Filed at 7:21 p.m. ET

WASHINGTON (AP) -- Scientists advising the government on genetically engineered corn say more research is needed to determine its impact on the environment and assess the health risks of new varieties of the grain.

The corn, known as Bt for a bacterium gene it contains, is genetically altered to produce its own pesticide to kill an insect pest. Some research has suggested the corn could be harming an unintended target, Monarch butterflies, in farmers' fields.

The Environmental Protection Agency, which released a report Thursday by the scientific advisers, is considering whether to renew registrations for gene-altered varieties of corn and cotton.

The panel said extensive field studies of the corn need to be done. ``Sound science must guide the agency's decisions. Inappropriate conclusions drawn from inappropriate database are to be avoided,'' the scientists said.

In a section of the report that could pose problems for companies developing new varieties of biotech corn, the scientists said there was ``no data or criteria'' to make ``absolute'' assessments of the potential of new corn proteins to cause allergic reactions in people.

The National Academy of Sciences last year also recommended developing new ways to test genetically engineered crops to see how allergenic they might be.

The biotech industry was put on the defense last fall when a variety of biotech corn that was not approved for human consumption was found in taco shells and other food products. That variety, known as StarLink, has since been withdrawn from the market, and the EPA is not considering renewing its license.

StarLink contains a protein that breaks down slowly in the digestive system, a sign that it could be allergy inducing.

Other varieties of biotech corn digest more quickly, and the government says they pose no health risk.

The EPA said last fall that biotech corn posed little risk to the butterflies or anything else it was not supposed to harm.

Some scientists on the 20-member panel thought that was ``overly optimistic,'' while others believed the EPA's conclusion was accurate, given the research that has been published so far, the report said. There appeared to be little disagreement among the scientists that additional studies were needed.

``There is a lot of work that industry and EPA needs to do before they can even think about'' reregistering the biotech corn, said Jane Rissler, a biotechnology expert with the Union of Concerned Scientists. ``To me this report has delay written all over it. It says in so many ways that a lot of work needs to be done.''

A series of studies sponsored by the Agriculture Department last summer should address the scientists concerns about the corn's impact on Monarch butterflies, said Val Giddings, vice president of food and agriculture for the Biotechnology Industry Organization.

Results of those studies are expected to be published in a scientific journal this spring. Scientists involved in the research say it suggests there is little risk to Monarchs.

``EPA will take into account those studies,'' Giddings said.

He criticized the scientists for setting what he called a ``zero-risk standard'' for biotech crops that would be impossible to meet.

``If that were applied to foods in the existing food supply, many foods generally recognized as safe would be eliminated,'' such as peanuts, soybeans and milk, of which cause allergic reactions, he said.

Registrations for existing biotech corn and cotton crops are due to expire in September.

The EPA said in a statement that would do a ``comprehensive evaluation'' of those crops, ``taking into account all data available to the agency.''

On the Net: Environmental Protection Agency's Office of Science Coordination and Policy's scientific advisory panel: http://www.epa.gov/scipoly/sap/

Category: 29. GMOs