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    Common, cheap ingredients can break down some ‘forever chemicals’

    There’s a new way to rip apart harmful “forever chemicals,” scientists say.

    Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, are found in nonstick pans, water-repellent fabrics and food packaging and they are pervasive throughout the environment. They’re nicknamed forever chemicals for their ability to stick around and not break down. In part, that’s because PFAS have a super strong bond between their carbon and fluorine atoms (SN: 6/4/19). Now, using a bit of heat and two relatively common compounds, researchers have degraded one major type of forever chemical in the lab, the team reports in the Aug. 19 Science. The work could help pave the way for a process for breaking down certain forever chemicals commercially, for instance by treating wastewater.

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    “The fundamental knowledge of how the materials degrade is the single most important thing coming out of this study,” organic chemist William Dichtel said in an August 16 news conference.

    While some scientists have found relatively simple ways of breaking down select PFAS, most degradation methods require harsh, energy-intensive processes using intense pressure — in some cases over 22 megapascals — or extremely high temperatures — sometimes upwards of 1000⁰ Celsius — to break the chemical bonds (SN: 6/3/22).

    Dichtel, of Northwestern University in Evanston, Ill., and his team experimented with two substances found in nearly every chemistry lab cabinet: sodium hydroxide, also known as lye, and a solvent called dimethyl sulfoxide, or DMSO. The team worked specifically with a group of forever chemicals called PFCAs, which contain carboxylic acid and constitute a large percentage of all PFAS. Some of these kinds of forever chemicals are found in water-resistant clothes.

    When the team combined PFCAs with the lye and DMSO at 120⁰ C and with no extra pressure needed, the carboxylic acid fell off the chemical and became carbon dioxide in a process called decarboxylation. What happened next was unexpected, Dichtel said. Loss of the acid led to a process causing “the entire molecule to fall apart in a cascade of complex reactions.” This cascade involved steps that degraded the rest of the chemical into fluoride ions and smaller carbon-containing products, leaving behind virtually no harmful by-products.     .

    “It’s a neat method, it’s different from other ones that have been tried,” says Chris Sales, an environmental engineer at Drexel University in Philadelphia who was not involved in the study. “The biggest question is, how could this be adapted and scaled up?” Northwestern has filed a provisional patent on behalf of the researchers.

    Understanding this mechanism is just one step in undoing forever chemicals, Dichtel’s team said. And more research is needed: There are other classes of PFAS that require their own solutions. This process wouldn’t work to tackle PFAS out in the environment, because it requires a concentrated amount of the chemicals. But it could one day be used in wastewater treatment plants, where the pollutants could be filtered out of the water, concentrated and then broken down. More

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    Electrical bacteria may help clean oil spills and curb methane emissions

    The small motorboat anchors in the middle of the Chesapeake Bay. Shrieks of wintering birds assault the vessel’s five crew members, all clad in bright orange flotation suits. One of the crew slowly pulls a rope out of the water to retrieve a plastic tube, about the length of a person’s arm and filled with mud from the bottom of the bay. As the tube is hauled on board, the stench of rotten eggs fills the air.

    “Chesapeake Bay mud is stinky,” says Sairah Malkin, a biogeochemist at the University of Maryland Center for Environmental Science in Cambridge who is aboard the boat. The smell comes from sulfuric chemicals called sulfides within the mud. They’re quite toxic, Malkin explains.

    Malkin and her team venture out onto the bay every couple of months to sample the foul muck and track the abundance of squiggling mud dwellers called cable bacteria. The microbes are living wires: Their threadlike bodies — thinner than a human hair — can channel electricity.

    Sairah Malkin, of the University of Maryland Center for Environmental Science, cuts holes in a large sediment coring tube to sample mud collected from the bottom of the Chesapeake Bay.Clara Fuchsman

    Cable bacteria use that power to chemically rewire their surroundings. While some microbes in the area produce sulfides, the cable bacteria remove those chemicals and help prevent them from moving up into the water column. By managing sulfides, cable bacteria may protect fish, crustaceans and other aquatic organisms from a “toxic nightmare,” says Filip Meysman, a biogeochemist at the University of Antwerp in Belgium. “They’re kind of like guardian angels in these coastal ecosystems.”

