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Statistics show occupational skin disease to be one of the most common causes of occupational ill health. Given that in addition to skin disease we must consider systemic toxic effects on body organs and systems due to skin uptake, perhaps it is time to consider whether our traditional approach to managing skin exposure in the working environment properly reflects the latest scientific knowledge about the skin and how it interacts with our immediate environment.
This interaction is almost unimaginably complex. There is also much we do not yet fully understand about how this works. This article takes a brief look concentrating on some of the factors that we need to include in our approach to creating and maintaining a ‘skin safe’ workplace.
Workplace exposure to chemicals
Basically, there are three main routes by which human exposure to chemicals in a workplace can occur. These are inhalation, ingestion and dermal. Each has its own particular characteristics affecting how the risk of damage to health is assessed. Until now it has been common practice to consider each separately. This article will challenge this practice and explain why we frequently need to integrate the three routes if we are to
produce a valid risk assessment for a particular task or workplace situation. It will then review what methods currently exist to achieve this and their limitations and suggest what needs to be done to ensure that risk assessments for chemical exposure reflect the total picture.
The routes of exposure
Inhalation – taken into the respiratory system via the nose or mouth. Substances must be airborne and in the breathing zone. Particle size must allow them to enter the respiratory system either as ‘inhalable’, i.e. able to reach the upper parts of the respiratory system, or ‘respirable’, i.e. able to penetrate through to the gas exchange region of the system (alveoli), where they can be absorbed into the blood stream to cause or contribute to systemic toxic effects and allergic reactions.
“we must consider systemic toxic effects on body organs and systems due to skin uptake”
Ingestion – taken into the digestive system either directly through the mouth or indirectly, for example by redirection from the respiratory system due to mucociliatory transportation, then swallowed.
Dermal – contact with the skin, such as through the hands.
Injection – a fourth possibility, i.e. through sharp objects penetrating the skin and allowing a chemical or micro-organism to enter the body. However, in the context of the interaction between the three main routes this is not of significance and will not be discussed further.
Effect on health
Inhalation – if inhalable, a chemical (be it dust, fume or aerosol) may cause irritant damage to the upper part of the respiratory system, if
respirable there can be entry into the blood stream then transmission to a target organ or system. The alveoli is about 70m2 and is the region where the gas exchange vital for life occurs. It is extremely vulnerable to damage should any harmful chemicals reach it, either in gas or particulate form. Ingestion – a chemical will enter the digestive system – possibly in modified forms due to metabolisation in the skin or subsequently in the liver. It can then enter the blood stream and finally reach a target organ or system. Case studies show that this can result in allergic reactions such as dermatitis. Dermal – the chemical may cause direct local damage through denaturing of skin cells (corrosion, irritation), systemic effects through absorption into the skin and initiating a response from the immune system (allergy) or penetration and causing or contributing to damage to internal organs or systems. There is potential for metabolisation in the skin causing either an increase or decrease in toxic properties.
Risk assessment is task based
When considering the risks to health from the presence and use of chemicals in a workplace the risk assessment forms the basis on which decisions will be made regarding the need to eliminate or adequately control any exposure of the person to these.
A simple definition of what constitutes a risk assessment is:
“A risk assessment is nothing more than a careful examination of what, in your work, could cause harm to people, so that you can weigh up whether you have taken enough precautions or should do more to prevent harm.” – European Agency for Safety & Health at Work.
How should we approach this when considering risk assessment for skin exposure to chemicals in the working environment?
The ‘traditional’ approach
In what might be referred to as the ‘traditional’ approach, one that has been common practice for many years, the risk assessment process involves:
- Identifying any substances in the workplace that are classified as hazardous
- Identifying any actual, or potential, exposure to these
- Assessing the potential for such exposure to result in damage to health and its severity
This approach presents significant risks if applied to risk assessment for skin exposure to chemicals as the rest of this article will show.
