Occurrence and Spatial Distribution of Microplastics in the Surface Waters of Lake Naivasha, Kenya.

Microplastics are emerging threat contaminants that have been shown to provide toxic pollutants, either from the environment or from their inherent toxic monomers and additives, a pathway into the aquatic food web. In the present study, the occurrence, abundance, and composition of microplastic load in the surface water of Lake Naivasha (Kenya) was determined. The surface water physicochemical parameters were measured in situ; microplastic samples were collected using plankton net trawls and treated with H2 O2 to decompose organic matter. The microplastic particles recovered were classified both by visual observation and by attenuated total reflection-Fourier transform infrared spectroscopy. The average microplastic concentration range in surface water was 0.183 ± 0.017 to 0.633 ± 0.067 particles/m2 , with the mean concentration being 0.407 ± 0.135 particles/m2 . Fragments, fibers, and films were identified and were mostly composed of polypropylene, polyethylene, and polyester. We also performed correlational analysis, which showed a strong positive association between microplastic quantity and turbidity, total nitrogen, and total phosphorus in the lake. The high variability in microplastic densities exhibited between the sampled locations was attributed to human activities, water and wastewater intake through rivers and tributaries, and the presence of local wind patterns responsible for the general water circulation. Our assessment adds to the growing documentation of microplastic presence in freshwater ecosystems, and provides a baseline for future monitoring and assessment in sediment and biota of Lake Naivasha and other Kenyan freshwater systems. Environ Toxicol Chem 2020;39:765-774.