Ebong, G. A., E. I. Udoessien, and B. N. Ita. “Seasonal Variations of Heavy Metal Concentrations in Qua Iboe River Estuary, Nigeria”. Global Journal of Pure and Applied Sciences, vol. 10, no. 4, Nov. 2004, pp. 611-7, doi:10.4314/gjpas.v10i4.16446.