• Copper-based chemicals may be contributi

    From ScienceDaily@1:317/3 to All on Thu Jan 13 21:30:36 2022
    Copper-based chemicals may be contributing to ozone depletion
    Some ozone-destroying chemicals are unaccounted for. Are copper-based fungicides producing them?

    Date:
    January 13, 2022
    Source:
    University of California - Berkeley
    Summary:
    As Earth's ozone layer recovers from past emissions of now-banned
    CFCs and halons, other chemicals are emerging as major causes
    of stratospheric ozone depletion. Atmospheric scientists have
    been searching for the sources of about one-third of the major
    threats, methyl bromide and methyl chloride. New research shows
    that copper-based compounds in common use generate these compounds
    when interacting with soil and seawater, with sunlight boosting
    production by a factor of 10.



    FULL STORY ========================================================================== Copper released into the environment from fungicides, brake pads,
    antifouling paints on boats and other sources may be contributing
    significantly to stratospheric ozone depletion, according to a new study
    from the University of California, Berkeley.


    ==========================================================================
    In a paper appearing this week in the journal Nature Communications,
    UC Berkeley geochemists show that copper in soil and seawater acts as
    a catalyst to turn organic matter into both methyl bromide and methyl
    chloride, two potent halocarbon compounds that destroy ozone. Sunlight
    worsens the situation, boosting production of these methyl halides by
    a factor of 10.

    The findings answer, at least in part, a long-standing mystery about
    the origin of much of the methyl bromide and methyl chloride in the stratosphere. Since the worldwide ban on chlorofluorocarbon (CFC)
    refrigerants and brominated halons used in fire extinguishers starting
    in 1989, these methyl halides have become the new dominant sources
    of ozone-depleting bromine and chlorine in the stratosphere. As the
    long-lived CFCs and halons slowly disappear from the atmosphere, the
    role of methyl halides increases.

    "If we don't know where methyl bromide and methyl chloride are coming
    from, then how can we make sure that those compounds are reduced
    along with CFCs?" said the paper's senior author, Robert Rhew, UC
    Berkeley professor of geography and of environmental science, policy
    and management. "By 2050, we should be back to relatively normal ozone,
    but things like the continued emissions of methyl bromide and methyl
    chloride are road bumps in the road to recovery.

    Copper usage in the environment is projected to increase rapidly in the
    next few years, and this should be considered when predicting future
    halogen load and ozone recovery." Earth's ozone layer is critical to protecting us from cancer-causing ultraviolet light from the sun, but
    chemicals containing chlorine and bromine - - such as CFCs and halons --
    were found in the 1980s to destroy the ozone, creating thinner layers in
    the stratosphere that let in more of the dangerous radiation. Despite
    a ban on production of CFCs and halons, the major sources of halogens,
    the ozone layer has yet to repair itself. Last year, the hole in the
    ozone over Antarctica was about as bad as it's ever been, Rhew said.

    The persistence of the ozone hole is, for the most part, due to the
    persistence of banned ozone-depleting compounds, which take decades to dissipate in the stratosphere. But some ozone-depleting chemicals are
    still being emitted. Even some replacements for banned refrigerants are
    coming under scrutiny.



    ========================================================================== Among the major contributors today are methyl chloride and methyl
    bromide. One atom of bromine is 50 times more destructive to ozone than
    one atom of chlorine.

    Though methyl bromide is banned for use as an agricultural soil fumigant,
    it is still used as a pesticide for quarantine and pre-shipment of
    agricultural products. And methyl chloride is used as a chemical
    feedstock, although most of its emissions are believed to be from
    biomass burning or natural in origin. But the total amount of these
    methyl halides produced each year still do not add up to the observed
    yearly addition of these chemicals to the atmosphere, a fact that has
    puzzled scientists for more than 20 years.

    About one-third of the methyl bromide and methyl chloride in the
    atmosphere comes from unknown sources, Rhew said. The new findings
    suggest that copper is an important, if not the major, source of the
    missing methyl bromide and methyl chloride.

    "We've banned methyl bromide, but are other changes that we're making
    in the environment causing large emissions of this compound into the atmosphere? With the increase in the use of copper, it appears that copper-catalyzed production is an increasing source, as well," Rhew said.

    First author and former UC Berkeley doctoral student Yi Jiao, now a postdoctoral fellow at the University of Copenhagen in Denmark, noted
    that copper compounds are allowed on organic crops, a legacy of its
    use in farming since the 1700s, including as a major antifungal agent
    in the Bourdeax mixture used since the 1880s in France to prevent downy
    mildew on grapes. Copper contamination of soils is a major issue today
    in Europe because of this history. The ozone-depleting power of copper
    is another cause for concern, the authors said.



