Olawoyin, Richard; Oyewole, Samuel A.; Grayson, Robert L. (2012). “Potential risk effect from elevated levels of soil heavy metals on human health in the Niger delta”. Ecotoxicology and Environmental Safety. 85: 120–130. doi:10.1016/j.ecoenv.2012.08.004. PMID22921257.
Olawoyin, Richard; Oyewole, Samuel A.; Grayson, Robert L. (2012). “Potential risk effect from elevated levels of soil heavy metals on human health in the Niger delta”. Ecotoxicology and Environmental Safety. 85: 120–130. doi:10.1016/j.ecoenv.2012.08.004. PMID22921257.