Oct 19, 2010
Environmental impacts of genetically modified Bt maize
“The impact of Bt maize on water bodies in Europe has not been sufficiently researched”
Whether Bt maize can harm aquatic organisms like caddis-fly larvae has become a key topic in the scientific debate about the biosafety of Bt maize. The German ban on the cultivation of Bt maize MON810, which has been in force since 2009, is based in part on the results of a study published in 2007. A team of researchers led by Rosi-Marshall of Loyola University Chicago (USA) demonstrated in laboratory tests that caddis-fly larvae showed increased mortality and lower growth rates when they were exposed to the Bt protein Cry1Ab. Other scientists have challenged the significance of this study.
Dr Steffi Ober, an expert on genetic engineering and nature conservation at Germany’s Nature and Biodiversity Conservation Union (NABU) talks about the potential impacts of Bt maize on water bodies: “Fundamental data is still missing, so the precautionary principle should apply.”
The water-dwelling larvae of the caddis-fly are related to the moths that the Bt protein targets. This means that they could be harmed by Bt maize. Photo: Wikimedia
When silage maize is harvested, the plants are chopped into small pieces on the field itself. Parts of Bt maize plants could therefore be carried straight into nearby water bodies by wind and rain, where they could harm non-target organisms like caddis-flies.
During the maize-flowering period, the male flowers dispense a lot of pollen that can be carried into water bodies by the wind.
Caterpillars of the small tortoiseshell butterfly on their food plant (stinging nettle).
A project by Germany’s Federal Agency for Nature Conservation (BfN) which runs until 2011 is designed to facilitate a more accurate assessment of the risks posed by Bt maize cultivation in protected areas and water bodies in Brandenburg. The researchers are checking to what extent non-target organisms like caterpillars are exposed to Bt maize pollen on their food plants. They are also measuring how much Bt maize (pollen or litter) enters water bodies.
The doubts expressed centred around the belief that these effects occurred only when Bt- concentrations were used in higher concentrations than can be expected in the field, and on the fact that the original study did not have proper controls. The observed effects could not therefore be clearly attributed to the Bt protein. A study published this year by the University of Maryland (USA) also challenges Rosi-Marshall’s conclusions. The researchers led by Peter Jensen were able to show that Bt maize plant parts no longer had any impact on two species of caddis-fly larvae or the European corn borer two weeks after harvest. The Bt proteinin water bodies would appear to be broken down quickly under natural conditions to a point where it is no longer active.ist.
GMO Safety spoke to Steffi Ober of Germany’s Nature and Biodiversity Conservation Union (NABU) about these findings. Dr Ober is involved in a research project by the Federal Agency for Nature Conservation (BfN) to enable a more accurate assessment of the risks posed by Bt maize cultivation in protected areas and water bodies in Brandenburg.
GMO Safety: In her laboratory study, Rosi-Marshall came to the conclusion that caddis-fly larvae can be harmed by the Bt protein Cry1Ab. The new study by Peter Jensen challenges this finding. His study found that most of the Bt plant material does not enter water bodies until months after harvest and that the Bt protein it contains is inactive after just two weeks. Does this mean that Bt maize can be given the all-clear?
Steffi Ober: We can’t talk about an all-clear because the Jensen paper assumes there is a big distance between the maize field and water bodies. However, we have to look at the special situation in Germany, which differs fundamentally from maize cultivation in the USA. Whereas agricultural areas and protected areas in the USA tend to be large and far apart, in Brandenburg, for instance, the Natura 2000 areas s and fields are much closer to one another. The maize fields often stretch right down to the water’s edge. Since silage maize is chopped up on the field in Germany, this means that fresh plant material containing Bt toxin could enter the water immediately. This material must surely contain Bt toxin that is still bioactive that could immediately be ingested by caddis-fly larvae and a few other aquatic organisms.
GMO Safety: Does that mean, put simply, that caddis-flies are not at risk from Bt maize in the USA, but that we need more research in Germany?
Steffi Ober: It’s not quite as simple as that. Jensen’s research in the USA throws up some important research questions. In general, the publication poses more questions than it answers. So there is no all-clear for the situation in the USA. Firstly, the absence of any effect on the research organisms could be attributable to other factors and, secondly, there are organisms that are more sensitive to Bt toxin than the European corn borer. In theory, it could be possible for these organisms to be harmed even if the European corn borer shows no effects.
Neither do we know what happens to the Bt concentrations in the first two weeks. All we have is a statement that the Bioassay produces a positive result at time 0 and that after two weeks no Bt toxin effect can be detected on the larvae. Since the bioassay did not involve the usual ‘positive control’ group, the test system may have been defective. Yet this question is extremely important for interpreting the results.
After all, the indications of possible negative effects on other Non-target Organisms like crane flies and water lice have not been adequately clarified. One Bt plant was found to have negative effects on these insects, while another Bt plant was not. It is possible that the varietal background of a transgenic plant has impacts on the plant’s toxicity. We see a need for further research here.
GMO Safety: Has the ‘Bt maize and water body’ issue been neglected too much in risk assessments generally?
