Influence of seasonal variations on contamination level and ecological risk of heavy metals in the surface sediments of the inner Gulf of Thailand

Abstract

The Inner Gulf of Thailand is a marine resource that provides ecological and economic value. Meanwhile, its can be acted like pollutions sink, especially heavy metals. After that, the extensions of industrialization, agriculturalization, and urbanization can degenerate to the inner Gulf environment quality. Therefore, this thesis was aimed to study the spatial distribution and seasonal variation of heavy metal concentration (Cd, Pb, Cu, Co, Ni, Mn and Zn) in surface sediment including the Mae Klong, the Tha Chin, the Chao Phraya and the Bangpakong River estuaries. Moreover, the contamination status and ecological risk were also evaluated. The results shown the seasonal mean values of Cd, Pb, Cu, Co, Ni, Mn, Zn are in a range of 0.13−0.19, 12.48−16.76, 7.40−15.49, 19.22−23.95, 47.64−73.03 mg/kg, respectively. The contamination status in this study, the comparison of heavy metals with Thailand’s sediment quality guidelines (SQGT) and NOAA (TEL−PEL) shown that Pb, Cu, Co, Ni, Mn, and Zn were exceeded over guideline values. For enrichment factor (EF) and geo-accumulation index (Igeo), the enrichment factor of Cd (0.05−10.03) and Zn (0.01−11.98) are considered as minor enrichment to severe enrichment level. And the enrichment factor of Cu (0.09−3.49) and Pb (0.19−5.18) are considered as minor enrichment to moderately severe enrichment. But the geo-accumulation index of all stations is considered as low contamination. The potential ecological risk (Er) and risk index (RI) are considered as low risk level. The result show that the influence of seasonal variation to heavy metal concentration of Cd and Zn in southwest monsoon season (Jul 2017 and Jul 2018) are not significantly different but higher than other seasons (p<0.05), Cu and Mn average concentration in both southwest monsoon season (Jul 2017 and Jul 2018) and northeast monsoon season (Dec 2017) are not significantly different but higher than dry season (May 2018) and Ni and Co in southwest monsoon season 2018 are the highest as significant (p<0.05) although contamination status and potential ecological risk following the heavy metals concentration distribution.