Normalisation and heavy metal contamination in mangrove sediments

The concentrations of Zn, Ni, Cr, Cu, Mn, Fe and Al in surface sediments collected from three mangrove sites in Hong Kong were determined following aqua regia digestion. The heavy metal concentrations were normalised to reference elements to facilitate comparison between mangrove sites. Iron was found to be a good normaliser for Mn (r= 0.892), Zn (r= 0.443) and Ni (r = 0.318) in 45 sediment samples from three mangrove sites. However, the correlation coefficients between Fe and Cu, and Fe and Cr were low. Total organic carbon and aluminum could be alternate normalisers for certain heavy metals such as Cu and Cr in mangrove sediments. Among three mangrove sites in Hong Kong, Sha Tau Kok was contaminated with Zn and Cu, elevated levels of Mn and Ni were recorded in Chek Keng and Sai Keng was enriched with Cr based on the ratios between metal and normaliser concentrations.