Pesticides Are Destroying Frogs & Humans

Study finds DDT may spur disease
Toronto Globe & Mail
By MARTIN MITTELSTAEDT
ENVIRONMENT REPORTER


Wednesday, April 24, 2002 ­ Page A1

Frogs given trace amounts of DDT and other pesticides experience a
near-total collapse in their immune systems, a finding that could help
explain the rise in human autoimmune diseases such as asthma and allergies,
Canadian researchers say.

The scientific team also says the work could shed light on the global
decline in amphibians, animals that may no longer have strong enough immune
systems to survive exposures to viruses and parasites.

The pesticides had an effect on frogs identical to cyclophosphamide, a drug
used on human transplant recipients to suppress their immune systems so they
don't reject their new organs.

Frogs and mammals essentially have the same type of immune system, so the
finding could have implications for humans, who also have elevated pesticide
exposures.

In other areas they have been suffering from horrific physical defects, such
as growing extra limbs.

The findings on immune-system impairment have received peer review and will
be published in a research journal later this year.

In laboratory experiments, the team injected northern leopard frogs --
shiny, brown-green amphibians common in Canada's swamps and forests --
with tiny, sublethal doses of DDT, dieldrin or malathion. For comparison
purposes, some other frogs were given the immune-suppressing drug
cyclophosphamide.

DDT and dieldrin, two deadly insecticides on the United Nations' list of the
most toxic substances ever produced on Earth, have been banned in Canada,
but they resist decay and continue to be found throughout wildlife in Canada
and in human tissues decades after they were in widespread use.

Malathion is still widely used on crops in Canada and for mosquito control.
It is often sprayed from planes in large-scale efforts to control
mosquitoes, such as recent programs to control the West Nile virus in New
York City and to knock down populations of the insect in Winnipeg.

Health Canada's Pest Management Regulatory Agency is reviewing its
registration for malathion, while regulators in the United States have
recently given it a clean bill of health for mosquito control.

The pesticide research project was funded by Health Canada and Environment
Canada.

The experiments found that frogs injected with DDT, malathion or
cyclophosphamide had only 1 per cent to 2 cent of normal antibody
production, while dieldrin led to 30 per cent of normal production, two
weeks after exposure. It took frogs 20 weeks of living in a pesticide-free
environment to have their immune systems return to normal.

In human terms, impaired immune systems could lead to people dying of common
colds or other infections that a healthy person would be able to resist
easily. Frogs live in bacteria- and parasite-infested environments, and
consequently may not be able to shake illnesses because of their weakened
immune systems, according to the research.

In their experiments, the researchers also tested wild leopard frogs from a
number of locations in Ontario and found major differences in their immune
systems, depending on their exposure to pesticides.

Specimens collected near Point Pelee National Park in Southwestern Ontario
had weaker immune systems, compared with those from regions of the province,
such as around Collingwood, less polluted by agricultural chemicals.

Point Pelee is a DDT hot spot because a children's camp in the park was once
heavily sprayed to kill mosquitoes and it lies near one of Canada's largest
concentrations of farms. The research project was prompted partly to
investigate the mysterious disappearance of leopard frogs in Point Pelee, to
see if it was linked to DDT.

Many experiments use exceptionally high chemical doses -- hundreds of times
normal environmental exposures -- to cause deleterious effects, but the frog
tests were conducted with doses of less than one part per million.


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