Preface

Almost sixty years after plastic pollution first appeared in the scientific literature much progress has been made, and we now have a much better understanding of what are the main sources and impacts of many synthetic polymers commonly found in the marine environment. Research has shown that a wide range of marine organisms is negatively interacting with plastic litter and for some species, a major proportion of the population has ingested plastic fragments and fibers. Laboratory experiments have also demonstrated wide-ranging harmful effects and global concern is growing about the physical and toxicological harm that ingesting plastic debris might cause to natural populations. Many open questions, however, still remain to be addressed and today, after a considerable body of research has been published, a clear understanding of the global plastic cycle is still far from being achieved. It is widely assumed for instance, that most plastic debris derive from land-based sources, although some studies recently suggested that sea-based sources also play an important role. Nevertheless, there is a surprising mismatch between the estimates of the global inputs of plastic from land, and the total amount of plastic floating at sea. Recent studies suggested that backshores and coastal margins, the water column, or deep-sea sediments, can all be accounted for this missing fraction, however, the fluxes and fate of most plastics entering the ocean every year are currently unknown. There is also a debate about whether the volume of plastics measured at sea over the last decades has kept pace with the global growth in plastic production, as no evidence of increase has been found by many authors. In addition, most figures about the longevity of synthetic materials at sea, are still anecdotal, and solid data about the actual degradation rates of plastics in a range of environmental conditions are urgently required. Reliable information is also missing about toxicological impacts and degradation times not only of the most commonly used polymers, but also about some of the most widespread environments of our planet. The deep-sea for instance, or the water column, that are the two largest ecosystems of the world, are greatly understudied, especially if compared to surface, estuarine or coastal waters, despite comprising the majority of marine habitats worldwide. Altogether, these findings suggest that our understanding of the global plastic cycle is largely incomplete and many of the biological, physical, and geochemical processes that influence the horizontal and vertical displacement of plastics in oceanic environments, still need to be investigated in greater detail. Technological development will likely play a pivotal role in future research on plastic pollution. Improvement in the capabilities of remote sensing, ocean modeling, and deep-sea exploration, together with the development of innovative and low-cost sensors, all have the potential to enormously improve data availability, facilitating in turn, a more holistic understanding of the complex mechanisms involved with the cycling of plastics through natural ecosystems. At the same time, the harmonization of sampling procedures and analytical protocols is an imperative priority for the coming years of research. Global standardization of reporting procedures will improve the efficacy of large-scale monitoring programs, enhancing the reliability and inter-comparability of long-term data series, allowing, in turn, a more effective evaluation of current and future mitigation measures. By looking at the history of other anthropogenic contaminants (e.g., heavy metals, pesticides, etc.), great efforts have been made by the scientific community to harmonize analytical protocols, thus allowing meaningful conclusions to be drawn. Standardization of data collection has been already the focus of countless workshops and of many large international projects, as well as of many efforts led by international bodies, private associations, and intergovernmental organizations worldwide. So, the road is paved, and it is just to be hoped that these international efforts will greatly accelerate in the coming years, allowing the scientific community to move one step forward in the comprehension of this relatively new environmental issue. The chapters that follow all move in this direction, presenting critical information on the distribution, fate, and transport of plastic litter in the marine environment, placing a special emphasis on the impacts that plastic pollution is having on marine organisms, their food webs, and on marine ecosystems as a whole. Given future projections in global plastic production and consumption patterns, it seems inevitable that the quantities of plastic waste will keep increasing in the coming years. Nevertheless, the likely trajectories, environmental sinks or accumulation and degradation patterns are much less clear. Further research into the impact, behavior, and residence time of marine plastic litter will help inform stakeholders and policymakers that aim to tackle, probably not one of the most pressing, but surely one of today's most visible environmental problems. What is now clear is that the number of plastic items currently entering the marine environment needs to be drastically reduced. This can be only achieved through bold international regulations, aimed at reducing waste generation, and at promoting reuse and repair of used items, according to those virtuous examples of zero waste policies already implemented by many communities around the world. These principles are key to the implementation of a more circular economy and at the same time, they really have the potential to greatly improve the resource efficiency of our societies. Scientific research still sits at the basis of knowledge, and thanks to the tireless efforts of many researchers, a broad recognition has been now achieved by the general public, that plastic debris does not belong to the ocean and that the numerous societal benefits that derive from our everyday-use of plastics can be also achieved without emitting plastics into the environment. Marie Sk?odowska-Curie once said that "nothing in life is to be feared, it is only to be understood. And now is the time to understand more, so that we may fear less". And so, we should all be confident that with a little hope, scientific progress can really help us navigate the future, ultimately diverting our debauched legacy to more sustainable alternatives, for the entire planet, and all generations to come.