Urban use of reclaimed water associated with health risks

Reclaimed water has been widely used in urban area. However, residual pathogens in the recycled water have been frequently reported, and are identified as the main source of health risks for wastewater reuse. Thus, the paramount need is to ensure the safety of all potential end users. Common applications of reclaimed water such as road cleaning, greenfield irrigation or landscape fountain tend to produce significant amounts of aerosols, and people exposed to the aerosols containing pathogens might get illnesses. However, the relevant studies are rare and the amount of reclaimed water inhaled was often simply estimated by hypothesis.

This study entitled "Aerosol exposure assessment during reclaimed water utilization in China and risk evaluation in case of Legionella" is published online in Frontiers of Environmental Science & Engineering in 2022.

In this study, the research team estimated the health risks associated with the potential exposure of airborne Legionella emitted from the urban use of reclaimed water in China. Nationwide questionnaire was designed to investigate the exposure habits of Chinese population in different scenarios: 1) people walk on the sidewalk where road cleaning is taking place; 2) people walk along a greenfield in a park for recreational purpose where irrigation system is on operation; 3) people pass by the ornamental landscape fountain. The results indicated that annual infection probability of populations exposed to Legionella for three scenarios, 0.0764 for road cleaning, 1.0000 for greenfield irrigation, 0.9981 for landscape fountain, were markedly higher than the threshold recommended by WHO (10⁻⁴ per person per year) according to the concentration distribution of Legionella in the reclaimed water. An age-, educational background-, region- and gender-specific data in annual infection probability also showed different tendencies for some subpopulations.

The risk assessment results indicated that actions need to be taken to reduce the exposure and potential transmission of Legionella during water reuse. Reclaimed water can be disinfected in storage tank before used for road cleaning and landscape fountains. Reducing the retention time of water in tank could also effectively mitigate the growth of Legionella. A warning sign should be set up in a prominent place in the park when using reclaimed water, considering that the high risks of certain subgroups are mainly due to the coincidence of their recreational activities with the time of reclaimed water utilization.