A more realistic approach
We generally purchase chemicals to use for one or more tasks. It is when they are actually used that the risk of damage to health arises. Furthermore, when we use them we frequently alter their properties and, as a result, may change the hazard. The hazard resulting from the use of one or more chemicals will depend upon how they are used. As Table 1 shows, different tasks may have different effects on the same chemical, such that the hazard that arises may be specific to that task.
There are also many hundreds of chemicals that, although not formally classified as hazardous to the skin, can cause damage to health should skin contact occur. These will usually not appear on a safety data sheet.
In the UK this has been recognised by the Health and Safety Executive. The current Approved Code of Practice for the Control of Substances Hazardous to Health regulations contains the following statement:
‘Paragraph 10 – Employers should regard a substance as hazardous to health if it is hazardous in the form in which it may occur in the work activity. A substance hazardous to health need not be just a chemical compound, it can also include mixtures of compounds, microorganisms or natural materials, such as flour, stone or wood dust.’
From this it follows that the task largely defines the hazard, thus our starting point for any risk assessment for chemical exposure must be defining the task. We need to establish exactly what happens during the task, what chemicals are used in the task and what effect the way in which they
are used will have on the actual effect on those exposed during the task. Only then will we be in a position to determine the real hazard and to assess the risk of damage to health.
Of course, we will frequently be faced with a situation where more than one of these changes occur during the task. So, the hazard might also be different at different stages within the task. Also, it is not unusual for the same chemical to be used for the same – or possibly even a different task – and such repeated use can result in further changes.
Given these complications, is there a simple, validated system that enables us to establish the real hazard on which we need to base our risk assessment? Consider that the European Chemical Agency (ECHA), the agency responsible for the implementation and operation of the EU Registration Evaluation Assessment and restriction of Chemicals (REACH) regulation states: ‘For the time being there is no EU-wide system in place to assess the combination effects and risks of chemicals.’ (from ‘Chemicals in our life’).
“there is no scientific method of measuring the results of the body’s exposure to risk through dermal contact”
Thus, there is no simple method that can be applied by those with no, or limited, knowledge of chemistry to be certain that the hazard has been correctly identified. Unless the hazard has been correctly established, however, is there not a significant possibility that the risk assessment may incorrectly identify the health hazard?
Measuring exposure
There are actually no practicable direct exposure measurement techniques for any of the routes of exposure. Even with inhalation, where we have exposure limits, we are not measuring the amount inhaled but rather the amount in the immediate environment that is likely to be inhaled.
Can the measure of the level of contamination in the environment be a direct and accurate measurement of the chemical the particular individual has inhaled? Considering in particular that:
- Individual lung capacities, and therefore the volume of air that is inhaled, can vary
- The amount inhaled over time will vary depending upon circumstances, for example, as a result of physical exertion
With inhalation we then have to distinguish between inhalable and respirable levels, a further complication that is not always easy to determine and that can vary depending upon a variety of workplace environmental factors.
With skin the situation is even more complicated. As the European Agency for Safety and Health at Work has stated:
“There is no scientific method of measuring the results of the body’s exposure to risk through dermal contact. Consequently, no dermal exposure standards have been set.”1
In the first place the skin represents a large surface area, different parts of which will respond differently to exposure to the environment or contact with a chemical (Table 2). Assuming skin exposure measurement were practicable, how would one collate and interpret the measurement of exposure, almost certainly at different levels, of hand, face and upper body to a specific chemical and the resultant potential for damage to health to occur?
Ambient conditions can also play a significant role in the uptake of chemicals as a result of skin contact. Table 3 shows the results from a study by the UK’s Health and Safety Laboratory.2
As can be seen, there are significant differences both in location on the body and ambient condition. In addition to this we need also to consider variations in skin condition.
There are seasonal variations in the skin’s reaction to contact with a chemical, individual variations, e.g. atopy, variations due to skin care, other activities other than the one under consideration both at and away from work and their effect on the skin.
We then have to consider what we will be measuring. Table 4 illustrates the potential complexity and difficulty in interpreting the measurement.
Of course, in many tasks there will be more than one of these factors to consider.
