Phthalates in Surface Waters of the Selenga River (Main Tributary of Lake Baikal) and Its Delta: Spatial-Temporal Distribution and Environmental Risk Assessment

The Selenga River provides about half of the water and chemical runoff into Lake Baikal and plays an important role in the sustainability of the ecosystem of this large natural freshwater lake. Phthalate esters (PAEs) are organic compounds that can disrupt reproductive and endocrine systems. This study focused on investigating the distribution of six priority phthalates in the Selenga River and its delta utilizing SPE-GC/MS. The study found that the highest levels of sigma 6PAE were observed during the high-water years, 2021 and 2023, and were evenly distributed along the river from the sampling sites upstream of Ulan-Ude to the delta channels. In contrast, the mean annual sigma 6PAE content was relatively low in the low water period of 2022. Dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) are the two dominant phthalates found in the surface waters of the Selenga River and delta channels. In 2021, the average total concentration of six phthalates (sigma 6PAE) ranged from 8.84 to 25.19 mu g/L, while in 2022 it ranged from 0.45 to 4.01 mu g/L, and in 2023 it ranged from 5.40 to 21.08 mu g/L. The maximum level for the sum of phthalates was 61.64 mu g/L in 2021, 13.57 mu g/L in 2022, and 30.19 mu g/L in 2023. The wastewater treatment facilities in Ulan-Ude were identified as a stable local source of phthalates. In some cases, PAE concentrations exceeded maximum allowable concentrations, particularly for DEHP. This could have adverse effects on aquatic organisms.