Editorial: Microplastics in the Marine Environment: Sources, Distribution, Biological Effects and Socio-Economic Impacts

Editorial on the Research Topic Microplastics in the Marine Environment: Sources, Distribution, Biological Effects, and Socio-Economic Impacts Introduction From all the synthetic materials ever produced, plastic is the most versatile, overthrowing both glass and metal in many applications, due to its low weight and cost Plastic pollution is intrinsically linked to consumption habits and waste management practices globally [ ]recommendations need to be aligned with regulations and with the adequate use of market-based instruments, so that solving this problem is addressed holistically Mater 400:123110 doi: 10 1016/j jhazmat 2020 123110 João P Frias1*†, Juliana A Ivar do Sul2*†, Cristina Panti3*† and André R Lima4*† * 1Marine and Freshwater Research Centre (MFRC), Galway-Mayo Institute of Technology (GMIT), Galway, Ireland * 2Leibniz Institute for Baltic Sea Research, Rostock, Germany * 3Department of Physical, Earth and Environmental Sciences, University of Siena, Siena, Italy * 4Department of Biosciences, Marine and Environmental Sciences Centre (MARE), University Institute of Psychological, Social and Life Sciences (ISPA), Lisbon, Portugal


INTRODUCTION
From all the synthetic materials ever produced, plastic is the most versatile, overthrowing both glass and metal in many applications, due to its low weight and cost. Global plastic production started shortly after WWII, around the 1950's (PlasticsEurope, 2010), and became a popular household item around the same time (Time, 1955). Since then, global production has been exponentially increasing at a rate of 8% per annum (PlasticsEurope, 2020). Notably, it took only 10 (1965) to 17 (1972) years until researchers started noticing the first evidence of plastics in the marine environment (Carpenter and Smith, 1972;Ryan, 2015). Between the 1960's and the 1990's, several studies reported direct consequences of plastic interaction with vessels, particularly entanglement of propellers, and with wildlife, via entanglement or ingestion (Ryan, 2015). Consistent findings throughout the world led to calls for action, due to the likelihood that over time the problem would be amplified by fragmentation of larger plastic items into smaller pieces (Carpenter and Smith, 1972). Microplastic research is now a well-established research field, with at least 2,500 papers published so far on this topic (Zhang et al., 2020).
Despite being a relatively recent research field, microplastic pollution has gone beyond the realm of academia into the general public. Several stakeholders with different vested interests are involved in this topic, from standardization bodies to grassroot movements, from national agencies to research institutions. Plastic has become a social issue, due to its economic and environmental consequences, which affect human activities and the natural cycles of the planet. In order to contribute to the debate, this Research Topic (RT) highlights recent research developments in the microplastic field, in a diverse set of topics that cover relevant aspects from methodologies to modeling, and from impacts on fauna to legislation. A total of 23 research papers from 43 primary and partner institutions, in four continents and spread across 15 countries (Figure 1A), reveal the prevalence of this global problem, and report on some of the solutions ahead.

A SHORT BIBLIOMETRIC ANALYSIS OF PAPERS PUBLISHED IN THIS RT
The author's keywords from each paper were compiled and analyzed in the software VOS viewer to illustrate the diversity of topics explored here (Van Eck and Waltman, 2010). The set of 21 papers (with their final versions published by 01.03.2021) in this RT had a total of 152 keywords. To standardize keywords describing the same concept, a thesaurus was created ( Table 1). For example, polyethylene, polypropylene and other polymer types were all grouped under the keyword "polymers." As such, a total of 67 keywords are presented in the final set. The  most popular keyword is "microplastics" (N = 10 occurrences), followed by "fish" (N = 5), "plastic pollution" and "plastic ingestion" (N = 4). The keywords "polymers, " "spectroscopy, " and "marine debris" appeared in three papers each (N = 3). All other keywords appeared in one or two publications only, indicating a generally very low frequency of used keywords and therefore a variety of studied topics ( Figure 1B). This RT included a relatively high number of papers using fish as a model organism (see "fish" in Figure 1B), either by exploring combined effects of (nano-micro) plastics and organic pollutants in teleost (Trevisan et al.; Bour et al.; Ašmonaite et al.; Abihssira-García et al.) or by improving extraction and analysis methods for predicting plastic ingestion in fish (Dawson et al.; Pedà et al.; Pequeno et al.). In the same cluster, the keyword "plastic ingestion" included papers that explored the transfer of microplastics particles among successive levels in marine trophic webs or potential transfer of plastic additives and chemicals from plastics to biota when ingested (Costa et al.; Kühn et al.). Also grouped together are papers using the keyword "polymers" showing works that explore polymer-specific effects of particles in model-animals (Santana et al.).
Papers with more general approaches are clustered around keywords such as "plastic pollution" and "marine debris" (Figure 1B, in yellow). These are papers related to legislations to mitigate plastic (marine) pollution (Da Costa et al.; Galaiduk et al.), potential bioindicators of (micro)plastic pollution (Reichelt and Gorokhova; Fossi et al.), but also to method development with potential to be used over large geographical areas (Enders et al.; Haseler et al.; Rodrigues et al.; Tagg et al.) and modeling of microplastic sources into the environment (Balthazar-Silva et al.; Gorman et al.; Schernewski et al.; Piehl, Atwood et al.; Piehl, Hauk et al.).

CONCLUSION
We considered this special issue to be very successful both in terms of number of papers published and variety of studies targeting several microplastic pollution issues. Notorious research advancements and science breakthroughs, as well as technological developments, are highlighted here based on the efforts of the microplastic scientific community over recent years. Manuscripts in this RT aim at fulfilling knowledge gaps while creating new research questions to fully understand the ubiquitousness of plastics in the environment. Although there is still a long way to go within this research extensive knowledge gathered so far [see for example Galgani et al. (2021)] will allow decision makers to make better decisions surrounding this global problem, while consolidating microplastic pollution as a permanent research field.
Plastic pollution is intrinsically linked to consumption habits and waste management practices globally. Therefore, recommendations need to be aligned with regulations and with the adequate use of market-based instruments, so that solving this problem is addressed holistically. One thing that the global pandemic brought to sight is that behavior change is possible, and when we work together reduction and prevention can be achieved. For example, understanding how to tackle losses and emission throughout the entire supply-chain will effectively reduce the abundances of plastic marine litter in the environment. That is an excellent way to start to flatten the current plastic pollution scenario worldwide.

AUTHOR CONTRIBUTIONS
All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.