Microplastics and Nanoplastics in Aquatic Environments: Aggregation

Dec 21, 2017 - Below, the existing literature on NP and MP aggregation and deposition has been summarized and critically analyzed. .... For example, H...
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Critical Review

Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport Olubukola Alimi, Jeffrey Farner Budarz, Laura M Hernandez, and Nathalie Tufenkji Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b05559 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 22, 2017

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Microplastics and Nanoplastics in Aquatic

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Environments: Aggregation, Deposition, and Enhanced

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Contaminant Transport

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Olubukola S Alimi, Jeffrey Farner Budarz, Laura M Hernandez, Nathalie

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Tufenkji*

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Department of Chemical Engineering, McGill University,

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Montreal, Quebec, Canada H3A 0C5

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Corresponding Author. Phone: (514) 398-2999; Fax: (514) 398-6678; E-mail: [email protected]

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Abstract

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Plastic litter is widely acknowledged as a global environmental threat and poor

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management and disposal lead to increasing levels in the environment. Of recent concern

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is the degradation of plastics from macro- to micro- and even to nanosized particles

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smaller than 100 nm in size. At the nanoscale, plastics are difficult to detect and can be

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transported in air, soil and water compartments. While the impact of plastic debris on

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marine and fresh waters and organisms has been studied, the loads, transformations,

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transport, and fate of plastics in terrestrial and subsurface environments are largely

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overlooked. In this review, we first present estimated loads of plastics in different

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environmental compartments. We also provide a critical review of the current knowledge

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vis-à-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and

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contaminant co-transport in the environment. Important factors that affect aggregation

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and deposition in natural subsurface environments are identified and critically analyzed.

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Factors affecting contaminant sorption onto plastic debris are discussed, and we show

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how polyethylene generally exhibits a greater sorption capacity than other plastic types.

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Finally, we highlight key knowledge gaps that need to be addressed to improve our

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ability to predict the risks associated with these ubiquitous contaminants in the

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environment by understanding their mobility, aggregation behavior and their potential to

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enhance the transport of other pollutants.

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1.0 Introduction

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Currently, the global production of plastics exceeds 320 million tons (Mt) per year,1 with

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production expected to double in the next 20 years.2 Of this, only 6-14% is recycled,

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meaning up to 86% ends up either in landfills (21–42%) or released into the environment

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due to mismanagement through a variety of pathways (Figure 1).2-6 Indeed, with the

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widespread use of different plastics, the current era has been referred to as the

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Plasticene.7 Plastic debris has been detected in air,8 oceans,5, 9, 10 soils,11-13 sediments,14, 15

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and surface waters worldwide.16 It is estimated that in Europe and North America, the

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amount of microplastics (MPs) transferred every year from wastewater treatment plants

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(WWTPs) to agricultural soils as biosolids is greater than the total burden of MPs

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currently present in ocean water.3

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Plastics are produced through the polymerization of various monomers and additives

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resulting in a spectrum of characteristics such as polarity and “glassiness”.17, 18 These

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differences in composition will impact their affinity for other pollutants and potential

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risks associated with them.19 The most commonly detected plastics in the environment

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are polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polyethylene

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terephthalate (PET) and polystyrene (PS).20

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The presence of MPs in the environment had been largely overlooked until recently;

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however, the number of studies is now growing rapidly due to the global ubiquity of

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plastic and its potential threat to human health and biota. Large plastic debris breaks

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down to form macroplastics (herein defined as >25 mm in size), mesoplastics (5-25 mm),

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MPs (