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I recently heard someone say that frogs are today's canary in the mineshaft. I assumed this means that something bad is happening to frogs, but I didn't get the whole story. Can you tell me more?
Frogs and other amphibians have been disappearing at an alarming rate
for quite some time. Scientists believe these population declines
and outright extinctions are the result of a combination of environmental
factors, ranging from climate change to the paving over of wetlands.
One particular factor that has received a lot of attention in recent years is the effect of pesticides known as "endocrine disruptors." These chemicals' use is so widespread that their presence is practically ubiquitous. They are found in rainwater, oceans and even human bodies.
A recent study, dubbed "the most important paper in environmental
toxicology in decades," found that a common pesticide called atrazine
effects the sexual development of frogs, even at extremely low doses.
The presence of atrazine at levels as low as 30 times below
acceptable Environmental Protection Agency limits caused a large percentage
of tadpoles to develop both male and female sex organs.
 The lead scientist
on the study has said, "I'm not saying it's safe for humans. I'm not
saying it's unsafe for humans. All I'm saying is that it makes hermaphrodites
of frogs." Clearly the jury is still out on whether the human species
is threatened. But until we know for sure, it makes sense to apply
the precautionary principle — using alternatives to pesticides
like atrazine until they can be proven safe, instead of waiting after
they have definitively caused a public health disaster before pulling
them off the market.
The sorry state of frog populations has been described by more than one scientist as "a canary in the mine shaft sort of thing." When the canary keels over, you take steps to make sure you are safe before digging further.
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