DECONTAMINATING EARTH

We’ve sure made a mess of the place. Red rivers, black snow, and much worse. It all needs to be cleaned up. Here’s how we’ll do it.

Mercury, arsenic, and oil. Earth is toxic, and millions die annually as a consequence of the contamination. But now, experts aim to decontaminate the planet by means of new methods, which involve anything from vapour and plant roots to vacuum pumps and electrodes.

In the summer of 1956, a fisherman by the name of Aage Hansen noticed how the sea water off Harboøre Tongue had become yellow, as the smell of dead animals filled the air. He set out to find out why, sailing to the island of Sandø, where he found lots of dead sea gulls and fish. He had discovered the disastrous effects of contaminated soil and water on the west coast of Jutland, for which the Cheminova chemical plant was responsible. Ever since the factory was built in 1953, it had discharged untreated waste water, and in 19571962, Cheminova also deposited its solid waste in a dune hollow on the North Sea. In those days, it was believed to be a safe location in which to place toxins such as the parathion insecticide and mercury; chemicals that we now know to be very harmful.

Cheminova is not by far the only or worst example of this type of toxic contamination in the world. Globally, 61 million people are subjected to hazardous quantities of toxin from contaminated soil. But near the Danish chemical plant, engineers are developing a method, which – via heat treatment and special carbon filters – has the potential of removing mercury directly from the soil – for the first time ever.

Soil contamination kills millions

The contamination of the world’s soil seriously gathered momentum with the Industrial Revolution. From the mid1700s, steampowered machines, coal burning, and the use of chemicals were introduced in factories. Soon, the first consequences could be observed, such as in 1873, when a greenishyellow pea soup of soot and sulphur dioxide covered London. At least 268 people died as a consequence of the acidic carbon fog.

Today, the world is seeing still more contamination, and over the past 40 years, 33 % of its arable land has been lost to erosion and toxins. Particularly the quantities of heavy metals and mineral oils in the ground are huge, and in Europe, they account for 37 and 34 % of total soil contamination, respectively. The heavy metals include toxic substances such as lead, mercury, cadmium, and arsenic, which are characterised by their ability to accumulate in living organisms over time. In this way, lead and other nasties, can replace other substances such as iron or calcium in the body and restrain the brain’s neurotransmitters, damaging IQ and memory. The second largest source of contamination, mineral oil, also accumulates in the body, such as in the spleen and the liver, and consists of a series of petroleum distillates from petrol refining, industrial coolants, etc. Some of the oil contains toxic tar compounds, PAHs, which are linked with increased risk of a series of cancer types.

The EEA estimates that there are 2.5 million contaminated areas in Europe, and in total, the pollution of the world’s air, water, and soil claims nine million lives annually, according to a study from 2017 published by the Lancet. Environmental agencies claim that mercury is the worst, affecting an estimated 19 million people.

Mercury poisons brain and lungs

Since the Industrial Revolution, mercury like that of Harboøre Tongue has continuously

16% of all deaths in the world are due to contamination of soil, air, and water.

constituted an environmental problem throughout the world, particularly as it is liberated into the atmosphere in connection with coal burning. Coal includes mercury, that, when burned, binds to dust particles or turns into airborne vapour, that can spread across thousands of km. The atmosphere's mercury content is now up to 6 times higher than before the Industrial Revolution.

Mercury also ends up in nature as a consequence of gold mining, chemical deposits, or garbage dumps, where anything from old thermometers to batteries and paint leak mercury. In mines, mercury is even added directly to the soil to extract gold ore.

The problem with the heavy metal is that it easily binds to other substances and might migrate into the food chains of animals. From bacteria to plankton to fish, it could finally end up in the human body, where it might restrict important enzymes in the central nervous system, which controls muscle motion. So, mercury contamination could cause paralysis. In the brain, the mercury can also break down nerve cells and cause brain injury – particularly in the embryonic stage and in children. If you inhale mercury vapour, it could also harm your lungs and cause respiratory problems. If it reaches your stomach, it could bind to enzymes, which are normally

responsible for digesting fat, proteins, and carbohydrates from food. This might cause ulcers and digestion difficulties.

