The herbicide atrazine has been suspected of affecting sexual development by inducing aromatase, resulting in the increased conversion of androgens to estrogens. We used snapping turtles (Chelydra serpentina), a species in which sex is dependent on the production of estrogen through aromatase activity in a temperature-dependent manner, to investigate if environmentally relevant exposures to atrazine affected gonadal development. Eggs were incubated in soil to which atrazine was applied at a typical field application rate (3.1 L/ha), 10-fold this rate (31 L/ha), and a control rate (no atrazine) for the duration of embryonic development. The incubation temperature (25 degrees C) was selected to produce only males. Although some males with testicular oocytes and females were produced in the atrazine-treated groups (3.3-3.7%) but not in the control group, no statistical differences were found among treatments. Furthermore, snapping turtle eggs collected from natural nests in a corn field were incubated at the pivotal temperature (27.5 degrees C) at which both males and females normally would be produced, and some males had oocytes in the testes (15.4%). The presence of low numbers of males with oocytes may be a natural phenomenon, and we have limited evidence to suggest that the presence of normal males with oocytes may represent a feminizing effect of atrazine. Histological examination of the thyroid gland revealed no effect on thyroid morphology.

To determine the relative effects of pesticides in current use and persistent residues of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), we examined endocrine and immune responses in tree swallow (Tachycineta bicolor) and eastern bluebird (Sialia sialis) chicks from pesticide-sprayed apple orchards and reference sites in southern Ontario, Canada, during 2000 to 2001. Nests were exposed to as many as seven individual pesticide applications and up to five mixtures of pesticides during the egg-incubation and chick-rearing stage. Eggs collected from sprayed orchards contained higher p,p'-DDE concentrations than eggs from reference sites. In 16-d-old tree swallows, no significant differences were found in body mass, basal corticosterone concentration, or the corticosterone stress response following a 10-min restraint of chicks sampled from sprayed orchards and reference sites. Challenge with adrenocorticotrophic hormone (ACTH), however, produced a higher level of corticosterone secretion in tree swallow chicks from sprayed orchards relative to chicks from reference sites. Multiple regression analysis revealed no correlation between corticosterone concentrations and exposure to pesticide sprays or p,p'-DDE in tree swallow chicks. In contrast, bluebird chicks from sprayed orchards were less responsive to challenge with ACTH and a significant negative association was found between the response to ACTH challenge and p,p'-DDE concentration in eggs. The phytohemagglutinin (PHA)-induced cutaneous basophil hypersensitivity response was similar between exposure groups in both tree swallow and bluebird nestlings. Examination of immune organs revealed that tree swallow chicks from sprayed orchards had significantly greater thymic lymphocyte density and cortical/ medullary ratios and significant splenic B-cell hyperplasia relative to reference chicks. Our results indicate that modulation in the hypothalamus-pituitary-adrenal axis in songbird chicks tested are most associated with high p,p'-DDE egg concentrations. An alteration in the endocrine or immune system may compromise songbird survival immediately after fledging or during migration.

This study examined the associated effects of pesticides and persistent residues of p,p'-DDE on thyroid function in 16-day-old tree swallows (Tachycineta bicolor) and 12-day-old eastern bluebirds (Sialia sialis). Apple orchards sprayed with pesticides in current use and reference sites were chosen for study in southern Ontario, Canada, during 2000-2001. We assessed thyroid hormone concentrations (plasma and muscle thyroxine [T4], and triiodothyronine [T3]) and the response to a challenge with thyroid stimulating hormone (TSH) as well as parameters of thyroid histology. Individual nests were exposed to as many as seven individual pesticide applications and up to five pesticide mixtures. Concentrations of p,p'-DDE in eggs from both species were highest in orchard sites, and ranged from 0.05 to 5.44 mg/kg wet weight for tree swallows, and from 0.17 to 95.4 mg/kg for eastern bluebirds. In 2000, tree swallows from sprayed orchards had elevated plasma T4 concentrations, and thyroid glands with collapsed follicles, hypertrophic epithelia, and higher follicular epithelial cells relative to chicks from reference sites. Plasma T4 concentration was positively correlated with the total number of pesticide mixtures applied during egg incubation through chick rearing. In 2001, basal plasma T3 concentration in tree swallow chicks did not differ between orchard and reference sites, though there were differences among orchards; T3 was positively correlated with total number of individual sprays applied during egg incubation through chick rearing. Tree swallows challenged with TSH showed no significant difference in thyroid hormone concentration or follicular epithelial cell height between exposure groups; however, a significantly greater proportion of chicks from reference sites were found to have thyroids with focal or diffuse hypertrophic epithelia relative to orchard chicks. In 2001, bluebirds from sprayed orchards had significantly higher T3 concentrations in response to TSH challenge; this response was positively correlated with the total number of pesticides applied during egg incubation through chick rearing.