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The world’s population is growing and more people need more food. But indiscriminately expanding agricultural land and practice is not desirable. Cutting forests to plant more crops will only push already-fragile ecosystems over the edge. Dousing fields with pesticides is similarly toxic and depletes soils and groundwater.
The genetically modified (GM) crops provide a way out. In the 1990s, researchers found a way to modify a plant’s genome and make specific changes that prevented insects from eating them. In the Bt cotton grown in India and Bt brinjal in Bangladesh, scientists added a gene from the bacterium Bacillus thuringiensis to the plants’ genomes, making them produce a toxin that kills some insects.
Weeds threaten farms but spraying herbicides to kill them may kill the crops as well. Now there are herbicide-tolerant (HT) GM crops immune to some weed-killing substances, helping farmers kill the weeds alone. Researchers can also modify crops to have higher yield and/or more nutrients, reducing the need to plant more crops.
The advent of GM crops has helped farmers practise sustainable methods while increasing food production. But depending on the kind of GM crops being grown, there are still broader, longer term effects. Frederik Noack, an economist at the University of British Columbia (UBC), Canada, and others delved into the scientific literature surrounding how farming GM crops may affect human health and the environment.
Their review, published in Science in August, said there are negligible adverse health effects of actually consuming GM crops whereas the farming methods have complex effects.
“What’s complicated about GMs is you’re not just adding a new genetic organism, you’re also adding a whole suite of management changes that come along with it,” Risa Sargent, an ecologist at UBC and one of the review’s authors, said. “The evidence is that those management changes are the risk, not the genetics of the organism per se.”
The use of insecticide-resistant crops, like ones with the Bt toxin trait, has shown low levels of risk and resulted in farmers spraying less insecticides.
“To me, this trait is one of the more positive stories about GM,” said Devang Mehta, a plant biologist at KU Leuven in Belgium. “If you look at India … you see a reduction in insecticide use. Farmers are getting less poisoned by those insecticides because they don’t use those insecticides anymore.” This is important because Indian farmers often lack specialised protective gear.
In some cases, however, pests can develop resistance to the Bt toxin over time, leading to increased pesticide use. This can be countered by diversifying the kinds of Bt crops being planted, including areas where non-Bt crops are planted side-by-side, or by adding more genes to bolster the plant’s resistance to pests.
“If we put in just a single resistance gene, you place a lot of pressure on the pathogen to overcome that gene, but if you create a stack of multiple resistance genes, it’s much more difficult for the pathogen to overcome it,” said Brande Wulff, a plant and food scientist at the King Abdullah University of Science and Technology (KAUST), Saudi Arabia.
The effects are more nuanced with HT crops, however. They are generally made to resist a specific broad-spectrum herbicide. The farmers benefit because they don’t need to expend more labour and money to mechanically remove the weeds: they can just use the herbicide and not worry about their crops dying.
This also reduces tilling, where farmers turn the soil over to kill some weeds before planting crops. Tilling can release carbon trapped in the soil, so no-till agriculture reduces carbon emissions to some extent.
But only a few major companies are developing most of these HT crops in the U.S., so farmers don’t have much say in which herbicide to use.
“GM can be whatever you want it to be. But what it will be depends on who develops it,” Noack said. “The benefit of [HT crops] for the company is that they also sell the herbicide. You can only use that specific herbicide.” The most prominent one companies sell now is glyphosate.
There is no straightforward answer to whether these for-profit companies always keep the environment in mind when they develop and sell their HT crop seeds and the accompanying herbicide.
According to the review, farmers adopting HT crops hasn’t mitigated herbicide use; in some cases it has even led to an increase, especially of glyphosate.
“Initially, people thought glyphosate would be less toxic because it decays pretty fast if it gets into the environment,” said Noack. “Now, very recent studies are showing that it’s actually really harmful for human health.”
A lot of the increased use is also driven by weeds rapidly developing resistance against the herbicides. The more farmers are driven to using a specific herbicide, including glyphosate, the more the weeds can become resistant.
“It’s a little bit similar to the antibiotic resistance in medicine, right? Where if you constantly use the same antibiotic, you have a big problem because the bacteria become resistant to that,” Mehta said. “… if you use the same herbicide over and over in your field, you are building that problem slowly.”
To counter the weed’s resistance to glyphosate, some GM crops have additional modifications that equip them to also resist dicamba, a broad-spectrum herbicide. However, dicamba is potentially more toxic to humans and good at spreading around.
“If you are the neighbour of the farmer who uses that herbicide, and you don’t plant GM crops, it just kills all of your crops,” Noack said. “The general problem is each time we come up with a new pesticide, we’ll create problems downstream.”
Scientists ascertain a pesticide’s toxicity by testing its short-term effects on rats, although that doesn’t reveal the full extent of its effects. “That’s of course a very different question than to see what’s the long-term impact on infant health,” Noack added. “If it’s causing cancer, we won’t see that in the rat population because the rats won’t live long enough to show that.”
“Industry wants the release right away. They’ve developed some new technology. They want to be able to sell it, which makes sense. That’s the capitalistic driver of it,” Sargent said. “But we can’t just give pesticides to people and see what happens. Often it takes years and years of very careful science to tease out the impacts.”
Noack believes another reason resistance develops and spreads is if the farmers all plant the same crops and use the same herbicides. Crop rotation — where farmers plant different crops in the same area — can help reduce the reliance on agro-chemicals and lower resistance.
Sargent suggested using evidence-based precautionary measures of pest management, which involve not excessively using herbicides to kill every weed in the field. “Let’s say a complete ban on pesticides is one extreme, and probably our current agricultural system in many places is the other extreme. Somewhere in the middle is an approach such as … or integrated pest management,” she said.
“The protocol is that there’s a certain level of accepted weeds in a field that would be determined between a … specialist and the farmer working together.”
The few companies that make and sell HT crops have monopolised their production. It’s prohibitively expensive to regulate GM crops (more than $40 million for a single GM trait to be regulated and eventually commercialised), leaving most government institutions and smaller companies behind.
Modern tools like CRISPR help scientists make targeted changes to a plant’s genome, cutting the cost of development. People are also more accepting of GM when the plant doesn’t have foreign genes. But the costs of regulation and ensuring nothing harmful enters the market is still too high for institutions that don’t only work for profit.
“I think the problem is that a lot of the regulations, including in India, are based on ‘is it a GM or is it not a GM’. It’s not about whether it’s herbicide, insecticide or nutrition,” said Mehta. “They don’t care about the trait, they care only about the method, which is a very black and white way of doing things.”
The review also found more data is required to assess the true impact of GM on biodiversity. In some places, the number of insect pollinators has dropped but whether that’s due to GM crops or to urbanisation, climate change, and/or other drivers of habitat loss is unclear.
“We have very little longitudinal data on species trends for almost any species. For most insects, most amphibians, most mammals, how would you possibly go back and say, ‘here are the clear effects on biodiversity’ when we have almost no data?” Sargent asked.
Another confounding factor is that a lot of the research on GM and biodiversity is sponsored by industries, according to Sargent, which is muddying the waters.
Mark Tester, a botanist at KAUST, said many of the potential environmental effects attributed to GM crop-farming are not unique to GM: they’re just the natural consequences of agriculture. “You can think of it as a war between agriculture and nature, where we’re trying to feed eight billion people,” he said. “We’re using the same amount of land that we were using for feeding six billion, which means we must increase production efficiencies by 30%.”
“That’s definitely difficult.”
Rohini Subrahmanyam is a freelance journalist in Bengaluru.
Published - November 21, 2024 05:30 am IST