revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 298
2. HEALTH EFFECTS
Studies that report an association between dental amalgam and adverse effects.
Echeverria et al. (1995) evaluated the behavioral effects of low-level exposure to Hg among dentists who
had either been exposed to mercury or not as measured in a selection procedure where the exposed group
was defined as those with urinary mercury levels greater than 19 µg/L. Exposure thresholds for health
effects associated with elemental mercury exposure were examined by comparing behavioral test scores of
19 exposed (17 males, 2 females) with those of 20 unexposed dentists (14 males, 6 females). The mean
urinary Hg of exposed dentists was 36.4 µg/L, which was 7 times greater than the 5 µg Hg/L mean level
measured in a national sample of dentists (urinary Hg was below the level of detection in unexposed dentists
for this study). To improve the distinction between recent and cumulative effects, the study also evaluated
porphyrin concentrations in urine, which are correlated with renal Hg content (a measure of cumulative body
burden). Significant urinary Hg dose-effects were found for poor mental concentration, emotional lability,
somatosensory irritation, and mood scores (tension, fatigue, confusion). Individual tests evaluating cognitive
and motor function changed in the expected directions but were not significantly associated with urinary Hg.
However, the pooled sum of rank scores for combinations of tests within domains were significantly
associated with urinary Hg, providing evidence of subtle preclinical changes in behavior associated with Hg
exposure. Coproporphyrin, one of three urinary porphyrins altered by mercury exposure, was significantly
associated with deficits in digit span and simple reaction time. Exposed dentists placed significantly more
amalgams per week (28.0) than unexposed dentists (19.8). No significant differences were found between
exposed and unexposed dentists for the overall number of years in practice or the number of amalgams
removed per week.
Altmann et al. (1998) compared visual functions in 6-year-old children exposed to lead and mercury levels,
in a cohort of 384 children (mean age 6.2 years) living in three different areas of East and West Germany.
After adjusting for confounding effects, statistically significant lead-related changes were found only for
some of the visually evoked potentials (VEP) interpeak latencies, while some of the contrast sensitivity
values were significantly reduced with increasing mercury concentrations. All other outcome variables were
not significantly related to lead or mercury levels. The authors concluded that even at blood lead levels in
the range of 14–174 µg/L and at very low urinary mercury levels subtle changes in visual system functions
can be measured. The geometric means of urinary mercury concentrations were 0.161, 0.203, and 0.075 µg
Hg/24 hours for subjects of the three study areas (0.157 µg Hg/24 hours for the total study); the average
numbers of amalgam fillings were 0.76, 1.10, and 1.88, respectively (1.15 amalgam fillings for the total
study).