Assessment of ecological risk and spatial-temporal variations of heavy metals in surface sediment from blood cockle cultivation areas at Bandon Bay, Thailand

Surface sediment samples from blood cockle cultivation areas were collected to assess heavy metal pollution in Bandon Bay during February and August of 2021. The concentration of As, Cr, Cu, Cd, Pb, and Zn were evaluated to determine the contamination status in the dry and wet seasons. The ecological risks were evaluated using four heavy metal indices: geo-accumulation index ($I_{\mathrm{geo}})$, contamination factor (CF), pollution load index (PLI), and potential ecological risk index (PER). The results revealed that the mean concentrations of heavy metals ranged from high to low with Zn>Cr>Pb>As>Cu>Cd. Seasonal distribution of heavy metals in sediments showed that the dry season had higher concentrations than the wet season. Meanwhile, the $I_{\mathrm{geo}}$ and CF indicated that the level of As and Cd contamination in the sediments varied from polluted to strongly polluted. According to the PLI and PER, the surface sediments in Thathong area of Bandon Bay were at a low to moderate level of ecological risk for As and for Cd an ecological risk as high as 65.34. Based on these findings, frequent monitoring of the contamination levels is recommended to effectively minimize and mitigate the threat posed by heavy metal pollution in Bandon Bay.