Interaction between the routes
Traditionally, in occupational hygiene it has been the general practice to treat each route of exposure as a separate issue, disregarding the evidence of interaction between the three main routes. The following is just one example of the evidence that exists proving there are links between the three routes.
“Studies in animals have shown that skin exposure to trimellitic anhydride and diisocyanates can cause sensitisation of the respiratory area in a way that any further inhalation challenge with the same chemical will elicit a pulmonary reaction. This is a very important issue because it means that for successful risk assessment and prevention of respiratory sensitisation in the workplace, protection from skin exposure is as important as protection against inhalation.”3
In more than one case of allergic contact dermatitis, initially assumed to have been due to skin exposure to a sensitising chemical in a workplace, investigation revealed the true cause to have been in diet, resulting in an increase in dietary uptake in already sensitised persons.
Is it just skin exposure?
Where we are concerned with the skin, we need to consider the potential effect, or contribution to the effect, of non-skin exposure. Indeed, the alternative is also something that we may need to keep in mind.
The diagram above shows the potential effects of each route of exposure and the potential for two or more routes to result in a cumulative effect or simultaneously more than one effect.
The following is a brief description of each of the ill-health conditions, including where each may be due to only one route of exposure or possibly more than one. It is based on the evidence that exists that there are links between the three routes.
COPD
Chronic Obstructive Pulmonary Disease (COPD) is the name for a group of lung conditions that cause breathing difficulties. It includes:
- Emphysema – damage to the alveoli in the lungs
- Chronic bronchitis – long term inflammation of the airways in the respiratory system
COPD is a common condition that mainly affects middle-aged or older persons, particularly those who smoke. Many do not realise initially that they have it. It is irreversible. The breathing problems tend to get worse over time and can eventually result in severe disability. Treatment can usually halt but not reverse the progression.
Workplace aggravated asthma and occupational asthma
Workplace aggravated asthma is asthma caused initially due to conditions not associated with the working environment, but where the working environment can exacerbate the condition. Occupational asthma is asthma that is directly initiated by exposure to chemicals within the working environment. The aetiology is the same for both conditions. There is evidence that skin exposure may be implicated, particularly where it can be shown that the causative chemical (or chemicals) can penetrate the skin and initiate the appropriate reaction in the immune system.
Systemic toxic effect
A systemic toxic effect occurs where one or more chemicals have been absorbed into the body in a form whereby they can reach a target organ or system and cause damage. This damage can be irreversible and severe, sometimes potentially fatal.
One study of the use of methylene dianiline showed that uptake via the skin was over four times greater than that due to inhalation.
It is the total dose reaching the target organ, regardless of the route(s) by which this occurs, which creates the potential for damage to health. It is clear that we need to include in our risk assessment the uptake by all three routes when attempting to assess the potential for damage to health due to systemic toxic effects, another reason why regarding the three routes as separate and discrete is not correct.
Chemical skin burn
A chemical skin burn results from total destruction of the cells forming the outer layer of the skin and subsequent damage to the underlying tissue. Chemicals that can cause this are generally classified as corrosive.
Systemic contact dermatitis
Dermatologists have long differentiated between allergic contact dermatitis – that caused by an overreaction of the immune system due to skin contact with the causative chemical – and systemic contact dermatitis, an overreaction of the immune system due to exposure by either inhalation or ingestion, or both.
Irritant contact dermatitis
Irritant Contact Dermatitis (ICD) is where the chemical causes denaturation of the cells in the outer layers of the skin. Whilst occasionally this may be acute and from exposure to a single chemical, in the majority of cases ICD is chronic as a result of repeated exposure of the same area of skin to a number of different chemicals capable of causing direct damage to the skin cells.
The damage will be visually asymptomatic (but can be detected by biological monitoring techniques) until the skin finally succumbs and the damage becomes visible. Since the problem is only as a result of skin contact with the causative chemicals, the skin is the only significant route of exposure. There is almost no chemical that, under certain circumstances, cannot be irritant, even water.
