Can Contaminated Irrigation Water Drive Pharmaceutical Uptake and Transformation in Rice Paddy? Unveiling Pathways, Natural Attenuation Mechanisms, and Health Risk Assessments

Contaminant uptake by crops and its subsequent transmission to humans via ingestion are a pressing environmental concern. The objective of this study is to delineate the uptake of emerging contaminants such as pharmaceuticals in food crops in a densely populated area. We executed a field experiment to investigate the fate of the pharmaceuticals carbamazepine (CAR) and sulfamethoxazole (SMX) in rice paddies irrigated with contaminant-spiked water. We experimented on designated field plots using three different dosages: low (500 μg), medium (1000 μg), and high (5000 μg). Using contaminant-spiked water enhanced straw yield while not affecting grain yield. Both pharmaceuticals were detected in soil and plant tissues, with CAR uptake 3-fold higher than SMX. Contaminants were primarily attenuated in soil, root, or shoot, resulting in minimal grain accumulation: 0.25–1% (CAR) and 0.1–0.6% (SMX). CAR-irrigated rice grains showed HQ > 0.1 and contained carcinogenic metabolites (10,11-epoxy carbamazepine, 9-acridine-carboxaldehyde, and acridine), while SMX metabolites exhibited lower toxicity. Notable shifts in microbial composition were observed in contaminated plant and soil samples. This study highlights concerns regarding the long-term human and soil health risks from using pharmaceutical-contaminated irrigation water due to toxic metabolite formation and shift in soil and plant microbial communities.