Evaluating the risk of mixtures in the indoor air of primary school classrooms

In school environments, children are constantly exposed to mixtures of airborne substances, derived from a variety of sources, both in the classroom and in the school surroundings. It is important to evaluate the hazardous properties of these mixtures, in order to conduct risk assessments of their impact on children’s health. Within this context, through the application of a maximum cumulative ratio approach, this study aimed to explore whether health risks due to indoor air mixtures are driven by a single substance or are due to cumulative exposure to various substances. This methodology requires knowledge of the concentration of substances in the air mixture, together with a health-related weighting factor (i.e. reference concentration or lowest concentration of interest), which is necessary to calculate the hazard index. Maximum cumulative ratio and hazard index values were then used to categorise the mixtures into four groups, based on their hazard potential and therefore appropriate risk management strategies. Air samples were collected from classrooms in 25 primary schools in Brisbane, Australia. Analysis was conducted based on the measured concentration of these substances in about 300 air samples. The results showed that in 92 % of the schools, indoor air mixtures belonged to the ‘low concern’ group, and therefore, they did not require any further assessment. In the remaining schools, toxicity was mainly governed by a single substance, with a very small number of schools having a multiple substance mix which required a combined risk assessment. The proposed approach enables the identification of such schools and thus aids in the efficient health risk management of pollution emissions and air quality in the school environment.