REHOVOT, ISRAEL—December 23, 2020—As the plastics in our oceans break up into smaller and smaller bits without breaking down chemically, the resulting microplastics are becoming a serious ecological problem. A new study by the Weizmann Institute of Science, published in Nature Communications, reveals another troubling aspect of microplastics (defined as particles smaller than 5 mm across): they are swept up into the atmosphere and carried on the wind to far-flung parts of the ocean, including those that appear to be plastic-free. Analysis reveals that such minuscule fragments can stay airborne for hours or days, spreading the potential to harm the marine environment and, by climbing up the food chain, to affect human health.
“A handful of studies have found microplastics in the atmosphere right above the water near shorelines,” says Dr. Miri Trainic, who is in the groups of Prof. Ilan Koren of the Department of Earth and Planetary Sciences and Prof. Assaf Vardi of the Department of Plant and Environmental Sciences. “But we were surprised to find a non-trivial amount above seemingly pristine water,” she adds.
Prof. Koren, Prof. Vardi, and Prof. Yinon Rudich of the Department of Earth and Planetary Sciences have been collaborating for a number of years on studies designed to understand the interface between ocean and air. While the way in which oceans absorb materials from the atmosphere has been well studied, the opposite-direction’s process – aerosolization, in which volatiles, viruses, algal fragments, and other particles move from seawater into the atmosphere – has been much less investigated.
As part of this ongoing effort to do so, aerosol samples were collected for study in the Weizmann labs during the 2016 run of the Tara research vessel, a schooner on which international research teams come together to study the effects of climate change, primarily on marine biodiversity. To collect their samples, the Weizmann team affixed the inlet of their measuring equipment to the top of one of Tara’s masts (so as to avoid any aerosols produced by the schooner itself), with Dr. J. Michel Flores, of Prof. Koren’s group, joining the mission to oversee the collecting as the schooner sailed across the North Atlantic Ocean.
Identifying and quantifying the microplastic bits trapped in the aerosol samples was challenging, as the particles turned out to be hard to identify under the microscope. To understand exactly which types of plastic were getting into the atmosphere, the team worked with Dr. Iddo Pinkas of the Institute’s Chemical Research Support group to conduct Raman spectroscopy and determine the particles’ chemical makeup and size. The researchers detected high levels of common plastics – polystyrene, polyethylene, polypropylene, and more – in their samples. Next, by calculating the shape and mass of the microplastic particles, along with the average wind directions and speeds over the oceans, the team showed that the source of these microplastics was most likely the plastic bags and other plastic waste that had been discarded near the shore and made its way into the ocean hundreds of kilometers away.
Checking the seawater beneath the sample sites showed the same types of plastic as in the aerosols, providing support for the idea that microplastics enter the atmosphere through bubbles on the ocean surface or by being picked up by winds, and are transported on air currents to remote parts of the ocean.
“Once microplastics are in the atmosphere, they dry out, and they are exposed to UV light and atmospheric components with which they interact chemically,” says Dr. Trainic. “That means the particles that fall back into the ocean are likely to be even more harmful or toxic than before to any marine life that ingests them.”
“On top of that,” adds Prof. Vardi, “some of these plastics become scaffolds for bacterial growth for all kinds of marine bacteria, so airborne plastic could be offering a free ride to some species, including pathogenic bacteria that are harmful to marine life and humans.”
“The real amount of microplastic in the ocean aerosols is almost certainly greater than what our measurements showed, because our setup was unable to detect those particles below a few micrometers in size,” Dr. Trainic says. “For example, in addition to plastics that break down into even smaller pieces, there are the nanoparticles that are added to cosmetics and which are easily washed into the ocean, or are formed in the ocean through microplastic fragmentation.”
The size of plastic particles matters, and not only because lighter ones may stay airborne for longer periods. When they do land on the water’s surface, they are more likely to be eaten by equally small marine life, which, of course, cannot digest them. Thus, every one of these particles has the potential to harm a marine organism or to work its way up the food chain and into our bodies.
“Last, but not least, like all aerosols, microplastics become part of the large planetary cycles – for example, carbon and oxygen – as they interact with other parts of the atmosphere,” says Prof. Koren.
“Because they are both lightweight and long-lived, we will be seeing more microplastics transported in the air as the plastics that are already polluting our oceans break up – even if we do not add any further plastics to our waterways,” he adds.
Prof. Ilan Koren’s research is supported by the de Botton Center for Marine Science, which he heads; the Sussman Family Center for the Study of Environmental Sciences, which he heads; the Dr. Scholl Foundation Center for Water and Climate Research, which he heads; Scott Eric Jordan; the Yotam Project; the Estate of Emile Mimran; and the European Research Council.
Prof. Yinon Rudich’s research is supported by the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research, which he heads; the Helen and Martin Kimmel Institute for Magnetic Resonance Research, which he heads; the Nancy and Stephen Grand Research Center for Sensors and Security, which he heads; the Dr. Scholl Foundation Center for Water and Climate Research; the David and Fela Shapell Family Foundation INCPM Fund for Preclinical Studies; the Mary and Tom Beck – Canadian Center for Alternative Energy Research; the Benoziyo Endowment Fund for the Advancement of Science; the de Botton Center for Marine Science; Dana and Yossie Hollander; the Ben B. and Joyce E. Eisenberg Foundation; the Zuckerman STEM Leadership Program; Paul and Tina Gardner; Seed for Peace, Inc; the Estate of Fannie Sherr; the Estate of David Levinson; the Estate of Raymond Lapon; and the Estate of Betty Weneser.
Prof. Assaf Vardi’s research is supported by the Willner Family Leadership Institute for the Weizmann Institute of Science; the de Botton Center for Marine Science; the Bernard and Norton Wolf Family Foundation; Claire and Marc Perlman; Scott Eric Jordan; the Estate of Emile Mimran; and the Estate of Bernard Berkowitz.
Dr. Iddo Pinkas is the incumbent of the Sharon Zuckerman Research Fellow Chair.