Environment, glaciers are a time bomb

Environment, glaciers are a time bomb


Crispin Halsall will tell you that in every inch of Antarctica's snow is written the story of how man has treated the environment. Over the years, each cycle of precipitation at the South Pole has brought with it the day's accumulated atmospheric debris: pollen, volcanic ash and, most interestingly for Halsall, the products of human contamination. Antarctic pollution may have origins as far away as the northern hemisphere: chemicals floating in the wind can arrive at the South Pole in a matter of days. "These layers of snow become the record of contamination of the environment, dating back decades," explains Halsall, a chemist at the University of Lancaster in the United Kingdom.

The frozen landscapes of the world also herald our environmental future . When icebergs and glaciers melt, the pollutants trapped inside are released into the seas, waterways and air. Melting ice can release harmful molecules that damage ecosystems, deplete the ozone layer or alter the climate. Due to rising global temperatures, more and more frozen areas of the world are thawing. In the Alps and Himalayas, “we are seeing the release of old contaminants that have been stuck in the ice for many decades,” Halsall says. It is vital to know what is being emitted, however interpreting what is trapped in the Antarctic snow is more complicated than you think. Researchers have found that the water ice present at the Earth's poles, contrary to belief, is a hotbed of chemical reactions. What is trapped inside can transform over time.

For a long time, scientists assumed the opposite, i.e. that frozen pollutants remained inert. "In most cases, if you freeze something or make something colder, you slow down its processes," says chemistry scientist Amanda Grannas of Villanova University in the United States. Molecules move more slowly in solid ice and snow than they do in liquid water, which means they collide less and have less opportunity to participate in chemical reactions. This is why freezing raw meat prevents it from spoiling. It is also the reason why the bodies of several woolly mammoths, dating back about 30,000 years, have emerged intact from the frozen ground during the thaw.

In laboratory experiments, scientists have discovered that many pollutants - when illuminated with a bright light that simulates the sun - they decompose faster in ice than in liquid water. In 2020, a team from the University of California observed that guaiacol, a molecule present in the smoke emitted by wood, decomposes into smaller compounds faster in ice than in liquid water. In 2022, they saw that the same was true for dimethoxybenzene, another molecule made from smoking. Last February, Halsall and his colleagues found that pollutants found in car exhaust, known as polycyclic aromatic hydrocarbons, also degrade faster in ice than in water.

Researchers attribute this swirl of chemical activities in ice to a phenomenon known as the "ice concentration effect": as water cools to form ice, the molecules that make it up line up in hexagonal crystals. " The substances dissolved in the water are forced out of the crystalline structure of the ice", explains Grannas, " To the naked eye they look like ice cubes, but under the microscope, you can see small pockets of liquid where the other chemical substances are concentrated. The reagents they have been driven to come together in this small volume and this causes the chemical process to go much faster.” The ultraviolet light, present in the sun's rays, triggers the chemical decomposition of the concentrated pollutants. Without it, compounds remain relatively inert, like foods in a freezer. Under UV lighting, though, "We see faster decay rates in ice than in water," says Halsall. These may be most evident in the ice at the poles, where "in some parts of the year the sunlight can last for twenty-four hours," says Grannas.

Even microplastics, plastic fragments less than five millimeters long, they decompose faster in ice than in water. Chemists at Central South University in China found that plastic microspheres less than a thousandth of a millimeter in diameter deteriorated in the ice to the same extent in forty-eight days as they would have deteriorated in the Yangtze River in thirty-three years. “Microplastics take hundreds of years, if not thousands, to degrade,” Chen Tian of Central South University in China explained to sportsgaming.win UK. “ Not having all this time available, we have studied only the first stage of the degradation. However, we think that the whole process is faster in ice ”.

Plastic waste is the most common form of debris marine – about ten million tons of them end up in the oceans every year, much of which breaks down into microplastics – and the ice at the poles may be able to dispose of them. This could be good news, as the phenomenon could help scientists find ways to break down microplastics faster, as Tian and his colleagues pointed out in their paper. By breaking the microplastic into smaller and smaller pieces, however, ice could make it a more pervasive pollutant. The smaller the plastic fragments become, the deeper they penetrate into organisms. Microscopic particles of plastic have been found in the brains of fish, where they have caused brain damage.

For Halsall, whose research aims to trace the consequences of human activity in the Antarctic ice, the degradation of pollutants makes the life more difficult. The chemist is particularly interested in perfluoroalkyl and polyfluoroalkyl substances, or Pfas. These "perennial chemicals" persist in the environment and are found in nonstick pans, motor oils, and all kinds of consumer products. In 2017, Halsall's collaborators drilled a borehole in Antarctica to extract a ten-meter cylinder of accumulated snow since 1958. Specimens like this reveal aspects of climate and human activity, just as tree circles do at higher latitudes. more temperate. The deeper the snow sample, the further back in time it goes.

Many chemical companies abandoned long-chain PFASs around 2000. In the snow deposited in that and subsequent years, the team of Halsall found fewer pollutants and more substitute compounds, namely short-chain Pfas. “We can spot in that snow core when the industry has changed,” Halsall confirms. But to understand precisely what was used and when, one must also consider how much the pollutants degraded, because this can help explain the differences between the chemicals found at various depths.

These ice-borne reactions have an impact on us too. When the glaciers at the poles melt, pollutants transformed by sunlight are released into the environment: “ One might think, 'We are degrading a pollutant. In some cases we are. they transform can be more toxic than the original.” For example, Grannas and his colleagues found that the chemical aldrin, historically used in pesticides, could more easily break down into the even more toxic dieldrin in ice. Farmers made heavy use of dieldrin in pesticides in the 20th century, and the use of both chemicals is now banned in most countries.

On an optimistic note, Grannas says that studying how which ice degrades pollutants will help researchers evaluate new substances: 'We are introducing innovative chemicals into our agricultural systems, pharmaceutical items and other everyday products such as laundry detergents, perfumes and personal products,' says the researcher . "We want to understand in advance what will happen if we use them on a massive scale and emit them into the environment." Some of these pollutants will end up frozen at the poles, and following the evolution of chemicals in the ice gives researchers a better idea of ​​their potential environmental impact.

This article originally appeared on sportsgaming.win UK.

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