Organophosphate Diesters in Surface Sediments of Black-Odorous Urban Rivers across China: Occurrence, Spatial Distribution, and Ecological Risks

To assess the contamination levels of organophosphate diesters (di-OPEs) in large-scale urban water bodies, this study investigated four di-OPEs (bis(2-chloroethyl) phosphate [BCEP], bis(1-chloro-2-propyl) phosphate [BCIPP], bis(1,3-dichloro-2-propyl) phosphate [BDCIPP], and bis(2-ethylhexyl) phosphate [BEHP]) in surface sediments from 173 black-odorous urban rivers across China. Di-OPEs were ubiquitously detected (not detected to 484 ng/g dry weight), dominated by BEHP (58.8% ± 24.5%) and BCIPP (32.3% ± 25.5%). Spatially, total di-OPEs followed a regional trend of Northeast ≈ East > Central ≈ West China, which correlated significantly with urban gross domestic product and wastewater treatment capacity, implying industrial inputs. High molar concentration ratios of di-OPEs to their parent tri-OPEs (medians: 0.74–3.26) suggested significant tri-OPE degradation contributions. Correlation analyses suggested that chemical hydrolysis and microbial activity, associated with a high abundance of putative OPE-degrading bacteria, may synergistically regulate the degradation sources of di-OPEs. Screening-level acute risk quotients exceeded chronic values by 1–2 orders of magnitude, with BEHP posing widespread high acute risks (risk quotient >1.00) at 96.0% of sites. These benchmark findings emphasize the necessity of regional source control and pollutant management frameworks to secure urban aquatic safety.