Genetically modified crops are so pervasive that food companies that don't use GMO ingredients still have traces in their products.
Genetically modified crops are so pervasive that food companies that don't use GMO ingredients still have traces in their products. - 
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California voters get to do more than elect officials next month: They'll be making law. There are propositions on the ballot to do everything from increase sales taxes to fund schools to abolish the death penalty. One proposition getting national attention: Prop 37.

If it passes, it will require labels on some genetically engineered foods. Foods subject to the law would be labeled as "Partially Produced with Genetic Engineering" or "May be Partially Produced with Genetic Engineering."

To be clear, these labels wouldn't be required on everything. The proposition excludes a number of foods -- including meat (even if the animal is fed genetically engineered crops), alcohol, meals from restaurants and organics.

It also excludes products where the producer has documentation showing they didn't intentionally use genetically modified organisms when they grew or made the food.

You might think that not intentionally using GMOs would mean the same as not containing GMOs. Right? Turns out it's not that easy especially when you're dealing with crops like corn and soy, which are dominated by genetic engineering in this country.

Michael Smulders is the founder of Bakery on Main, which makes non-GMO certified granola and oatmeal in Connecticut. "You can't grow food in a controlled environment," Smulders says, "you may have one farmer next door to another farmer. One farmer is growing genetically modified, one farmer is not." Pollen blows around. Crops get contaminated.

In order to keep his non-GMO certification, Smulders has to show that his ingredients are less than 0.9 percent. That isn't easy, and isn't cheap. "The ingredients can be two and three times the price," he says, "especially when you include the testing, which can be expensive."

That 0.9 percent standard is set by the Non-GMO Project, a nonprofit that certifies food producers like Bakery on Main. "We've set a threshold that is still incredibly difficult to meet," says executive director Megan Westgate, "but it matches what's used in the EU."

Supporters say the law created by California's Proposition 37 would be simpler than all that. "If a manufacturer is intending to use genetically engineered crops than they have to label," says spokesperson Stacey Malkan. "If they are intentionally not going to use genetically engineered crops, then they are exempt." No testing required.

That exemption will require a whole lot of paperwork -- up and down the food chain -- but it won't insure a meal without genetically modified ingredients.

If your dinner includes processed foods made with one of the big genetically engineered crops -- like corn or soy -- tests are likely to show some GMOs.

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Follow Adriene Hill at @adrienehill