Miguel de Castro Neto, from Nova University and one of the authors of the study, Impact of COVID-19 lockdown measures on waste production behaviour in Lisbon", said, quoted in a statement, that the work allowed to show this decline in the volume of waste collected and that the main cause was the drop in tourism. "We also realised that in Lisbon the changes were directly linked to the type of waste and the spatial distribution of its production within the city. Residential areas with higher population density were those where there was a smaller decrease in waste production, while areas that had high tourism rates had a greater drop," he said.