by Dr. Joe Cummins
(Feb. 14, 2002 - CropChoice guest column) -- Glufosinate (Basta, Liberty) is a herbicide used extensively in Europe and North America with genetically modified (GM) crops, it is similar to glyphosate (RoundUp) in eliminating most green plants that have not been genetically modified. Glufosinate is usually used as an ammonium salt. The herbicide inhibits photorespiration by causing a buildup of ammonia and a loss of the amino acid glutamine. In GM crops a bacterial gene for an enzyme - phosphoinothricin acetyl transferase (PAT) that inactivates the herbicide by adding an acetyl group to it - is used to confer herbicide tolerance to the crop. Glufosinate is used extensively even though the herbicide may have severe side effects on humans, farm animals and beneficial insects. A number of current studies describing those side effects are given below along with some studies on the fate of herbicide in genetically modified crops and conventional crops.
Glufosinate causes convulsions in humans and experimental rodents by brain cell glutamate receptor activation (glufosinate and glutamate are structurally similar)according to Matsumura et al (1). Glufosinate also stimulates nitric oxide production in the brain through N methylDaspartate (NMDA) receptors (2). Birth defects have been caused by exposure of the human father to the herbicide (3). Maternal exposure caused behavioral defects in rodent off-springs (4). Glufosinate was found to trigger apoptosis (programmed cell suicide) in the developing brain of the embryonic mouse(5). Numerous well established studies showing brain damage and birth defects seem to have been ignored by those regulating use of the herbicide.
Bystander or beneficial insects have been detrimentally effected by the herbicide. Kutlesa and Caveny (6) found that the herbicide had a number of neurotoxic impacts on the skipper butterfly at levels of herbicide experienced in the field. Ahn et al (7) found that glufosinate was toxic to some but not all predatory insects at levels of the herbicide experienced in the field. Studies showing that helpful predatory insects or bystander insects are poisoned by the herbicide seem to have been ignored by regulators of the herbicide.
Muller et al (8) studied glufosinate metabolites in transgenic and unmodified sugar beet, carrot, purple foxglove and thorn apple they found unmodified crops contained glufosinate maily while GM crops contained higher levels of glufosinate and acetyl glufosinate. Beriault et al (9) studied phloem transport of glufosinate and acetylglufosinate in canola in GM canola and unmodified canola and found that both chemicals were highly mobile.
It is rather distressing to note that there do not seem to be peer reviewed studies on the metabolism of the high levels of acetyl glufosinate in harvested GM crops to highly neurotoxic and teratogenic glufosinate. Certainly gut bacteria are well known to contain enzymes that remove acetyl groups from glufosinate and mammalian enzymes may also be capable of removing the acetyl group from glufosinate. Even though glufosinate is being used widely with GM crops in North America its safety is far from proven and its impact on humans and farm animals is difficult to trace because the GM products are not labeled for consumption.
1. Matsumura,N,Takeuchi,C,Hishikawa,K,Fujii,T and Nakaki,T "Glufosinate ammonium induces convulsion though NmethylDaspartate receptors in mice" Nerosci Lett 2001 ,304,123-5
2. Nakaki,T ,Mishima,A, Suzuki,E, Shintani,F and Fujii,T "Glufosinate ammonium stimulates nitric oxide production through NmethylDaspartate receptors in rat cerebellum" Neurosci Lett 2000, 290,209-12
3. Garcia,A, Benavides,F, Fletcher,T, Orts,E "Paternal exposure to pesticides andcongenital malformations"Scand J WorkEnviron Health 1998,24,445-7
4. Fujii,T "Transgenerational effects of maternal exposure to chemicals on the functional development of the brain in the offspring" Cancer Causes Control 1997,3,524-8
5. Watanabe,T "Apoptosis induced by glufosinate ammonium in the neuroepithelium of the developing mouse embryo in culture"Neurosci Lett 1997,222'17-20
6. Kutlesa,N and Caveny,S "Insecticidal activity of glufosinate through glutamine depletion in a caterpillar" Pest Manag Sci 2001 ,57,25-32
7. Ahn,Y,Kim,Y and Yoo,J "Toxicity of the herbicide glufosinate ammonium to predatory insects and mites Tetranychus urticae" J Econ Entomol 2001,94,157-61
8. Muller,B, Zumdick,A, Schuphan,I and Schmidt, B "Metabolism of the herbicide glufosinate ammonium in plant cell cultures of transgenic and non-transgenic sugarbeet,carrot,purple foxglove and thorn apple: Pest Manag Sci 2001,57,46-56
9. Beriault,J,Horsman,G and Devine,M "Phloem transport of D,L-glufosinate and acetyl-L-glufosinate in glufosinate-resistant and susceptible brassica napus" Plant Physiol 1999,121,619-28