The Laki Dry Fog in Europe (1783): 18th C Living Conditions, Part 6

Human Illnesses in the 18th C associated with volcanic eruptions

Having looked at the diseases that were common during this period, we shall now turn our attention to those that could have been caused or at least exacerbated by the Laki eruption.

These afflictions fall into three main categories, namely: those connected with the respiratory system, those connected with the head, and miscellaneous. A great part of Northern Europe was affected by the dry fog, and its effects ranged from the benevolent in parts of eastern and southern Europe, to the distinctly unpleasant in France and the Netherlands. It is these effects which will now be discussed relative to their impact on human health.

Given the extent of medical knowledge at the time, it is not surprising that a whole host of symptoms, ranging from difficulty in breathing, tingling hands, and loss of appetite, to diarrhoea and dysentery, were blamed on the fog, whether or not it was the actual cause.

Volcanic Ash

As can be seen from the accompanying electron micrographs of more recent volcanic events, Figs.1 – 3, volcanic ash is composed of irregularly-shaped particles with sharp, jagged edges.

Whereas volcanic ash is defined as pyroclasts having a diameter of 2mm or less (those having a greater diameter are known as lapilli), the very fine ash which is of concern to us has a diameter of < 15 μm or smaller. The importance of the grain size of ash particles and their ability to be inhaled into the lungs is graphically illustrated in Fig.4. This shows that particles of < 15 μm are likely to effect the upper respiratory tract, particles of < 10 μm may be inhaled as far as the lungs, whilst particles of < 4 μm and smaller have the potential of penetrating as far as the alveolar region: limited human studies indicate that ultrafine particles, of < 0.1 μm, are the most toxic.

Fig 4 Diagram of the lung showing the anatomy of the lung and airways, and the penetration of ash and gas particles of different sizes associated with their potential health effects. Image From Horwell and Baxter, 2006

Respiratory effects of volcanic ash

Surface properties and mineral composition are thought to influence the health effects of ash particles. Freshly erupted ash particles have had no time to weather, they are still rough and have not been leached or oxidised, thus making it easy for them to adsorb sulphuricor other acids from gasses in the volcanic plume. This in turn may cause added irritability when inhaled. Should Fe2+ be present in the ash, it could result in the generation of free radicals through interaction with hydrogen peroxide already present in the lungs, and this in turn, could provoke a toxic reaction akin to that produced by crystalline silica.

The morphology of particles may also have a health impact. For example, fibrous particles having a diameter < 3 μm and a length > 5 μm may have an effect similar to asbestos, although in a recent study, Damby et al state that:

Few fiber-like particles were observed, but those present comprised glass or sodium oxides, and are not related to pathogenic natural fibres, like asbestos or fibrous zeolites, thereby limiting concern of associated respiratory diseases.

Volcanic Gases

K.W.Kizer writing about the various gaseous products produced by volcanic activity describes them as follows:

  • Gases and vapours: The gaseous state of an element which normally exists in a liquid or solid form and can be readily reverted to this form by decreases in temperature or increases in pressure, for example, mercury.
  • Aerosols: Droplets or particles suspended in a gaseous medium. Aerosols composed of tiny droplets of sulfuric acid are commonly formed during explosive volcanic eruptions.
  • Fumes: Aerosols of solid particles, usually less than < 0.1 μm in size, usually formed by the escape of volatiles from molten materials.
  • Smoke: Volatile gases or particles, usually less than < 0.5 μm in size, produced by combustion.

The following table lists the illnesses which were reported in conjunction with the Laki dry fog in Europe in 1783.

To summarise, the respiratory symptoms as reported by Brugmans (1787), de Lamanon (1783) and van Swinden (1783), certainly seem to point to SO2   exposure, as do the sore throats described by Harreaux (1858) and Dreux (1783). The pestilence of the throat described by Dreux (1783), is unusual because it affected the inhabitants of Champersu for some 10 months, the latter six of which were after the fog had left Europe. It has been suggested that as he described the illness as an affliction, a large number of people may have been affected, and the long-term nature of the sickness could have been a period of chronic bronchitis during the winter of 1783/84, brought about by the protracted exposure to pollution during the previous summer.

The severe headaches noted by Brugmans and de Lamanon, and the loss of appetite noted by Anon (1784), are symptoms of exposure to H2S. Headaches may also be caused by exposure to particulate fluorine.

