Determination of heavy metal profiles in dated sediment cores from Sai Kung Bay, Hong Kong

Abstract

Eight sediment cores from Sai Kung Bay area were sampled and analysed for Cd, Cr, Cu, Fe, Ni, Pb, Zn, Ca, and organic matters. The cores were dated from an overall consideration of the 210Pb and maximum 137Cs activities, and historical records of previous land use, past heavy typhoon and rainstorm activities. Contamination by Cd, Cr, Cu, Pb, and Zn was found at coastal cores with a mean Enrichment Factor of 5.0, 1.0, 1.7, 1.4, and 1.3, respectively. The overall mass sedimentation rates were found varying from 0.111 - 0.454 g/cm2·y and recent average anthropogenic fluxes in μg/cm2·y for coastal/offshore cores were estimated as 0.52/0.028(Cd), 2.0/0.26(Cr), 7.6/0.92(Zn), 2.8/1.4(Cu), and 2.9/2.3(Pb), respectively. The major problem is Cd and Cr, in particular at coastal cores. The heavy metal input to the Sai Kung Bay areas was found to change considerably over the past 50 y starting from a low background level, via an intermediate period with cottage industries discharging Cr and Cd, to recent years with rapid urbanization and heavy boating activities emitting Cu, Pb, and Zn in addition to Cr and Cd. A rapid increase in heavy metal contents and a significant decrease in biological activities were found at the recently deposited coastal sediments, indicating a problem requiring urgent remedial action to stop further deterioration of the coastal environment of the beautiful resort area at Sai Kung Bay.