Landfill detoxifiers: chemical contamination – sciencedaily

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The production of chemicals is a heavy business. Often, only a small part of what is actually demanded is produced in the factory. The important rest is unusable – or worse yet. Examples? The “Agent Orange” defoliant used by the US military during the Vietnam War was hastily produced. It contained dioxin as an impurity. As a result, not only did the trees in the combat zone lose their foliage, but American soldiers and Vietnamese civilians also fell ill with cancer years later.

There are also examples from agriculture: in the production of the insecticide lindane, a hexachlorocyclohexane (HCH), only less than 15 percent of the desired substance is produced; 85 percent of the reaction broth is hazardous waste. In the 1950s, this toxic mixture was still sprayed entirely on fields and orchards. Later, the effective lindane was separated and sold neat, the remainder going to landfill. There the chemicals are often still found today. Lindane has been banned in the EU since 2007 and has not been used in Switzerland for some time.

Flame retardant hexabromocyclodecane (HBCD) is also a mixture of several substances. It was invented in the 1970s, produced at a scale of several 10,000 tonnes per year and used in polystyrene insulation boards for house facades, in textiles and in plastics for electrical appliances. It has been banned worldwide since 2014. In Switzerland, plastic containing HBCD is not recycled, but must be destroyed in waste incineration.

Internationally prohibited

Since 2004, the Stockholm Convention on Persistent Organic Pollutants has regulated the handling of these long-lived environmental toxins. Switzerland ratified the agreement in 2003, but all of these substances are already in the environment – and finely distributed. HBCD is found in sewage sludge, fish, air, water and soil. In 2004, the World Wide Fund for Nature (WWF) took blood samples from eleven European environment ministers and three health ministers and detected HBCD and lindane in the blood of each of them. .

Bacteria, the rescuers of the soil

This begs the question: can we salvage or detoxify chemical waste from past generations? Fortunately, scientists don’t shy away from difficult places in their search for solutions. In 1991, they almost simultaneously discovered three strains of bacteria that could consume lindane and its unnecessary chemical brethren at chemical waste sites in France, Japan, and India: Sphingobium francense, Sphingobium japonicum, and Sphingobium indicum. Could these bio-cleaners also digest the flame retardant HBCD and other toxins?

Empa chemist Norbert Heeb and Eawag microbiologist Hans-Peter Kohler, as well as researchers from the Zurich University of Applied Sciences (ZHAW) and two Indian institutes, put them to the test. They modified the genes of Indian bacteria and produced enzymes that degrade HCH in pure form. An enzyme is a protein molecule, a biocatalyst so to speak, with which bacteria, but also other living cells, can build or break down chemicals. The polluting molecule HCH fits into the enzyme like a key in a lock. Then part of the molecule is separated. The now harmless fragments are released again and the enzyme is ready to absorb the next polluting molecule.

Changes open up opportunities

Working with undergraduate student Jasmin Hubeli, Heeb studied not only enzyme variants found in landfills, but also an enzyme obtained from a genetically engineered strain of bacteria. Here, the researchers had deliberately enlarged the “keyhole” so that the larger HBCD molecules could be broken down more easily. The result: The genetic modification influenced the rate at which the pollutant was broken down. Empa researcher Heeb is optimistic about their results: “This means that we now have the possibility of using biological methods to render harmless these long-lived toxins produced by mankind and distributed over many areas. large areas ”. However, there is still a long way to go. The principle of locking and keying useful enzymes has yet to be defined in more detail before tailor-made enzymes for chemical toxins are available in the future.

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