Saharan dust caps, ambient air quality and cardiovascular health
Air pollution is a serious health problem that causes some 8 million deaths a year from respiratory and cardiovascular conditions as well as cancer. Many of these conditions occur in urban areas, where the air contains gases and particles in suspension from emissions of fossil fuel combustion (cars and industry), and from the burning of biomass. In Central Europe, Asia and South America, air quality and health problems are linked to these types of emissions. The World Health Organization recommends that the population should not be exposed to concentrations of respirable particles, or PM10 (particulate matter smaller than 10 microns), greater than 50 micrograms per cubic meter of air (µg/m3) on average over a 24-hour period.
There are regions where poor air quality is also induced by the presence of suspended desert dust in the environment. Desert dust is an agent that degrades air quality in the so-called Dust Belt, which extends across North Africa, the Middle East and inland Asia. The winds associated with certain weather scenarios favour the emission and transport of dust, affecting ecosystems and giving rise to biogeochemical processes that influence the climate and the health of the population.
In Spain, the largest impacts of Saharan dust limes occur in the Canary Islands, where concentrations of respirable particles (PM10) are usually around 20 µg/m3under normal conditions, and between 50 and 500 µg/m3during lime episodes. These values are much higher than those recorded in Southern Europe (peninsular Spain, Italy and Greece) under Saharan dust conditions, where they are usually between 20 and 60 µg/m3.
Recently, the Canary Islands have suffered one of the most intense episodes of Saharan calima in recent decades. Between 22 and 24 February 2020 the concentrations of PM10particles exceeded 1000 µg/m3, with records of up to 3200 µg/m3.
Epidemiological studies observe that there is an association between desert dust and mortality from cardiovascular and respiratory conditions. However, the risk groups and the patho-physiological mechanisms by which dust exposure affects health are still unknown. Studies by the CSIC and the University Hospital of the Canary Islands show that exposure to high concentrations of desert dust during calima worsens the prognosis of patients admitted for heart failure.
One of these studies, recently published in the Journal of Clinical Medicine, was carried out in Tenerife and involved the 829 patients admitted to the University Hospital of the Canary Islands during the period 2014-2017 with the diagnosis of heart failure. The patients were given data on cardiovascular risk factors, clinical history, biochemistry, precipitating factors of heart failure, data on intra-hospital treatment and the concentrations of suspended particles in the ambient air to which they had been exposed. Statistical analysis of the data showed that the only variable that differentiates the group of patients who died from the group of patients who survived was exposure to high concentrations of Saharan dust. Six percent of the patients admitted with heart failure during this study died (the average number of deaths from heart failure in Spain is 9%), and of these deaths 86% had been exposed to high concentrations of Saharan dust (concentrations greater than 50 micrograms per cubic meter of air). Heart failure especially affects people over 60 years of age, with symptoms such as shortness of breath, tiredness and difficulty in breathing when lying down; the heart has difficulty in pumping blood.
The results of this line of research have implications for air quality management in part of the Macaronesia and North Africa. Progress needs to be made in identifying the risk groups that are affected by exposure to desert dust in order to be able to properly manage Saharan dust haze predictions and take health protection measures. In addition, it is necessary to identify patho-physiological mechanisms and to integrate the knowledge generated into the training of health personnel.
By Sergio Rodríguez