10News reporter Marti Emerald went undercover to see how much mercury is in your favorite sushi.

Joining 10News was Eli Saddler from www.GotMercury.org -- a group that wants tougher standards on mercury in fish.

The 10News Investigative Team hit the road, shopping some of the biggest and smallest sushi bars in San Diego County.

"The U.S. standard of one part per million is one of the weakest standards in the developed world," said Saddler.

Japan sets safe mercury levels at half the Food and Drug Administration limit, 10News reported.

The big concern is tuna -- the most popular sushi of all and the highest in mercury.

"Big tuna at the top have mercury, and there's no way to get it out because they're always eating other fish with lots of mercury," said Saddler.

10News wanted to see how much mercury was in tuna, so the investigative team purchased yellow fin, blue fin and big-eye tuna sushi from 10 restaurants in the Gaslamp, Mission Valley, Mission Bay, La Jolla, North County, South Bay and East County.

The fish was divided into samples of two ounces each.

If the mercury levels are high, it could be enough to put a woman of average weight or a young child over the level of mercury that is safe to consume in a week, according to the Environmental Protection Agency (EPA).

10News took the sushi samples to EMA Analytical to measure for mercury.

Public health officials agree pregnant women and young children should avoid eating tuna, swordfish and king mackeral, which are all high in mercury compared to other fish.

All the samples that 10News had tested come in below the FDA limit for mercury. But 20 percent -- one in five -- exceeded the government's recommended limit for pregnant and nursing women and young children, 10News reported.

The recommended limit is .73/parts per million (ppm).

The yellow fin roll at Sushi Ota at Mission Bay came in just under .8 ppm of mercury.

Yellow fin tuna at Kanpai in Chula Vista came in at .9 ppm of mercury.

The highest mercury reading came from the nation's biggest sushi chain -- Benihana in Mission Valley. Its tuna came in at .967 ppm of mercury.

Restaurants in California are required to post mercury warnings as part of a disclosure settlement with the California attorney general.

Click here to see the warning.

10News contacted the restaurants about the high mercury levels and is still waiting to hear back.

To test your mercury tolerance, click here.