Question 69

Control measures for wood dust 7

Answer 69

 Changing a process or method of work to reduce the generation of dust to a minimum.  Providing dust control equipment, for example: local exhaust ventilation at woodworking machines.  Maintaining LEV plant and equipment in efficient working order.  Respiratory protective equipment where necessary.  Other PPE, such as eye protection, overalls and gloves, where necessary.  Arrangements for laundering dusty work clothes.  Good washing facilities with hot and cold water, soap and towels.

Question 70

Toxicology is

Answer 70

the science of adverse effects of chemical substances on living organisms.

Question 71

Toxicological studies aim to assess the adverse effects related to different doses in order to find this ‘acceptably safe’ level. The work is carried out in two phases:

Answer 71

1) By collecting data on the properties of chemicals, results of studies and accidental misuse of chemicals. 2) By predicting the effects of chemicals in different situations.

Question 72

Human toxicity information should be generated whenever possible by means other than vertebrate animal tests, for example: 3

Answer 72

 in vitro methods  qualitative or quantitative structure-activity relationship models  information from structurally related substances (grouping or read-across).

Question 73

The use of acute toxicity data is mainly to label and classify chemicals based on their toxicity, for application to the human situation, however as mentioned there have been numerous challenges to the approach, on a range of grounds including: 5

Answer 73

 Human exposures are more likely to be repetitive low-doses than a single massive dose as per animal tests.  Different species deal with and react to chemicals differently including the rates and routes of metabolism and in absorption, distribution, and excretion; the target organs involved; and sensitivity to toxicity.  There is often a high degree of variability in acute toxicity data obtained from rodents of different ages, sexes, and genetic strains. Environmentally dependent variables such as: weight, diet, temperature and humidity also influence results.  Animal testing is costly and time-consuming, and can delay the timely regulation of human health protection.  Animal tests for acute toxicity have never been validated to modern standards.

Question 74

The NOAEL is

Answer 74

the highest point on the exposure-response curve at which no adverse health effects are observed.

Question 75

The LOAEL is

Answer 75

the lowest point on the exposure-response curve at which adverse health effects are observed.

Question 76

Ames test description

Answer 76

The test uses a strain of Salmonella typhimurium that carries a defective (mutant) gene making it unable to synthesize the amino acid histidine (His) from the ingredients in its culture medium. The altered Salmonella strains are combined in a test tube with the chemical of interest and animal liver enzymes which detect what might happen if the chemical entered a human body. The Salmonella are then transferred to a petri dish to grow for one or two days. The altered Salmonella used for the test require the amino acid histidine to grow, and a positive result in the test indicates that the test substance has induced a back mutation in the Salmonella meaning it no longer requires histidine to grow.

Question 77

QSAR models are

Answer 77

Quantitative Structure Activity Relationships (QSAR) are mathematical, computer based, models which are designed to predict the physico-chemical properties, human health and environmental effects of a substance from knowledge of its chemical structure (molecular descriptors).

Question 78

‘Read across’ is

Answer 78

a technique of filling data gaps. To ‘read across’ is to apply data from a tested chemical for a particular property or effect (cancer, reproductive toxicity, etc.) to a similar untested chemical.

Question 79

Epidemiology is

Answer 79

the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

Question 80

Epidemiology has an important role notably in: 3

Answer 80

 Establishing the causes and determinants of occupational ill-health.  Ensuring adequate recognition and quantification of this.  Determining appropriate occupational exposure limits.

Question 81

Cross sectional studies

Answer 81

In a cross-sectional study, the prevalence of a particular disease or of a set of symptoms or other indication of ill-health is investigated in a single time-point (or over a relatively narrow period of time). Comparisons can then be made in the frequency of ill-health for example between workers exposed to a particular hazard, and those who are not, or between workers experiencing different degrees of exposure. A cross sectional study can determine the prevalence rate, which is defined as the number of existing cases of disease divided by the population at a specified time point. For example if a chest X-ray survey of quarry workers is conducted it might show that workers in quarries with high exposure to quartz (a crystalline form of silica) might have a higher prevalence of pneumoconiosis than those in quarries with little or no such exposure.

Question 82

Cohort studies

Answer 82

The study begins with a group of people free of disease (or outcome of concern). The group is sub-classified according to exposure to a suspected cause (for example: smokers and non-smokers) and followed over time to determine the development of new cases of disease (for example: lung cancer) in each group. The incidence rate (number of new cases divided by population exposed) of disease in both groups can be calculated and the relative risk (RR) of disease in the exposed group compared to the non-exposed group can be determined. A relative risk of 3 – 4 (i.e. the exposed group is 3 to 4 times more likely to develop the disease of concern, than the non-exposed group) is considered to be a good indication of a causal relationship between cause and effect, although on its own is no guarantee of a causal relationship.

