Sediments shifting from sink to source of conventional and emerging organophosphate esters

Organophosphate esters (OPEs) are emerging pollutants of growing concern, yet their release potential from sediments in surface water environments remains poorly understood. To evaluate this potential, this study investigated the spatiotemporal occurrence, concentration profiles, organic matter influence, and ecological risks of 12 conventional OPEs (c-OPEs) and 3 emerging OPEs (e-OPEs) in Taihu Lake sediments during winter and summer. Most target OPEs were frequently detected, with total concentrations significantly higher in summer (73.7-165.0 ng/g dw) than in winter (36.7-84.7 ng/g dw) but no significant spatial difference in either season. Concentration profiles followed a consistent order in both seasons: halo-OPEs > alkyl-OPEs > aryl-OPEs ≈ e-OPEs. Particularly, five c-OPEs such as tributyl phosphate (TBP), triethyl phosphate (TEP), tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), and triphenyl phosphate (TPhP), along with the e-OPE bisphenol A bis(diphenyl phosphate) (BDP), were the dominant contributors to seasonal variation. Their sediment partitioning was potentially related to hydrophobic interactions with sediment dissolved organic carbon. In sediments, aromatic protein II and humic acid-like substances (the dominant fluorescent components of dissolved organic matter, DOM) were likely to positively affect TBP, TEP, and TPhP, as did aromatic protein II for BDP. However, the fluorescent DOM showed no significant correlation with TCPP, suggesting possible influences of non-fluorescent DOM. Fugacity fraction analysis revealed that the OPEs with log K_ow < 7.5 exhibited a release trend from sediments to water, indicating a shift of sediments from a "sink" to a "source". This release potential would further elevate the ecological risk of OPEs in surface water, which already exhibited a moderate combined risk (risk quotients of 0.25 in winter and 0.34 in summer). Notably, the risks of e-OPEs such as BDP might be underestimated, warranting additional toxicity data for aquatic organisms.