Bt products are found to be safe for use in the environment and with mammals. The EPA (environmental protection agency) has not found any human health hazards related to using Bt. In fact the EPA has found Bt safe enough that it has exempted Bt from food residue tolerances, groundwater restrictions, endangered species labeling and special review requirements. Bt is often used near lakes, rivers and dwellings, and has no known effect on wildlife such as mammals, birds, and fish.
Humans exposed orally to 1000 mg/day for 3-5 days of Bt have showed no ill effects. Many tests have been conducted on test animals using different types of exposures. The results of the tests showed that the use of Bt causes few if any negative effects. Bt does not persist in the digestive systems of mammals.
Bt is found to be an eye irritant on test rabbits. There is very slight irritation from inhalation in test animals which may be caused by the physical rather than the biological properties of the Bt formulation tested.
Bt has not been shown to have any chronic toxicity or any carcinogenic effects. There are also no indication that Bt causes reproductive effects or birth defects in mammals.
Bt breaks down readily in the environment. Because of this Bt poses no threat to groundwater. Bt also breaks down under the ultraviolet (UV) light of the sun.
Even with such widespread use of Bt-based products in the past 50 years, only two incidents of repored allergic reaction have been reported to the EPA. In the first incident, it was concluded that the exposed individual was suffering from a previously diagnosed disease. The second involved a person that had a history of life-threatening food allergies.Upon investigation, it was found that the formulation of Bt also contained carbohydrate and preservatives which have been implicated in food allergy.
Reference: Bacillus thuringiensis: Biology, Ecology
and Safety, Glare, T.R., O'Callaghan, M. (2000) ISBN 0-471-49630-8