Thyroid Function in Nestling Tree Swallows and Eastern Bluebirds Exposed to Non-Persistent Pesticides and p, p?-DDE in Apple Orchards of Southern Ontario, Canada

Abstract

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.

Polyhalogenated aromatic hydrocarbons and metabolites: Relation to circulating thyroid hormone and retinol in nestling bald eagles (Haliaeetus leucocephalus)

“…Confounding influences include gender [46]; correlative relationships with other compounds that occur in higher concentrations and also impact thyroid hormones [47]; and timing, insofar as hormones change over short time scales, and even small differences in sampling age could alter perceived relationships [42,48]. Methodological issues include whether free versus bound hormones are measured (Table 2; [50]) and whether plasma or thyroid gland T4 content is measured, with the latter suggested as a better measure of endocrine disruption [51].…”

Topical dose delivery in the reptilian egg treatment model

“…For example, obstruction of the pores of the shell and shell membrane could alter oxygen, carbon dioxide, and water exchange that may secondarily affect energy metabolism and, perhaps, thereby alter internal temperatures. Regardless of the biological end point measured, the potential interpretational challenges created by ambiguous dose data also are critical for other experimental systems in which chemicals have been applied to eggs, such as topical application of herbicides or pesticides to avian eggs to simulate exposures arising from agricultural spraying practices [67–83].…”

“…26, 2007 917 pores of the shell and shell membrane could alter oxygen, carbon dioxide, and water exchange that may secondarily affect energy metabolism and, perhaps, thereby alter internal temperatures. Regardless of the biological end point measured, the potential interpretational challenges created by ambiguous dose data also are critical for other experimental systems in which chemicals have been applied to eggs, such as topical application of herbicides or pesticides to avian eggs to simulate exposures arising from agricultural spraying practices [67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. The interpretational challenges presented by ambiguous dose assumptions are not unique to in ovo exposures or endocrine mechanisms; however, the challenges may be exacerbated disproportionately in complex experimental system and for complex biological pathways, such as those mediated by the endocrine system.…”

Sex‐specific changes in thyroid gland function and circulating thyroid hormones in nestling American kestrels (Falco sparverius) following embryonic exposure to polybrominated diphenyl ethers by maternal transfer

“…The functioning of the thyroid gland was assessed using an intramuscular injection of TSH, thereby mimicking the release of TSH from the pituitary gland to trigger production and release of primarily thyroxine from the thyroid gland . This is a nondestructive tool used by veterinarians for assessing thyroid gland function in birds , with limited application in avian ecotoxicology to date , the present study's experiments being its first use in kestrels.…”