A numerical kinetic model was developed to simulate the bioaccumulation of toxic chemicals under natural exposure conditions where benthic sediment plays an important role in bioavailability. Based on a three compartment dynamic system, a set of simultaneous first-order ordinary differential equations was derived and numerically solved by employing the fourth order Runge-Kutta method. The model was validated against data obtained from the bioaccumulation of two chlordane isomers into goldfish in the presence of sediment. The model predictions agreed well with the experimental results. The experimental results indicate that sediment significantly lowers the amount of chlordane available to fish and acts as a reservoir of chlordane to water. The developed model was capable of simulating the role of sediment in bioavailability of chemicals to fish in sediment/water systems.