Published: Aug 16, 2010 10:40 AM EDT
Updated: Aug 15, 2010 8:56 PM EDT

CAPE CORAL, Fla. - A warning for parents as you do your back-to-school shopping: You might think you know exactly what's in your child's backpack, but some of what's in those book bags could be toxic.

Binders, pencil cases, lunch boxes-- all are school essentials. But when made out of the wrong material, they could be dangerous. 

"Many school supplies are made out of PVC plastic also known as vinyl," says Mike Schade with the Center for Health, Environment and Justice. "PVC is unfortunately the most toxic plastic for human health and the environment."

So toxic in fact, the CHEJ says chemicals released by PVC are linked to chronic diseases like asthma, obesity and even cancer.

"That's definitely a concern and that's something that I would consider when making purchases," says Lisa Perrault.

Perrault is a teacher at Challenger Middle School in Cape Coral. She's stocking up on supplies for her classroom and she says she'll be extra cautious now.

"Safety is the number 1 priority for kids in our class," she says.

Safety is critical, but for parents on a tight budget...

"With this many kids, we pretty much go most economical," says dad Robert Ring. "They don't really chew on their pens or chew on their notebooks, so I think we're pretty safe with that."

These days, it's easy to avoid dangerous toxins. Just trade out plastic, for the more eco-friendly cardboard.

Products made with PVC include the recycling symbol with a number 3 inside. The letter "V" or letters "PVC" can sometimes be found underneath the symbol.