    Now, scientists are studying how these living electrical filaments might do good in other ways. Laboratory experiments show that cable bacteria can support other microbes that consume crude oil, so researchers are investigating how to encourage the bacteria’s growth to help clean up oil spills. What’s more, researchers have shown that cable bacteria could help slash emissions of a potent greenhouse gas — methane — into the atmosphere.

    There’s plenty of evidence that cable bacteria exert a strong influence over their microbial neighbors, Meysman says. The next step, he says, is to figure out how to channel that influence for the greater good.

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    Electric life

    Under the microscope, cable bacteria resemble long sausage links. Their multicellular bodies can grow up to 5 centimeters long. Embedded in the envelope of each cell are parallel “wires” of conductive proteins, which the bacteria use to channel electrons. According to Meysman, the wires are more conductive than the semi­conductors found in electronics.

    About a decade ago, a team of scientists first discovered cable bacteria, in sediment collected from the bottom of Denmark’s Aarhus Bay. Since then, cable bacteria have been found on at least four continents, in streams, lakes, estuaries and coastal environments. “Name me a country, and I’ll show you where the cable bacteria are,” Meysman says.

    Most often, cable bacteria nestle shallow in the sediment, with one end positioned near the surface where there is oxygen and the other end plugged into deeper, sulfide-rich zones. Using their filamentous bodies as electrical conduits, cable bacteria snatch electrons from sulfides on one end and off-load them to oxygen — an eager electron acceptor — at the other, says Nicole Geerlings, a biogeochemist at Utrecht University in the Netherlands. Similar to how batteries charge and release energy by transferring electrons between an anode and cathode, cable bacteria power themselves by channeling electrons, she says. “The electron transport gives [cable bacteria] energy.”

    This unique lifestyle allows cable bacteria to survive in an environment that many organisms could not endure.

    A cable bacterium (right) has a multicellular, segmented body that can grow up to 5 centimeters. Electrically conductive, parallel fibers (visible in the close-up at left) encase the body.From left: N. Geerlings/Utrecht Univ.; Silvia Hidalgo Martinez/Univ. of Antwerp

    Toxic fire wall

    In 2015, Malkin, Meysman and colleagues reported that cable bacteria may help to counteract the onset of euxinia — a fatal buildup of sulfides in oxygen-starved bodies of water. Euxinia can trigger mass die-offs of fish, crustaceans and other aquatic life.

    The lethal phenomenon can occur after fertilizers or sewage are washed into the sea or lakes. That flow of nutrients can trigger algal blooms. When those nutrients are depleted, the blooms die, and large quantities of organic matter sink and accumulate on the sediment. Microbes then decompose the dead material, devouring much of the oxygen in the surrounding water in the process. When oxygen levels become critically low, sulfides may begin to leak from the sediment into the water, giving rise to euxinia.

    Sediments near the bottom of this core sample, taken from the Chesapeake Bay, are probably dark due to the presence of sulfides, while sediments near the top are lighter because cable bacteria have removed the sulfides.S. Malkin

    While studying cable bacteria in a brackish body of water in the Netherlands, Malkin and colleagues discovered a thin layer of rust coating the lake’s bottom. As the cable bacteria pulled electrons from sulfides, converting the noxious chemicals into less-harmful sulfates, the water within the sediment became more acidic, which dissolved some minerals containing iron. The now-mobile iron percolated upward in the sediment, until it interacted with oxygen to form rust.

    This layer of rust could capture sulfides that would otherwise flow into the water, acting as a “fire wall” that could delay euxinia for over a month, or even prevent it altogether, the researchers reported. Even when the cable bacteria’s population dropped, the rust layer persisted, protecting other aquatic creatures from sulfide exposure. The rust may explain why even though instances of nutrient pollution, algal blooms and oxygen depletion are relatively common, reports of euxinia are rare.

    Oil cleanup

    Some researchers are trying to harness the bacteria’s electrical abilities to tackle another devastating threat to coastal ecosystems — oil spills.

    When an oil spill happens in a body of water, booms, skimmers or sorbents are often deployed to limit the spread of hydrocarbons on the surface. But oil may also wash onto beaches, mix with sediments in shallow waters and aggregate onto sinking particles of organic debris, hitching a ride to the seafloor.

