Heavy metal and nutrient contamination of marine sediments in Hong Kong

A monitoring programme was performed to use marine sediments as an indicator of marine contamination in Hong Kong. A total of 51 samples were collected from eight marine sites and analysed for pH, redox potential, salinity, total-N, total-P, total organic carbon, and total Cu, Zn Pb, Cr and Cd. Sites with high industrial or aquacultural activities contained high total organic carbon contents, total-N and total-P contents. Sediments from sites with high industrial activities also enriched with heavy metals. Metal speciation results indicate that Cu and Cr existed mainly in the organic fraction, Pb and Zn were distributed approximately equally in both the organic and residual fractions while Cd mainly occurred in the residual fraction. The Cu, Cr and Zn contents were highly correlated with total organic carbon contents. All samples were classified as non-acid forming according to the net acid generation test and only samples from the industrial site released a high concentration of heavy metals under a complete oxidising condition. The present study reveals that organic and heavy metal pollution is serious in the manne sediments of Hong Kong, and industrial and aquacultural activities are probably the major sources of contamination.