Land use as a primary driver of microplastic transport into Lake Victoria: Evidence from three Kenyan tributary catchments

Microplastic (MP) pollution threatens freshwater ecosystems globally, yet understanding catchment-level transport pathways remains limited for Africa's largest lake, Lake Victoria. This study examined the relationship between land-use intensity and MP occurrence, and mapped the spatial distribution of MP hotspots, across three tributaries (Kisat, Nyando, and Sondu) draining into Winam Gulf, western Kenya. MP abundance data from six sampling stations (upper and lower reaches of each river) were analyzed against catchment land-use intensity using regression analysis, with spatial distribution mapped via Geographic Information Systems (GIS). Regression analysis revealed a strong positive relationship between MP abundance and land-use intensity (R = 0.89, R² = 0.79, p = 0.018), indicating that 79% of the variation in MP occurrence across sites was explained by the intensity of surrounding human activity. MP abundance ranged from 0 to 4 particles/m³, with the highest levels in the urban-industrial river Kisat (77.7% of total MPs recovered). Polymer identification via Fourier-transform infrared spectroscopy (FTIR) linked polypropylene (PP; 44.4%) and ethylene-propylene-diene terpolymer (EPDM; 33.3%) to municipal and vehicular sources, while low-density polyethylene (LDPE; 22.2%) was associated with agricultural land use in the Nyando catchment. GIS spatial analysis identified lower Kisat as the principal contamination hotspot (severe; 44.4% of total MPs), with upper Kisat as a secondary hotspot (moderate; 33.3%). This study identifies river Kisat as a priority intervention site, demonstrates that land use is the dominant determinant of MP loading among the catchments studied, and provides a spatial evidence base to inform pollution-control policy for the Lake Victoria basin. The study  recommends targeted waste management interventions in Kisumu City and agricultural plastic reduction programs in the Nyando catchment to reduce MP loading into Lake Victoria, supporting Sustainable Development Goals 6 (Clean Water and Sanitation) and 14 (Life Below Water).