Studies on ingestion of microplastics by bivalves

Abstract- Microplastics are recognized as pervasive pollutants of marine environment as they are bioavailable to a variety of organisms for ingestion. Filter feeding organisms are more susceptible to microplastics ingestion due to their mode of feeding. Evidence of ingestion of microplastics by three species of bivalves (Pernaperna, Pernaviridisand Crassostrea madrasensis) from three regions of Keralaas well as the physiological effects of exposure to microplastics in Pernapernaand Pernaviridis were investigated. Fate of microplastics in the digestive tract was also tracked by examining the faeces and pseudofaeces. The mussel species, P. pernaand P. viridiswerefound to ingest foreign particles in the wild. The microplastic particles ingested by P. pernawere characterized by Fourier transform infrared (FT-IR) spectroscopy as polypropylene. For laboratory uptake studies, P. pernaand P. viridiswerefed with orange fluorescent polystyrene beads of 10micron size along with algal feed at a concentration of 200 particles per L and 600 particles per L. Bothmussel species were found to ingest microplastics in captive conditions. Algal clearance rate of both species was reduced substantially at high concentration of microplastics. Accumulation and retention of microplastics in the digestive system of both mussel species were prevented by defense mechanisms such as ejestion through faeces and pseudofaeces. In both species, depuration was effective in eliminating the accumulated microplastics from the digestive tract. However, a few particles were retained in the tissue even after 5 days of depuration, possibly indicating threat of transfer to higher trophic levels on conditions of continuous exposure. To sum up, field studies and laboratory uptake studies proved the contamination of mussels through microplastic pollutants. These particles can compromise the life processes of bivalves leading to lower growth and economic loss to the farmers as well as to the more serious impacts of biomagnification.