Taking a deep breath in that new sports car might not be such a good idea. The new car smell many drivers love actually comes from the off-gassing of chemicals in your car's interior. And some of the compounds might be toxic. A Michigan environmental watchdog, the Ecology Center, has just released the results of its annual test of chemical levels in the interiors of 200 vehicles. Here's what you should know:

Where does the smell come from?
That fresh "new car smell" comes from "chemicals emitted from things like the steering wheel, dashboard, and seats," says Jennifer Geiger at the Chicago Tribune. The Ecology Center says that long-term exposure to these chemicals can be hazardous to your health. And after their homes and offices, Americans spend more time — 1.5 hours — in their cars every day than anywhere else.

What kind of chemicals are they?
The Ecology Center identified more than 275 chemicals, some of which are associated with allergies, birth defects, impaired learning, liver problems, and cancer. They included chromium and lead, as well as volatile organic compounds that come from brominated flame retardants and other additives in some cars' plastic parts. High temperatures can make the concentrations worse. "Vehicle interiors contain a unique cocktail of hundreds of toxic chemicals," says Ecology Center research director Jeff Gearhart. "Automobiles function as chemical reactors, creating one of the most hazardous environments we spend time in."

Are they really that dangerous?
Not all agree. The Vinyl Institute, a trade association representing plastic manufacturers, opposed the report, saying that PVC (polyvinyl chloride) is widely and acceptably used in a number of consumer products. "The Ecology Center likes to issue scary reports about materials in cars and homes," representative Adam Blakely tells USA Today, "but in fact they have no data showing actual injuries, and, in fact, no data showing exposures that would suggest harm."

Which cars are considered the most dangerous? 
The non-profit tested 200 car models from 2011 and 2012 and ranked them from least toxic to most toxic. The safest vehicles with the lowest levels of potentially harmful chemicals were the 2012 Honda Civic, the 2011 Toyota Prius, and the 2011 Honda CR-Z. As for the most dangerous, the 2011 Mitsubishi Outlander Sport tied with the 2011 Chrysler 200 SC, with the 2011 Kia Soul and 2011 Nissan Versa close behind. 

Sources: Chicago Tribune, HealthyStuff.org, USA Today, Web MD, ZDNet