Maryland environmental officials are warning residents to moderate their consumption of 15 species of fish from the state’s waterways because they have levels of chemicals that could cause health problems.

The guidance is the latest, and broadest, from the Maryland Department of the Environment, which has been monitoring so-called forever chemicals, officially known as per- and polyfluoroalkyl substances (PFAS).

The agency has joined others around the country in recent years in paying closer attention to the man-made chemicals that can linger and accumulate in the human body.

Which kinds of fish got warnings?

Among the species with the most PFAS warnings are large and smallmouth bass, sunfish (including bluegill) and white perch caught in certain Maryland waterways.

The advisories are issued by water body — meaning a fish species caught in one area may be safer to eat than the same species caught elsewhere. State environment officials suggested limits between one and eight meals a month for certain species, and listed some species to avoid altogether for pregnant and nursing women and children.

No fish was deemed unsafe for all people. And notably, blue crabs and oysters found in Maryland waterways are OK to eat — their PFAS levels weren’t concerning.

What are PFAS?

The forever chemicals, called PFAS, have been produced for decades to add fire- and waterproofing or nonstick qualities to common products such as microwave popcorn bags, clothing and cooking pans. They are also used in fire-extinguishing foam.

The qualities that make the chemical durable also make them long-lasting. They leach in the soil and water and then end up in crops and drinking water. People consume the food and water, and also gain exposure directly from the packaging and clothing.

What are the health concerns?

PFAS generated little public interest for a long time, but in recent years there have been numerous studies linking exposure to the environmentally persistent chemicals over time to health concerns.

Scientists have found PFAS can damage people’s livers and the immune systems. The chemicals also cause low birth weight, birth defects, delayed development and newborn deaths in lab animals, according to the U.S. Centers for Disease Control and Prevention.

What is Maryland doing about PFAS?

Department of Environment officials have added a lot of testing for PFAS, in addition to other contaminants. The last round of testing in 2021 led to advisories for three fish species in one creek in Prince George’s County.

The agency also tests drinking water, and has been working to reduce the levels, sometimes by switching water sources in communities. About 10 states, including New York, New Jersey and Pennsylvania, have issued limits on PFAS in drinking water.

Maryland also banned the sale of products with PFAS, including food packaging, carpets and firefighting foam.

What can people do to reduce their risk?

It’s difficult to eliminate the risk because of the durability of the chemicals already are in the environment. For now, the primary means of destroying them is incineration, which is costly and potentially hazardous.

Instead, people can avoid products that contain the chemicals and filter their drinking water. (The Environmental Working Group recommends these filters.)

On the national level, the U.S. Environmental Protection Agency has been releasing data on PFAS in drinking water and plans to regulate a half-dozen of the chemicals. The EPA and others, including scientists at Johns Hopkins University, also are exploring ways of cheaply and effectively filtering home drinking water, municipal drinking water systems and crop irrigation.