Question 83

Cohort studies may be conducted prospectively which means

Answer 83

they start in the present and track exposures and outcomes into the future. This poses ethical problems as if a cause and effect relationship is suspected an immediate intervention is the appropriate course of action. This would protect individuals but would ruin the natural experiment so that no meaningful data would be generated

Question 84

Cohort studies are often conducted retrospectively

Answer 84

The study is conducted in exactly the same way as a prospective study but the starting point is some time in the past.

Question 85

case control study

Answer 85

starts with a population of individuals with the disease under investigation (Cases) and compares them with a carefully matched control group of individuals without the disease (Controls). A food poisoning outbreak at a party provides a practical example of a case-control study. Of a hundred guests 60 developed food poisoning. These are the cases and the 40 who did not get food poisoning are the controls. The range of foods at the buffet are the suspected causal agents and by interviewing each guest (cases and controls) the odds of each group having consumed each food type can be calculated and the Odds Ratio might show that those who suffered food poisoning (cases) were four times more likely to have ate the chicken drumsticks, for example, than those who did not get food poisoning (controls).

Question 86

Inferring causation (3 steps)

Answer 86

Demonstrate a statistical relationship betweencause and effect (RelativeRisk or Odds Ratio)Eliminate non-casualexplanations● Confounding● Bias● ChanceApply causal criteria to substantiate casual relationship

Question 87

non-causal explanations (list)

Answer 87

ChanceBiasConfounding

Question 88

Confounding…

Answer 88

results from multiple associations between the exposure, the disease and some third factor (the ‘confounding variable’) which is associated with both the exposure and independently affects the risk of developing the disease. An example of confounding is the observed association between air pollution and cardiac or pulmonary disease. There now appears to be little doubt that a causal association exists between say particulate air pollution and respiratory morbidity and mortality. However, an unsophisticated study simply relating air pollution to ill health and death might lead to the conclusion that the association is much stronger than it really is. This is because of confounding variables such as temperature. Low temperatures in winter may contribute to increased mortality. In addition, low temperatures (in meteorological conditions of inversion) may favour increased pollution levels. If the confounding caused by temperature is taken into account i.e. it is resolved, then the association between air pollution and health becomes weaker.

Question 89

Selection and participation bias: This occurs if

Answer 89

the study populations being compared are not strictly comparable, for example: in a study to determine the effect of a Workplace Health Promotion (WHP) programme on ‘sickness absence’, the rate of subsequent sickness absence might have been compared between those who participated in the WHP programme and those who did not. What if the results appeared to show that the WHP group had lower rates of sickness absence? Would one be entitled to conclude that WHP resulted in less sickness absence?

Question 90

Observation bias: This occurs if

Answer 90

non-comparable information is obtained from each study group, for example: if one was conducting a case-control study to determine whether scleroderma (systemic sclerosis) was associated with occupational exposure to certain hazards (such as trichloroethylene or silica), bias could arise if the interviewer knew (or could tell) which people were the cases and which were the controls. He/she might seek more detail about exposures from the cases than the controls who did not have the disease. Thus, observer bias would have influenced the results.

Question 91

Recall bias might arise if

Answer 91

the cases (suffering from the disease) having previously pondered about possible causes of their misfortune, were to recollect more detail about their past exposures, than the controls (who may have no real motivation to reflect at length on their past occupations).


Question 92

Chance

Answer 92

Imagine that the frequency of back pain among employees in a particular workplace needed to be determined. Rather than questioning all the employees, it would be easier to administer questionnaires to only a sample of this population and from them, estimate the frequency of back pain in the workers. As a consequence it must be borne in mind that chance may affected the results because of random variation in the population. It could be that, by chance, the selected sample was a particularly fit and healthy group and consequently the frequency of back pain in the workplace population at large may be underestimated.

Question 93

Criteria for determining causation Sir Austin Bradford-Hill established nine key criteria that should be considered before concluding that a relationship is causal as long ago as 1965. These have been reviewed and revised extensively over the last fifty years yet remain essentially the same. (list all 9)

Answer 93

TemporalityReversibilityStrength of association Exposure-response Exposure and dose ConsistencyBiologic plausibility AnalogySpecificity

Question 94

The fundamental problem with epidemiological studies is that

Answer 94

they cannot prove a causal relationship. A high relative risk (or odds ratio) can strongly infer causation but this is not the same as saying that exposure to agent X causes disease Y. The scientific evidence shows a strong link between smoking and lung cancer, however cigarette smoking is neither a necessary cause (people who have never smoked get lung cancer) nor sufficient cause (people who smoke all their lives might not get lung cancer) of lung cancer

Question 95

There are a number of factors that determine the type of toxic effect a chemical can have on you. These factors include the:

Answer 95

 Route(s) of entry by which the chemical gets into the body (chemicals have different routes of entry. Some chemicals can enter the body in more than one way. Different health effects can occur depending on the route of entry).  Physical form of the chemical (solids, dust, fibre, liquid, vapour, gas, mist).

