Occurrence, spatial variation, seasonal difference, and ecological risk assessment of organophosphate esters in the Yangtze River, China: From the upper to lower reaches

A comprehensive contamination profile of organophosphate esters (OPEs) in the Yangtze River in China has not yet been characterized. In this study, we investigated the occurrence, spatial variation, and seasonal difference of 18 se-lected OPEs in surface water samples of the Yangtze River mainstream. To characterize the contamination profile of the OPEs, we collected 144 Yangtze River water samples from 72 sampling sites in December 2020 and June 2021. Four alkyl-OPEs [trimethyl phosphate, triethyl phosphate (TEP), tributyl phosphate, and tris(2-butoxyethyl) phos-phate (TBOEP)] and three halogenated OPEs [tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and tris(1,3-dichloro-2-propyl) phosphate] were the most frequently detected target compounds (>95%). TCIPP (median: 34.6 ng/L), TEP (median: 26.2 ng/L), and TCEP (median: 17.9 ng/L) were the most abundant com-pounds, while the median values of the others were below 10 ng/L. Additionally, the concentrations of most OPEs gradually/dramatically increased from upstream to downstream Yangtze River. Notably, the median concentration of summed OPEs in Shanghai (415 ng/L; downstream) was approximately ten times higher than that in Qinghai (45.7 ng/L; upstream). Urban sampling sites had significantly or slightly higher concentrations of most OPEs than rural sampling sites. Moreover, the OPE concentrations in the river water differed between the winter and summer. The concentrations of summed OPEs (median: 117 vs. 106 ng/L), summed alkyl-OPEs (67.0 vs. 45.8 ng/L; p < 0.05), and summed aryl-OPEs (0.48 vs. 0.17 ng/L; p < 0.05) were slightly or significantly higher in December than those in June; nevertheless, summed halogenated OPEs were slightly higher in June (62.2 vs. 50.2 ng/L) than that in December. Compared with previously reported data for OPEs in other major rivers worldwide, the Yangtze River water had relatively lower concentrations of the OPEs than those in the rivers of developed countries and regions. Ecological risk assessment suggested that tris(2-ethylhexyl) phosphate and TCEP posed relatively high risks (RQ: 1.01 and 0.98, respectively) at the maximum concentration, and TBOEP posed a moderate risk (RQ: 0.25). This is the first study to comprehensively characterize the contamination profile of the Yangtze River by the OPEs.

Automated summary

This study is the first to comprehensively characterize the contamination profile of organophosphate esters (OPEs) in the Yangtze River. The results showed that alkyl-OPEs and halogenated OPEs were the most frequently detected compounds, with concentrations gradually increasing from the upstream to downstream of the river. Urban sampling sites had higher concentrations of OPEs compared to rural sites, and there were seasonal differences in OPE concentrations in the river water.