Bioaccumulation and genotoxic effect of heavy metal pollution in marine sponges from the Niger Delta

In this study, levels of Al, Cu, Ni, Cd, Cr and Pb were quantified in seawater, sediments, and sea sponges from six sites in the Niger Delta and one relatively clean site outside the Niger Delta area using Inductively Coupled Plasma Optical Emission Spectroscopy and Inductively Coupled Plasma Mass Spectrometry. The metal levels in sponge tissues in μg/mg ranged from 0.22 ± 0.03-0.70 ± 0.10 (Al), 0.002 ± 2.2 × 10^{-5 -} 0.004 ± 5.6 × 10^-5 (As), 2 × 10^-5 ± 5.3 × 10^-6 -1.5 × 10^-3 ± 4.6 × 10^-6 (Cd), 2.3 × 10-3 ± 1.4 × 10-5 -0.02 ± 2,2 × 10^-4 (Cu), 2.5 × 10^-4 ± 8.6 × 10^-6- 2.0 × 10^-3 ± 1.4 × 10^-5 (Pb). In Sediment samples in mg/kg, the ranges were (0.883 ± 0.114-73.33 ± 0.10 (Al), 0.0007 ± 0.026-0.304 ± 0.009 (As),0.0086 ± 0.0045-0.198 ± 0.010 (Cr); 0.005 ± 0.001-0.063 ± 0.001 (Cu), 0.039 ± 0.004-0.0783 ± 0.0024(Ni), 0.0017 ± 0.002-0.056 ± 0.0046 (Pb). In the water sample, the metal levels in mg/L 0.06-0.92 (Al), 0.001-0.007 (Cd), 0.001-0.001 (Cr), 0.01-0.02 (Cu), 0.003-0.01 (Ni), 0.001-0.01(Pb). Metal levels in all sampling sites occurred in the order of decreasing concentration as Al > Cu > Ni > Cd > Cr > Pb (in seawater), Al > Cr > Ni > Pb > Cu > Cd (in sediment) and Al > As>Cu > Pb > Cd (in the sponge). The study further assessed DNA strand breaks in sea sponges as a biomarker of genotoxicity using the comet assay. There was a strong correlation between % DNA strand breaks in sponge cells from all sample locations and aluminium levels in sponge tissues from all sample locations. The highest metal levels were recorded in Sea sponges, followed by Sediment and then Sea water, with aluminium significantly higher than other metals in all three matrices studied. We, therefore, conclude that sea sponges are excellent sentinel species for toxic metal bioaccumulation, and DNA strand breaks are an efficient biomarker for aquatic pollutants biomonitoring.