Fungi as an emerging waterborne health concern: impact of treated wastewater discharge versus aerosolization†

The discharge of treated wastewater effluents into river-fed irrigation canals results in a de facto form of water reuse. Waterborne fungal populations in such environments pose a unique human health concern given that opportunistic fungal pathogens can be proliferated during spray irrigation of crops. In the present study, we consider two different routes (effluent discharge versus bioaerosols) through which wastewater treatment plants (WWTPs) can impact the presence and abundance of fungal communities in irrigation canals of the Rio Grande river basin in New Mexico. Site A was selected to investigate the influence of effluent discharge from a WWTP on waterborne fungal communities in a receiving irrigation canal. Site B represented an irrigation canal that was directly adjacent to a WWTP but that receives no effluent discharge (to exemplify bioaerosolization exclusively). Sampling dates were chosen to capture variations in weather and stream flow conditions at each of the two sites. Results indicated that treated wastewater discharged into the canal had a distinct impact on fungal community composition, especially under low wind and flow conditions. When stream flow was highest, variations along the canal at Site A were minimal. The highest occurrence of pathogen-associated genera was observed at Site B under high wind conditions with an average relative abundance of 20.9 ± 13.1% (peak of 39.3%) and was attributable to bioaerosol emissions from the WWTP and a nearby livestock facility. Such genera included Alternaria, Cladosporium, and Cryptococcus. These findings suggest that although treated effluent discharge can directly impact irrigation canal fungal community composition, bioaerosols likely have a larger overall effect on the spread of potential fungal pathogens.