How do you know if your fish is safe to eat?

As this ScienCentral video reports, food safety experts at Purdue University say a new technique can make screening fish for contaminants much faster.

Safety First

We’ve all heard that eating fish is healthy. That is, if that fish isn’t contaminated.

“The consumer - especially a woman in her childbearing years - needs to be discerning,” explains Charles Santerre, associate professor of food and nutrition at Purdue University specializing in chemical contaminants in food. “A woman should carefully choose the fish she eats today to protect her baby tomorrow.”

Santerre and his team study fish in order to find out more about typical fish contaminants, such as PCBs, or polychlorinated biphenyls. PCBs and methylmercury, a form of mercury found in fish, are particularly harmful to infants and young children. This is true whether they eat the fish themselves, or get a dose from their mothers during pregnancy or nursing. “It takes six years to rid the body of PCBs,” explains Santerre, “and one year for mercury.” Methylmercury, if eaten regularly, can harm the developing nervous system of a fetus or infant. PCBs have also been linked to low birth weight and decreased IQ.

Santerre’s goal is to help determine whether fish is contaminated. “We want to improve the information that’s collected by the state health departments, so that they better know what contaminants are in foods.” Santerre and his co-workers helped develop a faster and cheaper way of detecting tainted fish. They take a small piece of fish and grind it up. Then they run a liquid, called a solvent, through the ground up fish that pulls the PCBs out of it. Then they mix the PCBs with antibodies, proteins that help fight infections and that are produced by certain cells in the immune system. The antibodies in this particular test are special, because they bind to PCBs and they have tiny magnetic particles attached. By placing a magnet next to the tube containing the antibody-PCB mixture, the researchers can “hold” the antibodies and PCBs in the tube while they pour everything else out of the tube. Lastly, they add a few chemicals that indicate the amount of PCBs in the sample by changing color. If there’s a lot of PCB in the fish sample, the researchers can deduce that fish of that species from that body of water are not healthy to eat.

“Up until recently,” Santerre says, “if you sent one sample of fish into a laboratory, it would cost between $200 and $500 and it would take weeks to analyze the sample. This rapid assay allows us to analyze these in an afternoon for maybe $25 to $40 per assay - per test. So by developing this, we’ve been able to improve the data that states collect so they can build their fish consumption advisories and protect women.”

Try Salmon

Santerre suggests that pregnant women, nursing mothers, and young children avoid certain fish, including swordfish, shark, king mackerel, and tilefish, because these fish can contain high levels of mercury. Instead, he recommends salmon, because it’s low in contaminants. “Salmon is an ideal source for omega-3 fatty acids, which are necessary for brain development in babies and cardiovascular health in adults.”

Santerre also says that pregnant and nursing mothers can eat other fish, such as tuna, but in limited quantities, and that canned tuna tends to be safer than tuna steak.

Most of all, he wants people to continue to eat fish. “That’s the number one point in any presentation we deliver - fish is important nutritionally, so it’s important that people eat fish.”

Santerre’s research was published in the Journal of Food Science. It was funded by the Illinois-Indiana Sea Grant Program, Purdue University Research Foundation, the USDA Agricultural Research Service and the USDA Cooperative State Research, Education, and Extension Service.