Determination of heavy metal levels in surface water and sediment of Mini-Ezi Stream, Elele-Alimini, Rivers State, Nigeria

Abstract

Mini-Ezi Stream is one stream of significant importance in Elele-Alimini area of Rivers State, Nigeria, receiving array of wastes bearing heavy metals, which originate from household, agricultural and other anthropogenic activities. Consequently, this study evaluated the levels of heavy metals (Fe, Pb, Zn, Cu, Cd, Cr, Mn and Ni) in water and sediment samples of Mini-Ezi Stream. Samples were collected monthly for 12 months (to cover both wet and dry seasons), preserved, digested and analyzed using Perkin Elmer Analyst 300 Atomic Absorption Spectrophotometer (AAS). Data obtained showed that the level of Fe, Pb, Cr, Cu, Cd, Zn, Ni and Mn were 0.78 ± 0.09 mg/l, 0.01 ± 0.01 mg/l, 0.02 ± 0.01 mg/L, 0.01 ± 0.01 mg/L, 0.001 ± 0.00 mg/l, 0.015 ± 0.01 mg/l, 0.005 ± 0.01 mg/l and 0.012 ± 0.01 mg/l in water and sediments 5.98 ± 2.43 mg/kg, 0.01 ± 0.01 mg/kg, 0.05 ± 0.02 mg/kg, 0.09 ± 0.03 mg/kg, 0.03 ± 0.01 mg/kg, 1.52 ± 0.69 mg/kg, 0.03 ± 0.01 mg/kg and 0.89 ± 0.23 mg/kg respectively. The results obtained revealed that all metals tested for water, were present in this order of decreasing concentration: Fe > Cr > Zn > Mn > Cu ≈ Pb > Ni > Cd, while in sediment, the sequence was: Fe > Zn > Mn > Cu > Cr > Cd ≈ Ni > Pb. Generally, the mean concentrations of the metals were within the National and International permissible limits in both water and sediments, except for Fe (0.78 ± 0.09 mg/L) in water that exceeded the limit. The concentrations of the metals were generally higher in dry season than in wet, though there was no significant difference (p>0.05). The presence of all the metals in water and sediment indicate potential danger, hence there is need for routine monitoring.