An experimental approach to understanding plastic leachate impacts on marine microorganisms

Plastics in the world’s oceans are exposed to diverse environmental stressors that fragment them, accelerating the leaching of associated additives. The impact of potentially toxic plastic degradation products and additives on marine microorganisms remains poorly understood. We assessed the impact of plastic leachate on marine microbial communities in vitro by exposure to one of four plastic leachates (from linear low-density polyethylene [LLPDE], polyamide-6 [or polycaprolactam; PA6], polyethylene terephthalate [PET] and polylactic acid [PLA]), prepared by immersing plastics in artificial seawater salts broth for three months at 80 °C. Microbial communities were then exposed to different leachates, noting that lower concentrations of plastic additives leached from the more inert plastic types (LLDPE and PET), as determined by GC-MS. PLA-leachate exposed communities differed significantly in composition from other plastic-leachate-exposed communities (PERMANOVA, P =0.001) as assessed by 16S rRNA gene and ITS region amplicon sequencing. Communities exposed to PLA-leachate contained a higher proportion of Proteobacteria, specifically Halomonas spp., previously reported to degrade LDPE and common plasticisers. Greater relative abundances of Psathyrellaceae fungi also distinguished these communities from those exposed to other plastic leachates. However, despite significant differences in the structure of communities exposed to PLA-leachate, we found no difference in the relative abundances of gene transcripts associated with plastic degradation. While biodegradable plastics such as PLA may persist for shorter times in the environment than more inert plastics, our study indicates greater consequences for marine microbial communities.