    Cleaning up oil at the bottom of the sea is a difficult job, says Ugo Marzocchi, a biogeochemist at Aarhus University in Denmark. “I am not aware of a very effective way to remove hydrocarbons from the seafloor,” he says. “In inland freshwater systems, what is generally done is to dig out the sediments,” he says, an expensive strategy that would be even more costly at sea.

    [embedded content]
    Electrical cable bacteria (white filaments) emerge from the seafloor sediment (at bottom) stretching their bodies to reach a zone of oxygen in the water. The stringy organisms use the oxygen to offload electrons they’ve harvested from harmful sulfides found in the sediment. As sulfide concentrations go down, the water becomes more habitable to microbes that can clean up oil spills.

    Some soil-dwelling microorganisms can use hydrocarbons to fuel their metabolism, and researchers have been studying how some of these oil burners might assist in the cleanup of contaminated sediments. But as they break down hydrocarbons, the microbes generate those concerning sulfides, which are detrimental to the microbes’ own survival, Marzocchi says. In other words, the microbes can help clean up the oil for only so long before they’re overwhelmed by their own toxic waste.

    Cable bacteria might be just the solution, Marzocchi thought. In 2016, researchers reported finding evidence of the electrical microbes in a tar oil-contaminated groundwater aquifer in Germany. Knowing that cable bacteria could occupy sediments contaminated with hydrocarbons, Marzocchi and colleagues reasoned that these bacteria might be able to assist oil-burning microbes and accelerate oil cleanup.

    The researchers filled several containers with oil-contaminated sediment from Aarhus Bay — which contained naturally occurring oil-eating bacteria. The group then injected a few containers with cable bacteria and monitored the degree of hydrocarbon degradation in all of the containers over seven weeks. By the end of the test, the concentration of alkanes — a type of hydrocarbon — in the sediment with cable bacteria had dropped from 0.125 milligrams per gram of sediment to 0.086 milligrams per gram — a 31 percent drop. That’s 23 percentage points more than the 9 percent decrease in the control samples. Cable bacteria helped accelerate the metabolic activity of their oil-eating neighbors by converting the toxic sulfides into sulfates. The sulfates didn’t harm the oil-eating microbes — in fact, they used the chemicals as fuel.

    The researchers are now trying to develop methods to promote cable bacteria growth in the field and see if it’s possible to enhance their effect on oil degradation. One catch is that in oil-contaminated sediment, oxygen is quickly used up by the microbes that break down hydrocarbons. That’s a problem since cable bacteria need access to oxygen. Salts that slowly release oxygen or nitrate — which cable bacteria can use in place of oxygen — might help spur the electrical organisms’ growth at oil spills. But more work is needed to identify the right chemical components and dosage, Marzocchi says.

    Meanwhile, scientists are investigating how cable bacteria might help reduce emission of another hydrocarbon — one that accumulates in the sky.

    Methane at the root

    Colorless, odorless methane is the simplest hydrocarbon (SN: 8/15/20, p. 8). It consists of a single carbon atom attached to a quartet of hydrogen atoms. And it’s a potent greenhouse gas — more than 25 times as effective at trapping heat in the atmosphere as carbon dioxide.

    One major source of methane is rice paddies (SN: 9/25/21, p. 16). During the growing season, rice farmers typically flood their fields to help stave off weeds and pests. Methane-producing microbes — aptly named methanogens — thrive in these waterlogged soils. Paddy-dwelling methanogens are so prolific that rice fields are estimated to generate about 11 percent of all human-induced methane emissions.

    But cable bacteria like paddies too. In 2019, Vincent Scholz, a microbiologist at Aarhus University, and colleagues reported that cable bacteria could flourish among the roots of rice plants and several other aquatic plant species.

    In an experiment, pots of rice plants grown in soils with cable bacteria (right) developed orange layers of rust and emitted less methane than pots without cable bacteria (left).V.V. Scholz/Aarhus Univ.

    That discovery inspired the researchers to investigate how the bacteria interact with methanogens in soils that grow rice. The team grew its own rice plants — some potted in soils with cable bacteria, and some without — and monitored methane emissions.

    To the researchers’ surprise, adding cable bacteria reduced rice soil methane emissions by 93 percent. In the process of removing electrons from sulfides, the bacteria generate sulfates, which other microbes can use as fuel. These sulfate-consuming microbes outcompeted methanogens for nutrients such as hydrogen and acetate in the rice soils, the researchers found. The results were “quite amazing,” Scholz says, though the effectiveness of the electrical microbes in real rice fields has yet to be tested.