Steffi Ober: Yes, because is was practically nonexistent until 2007. The research by Rosi-Marshall in 2007 does at least clearly show that caddis-fly larvae, for instance, can be harmed by Bt toxins. The larvae are very opportunistic and feed on whatever happens to be available, including Bt maize. Pollen grains are regularly found in the intestines of caddis-fly larvae. So it is likely that they ingest maize pollen directly, as Rosi-Marshall was able to demonstrate. However, there are still no systematic toxicological or ecotoxicological tests for the sensitivity of this group to the various Bt proteins, even though caddis-flies play an important role in the ecological complex of interactions. The impact of Bt maize on water bodies in Europe has not been researched. There are just a few papers from the USA on this topic.
GMO Safety: You appear to believe that caddis-flies are particularly deserving of protection. What ecological role to caddis-flies play in aquatic environments?
Steffi Ober: The various types of water body in Brandenburg, for example, are relatively intact with high numbers of caddis-fly species and a high level of species diversity. There are 1400 species of caddis-fly in Europe. Austria, Switzerland and Germany have around 300 species each, including many that are on the red list of endangered species. They are an important part of the biocoenosis and of the food web. Some species are an important basic component of the fish diet. If caddis-flies were to disappear from streams, rivers and lakes, this would lead to a significant depletion of fauna and restrict ecosystem functions.
GMO Safety: What are the aims of your project in Brandenburg?
Steffi Ober: The state of Brandenburg is rich in protected biotopes that contain water bodies. Maize cultivation increased by 40 per cent in Brandenburg between 2005 and 2009. In 2007 and 2008, MON 810 maize containing the Bt toxin Cry1Ab was grown. For the enforcement of nature conservation laws in the regional authorities, this then poses the general question of how to assess the risk posed by Bt maize cultivation to protected areas. The project aims to facilitate a more accurate assessment of inputs of maize material into the environment.
GMO Safety: Which concrete questions do you hope to answer in your project?
Steffi Ober: The project has several parts. We want to clarify the extent of the potential Bt toxin input in protected areas and the possible risks that this poses for protection targets like butterflies and aquatic ecosystems. One key part of the project is dealing with pollen inputs. Preparatory projects over a number of years have developed models for estimating worst-case scenario figures for inputs of Bt pollen into the surrounding landscape as a function of the location of the maize fields, meteorological conditions and field size. One of the aims of this project is to validate this model using field data so as to obtain a more accurate assessment of Bt pollen inputs carried by air into protected areas. To measure the exposure of non-target organisms, e.g. caterpillars, more accurately, we are also studying the distribution of the pollen grains that leave the maize field and land on various insect food plants. We are interested in where exactly on the leaf structures the pollen grains accumulate. Our hypothesis is that the distribution of pollen grains is very uneven. Caterpillars like to eat pollen and can therefore be exposed to very different doses, depending on whether they eat the edge of the leaf or the central axis.
GMO Safety: What research is being conducted on the input of Bt plant material into water bodies?
Steffi Ober: We are measuring the input of maize plant material into water bodies in the form of pollen, litter and other plant remains. Almost all the maize grown in Brandenburg is silage maize. The maize is chopped up during harvesting and transported in its chopped state. Some is lost through the wind and as a result of the harvesting method and either stays on the field or enters the surrounding areas. If there are ditches or other water bodies next to the maize fields, the chopped plant material enters the aquatic ecosystems immediately. This is very different from the situation in the USA. There, it is just the cobs that are harvested and the whole maize plant is left on the field.
GMO Safety: Which species of animal in the water bodies you are studying could be harmed by Bt toxins?
Steffi Ober: We are not currently in a position to answer this question, since we do not have the relevant effect data. To identify animal groups that might be exposed to the toxin, we will be holding workshops to define potential non-target organisms and effect chains. We will propose the resulting research questions for further research. We will finish our research in 2011 and present the results at the same time.
GMO Safety: Will your research also measure how long Bt proteins in pollen or other plant remains remain bioactive under real environmental conditions? It is surely only with this kind of data that the actual risk for certain animal groups can be assessed.
Steffi Ober: A risk analysis consists of several stages. First of all, it is important to be able to assess the exposure level. Fundamental data is still missing here and we will be able to go a long way towards closing this gap. It is the combination of exposure and effect data that will give us the potential risk. However, a final, comprehensive risk analysis is not achievable in our relatively small project.
GMO Safety: So research like this would have to follow then, in order to be able to measure the risk for the biotopes being investigated?
Steffi Ober: Yes, the idea is for this kind of research to follow. However, this raises the issue that we currently do not have some basic data relating to aquatic systems and therefore the precautionary principle should apply. The question of how long Bt protein persists in the environment or the question of bioactivity are not enough on their own. In view of the complexity of ecosystems, asking for a clear-cut answer does not reflect the reality.
GMO Safety: Thank you for talking to us.
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Studies: Impacts of Bt maize on water bodies
- Tank J.L., Rosi-Marshall E.J. et al. (2007) Toxins in transgenic crop byproducts may affect headwater stream ecosystems. PNAS, Vol. 104 (Abstract)
- Tank J.L., Rosi-Marshall E.J. et al. (2010) Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape. PNAS, online veröffentlicht am 27.09.2010, (Abstract)
- Jensen P.D. et al. (2010) Exposure and Nontarget Effects of Transgenic Bt Corn Debris in Stream; Environmental Entomology, 39(2), pp.707-714, (Abstract)