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EPA document explains agency's confidence in Bt crops

A 107-page document prepared by the U.S. Environmental Protection Agency gives a detailed explanation of how insect-protected crops are regulated and assessed for safety. The document was prepared in response to a petition by activist groups, which had challenged EPA on the safety of crops that contain an insect-resistant gene from Bacillus thuringiensis (Bt) a common soil bacterium. Bt cotton, corn and potatoes have been developed through biotechnology to provide in-plant protection against targeted harmful insects.

In a concise statement of EPAís confidence in the environmental safety of Bt crops, the document states:

"EPA is aware of no data indicating that unreasonable adverse effects on the environment have occurred during the period that Bt crops have been registered and used (since 1995)ÖMoreover, EPA has no reason to believe that such effects may occur during the continued duration of the current registrations."

In the response to the petition, EPA explains why the agency is confident that Bt crops will not

  • cross-pollinate with weeds or other plants in the environment;
  • have an adverse effect on non-target beneficial organisms;
  • have unintended effects on soil ecology;
  • cause pests to become resistant to Bt, which organic farmers use in spray form.

The report details clearly that EPA fully considered possible long-term effects of in-plant insect protection and did not overlook any of the issues raised by the petitioners. The report also shows that EPA has reviewed extensive data, including some published studies that raise issues about the safety of Bt crops. EPA explains that the preponderance of data demonstrate the safety of Bt crops. The report points out that laboratory studies that raise concerns among some groups have not been validated by field studies, which show that Bt crops provide a beneficial effect.

The document also explains that EPA considered the risks and benefits of Bt crops in comparison with existing agricultural practices, including chemical insecticide use, which is being significantly reduced as farmers adopt Bt technology.

The document, dated April 20, 2000, is officially titled "Response of the Environmental Protection Agency to Petition for rulemaking and collateral relief concerning the registration and use of genetically engineered plants expressing Bacillus thuringiensis endotoxins." The full report is available on the EPA website: www.epa.gov/oppbppd1/biopesticides/news/news-greenpeace.htm

The following are significant points quoted from the report:

  • Pollen transfer to wild plants is not likely. "EPA has assessed each of the Bt plant pesticide registrations for likelihood of transgene movement to weedy relatives. EPA believes that in almost all cases, the likelihood of occurrence of such movement is almost non-existent because compatible weedy relatives of Bt crops either do not occur in the United States or are isolated from areas of commercial production. Where compatible weedy relatives do exist in isolated geographic pockets, EPA has imposed stringent sale and distribution restrictions to prevent even the possibility of transgene movement to weedy relatives."
  • Protection for non-target insects. "EPA assesses the toxicity ofÖBtÖto potentially exposed non-target organisms by single species laboratory testing. If toxicity to a particular species is observed, the amount of exposure is quantified and a risk assessment is performed to determine if adverse effects would be expected at the concentrations used under field conditions...Detrimental effects to an individual species observed only under laboratory conditions does not constitute a sufficient basis to declare such species at riskÖEPA believes that evidence supports a conclusion that non-target beneficial organisms are maintained or enhanced in fields where Bt plant-pesticides are usedÖDensities of predatory and non-target insects are generally higher on Bt crops that non-Bt crops solely because Bt crops are not subjected to spraying with nonspecific pesticidesÖEPA believes that available scientific data and information indicates that cultivation of Bt crops has a positive ecological effect, when compared to the most likely alternatives."
  • Bt crops reduce the use of chemical insecticides. "Under normal circumstances, Bt crops require substantially fewer applications of chemical pesticides. This should result in fewer adverse impacts to non-target organisms because application of nonspecific conventional chemical pesticides is known to have an adverse effect on populations of non-target beneficial organismsÖThere is actual data demonstrating that cultivation of these crops has led to decreases in the amount of synthetic chemical insecticides applied."
  • Decomposing Bt crops are not a threat to soil organisms. EPA says the assertion that Bt in crop residue could cause harm to soil organisms "is speculative based on limited laboratory studies which are not applicable to actual field conditions. Soils are the natural habitat of all Bt species (Bacillus thuringiensis is a soil bacterium); therefore Bt is already naturally present during the crop growing seasonÖandÖconstantly available for ingestion by all soil invertebrates." EPA also addressed a study, which petitioners claimed had demonstrated that Bt binds to soil. EPA pointed out that the study showed Bt binding to clay only when the soil had low pH levels (4.9-5.1), which means that in actual agricultural settings, the soil would not be acidic enough to facilitate binding. In order for farmers to grow crops, "Agricultural soils are limed when necessary to be at a pH range of 5.8-7.3ÖTo date, there are no reports of any detrimental effects on the soil ecosystems from the use of Bt crops."
  • Programs are in place to protect against insect resistance. The paper explains that Bt crops deliver a consistent, high dose to eliminate most target pests. It also explains how EPA has mandated the planting of refuges (areas of non-Bt crops) to ensure a supply of susceptible insects to mate with any rare resistant insects that survive exposure to Bt so their offspring would be susceptible. "The high dose/structured refuge strategy has been widely endorsed by the scientific communityÖEPA believes it is significant that, after four years of full-scale commercialization of Bt crops, with approximately 17 million total acres of Bt corn, Bt potato and Bt cotton planted in 1998, EPA has received no confirmed evidence that field resistance to any Bt endotoxin expressed in these crops has occurred in any insect species."
  • Insects are more likely to develop resistance from foliar sprays. EPA points out that foliar sprays used by organic growers do not deliver a consistent high dose. "EPA believes that it has been demonstrated that the best way to reduce the selection pressure of foliar Bt sprays is to minimize their use as much as possible. Unique to plants expressing Bt, however, is the ability to produce season-long expression at relatively high dosesÖMoreover, Bt spraysÖmay pose an even greater selection pressure on the target pest than the relatively high levels of Bt toxins produced in Bt plants."