Ladybird on Maize

Hazards to non-target insects and mammals from multi-trait Bt insecticidal crops are being ignored by regulators, a new scientific review shows. Claire Robinson reports

An increasing number of “stacked-trait” GM Bt insecticidal crops combining several Bt toxins in one variety are coming onto the market. We’re assured that they’re safe. But evidence presented in a comprehensive new review throws this claim into question.

Stacked-trait GM crops are produced by cross-breeding single or double-trait GM Bt crops. They have been approved as safe based on several assumptions.

For example, individual Bt toxins are often thought only to harm a few target insect pests and not to affect non-target and beneficial organisms, like ladybirds and lacewings. Also, regulators accept the argument from the industry and allied scientists that if the single Bt toxins included in the stacked crop are individually deemed safe, a combination of several Bt toxins and other GM traits present in stacked GM Bt crops will also be safe.

But these assumptions are shown to be false by scientific evidence, the new review shows. The authors, Angelika Hilbeck of the Swiss Federal Institute of Technology and Mathias Otto of the German Federal Agency for Nature Conservation, reviewed the scientific literature for evidence of Bt toxin effects on non-target organisms and for combined effects of several Bt toxins acting together. Then they compared their findings to the regulatory dossiers provided by industry to support approval of stacked-trait GMOs.

Their findings make for sobering reading.

Bt toxins don’t only affect certain insect pests

First, Hilbeck and Otto addressed the declaration made by industry and regulators that Bt toxins are specific to certain insect pests and no documented cases of non-target effects on beneficial insects exist. They found that the evidence points to the opposite conclusion. Research studies show that individual Bt toxins can have harmful effects on beneficial and non-target organisms. But the industry dossiers submitted to regulators ignore these studies and maintain the fiction that Bt toxins only harm the target insect pests.

Lead researcher Hilbeck commented in an interview, “The notion of a narrow specificity for Bt toxins is not true. Those who talk of narrow specificity base this on a narrow definition of an effect – the ‘quick kill’ effect.

“This is an economic concept: you want a quick kill for economic reasons, to save the crop from pest-induced damage.

“But Bt toxins are not fast-acting toxins. Even in target pests, Bt toxins don’t kill quickly – it takes most susceptible insects a day or more to die. The Bt toxin in GM crops is expressed in the crop plant for months at a time. Residues linger in soil and aquatic systems.

“Regulatory tests need to look at long-term and sublethal effects, because that is what non-target organisms are likely to be exposed to. Currently these tests are not required. Yet we found a lot of evidence in the scientific literature that non-target organisms such as ladybirds, water fleas, lacewings and even slugs are adversely affected by Bt toxins.”

Hilbeck warns that mammals may be affected, too. She mentions a separate newly published review, which concluded that Bt toxins “cannot be considered innocuous, as they have some physiological effects that may become pathological”.

Hilbeck suggests a direction for future research on non-targets: “We have to extend the definition of ‘effect’ from the economic to the ecological.” She believes that pre-market safety testing should include long-term animal feeding studies with the complete stacked-trait crop. Currently these are not required by any regulator in the world.

“Drastically increased” Bt toxin load

Another commonly ignored issue in risk assessment of stacked-trait Bt crops is the large amount of Bt toxins expressed in them – which is far higher than in single-trait Bt crops. Together, the pyramid of different Bt toxins go to make up what the researchers call a “drastically increased” Bt toxin load.

And in spite of frequent claims that Bt crops reduce or eliminate pesticides, stacked-trait Bt crops contain far more insecticide than the amount of chemical insecticide that is supposed to be displaced. For example, SmartStax GM maize contains six different Bt toxins (as well as two herbicide-tolerant traits). The total Bt insecticidal protein production of the crop is estimated at 4.2 kgs/ha, 19 times the average conventional insecticide rate of application in 2010.

Yet SmartStax stacked-trait maize was approved for EU food and feed imports without thorough safety testing of the whole GM crop containing the complete Bt toxin package in laboratory animals or non-target organisms. In an interview, Hilbeck commented that only the individual isolated Bt toxins that went into developing the stacked-trait crop may have been tested by industry for short-term safety in few insect feeding trials.

Combination toxic effects ignored

As well as the increased amount of Bt toxins found in stacked-trait crops, there is also the question of whether potential interactions and combined toxic effects of the different GM traits and chemical residues contained in stacked-trait Bt crops could harm consumers and non-target insects. And both GM and non-GM seeds are often treated with neonicotinoid insecticides, which add to the cocktail of known and potential toxins.

