Tuna salad

When researchers at the University of Las Vegas tested mercury levels in canned tuna, they were in for a rude awakening.

Of the 300 samples tested, representing three top national brands (unnamed):

  • 55% exceeded the Environmental Protection Agency’s standards for mercury levels ( 0.5 parts per million, or ppm).
  • 5% of the samples exceeded 1.0 ppm.

Mercury poisoning can cause central nervous system damage, hearing loss and diminished vision, and the effects are more pronounced in developing fetuses, infants and children.

“Canned tuna accounts for more than a quarter of the nation’s seafood consumption and creates some significant regulatory challenges,” says Shawn Gerstenberger, PhD, a professor of environmental and occupational health. “With pregnant women and children the most susceptible to mercury poisoning—yet also among the top consumers of canned tuna—federal agencies need to urge distributors to expressly state mercury levels contained in their products.”

Researchers tested cans purchased in area grocery stores over a 4-month period, separating samples by brand, type (white vs. light), packaging medium (oil vs. water), lot number and expiration date. All brands tested contained samples with mercury levels higher than the recommended EPA limits for safe consumption.

White tuna, across all brands, registered the highest mercury concentrations because it comes from albacore—a species that’s more susceptible to mercury pollution from human sources.

“Mercury concentration in fish has a lot to do with the environment they’re in, but since the locations of where the fish are harvested are not made available to consumers, it is very difficult to positively identify and reduce the source of the exposure,” Dr. Gerstenberger says.

The study, published in Environmental Toxicology & Chemistry, recommends that regulatory agencies require the tuna industry to provide detailed information on mercury content and disclose the locations where tuna are caught.

Researchers are also pushing for more consistent consumption guidelines to reduce consumer confusion. According to the EPA, the average child can consume  no more than one can of tuna every 18 days.

Photo: Keith McDuffee