Spatial variation of heavy metals in surface sediments of Hong Kong mangrove swamps

The degree of heavy metal contamination in the fine-grained (< 63 mu m) and sand-sized (2 mm-63 mu m) fractions of surface sediments in 18 different m angrove swamps (144 random samples) in Hong Kong was examined. Higher conce ntrations of heavy metals were found in the fine-grained than the sand-size d fractions of the sediment; however, the differences between these two fra ctions became less significant when the swamp was more contaminated. The pr incipal component analyses show that the 18 mangrove swamps, according to t he median concentrations of total heavy metals, were clustered into four gr oups. The first group included three mangrove swamps in Deep Bay region whi ch are seriously contaminated, with heavy metal concentrations in sediments around 80 mu g g(-1) Cu, 240 mu g g(-1) Zn, 40 mu g g(-1) Cr, 30 mu g g(-1 ) Ni, 3 mu g g(-1) Cd and 80 mu g g(-1) Pb. The second cluster, made up of another four swamps distributed in different geographical locations (two in Sai Kung district and two in Tolo region), also had elevated levels of Cu, Pb, Ni and Cr in the sediments. Field observation reveals that these seven stands received industrial, livestock and domestic sewage as well as pollu tion from mariculture activities, suggesting that anthropogenic input is th e main source of heavy metal contamination in Hong Kong mangroves. The sedi ments from other mangrove swamps were relatively uncontaminated. (C) 2000 E lsevier Science Ltd. All rights reserved.