Food and feed quality are crucial to human and animal health. Quality can be defined as sufficiency of appropriate minerals, vitamins and fats, etc. but it also includes the absence of toxins, whether man-made or from other sources. Surprisingly, almost no data exist in the scientific literature on herbicide residues in herbicide tolerant genetically modified (GM) plants, even after nearly 20 years on the market.
In research recently published by our laboratory (Bøhn et al. 2014) we collected soybean samples grown under three typical agricultural conditions: organic, GM, and conventional (but non-GM). The GM soybeans were resistant to the herbicide Roundup, whose active ingredient is glyphosate.
We tested these samples for nutrients and other compounds as well as relevant pesticides, including glyphosate and its principal breakdown product, Aminomethylphosponic acid (AMPA). All of the individual samples of GM-soy contained residues of both glyphosate and AMPA, on average 9.0 mg/kg. This amount is greater than is typical for many vitamins. In contrast, no sample from the conventional or the organic soybeans showed residues of these chemicals (Fig. 1).
Crop spraying, South Africa, Thomas Bøhn
This demonstrates that Roundup Ready GM-soybeans sprayed during the growing season take up and accumulate glyphosate and AMPA. Further, what has been considered a working hypothesis for herbicide tolerant crops, i.e. that, as resistant weeds have spread:
“there is a theoretical possibility that also the level of residues of the herbicide and its metabolites may have increased” (Kleter et al. 2011)
is now shown to be actually happening.
Monsanto (manufacturer of glyphosate) has claimed that residues of glyphosate in GM soy are lower than in conventional soybeans, where glyphosate residues have been measured up to 16-17 mg/kg (Monsanto 1999). These residues, found in non-GM plants, likely must have been due to the practice of spraying before harvest (for desiccation). Another claim of Monsanto’s has been that residue levels of up to 5.6 mg/kg in GM-soy represent
“…extreme levels, and far higher than those typically found” (Monsanto 1999).
Figure 1. Residues of glyphosate and AMPA in individual soybean samples (n=31). For organic and conventional soybeans, glyphosate residues were below the detection limit.
Seven out of the 10 GM-soy samples we tested, however, surpassed this “extreme level” (of glyphosate + AMPA), indicating a trend towards higher residue levels. The increasing use of glyphosate on US Roundup Ready soybeans has been documented (Benbrook 2012). The explanation for this increase is the appearance of glyphosate-tolerant weeds (Shaner et al. 2012) to which farmers are responding with increased doses and more applications….