Clair, JJ, JA Bantle and J Dumont. 1998. Photoproducts and metabolites
of a common insect growth regulator produce developmental deformities
in Xenopus. Environmental Science and Technology 32:1453-1461.
laboratory experiments with the African clawed toad, Xenopus
laevis, embryos, La Clair et al. show that the insect
growth regulator S-methroprene itself poses little risk to toads
at levels commonly encountered in the environment. But, when toad
embryos encounter the breakdown products of methoprene caused by
this compounds reaction with sunlight, water and microorganisms,
the exposures "dramatically interfere with normal amphibian
and the relevant breakdown products interfere with the retinoid
hormone system. S-methoprene is widely used in the US to control
mosquito populations. The levels of S-methoprene and its breakdown
products that should result from "proper use" of the compound
(i.e., at the recommended spray level) are low compared to those
necessary in these experiments to cause the observed deformities.
La Clair et al. note, however, that the breakdown products
may be concentrating in the environment in ways that are not easily
mimicked in laboratory experiments. They also note that methoprene
is widely used in many insecticidal applications, and even if each
application is carried out correctly, the combined impact may push
exposures to a level that is biologically significant.
note that S-methoprene is added to sprays against fleas in preparations
available in grocery, pet and pest-control stores. At the concentration
level in these consumer preparations, a single application to a
10-pound pet would be enough to contaminate approximately 110,000
liters (roughly 29,000 gallons)
results are important for two reasons. First they show that frog
deformities can be produced by contamination. Second, they confirm,
once again, that studies of contamination must be carried out in
ways that reflect the real world. In this case, it would not have
been sufficient merely to observe the impact of the active ingredient
(S-methoprene) itself. Important effects were evident only once
the experiment focused on the breakdown products of the active ingredient.
researchers, however, contend that retinoids are not important to
frog deformities. More...