Impact of outdoor and indoor air quality in secondary schools and homes on children’s respiratory health in Malta

Abstract

Background: As seen in the International Study of Asthma and Allergies in Childhood (ISAAC) studies, children in Malta have a very high prevalence of symptoms pertaining to asthma and allergies. It is also one of the most densely populated countries in the world, with a high vehicular density, a central industrial and maritime hub and two coastal power stations running on heavy fuel oil. One of the main risk factors for asthma remains air pollution, known to worsen asthma prevalence and its control, particularly amongst children. Particulate matter (PM) of aerodynamic diameter of less than 2.5 micrometres (PM2.5), has quickly become known as one of the most ubiquitous and dangerous air pollutants of our times, able to penetrate deeply within the lung, due to its small size. Malta has often reported very high outdoor concentrations of PM2.5, yet we know little about the local respiratory morbidity caused by this PM. In Malta, indoor PM2.5 concentrations has been even less well studied, yet schoolchildren spend the majority of their times indoors, either at school or at home. Recently the SINPHONIE study looked into the respiratory effects of indoor air pollution at primary schools in Malta. However, there are no studies on the effects of outdoor and indoor PM2.5 concentrations amongst our Maltese adolescents, at their schools and homes. The primary aim of the present research study was to look at the effects of analysed PM2.5 levels and its components, on the respiratory symptoms in Malta amongst adolescent school children; comparing the indoor and outdoor levels at the schools they attended and the homes they live in. The assessment was performed in two ways: Associations of PM exposures with asthma cases and controls, as well as children living in the different geographical locations in Malta. Finally, the results of this research were compared with the closest neighbouring country Sicily, with whom as a population, there are similarities in climate and culture, and with whom the RESPIRA study collaborated. Particulate matter remains the most heterogenous and complex air pollutant, differing in its composition depending on the sources present, as well as with its interplay with weather and seasonality. Thus, its main components were studied by collecting PM2.5 was analysing its constituent elements (anions, cations, metal oxides), and its elemental and organic carbon content. We also studied variations in its concentrations in accordance with weather changes and various dwelling characteristics. Method: The study was started during the scholastic years of 2012 and 2013, with six secondary schools included from the north, south and central localities of Malta. Using a validated RESPIRA questionnaire, based on the ISAAC questionnaire, an assessment of the current prevalence of respiratory symptoms, asthma and allergies amongst the Maltese adolescents was preformed, together with information on their school and home environment, in order to identify children who are symptomatic cases from asymptomatic controls. Within the same time period, the indoor and outdoor PM2.5 was collected at the schools and homes of the case / control cohort. PM2.5 was collected by gravimetric impaction onto teflon and quartz filters for both quantitative and qualitative analysis, allowing for the identification of the PM2.5 components (i.e., sea, crustal, secondary inorganics, traffic and organic PM components). Further data was obtained from the two Environment and Resource Authority (ERA) PM2.5 monitoring stations in Malta, with accompanying weather data from the Luqa airport meteorological office, for the study period held in 2012. At the schools, traffic counts of passenger cars and heavy vehicles were also collected. For both schools and homes, specific building characteristics were noted, which could affect their outdoor and indoor air quality. Results:1075 secondary schoolchildren and 862 parents participated in the study by completing the questionnaires: 380 males; 482 females (male to female ratio of 1:1.3); mean age of 12.5 years; mean BMI of 21.5 kg/m2. There was a high prevalence of asthma and allergies in Malta, which was consistent with previous ISAAC studies: cumulative and current wheezing at 32% and 13% respectively; doctor diagnosed asthma at 18%; cumulative and current rhinitis at 31% and 27% respectively. This current research found elevated outdoor PM2.5, Elemental Carbon (EC) and Organic Carbon (OC) concentrations, above the WHO, US-EPA and EU safety thresholds for PM. The indoor PM2.5 was significantly higher than the outdoors, particularly during the colder months due to insulation and domestic heating. Outdoor organic PM components were found to be associated with increased respiratory morbidity amongst secondary schoolchildren, including chronic cough, dry and irritative cough, sore throat and wheezing on exercise. The highest prevalence for asthma and allergies was found in the central area of Ħamrun, which is highly urbanised and contains the industrial and maritime-hub, together with a local power-station. The highest indoor and outdoor PM2.5, traffic and organic components were recorded in the central area of Ħamrun. There were no significant differences in pollutant levels between schools and homes, and minimal differences between cases and controls. However, there were some important building characteristics which effected the PM2.5, EC and OC concentrations including dwelling type (i.e., flats), smaller living spaces and lesser window apertures, the use of fireplaces for domestic heating and indoor smoking.