The conference “Nano and microplastics in technical and freshwater systems – Microplastics2018” took place in Ascona, Switzerland, on October 28-31, 2018. The platform and poster presentations given for a plenary of around 100 international attendees addressed “sources, releases, uptake and toxicity of microplastics.”
Richard Thompson from the University of Plymouth, UK, gave a keynote lecture titled “How concerned should we be about microplastics?” Reviewing the current data on the environmental occurrence and hazards of microplastics, Thompson summarized that the current levels in the organisms are “still low” and do not appear to cause much harm. However, they should be seen as a “warning signal” symptomatic of an “inefficient outdated business model.” This means that “we need to think about changing our ways,” Thompson said. He pointed out that the negative consequences of plastics are not directly coupled to societal benefits, therefore the problem of plastic pollution could be tackled by “redirect[ing] the flow,” “block[ing] the holes,” and “clean[ing] up.” Even though the risks from microplastics in particular may still be considered “small” at present, the current interest in plastics offers a suitable moment to promote efforts aimed at designing sustainable products and optimizing waste management practices. As an example of the innovations ahead, Michael Sander from the ETH Zurich, Switzerland, presented his group’s research on the biodegradation of synthetic polyesters in soils (FPF reported).
Several presentations addressed the sources of microplastics, many focusing on synthetic textiles. Christian Laforsch from the University of Bayreuth, Germany, presented evidence for plastic packaging being a significant source of microplastics released into the environment with the organic fertilizer (compost) applied to agricultural soils (FPF reported).
Gunnar Gerdts from the Alfred Wegener Institute, Germany, presented the challenges impeding the development of standardized methods for microplastics analysis, addressed by the BASEMAN project, with participants having analyzed microplastics in diverse matrixes ranging from waste water treatment plant effluents to arctic ice. He explained that different stakeholders appear to have different needs. For example, regulators would want a cheap and quick method to enable comparable monitoring in different environmental compartments and appear to be willing to accept inferior sensitivity in terms of concentrations and sizes of detected particles. In contrast, academic scientists would favor investing additional resources shall these be needed to develop methods for measuring smaller particles which could be more relevant. The scientists would also apprehend that different environmental compartments likely require different sample preparation and measurement methods.
Several presentations addressed the specific methods for sampling and analyzing microplastics in more details. Patricia Burkhardt-Holm from the Department of Environmental Sciences, University of Basel, Switzerland, showed how castor oil can be used to separate microplastics from soil and sediment samples based on their hydrophobicity, while Friederike Stock from the Federal Institute of Hydrology, Koblenz, Germany, presented a method to sample microplastics based on electrostatic interactions. Microplastics can also be separated based on density flotation and further cleaned up by enzymatic purification.
Analysis methods include asymmetrical flow field-flow fractionation and detection by Raman spectroscopy or Fourier Transform Infrared spectroscopy (FTIR). The two detection methods are in many ways complementary to each other and their modifications are currently able to measure particle sizes down to 1 µm (FPF reported). Methods allowing to go below this limit include nuclear magnetic resonance spectroscopy (NMR), presented by Boris Eyheraguibel from the Institute of Chemistry, University Clermont Auvergne, France, and thermal extraction/desorption-pyrolyse-gas chromatography coupled with mass spectrometry (TED-Pyr-GC/MS), presented by Julia Reichel from the Department of Civil, Geo and Environmental Engineering, Technical University of Munich, Germany. The latter method “enables identification of the adsorbed pollutants and the type of plastic in one single analysis” step. As an alternative approach to study environmental fate and behavior of microplastics, Denise Mitrano from the Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Dübendorf, Switzerland, presented a method to prepare particulate plastics doped with metals that can then be used as easy-to-measure proxies.
The hazards of microplastics were addressed in several overview presentations and study reports. Ceri Lewis gave an overview of research on biological interactions of microplastics in marine ecosystems carried out by herself and Tamara Galloway at the University of Exeter, UK. For example, recent findings demonstrated that the so-called “marine snows can transport microplastics of different shapes, sizes, and polymers away from the water surface and enhance their bioavailability to benthic organisms,” such as mussels. A recent study with captive grey seals fed wild-caught Atlantic mackerel indicated that trophic transfer of microplastics represents “an indirect, yet potentially major, pathway of microplastic ingestion for any species whose feeding ecology involves the consumption of whole prey, including humans.”
Rainer Lohmann from the University of Rhode Island, U.S., focused on the interaction between organic pollutants and microplastics in the aquatic environment. The microplastics’ contribution to the burden of persistent organic pollutants that the organisms are exposed to appears to be rather low at present (FPF reported). Modeling also suggests that only a “minor fraction of [polar] pollutants in water bodies is [currently] associated with microplastics,” as Sven Seidensticker from the Center of Applied Geoscience, Eberhard-Karls University Tübingen, Germany, presented. Further, there have been calls to consider microplastics themselves to be persistent organic pollutants (FPF reported), but the (still) inconclusive evidence for bioaccumulation and the relatively low toxicity observed would not support this notion. A more significant exposure issue could concern chemical additives incorporated in polymers themselves (FPF reported). Microplastics could directly release the additives upon ingestion and could also carry these chemicals over long distances, but more research is required to better understand these paths. The challenges in testing and interpreting bioaccumulation and toxicity studies on microplastics were also discussed by Todd Gouin from TG Environment, UK, who summarized the conclusions from the report currently being prepared by the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC), expected to be released by the end of the year.
