The state attorney general has accused several large California grocery stores, including Trader Joe’s and Whole Foods, of selling lead-tainted ginger and plum candies in a case that underscores how little consumers know about the food they eat.

The suit also offers a glimpse into the highly complex world of food sourcing and labeling. Even as the movement for more labeling picks up steam, environmentalists and food scientists increasingly are confronted with the reality that our food may always be partly shrouded in mystery.

“The fact is that you have a lot of food that you don’t know where it comes from,” said Ted Ning, executive director of Lifestyles of Health and Sustainability, a Colorado-based organization that advocates for environmentally and socially sustainable goods and services.

The lawsuit, filed April 30 in San Francisco Superior Court, argues that Trader Joe’s, Whole Foods, Target, 99 Ranch Market, Island Pacific Supermarket, Marina Food and other retailers have been selling candy, snacks and bulk food made with ginger or dried plums that contains dangerously high levels of lead.

The companies did not alert customers to the lead, the suit charges, and that violates California’s Proposition 65, which requires businesses to warn consumers about harmful toxins in food, toys, jewelry and other products.

The retailers have been notified of the lawsuit, and the state is expecting a response in June. Retailers declined to comment on the case, but at least one, Target, has already pulled off its shelves the products named in the suit.

Lead-tainted food can end up in customers’ shopping carts more easily than they think, said Michael Hansen, senior staff scientist at Consumers Union and a national expert on food safety. He said many retailers get products, particularly those made with ginger, from Asia, where food is less expensive and often produced in contaminated environments with little oversight.

“In China, there is booming agriculture, and even though there are some laws, there’s no enforcement,” he said. “It’s the Wild West.”

Many overseas food manufacturers don’t test their food, some retailers don’t ask enough questions about the products they buy, and the U.S. Food and Drug Administration doesn’t provide enough oversight for foods entering the country, Hansen said.

Another danger for consumers is that stores have a history of pleading ignorance to food contamination, issuing a recall and an apology only after a problem is discovered, said Charles Margulis, communications director for the Center for Environmental Health, an Oakland-based advocacy group that initiated the lawsuit.

“It’s in any business’s interest to not know about the toxic chemicals that are in their products,” he said. “If they simply don’t know about it, there’s no liability for them.”

However, cases like this may change that. Attorneys and experts say retailers are facing intense pressure from state authorities to improve food testing standards and force overseas vendors to clean up their growing and packaging practices.

“Stores are the ones in the hot seat,” said Ann Grimaldi, an attorney with McKenna Long & Aldridge in San Francisco who has defended businesses in similar cases.

Target already has removed the Archer Farms brand candied ginger from stores.

“Target is committed to abiding by state and federal laws and regulations, and we expect our vendors to do the same,” company spokeswoman Jessica Deede said. She declined to comment further on the lawsuit.

Trader Joe’s, however, continues to sell the Uncrystallized Candied Ginger named in the lawsuit, a spokeswoman said. Whole Foods said it is investigating the issue with suppliers, and customers who purchased the ginger products that are suspected of containing lead can return them for a full refund, spokeswoman Jennifer Marples said.

The Center for Environmental Health, which frequently sues businesses suspected of violating Proposition 65, started investigating the candies last year. The organization, the attorney general’s office as well as attorneys representing the retailers each declined to release the results from the lead tests, saying the information was confidential while the case is ongoing. But Lynda Gledhill, the attorney general’s press secretary, said in an interview that each of the products tested contained more lead than the maximum level considered safe in some candy, and at least one contained lead nearly seven times that limit.

Gledhill added that the lead levels were sporadic, “meaning it wasn’t something that was naturally occurring.” The results concerned the attorney general, she said, because ginger candy is especially popular with pregnant women and children.

Hansen said any food exceeding the limit set by Proposition 65 poses a danger to children, who often are most vulnerable to the effects of lead exposure.

According to the World Health Organization, exposure to some compounds of lead can cause a host of diseases, including cancer, damage to the nervous and reproductive systems and the kidneys, high blood pressure and anemia. Lead exposure is particularly damaging to the developing brains of fetuses and young children, and to pregnant women.

However, Grimaldi says the lead levels set by the state are too low and don’t take into account naturally occurring toxins that seep into the ground, where ginger grows.

“It’s a root. You’re going to naturally expect there to be chemicals,” she said. “You can literally walk down the street and breathe more lead.”

More testing will be done to determine where the lead came from. If food manufacturers can’t reduce or eliminate the lead, they will have the option to print a cautionary label on the package and continue selling in California. Or, stores can pull the products from their shelves and replace them with a different, toxin-free candy.

Contact Heather Somerville at 925-977-8418. Follow her at Twitter.com/heathersomervil.