    There are signs that cable bacteria are already plugged into real rice paddy soils. After analyzing genetic data collected from rice paddies in the United States, India, Vietnam and China, Scholz and colleagues reported in 2021 the presence of cable bacteria at sites in all four countries. Scholz is in Northern California this summer studying how cable bacteria live in rice fields and whether they’re already impacting methane emissions. He is also exploring ways to introduce cable bacteria to rice fields where they don’t yet exist or enhance the microbes’ numbers in fields where they do.

    There is still much to discover about how the wispy electrical conductors influence our world, Malkin says. Back in the Chesapeake Bay, she and colleagues have found that cable bacteria tend to flourish in the spring, a surge that has also been observed in the Netherlands. The findings add to a growing body of work that suggests cable bacteria are opportunistic organisms that interact with their environments in similar ways all around the world.

    If cable bacteria are already hard at work across the planet, then a bit of coaxing from researchers may be all it takes to turn the mud-dwelling creatures into the most helpful neighbors that a living thing could ask for. More

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    How to make jet fuel from sunlight, air and water vapor

    Jet fuel can now be siphoned from the air.

    Or at least that’s the case in Móstoles, Spain, where researchers demonstrated that an outdoor system could produce kerosene, used as jet fuel, with three simple ingredients: sunlight, carbon dioxide and water vapor. Solar kerosene could replace petroleum-derived jet fuel in aviation and help stabilize greenhouse gas emissions, the researchers report in the July 20 Joule.

    Burning solar-derived kerosene releases carbon dioxide, but only as much as is used to make it, says Aldo Steinfeld, an engineer at ETH Zurich. “That makes the fuel carbon neutral, especially if we use carbon dioxide captured directly from the air.”

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    Kerosene is the fuel of choice for aviation, a sector responsible for around 5 percent of human-caused greenhouse gas emissions. Finding sustainable alternatives has proven difficult, especially for long-distance aviation, because kerosene is packed with so much energy, says chemical physicist Ellen Stechel of Arizona State University in Tempe who was not involved in the study.

    In 2015, Steinfeld and his colleagues synthesized solar kerosene in the laboratory, but no one had produced the fuel entirely in a single system in the field. So Steinfeld and his team positioned 169 sun-tracking mirrors to reflect and focus radiation equivalent to about 2,500 suns into a solar reactor atop a 15-meter-tall tower. The reactor has a window to let the light in, ports that supply carbon dioxide and water vapor as well as a material used to catalyze chemical reactions called porous ceria.

    Within the solar reactor, porous ceria (shown) gets heated by sunlight and reacts with carbon dioxide and water vapor to produce syngas, a mixture of hydrogen gas and carbon monoxide.ETH Zurich

    When heated with solar radiation, the ceria reacts with carbon dioxide and water vapor in the reactor to produce syngas — a mixture of hydrogen gas and carbon monoxide. The syngas is then piped to the tower’s base where a machine converts it into kerosene and other hydrocarbons.

    Over nine days of operation, the researchers found that the tower converted about 4 percent of the used solar energy into roughly 5,191 liters of syngas, which was used to synthesize both kerosene and diesel. This proof-of-principle setup produced about a liter of kerosene a day, Steinfeld says.

    “It’s a major milestone,” Stechel says, though the efficiency needs to be improved for the technology to be useful to industry. For context, a Boeing 747 passenger jet burns around 19,000 liters of fuel during takeoff and the ascent to cruising altitude. Recovering heat unused by the system and improving the ceria’s heat absorption could boost the tower’s efficiency to more than 20 percent, making it economically practical, the researchers say. More

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    Underground heat pollution could be tapped to mitigate climate change

    The secret to efficiently heating some buildings might lurk beneath our feet, in the heat that humans have inadvertently stored underground. 

    Just as cities warm the surrounding air, giving rise to urban heat islands, so too does human infrastructure warm the underlying earth (SN: 3/27/09). Now, an analysis of groundwater well sites across Europe and parts of North America and Australia reveals that roughly a couple thousand of those locations possess excess underground heat that could be recycled to warm buildings for a year, researchers report July 8 in Nature Communications.

