Are bio-sourced nanoplastics inert for aquatic species? A toxicity study on three micro-algae species and a freshwater bivalve

Abstract

Concerns raised by ubiquitate plastic contamination are urging to develop alternative materials. In the recent years, bio-sourced polymers also coined as bioplastics have been proposed to mitigate plastic pollution while meeting industrial and commercial expectations. Like petro-sourced plastics, they are expected to break-down in the environment into fragments down to sub-micron size. However, only scarce data are available on the impacts of such biosourced nanoplastics once released into the environment. This study examines the effects on aquatic species of model nanoplastics made from several bio-sourced polymers (Bio-NPs) that are either already on market (PHA, PLA, PA11) or still under development (NIPU, PCAR). We exposed three species of micro-algae (at 10, 100, and 1000 g/L, for 24 and 48 hours, and one week) to test the effects of Bio-NPs on algal growth. We also exposed freshwater bivalves C. fluminea (at 1, 10 and 100 g/L, for one week) to test the filtration activity and gene expressions in response to Bio-NPs exposure. All five Bio-NPs tested generated growth inhibitions in at least one of the three algae tested. PLA and PA11 were the most deleterious ones for algal growth among the five tested Bio-NPs. The highest growth inhibitions were observed on the fresh water species D. subspicatus. Each Bio-NP tested resulted in significant decreases of the filtration rates of C. fluminea. PHA impaired filtration at the lowest concentrations tested (1 g/L), whereas PCAR, PA11 and NIPU led to significant effects only at higher concentrations (10 and 100 g/L). The results from gene expressions in C. fluminea showed strong inductions of all gene functions tested for all the five bio-NPs tested. These Bio-NPs triggered endocytosis and detoxification mechanisms. They impaired the mitochondrial metabolism and triggered oxidative stress and immune responses. PA11, NIPU and PHA exposures resulted in the strongest gene regulations. The present study brings brand new findings about a kind of nanoplastics that may be released into the environment in a near future as the use of bioplastics is growing fast. It will help better understanding the impacts of such fragmented bioplastic NPs on aquatic species.