may damage whales' hearing
A toxic chemical painted on the bottom of large vessels to protect against barnacles may cause hearing difficulties in whales and other mammals and could lead whales to beach themselves, according to a study by Yale researchers to be published in the March issue of Biophysical Journal.
The chemical tributyltin oxide (TBT) affects the mechanical activity of the outer hair cells, which modulate and boost incoming sound energy to the inner hair cells, according to senior author Joseph Santos-Sacchi, professor of surgery and neurobiology at the School of Medicine.
TBT is known to damage the immune system and the hormonal system of marine mammals, "but this is the first time it has been demonstrated that TBT could be working directly on the auditory system," says Santos-Sacchi. "It's well established that if you lose your outer hair cells you would have a hearing loss of 40 to 60 decibels."
Sensitive hearing in mammals, which are the only group of animals that have outer hair cells, relies on cochlear amplification resulting from the motor activity of outer hair cells. The protein prestin, along with its interaction with intracellular chloride ions, are key to this motor activity.
The researchers found rapid and profound effects of TBT on the outer hair cells of guinea pigs they used in studying the effects of TBT on chloride ion exchanges across the outer hair cell membrane. Santos-Sacchi said TBT bypasses the normal chloride ion pathway, thereby altering the ion's modulating effects of prestin; this may have a negative affect on cochlear amplification.
"Since many marine mammals use echolocation or sonar to get around, it's possible this could be contributing to whales and dolphins beaching and hitting ships," Santos-Sacchi says. "This observation identifies a new environmental threat for marine mammals by TBT, which is known to accumulate in the food chain. It is now important to assess the impact of TBT exposure on marine mammal communication."
Co-authors include Lei Song and Achim Seeger of Yale. The research was supported by the National Institutes of Health.
-- By Jacqueline Weaver
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