In a viewpoint article (non-peer-reviewed) published on November 17, 2017 in the peer-reviewed journal Environmental Science & Technology, Allen Burton from the University of Michigan, U.S. expresses an opinion that “the environmental risk from microplastics . . . [is] overstated,” because “low microplastic exposure concentrations” mean that “there could be no risk.” He sees “the continuing publication of microplastics studies stating a severe environmental threat” as “disturbing,” particularly because “exposure is the most important part of the [risk] equation.” Therefore, Burton says that “the process of determining microplastics risk should be an analysis of true risk (realistic exposure relationships to adverse effects)” and should be “documented in the field” as opposed to laboratory studies.
In response to Burton’s viewpoint, two scientists published an extended debate article as a preprint in the PeerJ Preprints (last update July 12, 2018). Thomas Backhaus from the Department of Biological and Environmental Sciences, University of Gothenburg, Sweden calls for “avoiding hyperboles” in microplastics research, while Martin Wagner from the Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway finds that there are issues with prioritization and communication of research on microplastics. Both authors consider microplastics in the environment to be a “genuine research topic . . . worthy of scientific investigation.” However, Backhaus emphasizes that for him microplastics “is not an issue that warrants political or societal action just right now,” in particular what concerns the currently discussed restrictions on microbeads (FPF reported). With regard to the “broader issue of plastic pollution” as a whole, both authors agree that “curbing rampant plastic overconsumption, which is all too often paired with woefully inadequate waste management, is a global task at hand right now.”
An article published on July 19, 2018 in the peer-reviewed journal Environmental Pollution proposes a modeling approach for assessing risk of microplastics in the ocean. Using their model, Gert Everaert and colleagues from the Flanders Marine Institute, Ostend, Belgium, predicted that in 2100 there will be 10 to 49 particles per m3 floating in the ocean. This is a “50-fold increase compared to the present-day concentrations.” Based on the “effect data from the literature,” the authors derived “a safe concentration of 6650 buoyant particles per m3 below which adverse effects are not likely to occur.” Based on their estimations, the researchers conclude that “no direct effects of free-floating microplastics in the marine environment are to be expected up to the year 2100.” However, they say that “even today, the safe concentration can be exceeded in sites that are heavily polluted.” Furthermore, they “expect adverse ecological effects along the coast as of them second half of the 21st century.” To verify their findings, the authors call for “additional ecotoxicological research in which marine species are chronically exposed to realistic environmental microplastic concentration series.”
In their risk assessment, Everaert and colleagues did not consider the potential role of microplastics as chemical vectors. However, this role has been addressed recently in another article, published on June 20, 2018 in the peer-reviewed journal Environmental Science & Technology. In this manuscript, Noël Diepens and Albert Koelmans from the Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, The Netherlands, present “a generic theoretical model (MICROWEB) that simulates the transfer of microplastics and hydrophobic organic chemicals (HOC) in food webs.” First, the authors addressed a scenario where “HOCs in plastic and water are in equilibrium.” They found that persistent HOCs, like polychlorinated biphenyls (PCBs), “biomagnify less when more microplastics is ingested, because PCBs biomagnify less well from ingested plastic than from regular food.” In contrast, metabolizable HOCs, like polyaromatic hydrocarbons (PAHs), “biomagnify more when more microplastic is ingested, because plastic reduces the fraction of PAHs available for metabolization.” The authors also explored “nonequilibrium scenarios representative of additives that are leaching out.” They conclude that their model “can be used as a tool to assess prospective risks of exposure to microplastics and complex HOC mixtures for any food web, including those with relevance for human health.”
- Allen Burton Jr. (2017). “Stressor exposures determin risks: So, why do fellow scientists continue to focus on superficial microplastics risk?” Environmental Science & Technology 51(23): 13515-13516.
Thomas Backhaus and Martin Wagner (2018). “Microplastics in the environment: Much ado about nothing? A debate.” PeerJ Preprints (last update July 12, 2018).
Everaert, G., et al. (2018). “Risk assessment of microplastics in the ocean: Modelling approach and first conclusions.” Environmental Pollution (published July 19, 2018).
Noël Diepens and Albert Koelmans (2018). “Accumulation of plastic debris and associated contaminants in aquatic food webs.” Environmental Science & Technology (published June 20, 2018).