Superfund Research Program
Endocrine Disrupting Effects in a Sentinel Species
Project Leader: Ian P. Callard
Grant Number: P42ES007381
Funding Period: 2000-2012
Final Progress Reports
Contaminated groundwater plumes originating from the Massachusetts Military Reservation, a Superfund site on Cape Cod, raise concerns regarding the quality of the groundwater supply to the population of the area. In this project, Dr. Callard and his research team used turtles as sentinel species to monitor the wildlife reproductive effects and, by inference, the potential for human health impacts, of exposure to contaminated groundwater.
In the project investigators current work, which constitutes the final phase of the project, observation of the painted turtle (Chrysemys picta) field-trapped from ponds on Cape Cod extended and supported prior observations of reproductive deficits. In females, these deficits included lower levels of vitellogenin (an enzyme produced during egg development) and the estrogen estradiol-17 beta, lower oviduct weights, and fewer oocytes. In males, the investigators observed lower testicular weight and sperm count.
Possible loci in the hypothalamic-pituitary-gonadal-liver axis at which environmental contaminants may act were determined in turtles trapped from Moody Pond (a test site) and Washburn Pond (a reference site at a further distance). Specifically, gonadotropin and estrogen responses were assessed using plasma steroids and vitellogenin as markers. Basal vitellogenin levels were significantly lower in Moody Pond females; however, vitellogenin responses to estradiol-17 beta were the same in both groups, indicating a normal hepatic response to estrogen. In contrast, compared with Washburn animals, estradiol-17 beta secretion was not stimulated by gonadotropin in Moody Pond females. Basal plasma testosterone and the response to gonadotropin in males were similar, although steroid levels in Moody Pond animals were slower to return to baseline after gonadotropin injection.
The potential impact of xenobiotics on the gonad was investigated in adult, juvenile and embryonic turtles. Moody Pond adult males had a markedly reduced diameter of seminiferous tubules (where sperm cells mature) and higher incidence of gonial apoptosis than Washburn males. Moody Pond females similarly had more apoptotic oocytes and atretic (degenerating) follicles. In experiments with Trachemys scripta, another species of turtle, newly born turtles exposed to Moody or Washburn Pond environments in the laboratory showed comparable oocyte proliferation and apoptosis (cell death). However, spermatogonial proliferation was lower and apoptosis was higher in exposed males from Moody Pond. In T. scripta embryos, in ovo exposure to an environmentally relevant dose of cadmium reduced the number of gonia in the gonadal anlagen. The effects of cadmium extended into neonatal life, as seen by an increase in oocyte apoptosis in both species of turtles.
The results suggest that at the test site, but not the reference site, a low-level mixture of xenobiotic contaminants, including cadmium, may interfere with gametogenesis and the steroid metabolic pathways in exposed turtles.