Accumulation of trace metals in mangrove plant Soneratia Caseoralis in Songkhla Lake, Thailand

Abstract

Mangrove sediment and mangrove plant Soneratia caseolaris in Songkhla Lake, Thailand have been increasingly threatened by trace metal pollution. Mangroves receive trace metal pollution from upstream areas and the sea. However, little is known about the mangrove plant’s capacity to uptake and store trace metals. In this study, the concentrations of As, Cd, Pb and Zn in mangrove plant parts (leaf, root, and bark) of Sonneratia caseolaris and sediments were determined. Sediment and plant samples were digested using total metal concentration procedure and ICPMS techniques. It was found that the maximum values of total concentrations of As in mangrove sediments were classified as heavily polluted according to USEPA. The highest concentrations of As and Zn were found to be in bark whereas Cd and Pb in the root. The fractions of all the metals were measured using BCR techniques and their results revealed that the bioavailability fraction was greater than the residual fraction. The order of the amounts of trace metals present in the fractions was as follows; As: Oxidizable > Reducible > Residual > Exchangeable and the order of Cd: Exchangeable > Reducible > Oxidizable > Residual. Both BCF and TF values showed limited accumulation of these elements in their aboveground parts and thus presented a low food chain hazard except at Phawong and U-Taphao canals.