On May 11, 2021, peer-reviewed journal Environmental Science and Technology published work by Hans Peter Arp et al. presenting evidence that plastic pollution fulfills the criteria to be considered a planetary boundary threat. Namely, plastic pollution is (i) ubiquitous, (ii) not easily reversible, and (iii) disrupts key natural processes by creating ecotoxicological hazards. Previous work by the authors found plastic pollution fulfilled the first two criteria, but evidence published in the last few years and reviewed in this recent publication demonstrate “exposure of aquatic systems to weathered macro-, micro-, and nanoplastics and their leachates…will persist for long timescales” eventually accumulating to toxic levels.
Plastic pollution is presented as fulfilling the third criteria, “disruptive impact on a vital earth system process,” through two pathways: physical degradation into ever smaller pieces, and leaching of toxic chemicals into the environment. Plastics at the macro-, micro-, and nano- scale can negatively impact animals when mistakenly consumed as food, or by encumbering them until it is difficult or impossible to move (FPF reported). Humans also unknowingly consume microplastic and nanoplastic particles from our foods and drinks (FPF reported here and here). As plastics degrade, they release chemicals into the environment that do not naturally occur and can accumulate to potentially toxic levels.
Some substances, like endocrine disrupting chemicals, need only a low dose exposure to begin affecting an organism’s hormone system (FPF reported). Additionally, chemicals are often only studied in isolation, but, as the authors point out, the “planetary boundary [for chemical pollution] is difficult to constrain since each single chemical could represent a planetary boundary threat, but they usually co-occur with other chemicals, with poorly characterized mixture effects.”
The authors point out several difficulties and research holes around quantifying where exactly the plastic pollution planetary boundary lies, including (i) that few studies directly compare weathered plastic particles to natural particles, (ii) the interactive complexity of physical and chemical pollution mixtures, (iii) how plastic pollution adds to the other stressors in the environment (e.g. climate change) is unclear, and (iv) there are no established monitoring standards. Plastic pollution is only expected to increase as humans continue to use more plastic and the pollution already existing continues to break down. The paper concludes, “there is a risk that a planetary boundary threshold for environmental plastics could be crossed before it is known, or that through weathering it will, inevitably, be crossed in the future.”
Arp, HPH., et al. (May 11, 2021). “Weathering Plastics as a Planetary Boundary Threat: Exposure, Fate, and Hazards.” Environmental Science and Technology
Lim, X. (May 6, 2021). “Microplastics are everywhere – but are they harmful?” Nature News