Low occurrence of microplastic contamination in anchovies, a transboundary species, in Thai waters

In this study, size capture determination of the anchovies in the Gulf of Thailand (GoT) and the Andaman Sea showed length ranges of 6.00???9.90 cm and 3.50???12.00 cm and weight ranges of 2.23???8.00 g and 0.34???12.09 g, respectively. The occurrence of microplastics (MPs) in anchovies were investigated by randomly sampling 100 individual anchovies (GoT = 50, Andaman Sea = 50) from 2670 samples. The samples were digested with 10% potassium hydroxide for the analyses of types and amounts of MPs present. Surprisingly, a low level (approximately 8%) of MPs was found, and the size of the MPs was less than 500 ??m. All found MPs were of a fragment type with only three types of polymer (polyethylene, polyester, and rayon) identified by FT-IR spectrophotometer. The low occurrence of MP ingestion in the anchovy samples in our study was probably caused by: (1) the dilution effect of the schooling behaviour of anchovies diluting the amount of MPs ingested by a single individual; (2) the dilution effect depending on the seaward distance from the shore (point source of MPs); and (3) the short residence time (6???12 months) of the anchovies living in the ocean gathered by our study. As a result, the low accumulation of MPs was found in the anchovy samples. The appearance of MPs in anchovies is an alarming finding for food security and sustainability in Thailand.