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.

Science Illustrated - - CONTENTS -

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.

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