Simulation of the Fate of Triclosan in a Paddy Soil Co-Contaminated with Graphene Nanomaterials: Enhanced Formation of Bound Residues and Potential Long-Term Risks

The co-occurrence of graphene-based nanomaterials such as reduced graphene oxide (RGO) and triclosan in agricultural soils is an emerging concern. This study investigates the impact of RGO on the formation and characteristics of bound residues (BRs) of triclosan in paddy soil using 14C-isotope tracing and LC-QTOF-MS. Results demonstrate that RGO significantly enhances the accumulation of triclosan BR in a dose-dependent manner, with the highest concentration (1.19 mg kg–1; 57.0%) observed at 500 mg kg–1 RGO. While the BR is primarily associated with the humin fraction (>63.8%), RGO shifts the distribution of 14C-triclosan, enhancing its retention in humin by 1.89–7.59% and in humic acid by 20.7–52.1%. RGO may increase the sequestered BR (8.8–24.7%), and it enhances the covalent BR of triclosan by increasing the proportions of both ether- (3.78–4.58%) and ester-bound (22.8–39.5%) forms. Metabolite analysis reveals limited transformation of triclosan (0.057–0.082 mg kg–1) in BRs, with carboxylated derivatives identified as minor products. The findings indicate that RGO enhances the persistence of triclosan BRs, which may be attributed to strong adsorption and microbial inhibition, raising concerns about their potential future remobilization and entry into the food chain. This underscores the need to assess the ecological risks of nanomaterial co-contamination for soil health and sustainable agriculture.