The harmful effects of fog on health: more than dust, suspended minerals

The North African desert dust storm unusually generated one of the highest airborne dust concentrations on the Iberian Peninsula. The presence of this suspended particulate matter has detrimental effects on health, not only at the respiratory or ocular level, as is traditionally known, but also on cardiovascular health.

Health problems associated with exposure to air pollution have been described since the middle of the 20th century, when an increase in morbidity and mortality was recorded. From the 1970s, ambient air quality regulations began. Currently, the literature on health problems secondary to exposure to air pollution is abundant. In fact, a recent meta-analysis of 110 studies confirmed an increase in total mortality.

The composition of air can be classified according to the diameter of the particles that make it up, called particulate matter (PM). These PM have a diameter of less than 10 μm (PM10) and we will classify them as coarse PM with a diameter between 2.5 and 10 μm (PM2.5-10), fine PM with a diameter of less than 2.5 μm (PM2. 5) and ultrafine MPs with a diameter of less than 0.1 μm (PUF).

Air pollution is mainly composed of UFP and PM2.5 consisting of multiple gaseous pollutants (nitrogen oxides, ozone, sulfur dioxide, among others) and particulates (hydrocarbons, soot, metals, sulfate and nitrate, etc.) linked , mostly to combustion emissions (diesel and gasoline cars, power generation, industry, etc.). Government decrees recommend that the concentration of PM10 in ambient air be less than 50 μg/m3 to reduce the impact on health.

If we are interested in the dust of the desert or PM of non-anthropogenic origin suspended in the ambient air, called mists, it is PM2.5-10 coming from the main deserts of the planet. Among all the sources of production of this ore, the so-called dust belt stands out, a global geographical area that encompasses North Africa, the Middle East, South and Central Asia.

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Dust Belt encompasses North Africa, the Middle East, and small parts of North America and Southeast Asia. Particle transport trajectories across continents

North Africa is the geographic band responsible for the largest emission of non-anthropogenic dust into the atmosphere of the planet, followed by the Middle East and the Arabian Peninsula. These particles are mainly composed of clay minerals, magnesium carbonate, quartz and calcium. These mineral dusts from the Saharan desert generally follow three routes: towards the American continent, the Mediterranean Sea and the south of the European continent, and the Middle East, even reaching the point of being documented in East Asian countries. like Japan.

And how is this suspended MP generated? There may be a relationship with territories that contain extensive alluvial deposits, which are mobilized by alluvial fans or wadis in areas close to mountainous regions or with recent pluvial deposits. In fact, it is suggested that the production of these PM10 seems to be more closely linked to environmental and fluvial chemical processes than to wind processes, where the first actions separate the material from the soil and the source rock which later, when they settle on plains and dry, They can be easily moved by the wind.

This is what happens, for example, in the largest dust-producing region on the planet, located in central North Africa near the Ahaggar mountain range. This is supported by the fact that mineral dust in air is four times larger than when dissolved in water because it tends to form aggregates when suspended.

More than a respiratory problem

Desert dust or haze has traditionally been associated with health problems, usually of respiratory origin, due to the pathophysiology after inhalation of this PM. Asthmatic exacerbations are frequently found during episodes of desert sandstorms.

In Asia, there have been increases in admissions for pneumonia during times of these phenomena. This may be due to the movement of microorganisms that travel dissolved in the cloud of atmospheric dust and trigger pathologies in the oropharynx and upper respiratory tract, generating episodes of pharyngitis, tracheitis or allergic rhinitis, for example . Even, at the respiratory level, an increase in lung cancers has been described in the Dust Belt regions, specifically in Mauritania and Mali, which could be linked to exposure to desert dust.

From the cutaneous point of view, harmful effects can be found, in particular skin irritations after exposure to heavy metals such as nickel, which can cause contact dermatitis. The eye is another gateway for desert dust into the body. The development of more severe episodes of conjunctivitis in nomadic populations of Western Sahara has been linked to exposure to this suspended mineral moved by Irifi winds.

On the other hand, over the past decade, studies have been published on the effects on cardiovascular health. Most of this work has been done in geographic areas with low PM10 concentration when affected by desert dust storms, yielding different results.

The case of the Canary Islands and the Peninsula

However, the Canary Islands is a privileged geographical region due to the annual frequency and intensity with which these storms arrive from North Africa. A study in these islands, an area most exposed to African desert dust on the European continent, determined an increase in admissions for heart failure with PM10 exposures > 50 μg/m3.

Recently, a meta-analysis confirmed that exposure to desert dust increased cardiovascular mortality by 2% the day of exposure and 1% the day after exposure. Probably, the limited number of studies in areas with high exposure to desert dust such as North Africa and the Middle East (PM10 concentrations during suspended mineral storms up to 1000 μg/m3) generate few data to establish associations with clinical events. such as heart failure and acute myocardial infarction.

A study pointed out that in the Canary Islands, desert dust storms have a higher concentration of PM10 at low altitudes, where the population usually resides, during the winter season. This has happened consecutively since 2020. Similarly, in the Iberian Peninsula, in the winter of 2021, a desert dust storm reached the Pyrenees and we could glimpse in images how the snow turned brown.

The current episode has generated PM10 concentrations of 700 μg/m3 in cities like Guadalajara, Madrid or Toledo, and up to 1000 μg/m3 in Alicante and Murcia. This should lead us to propose warning and protection measures, particularly in the population at health risk, in the face of these innocuous atmospheric events originating from the planet’s deserts.

At present, we cannot confirm that climate change generates more episodes of haze or with a higher concentration of PM10. However, the climate crisis increases the extension of the desert areas of North Africa, and this increases the surface to generate suspended mineral dust.

For Nestor Baez Ferrer He is a specialist in cardiology. Doctor of Medicine from the University of La Laguna.


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