Selenium - Toxicology of Metals - page 786

been speculated that MeHg might serve as a methyl
donor for selenium (Alexander and Norseth, 1979;
Gregus et al ., 2001; Urano et al ., 1997).
Decreased levels of GSH-px in several organs
including the brain are seen after methylmercury expo-
sure. These are restored even when small amounts of
selenium are added (Ganther, 1980). Also other seleno-
proteins, such as the deiodinases, can be affected
by MeHg exposure (Watanabe, 2002). In macaques
exposed to MeHg, a coaccumulation of inorganic mer-
cury and selenium in thalamus and also in the occipital
pole of their brains (Bjorkman et al ., 1995). Interactions
between selenium and methylmercury have not been
described in humans.

7.7.11 Thallium

Thallium toxicity is prevented by selenate, and coad-
ministration of selenate and thallium increased the tis-
sue levels of both compounds (Levander and Argrett,
1969; Rusiecki and Brzezinski, 1966).

8 PREVENTION, DIAGNOSIS, PROGNOSIS,
AND TREATMENT

To prevent health problems related to occupational
selenium exposure maximum levels for the working
environment have been established.
Occupational exposure limits (OELs) (according to
WHO, IPCS, 1994 International Chemical Safety Cards,
http://www.cdc.gov/niosh/ipcsneng/neng0072.html):
TLV: 0.2 mg/m 3 as TWA; (ACGIH 2004). MAK: (inhal-
able fraction) 0.05 mg/m 3 ; Peak limitation category:
II(4); Carcinogen category: 3B; pregnancy risk group: C;
(DFG 2004). Swedish OEL: 0.1 mg/m 3 . OSHA PEL*:
TWA 0.2 mg/m 3 *NOTE: The PEL also applies to other
selenium compounds (as Se) except selenium hex-
afl uoride. NIOSH REL*: TWA 0.2 mg/m 3 *NOTE: The
REL also applies to other selenium compounds (as Se)
except selenium hexafl uoride. NIOSH IDLH: 1 mg/m 3
(as Se).
The few known cases of acute poisoning in
humans have shown uncharacteristic neurological
and gastrointestinal symptoms. The characteristic
garlic odor of the breath is not always reported. In
more long-term exposure, garlic odor of the breath
and nail, hair, and skin changes seem to have been
of diagnostic value. Except for two intoxications
(Carter, 1966; Yang et al ., 1983) that resulted in
death, the outcome of described intoxications has
been without sequel. This indicates that the prog-
nosis, in general, is good. Although the antidote
effects of chemicals such as arsenite and cyanide are
well documented in studies on laboratory animals,
there are no reports on cases where these antidotes
have been used in the treatment of systemic intoxi-
cations in humans. Dimercaprol may enhance the
toxicity of selenium in animals (Carter, 1966); but in
one successfully treated case (Civil and McDonald,
1978), vitamin C (4 g/day) and dimercaprol (150 mg
× 4/day) were used. Symptomatic treatment should
be given. After oral exposure, administration of
charcoal in slurry is recommended in Hazardous
Substances Data Bank (HSDB). Clothes should
be removed to decrease dermal exposure. Painful
skin, nail, and eye disorders have been successfully
treated with 10% solutions or ointments of thiosul-
fate (Glover, 1970).

7.7.8 Platinum

Cu-Diamminedichloroplatinum (cisplatin) is a potent
anticancer drug widely used in human cancer therapy.
However, a serious form of dose-related cumulative
renal toxicity limits its use in patients. Several selenium
compounds could effectively reduce the renal toxicity
of cisplatin without compromising antitumor activity
of cisplatin in animal models (Berry et al ., 1984; Naga-
numa et al ., 1983; 1984). The effi cacy of selenocysteine
conjugates seems to depend on activation to selenols
by ß-lyase (Rooseboom et al ., 2002).

7.7.9 Silver

In a number of animal species (e.g., rat, turkey, poults,
ducklings, and pigs), signs of selenium or vitamin E
defi ciency (e.g., liver necrosis, myopathy, and exuda-
tive diathesis) can be induced by feeding high levels
of silver. Such effects of silver could be antagonized by
administering even modest doses of selenium relative to
silver (Diplock, 1976; Ganther, 1980). Conversely, silver
ions can protect against selenium toxicity (Jensen, 1975).
Coadministration of selenium and silver causes changes
in organ levels of both elements. Retention of silver in
the body and especially in the blood plasma and kid-
neys is seen. Selenite inhibited biliary excretion of silver
(Alexander and Aaseth, 1981; Naganuma et al ., 1983).
Ag 2 Se precipitates were found in the glomerular base-
ment membrane of an argyria patient (Aaseth et al ., 1981).
This has later been confi rmed in other studies showing
silver-selenium complexes in argyria (Sato et al ., 1999).

7.7.10 Tellurium

In ducklings and pigs, tellurium, which belongs to the
same group as selenium in the periodic system, induced
signs of selenium and vitamin E defi ciency, which could
be counteracted in the ducklings by dietary selenium
(Van Vleet et al ., 1981).