Polyamide Microplastics and Common Antimicrobials in Treated Wastewater: Unveiling their Effects on Rice Plant Growth and Soil Microbiome dynamics

Abstract

Agricultural soils are increasingly contaminated with microplastics (MPs) and antimicrobial agents, yet the interplay between these pollutants and their effects on soil health, plant growth and development, and microbial communities remains underexplored. Here we investigated the influence of polyamide (PA) microplastics and three prevalent antimicrobials: sulfamethoxazole (SMX), ciprofloxacin (CIP), and triclosan (TCS) on rice plants. We assessed both the individual and combined effects on physiological and biochemical attributes of rice plants and soil bacterial communities, as well as the bioaccumulation of antimicrobials in soil and plant tissues. Our findings revealed that 1% of PA has a minimal effect on growth parameters and photosynthetic pigments in rice. In contrast, antimicrobials, particularly SMX at 50 mg/Kg, significantly hindered plant growth ( p < 0.0001), when tested alone or in combination with PA. In addition, the accumulation of TCS and CIP was enhanced in shoots and roots in the presence of PA while there was a decrease in SMX concentration in shoots in the presence of PA. PA and antimicrobials caused a slight change in abundance and diversity of soil bacterial communities, though the effects on alpha diversity were not statistically significant at each individual depth. However, when all depths were considered together, the TCS and PA + TCS treated soil displayed increased richness and evenness when compared to the other treatment groups. Similarly, beta diversity was significantly altered as determined by Unweighted_UniFrac analysis ( p < 0.05 ). Moreover, there was a 100 to 200-fold increase in the abundance of various antibiotic resistance genes such as sul1 and sul2 in response to antimicrobials treatment. These findings provide novel evidence on the interaction of antimicrobials loaded on MPs in the agroecosystem and their combined impacts on plants and soil microbiome.

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