Assessing exposure risk to microplastics by Indian Ocean pygmy blue whales

Microplastics (MPs) have attracted widespread attention due to their ubiquitous occurrence and harmful effects, however, limited data are available regarding the quantity and composition of MPs ingested by blue whales. In this study, MPs were detected in fecal samples obtained from pygmy blue whales ( Balaenoptera musculus brevicauda ) ( n  = 18, mean 0.82 items/g d.w) and seawater samples ( n  = 5, mean 143 ± 60.0 items/m 3 ) from the northern Indian Ocean. Six polymer types were identified using micro-Fourier-transform infrared spectroscopy (μ-FTIR), nearly half of which were polyethylene terephthalate (PET). The variety of shapes, colors, and polymer types of MPs in blue whale fecal samples indicated the diversity of ingested MPs. For pygmy blue whales, MP ingestion exposure was estimated as high as 1.74 (± 0.83) × 10 6 items/day according to typical filter-feeding rates estimated for this sub-species. We suggested that the ingested MPs were mainly from trophic transfer rather than environmental exposure, and this MP ingestion may pose a minimal risk of caloric deficit. This study provides essential baseline information on the MP loads in pygmy blue whales in the Indian Ocean and considers the potential adverse impacts of long-term exposure to MPs.