Brian Koch can tell you all about methylmercury, PFAS, and PCBs - the chemicals that show up in Illinois fish and fisheries.

As the Illinois Department of Public Health’s environmental toxicology program manager, his role is to issue the annual fish advisories. Those advisories tell anglers across the state – by county and by body of water – what chemicals are showing up in fish caught there, and how often sensitive populations should eat those fish.

The IDPH puts that information on its website, posts it to social media, and has booths at fishing conventions and the state fair. “We do try to do our best to get the information into the sport fisherman realm,” Koch said.

But they also need to get that information to those he calls “bucket fishermen” – the people who are sitting on their buckets and fishing rivers and ponds instead of in a boat. “They are at the same spot every day and probably eat fish every day,” Koch said.

Eating fish offers omega-3 and omega-6 fats, iron, iodine, and choline - all good for childhood brain development. The FDA recommends at least 8 oz. of seafood a week in an adult’s diet.

But those same fish can also have high levels of mercury, PFAS, and PCBs. This year, the state advisory includes guidance for PFOS.

PFAS and PFOS — part of a class of persistent “forever chemicals” – along with PCBs, can accumulate in the body over time. According to the National Institutes of Health, among other things, PCBs suppress the immune system and can reduce IQ during fetal development. PFAS and PFOS are linked to certain cancers.

Statewide, a mercury advisory exists, suggesting that people under the age of 15 and who are pregnant or nursing, or planning to do either, should not eat “predatory fish” like bass, walleye, or salmon caught in Illinois waters more than once a week.

Other predatory fish include: sauger, flathead catfish, gar, muskellunge, northern pike, and trout.

The online Fish Advisory Map allows anglers to click on their county to see which waterways have an advisory, which fish species are included, and what the suggested limits are for eating the fish.

Examples include the Chain O’ Lakes in Lake and McHenry counties. PCBs have been found in channel catfish, and PCBs and PFOS have been found in common carp, largemouth bass, bluegill, walleye, and white bass.

In Will County, on the Kankakee River, the amount of mercury found in smallmouth bass suggests no more than one serving of smallmouth bass caught there a week, and only once a month for “women of childbearing age and children.”

Common carp caught from the Wilmington Dam to the Illinois River have been found with PCBs, and all sizes of that fish should be limited to no more than one meal a month.

The biggest factors to consider are the ages of the person eating the fish and if the person is pregnant or planning to get pregnant, Annie Kim said. She is a registered dietitian at Northwestern Medicine Central DuPage Hospital.

“If you are breastfeeding, those things you eat are passed along in breast milk,” Kim said.

All fish have a level of mercury in them, as it is found naturally. “Even with salmon from Alaska,” there is likely an amount of mercury, Kim said.

“But, keep in mind the source of the fish and avoid the bodies of water that are site-specific,” with alerts, Kim said, adding that store-bought fish likely have a lower content of the concerning chemicals.

She, like Koch, realizes that for a portion of the population, fish they catch locally may make up a larger portion of a family’s diet.

It is hard to get a handle on the number of people who are subsistence fishing – using fish as a source for much of their protein intake, Koch said. Sometimes, outreach to those populations means walking riverbanks and talking to people about the concerns of overconsumption.

“What we want to convey is that eating fish has many health benefits. We are not meant to discourage eating fish, but to eat fish that is low in contamination,” Koch said.

For those who want to eat local fish, once a week is probably the best guideline – as long as that person is not under the age of 13 or pregnant, Kim said.

“Is two times a week going to hurt?” for an adult, Kim said. “For those not in a sensitive population, that is probably OK.”