Wastewater reuse for agriculture: Effluent storage limits transmission of antibiotic-resistant bacteria to crops
Year: 2026
Type: conference-paper
Abstract: BackgroundClimate change is increasing the demand for alternative water sources for crop irrigation, especially in arid and semi-arid regions. In response to this water scarcity, the practice of irrigating crops with sewage effluent from wastewater treatment plants (WWTP) is becoming more widespread. Irrigating with effluent can introduce microbial and chemical contaminants, posing a public health concern. This practice could increase the reservoir of antimicrobial resistant bacteria (ARB) and of the antibiotic resistance genes (ARGs) they carry in the harvested products and the soils irrigated with WWTP effluent. This study aimed to compare the contamination of crops by extended-spectrum beta-lactamase-producing Enterobacterales (ESBL-PE) and imipenem-resistant Enterobacterales (IRE) after irrigation with effluent, stored effluent or water.MethodsRadishes and rocket were grown for two months (May and June 2025) in a greenhouse experiment and irrigated with either fresh WWTP effluent, effluent stored for 21 days, or tap water. ESBL-PE and IRE were isolated from effluent, soil and vegetable samples. Isolates were identified using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and their antimicrobial susceptibility against 16 antibiotics belonging to 6 classes (β-lactams, quinolones, tetracyclines sulphonamides, aminoglycosides and phenicols) was determined. ResultsViable E. coli concentration was determined for each effluent sample and ranged from 2.0 x 104 to 2.5 x 105 colony-forming units (CFU)/100 mL). E. coli concentration in effluent stored for 21 days showed a 2 to 3-log reduction compared to fresh effluent (5.6 x 101 to 2.9 x 103 CFU/100 mL).Numerous ESBL-PE were isolated in fresh effluent samples at day 0, but their numbers gradually decreased over time (days 7 to 21). At harvest, 31 ESBL-PE and one IRE were isolated from vegetables irrigated with fresh effluent. Rocket leaves were more contaminated than radishes with 23 ESBL-PE (six E. coli, five K. pneumoniae, four Citrobacter sp., seven Enterobacter sp., one R. ornithinolytica) and one IRE Enterobacter sp. compared to seven ESBL-PE on radishes (two E. coli, four Citrobacter sp., one Enterobacter sp.). Only one ESBL-PE Citrobacter freundii was isolated from radishes irrigated with stored effluent.We identified 24 distinct resistance profiles in ESBL-PE isolated from vegetables. Twelve of these phenotypes were shared between water and vegetables, and five were shared between vegetables and soil. Conclusions/implicationsIn fresh effluent samples, E. coli number always exceeded the legal requirements imposed by European legislation (rank D requiring concentration <10,000 CFU/100 mL of E. coli). Storing effluent for 21 days is a promising way to reduce microbial load and potentially limit the risk of ARB transmission to vegetables. Indeed, storage allowed to obtain effluent with a E. coli concentration between 56 to 2,900 CFU/100 mL, corresponding to effluent of rank B to D.This study highlights the potential health risks associated with using WWTP effluent for irrigation. Storing treated wastewater for at least 21 days could be a cost-effective way of complying with current legislation and safeguarding public health.
Source: HAL
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7212411458