Integrated effects of polyamide microplastics and common antimicrobials in reclaimed water on the growth of lettuce (Lactuva sativa L.) and soil bacterial communities

Micropollutants coming from wastewater irrigation present a looming threat to agricultural productivity as well as ecological and public health. Reclaimed water from wastewater treatment plants intensifies soil with contaminants of emerging concern, such as microplastics (MPs) and antimicrobials (AMs). However, despite their co-existence in the soil, the impact of MPs on AMs bioavailability and accumulation in crop plants, on the composition and diversity of soil bacterial communities, and the abundance of ARGs in the soil have not been well-studied. In this study, we treated lettuce plants and soil individually with one type of MPs (polyamide) and three types of AMs, i.e., (sulfamethoxazole, ciprofloxacin, and triclosan) alone and in combination, and compared lettuce growth parameters and bacterial communities between the treatment groups and the control. Our findings revealed that lettuce plants exhibited phytotoxicity under AMs alone or in combination with PA-MPs. We observed a significant decrease in shoot and root lengths, their respective biomasses, and photosynthetic pigments. Moreover, bacterial alpha diversity was unaffected, while there were significant differences in beta diversity. Although there was only a slight change in abundance and diversity of bacterial communities, some specific antibiotic resistance genes such as sul1 and sul2 were significantly abundant under the co-treatment of the studied contaminants. The current study provides an insight into the ecological, agricultural, and public health risks of co-occurring contaminants in agroecosystem. Microplastics (MPs) and antimicrobials (AMs) interact in soil-plant continuum. Co-exposures of MPs and AMs significantly affected lettuce growth traits. Individual and combined applications of PA-MPs and AMs induced differential effects on soil bacterial communities. Single AMs or their combination with PA-MPs significantly increased sulfonamide resistance genes in the soil.