Variation of mercury in 4 major estuaries in the Gulf of Thailand during wet season

The Mae Klong River (MK), Tha Chin River (TC), Chao Phraya River (CP), and Bang Pakong River (BPK) are recognized as critical conveyors of terrestrial substances, including pollutants, into the Inner Gulf of Thailand (Inner GOT). This study sought to explore the presence of mercury (Hg), a highly toxic and bioavailable pollutant, in both water and surface sediment at the mouths of the four rivers in pre- and post-wet season (WS). The results revealed that the total mercury (T-Hg) concentrations in the water ranged from 10 ng/L (TC) to 125 ng/L (CP) in pre-WS and 17 ng/L (MK) to 1011 ng/L (TC) in post-WS. Notably, the post-WS concentrations of THg were relatively higher than the pre-WS, with an average concentration of particulate Hg (P-Hg) increasing by approximately 3-5 times. Consequently, the average P-Hg proportion to T-Hg of each estuary in the post-WS was comprised of greater than 67%. Moreover, a correlation was observed among salinity, total suspended solid (TSS) and particulate Hg (P-Hg). Similarly, the estuarine sediment, excluding MK, exhibited a higher average concentration of T-Hg during the post-WS period. The average T-Hg concentration in sediment ranged from 17 (BPK) to 119 (MK) & mu;g/kg in pre-WS and 15 (MK) to 140 (CP) & mu;g/kg in post-WS. The presence of organic matter (total organic carbon or TOC content), and clay-sized particles were identified as potential factors influencing the concentration of T-Hg in the sediment. In addition, a higher positive correlation was observed between T-Hg and silt-sized particles in BPK. In this study, both T-Hg in the water column and T-Hg in sediment increased during the post-WS period, suggesting that Hg transportation from sources to river mouths during WS were intensified. Furthermore, the correlation between T-Hg and fine-grained particle, as well as the greater T-Hg levels in the estuarine sediment, indicates that Hg may be transported from rivers to the offshore marine environment via the fine-grained fraction.

Automated summary

This study investigated the presence of mercury in water and surface sediment at the mouths of four rivers in Thailand. The results showed that mercury concentrations in both water and sediment increased during the post-wet season period, indicating intensified transportation of mercury from sources to river mouths.