silent spring rachel carson
Here’s something to look out for the next time you see footage on a documentary of the concentration camps in the Second World War.  You often see people being dusted with a powder. 
The  chances are that it is DDT.  At the end of the war Europe was on its knees with widespread destruction of infrastructure and a shortage of food.  Many people were displaced as well as hungry and were moving about trying to get back to their homes.  The situation was ideal for the emergence and wide spreading of disease.  But that problem, at least was avoided, thanks largely to DDT.  It had been developed as an insecticide in 1939 and was deployed in large quantities to prevent mites, the habitual spreaders diseases as the war ended in 1945.
For someone who grew up in the Seventies when DDT was a big story, it comes as quite a jolt to discover that DDT has in fact probably saved millions of lives.  I can’t think of many organic compounds that have ever had such a bad press.  The news was full of the problems caused by this particular pesticide.  The mention in Joni Mitchell’s hit Big Yellow Taxi gives the flavour.

Hey farmer farmer
Put away the D.D.T. now
Give me spots on my apples
But leave me the birds and the bees


Mistrust of chemicals in general is now so widespread that it is hard to remember that back in the Fifties and early Sixties people were generally positive about the benefits of chemistry.  DDT wasn’t the only recently invented life saver. Penicillin and other drugs were conquering disease.  In a world where people could remember rationing, chemical fertilisers increasing crop yields could only sound like a good thing.
But it was pesticides that really changed the sentiment.  The problems with the use of agricultural chemicals was the first big environmental issue that captured the public imagination, and set off the chain that led to today’s marketers going out of their way to stress just how natural everything is.  You can no longer enter a shop without seeing a graphic of a green leaf with drops of dew on it.
So what was the problem with pesticides, in particular DDT?  Prepare for another surprise.  Its problem is not its toxicity.  In fact if anything, its problem is that it isn’t toxic enough.  At one stage a pro-DDT chemist was very keen to demonstrate this by ostentatiously eating quite large doses of it in public.  He came to no harm. But his party piece was completely irrelevant to the real issue.
If you want to understand why DDT was a problem despite its relatively low level of toxicity and don’t have the time to enrol on an environmental science degree, consider reading Silent Spring by Rachel Carson.  This book is very nearly 50 years old now but it remains one of the books that anyone interested in the environment really must read.  This was the first book to bring the problems of pesticide use to the public attention.
Listen to one of the many stories detailed in Silent Spring.  It started in 1949 at a fishing reserve called  Clear Lake in America.  This was a project undertaken with great care.  The object was to get rid of the gnats that were troubling fishermen.  A close relative of DDT, DDD, was used.  This was thought to be less harmful to the fish.
The levels used were modest by any standards and should have been safe enough.  They started at 1 part per 70 million of water.  It worked well at first, but the gnats started to return  so in 1954 the dose was increased to a still very cautious 1 part per 50 million.
But soon the number of western grebes that lived on the lake started to fall.  The grebes, who dive below the surface of the water to catch their prey, were eating the contaminated fish that had eaten the contaminated insects, concentrating the insecticide in their bodies.  Some dead specimens were collected in 1957 and found to contain 1600 parts per million of DDD.  The concentration in the birds was around 8 million times higher than the dose that had been applied.
Even that was not enough to kill many of them, but it was enough to affect their ability to produce offspring.  The grebes soon became a rare sight.
What was going on? DDD is fat soluble, and so tends to accumulate in the fatty tissues of the insects to which it is applied.  The insects are eaten by birds or fish, which accumulate increasing quantities of the pesticide in their own fat, concentrating it as it moves up the food chain.  DDD is stable so it persists in the body for long periods.  Given its low toxicity, creatures can accumulate quite large amounts before it does them any harm.  In fact it is quite likely to do them no harm at all, enabling them to fly or swim around taking their dose of DDT around with them spreading it further afield.
But while they are getting on with living oblivious, the DDD might well still be at high enough level to harm their ability to reproduce.
This pattern was to be repeated time and again.  DDT  and other similar pesticides worked in exactly the same way.  Birds, at the top of the food chain but having a small body mass, would be hit worst.  The Silent Spring of the title was the spring that would come when there would be no bird song because all the birds had died. It is a harrowing image intended to shock.  But the diligent scientist Rachel Carson was able to back up what she was saying with a huge range of solid research.
Lets have a look at what was important.  It wasn’t the high toxicity of the chemical that was the problem. It was the combination of low toxicity, oil solubility and stability.  Also, look how difficult to predict the problem was.  The chemist we heard about earlier who ate the stuff had, we can be sure, done all the calculations to assess the risk of the dose to himself.   That was a simple enough problem and he knew what he was doing.   But he wouldn’t have been able to so easily predict how it would work in the field and would never have guessed the ability of biological systems to concentrate particular agents.  The conscientious project managers of Clear Lake had taken every reasonable precaution but had still created havoc for the wild life in their care.
At first sight this looks like a council of despair.  If things are so complicated shouldn’t we just conclude that there is no such thing as a safe level and ban everything?  But that is to give up too soon.  Mistakes can be learned from.  For instance, why use such stable molecules?  We now know you have to understand the system as well.   But as our understanding has grown this has become possible.  Everyone who works in the development of chemical products is now very well aware that simply looking at a safety data sheet isn’t enough to be sure that something is safe.
