Slags, ilmenite electrothermal smelting

Endpoint summary

Additional information

UGI (Upgraded Ilmenite) consists primarily of a titanate phase (solid solution) most of which is Ti in an oxidised form. Upon inhalation, a low rate of dissolution in the respiratory tract is assumed, based on the experimental verified inertness of the material in artificial respiratory media. Any material being released from UGI under physiological conditions will be in the form of ionic Ti, which is similarly the case for titanium dioxide: more specifically, the results from in vitro bioaccessibility testing in such fluids demonstrate a similar dissolution pattern of UGI and titanium dioxide (see summary reported under point 7.1.1 basic toxicokinetics), thus read-across from data on titanium dioxide is considered feasible without any restrictions.

The most recent evaluation of possible human cancer risks due to titanium dioxide exposure was performed by an IARC Working Group in February of 2006 (Baan et al. 2006). The Working Group considered the results of three cohort and one case-control epidemiological studies conducted in North America and Western Europe (Chen and Fayerweather, 1988; Fryzek et al., 2003; Boffetta et al., 2004 and Boffetta et al., 2001).

Chen and Fayerweather (1988) examined mortality and cancer incidence in a cohort of 1576 male workers exposed to titanium dioxide for more than a year in two titanium dioxide production plants in the United States. Mortality due to cancer was significantly lower than expected on the basis of national rates, and mortality due to lung cancer (9 deaths) was also significantly reduced (SMR=0.52; 95% CI 0.24-0.99). Nested case-control analyses found no significant associations between titanium dioxide exposure and risk of lung cancer, chronic respiratory disease, or chest roentgenogram abnormalities. In addition a subsequent nested case control study restricted to the oldest and largest of the two plants, was able to adjust for cigarette smoking habits, and also reported no increased risk with estimated exposure to titanium dioxide (Fayerweather et al., 1992).

Fryzek et al. (2003) conducted a retrospective cohort mortality study of 4241 workers (3,832 males) employed for more than 6 months at 4 production facilities in the US. Mortality from all cancers was lower than expected (SMR=0.8; 95% CI 0.7-1.0) but the number of lung cancer deaths (61) was close to expected (SMR = 1.0; 95% CI 0.8–1.3). Workers with the highest titanium dioxide exposure (packing, micronizing or internal recycle workers) had a similar mortality pattern, i.e., lower than expected deaths for all cancer with no excess for lung cancers. Internal analyses showed that relative risks of all cause mortality and mortality due to lung cancer and non-malignant respiratory disease fell with increasing cumulative exposure. The investigators concluded that the data indicate that workers at the US plants have not experienced increased risks of lung cancer or other significant adverse health effects as a result of their occupational exposures to titanium dioxide.

The largest cohort study (Boffetta et al., 2004) included 15,017 titanium dioxide workers (14,331 males) employed for more than a year in 11 plants in six European countries. Deaths due to all malignant neoplasms were fewer than expected (SMR = 0.98; 95% CI 0.91–1.05), but deaths due to lung cancer (306) were significantly higher than expected on the basis of national rates (SMR = 1.23; 95% CI 1.10–1.38). However, it was noted that lung cancer mortality rates were higher than corresponding national rates in eight out of ten locations where factories are located, i.e. the SMRs would have been lower if the investigators had used regional reference rates. Hext et al. (2005) noted that regional lung cancer mortality rates were approximately one fifth higher on average for workers in the study than national rates. Boffetta et al. (2004) undertook a very detailed and reliable exposure assessment for titanium dioxide and potential occupational confounders but internal analyses showed no evidence of an exposure– response relationship between estimated exposure to titanium dioxide dust and lung cancer mortality. The investigators concluded that the results of the internal analyses point towards the lack of a carcinogenic effect on the lung of titanium dioxide dust exposure, as experienced in this industry.

Siemiatycki (1991) conducted a hypothesis-generating case-control study in Montreal that included male patients with 20 different types of cancer and assessed exposure to 293 substances including titanium dioxide. A more refined analysis of the relationship between titanium dioxide and lung cancer in the Montreal study was later performed by Boffetta et al. (2001) and which incorporated an improved exposure assessment which resulted in several changes to the ascribed exposure status of subjects. Boffetta et al. (2001) included all 857 cases of lung cancer of the original study, but constructed a new group of 1066 controls comprising all 533 population controls and a random sample of 533 of the 1349 cancer controls (subjects with cancers of other organs) included by Siemiatycki (1991). Odds ratios (OR) were adjusted for confounders including smoking history and were not elevated for ever exposure to titanium dioxide (OR=0.9; 95% CI 0.5-1.5; 33 cases) or substantial exposure (OR=1.0; 95% CI 0.3-2.7; 8 cases).

The Working Group at IARC concluded that the studies do not suggest an association between occupational exposure to titanium dioxide as it occurred in recent decades in western Europe and North America and risk for cancer (IARC, 2006) and that the epidemiological studies on titanium dioxide provide inadequate evidence of carcinogenicity (Baan et al., 2006).

Since the IARC evaluation, Ramanakumar et al. (2008) has reported on combined results from the case-control study conducted by Siemiatycki (1991) and another large population case control study conducted in Montreal (Ramanakumar et al., 2006) which included 1236 cases of lung cancer (765 males) and 1512 population controls (899 males). OR adjusted for a number of possible confounders including smoking, were calculated using population and cancer controls in the former study, for male and female subjects in the latter study, and for the combined group of 2093 lung cancer cases and 3394 controls. In both studies there was no evidence of excess risk among subjects who had been exposed to titanium dioxide and also in pooled analyses, OR were close to unity for any exposure to titanium dioxide (OR=1.0; 95% CI 0.6-1.7; 76 cases) and substantial exposure (OR=1.2; 95% CI 0.4-3.6; 8 cases). The authors concluded that occupational exposure to titanium dioxide did not produce an excess risk of cancer, consistent with the evaluations of the IARC working group. In summary, no causative link between titanium dioxide exposure and cancer risk in humans has been demonstrated.