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    What’s more, even if humans managed to remove all this accumulated thermal pollution, existing infrastructure at about a quarter of the locations would continue to warm the ground enough that heat could be harvested for many years to come. That could reduce reliance on fossil fuels, and help mitigate climate change.

    This work showcases the impact that underground heat recycling could have if harnessed on a large scale, says hydrogeologist Grant Ferguson of the University of Saskatchewan in Saskatoon, Canada, who was not involved in the study. “There’s a lot of untapped potential out there.”

    Heat leaks into the subsurface from the warm roots of structures such as buildings, parking garages and tunnels, and from artificial surfaces such as asphalt, which absorb solar radiation. In Lyon, France, for example, researchers in 2016 found that human infrastructure warmed groundwater by more than 4 degrees Celsius.

    Scientists don’t fully understand how heat pollution alters underground environments. But warming of the subsurface can cause contaminants, such as arsenic, to move through groundwater more readily.

    Extracting the thermal pollution could be accomplished by piping groundwater to heat pumps at the surface. The water, warmed underground by all that trapped heat, could then warm buildings as it releases heat into their cooler interiors, says Susanne Benz, an environmental scientist at Dalhousie University in Halifax, Canada.

    Harnessing underground heat in this way could provide some communities with a reliable and low-energy means to warm their homes, Benz says. “And if we don’t use it, it will just continue to accumulate,” she says.

    Benz and her colleagues analyzed the population size, heating demand and groundwater temperature at more than 6,000 locations, most of which were in Europe. The researchers found that at about 43 percent of the locations — mostly those near highly populated areas — enough heat had accumulated in the top 20 meters of earth to satisfy a year’s worth of the local heating demand.

    Curious about sustainability, the researchers also identified places where the continuous flow of heat into the underground — and not just the stockpiled thermal pollution — was high. Their calculations show that if all of the accumulated heat was first extracted, the heat that continued leaking from existing infrastructure could be harvested at about 25 percent of the 6,000 locations. At 18 percent of locations, this recycled heat could satisfy at least a quarter of the heating demand of the local population.

    Constructing systems to take advantage of human heat pollution today could one day help residents harvest heat from climate change, the researchers say.

    Using climate projections for the end of the century, the team probed the feasibility of extracting underground heat in a warmer world. In the most optimistic warming scenario considered, which assumes greenhouse gas emissions peak about the year 2040, the researchers found that climate change would warm the ground enough by the end of the century that underground heat recycling at 81 percent of the studied locations could meet more than a quarter of locals’ heating demands. If there are no efforts to curb emissions, that number rises to 99 percent of locations.

    Though the researchers focused mostly on Europe, Benz says that other continents probably also possess abundant underground heat that could be harnessed. In Europe and elsewhere, heat recycling might be most feasible in suburban areas, she says, where there is sufficient accumulated underground heat to help meet local heating demands, and space to install heat recycling systems.

    Looking ahead, Benz plans to investigate whether cooling the subsurface can help reduce aboveground temperatures in urban environments. “This might actually be a little additional tool to control [aboveground] urban heat.” More

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    Flower shape and size impact bees’ chances of catching gut parasites

    Bees that land on short, wide flowers can fly away with an upset stomach.  

    Common eastern bumblebees (Bombus impatiens) are more likely to catch a diarrhea-inducing gut parasite from purple coneflowers, black-eyed Susans and other similarly shaped flora than other flowers, researchers report in the July Ecology. Because parasites and diseases contribute to bee decline, the finding could help researchers create seed mixes that are more bee-friendly and inform gardeners’ and land managers’ decisions about which flower types to plant.

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    The parasite (Crithidia bombi) is transmitted when the insects accidentally ingest contaminated bee feces, which “tends to make the bees dopey and lethargic,” says Rebecca Irwin, a community and evolutionary ecologist at North Carolina State University in Raleigh. “It isn’t the number one bee killer out there,” but bees sickened with it can struggle with foraging.    

    In laboratory experiments involving caged bees and 16 plant species, Irwin and her colleagues studied how different floral attributes affected transmission of the gut parasite. They focused on three factors of transmission: the amount of poop landing on flowers when bees fly and forage, how long the parasite survives on the plants and how easily the parasite is transmitted to new bees. Multiplied together, these three factors show the overall transmission rate.

