Spatial and seasonal variation of microplastics and surface water quality of the Njoro River and Lake Nakuru ecosystems, Kenya

Abstract

High levels of plastic pollutants threaten aquatic habitats as the plastic materials are ingested by aquatic organisms as food. This study assessed seasonal variations of microplastics and the water quality of the Njoro River and Lake Nakuru, Kenya. Selected water physico-chemical parameters were measured. Microplastic (MP) abundance in the surface water samples in the dry season was recorded as 47–649 MPs 300 l⁻¹ for sampling points in the Njoro River, and 54–508 MPs 300 l⁻¹ at Fisher’s Point in Lake Nakuru. Abundances during the rainy season were measured as 8–389 MPs 300 l⁻¹ and 28–259 MPs 300 l⁻¹ for the Njoro River and Lake Nakuru, respectively. Our study observed a significant contribution of microplastics from polymers, namely polyester (40%), polypropylene (25%), polyethylene (20%) and polyethylene terephthalate (10%). Recorded ranges of the water parameters were: salinity 0.085–2.59 ± 0.03 ppt; temperature 14.22–23.69 ± 0.07 °C; pH 8.8–9.3; turbidity 13.95–36.03 ± 0.35 NTU; total nitrogen 5.9–8.57 ± 3.24 mg l⁻¹; total phosphorus 7.49–9.41 ± 1.84 mg l−1; electrical conductivity 73.3–533.3 ± 0.64 μs cm⁻¹; and total dissolved solids 46.67–243.33 ± 0.11 ppm. These ranges were within the standards recommended by WHO and U.S. EPA. The results indicate the possibility for the quantity and mass of microplastic particles in Lake Nakuru to surpass those in the Njoro River.