[Pharmwaste] Study links agriculture to increase of intersex fish
in Potomac basin
dldebiasi at deq.virginia.gov
Wed Mar 5 09:40:00 EST 2008
Home | March 2008 | Study links agriculture to increase of intersex fish
in Potomac basin
Study links agriculture to increase of intersex fish in Potomac basin
Study cautions that condition is likely caused by multiple contaminants
and not just one source
By Karl Blankenship
Scientists have been perplexed for years as to why large numbers of male
smallmouth bass in the Potomac River basin contain immature egg cells,
but they offer some clues in a recent journal article.
Results published in the Journal of Aquatic Animal Health suggest that
the high rate of "intersex" characteristics in smallmouth bass from the
Shenandoah River and the South Branch of the Potomac appears to be
linked to areas with large human populations or intense agricultural
The results were not a complete surprise. The presence of intersex is
thought to be caused by exposure to estrogenic compounds in the water,
many of which are byproducts from human activities or chemicals used in
But unexpectedly, the new study reported that some of the highest
intersex rates-reaching 100 percent in some samples-came from
Past studies by scientists in other areas tended to find the strongest
links between intersex in fish with wastewater discharges or urban
"We were surprised when we saw it in the South Branch, and even in the
Shenandoah, at a higher level because we are not talking about huge
cities in those areas," said Vicki Blazer, a scientist with the U.S.
Geological Survey who led the study.
Intersex is thought to be caused by any of a number of chemicals-from
pesticides and other compounds used in agriculture to hormones from
birth control pills and other pharmaceuticals-which can affect the
The paper said a number of chemicals known to have estrogenic properties
were also found in the water where smallmouth bass were collected,
including several found in herbicides and pesticides used in
But the paper cautioned that it's "unlikely that only one contaminant or
source is responsible" for intersex. Rather, it suggested, the condition
is likely caused by exposures to multiple contaminants.
Making links to specific chemicals, or combinations of chemicals, is
difficult and is further complicated by the fact that most smallmouth
bass studied by scientists were 2 to 7 years old. Intersex, Blazer said,
is likely caused by chemical exposure in the first few weeks of fishes'
life. "You need to think about what was going on back when they were
really young fish," she said. "It is not a really easy thing to tease
out. We are working on it."
The notion that some human activity is causing the problem was bolstered
when the scientists examined smallmouth bass from less developed areas
outside the Potomac watershed, including the Greenbrier, Elk and Gauley
rivers in West Virginia. Intersex rates in those rivers were much lower,
ranging from 17 percent to 36 percent.
Blazer said even those sites were not truly unimpacted. Evidence of
chemicals suspected of causing intersex were still present, albeit at
Scientists discovered the intersex in smallmouth bass in 2003 while
investigating fish kills on the rivers. Under the microscope, they
unexpectedly spotted egg cells in the testes of male fish.
Intersex was not the cause of the fish kills, Blazer said-many of the
fish killed were other species that did not show intersex
But the fact that fish kills and high levels of intersex were found in
the same areas suggest that the same pollution issues may play a role in
both problems, she said. "To me, intersex is important as an indication
of environmental contaminants that might be affecting the fish health in
other ways, like the fish kill," Blazer said.
The exact causes of recurring fish kills on the Potomac and Shenandoah
remains under investigation.
Research is continuing to determine whether intersex is affecting fish
health or reproduction. Scientists are also continuing to examine fish
from other locations both inside and outside the Potomac basin to better
correlate intersex with land-based activities.
One surprise from that work is that-unlike other areas-intersex in
Potomac smallmouth bass does not seem to be linked to wastewater
discharges. When scientists examined fish above and below outfalls of
two wastewater plants in Maryland, Blazer said they found similar levels
of intersex. That suggests the chemicals causing the change may be
coming from more diffuse sources, such as stormwater runoff, she said.
Karl is the Editor of the Bay Journal.
The Bay Journal is published by the Alliance for the Chesapeake Bay for
the Chesapeake Bay Program.
Deborah L. DeBiasi
Email: dldebiasi at deq.virginia.gov
WEB site address: www.deq.virginia.gov
Virginia Department of Environmental Quality
Office of Water Permit Programs
Industrial Pretreatment/Toxics Management Program
PPCPs, EDCs, and Microconstituents
Mail: P.O. Box 1105, Richmond, VA 23218 (NEW!)
Location: 629 E. Main Street, Richmond, VA 23219
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