Concentration distribution and assessment of heavy metals in the surface sediments of the western Gulf of Thailand

Heavy metals (Cr, Cu, Zn, Cd, Pb, Hg, As), grain size, pH, Eh, total organic carbon, and total nitrogen of 157 surface sediments from the western Gulf of Thailand (GoT) were analyzed to determine the spatial distribution pattern, constraint factors, and pollution status of heavy metals in the surface sediments of the western GoT. The relationships of the heavy metals with sediment composition, pH, reduction/oxidation conditions, and total organic materials were evaluated by statistical analysis. Sediment compositions were the main factors controlling the concentrations of heavy metals as reported in many previous studies, while the hydrodynamic conditions, in particular the seasonal eddies, were an important factor controlling their distribution. Both sediment enrichment factor and geoaccumulation index were used to assess heavy metal accumulation. Only As reached the light contamination level near the upper GoT and the coastal area close to the Songkhla Province, due primarily to anthropogenic activities.