    Compared with plants with long, narrow flowers like phlox and bluebeards, short, wide flowers had more feces land on them and transmitted the parasite more easily to the pollinators, increasing the overall parasite transmission rate for these flowers. However, parasite survival times were reduced on these blooms. This is probably due to the open floral shapes increased exposure to ultraviolet light, speeding the drying out of parasite-laden “fecal droplets,” Irwin says.

    The findings confirm a new theory suggesting that traits, such as flower shape, are better predictors of disease transmission than individual species of plants, says Scott McArt, an entomologist focusing on pollinator health at Cornell University who wasn’t involved with the study. Therefore, “you don’t need to know everything about every plant species when designing your pollinator-friendly garden or habitat restoration project.”

    Instead, to limit disease transmission among bees, it’s best to choose plants that have narrower, longer flowers, he says. “Wider and shorter flowers are analogous to the small, poorly ventilated rooms where COVID is efficiently transmitted among humans.”  

    If ripping out coneflowers or black-eyed Susans isn’t palatable, don’t fret. Irwin recommends continuing to plant a diversity of flower types. This helps if one type of flower is “a high transmitting species,” she notes. In the future, she plans to conduct field experiments examining other factors that could influence parasite transmission, such as whether bees are driven to visit certain types of flowers more often in nature.   More

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    How to build better ice towers for drinking water and irrigation

    There’s a better way to build a glacier.

    During winter in India’s mountainous Ladakh region, some farmers use pipes and sprinklers to construct building-sized cones of ice. These towering, humanmade glaciers, called ice stupas, slowly release water as they melt during the dry spring months for communities to drink or irrigate crops. But the pipes often freeze when conditions get too cold, stifling construction.

    Now, preliminary results show that an automated system can erect an ice stupa while avoiding frozen pipes, using local weather data to control when and how much water is spouted. What’s more, the new system uses roughly a tenth the amount of water that the conventional method uses, researchers reported June 23 at the Frontiers in Hydrology meeting in San Juan, Puerto Rico.

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    “This is one of the technological steps forward that we need to get this innovative idea to the point where it’s realistic as a solution,” says glaciologist Duncan Quincey of the University of Leeds in England who was not involved in the research. Automation could help communities build larger, longer-lasting ice stupas that provide more water during dry periods, he says.

    Ice stupas emerged in 2014 as a means for communities to cope with shrinking alpine glaciers due to human-caused climate change (SN: 5/29/19). Typically, high-mountain communities in India, Kyrgyzstan and Chile pipe glacial meltwater into gravity-driven fountains that sprinkle continuously in the winter. Cold air freezes the drizzle, creating frozen cones that can store millions of liters of water.

    The process is simple, though inefficient. More than 70 percent of the spouted water may flow away instead of freezing, says glaciologist Suryanarayanan Balasubramanian of the University of Fribourg in Switzerland.

    So Balasubramanian and his team outfitted an ice stupa’s fountain with a computer that automatically adjusted the spout’s flow rate based on local temperatures, humidity and wind speed. Then the scientists tested the system by building two ice stupas in Guttannen, Switzerland — one using a continuously spraying fountain and one using the automated system.

    After four months, the team found that the continuously sprinkling fountain had spouted about 1,100 cubic meters of water and amassed 53 cubic meters of ice, with pipes freezing once. The automated system sprayed only around 150 cubic meters of water but formed 61 cubic meters of ice, without any frozen pipes.

    The researchers are now trying to simplify their prototype to make it more affordable for high-mountain communities around the world. “We eventually want to reduce the cost so that it is within two months of salary of the farmers in Ladakh,” Balasubramanian says. “Around $200 to $400.” More

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    Earth’s oldest known wildfires raged 430 million years ago

    Bits of charcoal entombed in ancient rocks unearthed in Wales and Poland push back the earliest evidence for wildfires to around 430 million years ago. Besides breaking the previous record by about 10 million years, the finds help pin down how much oxygen was in Earth’s atmosphere at the time.

    The ancient atmosphere must have contained at least 16 percent oxygen, researchers report June 13 in Geology. That conclusion is based on modern-day lab tests that show how much oxygen it takes for a wildfire to take hold and spread.

