Iron oxides – calculated on Fe
Documentation of proposed values of occupational exposure limits (OELs)
Authors: BRUCHAJZER ELŻBIETA , FRYDRYCH BARBARA , SZYMAŃSKA JADWIGA 
Published: July 2020

Iron (III) oxide, (Fe2O3, nr CAS 1309-37-1) in natural
conditions occurs as iron ore. The most common
(hematite) contains about 70% pure iron. Iron
(III) oxide is used as a red dye in ceramics, glass
and paper industries and as a raw material for
abrasive metalworking (cutting).
Iron (II) oxide, (FeO, CAS 1345-25-1) occurs as
a mineral wurtzite and is used as a black dye in
cosmetics and as a component of tattoo ink.
Iron (II) iron (III) oxide (Fe3O4, CAS 1309-38-2; 1317-
-61-9) is a common mineral. It has strong magnetic
properties (so called magnetite). It occurs in igneous
rocks (gabbro, basalt). It is the richest and the best
iron ore for industry.
Occupational exposure to iron oxides occurs in the
mining and metallurgical industry in the production
of iron, steel and its products. Welders, locksmiths,
lathes and workers employed in milling ores and
polishing silver are exposed to iron oxides.
According to data from the State Sanitary Inspection,
in 2013, 389 people in Poland were exposed to iron
oxide in concentrations exceeding the current NDS
(5 mg/m3) and in 2014 – 172 people.
After single and multiple intratracheal and inhalation
exposure of animals, transient intensification of
oxidative stress and inflammatory reactions were
reported.
Iron (III) oxide did not cause genotoxic and carcinogenic
effects. In literature, there are no data on its
effects on fertility, reproduction and pregnancy.
Data on chronic toxicity of iron oxides for humans
exposed in working environment are limited. In
epidemiological studies, all information presented
in the documentation comes from observations of
people exposed to the combined effects of iron
oxides and other factors. It is not stated whether
occupational exposure was related to the specific
iron oxide and to what concentrations workers
were exposed.
The most commonly encountered toxic effect in
the occupational exposure of iron ore miners and
iron welders and welders was minor lung fibrosis
lesions and iron-silicon dust (as seen in the RTG
study). Siderose is the occupational disease of miners
and iron ore metallurgists. Moreover, cases of
lung cancer have been reported in miners, steel
workers and welders, but they were caused by total
exposure to other compounds, including radioactive
radon, carcinogenic chromium, manganese, nickel,
other oxides (SiO2, ZnO, CO, NO, NO2, MgO) as
well as exhaust gases from diesel engines. According
to IARC, iron (III) oxide belongs to group 3 (cannot
be classified as carcinogenic to humans).
Iron (III) oxides can accumulate in a lung tissue, this
process may be responsible for the occurrence of
fibrosis sites, particularly in higher parts of external
lung parts. These effects were visible in the X-ray
examination only. Pneumoconiosis (siderosis) caused
by exposure to iron oxides is usually asymptomatic
(lack of clinical symptoms and changes in lung function
parameters).
The basis for the proposed MAC-TWA value
for inhalable iron oxide fraction was NOAEL of
10 mg Fe/m3. People exposed for more than
10 years to iron (III) oxide had no pulmonary
changes. After application of an uncertainty factor
of 2 (for differences in personal sensitivity in humans),
the MAC-TWA value for the iron oxide
fraction was proposed at 5 mg/m3 (calculated as
Fe). The same observations on humans were the
basis for calculating the MAC-TWA value for
respirable fraction of iron (III) oxide. On 12% of
workers exposed to respirable fraction at mean
concentrations of 10 ÷ 15 mg/m3, changes in
pulmonary X-ray were observed. The value of
10 mg/m3 was assumed as LOAEL. After applying
the appropriate uncertainty coefficients, the
MAC-TWA value for the iron oxide respirable
fraction was proposed at 2.5 mg/m3.
The authors propose to leave the short-term value
(STEL) of 10 mg/m3 for inhaled fraction for iron
oxides and to introduce STEL value of 5 mg/m3
for respirable fraction. It is recommended to label
the substances with "I" - irritant substance.