Effects of tidal current on pollution load index and potential risk of heavy metals in water column of the Chao Phraya River estuary

¹ Department of Environmental Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
² Program in Industrial Toxicology and Risk Assessment, Department of Environmental Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
³ Research Unit (RU) of Waste Utilization and Ecological Risk Assessment, Chulalongkorn University, Bangkok 10330, Thailand

^* Corresponding author: sarawut.sr@chula.ac.th

Abstract

This study investigates the effects of tidal currents on the pollution load index (PLI) and the potential ecological risk of heavy metals in the Chao Phraya River estuary, where the river meets the inner Gulf of Thailand. The research focused on six heavy metals: cadmium (Cd), arsenic (As), lead (Pb), copper (Cu), and zinc (Zn). Water samples were collected eight times over a 24-hour tidal cycle at different tidal stages: high tide, ebb tide, low tide, and flood tide, at varying depths. The results showed significant variations in metal concentrations influenced by tidal movements. Cadmium concentrations ranged from 6.43 to 7.53 µg/L, with the highest levels at the bottom during flood tides. Arsenic levels varied from 0.36 to 16.11 µg/L, peaking at the bottom during high tides. Lead concentrations ranged from 8.36 to 12.68 µg/L, with the highest at the bottom during high tides. Copper levels ranged from 1.92 to 5.53 µg/L, peaking at the bottom during low tides. Zinc concentrations ranged from 5.30 to 29.09 µg/L, with the highest at the bottom during flood tides. The PLI and risk index (RI) were calculated to assess contamination and ecological risks. The PLI values indicated that Cd and As posed the highest pollution risks, with values exceeding 8.03 for Cd during flood tide phases and 2.86 for As during low tide phases. The RI values showed that Cd and As presented considerable to very high ecological risks, with RI values ranging from 1,854 to 2,015, particularly during low and flood tides. These findings highlight the critical role of tidal currents in influencing heavy metal distribution and concentration in the Chao Phraya River estuary. Continuous monitoring and targeted management strategies are essential to mitigate the ecological risks posed by heavy metal contamination in this estuarine ecosystem. Addressing these issues is vital for protecting the health of aquatic life and human populations dependent on this critical environment