Exposures in the Glass Manufacturing Industry (IARC Summary & Evaluation, , ) (2024)

International Agency for Research on Cancer (IARC) - Summaries & Evaluations

For definition of Groups, see Preamble Evaluation.

4.1 Exposure data

There are five main sectors in the glass manufacturing industry:flat glass, container and pressed ware, art glass, special glass(e.g. optical, ophthalmic, electronic) and fibre glass (whichis not considered here). The basic steps in the manufacture ofglass products are melting, fining, hom*ogenization, annealingand forming. Art and special glasses are produced by pot processes,involving manual batch handling. Art glass production has changedlittle with time and, for the most part, still involves blowingby mouth. During the twentieth century, the production of flatglass and container glass has evolved from traditional batch processesto highly automated processes. The modern production of flat glassis the most highly automated and usually utilizes tank meltingwith the continuous feeding of batch ingredients and the float(Pilkington) process for forming. The production of containersand pressed ware has also become increasingly mechanized, withmechanical blowing or pressing of the molten glass.

Exposure to lead, arsenic and antimony oxides occurs primarilyin sectors of the industry where traditional, non-mechanized techniquesare used, such as in the production of crystal and other art glasses.Other potential exposures in glass manufacture include silica,asbestos, other metal oxides and polycyclic aromatic hydrocarbons.

4.2 Human carcinogenicity data

Four cohort studies of workers involved in glass manufacture -at a plant in Italy producing glass containers, among ceramicsand glass workers in Austria, at two glass factories in Finlandand among art glass-workers in Sweden - found increased risksfor lung cancer. Population-based case-control studies in Swedenand Canada also found increased risks for lung cancer in glass-workers;a population-based case-control study in China found a significantlyincreased risk for lung cancer in female glass-workers and a nonsignificantlydecreased risk in male glass, ceramics and enamelled product workers.None of the studies was specifically informative with respectto work in the flat-glass manufacturing industry. It is unlikelythat the increased risk for lung cancer can be explained by nonoccupationalrisk factors such as smoking, in view of the consistency and magnitudeof the findings, which were obtained in studies of various designsin different countries. When smoking habits were addressed inone of the studies, the estimated relative risk for lung cancerwas increased.

In general, no distinction was made in these studies between differentcomponents of the glass manufacturing industry. The only subgroupof glass-workers for whom specific findings were available wasglass-blowers. Population-based case-control studies in Swedenon glass-workers and in Canada on people exposed to glass dustfound small increased risks for stomach cancer, whereas in threecohort studies of glass-workers in Italy, Austria and Finlandthe risks for stomach cancer were not increased; in two of thecohort studies, the numbers of cases were small. Only the cohortstudy in Finland and the case-control study in Sweden specificallyreported findings on stomach cancer in glass-blowers; both showedstronger increases in risk in glass-blowers than in glass-workersin general.

The three cohort studies in Austria, Finland and Sweden showedlittle evidence of an increased risk for intestinal cancer. ASwedish population-based case-control study of colon cancer founda small increase in risk in glass-workers in general but a strongerincrease in glass-blowers.

Two population-based case-control studies, in Canada and the USA,showed non-significantly increased risks for urinary bladder cancerin glass-workers, but the numbers of cases were small. An Italiancohort study showed an increased risk for laryngeal cancer inglass-workers. In the Finnish cohort study, an increased riskwas seen for basal-cell carcinomas of the skin in male workers.

The evidence that favours a causal association between exposuresin the glass manufacturing industry and cancer is: a reasonablyconsistent association with lung cancer in all four cohort studies;a similar though less consistent association with lung cancerin three case-control studies; a larger lung cancer risk thancan reasonably be explained by non-occupational confounding factors;the presence of human lung carcinogens in some components of theglass manufacturing industry; and the finding of an increasedrisk for stomach cancers in several cohort and case-control studies.Findings that limit the interpretation of causality include: thepoorly characterized and heterogeneous exposures of workers inthe glass manufacturing industry, which are likely to result ina weak or null association between exposure and cancer risk insome studies; the absence of demonstrated dose-response relationships;the fact that, in some studies, risk estimates were made for thecombination of glass-workers and workers in other industries,thereby diminishing the degree to which results can be interpretedfor the glass manufacturing industry itself; and the relativelyfew studies of workers in the glass manufacturing industry.

4.3 Other relevant data

A single study reported an increased frequency of chromosomalaberrations in peripheral blood lymphocytes of subjects workingin a glass factory in the Czech Republic.

4.4 Evaluation

There is limited evidence that occupational exposures inthe manufacture of art glass, glass containers and pressed wareare carcinogenic.
This evaluation does not apply to glass fibre, which was evaluated previously (Vol. 43, 1988). The Working Group could not identify the specific exposure, process or activitythat is most likely to be responsible for the excess risk.

There is inadequate evidence that occupational exposuresin flat-glass and special glass manufacture are carcinogenic.

Overall evaluations

The manufacture of art glass, glass containers and pressed wareentails exposures that are probably carcinogenic to humans(Group 2A).

Occupational exposures in flat-glass and special glass manufactureare not classifiable as to their carcinogenicity to humans(Group 3).

For definition of the italicized terms, see Preamble Evaluation.

Previous evaluation: Vol. 43 (1988) (p. 39)