Several commentators, de Lamanon (1783), Harreaux (1858), Cote (1788), and Anon (1784), remarked that the fog had an unpleasant effect on the eyes, hurtful, stinging, tingling and tiring being the adjectives used. It is a characteristic of both SO2 and H2S that they cause ocular irritation in small concentrations.

We are now left with reports of sickness by de Broué and de Landelles in France and Brun (1786) in Norway. The term is so vague that it could be taken to mean nearly anything, however, Blomme (1892), gives us a clue when he mentions that a lot of people had suffered from a putrid fever and diarrhoea in Termonde, Belgium. The account by Blomme suggests that the sickness was gastroenteritis, the main symptoms being: diarrhoea (sometimes accompanied blood or mucus), sickness and stomach cramps. Sometimes these can be accompanied by a high fever, headache and aching limbs. Van Guens’ (1783) account of dysentery may also refer to gastroenteritis, which is a very common disease today (about 1 in 5 people in the UK develop a bout of gastroenteritis in a year), and due to a general lack of cleanliness, would have been much more prevalent in the 18th century than now.

The Malignant fevers in Spain as documented by Malda (1791), and Cowper’s (1783) report from England cannot, I think, be blamed on the Laki fog, neither can the heat stroke which incapacitated farm workers in Selborne, Hampshire, in the summer heatwave of 1783 (White 1783). According to the Mayo Clinic:

Heatstroke is a condition caused by your body overheating, usually as a result of prolonged exposure to or physical exertion in high temperatures. This most serious form of heat injury, heatstroke, can occur if your body temperature rises to 104 F (40 C) or higher…Untreated heatstroke can quickly damage your brain, heart, kidneys and muscles. The damage worsens the longer treatment is delayed, increasing your risk of serious complications or death.

The following table shows the detrimental effects that volcanic gases have on the population, and these can be classified into three groups, namely, those which are: irritant, noxious, or inert.

Major Toxic Compounds of Volcanic Gas and Ash Emissions and their Potential Effects on Health – IDLH (Immediately Dangerous to Life or Health) Values in bold

Of these, SO2 appears to have been, judging by contemporary accounts, the main constituent of the Laki fog. One can see from the above table, that only 100 ppm of the gas are needed to be immediately dangerous to health, whilst 0.5 – 1ppm may be distressing to asthmatics and exacerbate asthma attacks. Owing to the fact that Sulphur dioxide is very soluble, it mainly effects the mucous membranes of the upper respiratory tract, i.e. nose, throat, trachea and bronchi, where it reacts with the ambient moisture to form Sulphurous acid (H2SO3), a severe irritant. In healthy adults breathing difficulties may be experienced at 5 ppm, sneezing and coughing at 10 ppm, and bronchospasm and eye irritation at 20 ppm. Above 20 ppm, pneumonitis, ARDS or pulmonary oedema may be experienced, and although exposures of 50 to 100 ppm may be tolerated for more than 30 to 60 minutes, higher or longer exposures can cause death from airway obstruction.

Although SO2 would appear to have been the main constituent of the dry fog, other irritants were also present, but in much smaller quantities. HCl and HF, can both cause eye and throat irritation at low levels of exposure, but as they are very soluble, tend to be removed by the mucus linings of the upper respiratory tract before they can reach the alveoli. Notwithstanding this, the effects can be particularly severe for asthma and bronchitis sufferers. Ammonia, which was another irritant discharged by the eruption, is especially sensitive to the eyes and other delicate membranes.

H2S or Hydrogen sulphide, commonly known as bad egg gas, is a powerful, malodorous, noxious asphyxiant, which also acts as an irritant. It can act as a skin and eye irritant at a concentration of only 0.000125 ppm, whilst higher concentrations can lead to loss of smell, headaches, loss of appetite and irritation to the respiratory tract. Concentrations of between 500 to 1000 ppm will lead to fainting and ultimately death.

Although CO2, an inert asphyxiant, is emitted in huge quantities in volcanic eruptions, it quickly becomes diluted and is not a danger to life. However, when cold it is heavier than air, and in certain circumstances can flow along the ground becoming sufficiently concentrated and thus life threatening through asphyxiation. Concentrations exceeding 3% can quickly lead to headaches, dizziness, increased heart rate and difficulty breathing, whilst those in the region between 7-10% will rapidly cause unconsciousness, and above 15%, death. Fortunately however, Carbon dioxide, even if it had been transported in the Laki haze, would have been so diluted by the time it reached Europe as to have had no effect on the health of the population.

In the next article ,”Perceived causes of death within the Bills of Mortality”.

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