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(Reuters) - The refusal of some foreign buyers to purchase U.S. wheat after an unapproved genetically modified strain was discovered growing in a farm field in Oregon is the latest demonstration that the issue of biotech food safety is far from settled.
Japan and South Korea canceled purchases of U.S. wheat after the discovery of the experimental wheat developed by Monsanto Co. The furor erupted just days after a May 25 protest in cities around the world targeting Monsanto, the leading developer of crops with transgenic DNA.
At the crux of the concerns is the question of safety. While crop developers and U.S. regulators say that biotech crops on the market are safe, there are widespread fears that gene-altered crops, carrying DNA from other species, are harmful to humans and animals that consume them.
Both sides of the debate say scientific studies buttress their points.
"I think there is a strong international consensus that the current crops grown in the U.S. are safe to eat," said Greg Jaffe, director of biotechnology at Center for Science in the Public Interest, a health and food safety advocacy group.
Not so says Dave Schubert, who heads the cellular neurobiology laboratory at the Salk Institute for Biological Studies in San Diego, California.
"There is no evidence that any GM plant is safe to eat and there are solid data showing that necessary components of the GM technology, like herbicides, are toxic and carcinogenic," Schubert said. "Almost daily there are more problems coming to light."
It has been 17 years since Monsanto and rivals including DuPont and Dow Chemical rolled out genetically altered crops, and they say their tests show no safety concerns. Also, the chief U.S. authority for food safety, the Food and Drug Administration, says there is no need for either mandatory safety testing or labeling of foods made with GMOs.
FDA officials also say no credible independent research has found harm from GMOs, and many independent studies show genetically altered crops are as safe as conventional ones.
There are many studies to back them up. A group of seven scientists from Europe reviewing 24 animal-feeding studies in 2011 found that none of the studies showed evidence of health hazards, according to their article in the peer-reviewed Food and Chemical Toxicology journal.
An older 2003 Society of Toxicology position paper said potential adverse health impacts from biotech foods appeared no different from other foods.
But other studies indicate potential dangers. Some see a risk of new toxins or allergens stemming from new combinations of genes that would not occur naturally. Others say people or animals could be hurt by residues of the weed-killing chemicals that might linger in food made from biotech crops.
A report published in April by a researcher at the Massachusetts Institute of Technology said health problems could be linked to herbicides lingering in food. A study last year by French scientist Gilles-Eric Seralini and seven other researchers showed organ damage and increased tumor rates on rats fed Roundup Ready corn with trace amounts of herbicide.
Research published in 2008 by a group of Italian scientists found biotech corn appeared to harm the gut and immune systems of mice. Another mouse study in 2008 found liver problems after ingestion of GMO soy.
And a pair of Greek scientists in 2009 said they found enough evidence of harm from GMO foods to warrant extensive testing.
"Since these GM foods are going to be consumed by every human being they should be tested even more thoroughly than drugs, and more experiments are required in order to study the possible toxicity and make any conclusions," said the 2009 paper by Artemis Dona of the University of Athens Medical School, and Ioannis Arvanitoyannis of the University of Thessaly School of Agricultural Sciences. "Results indicate that many GM food have some common toxic effects."
The Biotechnology Industry Organization, which represents the interests of biotech developers, disagrees.
"The safety of biotech-derived food products has been thoroughly addressed by the international scientific community," said Colleen Lerro, a spokeswoman for the industry lobby.
GM crop manufacturers use DNA from other species, including types of bacteria, to splice into crops to alter the way they function in the fields. Popular crops not only survive treatments of toxic weedkiller; they manufacture their own toxins to kill insects.
When new biotech crops are developed, companies are not required to apply for FDA approval, but are encouraged to share testing data with FDA scientists. The agency signs off on such a "voluntary consultation" with a letter reminding the biotech company it is responsible for ensuring its GM food is safe.
In an October 2011 letter to Monsanto regarding a new genetically altered soybean, the FDA wrote that Monsanto's testing concluded the soybean "is not materially different in any respect relevant to food or feed safety" from other soybeans. The FDA added that: "It is Monsanto's continuing responsibility to ensure that foods marketed by the firm are safe, wholesome and in compliance" with regulations.
Jason Dietz, a policy analyst in the FDA's Center for Food Safety and Applied Nutrition, said the FDA is exerting responsible oversight. "We think our process is actually quite, quite good and protects public health," said Dietz.
"Firms producing these crops do extensive safety testing before marketing," Dietz added. "It is a firm's responsibility to ensure the safety of the food it markets."
Some scientists are critical of the FDA approach.
"Our regulation ... largely leaves the companies in charge of the safety testing protocols," said Doug Gurian-Sherman, a senior scientist specializing in food at the Union of Concerned Scientists, a pressure group. "That does not strike me as in the best interest of the public."
Reporting By Carey Gillam; Editing by David Gregorio