Abundance of microplastics in surface water of tropical reservoirs during contrasted season, the case of Dau Tieng and Tri An, Vietnam

Microplastic concentrations were studied in surface waters of two reservoirs playing an important role in water storage and supply in Vietnam, the Dau Tieng and Tri An reservoirs, by collecting water samples during dry and rainy seasons. Microplastic mean concentration (including all sites and seasons per reservoir) was of 3.96 ± 1.38 items m⁻³ at Dau Tieng and 4.04 ± 1.35 items m⁻³ at Tri An, and is in the range of concentrations found in other reservoirs studied worldwide. We noted that microplastic spatial distribution was driven by difference levels of anthropogenic activities and population density surrounding each area of the reservoirs. Between the two seasons, microplastic mean abundance did not change at the level of the Dau Tieng reservoir (4.36 ± 1.71 items m⁻³ and 3.57 ± 0.95 items m⁻³ during dry and rainy season, respectively), but their value significantly decreased at specific sites under intense anthropogenic activities during the rainy season. Meanwhile, in Tri An reservoir, mean microplastic abundance and size significantly decrease during the rainy season. Although the mean abundances are low value, ecological concern needs to be addressed because of the important touristic activities and their potential impact to the quality of the water and to the agriculture development of the surrounding areas. We therefore questioned microplastic as a new parameter to include into local environmental monitoring network, and we recommended to consider microplastic as an important parameter in the monitoring control of the surface water quality of the two reservoirs.