Antimony compounds

Antimony Trioxide: Scientific information

Risk Assessment

What is a risk assessment?

A risk assessment evaluates whether emissions of a chemical substance, occurring at each stage of its life-cycle (production, formulation, processing, use and disposal), affect human health or the environment. Risk evaluations are usually performed at local and regional levels, as well as at a continental scale.

Protection goals

Environment:
atmosphere, aquatic organisms, sediment- and soil-dwelling organisms, micro-organisms in waste water treatment plants, mammals and birds exposed via accumulation up the food chain.
Humans:
workers exposed at the workplace, consumers exposed via consumer products, men indirectly exposed via air, food, and drinking water.

EU risk assessment of Antimony Trioxide

The risk assessment (RA) of Antimony Trioxide was an obligatory risk assessment as prescribed by the EU Existing Substances Regulation (EEC No 793/93). It was finalised in May 2008 (summary of the outcome [PDF - 158 KB]).

More information on the EU Risk Assessment principles can be found on the website of the European Chemicals Bureau.

After the EU approval of the Risk Assessment (RA) on Antimony Trioxide, the members of the OECD also accepted the file (SIAP) at their meeting on October 14th 2008. The approval of the SIAP means in practice that all OECD member states (including those who signed the Mutual Acceptance of Data agreement such as South Africa, Brazil, Indonesia and soon China) have agreed to use this file to set environmental and health standards or to assess antimony trioxide. The SIAP has been made publicly available.

Human health

During the review process of the EU risk assessment, our organization filled a lot of data gaps with regard to the effects of Antimony Trioxide (ATO) to human health. Studies were commissioned to investigate acute toxicity (sensitisation, irritation and inhalation toxicity), toxicokinetics, mutagenicity and developmental toxicity. i2a also made a great effort to gather human exposure data from both producers and downstream users of ATO.

Using both existing and new research, the following conclusions were drawn in the risk assessment:

Workers:
concerns were identified only for (a) pulmonary toxicity, which requires risk reduction measures, and (b) skin irritation (under conditions of perspiration), which indicates the need for classification.
Consumers:
no concerns were identified after evaluating the following important exposure scenarios: drinking from PET bottles; contact with fabrics; sucking on toys; inhalation of indoor air.
Man exposed indirectly via the environment:
no concerns were identified after evaluating exposure via: the food, mother's milk, drinking water and outdoor air.

For workers' exposure, risk reduction measures will be proposed in a "transitional dossier" used for transferring the proposals for risk reduction (formerly done under the Existing Substance Regulation) to the new EU chemicals legislation REACH. These measures must ensure safe circumstances at the workplace.

More information with regard to the human health effects of ATO:

ATO is not a sensitizer nor an eye or respiratory tract irritant,
ATO is irritating to human skin for workers under conditions of perspiration (but does NOT require classification for it),
Acutely, ATO is not harmful via ingestion (LD50 > 20 g/kg body weight), nor via inhalation (4-h LC50 > 5 mg/L air),
For repeated (long-term) oral exposure, the NOAEL (no observed adverse effect level, i.e. the highest tested exposure level not giving rise to significant adverse effects) is 1686 mg/kg/d,
For repeated (long-term) exposure via inhalation, the NOAEC (no observed adverse effect concentration, i.e. the highest tested exposure concentration not giving rise to significant adverse effects) is currently 0.51 mg/m3, based on impaired lung clearance. This NOAEC was determined in a study with a high background incidence of lung inflammation in controls (Newton et al.(1994) study), therefore there is some uncertainty regarding the reliability of the numerical value.
ATO is not toxic to male or female reproductive tissues and no evidence of developmental toxicity was observed.
There is no concern for genotoxicity (i.e. chromosomal aberrations or DNA damage) at biological relevant concentration levels,
ATO is classified as carcinogen category 3, denoting that ATO is a substance causing concern but data available are inadequate. It is accepted that ATO is a threshold carcinogen, meaning that cancer may only result from long-term accumulation of ATO particles in the lungs, causing inflammation reactions which may later lead to fibrosis, and possibly tumour formation. Since the available studies investigating the adverse effects of long-term exposure via inhalation all have serious drawbacks hampering the evaluation of the adverse effects of ATO on the lungs, the US NTP (US National Toxicology Program) has nominated ATO for further research. In the end of 2007, a 14d range-finder on rats and mice was conducted by the US NTP, part of the conclusions are available on the NTP website. Subchronic and chronic toxicity studies in both rats and mice have started planned, as well as selected mechanistic studies.

Please note that the observation of adverse effects does not necessarily mean that there is a risk. To evaluate whether or not there is a risk, safe effect levels/concentrations should be compared to calculated or measured exposure levels/concentrations.

Classification & labelling:

Xn Harmful
R40 Limited evidence of a carcinogenic effect
S36/37 Wear suitable protective clothing and gloves
S2 Keep out of reach of children
S22 Do not breathe dust

For further information, see Science Overview [PDF - 158 KB]

Environment

For the environmental part of the EU risk assessment of antimony trioxide (ATO), i2a filled several data gaps (e.g. toxicity to soil and sediment organisms). Together with the human exposure data, i2a collected environmental exposure data from producers and downstream user of ATO.

Using the new information provided by i2a as well as carefully evaluated existing data, the following conclusions were drawn in the risk assessment:

(I) Freshwater organisms – no risk identified
(II) Freshwater sediment organisms – no risk identified, except for one production site and for textile back coating companies that did not provide environmental emission data
(III) Microorganisms in waste water treatment plants – no risk identified
(IV) Soil organisms – no risk identified
(V) Atmosphere – no risk identified
(VI) Secondary poisoning (i.e. advers. effects due to accumulation up the food chain) – no risk identified
(VII) Marine environment – currently there is no need for concern

It has been demonstrated that ATO does not pose a risk to the environment at continental, regional and at most local levels. Nevertheless, risk reduction measures will be proposed in the transitional dossier (used for transferring the proposals for risk reduction (formerly done under the Existing Substance Regulation) to the new EU chemicals legislation REACH) to ensure that the few identified local risks for freshwater sediment organisms (mentioned above) are properly controlled.

It is important to note that for textile companies, local sediment risks have only been calculated for those companies that did not provide emission data. For these companies, environmental concentrations were calculated according to a generic scenario using very conservative default values. For textile companies that provided emission data, no risks were identified.

Overview of PNECs derived in the EU risk assessment:

Note: a PNEC (predicted no effect concentration) is derived based on the results of reliable toxicity studies and represents the concentration that should not be exceeded to avoid adverse effects.

PNECsurface water = 113 µg Sb/L
PNECsediment = 11.2 mg Sb/kgdry weight (7.8 mg Sb/kgwet weight)
PNECmicroorganisms = 2.55 mg Sb/L
PNECsoil = 37 mg Sb/kgdry weight)
PNECmarine water = 11.3 µg Sb/L
PNECmarine sediment = 2.24 mg Sb/kgdry weight (1.6 mg Sb/kgwet weight)
PNECsecondary poisoning = 374.8 mg/kg food

Please note that the observation of adverse effects does not necessarily mean that there is a risk. To evaluate whether or not there is a risk, PNECs should be compared to calculated or measured exposure concentrations. The outcomes of the risk characterisation performed in the EU risk assessment report are mentioned above.

Classification & labelling:

ATO is not classified as dangerous for the environment (no R50/53 phrases need to be assigned).

For further information, see Science Overview [PDF - 158 KB]