Microplastics: Sources and distribution in surface waters and sediments of Todos Santos Bay, Mexico.

Microplastics (MPs) are ubiquitous and a threat to marine and freshwater environments. Effluent waters from secondary wastewater treatment plants (WWTPs) into Todos Santos Bay (TSB) were investigated as sources of MPs. MPs were detected in all analyzed matrices and presented variable morphologies. MPs from surface water samples (n = 18) varied from 0.01 to 0.70 plastic particles/m3 (pp/m3). Fragments (47 ±â€¯23%) and fibers (47 ±â€¯23%) were the most abundant particles found in the surface water samples. In sediment samples (n = 11), MPs varied from 85 to 2494 pp/0.1 m2. Sediment samples showed fragments of 70 ±â€¯19%, fibers 28 ±â€¯18% in mean. The range of MP values from WWTP effluents (n = 24) was 81 to 1556 pp/m3, and fibers (65 ±â€¯28%) were the most abundant MP particles. Several synthetic polymers (polypropylene, polyethylene, polyethylene-propylene, polyvinyl chloride, cellophane), and natural fibers (cotton and wood) were identified. The surface currents and the parameters that modulate them, are the main factors that dominate the distribution of MPs in surface waters. While in the sediments the parameters such as bathymetry and grain size distribution have more influence on their distribution in the marine environment, where the effluent waters from WWTPs only contributes MPs to the TSB.