Systematic Revelation of the Metabolic Fate of Typical Quaternary Ammonium Compounds in Wheat Seedlings

This study investigated the uptake and metabolism of three quaternary ammonium compounds (QACs), dodecyltrimethylammonium chloride (DTAC), dodecyldimethylbenzylammonium chloride (DBAC), and didodecyldimethylammonium chloride (DDAC), in hydroponically grown wheat seedlings. Root uptake followed the order DDAC > DBAC > DTAC, with DDAC concentrations being 4.7-5.0-fold higher than DBAC and 12.3-13.5-fold higher than DTAC after 72 h. Following a 0.5 h exposure, root and shoot QAC concentrations declined by 45.2%-60.2% and 39.8%-81.4% over 96 h, indicating active metabolism. A total of 24 DBAC metabolites were identified, including 10 hydroxylated, 8 glycosylated, and 6 malonylated derivatives, revealing two major pathways initiated by mono- or dihydroxylation, followed by glycosylation and malonylation. Using authentic standards, two hydroxylated DBAC products (C₇-OH-DBAC and C₁₁-OH-DBAC) were quantified for the first time. The C₇-OH-DBAC predominated over C₁₁-OH-DBAC, with root concentrations 1.8-4.3 times and shoot concentrations 3.0- 3.9 times higher, demonstrating regioselective internal hydroxylation distinct from microbial pathways (α/ω-hydroxylation). Similar patterns were observed for DTAC (21 metabolites) and DDAC (45 metabolites), further underscoring the role of alkyl chain number. These findings provide the first systematic insight into QAC fate in crops, essential for risk assessment of cationic pollutants.