Student Research: David Mayfield

MS, Toxicology (Tox), 1999
Faculty Advisor: Thomas M. Burbacher

The Effects of in utero Methylmercury Exposure on Vision and Hearing in Nonhuman Primates, Macaca fascicularis


The present study assessed visual and auditory functions in adult monkeys (Macaca fascicularis) exposed in utero to methylmercury (MeHg), a prevalent environmental pollutant. Maternal exposure of either 0, 50, 70, or 90 mg/kg/day of MeHg resulted in blood mercury levels at birth from 1.04 to 2.3 ppm for treated infants. There were 10, 9, 2 and 2 offspring produced, respectively. At approximately 15 years of age the monkeys were tested on a spatial visual contrast sensitivity task and an auditory pure tone detection task. For the vision test, a forced choice tracking procedure was utilized. The following spatial frequencies were assessed: 1, 4, 10, and 20 cycles per degree of visual angle. For the auditory test, a signal detection procedure was used. Frequencies of 125, 500, 1,000, 4,000, 10,000, 25,000, and 31,500 Hz were assessed for each ear separately. The results of these studies indicate that in utero exposure to MeHg has long-term effects on visual contrast sensitivity thresholds. Results from the auditory task suggest that auditory thresholds were not affected. Since previous studies have shown that pre- and postnatal or postnatal exposure to MeHg alone affects auditory thresholds, the results of this study point to the postnatal period as a possible critical window for MeHg indiced auditory toxicity.