Distribution of heavy metals in sediment along the Southern coast of Vietnam

Abstract

Abstract The heavy metals (HM), particularly As, Cd, Pb and Hg, are considered most toxic to biota and environment. In this study, spatial and seasonal distribution of HMs (Cd, Pb, Hg and As) were measured in two sediment fractions (< 63 μm and 63 – 500 μm) collected in the farming area of blood cockle. A total of 104 sediment sampled along the Southern coast of Vietnam between December 2012 and July 2015 were examined. The average concentrations (μg/g) of As, Cd, Pb and Hg in sediment fraction of 63 – 500 μm ranged from 4.16 to 16.8, < 0.004 to 0.219, 9.52 to 17.3 and 0.031 to 0.076, respectively. While, the mean levels (μg/g) of As, Cd, Pb and Hg in sediment fraction of < 63 μm ranged from 4.59 to 12.8, < 0.004 to 0.187, 9.94 to 14.6 and 0.042 to 0.080, respectively. Generally, no statistically significant differences were found for concentrations of HMs in both fractions between two seasons and among provinces. The concentrations of HMs analyzed in sediment were compared to quality guidelines for the protection of aquatic life recommended by the Canadian Council of Ministers of the Environment (CCME) and the Vietnamese organizations (QCVN 43 : 2012/BTNMT). HM levels in all samples were lower than the Vietnamese regulation and the probable effect level in the CCME guideline. However, As levels in 67/103 and 84/104 of two fractions of < 63 μm and 63 – 500 μm, respectively, exceeded the threshold effect level of 7.24 μg/g in the CCME standard. It suggested that As accumulated in sediment in these provinces could be harmful to the aquatic organism.