And Microplastics Delphine Kawecki† and Bernd Nowack*,†
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This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes. Article Cite This: Environ. Sci. Technol. 2019, 53, 9664−9676 pubs.acs.org/est Polymer-Specific Modeling of the Environmental Emissions of Seven Commodity Plastics As Macro- and Microplastics Delphine Kawecki† and Bernd Nowack*,† † Empa − Swiss Federal Laboratories for Materials Science and Technology, Technology and Society Laboratory, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland *S Supporting Information ABSTRACT: Plastic has been identified as an emerging contaminant in aquatic and terrestrial ecosystems. Uncertainties remain concerning the amounts present in the environment and the main responsible sources. In this study, the emissions of macro- and microplastics have been mapped for seven polymers in Switzerland. The modeling is based on a complete analysis of the flows from production and use to end-of-life using probabilistic material flow analysis. We estimate that 94 ± 34 g/capita/year of low-density polyethylene, 98 ± 50 g/cap/a of high-density polyethylene, 126 ± 43 g/cap/a of polypropylene, 24 ± 13 g/cap/a of polystyrene, 16 ± 12 g/cap/a of expanded polystyrene, 65 ± 36 g/cap/a of polyvinyl chloride, and 200 ± 120 g/cap/a of polyethylene terephthalate enter the Swiss environment. All polymers combined, 540 ± 140 and 73 ± 14 g/cap/a are emitted into soil as macroplastics and microplastics, respectively, and 13.3 ± 4.9 and 1.8 ± 1.1 g/cap/a are emitted into freshwater as macroplastics and microplastics, respectively. The leading emission pathway is littering for both terrestrial and aquatic environments. Construction, agriculture, and pre- and postconsumer processes cause important emissions of microplastics into soils, and postconsumer processes, textiles, and personal care products release most of the microplastics into waters. Because mass flows into soils are predicted to be 40 times larger than those into waters, more attention should be placed on this compartment. Our work also highlights the importance of referring to specific polymers instead of just “plastics”. ■ INTRODUCTION environmental compartment is sometimes not mentioned,25,28 26,27,29−31 Microplastics (MP) have been reported in numerous fresh- or the focus is only on aquatic environments. Existing 1−3 4 5 6−8 estimates for soil burdens are only preliminary and call for water systems in Europe, North America, Africa, Asia, 17,32 Downloaded via ETH ZURICH on August 20, 2019 at 17:52:58 (UTC). both in densely populated areas9 and remote systems.10 The more precise assessments. MP originating from macro- plastic fragmentation are often outside of the scope of presence of MP in soil is not as well documented as it is in − published MP-release studies26,29 31 or based on a rough freshwater since accurate methods for measuring MP 25,27 11−13 estimate of the fraction of mismanaged waste. In one concentrations in soil are still being developed; however, 28 See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. first estimates hint that burdens in soil may be consid- instance, the method of quantifying release remains unclear. 14,15 Some published emission assessments have focused entirely on erable. MP have been reported in soils where sludge has 33,34 16 the release of macroplastic to the oceans, likewise based on been applied but also in areas with reduced direct human 35 impacts.11 The main sources of MP to soil have been suggested roughly estimated fractions of mismanaged waste. To this to be compost and sludge application onto land, mulching day, large segments of the emission pathways are not well- 32 fi plastics, littering, street runoff, and atmospheric deposition.17 known, since data on speci c release processes is scarce and Emissions to outdoor and indoor air have so far only been subject to high variability. marginally addressed.18 To the best of our knowledge, no release model has − The risk associated with MP is currently under debate19 22 systematically investigated the material composition of the fl ff due to challenges arising in both hazard and exposure emission ows. The distinction between di erent polymers for assessments. Current preliminary risk assessments predict little the exposure assessment is needed for several reasons. First, a to no risk on average in marine23 and freshwater24 environ- risk assessment should ideally distinguish between individual ments. In order for science to support actions from policy makers and citizens, a solid assessment of the present degree of Received: May 15, 2019 pollution needs to be undertaken. MP emission assessments Revised: June 19, 2019 have been performed for Norway,25 Denmark,26 Germany,27,28 Accepted: June 20, 2019 Sweden,29 Europe,30 and the whole world.31 The receiving Published: July 9, 2019 © 2019 American Chemical Society 9664 DOI: 10.1021/acs.est.9b02900 Environ. Sci. Technol. 