In spite of these biological and chemical “cocktail” risks, Hilbeck and Otto say that most regulators, including the European Food Safety Authority (EFSA), still limit the environmental risk assessment of stacked-trait Bt crops to consider one Bt toxin at a time, in isolation. And that single Bt toxin is tested not as it is expressed in the GM Bt crop plant, but only as a single purified protein produced in bacteria, in testing schemes developed for the regulatory approval of acute toxins like synthetic insecticides.

The independent research group Testbiotech has previously warned that combination and synergistic effects of the elements in stacked-trait crops are being ignored by regulators.

That view is backed by first-hand experience of the author of this article at a public meeting of the European Food Safety Authority (EFSA), which issues safety opinions on GM foods and pesticides. A member of the EFSA GMO Panel asserted without qualification that the various GM traits and chemical residues combined in any authorized GMO stacked-trait crop “will not interact”. When challenged, the panel member presented no evidence for this broad claim.

Hilbeck and Otto put such claims to the test. They searched the literature for research on the combined and synergistic effects on beneficial and non-target organisms of multiple Bt toxins, or of Bt toxins together with other proteins, chemicals, or plant components. They found a number of studies showing interactions and combined effects, the mechanisms of which are not fully understood.

Crucially, in a finding that directly challenges EFSA’s reductionist “one-at-a-time” approach to stacked-trait crops, Hilbeck and Otto discovered that many synergistic interactions in target organisms were not predictable from single trait effects. They occurred when the individual components tested in isolation did not elicit a response at all or elicited only a sublethal response.

Modes of action of Bt toxins getting murkier over time

The assumed safety of Bt toxins for non-targets and human and animal consumers largely rests on their claimed specificity to insect pests. But this claim in turn rests on research on a narrow set of target insect pests, studying mostly a single type of Bt toxin.

And as scientific research and knowledge has grown, uncertainty about how Bt toxins exert their effects has increased. Hilbeck and Otto state in their paper that today there is “less scientific certainty” about Bt toxins’ mode of action than when Bt toxin genes were first engineered into GM plants 30 years ago.

The situation is made even murkier by the fact that one of the most promoted of possible modes of action has been cast into doubt by a case of apparent scientific misconduct. In 2012 it emerged that the researchers who came up with the proposal, husband and wife team Alejandra Bravo and Mario Soberon, had manipulated images in 11 papers. The researchers had offered the images as evidence for their proposed mode of action for Bt toxins. They have at least one patent related to their work.

The episode resulted in seven journals agreeing to publish corrections and to Bravo and Oberon resigning from chair positions they held at the National Autonomous University of Mexico.

Their model for Bt toxins’ mode of action has been critiqued by a Canadian team of researchers as “difficult to reconcile” with evidence generated by other investigations. The Canadian team concluded, “Many important questions concerning the mechanism by which insect cells are killed by Bt toxins remain just as poorly understood as they were before these models were put forward.”

The sum of known and unknown factors about GM Bt toxins lead Hilbeck and Otto to conclude that while stacked GM crops may offer benefits to some farmers, “these benefits may come with serious health and environmental risks” that should be experimentally studied before market approval. They recommend a “comprehensive examination of the systems, organs, tissues and cells” of non-target organisms and animal and human consumers, “especially the gastrointestinal tract, the immune system, the genitourinary tract and the respiratory and nervous systems.” They also call for further studies on the sub-chronic, chronic and immunotoxicological effects of Bt toxins, particularly on humans.

Review article: Specificity and combinatorial Effects of Bacillus thuringiensis Cry toxins in the Context of GMO environmental risk assessment

Angelika Hilbeck and Mathias Otto
Front. Environ. Sci., 9 November 2015

Stacked GM crops expressing up to six Cry toxins from Bacillus thuringiensis (Bt) are today replacing the formerly grown single-transgene GM crop varieties. Stacking of multiple Cry toxins not only increase the environmental load of toxins but also raise the question on how possible interactions of the toxins can be assessed for risk assessment, which is mandatory for GM crops. However, no operational guidelines for a testing strategy or testing procedures exist. From the developers point of view, little data testing for combinatorial effects of Cry toxins is necessary as the range of possibly affected organisms focuses on pest species and no evidence is claimed to exist pointing to combinatorial effects on non-target organisms. We have examined this rationale critically using information reported in the scientific literature. To do so, we address the hypothesis of narrow specificity of Cry toxins subdivided into three underlying different conceptual conditions (i) “efficacy” in target pests as indicator for “narrow specificity,” (ii) lack of reported adverse effects of Cry toxins on non-target organisms, and (iii) proposed modes of action of Cry toxins (or the lack thereof) as mechanisms underlying the reported activity/efficacy/specificity of Cry toxins. Complementary to this information, we evaluate reports about outcomes of combinatorial effect testing of Cry toxins in the scientific literature and relate those findings to the practice of environmental risk assessment of Bt-crops in general and of stacked Bt-events in particular.