It is no secret that workers can be exposed to dust and particles which, once in the deep lung, may trigger a number of inflammatory responses.  Antimony dusts are no exception, and for this reason workplace exposure limits are established in various jurisdictions.  These limits are calculated on the basis of the doses at which adverse effects were observed in animal tests, typically conducted under relatively worst-case conditions.

The 2017 NTP inhalation studies on antimony trioxide have prompted various agencies to revise the existing limits and calculate new ones, starting from the lowest dose having triggered adverse health effects (0.3 mg/m³ of respirable (< 7 µm) antimony trioxide).
  
For example, in January 2017, the American Conference of Governmental Industrial Hygienists (ACGIH), proposed a recommended threshold limit value (TLV®) of 0.03 mg/m³ for antimony trioxide in respirable particulate matter.  Following the response from i2a on the Draft Documentation accompanying the revised TLV, in January 2018 ACGIH decided to put all antimony substances on their ‘Under Study’ list (meaning that the TLV revision has been paused and will not reactivated before 2019 at earliest).

In May 2018, a new occupational exposure limit (OEL) of 0.006 mg respirable Sb/m³ for antimony trioxide and antimony trisulfide was published on the German BAuA webpage, as part of the German TRGS 900 (Technical Rules for Hazardous Substances).  Similarly to the ACGIH value, the recent German value is to be measured against much smaller, respirable, fractions of antimony normally present on a workplace (the OEL of 0.5 mg/m³ in place in various jurisdictions is to be measured against inhalable sizes of antimony).



The move towards a respirable OEL gives recognition to the condition that the adverse effects caused by antimony in the lung are most probably mediated by alveolar toxicity, whereby only respirable sizes can reach alveoli.
  
i2a is coordinating a workplace exposure monitoring program to determine for producers and users of antimony substances, what is the portion of inhalable versus respirable antimony that can be found on workplaces.  This campaign is associated with the implementation of guidelines aimed to minimize the exposure to dust in the workplace, and a general recommendation to use less or non-dusty forms of antimony substances, especially in workplaces with limited ventilation and respiratory protective equipment in place.

In order to achieve safe antimony workplaces, please participate in the workplace exposure monitoring campaign starting in 2019.

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US NTP studies

In December 2017 the US National Toxicology Program published its final report of the inhalation toxicology and carcinogenesis studies on antimony trioxide.
  
According to the NTP, under the conditions of these 2-year inhalation studies, there was some evidence of carcinogenic activity of antimony trioxide in rats and clear evidence of carcinogenic activity of antimony trioxide in mice.

These studies have triggered the (re-)evaluation of existing  risk assessments and classifications of antimony trioxide and other antimony substances.

It is i2a’s opinion  that the NTP studies confirm that inhalation of high quantities of very fine particles of antimony able to reach the deep lung may trigger a number of inflammatory responses, but these exposure conditions and the type of response observed in test animals are not representative of realistic human exposure and response to exposure. 


US NTP Report on Carcinogens

In August 2018 the US National Toxicology Program published its revised draft Report on Carcinogens (RoC) Monograph on antimony trioxide.

In this Monograph, NTP concludes that antimony trioxide is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals and supporting data from mechanistic studies.  It hence recommends the listing of antimony trioxide on the RoC.

It is i2a’s opinion  that the NTP assessment concentrated on the NTP studies and disregarded the equivocal and likely human irrelevance of most evidence when performing its assessment.  The listing of antimony trioxide on the RoC will not send the right signal or provide the right level of information to the producers and users of antimony trioxide.


REACH Regulation

i2a has lead the registration of 10 antimony substances under the REACH Regulation (1907/2006/EC), the EU‘s framework legislation on chemicals.  REACH stands for Registration, Evaluation and Authorisation of CHemicals.  

The 10 Registration Dossiers contain all information required by the regulation, and have used read-across of evidence as much as possible to prevent unnecessary vertebrate animal testing while performing a conservative hazard, exposure and risk assessments of each antimony substance and their various uses. They are regularly updated to reflect new evidence and comply with latest requirements.  An overview of the information gathered through this systematic exercise is available here.

Antimony metal and four trivalent antimony compounds have been selected for REACH Substance Evaluation (they have been included in the EU’s “Community Rolling Action Plan” (CoRAP)), in order to assess the new toxicological evidence regarding their potential carcinogenicity (i.e. NTP studies).  German REACH Competent Authorities (BAuA) are in charge of the Evaluation.

In preparation of this Evaluation, i2a has updated its REACH dossiers to include all most recent evidence, in the most recent format.  i2a has furthermore deployed a research program to address outstanding knowledge gaps resulting from the assessment of all recent evidence.  The results of this program aim to ensure a scientifically robust and regulatorily meaningful assessment of antimony substances.  i2a has established regular exchanges with BAuA to inform them about its work and deliverables.

It is expected that a final Substance Evaluation decision will be available in early 2020.  This final decision could include a request for additional toxicological and exposure information, and/or recommendation for follow-up regulatory action, such as a EU harmonized classification, or EU restrictions.  Once the additional information is generated and included in an updated version of the Registration Dossiers, it will be evaluated and a further decision-making will take place.  The Substance Evaluation process allows to proceed with a stepwise gap-filling process to achieve an efficient regulation of antimony substances.

In order to participate in a successful Substance Evaluation, you can:

  • Participate in the events organized by i2a (e.g. technical workshops, annual Antimony Days, etc.); and
  • Become a Member of i2a , as Full or Associate Member; and/or
  • Become a Member of the relevant Antimony Downstream user association(s); and
  • Contribute to the information requests by the given deadlines.
Download ECHA’s guide on how to act in Substance Evaluation.


CLP Regulation

i2a has determined the applicable classification for 10 antimony substances, following the criteria of the UN Globally Harmonized System (GHS).  The classifications reported by i2a take account of the purity profile and physical form of each substance, and all evidence considered to be relevant and reliable.

The (re-)evaluations of the new toxicological evidence on-going in the US and the EU, may lead towards a change in the existing classifications.  In addition to mandatory classifications (e.g. those listed in Annex VI of the CLP Regulation (1272/2008/EC)), i2a derives so-called ‘self-classifications’ that are reported in the REACH dossiers and recommended to the value chain.  These self-classifications  reflect the scientific opinion on the available evidence.

The REACH Substance Evaluation may furthermore result in a revision of the existing mandatory harmonized classifications under the EU CLP Regulation.





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