Effects of Perchlorate on Developing and Adult Birds

摘要

The research in this proposal was designed to establish safe exposure levels for ammonium perchlorate (AP) in developing and adult birds and to develop assessment endpoints for determining the impact of perchlorate exposure in birds. The main focus of the experimental work was to evaluate AP effects using an array of endpoints that measure thyroid function (a key target of perchlorate anion), growth and development during embryonic, early posthatching and adult life. Laboratory dosing studies of two wildlife species of birds, Bobwhite quail (Colinus virginianus) and Mallard ducks (Anas platyrhynchos), were used to investigate the following objectives: 1. To establish safe exposure levels of perchlorate for embryos, chicks and adults based on the effects of AP on thyroid function, growth and development. 2. To evaluate measurements of thyroid function that may be used as assessment endpoints for determining the impact of perchlorate exposure in birds. 3. An additional objective was added following the first year In Progress review to investigate the role of cations (sodium and ammonium) in combination with perchlorate anion. AP has been used as an oxidizer in solid rocket fuels and is a ground and water contaminant on a number of military bases. AP is persistent, water soluble and readily ionized, thus it is highly labile in environmental waters. Perchlorate effects on thyroid function are fairly well understood in laboratory mammals and in certain human clinical contexts. Perchlorate ion is known to compete with iodide transport into the thyroid gland in vertebrates. This results in iodine deficiency and consequent reduced thyroid hormone (TH) synthesis, which depending on the level of exposure, results in organismal hypothyroidism. THs are required for normal development and growth, as well as adult function of many critical systems (e.g., central nervous system, musculoskeletal system) in all vertebrates.