THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
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
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Malaysia
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DAPHNIA MAGNA NEGATIVELY AFFECTED BY CHRONIC EXPOSURE TO PURIFIED CRY-TOXINS
Thomas Bøhn, Carina Macagnan Rover, Philipp Robert Semenchuk
http://www.sciencedirect.com/science/article/pii/S0278691516300722
Abstract
Cry-toxin genes originating from Bacillus thuringiensis are inserted into genetically modified (GM) plants, often called Bt-plants, to provide insect resistance to pests. Significant amounts of Bt-plant residues, and thus Cry-toxins, will be shed to soil and aquatic environments. We exposed Daphnia magna to purified Cry1Ab and Cry2Aa toxins for the full life-span of the animals. We used single toxins in different doses and combinations of toxins and Roundup®, another potential stressor on the rise in agricultural ecosystems. 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. Animals exposed to 0.75 mg/L also showed a tendency towards increased mortality but with increased early fecundity compared to the controls. Roundup® stimulated animals to strong early reproductive output at the cost of later rapid mortality. We conclude that i) purified Cry-toxins in high concentrations are toxic to D. magna, indicating alternative modes-of-action for these Cry-toxins; ii) Cry-toxins act in combination, indicating that ‘stacked events’ may have stronger effects on non-target organisms; iii) further studies need to be done on combinatorial effects of multiple Cry-toxins and herbicides that co-occur in the environment.
Conclusions and Further Recommendations
Our new results support and complements earlier feeding studies with whole plant material (Bøhn et al., 2008, 2010; Holderbaum et al., 2015) and leads to the conclusion that both purified and plant produced Cry-toxins are negatively affecting survival and fitness of D. magna, an important filter-feeder in aquatic ecosystems worldwide. Further, our results confirm that high concentrations of Cry-toxins are able to harm the non-target organism D. magna, through environmental exposure. This indicates that: i) Cry-toxins have alternative modes-of-action than previously described, and ii) also other non-target organisms in relevant, i.e. exposed, aquatic ecosystems may be negatively affected by Cry-toxins. Both points warrant further investigations. We also conclude that potential negative effects on non-target organisms from stacked events that co-produce several Cry-toxins, and/or herbicide tolerance traits, likely will be stronger than from single event plants.
We need to improve the understanding of the fate of residues of transgenic material and Cry-toxins in run-off aquatic environments. We recommend more detailed studies under ecologically more realistic conditions, such as in mesocosm or field studies. The species pool for testing should include key species from different functional groups, and should represent the actual agricultural region for cultivation of the plants (Andow and Hilbeck, 2004; Gillund et al., 2013; Hilbeck et al., 2014). We also suggest further studies on the physiological effects of different Cry-toxins to gain a mechanistic understanding of their function to be better able to assess the risk of releasing them into the environment.
The lack of detailed studies on exposure and uptake pathways and modes-of-action of Cry-toxins, also in combination with agrochemicals like Roundup/glyphosate, are needed to understand observed negative effects of these key agricultural toxins. Further research efforts can lead to a development of improved management practices that will conserve species diversity and ecosystem functioning and services for the future.