Because
their bodies absorb just about everything in their immediate environment, frogs
are bellwethers of toxic pollution and what happens to them today happens to us
tomorrow and right now they are dying.
“Widely used pesticides can kill frogs within an hour, new research
has revealed, suggesting the chemicals are playing a significant and previously
unknown role in the catastrophic global decline of amphibians. The scientists
behind the study said it was both "astonishing" and
"alarming" that common pesticides could be so toxic at the doses
approved by regulatory authorities, adding to growing
criticism of how pesticides are tested. "You would not think products
registered on the market would have such a toxic effect," said Carsten
Brühl, at the University of Koblenz-Landau in Germany. "It is the simplest
effect you can think of: you spray the amphibian with the pesticide and it is
dead. That should translate into a dramatic effect on populations."
Trenton Garner, an ecologist at the Zoological Society of
London, said: "This is a valuable addition to the substantial body of
literature detailing how existing standards for the use of agricultural
pesticides, herbicides and fertilisers are inadequate for the protection of
biodiversity." Amphibians are the best example of the great extinction of species currently under
way, as they are the most threatened and rapidly declining vertebrate group.
More than a third of all amphibians
are included in the IUCN "red list" of endangered
species, with loss of habitat, climate change and disease posing the biggest
threats. Brühl had previously studied how easily frogs can absorb pesticides
through their permeable skins, which they can breathe through when underwater.
But pesticides are not required to be tested on amphibians, said Brühl:
"We could only find one study for one pesticide that was using an exposure
likely to occur on farmland."
His team chose widely used fungicides, herbicides and
insecticides. The most striking results were for a fungicide called
pyraclostrobin, sold as the product Headline by the manufacturer BASF and used
on 90 different crops across the world. It killed all the common European frogs
used as test animals within
an hour when applied at the rate recommended on the label. Other fungicides,
herbicides and insecticides also showed acute toxicity, even when applied at
just 10% of the label rate, with the insecticide dimethoate, for example,
killing 40% of animals within a week.
The study, published on Thursday in
Scientific Reports [will be live after
embargo], concluded: "The observation of acute mortality in a vertebrate
group caused by commercially available pesticides at recommended field rates is
astonishing, since 50 years after the publication of Rachel Carson's Silent
Spring one would have thought that the development of refined risk-assessment
procedures would make such effects virtually impossible." A BASF spokesman
disputed the findings: "This study was performed under laboratory
'worst-case' conditions. Under normal agricultural conditions amphibians are
not exposed to such pesticide concentrations. According to our knowledge, no significant
impact on amphibian populations has been reported despite the widespread and
global use of the fungicide pyraclostrobin." Brühl said the method, a
single spray directly on to the frogs, sometimes at just 10% of the label rate,
was a "realistic worst-case" scenario. He added that in the field,
multiple sprays of a variety of pesticides was likely and that chemicals might
run off into ponds where frogs lived. Sandra Bell, Friends of the Earth's
nature campaigner, said: "From frogs to bees, there is mounting evidence
that the pesticide bombardment of our farmland is having a major impact on our
precious wildlife. Strong action is urgently needed to
get farmers off the chemical treadmill.
"As well as banning the most toxic products,
governments must set clear targets for reducing all pesticides and ensure
farmers have safe and thoroughly tested alternatives."
Earlier this month, the world's most widely used insecticide
was for the first time officially labelled an "unacceptable"
danger to bees feeding
on flowering crops, by the European Food Safety Agency. The agency had
previously stated that current "simplistic"
regulations contained "major weaknesses".
"There is an urgency to address [the amphibian issue]
as pesticides will be applied again soon because it's spring, and that's when
we have all these migrations to ponds," said Brühl.
"We don't have any data from the wild about dead frogs
because no one is looking for them – and if you don't look, you don't find. But
the pesticides are very widely used and so have the potential to have a
significant effect on populations."