    ========================================================================== "Please note that organic agriculture is not a major cause for ozone
    depletion.

    However, copper-based fungicides appear to have atmospheric side effects
    that might be considered in terms of overall environmental impact," Jiao tweeted this week. "With widespread use of copper in the environment,
    this potentially growing impact should be considered when predicting
    future halogen load and ozone recovery." Copper + soil + sunlight =
    methyl halides The connection between copper and methyl halides was first revealed through a series of research projects conducted by UC Berkeley undergraduate researchers.

    Rhew asked them to test the impact of metal ions, starting by replicating previously published work on iron in soils. When this produced small
    amounts of methyl halides, Rhew then asked them to investigate a different metal -- copper -- in the form of copper sulfate, one of the most common
    copper compounds used today.

    "We replicated the iron experiment and then thought, 'Let's look at a
    different transition metal, like copper, and see if it has a similar
    effect,'" Rhew said.

    "When we added copper sulfate to soil, it produced a tremendous amount of methyl halides, and this surprised us. And then another undergraduate did
    the experiment with seawater, and that produced an impressive amount of
    methyl halides, as well. So, we knew there was a novel process going on,
    but we only had a few pieces to the puzzle until Yi conducted a suite of creative experiments to put it all together." Jiao and Rhew designed
    more thorough experiments, obtaining soil samples from an agricultural
    research plot called the Oxford Tract located near the UC Berkeley campus
    and subjecting them to various treatments, including different amounts
    of copper and oxidants. While copper alone in soil and seawater produced
    some methyl bromide and methyl chloride, the addition of sunlight and/ or hydrogen peroxide -- which is produced in soil by microbes or sunlight - - generated more than five times the amount of methyl halides and prolonged
    the activity of copper from about a week to between two and three weeks.

    When Yi sterilized the soil, the amount of methyl halide production rose
    even more. On the other hand, after burning off all the organic material,
    soil incubated with copper produced no methyl halides. That led him to
    focus on chemicals -- catechol and guaiacol -- often used as proxies for
    soil organic carbon because they each contain a phenol ring structure,
    like those found in organic matter.

    Adding increasing amounts of either copper sulfate or hydrogen peroxide to catechol-halide solutions increased emissions of methyl halides, as well, whereas emissions were near zero when any of these substrates was missing.

    Subsequently, Yi found that sunlight served a similar function as hydrogen peroxide in boosting methyl halide production. In seawater, exposing
    copper- amended solutions to sunlight increased emissions fourfold.

    The researchers suspect that one common form of copper ion, Cu(II), is oxidizing organic material to liberate methyl radicals, which readily
    combine with chlorine and other halogens in the soil or seawater to
    form methyl halides. Both sunlight and hydrogen peroxide subsequently
    reoxidize the copper -- from its cuprous (I) to cupric (II) state --
    so that it can act again and again to generate more methyl halides.

    "We did a back-of-the-envelope calculation to see the impact copper
    sulfate would have and estimated that it could be responsible for 4.1
    gigagrams of methyl bromide per year, which would be about 10% of the
    missing source," Rhew said. "That's pretty substantial, and that's only
    looking at copper sulfate.

    Maybe even more widely used is another copper compound called copper
    hydroxide.

    So, this is just the beginning of our understanding of what copper's
    impact is on halocarbon chemistry." Jiao noted that this also doesn't
    take into account the potential oceanic emissions associated with copper
    in runoff.

    Rhew said that much more research needs to be done to determine which
    copper compounds are the most potent producers of methyl halides in soil
    and seawater and how much is actually produced.

    "There's plenty of halide in soils, and there's plenty of organic matter
    in soil, so the magic ingredient is copper, which is regenerated by
    sunlight," he said. "This has opened our eyes to a whole new area of
    inquiry regarding the role of copper in the environment." The work was
    funded in part by National Science Foundation (EAR-1530375). Co- authors
    with Rhew and Jiao are former UC Berkeley undergraduates Jae Yun Robin
    Kim and Julien Vollering, former UC Berkeley postdoctoral researcher
    Julian Deventer, and visiting scholar Wanying Zhang from the University
    of Science and Technology of China.

    ========================================================================== Story Source: Materials provided by
    University_of_California_-_Berkeley. Original written by Robert
    Sanders. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Yi Jiao, Wanying Zhang, Jae Yun Robin Kim, Malte Julian Deventer,
    Julien
    Vollering, Robert C. Rhew. Application of copper(II)-based chemicals
    induces CH3Br and CH3Cl emissions from soil and seawater. Nature
    Communications, 2022; 13 (1) DOI: 10.1038/s41467-021-27779-3 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/01/220113151441.htm
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