Discharge of antimicrobial resistant genes in treated wastewater to recipients

Summary

The abundance of selected marker genes for antimicrobial resistance (AMR) in water samples collected from the effluent of three Norwegian wastewater treatment plants was quantified. 16S rRNA, Intl1 and Sul1 were the dominant antibiotic resistance genes (ARG) in the plant effluents. Equally high concentrations of most ARG that were measured in samples from all plants suggest that households and other diffusive sources play a dominant role as source for ARG in wastewater. The abundance of ARG seems to be independent of the treatment plant. At all plants, most of the ARG investigated are discharged to the recipient with the treated water. The presence of high ARG concentrations in samples collected from the recipient downstream of one of the plants was unexpected, and is explained by extraordinary circumstances in the section of the river where samples were collected. Conclusions on whether the treatment plant’s effluents contribute more to the total load with anthropogenic ARG in the recipient than other diffusive sources cannot be drawn at the moment.