Effect of aging on the toxicity of polyethylene microplastics on the estuarine bivalve Scrobicularia plana

Microplastics (MP) are now present in all ecosystems and undergo weathering processes, including physical or chemical degradation. Although most studies have been carried out on MP toxicity in the marine ecosystem, interest is growing for the terrestrial and entire aquatic compartments. However, the interface between both environments, also known as the soil/water continuum, is given little consideration in MP toxicity studies. Only a few studies considered the toxicity of artificially aged or soil field-collected MP on species living at this interface. The present study evaluates the impact of artificial and field aging polyethylene (PE) MP on the bivalve Scrobicularia plana, a key organism of the estuarine compartment, living at the soil/water interface. Clams were exposed for 21 days to environmental concentrations (0.008, 10 and 100 μg L-1) of unaged as well as artificially and field aged PE MP. Toxicity was assessed from individual to molecular levels including condition index, clearance rate, burrowing behavior, energy reserves, enzyme activities and DNA damage. Results showed differential effects at all biological levels depending on the type and the concentration of the MP tested. Indeed, a decrease in burrowing behavior was observed in S. plana exposed to aged and field PE at low concentration (0.008 μg L-1). In the gills of clams, exposures to aged PE (0.008 and 100 μg L-1), virgin PE (10 μg L-1) and field PE (all tested concentrations) decreased CAT activity while DNA damage increased after exposure to virgin PE (0.008 μg L-1 and 10 μg L-1) and field PE (0.008 μg L-1). Our findings suggest that aging modifies the toxicity profile of PE polymer on S. plana and considering plastic from field at environmental concentrations is important when performing ecotoxicological studies.