Vapour purification dethrones toxin

At Harboøre Tongue, the Danish government in 2006 tried to solve the problem of mercury contamination caused by Cheminova. Environmental engineers decided to encapsulate the toxins by placing steel plates 14 m into the ground around the toxin dump. The leakage was slowed down, but only temporarily. Over a long period of time, not even the steel barrier will prevent the pollution, as it will corrode.

So far, the only efficient method for removing mercury from the ground has been to retrieve it and take it someplace else. But this method is extremely expensive and environmentally unsustainable. So, experts from the Danish environmental services company Krüger have been given the assignment. The company has managed to remove mercury from contaminated soil in its lab, and now, the new technology is about to be tested in real life for the first time. 25 m3 of soil from the toxic dump near Cheminova are included in a pilot project that is to determine whether thermal purification could become part of the solution to the world’s mercury problems.

Basically, thermal purification involves the use of heat to make toxins in the soil evaporate. Traditionally, the soil has been carried to a lab, where it has been heated. When the toxin evaporates, it is sucked into a cooling chamber, where liquid and gas are separated. In this way, any toxic liquids are collected. At the same time, the rest of the toxins remain gaseous. The harmful substances are captured by filters, so clean air can finally be let into the atmosphere.

However, the method has been refined in recent years, and today, experts are working with on site heat treatment. Heating elements are buried in the ground at depths of 2-30 m, and on the surface, an insulating cover is placed. Installed together with the heating elements or in between them, steel pipes with a constant vacuum are placed, also known as collector wells. The heating elements remain in the ground for months, until the heat spreads to the entire area, and the toxins start to evaporate and rise. En route, they are captured by the vacuum wells, which suck up the toxic gases.

The challenge for Krüger is that mercury in the ground exists in many versions, as the metal is included in combinations with other substances such as sulphur. The toxic dump near Cheminova also includes a series of

71% of soil contamination in Europe is due to heavy metals and kerosene products.

different mercury remnants – such as phenyl and ethyl mercury from fungicides made by the chemical plant. As the compounds have different qualities and boiling points, etc., Krüger’s chemical decontamination must be broadly-based. So, the company has increased the temperature in the ground from 100 to 350 °C and developed a special sulphurimpregnated active carbon filter, that binds and captures all types of mercury vapours from the plant.

The pilot experiment will show, if the methods are efficient in the real world, which is impossible to copy 1:1 in the lab. Cloned bacteria consume oil Thermal purification is just one of a series of recent methods for cleaning soil of toxin. Scientists have also found out that you can encapsulate toxins by means of electricity. They bury electrodes into contaminated soil, sending a current through the soil layers, until the temperature increases so much that all the materials melt. Subsequently, everything hardens. The result is a type of glass, that traps the contamination.

However, encapsulation is rarely a permanent solution, as the soil is not really purified. Consequently, experts tend to prefer long- term methods such as thermal purification, but also increasingly biological treatment, which involves the use of bacteria and plants that can purify soil by breaking down hydrocarbons from fossil fuels.

Scientists have made microorganisms by cloning DNA strands from microbes, which normally live in petroleum reservoirs, where they break down oil accumulated in the ground. The bacteria are of the Rhodococcus type, which easily bind to oils and can oxidise their toxins. This is a process, in which oxygen reacts with the substances, so they give off electrons and can be broken down. New methods save billions The new heating and biological methods are particularly interesting, because they purify the soil more efficiently and safely than traditional methods. Moreover, they are much cheaper. The major expenses of traditional soil purification are due to the huge labour and transport ressources required to extract soil, carry it, and deposit it in designated waste areas. On site thermal heat treatment is very much cheaper than lab treatment, so analysts also see a market for the new soil purification technologies, that is expected to increase by 8 % annually up until 2021, when there will be jobs worth an estimated at more than $50 billion worldwide.

At Harboøre Tongue, toxin experts are working hard to obtain results before December. If everything goes well, the method can subsequently be scaled up to include the entire Cheminova mercury toxic dump. Subsequently, the world is waiting. At best, the efforts at the tongue are the beginning of a new era, in which yellow water and dead animals are things of the past.