There are many environmental concerns about GMO crops. We concentrate on just three:

1. Increased use of toxic herbicides and pesticides
2. Pleiotropy – unforeseen consequences
3. Contamination

1. Increased use of toxic herbicides and pesticides

The majority of GM crops are those which have been engineered to be herbicide (weed-killer) resistant.

‘Roundup ready’ soya, produced by Monsanto and grown extensively in North and South America, allows farmers to spray soya plants with Roundup - a toxic cocktail of glyphosate and other chemicals. This may not harm the genetically engineered crop – but the treatment creates chemical residues and run off, making it disastrous for surrounding ecosystems.

It also encourages the development of ‘superweeds’ which are resistant to glyphosate, such as the giant pig weed, which grows over 2m tall, or Morning Glory. The latter has evolved a reproductive system which ensures its tolerance of glyphosate. This was not something predicted by the genetic engineers.

"What kind of evolution are we causing due to impacts that we didn't quite foresee?" questions researchers from the University of Michigan.

Proponents of GM argue the Roundup-resistant engineered crop leads to cheaper and simpler weed management for farmers, it reduces tillage (and therefore carbon loss) and that it does not harm the environment or our health (believing glyphosate to be safer than other herbicides).

Critics of GM dispute this. They recognise the terrible damage to the life forms surrounding the crops: the risk to beneficial insects such as pollinators, the residues left in the soil, and the run off into fresh water sources such as rivers and streams. But there is also the potential health risk for humans and animals who consume the herbicide-treated crops.

Now scientists are creating GM crop varieties which are resistant to multiple herbicides, such as Dow’s multi-herbicide soybean, engineered to tolerate glyphosate, glufosinate and 2,4-D (an ingredient of the defoliant Agent Orange.) It appears this chemical treadmill benefits GMO seed companies, who also produce the agrichemicals.

2. Pleiotropy

DNA is a complex structure. Altering it in any way can create new consequences and structures in the cell’s composition, as well as its relationship with other cells. Chemists call this Pleiotropy.

Genes are not like Lego pieces – if you change or remove an element, there are ramifications way beyond the changed ‘piece’. In every organism, genes, proteins and pathways interact with one another and are regulated in a complex, multi-layered network process.

Despite scientists’ claims, it is impossible to predict the impacts of even a single gene modification. Pleiotropic effects have included alterations in the crop’s nutritional, toxic and allergenic properties.

For example, a GM soya tested in 1996, developed 27% higher levels of a major allergen, trypsin-inhibitor. In 2008 a GM maize had the unpredicted appearance of a new form of the protein which is a known allergen.

Even the new technique, called CRISPR, heralded for its accuracy, still has unknown effects on non-targeted cells. Put simply, CRISPR uses the Cas9 enzyme to cut DNA at a particular site. The cell then attempts to reseal this break using DNA repair mechanisms. These mechanisms do not always work perfectly, and sometimes segments of DNA will be deleted or worryingly rearranged. These are ‘off target’ effects which can create unforeseen problems in cell structure and lead to an unexpected new DNA.

CRISPR scientists rely on algorithms to predict the most obvious cell changes, but in a recent test case there were 100s of unforeseen effects.

None of these ‘off target’ changes would be picked up by the inadequate testing carried out to comply with GMO regulation.

3. Contamination

GM crops can – and do - cross pollinate with wild and non-GM plants. Other sources of contamination are the inadvertent spread of seed by farm machinery, as well as mixing seeds during storage.

Cross pollination will not only contaminate wild plants, affecting their natural genetic makeup, but will seriously compromise any organic or non GM farming system. Despite claims that GM and non-GM can co-exist, it is patently untrue.

For economic and geographical constraints, farmers cannot be expected to isolate their GM crops. Organic farmers will lose their registration, and in Canada, for instance, it is now virtually impossible to cultivate non-GM oilseed rape, such is the overwhelming GM presence.

New genetic engineering techniques, such as CRISPR, increase the danger of plants with altered genes spreading throughout whole wild populations. A gene 'drive’ system allows for an edited gene on one chromosome to copy itself into its partner chromosome. The result is that nearly all offspring will inherit the engineered gene. If just a few organisms with gene drives are released into the wild, the whole population could end up with the edited gene.