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bt toxins can harm non-target organisms, with stronger combinatorial effects

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Credit: Zing Deretsky, National Science Foundation

Dear Friends and Colleagues,

Bt toxins can harm non-target organisms, with stronger combinatorial effects  

Cry-toxin genes originating from Bacillus thuringiensis (Bt) are inserted into genetically modified (GM) plants, often called Bt-plants, to confer insect resistance to pests. Industry has consistently claimed that such insect protection is specific to target pests only i.e., not harmful to non-target species and biodiversity.

A new study exposed Daphnia magna (a waterflea which is an important filter-feeder in aquatic ecosystems worldwide) to purified Cry1Ab and Cry2Aa toxins for the full lifespan of the animals. Animals exposed to 4.5 mg/L (ppm) of Cry1Ab, Cry2Aa and the combination of both showed markedly higher mortality, smaller body size and very low juvenile production compared to controls. Moreover, exposure to two Cry-toxins gave stronger effects in combination. In addition the herbicide Roundup stimulated animals to strong early reproductive output at the cost of later rapid mortality.

This shows that Cry-toxins can have alternative modes-of-action in non-target organisms. The study also raises the concern that stacked GM plants that co-produce several Cry-toxins, and/or herbicide tolerance traits may have stronger negative effects on non-target organisms as compared to single-trait plants.

The researchers recommend more detailed studies on the combinatorial effects of multiple Cry-toxins and herbicides (like glyphosate/Roundup) that co-occur in the environment and on the physiological effects of different Cry-toxins. This will enable regulatory authorities to better assess the risks of releasing GM plants into the environment and the fate of residues of transgenic material and Cry-toxins in run-off to aquatic environments.

With best wishes,

Third World Network
131 Jalan Macalister
10400 Penang
Malaysia
Website: http://www.biosafety-info.net/

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