May 7, 2011

So far you were worried about DDT traces in blood; Now you have Bt insecticides in human blood

Environmentalists have been telling us about the presence of DDT residues in human milk. We also know that DDT has been found in the blood of Penguins, which tells us how rampant and widespread the use and abuse of the deadly chemical was (and still is despite the worldwide ban with some exceptions). It is because of the renewed interest and concern over the excessive use of persistent organic pollutants that the Stockholm Convention, which has representatives from 127 Governments who met in Geneva last week at the fifth meeting of the Conference of the Parties, agreed to add endosulfan to the list of POPs to be eliminated worldwide.

According to the Stockholm Convention website: "The action puts the widely-used pesticide on course for elimination from the global market by 2012. The Parties agreed to list endosulfan in Annex A to the Convention, with specific exemptions. When the amendment to the Annex A enters into force in one year, endosulfan will become the 22nd POP to be listed under the Convention."

All this seems to be on the expected lines. Decades after these were pressed into use, the negative impact of chemical pesticides have now become known. International effort is to phase out these deadly chemicals. But while we phase out the harmful chemicals, newer and more potent chemicals are being pushed into the market. Stockholm Convention will therefore continue to have a lot of work on hand and for many years ahead.

Wikipedia defines POPs as organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes.[1] I am not sure whether biological toxins -- like Bt -- would also fall in the same broader definition or probably we will have to carve out a new category for them, but the world is now beginning to wake up to the threat Bt toxins pose to human health and environment. I am not talking of the ongoing debate over the harmful health impacts of Bt toxins in GM foods (or other transgenes used for developing GM crops), but a recent Canadian study that points to the widespread presence of Bt-related insecticide in the blood of 93 per cent pregnant women and 80 per cent of fetuses.

As Glenn Davis Stone, Professor of Anthropology and Environmental Studies at the University of Washington in St Louis, asks: "What does this mean for health impacts? Nobody knows. There are some signs that high levels of glyphosate and gluphosinate disrupt fetal development, but the levels in the women in this study were low. I know of no evidence that Bt proteins in the blood are harmful, and Bt is quite safe for humans in most contexts. (And as one of our graduate students just suggested, we should look on the bright side — the babies should be protected from caterpillar bites.) But there’s no contesting the authors’ conclusion: “Given the potential toxicity of these environmental pollutants and the fragility of the fetus, more studies are needed.” A lot more.

As long as we don't know what the Bt insecticide proteins are doing in our body we can surely remain in stage of ignorant bliss. But I am sure this is reason enough for us to sit up and feel concerned. I am sure you don't want your body to sooner or later turn into an insecticide factory.

Prof Glenn Davis Stone has analysed this issue in his excellent blog post. [For those who would like to view his blog Fieldquestions, here is the link:  http://fieldquestions.com/]

Blood type: Bt

By Glenn Davis Stone

A new study by toxicologists and obstetricians looks in the bloodstreams of a sample of Canadians for pesticides associated with genetically modified foods (new acronym alert: PAGMF). They studied pregnant women, their fetuses (actually umbilical cord blood after delivery), and also a group of non-pregnant women. GM-associated insecticide was widespread in the blood samples; GM-associated herbicide was present but rare.

Some background: the overwhelming majority of GM crops grown in the world today are either herbicide tolerant (HT) or insect resistant (IR). Herbicide tolerance is from a gene for immunity to glyphosate (Roundup) or gluphosinate (Liberty) weedkiller, allowing the farmer to spray weeds without harming the crop. Insect resistance is via a gene from the soil microbe Bacillus thuringiensis (Bt) which produces an insecticide — hence the name “Bt crops.” Canada mainly grows a lot of HT canola, but it grows other GM crops too including some Bt maize (details here).

Bt insecticidal proteins were found in the blood of 93% of the pregnant women and 80% of the fetuses. The current thinking is they get into humans via meat from animals fed Bt crops — these proteins have been found in the guts of pigs and calves.

Evidence of weedkiller in the blood was much more scant. None of the samples from pregnant women or fetuses were contaminated; 5% of nonpregnant women had glyphosate and 18% had gluphosinate.

What does this mean for health impacts? Nobody knows. There are some signs that high levels of glyphosate and gluphosinate disrupt fetal development, but the levels in the women in this study were low. I know of no evidence that Bt proteins in the blood are harmful, and Bt is quite safe for humans in most contexts. (And as one of our graduate students just suggested, we should look on the bright side — the babies should be protected from caterpillar bites.) But there’s no contesting the authors’ conclusion: “Given the potential toxicity of these environmental pollutants and the fragility of the fetus, more studies are needed.” A lot more.

Should this affect what we eat? Or what we think about GM crops? Ah, as with so many things, it all depends on the counterfactual — i.e., what you compare it to. You can buy organic produce that is free of weedkiller, and organic or most grassfed beef will be Bt-free. You pay more for these foods, but then again they offer benefits beyond the avoidance of pesticides.

On the other hand, while low levels of Roundup in adult blood and the common occurrence of Bt in fetal blood may give us pause, try wrapping your mind around some of the findings on other pesticides. Start with this article by Rauh et al. that just came out in Environmental Health Perspectives. They have been studying the effects of exposure to chlorpyrifos in the womb.

Years ago Rauh et al. started looking at umbilical cord blood for chlorpyrifos in several hundred births. They found some problems right off the bat — for example, the babies whose mothers had chlorpyrifos in their systems were smaller. They checked the kids at 3 years, and found the chlorpyrifos kids had cognitive and behavioral problems. Now the kids are 7 and this new study shows the exposed kids to have slightly lower IQ’s and poorer memories.

The spread HT crops into Canada and several other countries has not reduced weedkiller use — actually it has led to increases especially in the use of Roundup, but also to less use of other more toxic sprays. The spread of Bt crops has reduced the use of chlorpyrifos and many other toxic insecticides, but we now know it means most babies (in Quebec anyway) are born with Bt in their blood. What that means for our health and our babies, we really don’t know, but it’s hard to resist the conclusion that it’s better than organophosphates in the blood, and worse than neither.

1 comment:

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