, other causes, including contaminants
and the introduction of exotic species, remain plausible contributors
to what is most likely a multi-factoral process. And given the ability
of some contaminants to reduce
disease resistance, it is not implausible to hypothesize that
contaminants are involved in the rapid pace at which amphibians
have succumbed to the fungal infection. No research has assessed
the impact of low-level atrazine exposure on the development of
frog immune competency.
added in August 2002: new research
confirms atrazine impairs frog immune systems
research by Hayes et al. also points out the crucial need
to carry out experiments assessing toxicological impacts at environmentally-relevant
levels. Prior work had seemingly dismissed atrazine as an endocrine
disruptor affecting frogs, but the research used exposures that
were 10,000 to 30,000 times higher than the dosage found by Hayes
et al. to produce developmental disruption:
teratogenesis,growth inhibition, and mortality in amphibians
in response to atrazine were not considered environmental concerns
of the high doses required to produce these effects. Effects
in the current study, however, occurred at levels 10,000 times
lower than the dose required to produce effects in amphibians
in these previous studies. Allran
and Karasov (2001) reached the conclusion that atrazine
was probably not a significant factor in amphibian declines
based on their studies of toxicity, deformities, and effects
on feeding and ventilation in leopard frogs that did not produce
noticeable effects below 3 ppm. The current data show that negative
effects on sex differentiation occur at doses 30,000 times lower
than effective doses reported by Allran and Karasov."