Abnormal Hormone Levels in Birds at Oil Sands

Tree swallows hatched near wetlands filled with tailings from Alberta's oil sands have above normal levels of thyroid hormones. The abnormalities could compromise survival of these birds because the hormones help regulate many critical physiological functions including metabolism, growth, development, moulting and timing of migration and breeding.

The massive heaps of tailings and processing water produced each day from Athabasca oil sands mining are being experimentally reclaimed in constructed wetlands. Up to 13 times higher than natural concentrations of polycyclic aromatic hydrocarbons (PAHs) have been measured in the sediments and highly elevated napthenic acids in the water.

These chemicals can enter the food web. Since insects that develop as larvae in water comprise most of a tree swallow's diet, the birds can become exposed to the toxins.

This first-ever study of how oil sands mining affects animal thyroids examined two hormones in birds at nests located 15 metres from wetlands with oil sands tailings and compared those with nestlings raised at a natural site. One tailings pond had not received new material for 11 years, another for three years, while tailings continued to be discharged into a third wetland.

Scientists found nestling tree swallows with elevated blood concentrations of the hormone triiodothyronine at the two sites containing the most recent tailings. Chicks not yet fledged at the two oldest tailings ponds also had significantly higher levels of thyroxine in their thyroid glands than birds from the natural site.

This research does not attempt to determine how the birds developed heightened levels of hormones. Exposure to chemicals in the wetlands containing oil sands by-products or the chemicals' altering of wetland ecosystems are both candidate causes. Nevertheless, the study's authors point out that the implications the unusual hormones levels have for the birds' health is a concern.

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