Allison Luengen, USF assistant professor of
environmental sciences, tests San Francisco Bay water for mercury contamination in the lab.
Allison Luengen, University of San Francisco assistant professor of
environmental sciences, is at the center of research to discover exactly how
mercury makes its way into San Francisco Bay and thereby the food chain of Bay
Area residents’ and develop possible mitigation measures for the contamination.
Visit any pier frequented by fishermen on the San Francisco
Bay or drop by San Francisco’s Fisherman’s Wharf and you’ll see signs warning
of the health risks associated with eating fish caught in the bay.
Tens of millions of pounds of mercury mined along the
California coast during the mid-to-late 1800s and early 1900s and used to
amalgamate with gold at slurry mines in the Sierra Nevada washed into Sierra
and delta waterways during the Gold Rush era, settling into soil and sediment
and making its way into San Francisco Bay.
Now it is in the food chain, contaminating bay fish such as
striped bass, sturgeon, and shark to such an extent that women of childbearing
age or pregnant or nursing women and children are advised to eat no more than
one meal of those fish a month. Women beyond childbearing age and men should eat
only two meals of those fish a month, according to the California Office of
Environmental Health and Hazard Assessment.
“Unlike hazardous materials sites that are geographically
contained and can be cleaned up using traditional methods, California’s mercury
contamination has seeped into streams and rivers for decades and become so
diffused from the mountains to the bay that it’s really hard to clean up,”
Luengen said.
Her research shows that mercury, in the form of
methylmercury, is absorbed by waterborne phytoplankton, tiny plant-like
organisms at the base of the food chain, which are then consumed by larval fish
and so on up the food chain.
By studying a number of tributaries to the San Francisco
Bay, Luengen, and fellow researchers Nicholas Fisher of Stony Brook University
and Brian Bergamaschi of the USGS Water Science Center, have zeroed in on water
chemistry and its ability to inhibit methylmercury from getting into the
phytoplankton and fish.
Understanding how chloride, water pH, and dissolved organic
matter (DOM) interact to affect the intake of methylmercury by phytoplankton
could offer solutions or strategies for preventing mercury from working its way
up the food chain, Luengen said.
The group’s most promising findings to date – presented at the
Goldschmidt: Earth, Energy, and the Environment conference in Knoxville, Ten.
in June – are that the presence of DOM, whether it’s decaying aquatic plant
life or storm drain runoff, decreases the accumulation of methylmercury in
phytoplankton. That doesn’t mean that dumping organic material in San Francisco
Bay tributaries is a silver bullet solution, however. More investigation is
needed to understand how DOM impacts the conversion of mercury into
methylmercury, as well as how it effects aquatic environments and their
inhabitants as a whole, Luengen said.
That is the focus of the next project Luengen is working on
with Fisher, along with Jonathan Cole, senior scientist at the Cary Institute
of Ecosystem Studies, for which the group recently received more than $200,000
in funding from New York State Energy Research and Development Authority. Their
latest research begins this summer and will take place on the Hudson River
Estuary.
