Abstract
Plastics of various chemistries pollute global water bodies. Toxic chemicals leach with detrimental and often unpredictable impacts on the surrounding ecosystems. We found that seawater leachates of plastic pre-production pellets from 7 recycle categories are acutely toxic to stage II barnacle nauplii; lethal concentration 50 (LC50s) were observed in 24-h leachates from dilutions ranging from 0.007 to 2.1 mg/mL of seawater. Based on previous observations that macro-organismal settlement on fouling management coatings of various toxicities can be used to predict the toxicity of the coating, we hypothesized that interaction of plastic pre-production pellets with emerging microbiomes would exhibit patterns indicative of the chemistry at the pellet surface. We used amplicon sequencing of bacterial 16S ribosomal RNA genes to characterize the microbiomes that developed from 8 through 70 days on pellets exposed to the same flowing ambient seawater. Diversity and composition of the microbiomes colonizing plastic pellets changed over time and varied with plastic type. Microbial taxa belong to taxonomic groups known to consume hydrocarbons, to be prevalent following marine oil spills, or to live on fouling management surfaces. Microbiomes were still distinct between plastic types at Day 70, suggesting that differences in the physicochemical characteristics of the underlying plastics continue to exert variable selection of surface microbial communities. A random forest-based sample classifier correctly predicted 93% of plastic types using microbiome compositions. Surface microbiomes have promise for use in forensically identifying plastic types and potential toxicities.
Highlights
Marine plastic pollution is a dire environmental concern throughout the global oceans, with its scale constantly growing (Jambeck et al, 2015; Brandon et al, 2019; Lau et al, 2020)
Over the 70-day study duration, operational taxonomic units (OTU) richness and Shannon Diversity Index (SDI) gradually increased on all plastics tested except for PVC, whose alpha diversity remained lower than other plastics throughout the study
A brief dip in richness and SDI was seen at Day 24 for several plastic types (i.e., HDPE, low-density polyethylene (LDPE), PC, polyethylene terephthalate (PET), PP) due to dominance of Rhodobacteraceae, but diversity returned to previous levels by Day 32
Summary
Marine plastic pollution is a dire environmental concern throughout the global oceans, with its scale constantly growing (Jambeck et al, 2015; Brandon et al, 2019; Lau et al, 2020). Between the years 2016 and 2040, an estimated 710 million metric tons of plastic are predicted to enter the environment, even if immediate and drastic action from all stakeholders is taken to curb plastic pollution (Lau et al, 2020). Environmental forces (e.g., oxidation, UV light, physical weathering) can alter the chemistry of additives and increase the rate of leaching (Teuten et al, 2009; Haider and Karlsson, 2000; Suhrhoff and Scholz-Böttcher, 2016; Walker et al, 2021) Due to these processes, plastics are dynamic, with both their surface chemistries and leachate compositions changing over time and generating novel environments. That plastics are chemically active and dynamic underscores the need to understand their interactions and toxicity in the marine environment (Diana et al, 2020)
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