Society has become increasingly reliant on plastics since commercial production began in about 1950. Their versatility, stability, light weight, and low production costs have fueled global demand. Most plastics are initially used and discarded on land. Nonetheless, the amount of microplastics in some oceanic compartments is predicted to double by 2030. To solve this global problem, we must understand plastic composition, physical forms, uses, transport, and fragmentation into microplastics (and nanoplastics). Plastic debris/microplastics arise from land disposal, wastewater treatment, tire wear, paint failure, textile washing, and at-sea losses. Riverine and atmospheric transport, storm water, and disasters facilitate releases. In surface waters plastics/microplastics weather, biofoul, aggregate, and sink, are ingested by organisms and redistributed by currents. Ocean sediments are likely the ultimate destination. Plastics release additives, concentrate environmental contaminants, and serve as substrates for biofilms, including exotic and pathogenic species. Microplastic abundance increases as fragment size decreases, as does the proportion of organisms capable of ingesting them. Particles <20 μm may penetrate cell membranes, exacerbating risks. Exposure can compromise feeding, metabolic processes, reproduction, and behavior. But more investigation is required to draw definitive conclusions. Human ingestion of contaminated seafood and water is a concern. Microplastics indoors present yet uncharacterized risks, magnified by the time we spend inside (>90%) and the abundance of polymeric products therein. Scientific challenges include improving microplastic sampling and characterization approaches, understanding long-term behavior, additive bioavailability, and organismal and ecosystem health risks. Solutions include improving globally based pollution prevention, developing degradable polymers and additives, and reducing consumption/expanding plastic reuse.

An increasing number of reports have been published concerning microplastic (MP) pollution in aquatic environments. Methods used in these studies continue to be updated and lack standardization, so that an up-to-date review pertaining methods for MP research is needed. This critical review examines the analytical methods, including sampling, identification, and quantitation, for MP research. Samples are generally collected from water, sediment, and biota gastrointestinal tract. Manta nets or trawls are prevalently used in surface water sampling, while direct shoveling or box-corer grab are commonly applied in sediment sampling. Microplastics in biota are generally obtained by dissecting organisms and separating livers, gills, and guts. Density separation is frequently chosen to separate MPs from sample matrices. Chemical digestion can dissolve other organic materials and isolate MPs for further identification. Visual sorting should be combined with chemical composition analysis to better identify the polymer type. Pyrolysis or thermal decomposition gas chromatography coupled with mass spectrometry, Fourier transform infrared spectroscopy, and Raman spectroscopy are currently the main technologies for MP identification. Units prevalently used to express MP abundance in water, sediment, and biota are "particles per m," "particles per m," and "particles per individual," respectively. As MP abundances often varied with the methods used, we recommend that analytical protocols of MPs should better be standardized and optimized. Despite the important progress in analysis of MPs, detection technologies for identifying nano-sized plastic particles are still lacking, and therefore should be developed swiftly.

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Global marine plastic pollution, which is derived mainly from the input of vast amounts of land-based plastic waste, has drawn increasing public attention. Riverine plastic outflows estimated using models based on the concept of mismanaged plastic waste (MPW) are substantially greater than reported field measurements. Herein, we formulate a robust model using the Human Development Index (HDI) as the main predictor, and the modeled riverine plastic outflows are calibrated and validated by available field data. A strong correlation is achieved between model estimates and field measurements, with a regression coefficient of r 2 = 0.9. The model estimates that the global plastic outflows from 1518 main rivers were in the range of 57,000–265,000 (median: 134,000) MT year–1 in 2018, which were approximately one-tenth of the estimates by MPW-based models. With increased plastic production and human development, the global riverine plastic outflow is projected to peak in 2028 in a modeled trajectory of 2010–2050. The HDI is a better indicator than MPW to estimate global riverine plastic outflows, and plastic pollution can be effectively assessed and contained during human development processes. The much lower global riverine plastic outflows should substantially ease the public’s concern about marine plastic pollution and financial pressure for remediation.

Plastic pollution has caused increasing global concern. Currently, model estimates of the riverine plastic inputs to the global oceans based on the concept of Mismanaged Plastic Waste (MPW) varied substantially, and no field measurements of riverine inputs were available. We conducted sampling at the eight major river outlets of the Pearl River Delta, South China with rapid economic growth and urbanization to provide field measured data for fine-tuning modeling results. Floating microplastics (MPs) were collected with a Manta net (mesh size of 0.33 mm) five times during 2018. Microplastic particles (0.3–5.0 mm) widely occurred in all sampling sites. The number and mass concentrations of MPs were in the ranges of 0.005–0.7 particles m–3 and 0.004–1.28 mg m–3 and were positively correlated with water discharges. The annual riverine input of MPs from the Pearl River Delta was estimated at 39 billion particles or 66 tons, which converts to 2400–3800 tons of plastic debris based on calculations described in Text S2. These values were substantially below the MPW-based model estimates (91,000–170,000 tons). The large difference between measured and modeling results may have derived from the large uncertainty in the MPW values assigned to the world’s countries/regions.