Ammonium perchlorate has applications in munitions, primarily as an oxidizer for solid rocket and missile propellants. It is also used as an air-bag inflator in the automotive industry, in fireworks, and as a component of agricultural fertilizers. Because of these uses and ammonium perchlorate’s high solubility, chemical stability, and persistence, it has become widely distributed in surface and ground water systems particularly in the southwestern United States. There is little information about the effects of perchlorate in these systems on the aquatic life that inhabits them. However, it is known that perchlorate is an endocrine disrupting chemical that interferes with normal thyroid function and that, in vertebrates, thyroid dysfunction impacts both growth and development.
The objectives of this project were to examine the long-term effects of perchlorate on developing amphibians (e.g., growth, metamorphosis) and on the general health and reproductive capacity of adult females. The studies examined the effects of perchlorate present in the water as well as perchlorate available through the food chain. Because perchlorate competes for iodine binding sites in the thyroid, the addition of iodine to culture water was examined to determine if perchlorate effects can be mitigated. Finally, perchlorate is known to affect normal pigmentation of amphibian embryos. This project sought to examine the effects of ultraviolet irradiation on pigment-altered embryos.
To examine the effects of perchlorate on adult female reproduction, adult females (Xenopus laevis) were induced to breed and the quality of egg clutches determined. These adults were then exposed to concentrations of perchlorate, following which they were bred again to the same males and the quality of egg clutches examined. During exposure, general health, food consumption, locomotor activity, and body weights was recorded. Following exposure, the females were necropsied to determine organ health/weights, thyroid histology, and perchlorate burden. The effects of long-term exposure on developing embryos (tadpoles) was studied by rearing young embryos of Xenopus and local Rana and Bufo species, in concentrations of perchlorate to examine embryo-lethal and abnormal development endpoints. Since some edible plants bioaccumulate perchlorate, native amphibian species were reared on perchlorate-laden food and their growth and development monitored. Thyroid histology, thyroxin levels, and perchlorate body burdens were monitored in treated embryos and adults. Laboratory tests were conducted with culture medium and native contaminated water with Xenopus and native species to determine if increased iodine levels mitigate the effects of perchlorate on this endocrine system.
This project attempted to provide basic information on the effects of perchlorate on developing amphibians and on the reproductive capacity of adult females. The data is useful for evaluating environmental risks from perchlorate-contaminated surface and ground water and will, in addition, provide guidance to organizations that must use or dispose of ammonium perchlorate stockpiles. The use of a variety of native amphibian species allows inter-species comparisons of perchlorate sensitivity. (Project Completed – 2008)