silica dust, crystalline, in the form of quartz or cristobalite - IARC ...

IARC MONOGRAPHS – 100C
Table 3.6 Incidence, numbers and histological types of lung tumours in female Wistar rats after
inhalation exposure to quartz and/or Thorotrast
Treatment
Number
of rats a
Lung tumours
Incidence
Total
number
Histological type
Observed
Bronchiolo-alveolar
adenoma
Bronchiolo-alveolar
carcinoma
Controls 85 – – – – –
Low-dose quartz 82 37 62 8 17 37
High-dose 82 43 69 13 26 30
quartz
Thorotrast (Tho) 87 3 6 – 5 1
Low-dose quartz 87 39 68 10 28 30
+ Tho
High-dose
quartz + Tho
87 57 98 16 47 35
a
Without the animals sacrificed 0 and 6 months after the end of inhalation exposure.
From Spiethoff et al. (1992)
Squamous cell
carcinoma
lung tumours in the untreated rats (0/45), nor in
those exposed to benzo[a]pyrene alone (0/19). In
the combined exposures to benzo[a]pyrene and
quartz, an increased incidence in lung tumours
was observed (Group A, 14/31, 11 squamous cell
carcinomas and three papillomas; Group B, 4/18,
two papillomas and two carcinomas) (Pylev,
1980). [The Working Group noted the absence of
a group exposed to quartz alone.]
(b) Hamster
Groups of 50 male Syrian golden hamsters
received weekly intratracheal instillations for
15 weeks in saline of 3 mg benzo[a]pyrene or
3 mg ferric oxide or 3 mg ferric oxide plus 3 mg
benzo[a]pyrene or 1.1 mg Sil-Co-Sil or 1.1 mg
Sil-Co-Sil plus 3 mg benzo[a]pyrene or 0.7 mg
Min-U-Sil or 0.7 mg Min-U-Sil plus 3 mg benzo[a]
pyrene or 7 mg Min-U-Sil or 7 mg Min-U-Sil
plus 3 mg benzo[a]pyrene. Fifty male controls
received saline alone. Survivors were killed at 92
weeks after exposure. Co-exposures with silica
caused an enhancement of the number of respiratory
tract tumours induced by benzo[a]pyrene
(mainly in the bronchus and lung) (Niemeier
et al., 1986; Table 3.7).
3.9 Synthesis
Studies of the carcinogenicity of crystalline
silica in experimental animal models have
shown quartz dust to be a lung carcinogen in rats
following inhalation and intratracheal instillation,
but not in mice or hamsters. Rats are known
to be more sensitive than are mice or hamsters
to the induction of lung tumours due to other
inhaled poorly soluble particles, such as carbon
black (Mauderly et al., 1994).
Quartz-induced lymphoma incidence was
also increased in several experiments in rats after
intrapleural administration, and in one study
in mice after subcutaneous administration.
Tridymite- and cristobalite-induced lymphomas
were observed in only a single experiment.
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