Mechanistic Modelling of Mercury Bioaccumulation and Biomagnification in the Coastal Food Web of Akwa Ibom State

Mercury bioaccumulation through coastal food webs represents a poorly characterised but potentially significant public health risk in Nigeria's oil-producing coastal states. This research develops a mechanistic food web bioaccumulation model for mercury in the coastal ecosystem of Akwa Ibom State and applies it to evaluate human dietary exposure risk and identify ecosystem-level controls on mercury transfer. Field sampling was conducted at eight coastal stations over 18 months, collecting water, sediment, phytoplankton, zooplankton, invertebrates, and fish tissue samples from 19 species representing all major trophic levels. Total mercury and methylmercury concentrations were measured by cold vapour atomic fluorescence spectrometry. Stable carbon and nitrogen isotopes were measured to construct a trophic structure framework for model parameterisation. A dynamic bioaccumulation model incorporating uptake from water and diet, biotransformation, and growth dilution was parameterised and calibrated against measured tissue concentrations. The model was coupled with a dietary exposure assessment using regional consumption survey data. Methylmercury concentration in apex predator fish species (Lutjanus spp. and Pseudotolithus spp.) reached 0.38 to 0.72 micrograms per gram wet weight, approaching WHO guideline limits for vulnerable populations. Biomagnification factor between primary producers and apex predators was 4.8 orders of magnitude. Sensitivity analysis identified methylmercury production rate in sediments and lipid content of intermediate trophic consumers as the dominant controls on apex predator tissue burden. Monte Carlo dietary exposure modelling estimated that 23 percent of high-consumption households exceed the provisional tolerable weekly intake for methylmercury. Keywords: mercury bioaccumulation, biomagnification, food web model, Akwa Ibom, coastal ecosystem.