Binti Abd Kadir, Azlin, et al. “Comparative Phytotoxicity of Azolla Pinnata and Lemna Minor in Treated Palm Oil Mill Effluent”. International Journal of Engineering and Technology, vol. 7, no. 4, Sept. 2018, pp. 2499-05, https://doi.org/10.14419/ijet.v7i4.12287.