Laserfiche WebLink
affect olfactory ability at a higher concentration than those <br />studied by Rehnberg and Schreck (1986). <br />Potential Role of Protective Mechanisms <br />An unexpected result of this research was that olfaction was <br />less sensitive to 96-h exposure to copper and zinc than to 24-h <br />exposure. The 96-h EC50 for copper was approximately 1.6 times <br />greater than the 24-h estimate. The 95a confidence interval for <br />24-h exposure to copper did not include the mean for the 96-h <br />exposure; likewise, the 96-h interval did not include the 24-h <br />mean, suggesting that the decrease in inhibition was a real <br />effect and not due to experimental variation. The decrease in <br />olfactory inhibition was even more pronounced for zinc. There <br />was a significant relationship between olfactory inhibition and <br />zinc concentration after 24-h exposure; but, not after 96-h <br />exposure. This outcome is contrary to the generally observed <br />pattern that toxic action increases with duration of exposure. <br />Several explanations can be offered to account for this <br />unexpected result. <br />There are several potential protective mechanisms that may <br />decrease effects of long-term exposure to copper and zinc on <br />olfactory receptors by sequestering, eliminating, or reducing <br />absorption of toxicants. First, exposure to copper and zinc has <br />been shown to increase mucus production in fishes (Sorensen <br />1991). Mucus provides a protective coat over olfactory sensory <br />cells. Odorants or contaminants must diffuse through the mucus <br />16 <br />