Pharmaceutical Residues, Antibiotic Resistance Genes, and Bacterial Communities in Lettuce Under Overhead and Surface Irrigation.

As water scarcity is becoming severer in many regions, crop irrigation with reclaimed water is becoming more popular. Reclaimed water often contains trace levels of pharmaceuticals (e.g., antibiotics). Thus, crop irrigation with reclaimed water could result in accumulation of pharmaceuticals in food crops. Bacterial community will also likely respond to the stress of pharmaceuticals from reclaimed water. This could potentially change the abundance and diversity of antibiotic resistant bacteria (ARB) and genes (ARGs) in food crops and soils. The transfer of pharmaceuticals, ARB and ARGs in food crops to humans via dietary exposure may pose potential risks to food safety and human health. Thus, this study investigated the accumulation of pharmaceuticals in greenhouse-grown lettuce under overhead or soil surface irrigation. The changes in bacterial communities and ARG profiles in lettuce shoots, roots, and soils were also explored. Lettuce shoots had greater concentrations of pharmaceutical residues and ARGs under overhead irrigation than under surface irrigation. Bacterial community was more diverse in soils than in lettuce. Bacterial communities and ARG profiles were altered by antibiotic stress imposed by the irrigation water. Our results suggest that irrigation practice could be optimized to reduce the potential risks to food safety, when reclaimed water is used for crop irrigation.