Heavy metal pollution profiles of dated sediment cores from Hebe Haven, Hong Kong

Abstract

Eight sediment cores from Hebe Haven were collected and studied for metals including Cd, Cr, Cu, Fe, Ni, Pb, Zn and Ca. 210Pb and 137Cs activities were determined to date the time of deposition of the sediment. Hebe Haven is a yacht area and is close to the urbanized coast with several dyeing factories. Except Cd, the greatest enrichment was found at locations closest to the Ho Chung Stream which carried domestic and industrial wastewater to Hebe Haven. Concentrations as high as 0.930, 120, 131, 42.3 and 50.9 mg/kg were found for Cd, Cr, Zn, Cu and Pb, respectively. The corresponding enrichment factors are 13(Cd), 7.0(Cr), 2.9(Zn), 5.2(Cu) and 2.4(Pb). The extent of pollution diminishes from the riverine source. Cr is a typical example because its enrichment was mostly attributed to the nearby dyeing operation. The distribution of Cd appears more complicated. A maximum concentration of 3.60 mg/kg was found at a location far from Ho Chung Stream and with no nearby municipal or industrial activity. No significant Fe and Ni enrichment was found in the area. Ca in all cores decreases towards the sediment-water interface. It is probable that the abundance of shellfish has decreased as a result of excessive exploitation as seafood and pollution. 210Pb activity and heavy metal concentrations of surficial layers have been 'diluted' by excessive deposition of Fe-deficient particles. This likely indicates the rapid deposition of coarser and sandy particles during the construction of a nearby large housing estate. Some 210Pb activity profiles have periodic low values in deeper layers, which should correspond to events of rapid deposition of erosion during heavy typhoons and rainstorms. Overall, the sedimentation rates calculated were in the range of 0.351-0.561 cm/yr. In one site (Core S4) close to the riverine source and with the best available dating data, the recent anthropogenic fluxes of heavy metals in μg cm-2 yr-1 are estimated as: 0.081(Cd), 22(Cr), 20(Zn), 6.4(Cu) and 7.4(Pb). | Eight sediment cores from Hebe Haven were collected and studied for metals including Cd, Cr, Cu, Fe, Ni, Pb, Zn and Ca. 210Pb and 137Cs activities were determined to date the time of deposition of the sediment. Hebe Haven is a yacht area and is close to the urbanized coast with several dyeing factories. Except Cd, the greatest enrichment was found at locations closest to the Ho Chung Stream which carried domestic and industrial wastewater to Hebe Haven. Concentrations as high as 0.930, 120, 131, 42.3 and 50.9 mg/kg were found for Cd, Cr, Zn, Cu and Pb, respectively. The corresponding enrichment factors are 13(Cd), 7.0(Cr), 2.9(Zn), 5.2(Cu) and 2.4(Pb). The extent of pollution diminishes from the riverine source. Cr is a typical example because its enrichment was mostly attributed to the nearby dyeing operation. The distribution of Cd appears more complicated. A maximum concentration of 3.60 mg/kg was found at a location far from Ho Chung Stream and with no nearby municipal or industrial activity. No significant Fe and Ni enrichment was found in the area. Ca in all cores decreases towards the sediment-water interface. It is probable that the abundance of shellfish has decreased as a result of excessive exploitation as seafood and pollution. 210Pb activity and heavy metal concentrations of surficial layers have been 'diluted' by excessive deposition of Fe-deficient particles. This likely indicates the rapid deposition of coarser and sandy particles during the construction of a nearby large housing estate. Some 210Pb activity profiles have periodic low values in deeper layers, which should correspond to events of rapid deposition of erosion during heavy typhoons and rainstorms. Overall, the sedimentation rates calculated were in the range of 0.351-0.561 cm/yr.