An assessment of heavy metal pollution in the East London and Port Elizabeth harbours

Abstract

The distribution of heavy metals (zinc, cadmium, copper, iron, manganese and lead) was investigated in seawater and in sediment samples from the East London and Port Elizabeth harbours. Both are ports of major importance to the area. The aim was to assess the impact of potential pollution sources, mainly from the cities' formal disposal to the sea, from industry and from dockyard and shipping activities around the harbour. At the East London harbour, metal concentrations in sea water range from 0.2 to 72.0 mg·ℓ-1 for Cd, from 0.6 to 42.6 mg·ℓ-1 for Cu, from 2.4 to 183.0 mg·ℓ-1 for Fe, from 0.6 to 16.3 mg·ℓ-1 for Pb, from 0.9 to 23.9 mg·ℓ-1 for Mn and from 0.5 to 27.6 mg·ℓ-1 for Zn. In sediments, metal concentrations using the total digestion method range from 0.12 to 1.63 mg·g-1 (dry weight) for Cd, 12.7 to 183.0 mg·g-1 (dry weight) for Cu, 1046.0 to 18 114.0 mg·g-1 (dry weight) for Fe, 3.2 to 84.2 mg·g-1 (dry weight) for Pb, 87.4 to5 49.0 mg·g-1 (dry weight) for Mn, 26.1 to 332.0 mg·g-1 (dry weight) for Zn. In the Port Elizabeth harbour, the concentration of metals in seawaters varied between 0.3 mg·ℓ-1 and 4.0 mg·ℓ-1 for Cd, between 0.5 mg·ℓ-1 and 11.3 mg·ℓ-1 for Cu, between 3.7 mg·ℓ-1 and 21.9 mg·ℓ-1 for Fe, between 0.6 mg·ℓ-1 and 4.2 mg·ℓ-1 for Pb, between 0.7 mg·ℓ-1 and 16.8 mg·ℓ-1 for Mn and between 0.7 mg·ℓ-1 and 16.2 mg·ℓ-1 for Zn. In sediments, values of metals also using the total digestion method ranged from 0.1 to 1.4 mg·g-1 (dry weight) for Cd, from 8.6 to 82.3 mg·g-1 (dry weight) for Cu, from 4219.0 to 15 182.0 mg·g-1 (dry weight) for Fe, from 9.0 to 61.9 mg·g-1 (dry weight) for Pb, from 103.0 to 499.0 mg·g-1 (dry weight) for Mn and from 18.8 to 126 mg·g-1 (dry weight) for Zn. The results are indicative of the contribution of heavy metal pollution from storm water drains and streams which carry runoff from industrial, urban and residential sources. Ship repair activities are also suspected to be responsible for elevated concentrations in the upper reaches of the harbour.


WaterSA Vol.27(2) 2001: 233-240