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DDT’s legacy – a ‘silent spring’ of the mind

We call them persistent chemicals for a reason.

Because they hang around in the environment and in our bodies for a very long time, breaking down, changing form and in some cases becoming even more toxic than when they were first used.

Such is the case with DDT.

Long banned in the West, this toxic pesticide is still found around 80% of the blood samples collected in the US.

The reason for this is that DDT (dichloro-diphenyl-trichloroethane) only very slowly breaks down into its more toxic form DDE (dichloro-diphenyl-dichloroethylene).

Also, while we may not be using it any more, we can still be exposed to it through fruits, vegetables and grains grown in countries where DDT is still being used and eating fish from historically contaminated waterways.

This week a new light was shone on the lasting effects of this persistent poison. It found that older people with Alzheimer’s disease had levels of the DDE their blood that were nearly 4 times higher than those who did not have the disease.

DDT is an organochlorine pesticide that was used extensively as an insecticide in the 1940s. It was banned in the United States in 1972 after being linked to extreme harm in wildlife and the environment.

It was not banned in the UK until 1984 and it is still used in other countries to combat the spread of malaria.

Malaria is, of course, a devastating disease, killing more than more than a million people every year,with the majority of deaths among children in Sub-Saharan Africa. But only in rare instances is DDT the most effective way to address it.

DDT’s harmful effects on the natural world compelled Rachel Carson to write her seminal book Silent Spring.

But it devastates human lives as well. Research over the years has linked it to reproductive effects including a higher incidence of undescended testicles, poor sperm quality, higher risk of miscarriage, premature delivery and reduced infant birth weight and reduced breast milk production.

Exposure has also been associated with  developmental delays among babies and toddlers exposed to DDT in the womb, reduced liver function and diabetes and it has also been linked to cancer – in fact the  IARC (International Agency for Research on Cancer) lists DDT as a possible human carcinogen.

This, however, first clinical study to link the pesticide to Alzheimer’s disease – the most common neurodegenerative disease worldwide and one that is expected to increase three-fold over the next 40 years.

Although this may be the first study to specifically link DDT with Alzheimer’s, it is not the first study to link pesticide exposure with this and other neurodegenerative diseases. Indeed, the association is well established.

We need to understand these effects, as the scientists of the current study suggest. But not just so we can produce a new drug to treat Alzheimer’s.

We need to understand these effects in a way that allows us finally to acknowledge that they are real and that they aren’t going away and that newer classes of pesticides are not likely to be any better or safer.

Look how long it has taken for us to get to grips with the devastating effects of DDT. Can we really afford to wait another 40 years to find out, for example, that the neonicotinoids (or neonics) that have been shown to give bees a kind of Alzheimer’s do the same thing to us?

What we need even more urgently than a new drug to combat an old problem is a sane and sustainable agricultural system that produces enough for us all without poisoning the world in the process.

We already know how to do it. In 2011 a report submitted to the United Nations General Assembly recommended that by using ‘agroecological methods’ (organic, biodynamic, and other methods that work with the environment instead of against it) we could double our food output in 10 years. The 2008 IAASTD report recommended the same thing (and see this link for more interesting papers on agroecology).

We know what needs to be done, we know it’s possible to do it – so what on earth is stopping us?

Pat Thomas, Editor