Dissipation patterns of trisiloxane ethoxylates in cucumber plants and field soils: Insights from different end-capping groups

Trisiloxane ethoxylates (TSEOn) have been found in multiple agro-environmental media due to their pervasive application in agricultural production. While some studies suggested that the differences in the toxicological effects of TSEOn were closely related to their end-capping groups, the environmental behaviors and fate of TSEOn congeners with varying end-capping groups in agroecosystems remain underexplored. This study investigated the dissipation patterns of 39 oligomers across three TSEOn congeners in cucumber, leaves, and soils through field trials, including TSEOn-H (hydroxy, n = 2-14), TSEOn-CH₃ (methoxy, n = 2-14), and TSEOn-COCH₃ (acetoxy, n = 3-15). All TSEOn oligomers dissipated following pseudo-first-order kinetics in cucumber, leaves, and soils with half-lives were 2.08-3.92 d, 1.77-4.44 d, and 5.06-19.80 d, respectively. TSEOn congeners in agro-environmental media presented different dissipation patterns affected by their end-capping groups. The interfacial behaviors of TSEOn-COCH₃ in the leaves differed from those of TSEOn-H and TSEOn-CH₃. The half-lives of TSEOn-H and TSEOn-CH₃ congeners in soils were significantly positively correlated with log K_OC, indicating that long-chain congeners preferentially partition to soil solid phases, leading to slower dissipation rates than short-chain congeners. Furthermore, long-chain TSEOn congeners may dissipate to short-chain congeners. The dietary risks of ΣTSEOn-CH₃ intake through cucumber fruits were deemed safe for different Chinese populations based on the margin of exposure (MOE) assessment. This study alerts us to the environmental behaviors and fate of organosilicone surfactants and provides a baseline reference to the dietary exposure risks of TSEOn.