SAfETY of Bt Insecticides to Humans

Studies of the direct effects of Bt strains used in insecticides on humans are rare because, like many other microbial and chemical products, Bt strains and formulations are tested on surrogate vertebrates, primarily rats and rabbits. Data maintained by various health agencies, as well as published summaries of these data, demonstrate that, for example, the Btk and Bti strains used in commercial formulations are not infective or toxic to these test vertebrate animals (Table 3.6). Similar results have been obtained repeatedly despite the very large amounts of test materials used in these studies, which are 100- to more than 1000-fold the amount of material used to control insect pests.36 As a result, most assessments of the safety of Bt to humans

TABLE 3.5

Effects of Bacillus thuringiensis subsp. israelensis on Aquatic Nontarget Organisms when Used in River Habitats for Control of Black Fly Larvaea

Major Croups Studiedb

Mayflies, Caddisflies, Dragonflies, Damselflies, Molluscs

Caddisflies, Stoneflies, Beetles, Mayflies, Dragonflies, and Damselflies Midges, Mayflies, Caddisflies

Midges, Caddisflies Mayflies, Stoneflies

Mayflies, Caddisflies,

Stoneflies, Beetles, Midges

Midges

Mayflies, Caddisflies,

Stoneflies, Midges, Gastropods

Midges

Midges, Stoneflies, Mayflies, Caddisflies

Mayflies, Stoneflies, Caddisflies, Midges,

Beetles

Formulation Sampling

Powder

Aqueous

Aqueous

Powder

Aqueous

Aqueous Aqueous

Aqueous

Aqueous

Powder

Drift

Substrate analysis

Drift

Drift

Substrate analysis

Drift and substrate analysis

Drift

Impact

No adverse effects

Location

Ivory Coast

No adverse effects Newfoundland

Increased drift, some midge

Ivory Coast

Substrate No adverse effects United States analysis

Substrate No adverse effects New Zealand analysis

No adverse effects South Africa

Drift and Mayfly and midge substrate mortality; some analysis gastropod reduction

Some reduction at 17x recommended application rate

Increased drift of two midge types; no other effects

No significant adverse effects

South Africa

Germany

Canada

United States a Modified from Lacey, L.A. and Mulla, M.S., in Bacterial Control of Mosquitoes & Blackflies: Biochemistry, Genetics, & Applications of Bacillus thuringiensis and Bacillus sphaericus, de Barjac, H. and Sutherland, D.J., Eds., Rutgers University Press, New Brunswick, NJ, 1990. b Other than midges, most of these groups have been shown to not be sensitive to the toxins of B. t. subsp. israelensis based on laboratory studies. Therefore, the increase in drift after application has been attributed to the increase in formulation particulates in the water due to the application.

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