Scientists are connecting the dots with evidence of increasing abnormalities among humans, particularly large increases in numbers of genital deformities among newborn boys. For example, up to 7 percent of boys are now born with undescended testicles, although this often self-corrects over time. And up to 1 percent of boys in the United States are now born with hypospadias, in which the urethra exits the penis improperly, such as at the base rather than the tip.

Apprehension is growing among many scientists that the cause of all this may be a class of chemicals called endocrine disruptors. They are very widely used in agriculture, industry and consumer products.

- New York Times columnist Nicholas Kristof, drawing a link between the current decline in amphibian populations and human illnesses and abnormalities. There has been mounting scientific evidence linking agricultural pesticides and chemical fertilizers to the decline of frogs, specifically.

The chemical atrazine, which is one of the most widely-used herbicides in the world, is a known endocrine disruptor that has been linked to frog decline in several studies. This morning, my dad emailed me the summary of a recent Penn State study that found that the combination of atrazine and phosphate (a common ingredient in fertilizer) "can produce a lethal effect to frog populations at concentrations that are often observed in wetland ecosystems."

As the scientists involved in the study noted, atrazine and phosphate are just two out of thousands of synthetic agrochemicals that have been added to our waterways, and it's unknown how all of these chemicals interact with each other.

Atrazine has been banned in Europe, but it's still used widely in the US. In his column, Kristof says the EPA is moving towards screening endocrine disrupting chemicals, but "at a glacial pace."

-Mark