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27th July 2011
Toxic chemicals come back to haunt us

A deadly mistake in the past may be coming back to haunt us, a new study by scientists reveals.  Thousands of miles away in the Arctic, toxic chemicals frozen in ice and snow are being released into the air for a second time as the earth warms up and the ice melts.  But what are those chemicals and how did they get there?  

In the past, we made the mistake of creating and using chemicals before learning more about them and their effects on the planet and living creatures.  The chemicals in question are mostly man-made and were created in industrial processes.  Many were used as pesticides for farming and were sprayed onto the land and released into the atmosphere - pesticides kill off, repel or prevent pests from damaging valuable crops.  The long name for these chemicals is Persistent Organic Pollutants, or POPs for short.  These chemicals are particles and although invisible they are very strong and durable.  They can last a very long time in the environment and can even grow more toxic when they enter the food chain of animals.  As if this wasn’t enough these super chemicals can also travel vast distances which is how they’ve ended up in remote regions such as the Arctic!

One of these POPs is called ‘dichlorodiphenyltrichloroethane.  No, we can’t say it either which is why it is more commonly known as DDT!  Its use as a pesticide became widespread after the Second World War.  What was not realised at the time, was that it was ‘bioaccumulative in its effects’.  That means that it was absorbed by creatures and was present in their fatty tissues.  The more they were exposed to DDT, the more DDT they absorbed.  So, for example, when DDT got into waterways it could be found in zooplankton, tiny creatures that live in open water.  Fish ate the zooplankton in large numbers, concentrating DDT in their own bodies.  Birds of prey, like the osprey then ate the fish, which gave them large doses of DDT.  

On the land, DDT found its way into earthworms, and other minibeasts, which were eaten by small birds like robins, which in turn were eaten by birds of prey like eagles.  The DDT did not kill the birds of prey, but it affected the way their bodies metabolised calcium.  This meant that their eggs had thinner, weaker shells, which would collapse under the adult bird whilst it sat on the eggs in the nest.  DDT brought many species of bird of prey to the brink of extinction, both in the UK and US.  For example, there were thought to be as many as 500,000 bald eagles in the US in the 1700‘s.  By 1950, there were just 412 breeding pairs in the whole of the US.  The use of DDT was banned in the US in 1972 and in the UK in 1984.  Bird of prey numbers have recovered as a result.

Because of this DDT is one of the most notorious of POPs and has been said to be a cause of cancer and many other illnesses in humans.  Traces of DDT can still be found regularly in food and is now found all over the world.  Efforts to ban and slowly prevent POPs from entering the atmosphere will now face the new challenge of global warming. 

Global warming is the warming of the earth as ‘greenhouse gases’ such as carbon dioxide are released into the atmosphere through the burning of fossil fuels like coal, gas and oil.  These greenhouse gases act like a blanket surrounding the whole planet, trapping the sun’s heat within the atmosphere and causing global temperatures to rise.  The Arctic has been one of the first places to feel the effects of global warming and new studies have shown a rise in levels of POPs as they are released a second time with snow and ice melt.

So, the mistakes of the past continue to be a considerable concern for us today as we can’t always predict how man-made chemicals, pollutants and genes will affect us in the future.  It looks like we’ll have to put up with continued POPs exposure for longer than anticipated.



Photograph by C. G. P. Grey

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