And the converse is also true.   Just because a risk can be identified with a chemical, it is not necessarily going to actually be harmful for a particular use.  It is often stated as a fact that the Romans suffered from lead poisoning because they used lead water pipes.  I have seen that given as a reason for the collapse of the empire.  Lead is certainly toxic and does leach into water from lead pipes.  But in fact the water also contained calcium which coated the lead in the pipes making it harmless.  The Romans would probably have been highly offended at the way we talk about them.   They were well aware of lead poisoning – they mined and processed the stuff after all – and would certainly have worked out that lead pipes were a problem if they had actually been.  It makes a useful warning about assuming that we know best.  It is always appealing to characterise of people as ignorant and stupid, but it is rarely justified.
We only have the one planet so it is really important that we treat it well, and that is as good a reason as I can think of to take an interest in environmental issues.  But I am always finding that whenever you study an issue that comes up, you learn a great deal beyond the bare facts of the case.  I often learn some more about chemistry or biology, but also about human nature and myself.  In many ways, the way a person or a society or a species responds to its problems defines what it is.
Silent Spring is sometimes described as the book that started the environmental movement.  This is an extravagant claim but it really is remarkable the extent to which so many things that trouble us today are already there in its pages.
Like a great many other people I read Silent Spring in the Seventies.  Back then it was already considered a classic.  I wondered how it would read now it is nearly 50 years old.  The first thing I noticed was how much work she put into getting over the idea that chemicals can be dangerous. Nowadays it seems a strange thing to stress.  But go back 50 years and chemistry was still synonymous with progress and a better life.  The other thing I noticed was just how familiar it all seemed even after so long.
Almost all the risks to individual health we still talk about today are already there in Silent Spring.  She talks about pesticide residues in food and the general environment being detected in humans.  Cancer causing chemicals, including estrogen disrupters get a mention.
How have her predictions stood up to the test of time?  Well, obviously there has not been a spring without birdsong.  The reckless use of pesticides has not continued.  Most of the chemicals described by name in the book are now banned.   Governments now take protection of the environment seriously, as do scientists like myself working in industry.  The message of the book invisibly pervades labs.
It also has to be said that with hindsight we can see that in many areas she was simply too pessimistic.  For instance, she warns of the risks of new chemical entities being created in the environment by the unpredictable reactions between different new synthetic compounds.  That sounds like a serious problem and one that should be considered, but I cannot think of a single instance when this has actually happened.
She also talks about an ever growing epidemic of cancer.  That too has failed to materialise.  In fact cancer rates are falling nearly everywhere. No one cause can be identified for this improvement.  It is probably simply the result of thousands of small and on their own not that significant initiatives by particular individuals, all of which added together starts to make an impact on the problem.
But it is easy to forgive Rachel Carson’s overestimation of the risks of cancer.  When she was writing it was a serious and growing problem.  In fact she herself was one of the victims of it.  She died of breast cancer in 1964 not long after Silent Spring came out.  She lived long enough to know that it had an enormous impact, though not long enough to realise just how long lasting and widespread that impact would be.  The public were impressed and the growing awareness of the risks of pesticides led to changes in legislation and the creation of the Environmental Protection Agency in the US and to similar bodies in other countries all around the world.
Even that understates her true significance.  Countless times I have mentally referred back to Silent Spring to understand a news story.  A good example recently is the dramatic reduction in bee numbers.  A number of theories have been put forward to explain this.  One suspect that has been fingered are the neonicotinoids, a new category of pesticide.  I haven’t looked into it closely enough yet but I wonder if this will turn out to be another case where the data on file looks quite sound and would suggest that there is no problem.  But will it turn out that there is some unexpected foible of bee anatomy, biochemistry or behaviour that makes them surprisingly susceptible, much like the grebes in the lake?  Time will tell.
I am sure that I am not the only scientist who has been deeply influenced by Silent Spring.  Its influence can also be seen in many environmental activists who consciously or unconsciously follow her template.   The combination of solid facts, clear writing and passion is an unbeatable one, and can achieve a great deal if you can pull it off.  If you think that is easy, give it a try.
And so I recommend that you read this book, but not particularly to learn about the risks of pesticides most of which have been long since banned, but for many other reasons.  You should read it if you aspire to explaining science to non-scientists.  The book deals with some very tricky areas of chemistry and biology.  But at no stage are the complexities dismissed with hand waving.  It is a humbling experience for those of us who sometimes try to do the same thing to realise just how difficult it is and just how well Rachel Carson does it.
If you want to campaign to make the world a safer and cleaner place (and what could be more worthy?), you should certainly read it.  It shows just how it can be done.  If you believe that all chemicals are toxic and that big corporations are malevolently out to do as much damage as they can get away with, you really really need to read this book.  Particularly if you think that looking up a chemical name on an online database and reading some random facts about constitutes ‘doing your own research’. You’ll see that there is a bit more to it than that.
As I finished my rereading of the book my main feeling was optimism.  Here was a book that had changed the world for the better.  Many of the problems that Rachel Carson set out have now been solved, some of them directly as a result of her clear and persuasive writing about them.  That is a great thing and we are all in her debt.

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