Uptake, translocation, and metabolism of sulfamethazine by Arabidopsis thaliana: distinguishing between phytometabolites and abiotic transformation products in the media.

Plant accumulation of antibiotic residues presents potential risks to human and ecosystem health. However, the phytometabolic pathways of antibiotics following plant uptake are still largely uncharacterized. This study investigated the phytometabolism of sulfamethazine (SMT) by Arabidopsis thaliana, using 14C-labeled and unlabeled SMT. SMT was accumulated in both roots and shoots of axenic A. thaliana plants (123.7 ± 12.3 and 22.7 ± 1.0 µg/kg fw, respectively) after 21 days of exposure. However, the parent 14C-SMT accounted for only 1.7 ± 0.01% of the total 14C-radioactivity in plant tissues. The majority of 14C-radioactivity taken up by plants was present as bound residues (42.0-68.2% of initially applied 14C-SMT), while extractable 14C-residues accounted for only 7.7-12.6%. A. thaliana metabolized SMT primarily through glycosylation at the N4-nitrogen atom. Additionally, other products, including pterin-SMT, methylsalicylate-SMT, N4-formyl-SMT, desulfo-SMT, hydroxyl-SMT, N4-acetyl-SMT, desamino-SMT, and 2-amino-4,6-dimethylpyrimidine, were also identified. Notably, a portion of the extractable metabolites was excreted into the culture media, requiring characterization of these metabolites as either excreted phytometabolites or abiotic transformation products of SMT based on comparisons between experimental and control reactors.