Chemical Contaminants
More than three-quarters of the Chesapeake Bay’s tidal segments are at least partially impaired by toxic substances, which can harm the health of both humans and wildlife.
Chemical contaminants are toxic substances that enter the environment from a range of human activities. Whether it’s pesticides put on farm fields, chemicals released by factories, household pollutants flowing into storm drains or pharmaceuticals entering wastewater, these contaminants can harm the health of humans and wildlife. While production bans have lowered the presence of some contaminants in the environment, others are still widely used today. As of 2024, chemical contaminants have impaired at least part of all of the tidal rivers that deliver water to the Chesapeake Bay.
What kind of chemical contaminants are found in the Bay?
Metals
Mercury, lead, copper, cadmium and other metals can enter waterways through a range of sources. Coal-fired power plants, incinerators, cars and trucks can release metals into the air; industrial facilities and old copper pipes can release metals into our wastewater; and old landfills and legacy industrial sites can release metals into the soil, groundwater and nearby streams. The most common metal found in the Bay watershed is mercury. Other metals are less widespread, and often contained to “hot spots” or specific regions of concern.
PCBs
PCBs, or polychlorinated biphenyls, act as a flame retardant in electrical equipment and have been used in the production of inks, adhesives, sealants, caulks and other widespread products. Although PCBs have not been produced in the United States since a 1977 ban, the chemicals continue to enter the environment through accidental leaks, improper disposal and legacy deposits. In the Bay watershed, PCB contamination is considered widespread.
PFAS
PFAS, or per- and polyfluoroalkyl substances, are used in many consumer and commercial products to resist heat, water and oil. Known as forever chemicals, PFAS do not break down easily and can persist in the environment for years. While some PFAS-containing products have been banned in the United States, and the U.S. Environmental Protection Agency (EPA) has set national drinking water standards for six PFAS, the ban on these chemicals is not complete and they remain widespread throughout the Bay watershed.
PAHs
PAHs, or polycyclic aromatic hydrocarbons, form when gas, coal and oil are burned, and have been detected at varying concentrations across the Bay watershed.
Pesticides
Pesticides are applied to the land to prevent, destroy, repel or reduce pests. During rainstorms, pesticides can seep into the groundwater or wash into rivers and streams, where they negatively affect water quality. While agriculture accounts for the majority of pesticide use, pesticides are also used in and around homes, businesses and schools.
Microplastics
Tiny plastic fragments known as microplastics enter our waterways through household and personal care products, as well as through the breakdown of larger plastic litter like bottles and bags. While litter in the Bay regularly flows into the ocean, an estimated 94% microplastics stay in the estuary, collecting near shorelines and in underwater grass beds. In 2020, researchers took 30 water samples from Maryland's portion of the Bay and found microplastics in every one.
How do chemical contaminants harm fish and wildlife?
Some of the most common chemical contaminants in the region can persist in the environment for decades. Once these contaminants enter the water, they can build up in the bodies of fish and other organisms, moving through the food web in a process called biomagnification.
Biomagnification begins when small, bottom-dwelling organisms absorb contaminants through contact with polluted water or sediment. When larger fish eat these organisms, toxics accumulate in their tissues. And when birds, mammals and other wildlife eat these contaminated fish, they accumulate chemicals faster than their bodies can remove them.
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Different contaminants can harm wildlife in different ways, often affecting their survival, growth and reproduction. Exposure to PFAS, for instance, has been linked to reproductive issues among fish; exposure to pesticides has been linked to eggshell thinning in wild birds; the consumption of microplastics has been linked to death, stunted growth and altered behavior in some fish; and several studies have shown that PCB concentrations in bald eagle eggs can contribute to their failure to hatch.
How can I avoid eating contaminated fish?
Fish consumption advisories are public health warnings issued when locally caught fish or shellfish may contain harmful levels of mercury, PCBs or other toxics. These advisories are not meant to discourage people from eating fish and shellfish, but to help people reduce their exposure to harmful chemicals.
Fish consumption advisories can be issued for the general public or for sensitive populations like pregnant women, nursing mothers or children. Recommendations about which fish is safe to eat depends on the species, the size, where it was caught and who is eating it. Some advisories recommend limiting the consumption of a certain species, while others recommend avoiding the species altogether.
How can you help?
To lower chemical contaminants in the Bay watershed, consider using non-toxic pesticides or chemical-free cleaning and personal-care products. You can also follow safe and legal disposal methods for paint, motor oil, other household chemicals and pharmaceuticals.