Accumulation and ecotoxicological risk of weathered polyethylene (wPE) microplastics on green mussel (Perna viridis)

Recent studies have shown that organisms including humans are exposed to microplastics directly or indirectly. The present study aims to examine the ingestion of these microplastics and the consequences of the same by studying the accumulation behavior of weathered Polyethylene (wPE) microplastics. The Perna viridis were exposed chronically to three different environmentally relevant concentrations of wPE for 30 days, followed by a one-week depuration phase. There was no mortality observed in the control and exposed groups, but the feeding rate was observed to have substantially decreased in the group exposed to higher concentration (3 μgL^-1) of wPE. It was also observed that a higher number of wPE particles accumulated in the intestine of exposed organisms. Interestingly, the present study revealed the presence of the substantial number of wPE particles in exposed organisms, which may adversely affect the internal organs as well as growth and reproduction. This study perceived that accumulation is marginally influenced by size of wPE. Similarly, biomarker analysis showed that wPE exposure significantly altered both the metabolism and histology of the internal organs of the exposed organisms. Overall, the study confirmed that the intestine was the most sensitive organ followed by gills, adductor muscles, and foot tissue adding new insights into the adverse effects of wPE in the marine ecosystem.

Early Colonization of Weathered Polyethylene by Distinct Bacteria in Marine Coastal Seawater

Plastic debris in aquatic environments is rapidly colonized by a diverse community of microorganisms, often referred to as the "Plastisphere." Given that common plastics are derived from fossil fuels, one would expect that Plastispheres should be enriched with obligate hydrocarbon-degrading bacteria (OHCB). So far, though, different polymer types do not seem to exert a strong effect on determining the composition of the Plastisphere, and putative biodegrading bacteria are only found as rare taxa within these biofilms. Here, we show through 16S rRNA gene sequencing that the enrichment of a prominent OHCB member on weathered and non-weathered polyethylene only occurred at early stages of colonization (i.e., after 2 days of incubation in coastal marine water; 5.8% and 3.7% of relative abundance, respectively, vs. 0.6% on glass controls). As biofilms matured, these bacteria decreased in relative abundance on all materials (< 0.3% after 9 days). Apart from OHCB, weathered polyethylene strongly enriched for other distinct organisms during early stages of colonization, such as a specific member of the Roseobacter group and a member of the genus Aestuariibacter (median 26.9% and 1.8% of the community, respectively), possibly as a consequence of the availability of short-oxidized chains generated from weathering. Our results demonstrate that Plastispheres can vary in accordance with the weathering state of the material and that very early colonizing communities are enriched with taxa that can potentially degrade hydrocarbons. Given the lack of persistent enrichment and overall community convergence between materials over time, common non-hydrolysable polymers might not serve as an important source of carbon for mature Plastispheres once the labile substrates generated from weathering have been depleted.