Cadmium - Toxicology of Metals - page 440

to the furnace (King, 1955). Similar levels have been
reported from a Japanese silver-cadmium alloy factory
(130

g/m 3 . In the United States, the threshold limit
values (ACGIH, 2006) for Cd are 10

1 or 5 µ

g/m 3 (8-hour

µ

g Cd/m 3 ; Tsuchiya, 1967) and from Belgian elec-
tronics, battery, and Cd production factories (31-134
µ

µ

g/m 3 (8-hour TWA) for the respirable TWA) and 2 µ

fraction.

g Cd/m 3 ; Lauwerys et al ., 1974). The mean value of
the Cd concentration in the air of workshops in China
was variable (0.61-3.54 mg/m 3 ; Lu et al ., 2001).
Reported exposure levels from the production of
cadmium stearate PVC stabilizers (20-700

5 TOXICOKINETICS

g Cd/m 3 ;
Suzuki et al ., 1965) and Cd pigments (20-7000 ug Cd/m 3 ;
Harada and Shibutanni, 1973) have varied considerably.
All these values refer to the total Cd concentrations
in air. Measurements of Cd concentrations in sepa-
rate particle-size fractions are rare; we know of only
one systematic study (Hassler, 1983) in which Cd was
monitored in the breathing zone of workers whose jobs
involved long-term exposure.
Signifi cant Cd exposure may also occur in lead, zinc,
and cadmium smelters, in the electroplating industry,
and in electric welding work using Cd-containing elec-
trodes.
Smokers in a Cd-exposed workplace may contami-
nate their cigarettes or pipes with Cd and increase their
Cd dose by up to approximately 20

µ

Data on absorption, retention, distribution, and
excretion of Cd are fundamental for the evaluation of
the risks to human health connected with Cd exposure.
Although an abundance of such data is available, a few
gaps in the present knowledge continue to hamper
exact evaluations.

5.1 Absorption

5.1.1 Inhalation

Cadmium exposure through inhalation occurs in the
form of an aerosol. General laws governing deposition
of particulate matter in the human lung indicate that,
depending on particle size, 10-50% of the inhaled par-
ticles will be deposited in the alveolar part of the lung
and a major part of the remainder on the tracheobron-
chial mucosa. Poorly soluble particles deposited on the
ciliated tracheobronchial mucosa will be transported
to the pharynx and swallowed into the gastrointesti-
nal tract (see Chapter 3). For fi nely dispersed (submi-
cron) Cd aerosols, as is the case with exposure through
smoking cigarettes, it can be calculated, on the basis of
the Cd concentration in cigarette smoke and autopsy
data from people who had smoked different quantities
of cigarettes, that absorption of the inhaled amount is
between 25 and 50% (Elinder et al ., 1976; Friberg et al .,
1974; Lewis et al ., 1972). The large differences in blood
Cd levels between smokers and nonsmokers (Friberg
and Vahter, 1983; Elinder et al ., 1983b) indicate that
the respiratory absorption may be even greater. These
observations are in accordance with recent general
knowledge concerning pulmonary deposition and
absorption of ultrafi ne particles (see Chapter 3). There
are no industrial data that allow the exact calculation
of absorption of inhaled Cd.
Animal data, both from single and chronic exposure
studies, indicate a high absorption of Cd through the

µ g per cigarette

(Piscator et al ., 1976).
With modern industrial hygiene technology, it is
possible to reduce the occupational air Cd concentra-
tions. This phenomenon has been demonstrated in a
battery factory (Adamsson et al ., 1979) and in a cad-
mium-zinc smelter (Ahlman and Koponen, 1980).
Exposure limits for Cd have been lowered in many
countries; as a result, exposure has decreased (Table 4),
but there is limited published literature documenting
current levels.
NIOSH currently recommends maintaining the
inhalation of Cd to as low a level as possible, and the
US OSHA has an 8-hour PEL of 5 g/m 3 . The National

Board of Occupational Health in Sweden has issued a
hygienic limit value for occupational exposure from
air of 5

µ

g/m 3 for
total dust (AFS, 2005). Cadmium is also listed as a car-
cinogenic compound. For Cd exposure in the working
environment, a medical checkup is compulsory in
Sweden with periodic determinations of blood Cd (cf.
Section 6 of this chapter). The intention for the future
is to limit exposure to all Cd compounds to either

µ g/m 3 for respirable dust and 20 µ

TABLE 4 Occupational Exposure Limits

China 0.01 mg/m 3 Sweden (resp.) 0.005 mg/m 3

Japan 0.05 mg/m 3 USA (ACGIH)

total dust 0.01 mg/m 3

Sweden (total) 0.02 mg/m 3 USA (resp.) 0.002 mg/m 3