Exploring source footprint of Organophosphate esters in the Bohai Sea, China: Insight from temporal and spatial variabilities in the atmosphere from June 2014 to May 2019

Organophosphate esters (OPEs) are still produced and used in large quantities in the world-wide, and the environmental burden and behavior have generated widespread concern, especially in some large-scale water-bodies. This study conducted a comprehensive assessment on the temporal and spatial variabilities and budget of OPEs to trace the source for the Bohai Sea (BS), based on a 5-year seasonal monitoring campaign (June 2014 to May 2019) of 12 atmospheric sites around the BS and our previous studies. The average concentration of Sigma 10OPEs in atmosphere during the sampling period was 7.65 +/- 6.42 ng m(-3), and chlorinated OPEs were the major compounds. The Seasonal-Trend decomposition procedure based on Loess (STL) analyzed that during the 5-year sampling period, the atmospheric concentrations of Sigma 10OPEs had a slightly increasing trend with a rate of + 0.092 ng m(-3) yr(-1), and the seasonal concentrations had a distinct seasonal distribution. The highest concentration of Sigma 10OPEs was observed at the sampling site of Dalian, followed by Tianjin, Yantai, and Bei-huangcheng. The estimation of the fugacity ratios and air-water gas exchange fluxes established that the concentration levels of two major components of chlorinated OPEs (tris-(2-chloroethyl) phosphate (TCEP) and tris-(1-chloro-2-propyl) phosphate (TCPP)) in the atmosphere were dominated by their volatilization from BS's seawater (1.24 +/- 0.46 t yr(-1) for TCEP and 5.15 +/- 2.15 t yr(-1) for TCPP), with 73% deriving from the coastal seawater. The budget assessment suggested that the volatile fluxes of TCEP and TCPP accounted for 8% and 29% of their storages (15.6 +/- 5.32 t for TCEP and 17.6 +/- 6.70 t for TCPP) in the BS seawater, which were mainly contributed by continental river input (20% for TCEP and 42% for TCPP). The efforts indicated that river inputs of TCEP and TCPP needed to be paid more attention for the improvement of environmental quality of the BS.

Automated summary

Organophosphate esters (OPEs) are still being produced and used in large quantities globally, raising concerns about their environmental impact, particularly in large water bodies. This study conducted a comprehensive assessment of OPEs in the Bohai Sea region, finding a slightly increasing trend in atmospheric concentrations over a 5-year period, mainly attributed to chlorinated OPEs.