Development of an Agent-Based Model of Microplastic Fate and Accumulation in the Lagos Lagoon Ecosystem with Implications for Food Chain Risk

The Lagos Lagoon constitutes West Africa's most economically significant estuarine ecosystem, supporting fisheries, recreation, and water supply for the Lagos metropolitan area, yet the fate and food chain accumulation of microplastic particles entering the lagoon from multiple urban waste pathways has not been investigated through a systems-level computational framework. This study develops a novel agent-based model of microplastic fate and food chain accumulation in the Lagos Lagoon, representing the largest-scale particle fate simulation attempted for any Nigerian water body. The model platform is NetLogo extended with hydrodynamic forcing from a calibrated MIKE 21 tidal flow model of Lagos Lagoon. Individual microplastic particles are represented as agents with properties including size, shape, density, and polymer type, with rules governing advective transport, settling, resuspension, biofouling, fragmentation, and ingestion by trophic level-specific agents representing zooplankton, filter-feeding bivalves, pelagic fish, and benthic invertebrates. An original bioenergetic accumulation model is derived for each trophic level, incorporating elimination kinetics parameterised from measured lipid content and metabolic rate data for Lagos Lagoon species. Model validation was conducted using microplastic concentration data from a 12-month field sampling programme at 18 stations across the lagoon, with polymer typing by Fourier-transform infrared spectroscopy and Raman microspectroscopy. The validated model predicted that filter-feeding bivalves accumulate 94 times higher microplastic mass concentrations than zooplankton over an annual cycle. Scenario modelling of a 50% reduction in plastic waste input reduced predicted fish microplastic body burden by 31% over 5 years. The study provides the first mechanistic, spatially explicit fate model for microplastics in Nigerian estuarine waters. Keywords: agent-based model, microplastic fate, Lagos Lagoon, food chain accumulation, trophic transfer