Sahara Dust
If you or those close to you suffer from asthma attacks you will be interested in the scientific link between the dust in the environment and your health. In this week’s edition of Cleaning Up The Mess, eco-toxicologist, UWI lecturer Dr Azad Mohammed and Dr Marissa Gowrie, who have worked jointly on a research programme on the magnitude and impact of Saharan dust in the Caribbean are our joint guest columnists on Cleaning Up The Mess.
Every year from February to October, our blue skies periodically disappear behind a blanket of haze which can be attributed to increased levels of Saharan dust in the atmosphere. For those who suffer from asthma or other respiratory distress, it is also a sign to restock the medicine cabinet with extra refills for antihistamines and inhalers. It becomes entrenched in their daily routines, keys, lunch bag, hair brush, and yes the inhaler. Just like we have grown accustomed to wet and dry seasons, asthma sufferers have grown accustomed to the on and off season for symptoms.
The “on” season usually coincides with the months from February to October, which represents the summer months in the northern hemisphere and the period which signals the start of the migration of Saharan dust from Africa, to the Americas. The migration of Saharan dust begins when storms in North Africa lift Saharan sand and dust into the upper atmosphere, where it is carried thousands of miles across the Atlantic Ocean into the Caribbean and southern parts of the Atlantic US. Movement of the clouds can be tracked using satellite imagery or by ground observations. Most people only notice the dust clouds when it shrouds the sunset in a yellowish haze and the hillsides disappear behind a blanket of haze.
Various studies have raised concern about the potential link between the dust levels and the impact on human health. Research which suggest that there may be a correlation between high concentrations of particles less than 2.5µm (0.0025mm) in diameter (PM2.5) and increases in emergency room admissions for respiratory and cardiovascular disease have been reported in North America, Asia and Europe. The primary health concern associated with Saharan dust is the particulate matter—microscopic dust (less than the thickness of hair, < 2.5µm) which can sidestep the lungs’ natural defences. These tiny particles can contribute to cardiovascular problems as well as respiratory diseases such as asthma, especially in children.
Recent research by Dr Monteil in Trinidad has shown that the symptoms of rhinitis in the student population exceeded 30 per cent. The reasons for such high prevalence of allergic disease in Caribbean youth remain obscure; however, preliminary data from Trinidad have hinted at a higher prevalence of these disorders among students attending schools in urban areas. In Barbados, studies have suggested that there was a 17-fold increase in the prevalence of asthma from 1973 to 1996, with acute asthma attacks accounting for 22.3 per cent of the Queen Elizabeth Hospital emergency room visits in 1999. This increase corresponded to the observed increase in African dust flux affecting Barbados. The dust particles also serve as a vehicle for the transport of known asthma triggers such as biological materials including bacteria, viruses, fungal spores and pollen. They have also been shown to transport various pollutants such as metals and pesticides.
To date, more than 200 species of viable bacteria and fungi have been identified from air samples collected during Saharan dust events in Trinidad and Tobago. However, there is still uncertainty as to whether dust clouds could transport other asthma triggers such as pollen. Recent research completed by Dr Marissa Gowrie of the University of the West Indies has sought to provide some light on this issue.
Dr Gowrie collected air samples for pollen enumeration over a two year period at Galera point, Toco, and at the University of the West Indies (UWI), St Augustine. This sampling covered both dust and non-dust periods over the two years. Data for other environmental triggers for asthma: Rainfall, relative humidity, temperature, barometric pressure and Saharan dust were also collected.
This data was then correlated with paediatric asthma admissions (children 15 years and younger) at the Accident and Emergency Unit of the Eric Williams Medical Sciences Complex (EWMSC) to help develop a predictive model of asthma incidences. Dr Gowrie found that very little African pollen is transported on these Saharan dust clouds. However, the studies did suggest that local pollen in the presence of other factors such as dust concentrations, relative humidity, wind speed and temperature variations contributed to increases in paediatric asthma. A predictive model based on the interactions of these factors was created, which is able to forecast paediatric asthma admissions for 84.7 per cent of the asthma cases studied over the two year period.
A key component of the model was the inclusion of lag time which took into account the incubation time before the onset of asthma symptoms. The model is able to forecast paediatric asthma a week in advance, using asthma admissions from three days prior. It showed that asthma increases when there is a certain combination of factors, specifically days of high pollen, high dust, high wind speed, and high temperature variations, coupled with two consecutive days of high relative humidity. Next week, look out for a special environmental series with guest columnist Dr Roodal Moonilal, Minister of Housing and the Environment.