Several California grocery store chains have begun posting warnings at fish counters advising women and children not to eat swordfish and shark, and to limit consumption of fresh tuna.

The warnings, which have been prompted by results of tests showing high mercury levels in certain types of seafood, were developed by the California Attorney General’s office in consultation with the health department and others. The warnings are interim and have yet to be finalised.

The warning posted at the stores states in part: “Warning! Pregnant and nursing women, women who may become pregnant, and young children should not eat the following fish: Swordfish, shark, king mackerel, tile fish. They should also limit their consumption of other fish, including fresh or frozen tuna.”

The interim warning also states that “mercury levels in canned tuna vary, but on average are lower than levels in many other fish.”

However, advocates urged the Attorney General to consider strengthening this statement, citing the latest research acknowledging low-level mercury exposure risks to sensitive populations from frequent consumption of seafood.

Last July, the US Food and Drug Administration’s food safety committee recommended that pregnant women and children be warned to limit consumption of canned tuna due to mercury. However, after several months, the FDA has yet to act.

Recently, the UK’s Food Standards Agency advised pregnant and breastfeeding women, and women who intend to become pregnant, to limit their consumption of tuna.