Most of the world’s commercial GM crops are engineered to be pesticide producing or herbicide-tolerant. The environmental effects of these crops are increasingly well documented, especially in North and South America where most GM crops are grown.
GM pesticide-producing crops
These crops kill specific pests by secreting toxins known as Bt, which originate from a bacterium. Peer-reviewed scientific evidence is mounting that these GM crops are:
- Toxic to harmless non-target species. Long-term exposure to pollen from GM insect resistant maize causes adverse effects on the behaviour1 and survival2 of the monarch butterfly, America’s most famous butterfly. Few studies on European butterflies have been conducted, but those that have suggest they would suffer from pesticide-producing GM crops3,4,5,6. These studies are all based on one type of toxin, Cry1Ab, present in GM maize varieties Bt11 and MON810. Much less is known about the toxicity of other types of Bt toxin (e.g. Cry1F, present in the GM maize 1507). Cry1F is highly likely to also be toxic to non-target organisms7, but requires separate study.
- Toxic to beneficial insects. GM Bt crops adversely affect8 beneficial insects important to controlling maize pests, such as green lacewings9, 10,11,12. The toxin Cry1Ab has been shown to affect the learning performance of honeybees13. The environmental risk assessment under which current GM Bt crops have been assessed considers direct acute toxicity alone, and not effects on organisms higher up the food chain. But these effects can be important. The toxic effects to beneficial lacewings came through the prey they ate. The single-tier risk assessment has been widely criticised by scientists who call for a more holistic assessment14,15,16,17.
- A threat to soil ecosystems. Many Bt crops secrete their toxin from their roots into the soil18. Residues left in the field contain the active Bt toxin .19, 20, 21, 22 The long-term, cumulative effects of growing Bt maize are of concern.23
Risk assessments so far fail to foresee at least two other impacts of Bt maize:
- Risk for aquatic life. Leaves or grain from Bt maize can enter water courses 24, 25, 26 where the toxin can accumulate in organisms27 and possibly exert a toxic effect28. This demonstrates the complexity of interactions in the natural environment and underlines the shortcomings of the current risk assessment.
- Swapping one pest for another. Several scientific studies show that new pests are filling the void left by the absence of rivals initially controlled by Bt crops29, 30, 31, 32. Plant-insect interactions are complex, are hard to predict and are not adequately risk assessed.
GM herbicide tolerant crops
These crops are generally associated with one of two herbicides: glyphosate (the active ingredient of Monsanto’s herbicide Roundup used with Roundup Ready GM crops, also sold by Monsanto), or glufosinate, used with Bayer’s Liberty Link GM crops. Both herbicides raise concerns, but many recent environmental studies have focussed on glyphosate, which is associated with:
- Toxic effects of herbicides on ecosystems. Several new studies suggest that Roundup is far less benign than previously thought. For example, it is toxic to aquatic organisms such as frog larvae and there are concerns that it could affect plants essential for farmland birds. Wider impacts may exist. Glyphosate is associated with nutrient (nitrogen and manganese) deficiencies in GM Roundup Ready soya, thought to be induced by its effects on soil microorganisms.
- Increased weed tolerance to herbicide. Weed resistance to Roundup is now a serious problem in the US and South America where Roundup Ready crops are grown on a large scale. Increasing amounts of glyphosate or additional herbicides41 are needed to control these ‘superweeds’, adding to the toxicity of food and the environment. Independent researchers complain about the lack of seed material made available for tests on environmental effects and are seriously concerned because those finding adverse effects face persecution by the pro-GM industry.
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