Equilibrium partitioning approach for metal toxicity assessment in tropical estuarine sediment of Bandon Bay, Thailand.

An equilibrium partitioning approach (EqPA) was employed to evaluate the metal toxicity and define sediment quality guidelines (SQGs) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and mercury (Hg) in the cockle cultivated areas located in Bandon Bay, Thailand. An assessment of metal toxicity using the [∑SEM]-[AVS] and [∑SEM]-[AVS]/foc models indicated no adverse effect on benthic organisms. The normalized total metal concentrations in this area were below the established SQG values for As, Cd, Cu, Ni, Pb, Zn, and Hg, namely respectively 21.3, 0.8, 84.6, 36.0, 34.6, 440.9 mg/kg dry weight, and 49.3 µg/kg dry weight on sand and calcium carbonate free with 1 % total organic carbon basis, suggesting low metal toxicity. This study provides locality adapted SQG values for supporting sediment quality management specifically in Bandon Bay, potentially serving as a model for other coastal areas.

Weekly variations of nutrients and their associations with phytoplankton blooms in the urban coastal waters of Andaman Sea coast: A case study in Patong Bay, Phuket, Thailand.

Nutrient inputs to coastal waters are among the main contributors to phytoplankton blooms that can damage coastal ecosystems. To understand the main causal factors and timing of phytoplankton blooms in Patong Bay, where phytoplankton blooms have frequent occurred for the last decade, variations in phytoplankton abundance and the dissolved inorganic nutrients (nitrogen (DIN), phosphorus (DIP), and dissolved silica (DSi)) were monitored weekly from December 2021 to December 2022. The results revealed that ratios of DIP and DSi to DIN in seawater had increased rapidly in approximately 1-7 days prior to the blooms of Chaetoceros and Eunotogramma. This suggests that the diatom blooms in this area are significantly controlled by an excess of DIP and DSi, in otherwise appropriate environmental conditions. Our findings provide a thorough understanding of the role of excess nutrients on phytoplankton blooms in urban coastal waters, supporting informed coastal management actions.

Seasonal microplastic variations in estuarine sediments from urban canal on the west coast of Thailand: A case study in Phuket province.

To improve knowledge of the relationships of human activities with microplastic pollution in the urban estuary in Phuket province, which has a densely populated city on the western coast of Thailand, a total of 463 plastic-like items from 24 sediment samples in the dry and the rainy seasons were identified by micro-Fourier transform infrared spectroscopy. The microplastic abundance ranged in 300-900 and 33-400 items/kg dry weight in the dry and the rainy seasons, respectively, indicating that the estuary is moderately contaminated with microplastics. The most abundant polymer types were rayon and polyester with colored fibers, suggesting that the microplastics deposited in this area originate mainly from washing effluents. Additionally, our findings show that the microplastic distribution is significantly governed by hydrodynamic energy in the estuary. This provides basic information for a better understanding of the fate of microplastics within estuary, and for management actions to address microplastics in urban estuary.