Several presentations addressed the leaching and toxicity of plastic additives released by microplastics. For example, Scott Coffin from the University of California, Riverside, U.S., presented the results of his dissertation evaluating biologically active compounds released from marine plastics debris. Both estrogenic and dioxin-like activity could be detected in the leachates from plastics recovered from the North Pacific Gyre, demonstrating that marine plastics can “release estrogenic plasticizers” and “transport adsorbed persistent organic pollutants.” In a more recent work, estrogenicity was tested in the leachates from 16 commonly ingested plastic items, additionally subjected to in vitro digestion simulating gut conditions in fish or seabirds. Significant biological estrogenicity was seen for several items tested, including a shopping bag and an expanded polystyrene (styrofoam) container. Simulated digestion increased the total estrogenicity detected in vitro by about an order of magnitude, coinciding with the increased release of estrogenic substances, including butyl benzyl phthalate (BBP, CAS 85-68-7).
Martin Wagner from the Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway, pointed out that, although the average concentrations of microplastics measured in the environment are indeed far lower than those shown to cause potential harm, suggesting a low risk at the moment, there is nonetheless a small overlap existing between the margins around the calculated values. This means that “some” sensitive species or regional ecosystems, including both marine and freshwater habitats, could be at risk already. Further, the observed mismatch between the concentrations measured in the field and shown to be toxic in the lab could be at least partially explained by the fact that the current detection methods are typically dealing with microplastics sized at least 10 µm or above, while much smaller particles, e.g. polystyrene microbeads, are commonly used for toxicity testing. According to Wagner, microplastics concentrations could show an “exponential” increase if lower-sized particles were measured. In ecotoxicity testing of microplastics, it is important to take into consideration the heterogeneity of microplastics with regard to polymers, additives, sizes and shapes, as this can affect their hazardous properties. For example, exposure to PET microplastics caused no significant effects on survival, development, metabolism or feeding activity of freshwater invertebrate, Gammarus pulex, while various impacts are often reported for small polystyrene beads. In the second part of his talk Wagner addressed the “toxicity to scientists and societies” resulting from controversies surrounding research on microplastics (FPF reported).
Microplastics2018 (2018). “Nano and microplastics in technical and freshwater systems – Microplastics2018.”
Microplastics2018 (2018). “Program.” (pdf)
Backhaus, T., and Wagner, M. (2018). “Microplastics in the environment: Much ado about nothing? A debate.” Peer Journal Preprints DOI 10.7287/peerj.preprints.26507v6.
Burns, E.E., and Boxall, B.A. (2018). “Microplastics in the aquatic environment: Evidence for or against adverse impacts and major knowledge gaps.” Environmental Toxicology and Chemistry 37:2776-2796.
Cabernard, L., et al. (2018). “Comparison of Raman and Fourier Transform Infrared Spectroscopy for the quantification of microplastics in the aquatic environment.” Environmental Science & Technology (published October 23, 2018).
Coffin, S., et al. (2018). “Comparisons of analytical chemistry and biological activities of extracts from North Pacific gyre plastics with UV-treated and untreated plastics using in vitro and in vivo models.” Environment International 121: 942-954.
Coppock, R.L., et al. (2017). “A small-scale, portable method for extracting microplastics from marine sediments.” Environmental Pollution 230:829-837.
Galloway, T., et al. (2017). “Interactions of microplastic debris throughout the marine ecosystem.” Nature Ecology & Evolution 1: 0116.
Galloway, T.S., and Lewis, C. (2016). “Marine microplastics spell big problems for future generations.” Proceedings of National Academy of Sciences USA 113:2331-2333.
Galloway, T., and Lewis, C. (2017). “Marine microplastics.” Current Biology 27:PR445-R446.
Gerdts, G., et al. (2017). “Defining the baselines and standards for microplastics analyses in European waters (JPI-O BASEMAN).” In: Fate and impacts of microplastics in marine ecosystems: From the coastline to the open sea. Baztan, J., et al. (eds). Elsevier. DOI: 10.1016/B978-0-12-812271-6.00118-6.
Kramm, J., et al. (2018). “Superficial or substantial: Why care about microplastics in the anthropocene?” Environmental Science & Technology 52:3336-3337.
Lambert, S., et al. (2017). “Ecotoxicity testing of microplastics: Considering the heterogeneity of physicochemical properties.” Integrated Environmental Assessment and Management 13:470-475.
Lambert, S., and Wagner, M. (2018). “Microplastics are contaminants of emerging concern in freshwater environments: An overview.” In: Freshwater Microplastics. Emerging environmental contaminants? Lambert S. and Wagner M. (eds.) Springer, Cham. DOI 10.1007/978-3-319-61615-5.
Loeder, M.G.J., et al. (2017). “Enzymatic purification of microplastics in environmental samples.” Environmental Science & Technology 51:14283-14292.
Mintenig, S.M., et al. (2017). “Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging.” Water Research 108:365-372.
Nelms, S., et al. (2018). “Investigating microplastic trophic transfer in marine top predators.” Environmental Pollution 238: 999-1007.
Porter, A., et al. (2018). “Role of marine snows in microplastic fate and bioavailability.” Environmental Science & Technology 52: 7111-7119.
Peeken, I., et al. (2018). “Arctic sea ice is an important temporal sink and means of transport for microplastic.” Nature Communications 9:1505.
Seidensticker, S., et al. (2018). ”A combined experimental and modeling study to evaluate pH-dependent sorption of polar and non-polar compounds to polyethylene and polystyrene microplastics.” Environmental Sciences Europe 30:30.
Weber, A., et al. (2018). “PET microplastics do not negatively affect the survival, development, metabolism and feeding activity of the freshwater invertebrate Gammarus pulex.” Environmental Pollution 234: 181-189.
Weithmann, N., et al. (2018). “Organic fertilizer as a vehicle for the entry of microplastic into the environment.” Science Advances 4:eaap8060.
Zumstein, M. T., et al. (2018). “Biodegradation of synthetic polymers in soils: Tracking carbon into CO2 and microbial biomass.” Science Advances 4:eaas9024.