Nasty chemicals

Some people talk a lot of rot about chemicals as if all chemicals are bad. Everything is made of chemicals. Some are 'good' while others are 'bad'. Water is a chemical; so is air. Some people think that if something is 'natural', then that's okay. But some natural chemicals are very poisonous: things like sulphur dioxide (that comes out of volcanoes) and ricin (a deadly chemical made by the castor oil plant). The difference between these natural chemical poisons and ones which humans have made is that life has got used to the natural poisons. It's learned to live with them over millions of years. Some life -- certain types of bacteria -- even eats poisons which would kill you or me.

But humans have made thousands of new types of poisons, called toxins, which living things have never seen before. Most of these new poisons have been made with good intentions. But they have quite unintended side-effects, and pollute much of the air we all breathe, the food we eat and the water we drink (or in my case, swim in).

The best known nasties are persistent organic pollutants (POPs). These include the pesticides farmers spray on food crops. POPs are very stable. They don't go away. Almost no life can break them down and make them harmless. Instead they tend to build up inside animals' bodies. This can mean they can't have babies or it can make them ill or even kill them.

Perhaps you've also heard of CFCs? These chemicals are not toxic but they do damage the atmosphere. They destroy a gas called ozone which shields the planet from the strong radiation of the sun. People sensibly agreed to stop making them at a meetings which came up with the Montreal Protocols. In many ways, this has been a success but some of it is not working very well . The 'hole' in the ozone shield gets bigger every year, especially over my home, the Antarctic. Another hole forms over the Arctic for the same reasons.

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