[Date Prev][Date Next][Date Index]


NEWS RELEASE -- University of Wisconsin Sea Grant Institute
For Immediate Release

For More Information:  
Philip Cook, Research Chemist, U.S. Environmental Protection Agency,
Duluth, Minn., (218) 529-5202
Richard Peterson, Toxicologist, University of Wisconsin-Madison, (608)
Donald Tillitt, Environmental Toxicologist, Columbia Environmental
Research Center, U.S. Geological Survey, Columbia, Mo., (573) 876-1886 
Scott Brown, Environmental Toxicologist, National Water Research
Institute, Burlington, Ontario, (905) 336-6250
Stephen Wittman, Program Information Specialist, UW Sea Grant Institute,
(608) 263-5371

Editors Note:  High resolution photos for this story are available for
downloading at 


MADISON, Wis. (Nov. 5, 2003) - A team of researchers has determined that
dioxin and similar toxic chemicals were high enough in Lake Ontario to
kill virtually every lake trout that hatched there from the late 1940s
to the late 1980s.  Their findings differ from traditional explanations
for the collapse of the lake trout population in Lake Ontario that focus
on overfishing and attacks by the parasitic sea lamprey.

The findings also suggest chemical contaminants may have complicated
efforts by the United States and Canada to restore healthy populations
of lake trout across the Great Lakes basin, according to Philip Cook, a
research chemist and environmental toxicologist at the U.S.
Environmental Protection Agency in Duluth, Minn., and lead author of the

The research results also show the importance and the feasibility of
investigating possible harmful effects of other contaminants that
haven't been studied well, Cook said.

The research was published in the September issue of the journal
Environmental Science and Technology.  The report details results from a
15-year collaboration among a team of toxicologists, chemists, chemical
and environmental engineers, and sediment dating experts.

In one part of the work, a group of researchers led by toxicologist
Richard Peterson at the University of Wisconsin-Madison found that, in
their early life stages, lake trout are among the most sensitive fish to
dioxin (specifically, 2,3,7,8-TCDD), PCBs and similar chemicals.  At
concentrations as low as 30 parts per trillion dioxin in egg tissues,
mortality of newly hatched fish exceeds normal rates.

"Thirty parts per trillion is an extremely small concentration,
approximately equal to one drop in 500,000 gallons of water," said
Peterson, who directed the UW-Madison component of the study with
support from the UW Sea Grant Institute.  

Dioxin, PCBs and similar chemicals pass from water and sediments into
small plants and animals near the bottom of aquatic food webs.  Because
they are retained in tissues, they accumulate as they are passed to
higher levels of food webs.  Animals near the tops of food webs, like
lake trout, generally have the highest concentrations of such chemicals
in their body tissues, Peterson said.

In their component of the study, Cook and his colleagues measured dioxin
and other chemicals in samples of sediments, herring gulls, adult lake
trout, other fish species and lake trout eggs from Lake Ontario. They
used mathematical models to estimate from these measurements the
concentrations in lake trout egg tissues between 1920 and 1990.

The researchers conclude that dioxin levels in lake trout eggs reached
the 30 ppt mortality threshold in the early 1940s.  By the late 1940s,
concentrations reached 100 ppt.  At that concentration, 100 percent of
juvenile trout can be expected to die, the authors reported.

Concentrations remained at or above these levels until about 1976, by
which time environmental regulations had sufficiently reduced toxic
contamination levels to again allow some egg survival, according to the
study.  By 1982, egg concentrations had dropped to the point that no
measurable direct mortality from dioxin was expected. 

"That's the good news of the study," Cook said.  "It shows that
pollution regulations can really be effective."

Cook points out, however, that researchers know much less about
so-called "sub-lethal" effects of contaminants on lake trout, doses that
do not kill the fish in laboratory tests but do impair critical
functions like vision or swim bladder inflation.

"In natural environments, these low levels of contaminants could impair
the recovery of lake trout populations," Cook said.  "Young fish may not
be able to flee from predators or find food, and that could be happening
out there today in the Great Lakes.  We don't know for sure about that -
we're in a grey area with these low levels."

The work is an "elegant piece of science" that drew upon multiple
sources of evidence to support its conclusions, according to Donald
Tillitt, an environmental toxicologist in the Biological Resources
Division of the U.S. Geological Survey in Colombia, Mo.

"It allows us to quantitatively look at the effects of these chemicals
[on lake trout]," Tillitt said. "It's a very significant piece of

"It's one of the nicest case studies that have been done," agreed Scott
Brown, an environmental toxicologist at Environment Canada's National
Water Research Institute in Burlington, Ontario.


Created in 1966, Sea Grant is a national network of 30 university-based
programs of research, outreach and education dedicated to the protection
and sustainable use of the United States' coastal, ocean and Great Lakes
resources.  The National Sea Grant Network is a partnership of
participating coastal states, private industry and the National Sea
Grant College Program, National Oceanic & Atmospheric Administration,
U.S. Department of Commerce.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
glin-announce is hosted by the Great Lakes Information Network (GLIN):
To subscribe: http://www.glin.net/forms/glin-announce_form.html
To post a message: http://www.glin.net/forms/glin-announce_post.html
To search the archive: http://www.glin.net/lists/glin-announce/
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *