GMOs or genetically modified organisms are a hot topic between the U.S. and the EU. One explanation for the difference in policies toward GMOs in the EU and the U.S. is consumer experience. In the U.S. consumers hold the FDA in high regard and trust their decisions on GMOs while in the EU consumer are more hostile towards GMOs. Many European companies and even Prince Charles made public statements against the use of GMOs which alter public perception. Another explanation is that buffering zones between GMOs and normal crops would be more costly in the densely packed landscape of Europe. In addition, both producers in the EU and in the U.S. now have incentives to maintain their positions on GMOs and lobby their governments. EU farmers would be harmed by eliminating the ban while U.S. farmers would gain. The EU is using the precautionary principle as their defense for their stance. The concept is that the side effects of using GMOs are still unknown so they could have negative health effects on consumers.

This article says there may be health/environmental risks to GMOs

http://rt.com/usa/usda-gmo-risk-report-537/

While this one explains the difference stances the EU and US have on GMOs as a result of culture and trade policy.

http://www.cfr.org/agricultural-policy/regulation-gmos-europe-united-states-case-study-contemporary-european-regulatory-politics/p8688