Empirical Investigation of Microplastic Distribution and Transport Pathways in the Lagos Lagoon System

This study empirically investigates the spatial distribution, morphological characteristics, and dominant transport pathways of microplastic particles in the Lagos Lagoon system, South West Nigeria, filling a critical research gap on microplastic contamination in West Africa's largest coastal lagoon. The Lagos Lagoon receives urban runoff, stormwater, and direct waste discharges from Africa's largest city, making it a significant microplastic sink and potential source for the adjacent Atlantic Ocean. Sampling was conducted at twenty-two stations covering the main lagoon body, principal tributary channels, intertidal sediments, and tidal outlet channels during both wet and dry seasons. Water column sampling used a 330-micrometre mesh manta trawl, while sediment samples were collected using stainless steel corers. Microplastic extraction employed hydrogen peroxide digestion, and particles were characterised by morphology, size class, and polymer type using Fourier transform infrared spectroscopy. Statistical analysis examined spatial and seasonal patterns and evaluated relationships with proximity to urban drainage outfalls and industrial zones. Results show microplastic abundances ranging from 1.2 to 48.6 particles per cubic metre in surface water and 180 to 2,840 particles per kilogram in sediment, with highest concentrations in the main lagoon embayment near industrial discharge points. Fibres dominate in water column samples while fragments are more abundant in sediment, indicating differential transport behaviour. Dry season concentration increases in the main lagoon indicate accumulation without wet season dilution. Seasonal transport flux calculations suggest the lagoon exports approximately 15 tonnes of microplastics annually to the coastal ocean. Keywords: microplastics, Lagos Lagoon, plastic pollution, coastal water quality, transport pathways.