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A team of researchers led by biologists at Dartmouth has found potentially
dangerous levels of mercury and arsenic in Lake Baiyangdian, the largest lake
in the North China Plain and a source of both food and drinking water for the
people who live around it.
Carol Folt (left) and Celia Chen ’78. (Photo by Joseph Mehling ’69)
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The researchers studied three separate locations in Lake Baiyangdian, all at
varying distances from major sources of pollution, such as coal emissions,
agricultural runoff, and sewage discharge. They found that concentrations of
arsenic and mercury in fish were above the threshold considered by the U.S. Environmental Protection Agency (EPA) to pose a
risk to humans and wildlife.
The findings were published online on Dec. 24, 2007, in the journal
Water, Air, and Soil Pollution.
“It’s important to study this system because it is typical of many
throughout China where human activity and industrialization are having
detrimental effects on the environment with major human health implications,”
says Celia Chen ’78,
research associate professor of biological sciences. “It makes
perfect sense to apply what we’re learning about lakes in the United States to
other places in the world, like China, that have a growing global impact.”
Chen and her team were curious to learn how arsenic and mercury, two toxic
environmental metals, moved through the food web in a freshwater ecosystem
known to be polluted and contaminated. In a process called bioaccumulation,
mercury and arsenic were found throughout the food web, from the water, into
the algae, through the tiny algae-eating zooplankton, to the fish. As expected,
the researchers found that more nutrient-rich environments supported larger
algal blooms, which resulted in lower concentrations of mercury and arsenic in
the water due to uptake by the algae.
In their previous work, the researchers found that when there is a lot of
algae present, mercury and arsenic are biodiluted, or more dispersed, so
zooplankton that eat the algae are exposed to lower levels of the metals and
transfer less to fish.
A fisherman on China’s Lake Baiyangdian. Dartmouth researchers found levels of
mercury and arsenic that are potentially hazardous to the people who depend on
the lake for food and water. (Photo by Paul Pickhardt)
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“Despite this potential interaction—a decrease in bioaccumulation due to
high algal biomass—the mercury and arsenic in this system are high enough to be
of concern to humans and wildlife that drink the water and consume fish,” says
Chen. “For example, we saw arsenic levels in the water that represent more than
fifty times the EPA-recommended limit for consumption of fish and
shellfish.”
Chen’s co-authors include Carol
Folt, dean of the faculty of arts and sciences and the Dartmouth Professor
of Biological Sciences, Paul Pickhardt at Lakeland College, and M.Q. Xu at the
Chinese Academy of Sciences in Beijing. Chen and Folt are both affiliated with
Dartmouth’s Center for Environmental
Health Sciences and its Toxic
Metals Research Program. Funding from the National Science Foundation and the National Institute of Environmental Health
Sciences supported this work.
By SUSAN KNAPP
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