Seasonal variation and potential environmental risk of pharmaceutical residues in West Lake and Yen So Lake, Hanoi

This study investigated the occurrence and seasonal variation of 16 pharmaceutical residues in surface water collected from West Lake (WL) and Yen So Lake (YSL), Hanoi. A total of 20 surface water samples were collected from each lake with a frequency of 5 samples every 3 months. The observation was performed for both rainy and dry seasons from January 2020 to December 2020 during the pandemic of Covid-19. The laboratory analyses revealed that pharmaceutical residues were widely distributed in these lakes. The total pharmaceutical concentration in YSL (21.3 – 49.9 µg/L) was higher than that in WL (15.7 – 38.6 µg/L). Among these, norfloxacin was detected at the highest concentration ranging from 0.83 – 21.2 µg/L and 0.61 – 17.3 µg/L in WL and YSL respectively while cefotaxime was not detected in WL and in 7/20 samples collected in YSL with concentration ranging from 0.05 – 2.1 µg/L. Total pharmaceutical concentrations were mostly observed significantly higher in the wet season than in the dry season for both lakes. The potential ecological risks of these compounds were also evaluated. Results showed that those compounds displayed from negligible to high risk. The result could provide the valuable situation of pharmaceutical residues in two main lakes in Hanoi and enhance the security information for humans living around these lakes.