By Dr. Colin Michie of AUC Medical School
Dr. Colin Michie has worked as a paediatrician in the United Kingdom, Africa, the Caribbean and the Middle East. He specialised in nutrition, haematology and infectious diseases. Now the Associate Academic Dean for the American University of the Caribbean Medical School in Sint Maarten, his enthusiasm is training medical students and healthcare teams to ensure they deliver better value health care.
The air that we breathe is a mixture. It contains gases such as oxygen on which our lives depend. We all breathe between 5 and 60 litres a minute, depending on whether we are sitting at rest or chasing after a minibus. So even if you are on holiday and spend a great deal of time sleeping, you will breathe over 7000 litres of air a day. Children are special (as always!) because they have a higher metabolic rate and breathe more litres of air a minute than adults.
With this large volume of breathing, we need to pay attention to what is in the air that we breathe. As we all know, there are many particles, motes, dust or specks in the air. These tend to be small so we usually do not notice them. Looking at actual measurements, the smallest particles we can see are of the order of 5-10 microns in size. There are a thousand microns in a millimetre, or 25 thousand microns in an inch. By way of examples, a single red cell is about 5 microns across. A hair is about 75 microns across. When describing air particles or aerosols, the term PM10 is used for particles up to 10 microns in diameter, PM2.5 for smaller ones up to 2.5 microns in size and smaller ones can be referred to as ultrafine particles. So we can see, if we have good eyesight, something the size of a red cell.
Some dust particles in the air are about this size, but a great deal are smaller. Particles in the air are often visible as a smoke or haze. With mists, cloud or fogs, the result of many tiny droplets of water, the particles are quite large. Tobacco smoke, diesel fumes or a candle flame produce some particularly ultrafine particles which we cannot see at the time, but will cause a film on other surfaces that appear as “dirt.” Hairsprays and talcum powder, as well as air fresheners and fabric protectors all release ultrafine particles into our homes and offices.
Human activity creates a large number of airborne particles directly, often as a result of processes of burning. The most obvious of these is smoking. Tobacco smoking remains a major challenge to the health of those who smoke and those exposed passively to the smoke they generate. The evidence is overwhelming and unequivocal. Tackling this habit is critical to reducing ultrafine particles in the air in homes and public places.
Our species is responsible indirectly for generating many other dust particles of all sizes by laying waste to the land. Removing trees, intensive grazing and climatic changes result in drying and damage to soils, creating more dust. The Sahara desert has expanded steadily since the 1970s; the Gobi desert continues to increase by over 1000 square kilometres a year. Winds passing over these drylands and storms such as haboob winds will send dust into the atmosphere. Dust storms are found on all continents and on Mars – they spread particles effectively on both planets.
Windborne or aeolian dust can travel long distances, with the smallest particles going further than large ones. Ultrafine dust particles from the Sahara can be found on St. Maarten and contribute to the atmospheric hazes we can see between February and October. Imaging from satellites show that the Sahara is the planet’s largest source of dust which then spreads on the North Atlantic trade winds. An estimated 20 million tons of the Sahara is thought to take to the air each year. Saharan dust is associated with illness in Africa and Europe. It has been identified in Alaska. In 2007, a dust cloud from a Chinese desert, Taklamakan, made a circuit of the entire planet in 13 days. Levels of particles in the atmosphere look set to increase in the outdoor air, wherever you live.
Caribbean studies have proposed links between Saharan dust and admissions with asthma in the children of Trinidad, Grenada and Guadeloupe. Those carrying out this work pointed out that Saharan dust contains not just minerals but also plant remains. Others in Italy have found that microbes including fungi might be cultured from the desert deposits around the Mediterranean Sea. Researchers in Athens have noted that the Saharan dusts add to poor air quality there, and may trap and combine with other pollutants to contribute to poor health outcomes.
Getting closer to your own environment, when did you last hear someone sneeze? This morning? In the last few hours? When someone sneezes, bacteria or viruses from their throat can spread up to 100,000 bacterial or viral particles up to eight meters in a turbulent bubble of air. Most of these organisms are not visible: they are ultrafine particles. A study in Maryland showed that students could produce an infective aerosol containing influenza virus from their breathing – they did not even have to cough or sneeze to spread the virus. Fine particles spread in our breath, if we are unwell, can therefore cause infections to develop in others. Illnesses including the ‘flu, chickenpox, measles or tuberculosis are passed on in this manner.
For this reason when we have a respiratory or throat infection, it is practical to use tissues of some sort for coughs and sneezes. It may be worth keeping coughing children at home rather than going to school as this can be modestly effective in limiting the spread of a virus as ultrafine airborne particles into our communities. Handwashing is also crucial at these times – virus particles can spread by contact too. Our communities need to include our animals too, as the spread of infections in horses, chickens or pets, for instance, is by the same route.
