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treated with MIG/SS fume. One lung tumour occurred in each of the MMA/SS
treatment groups: in the high dose group, an adenocarcinoma was reported; in the low
dose group, an anaplastic tumour was reported. No lung tumours appear to have
occurred in the MIG/SS treatment group or in the control group. The results of this
study, including data relating to survival, toxicity and tumour incidence, were
reported very briefly and therefore preclude critical examination. In addition, this
study does not conform to recognised procedures and, being further limited by the
apparent poor survival rate, cannot be taken as a reliable measure of the carcinogenic
potential of the welding fumes tested.
The carcinogenicity of fume particulate from the welding of stainless steel was
investigated in Sprague Dawley rats using the intrabronchial pellet implantation
technique (Berg et al. 1987). Fume from MMA/SS welding using a rutile electrode
was collected onto a glass fibre filter. The particulate fraction was removed from the
filter with care to avoid contamination by filter material. The elemental composition
of the particulate fraction, determined using particle-induced X-ray emission, was as
follows: Cr (3.6% by weight, including 0.8% as Cr VI ); Ni (0.25%); Fe (3.4%); Mn
(2.9%). Stainless steel pellets impregnated with a mixture of welding fume
particulate and cholesterol (1:4 w/w) were implanted in the left bronchus of each rat.
Each pellet contained, on average, 7.0 ± 1.0 mg of the mixture. Negative control
animals received cholesterol-only pellets; positive control animals received
benzo(a)pyrene + cholesterol pellets. There were 100 animals (50 females and 50
males) in each treatment and control group. Animals were killed 34 months after
implantation.
Body weight gain, organ weights and survival rates were similar in treatment and
control groups. The only lung tumour in the welding fume treatment group was a
sub-pleural squamous cell carcinoma in the right lung which appeared to be unrelated
to the treatment. There were 3/100 lung tumours in the positive control group. No
lung tumours occurred in the negative control group. Local fibrosis and squamous
metaplasia affected the lungs of some animals in treatment and control groups.
Tumour incidence in other tissues showed no significant variation between the three
groups. The study deviates from the recommended procedure in several respects. A
single dose level was used, amounting to a dose of approximately 1.4 mg particulate
per animal. Further, the intrabronchial implantation method does not accurately
reflect patterns of exposure that occur in the workplace and therefore does not provide
the most appropriate means for assessing carcinogenicity under conditions of
occupational exposure. The fairly low incidence of lung tumours in the positive
control group also casts some doubt on the reliability of this study. Nevertheless, the
findings of this study provide no evidence for carcinogenicity of the particulate
fraction of the MMA/SS welding fume tested.
Summary of animal carcinogenicity data
No carcinogenicity bioassays have been conducted with fume from the welding of
stainless steel involving exposure by inhalation. The available animal carcinogenicity
data are limited to an i.t. instillation study and an intrabronchial implantation study,
neither of which conform to internationally agreed guidelines for carcinogenicity
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