[Pharmwaste] Study: Farms Fuel Frog Deformities

Tue Sep 25 08:50:40 EDT 2007

http://news.yahoo.com/s/livescience/20070924/sc_livescience/studyfarmsfu
elfrogdeformities

Study: Farms Fuel Frog Deformities

Dave Mosher - LiveScience Staff Writer
LiveScience.com
Mon Sep 24, 5:35 PM ET

Frog-deforming infections caused by tiny parasites are increasing
because of North American farms' nutrient-rich watershed, a new study
shows. 

The excess nitrogen and phosphorus found in farm runoff causes more
algae to grow, which increases snail populations that host microscopic
parasites called trematodes, said Pieter Johnson, a water scientist at
the University of Colorado in Boulder. 

"This is the first study to show that nutrient enrichment drives the
abundance of these parasites, increasing levels of amphibian infection
and subsequent malformations," said Johnson. 

Johnson noted that he and his colleagues' work, which is detailed in the
Sept. 24 issue of the Proceedings of the National Academy of Sciences,
could also explain "a wide array of diseases potentially linked to
nutrient pollution." 

Frog species also are vanishing from Earth in the past few decades for
reasons that are difficult to tease apart, including habitat loss,
global warming and emerging diseases such as one caused by chytrid
fungus. Nutrient pollution and limb malformations also contribute,
Johnson said. 

A worldwide study of more than 6,000 species of amphibians recently
concluded that 32 percent were threatened and 43 percent were declining
in population. 

History of deformities 

Deformed frogs first gained international attention in the mid-1990s,
when a group of schoolchildren discovered a pond where more than half of
the leopard frogs had missing or extra limbs, Johnson said. Since then,
widespread reports of deformed amphibians have led to speculation that
the abnormalities were being caused by pesticides, increased ultraviolet
radiation or parasitic infection. 

Parasite infection is now recognized as a major cause of such
deformities, but the environmental factors responsible for increases in
parasite abundance have largely remained a mystery. 

"What we found is that nitrogen and phosphorus pollution from
agriculture, cattle grazing and domestic runoff have the potential to
significantly promote parasitic infection and deformities in frogs,"
Johnson said. 

The trematode life cycle involves three host species. The tiny parasites
form cysts in the developing limbs of tadpoles, causing missing limbs,
extra limbs and other malformations, Johnson said. Aside from this stage
and an infectious one in snails and the cyst stage in frogs, predators
complete the trematode life cycle by eating infected frogs and spreading
the parasite back into the ecosystem. 

Nutritious problem 

To discover the link between farms and the trematode infections, Johnson
and his team built 36 artificial ponds similar to farm stock tanks,
where frogs and salamanders often breed and deposit their eggs. 

The researchers then stocked each tank with snails and green frog
tadpoles and, in addition to adding nutrients, they dropped in parasite
eggs. In ponds with added nutrients, Johnson said, the total mass of
snails was 50 percent greater and parasite egg production was eight
times as great. 

The infection rate in frogs rose between two to five times in those
tanks, he added. 

"We were able to watch nutrient pollution move through the life cycle of
the parasite as it cascaded through the food web," he said. "Since most
human diseases involve multiple hosts, understanding how increased
nutrient pollution affects freshwater and marine food webs to influence
disease is an emerging frontier in ecological research." 

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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
Mail:          P.O. Box 1105, Richmond, VA  23218 (NEW!)
Location:  629 E. Main Street, Richmond, VA  23219
PH:         804-698-4028
FAX:      804-698-4032