Particles in the air cause problems to those with allergies. Those who suffer with hay fever, for instance, may be sensitive to the pollen from flowers in a room. Those with asthma or eczema may become unwell if there is an animal, house dust mites, mould or peanuts nearby. These problems demonstrate the fact that airborne particles affect our noses, lung and skin. They also show that the nature of the airborne particles is important. What are those small particles, what are they made of and can we protect ourselves against them?
One area that is a particular issue on this island is that of mould which can develop inside homes, releasing spores as dusts that result in respiratory problems. The quality of the air outside our homes, and that inside, are areas of international concern and something we can help improve. A critical filter to remove airborne particulates is the nose. Within our noses, we have several fine curled bones (turbinates) that are designed to help warm and moisturize the air we breathe, keeping our smell cells happy and ensuring particles of all sizes are captured in a mucus layer.
A system known as the muco-ciliary elevator moves mucus from deep into our lungs out to our throats and from the back to the front of the nose. This system reduces the risks of dusts of all types to our lungs and circulation. Dust size determines where it is likely to be filtered. Large particles are removed at the nose, but smaller ones such as PM10s (twice the size of a red cell) will be found in the lower respiratory tract, in the lungs themselves. Ultrafine particles can penetrate to the deepest places in our lungs, the alveoli. So if we breathe those 7000 litres a day, it is likely that this filtration system will protect us most of the time.
All of us will suffer if we breathe some types of particles. Take the case of asbestos in mines, quarries and buildings. Exposure to asbestos dust has been shown to frequently cause cancers. The dust from this mineral is particularly powerful in terms of the damage it can cause to the tissues of anyone working with it. Other occupational exposures in the mining industry are known to be related to a wide range of illnesses. So too is the exposure to particles in cigarette smoke, which has been shown to be hazardous in many different ways. The highest levels of particulates are usually related to the burning of oil and coal. Dense urban areas in very large cities such as Delhi or Beijing are known to be in this category.
It is logical to conclude that inhaling particles, particularly ultrafine particles, even if they are not infectious, is bad for your health. What do we know from many investigations is that particulates can affect your lungs and heart, making lung diseases, cancers and heart attacks more likely. If you are pregnant, your infant is likely to be born smaller. If you are elderly, your life-expectancy will be shorter. A European study of over 100 000 participants for an average of 11.5 years showed that increased exposures to PM10s was linked to an increased risk of heart attack.
In large conurbations in Europe and the USA, traffic exhaust has been found to be the single most serious preventable cause of heart attack in the general public. The international Agency for Research on Cancer (IARC) concluded in 2013 that outdoor air pollution is carcinogenic to humans, with the particulate matter most closely associated with cancers, particularly lung cancer, but also with malignancies of the kidneys and bladder. These large studies suggest there is no safe level of particulates if one considers human health and the health of children as the readout. The World Health Organisation (WHO) reported that in 2016, 91% of the global population lived in areas where WHO air quality guidelines were not met.
This article is not cheering. Dusts, including those from the Sahara, are likely to have negative effects on the health of all those living on these islands. For St. Maarten, there are several positive points. Mother Nature plays a part. For instance, rain removes many aerosol particles including ultrafine ones. Our frequent showers will help remove some particulate matter. Saharan dust contributes to those spots on vehicle windscreens after rain. Our frequent sunshine contains ultraviolet light which will destroy aerosols of viruses and bacteria in the atmosphere.
At a governmental level, there is an Energy Policy and an active charity, the Nature Foundation, both directing strategies at improving air quality by several different mechanisms. Although we cannot alter the Sahara or the trade winds, we can all play a valuable part in reducing some particles in the air that we breathe. In our homes and places of work, we need to become aware of dusts and how to avoid them. Stopping cigarette smoking is a critical first step. Keeping these special environments clean, free of mould, tobacco smoke or other products of burning is important. For those with allergic or respiratory problems, air purification systems or air conditioning in the bedroom can provide relief by filtering out as many particles as possible. Just remember those 7000 litres every day.
As a Caribbean island, as in other nations, policies promoting investments in cleaner transport, sustainable energy, municipal waste management and reducing the carbon footprint will reduce critical sources of air particles locally. Internationally, many have called upon the United Nations to undertake a global risk assessment of the hazards posed by the Sahara’s erosion. Strategies to limit this will require great collaboration and ingenuity. As the Sint Maarten government recorded in its National Energy Policy of 2014, “There is no Planet B”.
