Mercury

Mercury is a chemical contaminant that has been found in some species of fish caught in parts of the Chesapeake Bay watershed. As it moves through the food web, mercury can have many negative heath effects on humans, especially small children and developing fetuses.

Where Does Mercury Come From?

Power plants that burn coal for electricity produce about 40 percent of human-caused mercury emissions in the United States. Other sources include:

• Industrial boilers
• Burning of hazardous wastes, such as medical and municipal wastes
• Chlorine production
• Dental offices
• Consumer products, such as thermometers, electronics, fluorescent lightbulbs and some types of batteries

Mercury that has been released into the atmosphere can be deposited on cities, forests, rivers — and the Bay itself — via rain, snow or dry particles. Even if it does not fall directly onto a body of water, mercury can be carried by stormwater to the nearest stream or reservoir, where it can bind to sediment and remain for many years.

How Do Fish Become Contaminated With Mercury?

Once mercury is in the water, biological processes can turn it into a highly toxic form called methylmercury. Fish become contaminanted as methylmercury moves through the food web in a process called bioaccumulation:

• Small, bottom-dwelling aquatic organisms take up methylmercury while feeding or through skin contact.
• Fish then eat these contaminated plants and smaller organisms, and the methylmercury accumulates in their tissues.
• In turn, humans accumulate mercury in their bodies when they eat contaminated fish.

A number of fish consumption advisories have been issued in parts of the Chesapeake Bay and its tributaries to prevent people from unknowingly eating fish that could be contaminated with mercury.

What Effects Can Mercury Have on Human Heath?

In adults, mercury can affect fertility and blood pressure regulation. It can also cause tremors, memory and vision loss and numbness of the fingers and toes. There is growing evidence that mercury may lead to heart disease.

Mercury can be particularly hazardous to small children and women who are pregnant or nursing.

• Prenatal and infant mercury exposure can cause deafness, blindness, cerebral palsy and mental retardation.
• Even in low doses, mercury may affect a child's development by delaying walking and talking, shortening attention spans and causing learning disabilities.
• According to the Centers for Disease Control and Prevention, one in 12 women of childbearing age has mercury in her blood above the level that would pose a risk to a developing fetus.
• A 2005 study published by the National Institutes of Health reported that approximately 300,000 to 600,000 children are born in the U.S. each year with mercury levels associated with IQ loss.