Although plastics have become an essential material, permeating almost all aspects of modern living, many of the inherent properties that make them useful in such a wide variety of applications also make them a serious environmental threat. In a special issue of Science, "Our Plastics Dilemma," four Reviews, two Perspectives, a Policy Forum, an associated Report and two News features examine a wide range of topics related to plastics and the problems they present. "As for much new technology, their development and proliferation occurred with little consideration for their impacts, but now it's impossible to deny their dark side as we confront a rapidly growing plastic pollution problem," writes Science Senior Editor, Jesse Smith. "The time for preventing plastic pollution is long past - the time for changing the future of plastics in our world, however, is now."
Estimates of the amount of plastic floating at the ocean surface (measured in the hundreds to thousands of metric tons) only represent a small fraction of what is suspected to be annually discharged by rivers worldwide (several million metric tons). This has led some to speculate a large, yet-unidentified plastic sink that could help explain the rapid removal of river-sourced plastics from the ocean's surface. In the associated Report in this special issue, Lisa Weiss and colleagues show that this missing sink may not even exist. Weiss et al. performed a large-scale statistical reanalysis on updated data on microplastics. "We came to the conclusion that previous flux estimates contained several serious errors," Weiss explains in a related video. She and colleagues say that previous mass fluxes of microplastics were overestimated by two to three orders of magnitude, explaining why the residence time of plastics in the oceans appeared so short. Based on these findings, the authors suggest that the average residence time of microplastics at the ocean's surface could be as high as several years, rather than a few days. The results imply that ocean plastics have more time than previously thought to degrade at the surface before becoming entrained in seafloor sediments. Based on their results, "the need for a missing plastic sink becomes outdated and... unnecessary," says author Wolfgang Ludwig in the video.
In a pair of Perspectives, experts highlight the problematic history of early bio-based plastics and how designing future plastics for both chemical assembly and disassembly is essential to achieving an effective circular plastics economy. According to Rebecca Altman, early bioplastics - the broad category of plastics made from bio-based feedstocks like corn, sugar or wood - were neither clean nor green. Lessons from their overlooked and misunderstood past could help inform the future of greener, biodegradable plastics and plastic technology. Sarah Kakadellis and Gloria Rosetto highlight the technical, chemical, and biological routes to closing the plastic resource loop by designing plastics to be more broadly recyclable or biodegradable in the environment. "The fallacy of mechanical recycling has already taught us that technology alone will not and cannot solve the plastic pollution crisis. No silver bullet solution exists for the multifaceted nature of plastic pollution," write the authors. "Only through committed action and coordination across the value chain will a sustainable future for plastics be secured," write Kakadellis and Rosetto.
A Policy Forum by Nils Simon and colleagues argues the need for a binding global agreement to address plastic's long lifecycle and to combat plastic pollution. According to Simon et al., the international community has tended to view the plastics problem as an ocean- and/or waste-focused problem. However, plastics are ubiquitously found in increasing amounts worldwide, including in terrestrial environments and even inside the human body. The authors call for a new international treaty that addresses these concerns through the entire lifecycle of plastics, from the extraction of the raw materials needed for its manufacture to its legacy pollution.
The special issue also includes four Reviews that discuss the rapidly rising global threat that steadily accumulating plastic pollution poses for the environment, the evolutionary and ecological consequences of widespread plastic ingestion by wildlife, how plastics are best understood as emergent geomaterials with unique synthetic chemistries not previously seen in Earth's history, and how innovations in plastic recycling and polymer upcycling could help address our plastics dilemma and usher in the next generation of materials design. In addition, two features from Science's news department explore how enzymes are being used to aid in plastic recycling efforts and the ways in which museum conservationists are trying to preserve the plastic objects in their exhibits.