Genetically Modified Organisms (GMO)

Characteristics

Fate and Transport in the Environment

Exposure Pathway

Routes of Exposure

Methods for Measuring Exposure

Strategies for Preventing Exposure

Methods for Monitoring in the Environment


Harmful Effects

Dose Response

Absorption, Distribution and Metabolism

Sites of Toxicity

Biomarkers of Disease

Risk Assessment

References

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Dose Response

Several published studies have attempted to show dose-response data on genetically modified foods in any animals but have not yielded useful results. Some of these studies attempt to feed animals whole food, others administer concentrated doses of the food, while others use the purified novel protein from the GM food. Nearly all of the GM foods that have been tested for toxicity have shown No Adverse Effect Levels (NOAEL’s) at dosages far beyond the expected level of human consumption.

One example of an attempt to find dose-response information comes from a class of GMO’s originally developed in the 1980’s and are now in widespread use. These are the so-called “Roundup Ready” plants that contain a protein allowing the plants to tolerate glyphosate, the active ingredient in the herbicide Roundup. In acute toxicity studies mice that were fed the GM protein by oral gavage at dosages up to 572mg/kg body weight experienced no adverse effects. There were no significant differences between treatment and control groups in body weight, cumulative body weight, and food consumption. This dosage can be said to represent a NOAEL for this particular protein. According to the authors, 572mg/kg body weight is approximately 1300 times the highest potential human consumption if the protein were expressed in soybean, corn, tomato, and potato (Harrison et al, 1996).

Another example comes from transgenic varieties of tomato and sweet pepper that have increased resistance to a type of mosaic virus. Investigators carried out an acute toxicity assay, a micronucleus test, sperm aberration test, Ames test and 30-day animal feeding to assess the safety of the pepper and tomato. The acute toxicity test was used to assess the Median Lethal Dose (LD50). Rats were administered dosages up to 10g/kg body weight per day of lyophilized tomato and pepper powder for 1 week. The results yielded no signs of toxicity or mortality. The investigators concluded that the LD50 for these two GM vegetables was greater than 10g/kg body weight and that they were as safe as their non-GM counterparts. The other toxicity tests yielded similar results (Chen et al., 2003).

Studies do exist that have shown toxic effects of GM foods in animals. The most well known involves a transgenic potato engineered to produce a natural insecticide (Ewen & Pusztai, 1999). In this study, rats were fed GM potatoes for ten days and presented toxic effects in their stomach linings. The results were controversial because there was disagreement over whether it was the novel protein causing the effects or a component of the genetic engineering process. It is unclear from the published study what dosage was administered to the rats and the authors made no determination of a NOAEL or LOAEL.