Indium phosphide and other indium compounds: includes indium phosphide, indium arsenide, indium tin oxide, CIS, CIGS.
Identification of research needs to resolve the carcinogenicity of high-priority IARC Carcinogens. Views and expert opinions of an IARC/NORA expert group meeting, Lyon, France, 30 June - 2 July 2009. Lyon, France: International Agency for Research on Cancer, IARC Technical Publication No. 42. 2010 Jul; 42:16-24
The previous monograph on indium considered indium phosphide alone; since then, the use of other indium compounds [indium tin oxide (ITO), CIGS, and others] has burgeoned. More than 75% of indium is now used as ITO in flat panel displays. More than 300,000 workers are employed worldwide in the semiconductor industry, and a large number of workers are also employed in manufacturing flat panel displays and optoelectronics (including photovoltaics), and in reclaiming indium from spent indium-containing materials. Several studies of workers in the US semiconductor industry, including a large study by NIOSH of circuit board manufacturing workers and an even larger study by a semiconductor industry trade association, are currently underway. While these studies are attempting to characterize risk associated with work in specific departments or operations, they are unlikely to inform on cancer risk of indium compounds, because: 1) little indium exposure may have occurred in past circuit board manufacturing, 2) wafer fabrication workers (those most likely to have indium phosphide exposure) are typically exposed to a wide variety of other carcinogens, including arsenic, trichloroacetic acid, tetrachloroacetic acid, and more than 20 others (Cullen et al., 2001); and 3) little historical exposure monitoring information is likely available to provide estimates of exposure to indium phosphide or other potential carcinogens, which would be necessary to evaluate the contribution of indium to any observed carcinogenicity among wafer fabrication workers. A better approach may be to conduct (if feasible) epidemiologic studies (e.g., retrospective cohort studies) of workers involved in primary (e.g., zinc smelting) or secondary refining industries. Most primary indium refining occurs in Asia although there are two large secondary refineries in the United States and several elsewhere. Studies in secondary refineries may be more informative because of the presence of cadmium in zinc smelting. Also, the focus of secondary refineries on indium production suggests that exposures to other carcinogenic substances may be lower than those to indium. Analogy exists to the Group 1 carcinogenic metals (e.g., nickel, cadmium, and beryllium), for which the most informative studies have generally been conducted among the refiners and production facilities for these metals and metal compounds (IARC Monograph 100C, Straif et al., 2009). A series of case reports has identified pulmonary effects that may be occurring in indium-exposed workers in Asia. Studies of current exposure and biomarkers of genetic damage (using the metrics described below) of these and other indium-exposed workers may be informative in identifying early precursors of cancer. Further experimental research is needed into the mechanisms of indium compound induced toxicity and carcinogenesis with particular focus on formation of oxidative stress and inhibition protective protein synthetic mechanisms and DNA damage. Oxidative DNA damage from indium and/or arsenic exposures could be evaluated by measurement of 8- OHdG in accessible cells (e.g., nasal epithelium, buccal cells, and circulating lymphocytes) and also micronuclei micro-RNA profiling, and chromosomal aberrations.
Identification of research needs to resolve the carcinogenicity of high-priority IARC Carcinogens. Views and expert opinions of an IARC/NORA expert group meeting, Lyon, France, 30 June - 2 July 2009