Pesticides are being dragged through the mud, with two major announcements this week: that pesticide exposure during pregnancy may cause autism, and that they are responsible for declining bee populations. And rightfully so, many common pesticides are neurotoxins. Banning pesticides leaves us with only two solutions in agriculture: no pesticide use, or the growth of genetically modified crops that are resistant to pests - like Bt crops.
The current buzz around pesticides like neonicotinoids is due to the findings that these chemicals are causing the same kind of environmental degradation that DDT was causing in the 1960s. Neonicotinoids are neuro-active insecticides that are similar in structure to nicotine, and bind to nicotinic acetylcholine receptors (NAR).
In insects, these receptors are part of the central nervous system, while in mammals, these receptors are located in both the central and peripheral nervous systems. A low to moderate activation of these receptors causes nervous stimulation, much like a nicotine buzz. But when levels get too high, the receptors become irreversibly blocked by neonicotinoids, and this causes paralysis and death. Neonicotinoids bind more strongly to insect NAR than they do to animal NAR due to structural differences in the proteins, and so they have been deemed to be "selective" for insects.
Neonicotinoids are used preventatively - they are sprayed over crops or coated on seeds before there is an infestation. These compounds are absorbed and transported throughout the plant. The pesticides are then picked up by bees, among other pollinators, and can cause problems with navigation, food collection, learning, disease resistance, and reproduction. On top of that, Dave Goulson, one of the authors of the report which has not yet been published, stated that 90% of pesticides being used end up in the environment - water and soil - rather than on the crop. That means that farmers who use this product annually end up building up toxicity in the soil, which can affect terrestrial insects like earthworms, as well as animals. Neonicotinoids can also take up to 4 years to degrade in the environment.
Exposure During Pregnancy
A large-scale analysis of exposure to pesticides during fetal development was undertaken in California, that found that women who lived in close proximity to fields and farms where pesticides were applied experienced a 2/3 higher risk of having a child with autism spectrum disorder or some other developmental delay. Now, as a HUGE DISCLAIMER here: this does not mean that pesticides cause autism, only that exposure during pregnancy increases the risk of having a child with autism.
The pesticides that were looked at in this study included organophosphates, pyrethroids, and carbamates. Organophosphates and pyrethroids are neural agents, while carbamates inactivate the enzyme acetylcholinesterase, leading to cholinergenic poisoning.
Clearly, traditional chemical pesticides are neurotoxins that not only affect the insects they target, but also have drastic effects on the environment and human health. That's because these chemicals interact with proteins and pathways that insects share with humans and other animals. That's why they present a danger to humans.
There are two alternatives here, if we want to ban the use of pesticides in farming. The first is obviously, no pesticides. While this is ideal, it's not exactly practical, especially when we have more and more mouths to feed and less land on which to grow food. Farmers who don't use pesticides see a 10% reduction in yields. I have friends who would argue here that we should all grow our own food in community, backyard, rooftop, or patio gardens - and I agree! This is a great way to get natural, organic food without any added chemicals, but it's not feasible or practical for everyone.
So now we get to the real sciency part of this post (YAY!). I won't get into the really gritty parts of Bt crops, since I've already talked about it in another post. But the gist of it is that Bt crops, which produce Cry proteins that paralyze insect digestive tracts, only affect their target insects. These insects include flies and beetles, not bees, and definitely not humans. The Cry proteins interact with very specific receptors that are only found in the target species. The proteins are produced by the plant, so they are protected from UV light and other potential things that could cause degradation - so there's no need to reapply! And they don't end up in the soil or water supply because they degrade quite rapidly. Since they are contained in the plants, farmers and other animals are not exposed to large quantities. And the microbial species from which Cry proteins come from - Bacillus thuringiensis - have been used as a form of biological pest control since the 1920s.
Canada and the US currently grow Bt corn, tomatoes, soybeans, potatoes, and cotton. Bt crops saved US farmers $57 billion in the first 16 years of their commercialization (1996-2011), and an estimated 26.1 million hectares of land are currently planted with Bt crops. Given our ever-growing population and decreasing arable land, it only makes sense that we would want to exploit every possible option we have for agriculture - especially using those technologies that do not have a negative impact on environmental and human health.