Question 96

Some substances damage skin, while others pass through it and damage other parts of the body. Skin gets contaminated by:

Answer 96

 direct contact with the substance, for example: if you touch or dip hands in it  splashing  substances landing on the skin, for example: airborne dust  contact with contaminated surfaces (including contact with contamination inside protective gloves). 


Question 97

Physical form 5

Answer 97

DustSolidGasVapourLiquid

Question 98

Dust is divided into two categories depending on size:

Answer 98

 ‘Inhalable dust’ (sometimes referred to as total inhalable dust) is the total dust that will enter the nose and mouth and lungs during breathing.  ‘Respirable dust’ is dust of such a size that it is able to enter the lower levels of the lung during normal breathing (approx. 0.5 to 7.0 micron). Respirable dust is often in the form of long particles with sharp edges which cause scarring of the lung lining (fibrosis). This limits the capacity of the lungs and, therefore, the amount of air in the lungs.

Question 99

Fibres of 0.5 μm or less can enter the lungs and become trapped in the alveoli. These can cause lung damage, for example:

Answer 99

scarring (fibrosis), with a resulting loss of lung function. Larger fibres may be ingested by macrophages.

Question 100

Fume is formed by

Answer 100

the vaporisation or oxidation of molten metal, for example: lead fume/welding fume. The particles are usually less than 1μm and therefore are respirable.

Question 101

There are two types of defensive responses:

Answer 101

 Basic – preventing the chemical or biological agent entering the body: - the skin - the eye - the respiratory system - the digestive system  Auto-immune – attacking the agent directly: - innate (non-specific) - adaptive (specific)

Question 102

The air reaches the tiny air sacs (alveoli) in the inner part of the lungs with any dust particles smaller than

Answer 102

5-7 μm

Question 103

Besides macrophages, the lungs have another system for the removal of dust.

Answer 103

The lungs can react to the presence of germ-bearing particles by producing certain proteins. These proteins attach to particles to neutralise them.

Question 104

Several factors influence the effects of inhaled particles:

Answer 104

 Size and heaviness of the particles are important because large and heavy particles settle more rapidly.  Chemical composition is important because some substances, when in particle form, can destroy the cilia that the lungs use for the removal of particles.  Cigarette smoking may alter the ability of the lungs to clear themselves.  Breathing rates: the amount of dust settling in the lungs increases with the length of time the breath is held and how deeply the breath is taken which means manual labourers exerting themselves are at greater risk than sedentary workers.  Breathing is through the nose or mouth is also important. If breathing through the mouth the first defence mechanism of the nose is by passed.

Question 105

Dermatitis is inflammation of the skin caused by contact with a range of materials. These include detergents, toiletries, chemicals and even natural products like foods and water (if contact is prolonged or frequent). It can affect all parts of the body, but it is most common to see the hands affected. There are different types of contact dermatitis:

Answer 105

 Irritant dermatitis (sometimes known as ‘primary’ dermatitis).  Allergic dermatitis.

Question 106

Irritant dermatitis is usually caused by

Answer 106

chemicals etc. that dry out and damage the skin. It can occur quickly after contact with a strong irritant, or over a longer period from repeated contact with weaker irritants. Irritants can be chemical, biological, mechanical or physical. Repeated and prolonged contact with water (for example: more than 20 hand washes or having wet hands for more than 2 hours per shift) can also cause irritant dermatitis.

Question 107

Allergic dermatitis can occur when

Answer 107

the sufferer develops an allergy to a substance. Once someone is ‘sensitised’, it is likely to be permanent and any skin contact with that substance will cause allergic contact dermatitis. Often skin sensitisers are also irritants. The allergic reaction can show up hours or days after contact.

Question 108

2 types of immune system

Answer 108

The innate (non-specific) immune system is the first line of defence against invading micro-organisms. The innate immune system exists at birth, and does not change very much through life. It responds rapidly to infection, but has neither memory nor any specificity. The main cells used in the innate system are phagocytes which are attracted to an organism, bind to it, engulf it by endocytosis and release cytotoxic materials to kill it. Digestive enzymes are then released onto the organism. The process is known as phagocytosis. The adaptive (specific) immune system produces a slower response than that of the innate immune system, but the response is highly specific. Each lymphocyte is antigen specific (an antigen is the foreign substance on the surface of an invading organism). The adaptive system has a memory and therefore mounts a fast immune response to previously encountered microbes.

Question 109

The cells of the adaptive immune system are:

Answer 109

 B-lymphocytes which mature in the Bone and produce antibodies to eliminate a specific antigen.  T-lymphocytes which mature in the Thymus and are of two types: - T helper cells - T killer (cytotoxic) cells.

Question 110

Other defences include:

Answer 110

 the eye blinking to protect against excessive light  the eye watering to remove, for example, dust  the adrenaline ‘fight or flight response’ (note: this can also cause an over immune response, for example: to sensitising asthmagens)  pain from the skin, muscles etc.