Mercury - Toxicology of Metals - page 673

improvement, 33 were stationary, 28 regressed, and 5
died of other causes.
An American survey was conducted on 205 work-
ers whose mean age was 71 years. Of these workers,
104 had been heavily exposed to mercury vapor more
than 19 years previously, with mercury secretion in
excess of 600

There are few reports from human experience. Two
cases of mercury vapor exposure during pregnancy with
adverse outcomes have been reported (Carmona, 1982;
Derobert and Tara, 1950). In one case, the child survived
but with signs of brain damage. In the other case, a fi rst
pregnancy resulted in abortion and a second pregnancy
in neonatal death, but after recovery from overt mercury
poisoning the woman gave birth to a healthy child.
A study of 349 pregnant women exposed to mercury
vapor at the workplace (no concentration of mercury
was specifi ed) showed offspring with decreased birth-
weight and increased infi ltration with lytic lymphocytes
in placenta compared with 215 unexposed women (Mis-
honova et al ., 1980). By use of a case-reference design,
306 cases of mentally retarded Dutch children with
unknown causes were studied. The mothers' occupa-
tional exposure during the later stages of pregnancy
was compared between the cases and 322 reference chil-
dren who were mentally retarded for known reasons.
A signifi cantly increased odds ratio (8.7) was found for
mothers of the cases to have been exposed to mercury
during late pregnancy (Roeleveld et al ., 1993).

g/L in urine. The other 101 workers had
not been exposed. Conduction velocity in peripheral
nerves signifi cantly correlated with cumulative mer-
cury exposure, which suggests residual peripheral
neuropathy. Motor coordination was also reduced to
a statistically signifi cant degree, with a dose-response
association (Letz et al ., 2000).
In several investigations (Andersen et al ., 1993; Kishi
et al ., 1993; O'Carroll et al ., 1995), it has been shown
that neurological symptoms that arose after occu-
pational exposure to mercury vapor can remain for
decades after exposure has ceased, indicating that per-
manent damage has occurred.
In a Norwegian survey of 75 chloralkali workers
compared with 52 controls, a dose-related effect on
attention capacity and visuomotor capacity was found
12 years after the termination of exposure. This group's
exposure to mercury was considerably lower than that
of the aforementioned American cohort. For the Nor-
wegian workers, mean mercury secretion was approx-
imately 100

µ

6.1.2.5 Sensitive Groups
A large proportion of populations in both developed
and developing countries have dental amalgam resto-
rations. In most people, this exposure causes no known
adverse health effects. However, mercury, as with other
potent substances or pharmaca, is likely to induce
more serious side effects among sensitive persons
defi ned on a genetic basis. Several reports in the litera-
ture describe patients with neuropsychological symp-
toms who, during removal of amalgam restorations
and for some days after, experience an exacerbation
and exhibit conditions of illness (Berlin, 2003). These
symptoms fade when the exposure to mercury con-
comitant from removal of the amalgam has ceased and
return after renewed exposure. Such mercury-sensitive
patients have been subject to blind provocation tests
with inhalation of low concentrations of mercury vapor
in air (Stromberg et al ., 1999) or percutaneous patch
tests with mercury or mercury compounds (Marcus-
son, 1996; Marcusson and Jarstrand, 1998; Marcusson
et al ., 2000). These tests have confi rmed the occurrence
of high sensitivity to mercury in these patients.

g/L urine during their work period
(Mathiesen et al ., 1999).

µ

6.1.2.4 Effects on Fetal Brain Development
Fetal nerve tissue constitutes the cell type that
shows most sensitivity to the mercuric ion. Clear
effects on nerve growth arise at the concentration level
5-50 nmol/L or 1-10 ng/g tissue (Abdulla et al ., 1995;
Monnet-Tschudi et al ., 1996; Söderström et al ., 1995),
which is the concentration level found in neonatal
infants of amalgam-bearing mothers (Drasch et al .,
1994; Lutz et al ., 1996). Animal experimental studies
on rats and primates have shown that exposure to
mercury vapor gives rise to abortion, increased inci-
dence of neonatal death, and developmental disorders
in the brain resembling those seen after exposure to
methylmercury. This means migration disturbances
and permanent behavioral changes with a reduced
learning and adaptation ability (Berlin et al ., 1992;
Danielsson et al ., 1993; Newland et al ., 1996; Warfvinge
et al ., 1994). The effects have been seen to arise from a
mercury concentration in monkey fetus brains, which
is at a 10 times lower concentration than required
with exposure to methylmercury. In rats, it has been
shown that methylmercury exposure and exposure to
mercury vapor have an additive effect on fetal brain
development (Fredriksson et al ., 1996).

6.1.2.6 Other Organs
There is no evidence that the toxic effects of mercury
on organs other than the nervous system, such as the
kidneys, the immune system, and endocrine glands,
differ between exposure to mercury vapor and expo-
sure to mercuric mercury. Therefore, these effects are
discussed later under “Effects of Mercuric Mercury.”