Would you like a little mercury with that seafood?

King mackerel over 39 inches, shark and tilefish are not safe to eat if caught off the South Carolina coast because they contain harmful levels of mercury contamination, according to the S.C. Department of Health and Environmental Control.

To warn people about these species and other fish that might pose a public health concern, DHEC has launched its annual "Fish Smart, Eat Smart" campaign.

The state agency has posted fish advisories on its Web site and at public boat landings that warn pregnant women and children not to eat fish containing mercury. Mercury is a naturally occurring metal that is also produced by burning fossil fuels.

If eaten in large amounts, mercury can cause nervous system damage, particularly in infants.

S.C. Department of Environmental Conservation fish advisory Web site

DHEC says some fish contain mercury levels that are safe to consume in 8-ounce portions, about the size of two decks of cards. People may eat swordfish once a month and king mackerel between 33 and 39 inches once a week, said DHEC. There are no restrictions on king mackerel less than 33 inches.

Every year, DHEC determines which fish are contaminated by sampling catches from rivers, lakes, creeks, estuaries and the ocean. This year, DHEC collected more than 2,000 samples.

For the first time, it also collected cobia and red drum. Tissue samples from those fish are still being analyzed, said James Glover, manager of DHEC's aquatic biology section.

"For the most part, fish in the estuaries do not have as high levels of mercury as the large, long-lived ocean fish like swordfish and king mackerel," Glover said. "Fish in the estuaries, even crabs, show low levels and are safe to eat."