Microplastic occurrence in water and sediments at Bacalar Lake, Quintana Roo, México

Microplastics represents a global concern, but information available on tropical lakes is limited. Microplastic occurrence in water and sediments was assessed at Bacalar Lake. Plankton tows were conducted in July, October 2022, and March 2023 in four sites, while sediments were collected in 15 sites. In water, dominant microplastic were fibers, fragments, films, and beads/pellets, with similar abundance in July and October, and higher in March. Higher abundance occurred on S24 in October and March with 1.56 and 0.94 items/1000 m3. In sediments only fibers were found, (667 particles/kg) with transparent fibers (303 items) as the most abundant. The abundance of microplastics was lower (0.04 particles/kg), except for site S30 (0.88 particles/kg) in July 2022. Eighteen plastic polymers were identified in water and sediments, cellophane and copolymers Polystyrene: vinylidene chloride and polyethylene propylene: diene had percentages of 40%, 38% and 12%, respectively. In the water column, 85% of the microplastics corresponded to fibers composed of cellophane, Polystyrene: vinylidene chloride and polyethylene propylene: diene; and Alkyd resin, Polyvinylidene fluoride, and Polyamide 6+Polyamide 6.6 in fragments. In sediments, fibers represented 87%, and PS polymers dominated: Polystyrene: vinylidene chloride and cellophane, as well as polyethylene propylene: diene. The greatest abundance of microplastics was found in sites near to Bacalar Town and urban centers where tourism is most intensified. In general, the microplastic concentration in Bacalar Lake is low.