Comprehensive geochemical assessment, probable ecological and human health risks of heavy metals in water and sediments from dredged and non-dredged Rivers in Lagos, Nigeria

Abstract

The study was conducted to examine the geochemical distributions of heavy metals in water and sediments from of dredged and non-dredged riverine systems with a view to ascertaining source apportionment, and the deleterious ecological and human health risks. Ojo and Badagry Rivers were considered the dredge-mined sites, while Gbaji River was chosen as the non-mined site. The level of heavy metals in water samples are as follows; [Cd (0.040 - 0.360), Cu (0.010 - 0.130), Cr (0.001 - 0.080), Fe (0.170 - 1.040), Pb (0.001 - 0.050), Mn (0.050 - 0.230-), Zn (0.050 - 0.160), As (0.001 - 0.030), Co (0.003 - 0.040) and Ni (0.001 - 0.050) mg/L]. The Cd and Mn contents in the water from the mined sites were higher than their permissible limits. The heavy metal contents [Cd (0.190 - 1.490), Cu (1.390 - 5.950), Cr (1.180 - 2.630), Fe (144.820 - 261.490), Pb (1.960 - 24.250), Mn (5.170 to 24.110), Zn (5.180 - 35.420), As (0.170 - 0.690), Co (0.190 - 0.840) and Ni (0.740 - 2.140) mg/kg] in sediments were within the background levels, except for Cd from the mined sites. The hazard index was lower than 1 (HI ≤ 1), inferring no likelihood of non-carcinogenic incidents. Contrarily, the cancer risk index showed that exposure to sediments from the mined sites could result to cancer risk. The contamination and enrichment factors of the sediments from mined sites showed “high contamination” and “extremely enriched,” respectively. Notably, the potential ecological risk index of Cd (high) in sediments from the mined areas contribute significantly to the ultra-high risk of the ecosystems, which might result in ecological collapse of the riverine systems. The Nemerow multifactor index (YN) of the mined sites showed extreme pollution. The Coefficient variation, Pearson's correlation matrix and principal component analysis clearly indicates that heavy metals in water and sediments are from multiple rather than a single source. Although, this study could not ascertain whether the mining activities are solely responsible for the elevated heavy metals from the dredge-mined sites, since the study sites frequently experiences other anthropogenic activities, however, the study showed that significant pollution and ecological adversities are associated with water and sediment from the dredged-mined sites.