Ultraviolet rays in sunlight cause chemical breakdown of concentrated contaminants. Without it, the compound remains relatively inert, like food in a freezer, but under UV irradiation, “we generally find that ice decays faster than water,” he says. Halsall says. These accelerated decay rates could be more pronounced in polar ice, where “at certain parts of the year he can have 24-hour sunlight,” Grannas says. “It drives a lot of chemistry.”
Microplastics, pieces of plastic less than 5 millimeters in length, also degrade faster in ice than in water. A chemist at China’s Central South University found that microplastic beads less than a thousandth of a millimeter in diameter degraded in ice in 48 days to an extent that he degraded in the Yangtze River for more than 33 years. “It takes hundreds, if not thousands of years, for microplastics to decompose,” Chen Tian of Central South University, China, told WIRED in Chinese. “We didn’t have much time, so we only studied the first stages of decomposition. But we think the whole decomposition process should be faster in ice.”
Plastic waste is the most common form of marine litter. About 10 million tonnes of plastic end up in the ocean each year, much of it breaking down into microplastics. This could be good news because it could help scientists find ways to break down microplastics faster, Tian and her colleagues point out in their paper. breaking down into even smaller pieces could also make pollutants more prevalent than ever before. The smaller the plastic debris, the deeper it penetrates into the organism. Tiny plastic particles have been found in fish brains, causing brain damage.
For Halsall, whose research aims to track human activity in Antarctic ice, decomposing pollutants makes life more difficult. He is particularly interested in perfluoroalkyl and polyfluoroalkyl substances (PFAS). These “forever chemicals” remain in the environment and are found in non-stick frying pans, engine oils, and consumer products of all kinds. In 2017, Halsall’s collaborators cut into Antarctica and extracted his 10-meter-long snow column that had accumulated since 1958. Such specimens reveal climate and human activity. The deeper the snow sample, the further back you can go.
Many chemical companies stopped using “long chain” PFAS around 2000. Halsall’s team found less of that contaminant and more of its replacement compounds, ‘short-chain’ PFASs, in snow deposited after that year. “You can find that core of snow when the industry changes,” he says Halsall. But to understand exactly what was being used when, Halsall has to consider how much of the contaminant has decomposed.
These ice-derived reactions also affect the rest of us. “You might say, ‘We’re breaking down pollutants,’ and that’s a good thing,” he says Grannas. “In some cases, yes. But we’ve found that for some contaminants, the product can actually be more toxic than the original.” For example, Grannas and her colleagues They discovered that aldrin, a chemical historically used as an insecticide, can readily transform into dieldrin, a much more toxic chemical, in ice. (Farmers also used dieldrin extensively in pesticides in the 20th century, and the use of both chemicals is banned in most countries.)
More optimistic, Granas says studying how ice breaks down contaminants will help researchers evaluate new substances. “We are introducing new chemicals into agricultural systems, medicines and everyday uses (laundry detergents, air fresheners, personal products),” he says Grannas. “We want to understand in advance what happens when we use this on a large scale and release it into the environment.” By tracking , researchers can better understand potential environmental impacts. At the Earth’s poles, the interior of the ice is a place of upheaval.
