Distributions, transport and environmental effects of BTEX along the Pearl River-estuary-ocean continuum

Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) are important anthropogenic pollutants with implications for coastal ecosystems and atmospheric chemistry. However, their land-ocean spatial gradients and transport remain poorly understood. Here, we investigated aquatic and atmospheric BTEX across the Pearl River Basin-Pearl River Estuary (PRE)-northeastern South China Sea (SCS) continuum. Surface BTEX concentrations in the PRE (198 ± 137 ng L^-1) were significantly higher than those in rivers (29.4 ± 15.2 ng L^-1) and the northeastern SCS (39.8 ± 25.3 ng L^-1), possibly due to intensive industrial emissions and shipping activities. Using a LOICZ box-model framework, the apparent seaward export flux was estimated to be 0.547 ± 0.204 t d^-1. Although the ecological risks were low at the observed concentrations, potential effects associated with continuous BTEX inputs warrant attention. The entire continuum acted as a net source of atmospheric BTEX, with mean water-to-air fluxes of 6.56 ± 8.14, 233 ± 153, and 73.8 ± 46.5 g km^-2 d^-1 for rivers, the PRE, and the northeastern SCS, respectively. BTEX-derived ozone formation potential and secondary organic aerosol formation potential averaged 5.54 ± 4.24 and 0.084 ± 0.064 μg m^-3, respectively, highlighting the potential influence of BTEX on coastal atmospheric chemistry.