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Examining the scientific evidence against genetically modified foods

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Though the balance of evidence supports the idea that genetically modified foods are safe to eat and don't harm the environment, a few reports have suggested otherwise. Here are three of them.

•French scientists reported in September that rats fed a lifelong diet of Roundup-resistant corn developed more tumors and died earlier than rats fed conventional corn. The widely publicized study, published in the journal Food and Chemical Toxicology, was conducted by Gilles-Eric Seralini, the scientific head of an independent institute opposed to genetically modified foods.

Geneticists, statisticians and other researchers broadly panned the research for its small sample size and other methodological problems. It was reviewed and dismissed by the European Food Safety Authority, Germany's risk assessment agency and France's six scientific academies.

•A 1999 study in Nature by Cornell University scientists found that monarch butterfly larvae fed milkweed covered with pollen from genetically altered corn died in greater numbers than ones exposed to nonengineered pollen. The corn had been modified with a gene from a soil bacterium so it made a natural insecticide.

In five follow-up analyses published two years later in the Proceedings of the National Academy of Sciences, researchers concluded that caterpillars would have to be exposed to more than 1,000 grains of engineered pollen per square centimeter of leaf surface to suffer harm and that the highest levels of altered pollen they are exposed to comes nowhere close to this. The exception was one strain of modified corn, Bt176, that caused growth delays at lower concentrations.

Bt176 was never popular with farmers and is no longer sold in the U.S. But that was dumb luck, said Marcia Ishii-Eiteman, a senior scientist with the Pesticide Action Network in Oakland — and that experience makes the case for more stringent oversight, she said.

•A study this month by Chuck Benbrook of Washington State University reported that since 1996, when genetically modified crops were first planted in U.S. fields, rates of herbicide use — notably, Roundup — have risen steeply, though insecticide use fell. Benbrook, who conducted this research while he was the chief scientist at the advocacy group the Organic Center, documented a net pesticide increase of 404 million pounds per year.

Other scientists acknowledge that Roundup use has climbed as weeds developed resistance to the herbicide. But they say the report fails to factor in benefits: Roundup is less toxic than the herbicides it displaced and its use allows farmers to leave fields untilled, reducing soil erosion. Analysts wrote that Benbrook's report, in Environmental Sciences Europe, is at odds with other studies and contains assumptions and missing data that combine to overestimate herbicide use for engineered crops.

rosie.mestel@latimes.com

Copyright © 2014, Los Angeles Times
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