Characterization, source identification and hazard index assessment of ingested microplastics in farmed tilapia Oreochromis niloticus

Plastic pollution is ubiquitous in marine and freshwater environments. Tilapia Oreochromis niloticus is one of the most important cultured fish species in South Asia. However, limited research has been conducted on the impact and hazard risk assessment of microplastic (MP) pollution on tilapia. This study characterized ingested MPs and identified potential sources of MPs in the gastrointestinal tracts (GTs) of farmed tilapia and their health risk assessment. GTs of 36 fish samples were collected from 12 tilapia fish farms in the Noakhali District, Bangladesh. A total of 199 MPs particles were extracted from all fish samples. Mean MPs abundance in tilapia GTs did not significantly vary among fish farms (F = 1.464, p = 0.209). The highest MPs numbers were 8 to 10 MPs/GT in tilapia collected from Farm 2, while the lowest MPs numbers were 3 to 5 MPs/GT from Farm 9. This study revealed that fibres were the dominant MPs shape in tilapia GTs (90.95 %). In the GT of tilapia, black (25.13 %), blue (24.12 %), and red (23.12 %) were the dominant colour of MPs. Most MPs found in tilapia GTs were within 300–1500 µm in size and accounted for 80.90 % of the total extracted MP particles. Identified polymers in GT samples were polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), which were consistent with reported results in the literature. Observed polymer hazard index (PHI) value of this study demonstrated that PP (PHI = 14.79) and PET (PHI = 33.12) were “High” risk category (hazard level III), while PE (PHI = 507.65) and PVC (PHI = 307,730.77) fell under “Danger” (hazard level IV) and “Extreme danger” (hazard level V) risk category, respectively. When ingested, these polymers could enter the human body directly and have adverse health effects that require additional research. Hopefully, this study will increase our understanding of the hazard index assessment of ingested microplastics through the farmed Tilapia O. niloticus and guide future research.