Magnetic properties and heavy-metal contents of contaminated seabed sediments of Penny's Bay, Hong Kong

Magnetic properties and heavy-metal concentrations of vibrocore samples wer e found to be potential indicators of shipping contamination in seabed sedi ments in Hong Kong Harbour. Geochemical results of 74 vibrocores located of t Penny's Bay on Lantau Island revealed an enrichment of heavy metals in th e upper 1-2 m of the cores within the eastern part of the study site. Whole -core magnetic susceptibility measurements also showed a greater concentrat ion of magnetic particles in the surficial layer of these cores. A signific ant correlation exists between the magnetic susceptibility and the concentr ations of Pb, Zn and Cu, as well as the Tomlinson pollution load index (PLI ). The proximity of these cores to a major navigation fairway and an anchor age site suggests probable contamination of the surficial seabed sediments by shipping-related wastes. A study of the magnetic properties of one of th e cores, VT60, revealed a difference in the magnetic properties between the contaminated and the uncontaminated sediments. Samples from the contaminat ed zone exhibited relatively stronger magnetic remanence and susceptibility . The two groups of samples also formed distinct trends on the hysteresis r atios plot. A level of unusually high magnetic susceptibility within the co ntaminated zone was attributable to the presence of strongly magnetized gra nules, which were probably refuse from shipping-related activities. Geochem ical and magnetic results were also conducted on samples of different size- fractions from this core. The < 63 mum fraction was found to contain a rela tively higher magnetic susceptibility and greater heavy-metal content. (C) 2001 Elsevier Science Ltd. All rights reserved.