It's convenient and a staple in most kitchens, but a lot of canned food still contains a chemical linked to birth defects and cancer, CBS San Francisco reports.

Bisphenol A, or BPA, has been removed from baby products, reusable water bottles and most toys. But the chemical is still being used in a lot of food packaging.

The Center for Environmental Health recently tested more than 250 cans purchased at supermarkets and dollar stores for BPA. Researchers found nearly 40 percent contained the chemical. That's down from 67 percent two years ago, but the number still concerns some experts.

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"It's still much too high," Charles Margulis of the Center for Environmental Health told CBS News. "We need to get it down to zero."

BPA is used in the linings of cans, but some studies show that low levels of the chemical can seep into the food.

The U.S. Food and Drug Administration says BPA is safe at the current levels occurring in food. But the state of California recently added BPA to its Proposition 65 list as a chemical known to cause reproductive toxicity.

Margulis says there are a variety of potential health concerns.

"BPA is known to cause birth defects, and it's also linked to breast cancer, obesity and many other serious health problems," he said.

Margulis also pointed out that low-income Americans may be most at risk.

The study found more than half the cans purchased at 99 Cents Only contained BPA.

"In many areas, dollar stores are the only places people can go for fruits and vegetables," said Margulis.

His advice is for consumers buy fresh fruits and vegetables and organic items when possible.

A number of major food manufacturers have either taken BPA out of their products or are in the process of doing so. Some companies have even added labels to their products letting consumers know they are BPA-free.

The supermarkets whose cans were tested for the study told CBS News that they are working with manufacturers to phase BPA out of all the cans in their stores.

The Dollar Store and 99 Cent Store did not immediately respond to requests for comment on the study.