Siddig, Nahid, Asma Ahmed, Sarra Saad, and Faisal Koua. “Heavy Metals Accumulation from Sewage Sludge in the Nile Tilapia Oreochromis Niloticus (Trewavas, 1983) During a Sludge-Earthworm-Fish Short-Term Cycling”. Italian Journal of Food Safety 8, no. 1 (March 19, 2019). Accessed August 22, 2019. https://www.pagepressjournals.org/index.php/ijfs/article/view/7257.