A scientific perspective on microplastics in nature and society: Evidence review report

Scope and Objective
\nMicroplastics are plastic particles of mixed shape that are present in air, soil, freshwater, seas, in biota, and in several components of our diet. NMPs are below 5 mm in size (Arthur, 2009) and come from a variety of sources, including fisheries, products and textiles (use and breakdown), agriculture, industry, waste, and others. Because of fragmentation and degradation of larger plastic items and of microplastics, it is plausible that nanoplastics will be formed. Scientists, policy-makers and the public are becoming increasingly concerned about both the ubiquity of nano- and microplastics (NMPs) and the uncertainties surrounding their impacts, hazards and risks to our environment and to human health. Heightened media attention on plastic pollution is observed. If the occurrence and concentrations of NMPs continues to rise, either from intentionally produced NMPs, or NMPs formed by the degradation of larger plastic items, what can science tell us about the risks and what sense can be made of this complex evidence base?
\nThe scientific evidence base and policy context are being reviewed by the European Commission’s Science Advice Mechanism (SAM). As part of this mechanism, this Evidence Review Report offers a scientific perspective on the state-of-the-art knowledge about the implications of NMPs in nature and society and highlights the unique features and complexities of the topic. In this report, a SAPEA working group rapidly reviews the current knowledge about NMPs and offer their conclusions on that knowledge as it stands today. They also highlight uncertainties and knowledge gaps in order to inform appropriate future actions. 
\nMany agencies, groups and discussion forums are bringing together experts specializing in plastics and microplastics to share their perspectives on microplastics pollution and to look at potential policy needs. Both the scientific evidence base and the policy context is evolving quickly. What is unique about this report is that it is an interdisciplinary analysis by independent scientists, free from political institutional influences, coordinated by the European Scientific Academies. The ERR provides the first step in a 2-step process that feeds into a Scientific Opinion on the subject in 2019, which will be written by the European Commission’s Group of Chief Scientific Advisors (GCSA). At current, a systematic overview on policy options and their predicted efficiency and relevance to reduce current and future risks of NMP in Europe is not available and so this is welcomed by the working group. 
\nThis report distinguishes clearly between what is known, what is partially known and what is not known where possible and the broad scope for it is outlined in a statement that was issued by the GCSA, in July 2018 (GCSA, 2018). Nano- and microplastics in the environment (as reviewed in Chapter 2) are solely the result of human activity, and it is essential to understand the contributing factors of society within the system. A unique aspect of this report is that it reviews evidence from the social and behavioural sciences (in Chapter 3) in conjunction with the natural sciences evidence, which is crucial to designing effective policies. The working group also reviews current computer modelling performed on the topic (Chapter 2) and briefly reviews plastic-related policies. In chapter 4, a review of the scientific underpinnings to current policies is given, and it is noted where they do or (as in most cases) do not include NMPs. 
\nThis report is the result of discussions at two physical meetings, held in Brussels and Amsterdam, and one workshop held in Berlin. The authors worked remotely and wrote this report within twelve weeks, from September to November 2018. For the specialized reader, the detailed evidence that underpins this report can be found within the sections of each chapter and more information can be found within the 435 references. The main conclusions reached by the working group can be found at the end of each chapter. A digest and combined summary can be found in Chapter 5, which also presents some solutions for society, as potential options derived from this scientific evidence. 
\nConclusions 
\nThe number of papers is growing exponentially in this field, but the knowledge is not growing at the same rate - there is some redundancy and marginality in the papers. The SAPEA working group concludes that a lot is already known about nano- and microplastics, and more knowledge is being acquired, but some of the evidence remains uncertain and it is by its nature, complex (for instance, differences in size, shape, chemical additives, concentrations, measurements, fates, unknowns, human factors, media influences, actions and behaviours, as reviewed in the report). While members of the working group have diverging interpretations of some of the evidence, they review and present their views in a non-biased way, also presenting where they found consensus.
\nThey conclude that there is a need for improved quality and international harmonisation of the methods used to assess exposure, fates and effects of NMPs on biota and humans. We have a fair knowledge of microplastics concentrations for freshwaters and the ocean surface, but little is known about air and soil compartments and about concentrations and implications of NMPs below the ocean surface. The working group concludes from this evidence that, while ecological risks are very rare at present, there are at least some locations in coastal waters and sediments where ecological risks might currently exist. If future emissions to the environment remain constant, or increase, the ecological risks may be widespread within a century. Little is known with respect to the human health risks of nano- and microplastics, and what is known is surrounded by considerable uncertainty (Section 2.6), however the relevant conclusion of this working group is that we have no widespread risk to NMPs at present. Most micro plastics go in and out of most organisms, and as with many chemicals, ‘the poison is in the dose’. 
\nIt has been demonstrated in the laboratory that at high exposure concentrations and under specific circumstances, nano- and microplastics can induce physical and chemical toxicity. This can result in physical injuries, inducing inflammation and stress, or it can result in a blockage of the gastrointestinal tract and a subsequent reduced energy intake or respiration. Sections 2.5 and 2.6 of this report review evidence of studies in several aquatic organisms, where, for example, researchers conclude that exposure to microplastics in the laboratory has a significant, negative effect on food consumption, growth, reproduction and survival, once effect thresholds are exceeded. But we have no evidence that this happens in nature.
\nMost these effect studies, however, are either performed using concentrations that are much higher than those currently reported in the environment, or are performed using very small microplastics, for which limited exposure data exists, or only used spherical ones which are not representative of real world types of particles or used relatively short exposure times. Currently, it is not known to what extent these conditions apply to the natural environment. This limits the reliability of the risk assessment for nano- and microplastic. 
\nWhile inflammatory evidence is seen in animal models, we don’t know if this translates to humans or not. In humans, workers/occupational exposure to microplastics can lead to granulomatous lesions, causing respiratory irritation, functional abnormalities and other (such as flock workers lung). The chemicals associated with microplastics, can have additional (and difficult to assess) human health effects, such as reproductive toxicity and carcinogenicity , however, the relative contribution to chemical exposure via NMP among the mix of chemicals, is probably small at present (section 2.5.6), although the number of assessments remains limited. Therefore, the degree of this toxicity and impacts for environmental NMPs remains uncertain’.. With a sparse evidence-base for both dietary and airborne microplastics concentrations, especially concerning the inhalable size fraction, it is unclear what the human daily intake of nano- or microplastics is, yet this knowledge is essential for estimating health effects. 
\nThere is a need to understand the potential modes of toxicity for different size-shape-type NMP combinations in carefully selected human models, before robust conclusions about ‘real’ human risks can be made, though the occurrence and impacts are beginning to be measured. Meanwhile, very little is known about nanoplastics (as opposed to microplastics), and this should be addressed before any pertinent assessment can be made about their impacts and risks.
\nThe currently known detail about environmental and health impacts to date, sources, occurrences, fates, hazards and risks, can be found in Chapter 2 and the full list of conclusions of the Chapter can be found in Section 2.7. 
\nThere is a considerable influence from the media and politics in parallel to the scientific communications on the public discourse of NMP. Chapter 3 of this report highlights how insights from sociology, psychology, media and communication studies and organisational studies have an important role to play in understanding the interplay between natural science insights and the planning of effective societal responses. These disciplines are necessary in the design of successful policies and interventions and in societal engagement to reduce NMP pollution (and macroplastics as contributors to NMP, although they are not the focus of this review). A conclusion of this working group is that communicating transparently about the uncertainties in the scientific evidence is a safer approach than assuming a lack of risk, especial