Allergic contact dermatitis and allergic contact urticaria
Allergic Contact Dermatitis (ACD) is a type IV immune response; Allergic Contact Urticaria (ACU) is a type I immune response. Both result in the appearance of a visible skin reaction, usually a rash but possibly blistering, etc. Whilst most ACD or ACU is due to skin contact with the causative chemical there is evidence that both inhalation and ingestion can initiate an allergic response in the skin, usually in someone who has already become hypersensitive (sensitised) to the particular chemical.
Non-allergic contact urticaria
There is a range of skin reactions that is classified as contact urticaria but where this does not involve the immune system. Some reactions, such as cholinergic (heat related), and dermographic urticaria, do not require what we might term contact or exposure to any chemical hazard. Others are as a result of some chemical exposure, e.g. nettle rash.
Complexities of chemical protection
I have a question for you: how well are your gloves protecting against chemical hazards? In a large number of cases the answer will be: “Not as well as I thought!”
The way in which gloves work as protection against chemical hazards is far more complex than many realise. Many factors can affect how well and for how long a glove will protect. It is common when investigating skin problems in the workplace to find that the inadequate performance of gloves is a contributory factor.
If we start with the manufacturer’s published permeation breakthrough time this does not indicate the performance that will be obtained when the glove is actually used for a specific task. What it will do is indicate which gloves are totally unsuitable for the application and which might provide some degree of protection. Note that the EN and ASTM tests for permeation breakthrough (transmission through the glove at a molecular level and undetectable by the wearer) are flawed in that they test gloves at room temperature and not at skin temperature, the temperature at which the glove will generally be when worn. The difference can be significant; in some cases the permeation breakthrough time will be reduced by as much as 80%! In addition, at least one study monitoring for permeation breakthrough time measured the effect of stretching by 20%, the amount of stretch over the knuckles on a well-fitting glove. They found that the reduction could range from 30-80%. In many cases the gloves will have to protect against mixtures, and this can lead to some interesting results. For example, one glove tested separately against two solvents showed a permeation breakthrough time for each in excess of four hours. When the solvents were mixed at 1:1 the time dropped to just nine minutes!
There are other factors that can affect glove performance, such as concomitant degradation and abrasion.
Of course, once we have determined which glove will actually provide adequate control of exposure, we need to establish whether it is suitable for the task in question. The general rule tends to be that the greater the level of protection required the less dexterity will exist, possibly rendering that glove unsuitable for the task.
Another concern for those who intend to provide gloves for their workforce is the training required on the correct use of gloves. Unless the correct technique is used when removing gloves it is all too easy for the hands to become contaminated with the chemicals against which they were supposed to protect. In one study every single person managed to contaminate their hands on removing gloves. When trained this was reduced by half. However, this still means that for half of those using gloves they were still failing to protect. Ongoing training has been shown to achieve further reductions to more acceptable levels, but particularly where the chemical has a high toxicity this is a factor that should not be overlooked.
From this it should be apparent that the selection and use of gloves for protection against chemical hazards is far from simple. In this short article it has not been possible to provide a detailed system, but merely to raise awareness that unless this is done correctly workers’ health may be at risk – despite the cost of providing gloves.
Conclusions
Identifying the risk of damage to health due to chemical exposure in a workplace is not as simple as many assume. Simplistic approaches represent a high potential for an invalid risk assessment which could ultimately endanger the health of those in the workplace. A more comprehensive approach is required. Unfortunately, at present there is no validated, simple method for achieving this. Much work is required if we are to be confident that we can reliably identify and assess the risk and be able to establish the extent to which any exposure must be managed. <
References
1 Occupational skin diseases and dermal exposure in the European Union (EU25):policy and practice overview – European Agency for Safety and Health at Work.
2 Factors affecting the extent of dermal absorption of solvent vapours: A human volunteer study, Jones K, Cocker J, Dodd LJ, Fraser I, Ann.Occup.Hyg, 47, 2, 2003.
3 Elena Gimenez Arnau in Chemical Respiratory Allergy – Dermatotoxicology, Klaus-Peter Wilhelm, Hongbo Zhai, Howard I Maibach.