2019, 53, 9664−9676 Environmental Science & Technology Article materials, since toxicities may be different depending on the included in the masses reported. More details on the material material itself and the additives included. Since release definition are available in the first study.40 pathways may also be very different depending on the life- Flows Considered. The basis for assessing the flows of the cycle of the material,36 the exposure is also polymer dependent. polymers to the environment is the modeled life-cycle of the Second, if fate models are to be developed, a differentiation polymers within the anthroposphere.40 Some adjustments to between lower and higher material densities needs to be made. the life-cycle description were necessary compared to the At last, for the implementation of the MP release into life cycle previous study to permit the modeling of emission flows. First inventories (LCI), a distinction between material and life-cycle of all, additional product categories were included to the 35 stage is needed. already defined in the previous study: wet wipes, sanitary pads, The goal of this study is therefore to quantify the emissions panty liners, tampons, tampon applicators, cotton swabs, of different plastics based on a complete analysis of the life- disposable cutlery, straws, and shotgun cartridges. Second, a cycle of all products containing the chosen materials. This distinction between preconsumer waste generated by textile or ff modeling is being undertaken for di erent polymers, with an plastic industries was made in order to model the emissions of increased level of detail compared to existing studies, and pellets more accurately (Figure S16). targets both macro- and microplastics. This allows us to Building on the description of the life-cycle, emission flows ff compare in a complete picture the di erent emission sources were included describing the initial emission and the pathways of plastic to the environment, identify the polymers emitted, followed until the final release into the environment (Figures and pinpoint possible points of action. The model focuses on S17−21 and Figure S11). Emissions of macroplastic and MP emissions to water and soil environments without including are tracked individually by creating separate compartments for fate processes such as fragmentation of macro- to micro- both sizes of plastic in our system. This permits to account for plastics. The modeling is based on probabilistic material flow ff 37 the di erent processes responsible for the MP release to analysis (PMFA) which allows us to account for the various freshwater and soils. MP emissions occur for both MP that are uncertainties associated with the data sources. Moreover, by designed as particles for their use, for example, preproduction considering the whole life-cycle, all emissions may easily be pellets and MP in personal care and cosmetic products compared to one another and no double accounting occurs. (PCCP), and for MP generated from the wear of products, for The modeling was done separately for seven of the most highly instance, fibers shed from textiles (SI chapter 4). MP can also used thermoplastics. Switzerland was used as the geographic originate from the abiotic or biotic degradation of macro- region due to the high availability of data. plastics. In order to account for all types of sources, emission fl ■ METHOD ows of both MP and macroplastics are considered. No fate processes are implemented in water and soil environments. A Algorithm. Material Flow Analysis (MFA) is an established simple air deposition model is nevertheless implemented since method for analyzing the flows of materials through the 38,39 particles do not stay in the air for longer time periods. The anthroposphere in a systematic fashion. The probabilistic emissions of MP and macroplastics will be presented separately MFA (PMFA) method used in this work builds upon MFA by throughout this study. MP include all particles smaller than 5 including a systematic uncertainty analysis and propagation ff 37 mm, with no strict lower size threshold since the di erent data using Monte Carlo simulations. This method has already underlying the model may have varying lower thresholds, and been used for modeling the flows of polymers through the − macroplastics include all pieces larger than 5 mm. anthroposphere40 as well as several other materials.41 43 The A total of 168 flows were used to model the life-cycles of the basic principle of the model relies on two mathematical polymers in Switzerland for the year 2014, mostly on the basis objects. The first object is a transfer coefficient (TC) matrix, of the original study.40 They represent the flows of plastic which describes all the flows from one process to another. The through production, manufacturing, use, and end-of-life. In second object is an input vector containing all the external fl inputs to the defined system.