6.1—The safety of glufosinate herbicide tolerant crops

Glufosinate herbicide tolerant crops are safe to eat

See Genetic Roulette’s False Claims at Bottom of Page

Analysis of Peer-Reviewed Research:

This section of Genetic Roulette is a repetition of concerns that were raised in section 5.3, and is based on the same misunderstandings.  Jeffrey Smith is unfortunately unaware that only extremely minute quantities of herbicide could possibly be present in food. Although some herbicide residues may persist on leaves, very little get into the seeds we eat.  When the glufosinate herbicide about which Smith is concerned is deliberately fed to laboratory animals, it is very quickly eliminated in faeces and very little enters into the body.  These processes of herbicide elimination go on much more quickly and effectively when small amounts of herbicide are given to rats.  This is why legal limits on allowable quantities of herbicide residues in foods provide adequate protection that the food from glufosinate-tolerant plants is safe and wholesome. It is unfortunate that Genetic Roulette doesn’t inform readers that dietary herbicide is quickly eliminated in faeces, and that regulatory agencies take full account of any bacterial reactivation in the gut when they set legal limits for food.

See also

5.3 – Transgenes and Gut Survival

1. Very little glufosinate herbicide residue on a plant ends up on the seeds.  Jeffrey Smith raises worries about herbicide residues getting into food.  The parts of existing genetically modified plants such as corn and soybeans that we eat are not where the herbicide is applied.  Careful measurements have been done and only a tiny fraction of herbicide residues on crops get into the seed which we eat.  Smith is unaware of the scientific paper that provides this information (Ruhland and others 2004).  Fortunately glufosinate has very low toxicity to animals or humans, so that in any event low exposure is not hazardous. Regulatory agencies set limits on the maximum permissible level of residues for each pesticide and crop (for example in the US EPA sets tolerances, see: www.epa.gov/pesticides/factsheets/stprf.htm).

2.  Re-activation of herbicide by bacteria is assumed to occur when safety factors are set by regulatory bodies. Jeffrey Smith is concerned that re-activation of herbicide by bacteria in the gut may expose us to unexpected risks.  In setting limits on the amount of herbicide levels that are acceptable, including safety factors, regulatory agencies assume that any herbicide present will be fully reactivated by bacteria. In safety assessments, inactive herbicide is treated as if it were fully active, and the possibility that bacteria can increase the toxicity of glufosinate herbicide residues has been factored into legally allowable levels of herbicide in food (FAO-WHO 1999).

3.  Almost all of the glufosinate herbicide residues in food are quickly eliminated in faeces. Laboratory experiments to see how of herbicide residues are handled by the body have been carried out with different animals and they show that glufosinate is rapidly eliminated from the body.  Only a very small percentage of dietary herbicide enters the body, and that which does is quickly eliminated in urine.  Elimination of herbicide residues from the diet occurs much more rapidly when low amounts are present.  These processes of residue excretion are part of safety assessment for herbicide residues but are not discussed by Smith  (FAO-WHO 1999).

4. Absence of herbicide in the gut means that the herbicide resistance genes offer no selective advantage to bacteria. The possibility that bacteria in the gut might promote herbicide toxicity was raised in an earlier section of Genetic Roulette. This scenario was found to be implausible in our section 5.3.


FAO-WHO (1999). Toxicological evaluations (glufosinate ammonium). Joint meeting of theFAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Core Assessment Group Rome, 20-29 September 1999. jan www.inchem.org/documents/jmpr/jmpmono/v99pr06.htm accessed 12 2009

Ruhland M, Engelhardt G, Pawlizki K (2004). Distribution and metabolism of D/L-, L- and D-glufosinate in transgenic, glufosinate tolerant crops of maize (Zea mays L ssp mays) and oilseed rape (Brassica napus L var napus). Pest Management Science 60: 691-696. Only a tiny fraction of herbicide gets into seeds.

Genetic Roulette Falsely Claims:
Glufosinate-tolerant crops may produce herbicide “inside” our intestines

1. Some crops are engineered to withstand glufosinate-based herbicide.

2. The crops transform the herbicide into a compound regarded as nontoxic, called NAG, which remains in the plant.

3. Once humans or animals consume NAG, gut bacteria can revert some NAG back into toxic herbicide.

4. The herbicide has known toxic effects, acts as an antibiotic and many kill-off or disturb gut micro-flora.

5. If the herbicide-tolerant gene transfers to gut bacteria, it could magnify the problems.

Genetic Roulette worries that trace amounts of herbicide in glufosinate herbicide-tolerant crops may be harmful, and that inactive herbicide may be reactivated by the bacteria of the gut.