Occurrence of microcystins in water, sediment, and aquatic animals in Dau Tieng Reservoir, Vietnam

This study investigates the variations of microcystins (MCs) in water, cyanobacterial blooms, sediment, and aquatic organisms collected from the Dau Tieng Reservoir (DTR). Vietnam. Highperformance liquid chromatography (HPLC) was employed to measure MC concentrations in various target samples. Results indicate that Microcystis spp. dominates as the primary MC producer in the DTR. The average concentrations of analyzed MCs in surface water ranged from 1.10 to 5.54 µg/L, temporally and spatially. In sediment, average concentrations varied from 0.15 to 1.13 µg/g wet weight (WW) temporally and from 0.41 to 0.72 µg/g WW spatially. MCs were detected in different organs of fish species (Oreochromis sp. and Labiobarbus sp.) and in the entire soft tissues of bivalve (Corbicula sp.) and gastropod (Assiminea sp.). The highest observed MC concentration in July was 0.83±0.22 µg/g WW in the intestines of fish Oreochromis sp. The presence of MCs in grass shrimp Palaemonetes sp. was observed solely in June, reaching a concentration of 0.28±0.19 µg/g WW. This is the first report of MC accumulation in the grass shrimp Palaemonetes sp. during field collection. For the bivalve Corbicula sp., the presence of analyzed MCs was consistent throughout the study period, except for March and September, with the highest concentrations in July at 0.77±0.1 µg/g WW. Pearson correlation analysis revealed significant positive correlations between MCs in water and sediment with MC concentrations in aquatic animals, indicating the potential transfer of MCs across different trophic levels. The estimated daily intake values for analyzed MCs indicate that fish collected from the DTR are considered safe for consumption, as long as only the edible organs, such as the muscle, are consumed. However, bivalves or gastropods collected from the DTR are not safe for human consumption. This study underscored the importance of monitoring MC accumulation in aquatic animals used as food to mitigate adverse effects on human health.