Student Research: Kathleen M. Buller

MS, , 1994
Faculty Advisor: Michael S Morgan

A Behavioral Evaluation of Mercury Exposure Among Dentists


Abstract

The effect of exposure to low level Hg among dentists was evaluated examining motor and cognitive functions, and symptoms. The hypothesis was that motor function would be more readily affected in comparison to cognitive functions, which may be altered to a lesser extent. Nineteen referent (mean urinary Hg concentration = 1.3 ug/L) and 26 exposed (mean = 32.0 ug/L) dentists were compared. Subjects provided a spot urine sample and completed an hour long assessment consisting of a medical history, dental practice questionnaire, and symptoms; 5 motor tests: Intentional Steadiness, Maze Coordination, Finger Tapping, Simple Reaction Time, and Resting Steadiness; and 6 behavioral tests: Rey's Auditory-Verbal Learning (RAVLT), Digit Span, Symbol-Digit Substitution, Benton Visual Retention, Stroop, and Trailmaking. Multivariate regression analysis evaluated the impact of urinary mercury controlling for the effect of age, alcohol in breath, nitrous oxide use per week, and vocabulary. O'Brien pooled rank sum scores summarized the effet of mercury on performance. A dose-effect curve was considered statistically significant when p < .05. Adverse deficits in motor function were found among exposed subjects for Intentional Steadiness (p < .03), Maze Coordination (p < .02), Finger Tapping (p < .03). Cognitive deficits were found for RAVLT delayed (p < .03), Digit Span (p < .05), and Symbol-Digit number corect (p < .05) when compared to the referent group. Three out of the 6 cognitive tests met statistical significance. Urinary mercury was not associated with increases in reported symptoms as measured by the Neuropsychological Symptom Checklist and Brief Symptom Index. The summary rank scores found motor function to be the only domain to be affected by exposure to mercury. Multiple motor deficits appeared just above 25 ug Hg/L, a proposed biological threshold value.