* If contaminated, crops cannot be marketed as organic or sold to European Union markets, which established a moratorium on GMOs five years ago due to related human health concerns.

* Chemical corporations hold patents on all GMOs, and they have sought penalties against farmers whose crops were inadvertently contaminated.

* "Superweeds" develop as herbicide-resistant traits spread to ordinary weeds, and "superpests" evolve as bugs become immune to high levels of toxins.

* In 1999, a Cornell University study showed bacteria from GMO corn made the caterpillars of monarch butterflies grow slower and die faster.

* In 2000, a GMO corn approved only for animal feed due to concerns that it may trigger severe allergic reactions turned up in taco shells, corn chips, and muffin mixes in the U.S.

* In 2003, tests in Mexico found GMOs contaminating corn and other plants representing thousands of years of purity in all nine regions tested, even though their use has never been authorized.