Effects of organochlorine contaminants on thyroid hormone levels in Arctic breeding glaucous gulls, Larus hyperboreus.

Abstract

Studies on glaucous gulls (Larus hyperboreus) breeding in the Barents Sea have reported that high blood levels of halogenated organic contaminants in this species might cause reproductive, behavioral, and developmental stress. However, potential endocrine system modulation caused by contaminant exposure has yet not been reported in this Arctic apical predator. In this present study we aimed to investigate whether the current levels of a selection of organochlorines (OCs) were associated with altered circulating levels of thyroid hormones (THs) in free-ranging adult glaucous gulls breeding at Bear Island in the Barents Sea. Blood concentrations of 14 polychlorinated biphenyls, hexachlorobenzene (HCB), oxychlordane, and p,p´-dichlorodiphenyldichloroethylene (p,p´-DDE) were quantified, in addition to free and total thyroxine (T 4 ) and triiodothyronine (T 3 ), in plasma of 66 glaucous gulls in the spring of 2001. Negative correlations were found between plasma levels of T 4 and T 4 :T 3 ratio, and blood levels of OCs in male glaucous gulls. Despite their relatively low contribution to the total OC fraction, HCB and oxychlordane were the most prominent compounds in terms of their negative effect on the variation of the T 4 :T 3 ratio. Moreover, lower T 4 levels and T 4 :T 3 ratios were measured in glaucous gulls breeding in a colony exposed to high levels of OCs, compared with a less exposed colony. Levels of T 3 were elevated in the high-OC-exposed colony. This may indicate that the glaucous gull is susceptible to changes to TH homeostasis mediated by exposure to halogenated organic contaminants.

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].…”

Environmental chemicals and thyroid function

“…However, other studies found no measurable thyroid effects (94). Blubber concentration of DDT correlated negatively to TT3 and free T3 in seals (26, 27), whereas a study of sea-gulls showed no correlations with THs (95).…”

“…This indicated an increased peripheral T4 metabolism, which may represent local hypothyroidism in the fetal brain, where 5 0 DII is responsible for deiodination of T4 to the biologically active T3. Wildlife observations of HCB exposure showed negative correlations to the ratio TT4/FT4 in polar bears (25), and to T4 and T4/T3 ratio in gulls (95). A study of seals found no associations of THs to HCB (27).…”

A three‐generational study of In ovo exposure to PBDE‐99 in the zebra finch

“…All sample tests were done in duplicates. Readings with a coefficient of variation greater than 15% were excluded from the final data set [21].…”