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

MERCURY
2. HEALTH EFFECTS
parameters. Exposed monkeys were found to produce smaller or slower transitions than controls. The
magnitude and stability of lever-press durations for controls and exposed monkeys were indistinguishable
early in the experiment, but at the end, the exposed monkeys had longer lever-press durations and the
session-to-session variability was much greater. One monkey's exposure began during the third week of
gestation (earlier than any of the others) and its behavior was so erratic that some of the analyses could not
be accomplished. Long-term effects of prenatal mercury vapor exposure included instability in lever-press
durations and steady-state performance under concurrent schedules of reinforcement as well as aberrant
transitions (Newland et al. 1996).
Organic Mercury. No studies were located regarding developmental effects in humans or animals after
inhalation exposure to organic mercury.
The highest NOAELs and all reliable LOAELs for developmental effects in each species and duration
category are recorded in Table 2-1 and plotted in Figure 2-1.
2.2.1.7 Genotoxic Effects
There is inconclusive evidence that occupational exposure to metallic mercury and to organic and inorganic
mercury compounds, primarily through inhalation, causes structural and numerical chromosome
aberrations in human lymphocytes. In one study, significant increases in the frequency of acentric
fragments (chromosome breaks) occurred in 4 workers exposed to high concentrations of metallic mercury
and in 18 workers exposed to a mixture of mercuric chloride, methylmercuric chloride, and ethylmercuric
chloride (Popescu et al. 1979). Mercury concentrations in the workplace ranged from 0.15 to 0.44 mg/m 3 ;
the urinary excretion level of mercury for both exposed groups was .890 µg/L. The findings of this study
are suspect because the control group was not matched for sex, smoking habits, or sample size.
Additionally, one of the four individuals in the metallic mercury group had a history of benzene poisoning,
which was reflected in the unusually high frequency of abnormal chromosome morphology seen in this
individual. No difference in the incidence of aneuploidy was found between the exposed workers and the
controls. In an earlier study, an apparent association between increased chromosome aberrations and
workplace exposure to mercury (as measured by urinary mercury levels) was reported (Verschaeve et al.
1976). However, the study was not well controlled (i.e., not matched for sex, smoking habits, or sample
size), and the only significant increase in structural aberrations occurred in the three workers exposed to
ethylmercury. Significant increases in aneuploid were also noted for the exposure groups compared to the
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