Numerous prior posts have noted various theories and evidence for the reduction in number of frogs found in various environments. Taking a step back from focusing on agricultural lands and practices, some researchers are surveying the presence of frogs, including intersex frogs (those with both male and female characteristics) in a variety of landscapes, including woodlands, suburban yards, and urban settings.
Some studies to date have indicated that intersex frogs and other adverse impacts are quite likely to be found in suburban and urban settings. Though causation has not been identified, several theories have been developed. For example, it is well known that there may be heavy chemical usage in suburban settings (e.g., lawn and yard care, such as atrazine and the fungicide chlorothalonil). In other areas, evidence of contaminated ponds appears to be the result of leakage from both sewer lines and from septic systems (e.g., shown by the presence of common indicator chemicals such as caffeine). Since it is well known that many prescription drugs, including contraceptives, are flushed when no longer needed or being utilized, such leakage could expose frogs and other wildlife to a wide variety of drugs and chemicals. [This is another reason why take-back programs for prescription drugs are gaining in popularity.]
Other research suggests that earlier studies may have missed key factors. For example, the death rate of tadpoles was higher in glyphosate impacted runoff that has the scent of predators (such as dragonflies) than runoff without such a scent. Further work pointed to the depth of the water into which the runoff ran as an important factor; survival rates went up in deeper waters even when the scent was present. Thus, the configuration of the impacted water body can have a significant influence on the outcome.
Thus, understanding in a broad ecozone context what is impacting our bug-eating proverbial canaries in the coal mine is, not surprisingly, a more complex question than has been assumed.
Studies about these and related matters can be found at http://www.pnas.org/content/104/21/8897.full, http://www.crcnetbase.com/doi/abs/10.1201/9781439817957-c5, http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.2009.04453.x/abstract, http://www.springerlink.com/content/g16n23867h1172x0/, and http://www.epa.gov/opp00001/reregistration/atrazine/.