Theoretical Framework for Predicting Persistent Organic Pollutant Bioaccumulation in the Niger Delta Food Web: A Quantum Chemical and Molecular Modelling Approach

Understanding the bioaccumulation potential of persistent organic pollutants in complex aquatic food webs requires integration of molecular-level physicochemical properties with ecosystem-level trophic dynamics, a synthesis largely absent from Nigerian environmental chemistry literature. This dissertation develops and validates a theoretical framework combining quantum chemical descriptors from density functional theory calculations with fugacity-based food web bioaccumulation models for predicting the fate and bioaccumulation of polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers in the Niger Delta food web. Quantum chemical calculations at the B3LYP/6-31G(d,p) level of theory were used to compute molecular descriptors including HOMO-LUMO gaps, polarisability, electrostatic potential maps, and solvation free energies for 45 target compounds. These descriptors were used to develop quantitative structure-property relationships for octanol-water partition coefficients and bioconcentration factors. Fugacity model parameterisation incorporated site-specific temperature, lipid content, and dietary data from field campaigns in Delta and Rivers States. Model predictions were validated against measured concentrations in collected tissue samples from 12 species spanning five trophic levels. The developed framework achieves prediction accuracy within a factor of two for 78 percent of tested compounds. Novel theoretical contributions include the application of DFT-derived polarisability as a superior predictor of bioaccumulation in high-lipid marine invertebrates compared to empirical logKow values. The framework represents an original computational chemistry contribution to tropical food web contamination modelling and provides a predictive tool for risk prioritisation of new chemicals entering the Niger Delta ecosystem. Keywords: persistent organic pollutants, bioaccumulation, density functional theory, Niger Delta, food web model