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    While oxygen makes up 21 percent of our air today, over the last 600 million years or so, oxygen levels in Earth’s atmosphere have fluctuated between 13 percent and 30 percent (SN: 12/13/05). Long-term models simulating past oxygen concentrations are based on processes such as the burial of coal swamps, mountain building, erosion and the chemical changes associated with them. But those models, some of which predict lower oxygen levels as low as 10 percent for this time period, provide broad-brush strokes of trends and may not capture brief spikes and dips, say Ian Glasspool and Robert Gastaldo, both paleobotanists at Colby College in Waterville, Maine.

    Charcoal, a remnant of wildfire, is physical evidence that provides, at the least, a minimum threshold for oxygen concentrations. That’s because oxygen is one of three ingredients needed to create a wildfire. The second, ignition, came from lightning in the ancient world, says Glasspool. The third, fuel, came from burgeoning plants and fungus 430 million years ago, during the Silurian Period. The predominant greenery were low-growing plants just a couple of centimeters tall. Scattered among this diminutive ground cover were occasional knee-high to waist-high plants and Prototaxites fungi that towered up to nine meters tall. Before this time, most plants were single-celled and lived in the seas.

    Once plants left the ocean and began to thrive, wildfire followed. “Almost as soon as we have evidence of plants on land, we have evidence of wildfire,” says Glasspool.

    That evidence includes tiny chunks of partially charred plants — including charcoal as identified by its microstructure — as well as conglomerations of charcoal and associated minerals embedded within fossilized hunks of Prototaxites fungi. Those samples came from rocks of known ages that formed from sediments dumped just offshore of ancient landmasses. This wildfire debris was carried offshore in streams or rivers before it settled, accumulated and was preserved, the researchers suggest.

    The microstructure of this fossilized and partially charred bit of plant unearthed in Poland from sediments that are almost 425 million years old reveals that it was burnt by some of Earth’s earliest known wildfires.Ian Glasspool/Colby College

    The discovery adds to previous evidence, including analyses of pockets of fluid trapped in halite minerals formed during the Silurian, that suggests that atmospheric oxygen during that time approached or even exceeded the 21 percent concentration seen today, the pair note.

    “The team has good evidence for charring,” says Lee Kump, a biogeochemist at Penn State who wasn’t involved in the new study. Although its evidence points to higher oxygen levels than some models suggest for that time, it’s possible that oxygen was a substantial component of the atmosphere even earlier than the Silurian, he says.

    “We can’t rule out that oxygen levels weren’t higher even further back,” says Kump. “It could be that plants from that era weren’t amenable to leaving a charcoal record.” More

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    Corals may store a surprising amount of microplastics in their skeletons

    A surprising amount of plastic pollution in the ocean may wind up in a previously overlooked spot: the skeletons of living corals. 

    Up to about 20,000 metric tons of tiny fragments called microplastics may be stored in coral skeletons worldwide every year, says ecologist Jessica Reichert of Justus Liebig University Giessen in Germany. That corresponds to nearly 3 percent of the microplastics estimated to be in the shallow, tropical waters where corals thrive.

    Corals have been observed eating or otherwise incorporating microplastics into their bodies (SNS: 3/18/15). But scientists don’t know how much of the debris reefs take up globally. So Reichert and colleagues exposed corals in the lab to microplastics to find out where the particles are stored inside corals and estimate how much is tucked away.

    Corals consumed some of the trash, or grew their skeletons over particles. After 18 months, most of the debris inside corals was in their skeletons rather than tissues, the researchers report October 28 in Global Change Biology. After counting the number of trapped particles, the researchers estimate that between nearly 6 billion and 7 quadrillion microplastic particles may be permanently stored in corals worldwide annually.

    Tiny plastic particles (black spots in this image of coral that has had its tissue removed) end up trapped in coral skeletons when corals grow over the fragments or ingest them.J. Reichert

    It’s the first time that a living microplastic “sink,” or long-term storage site, has been quantified, Reichert says.

    Scientists are learning how much microplastic is being introduced to the oceans. But researchers don’t know where it all ends up (SN: 6/6/19). Other known microplastic sinks, such as sea ice and seafloor sediments, need better quantification, and other sinks may not yet be known.

    Reefs are typically found near coasts where polluted waterways can drain to the sea, placing corals in potential microplastic hot spots.

    “We don’t know what consequences this [storage] might have for the coral organisms, [or for] reef stability and integrity,” Reichert says. It “might pose an additional threat to coral reefs worldwide.”  

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