Testing the factors controlling the numbers of microplastics on beaches along the western Gulf of Thailand.

Microplastic pollution is one of the most significant global environmental concerns. This study represents a first attempt to establish connections between the concentration of microplastics and both ocean surface circulation direction and land-based sources along the western Gulf of Thailand. Microplastics at the high-tide line from 25 beaches in 5 provinces were quantified. Observed amounts range from 20 to 273 (max. 5741) pieces/kg. Sheets were the most common shape and black the most common color of microplastics. Our study showed a significant, positive correlation between the number of microplastics and land-based sources (e.g., aquatic industries). While human activities were the dominant factor affecting microplastic concentrations, the newly designed surface circulation direction (SCD) index reflected relative changes in microplastic amounts. Our study identified several locations with substantial microplastic pollution which require a proper management system with appropriate laws and regulations, and a public awareness campaign about effects of microplastics on ecosystems.