Air change rates and infection risk in school environments: Monitoring naturally ventilated classrooms in a northern Italian urban context

The importance of building ventilation in avoiding long-distance airborne transmission has been highlighted with the advent of the COVID-19 pandemics. Among others, school environments, in particular classrooms, present criticalities in the implementation of ventilation strategies and their impact on indoor air quality and risk of contagion. In this work, three naturally ventilated school buildings located in northern Italy have undergone monitoring at the end of the heating season. Environmental parameters, such as CO2 concentration and indoor/outdoor air temperature, have been recorded together with the window opening configurations to develop a two-fold analysis: i) the estimation of real air change rates through the transient mass balance equation method, and ii) the individual infection risk via the Wells-Riley equation. A strong statistical correlation has been found between the air change rates and the windows opening configuration by means of a window-to-volume ratio between the total opening area and the volume of the classroom, which has been used to estimate the individual infection risk. Results show that the European Standard recommendation for air renewal could be achieved by a window opening area of at least 1.5 m2, in the most prevailing Italian classrooms. Furthermore, scenarios in which the infector agent is a teacher show higher individual infection risk than those in which the infector is a student. In addition, the outcomes serve school staff as a reference to ensure adequate ventilation in classrooms and keep the risk of infection under control based on the number of the students and the volume of the classroom.

Ventilation strategies to reduce airborne transmission of viruses in classrooms: A systematic review of scientific literature

The recent pandemic due to SARS-CoV-2 has brought to light the need for strategies to mitigate contagion between human beings. Apart from hygiene measures and social distancing, air ventilation highly prevents airborne transmission within enclosed spaces. Among others, educational environments become critical in strategic planning to control the spread of pathogens and viruses amongst the population, mainly in cold conditions. In the event of a virus outbreak - such as COVID or influenza - many school classrooms still lack the means to guarantee secure and healthy environments. The present review examines school contexts that implement air ventilation strategies to reduce the risk of contagion between students. The analysed articles present past experiences that use either natural or mechanical systems assessed through mathematical models, numerical models, or full-scale experiments. For naturally ventilated classrooms, the studies highlight the importance of the architectural design of educational spaces and propose strategies for aeration control such as CO₂-based control and risk-infection control. When it comes to implementing mechanical ventilation in classrooms, different systems with different airflow patterns are assessed based on their ability to remove airborne pathogens considering parameters like the age of air and the generation of airflow streamlines. Moreover, studies report that programmed mechanical ventilation systems can reduce risk-infection during pandemic events. In addition to providing a systematic picture of scientific studies in the field, the findings of this review can be a valuable reference for school administrators and policymakers to implement the best strategies in their classroom settings towards reducing infection risks.

Biological and chemical tools in the toxicological risk assessment of Jarama River, Madrid, Spain

Four river water samples (R) and three sewage samples (S) were collected at different points in the Jarama River, Spain. Organic concentrates were tested on the RTG-2 in vitro cytotoxicity test and analyzed by HPLC and GC/MS. The cytotoxicity assessment demonstrated a progressive increase in the toxicity of the river water when moving downstream. A wide range, from slightly harmful to highly toxic, was observed for sewage samples. The most toxic samples produced decreases of 95% to 100% in the ATP content, cell viability and cell detachment (a parameter to estimate mortality). The most toxic organic concentrates (the sewage from an urban + industrial effluent collected in Paracuellos, Madrid, Spain, and the river 100 m downstream from the discharge of this effluent) were fractioned by an HPLC system. Each chromatographic peak was collected as a fraction of the whole concentrate. The cytotoxicity of each fraction was also assessed on RTG-2 cells. A toxic peak with a retention time of 38.3 min was detected in both samples; this time belongs to the PAHs retention time interval under our chromatographic conditions. Analytical procedures identified fluorene (0.62 microg/l) and benz(a)anthracene (0.44 microg/l) in the sewage and anthracene (0.40 microg/l) and benz(a)anthracene (0.14 microg/l) in the river water. However, the observed cytotoxicity could not be explained by the PAH concentrations. Five additional toxic peaks were observed in each sample. Results suggest that the combination of HPLC with cost-effective toxicity tests produces a useful tool to define environmental management decisions when the chemical analysis cannot identify the substances responsible for the environmental risk.