Is the antimony trioxide used as a catalyst in the manufacture of PET a carcinogen?

Frequently Asked Questions Concerning PET and Antimony Trioxide

If antimony trioxide may be carcinogenic, how can it be permitted in PET where it may migrate into food?

After review of the available evidence, regulatory authorities have concluded that any evidence for carcinogenicity by inhalation is irrelevant for exposure by ingestion. By ingestion, there is no evidence that antimony compounds are associated with increased development of any tumors in animals. Chronic studies by ingestion have shown no excess tumor formation.  Even the evidence in regard to its carcinogenic potential by inhalation is of such a weak nature that the US-National Toxicology Program (NTP) is in the process of planning new studies to more definitively understand the significance of the previous data which has shown contradictory results.

Why is the National Toxicology Program (NTP) planning to study antimony trioxide?

According to the National Toxicology Program website, chemicals studied by the NTP are selected mainly on the basis of human exposure, production levels, chemical structure, and available toxicological data. Selection of an agent for a study does not imply that the agent is hazardous or a potential carcinogen in laboratory animals; likewise, an agent not selected for toxicologic study by the Program should not be taken to mean that the agent is not potentially hazardous or potentially carcinogenic in laboratory rodents.

Antimony trioxide was nominated in 2005 by the National Institute of Environmental Health Sciences. The rationale for nomination was based on significant human exposure in occupational settings and a resulting need for two-year exposure carcinogenicity studies to support the occupational exposures. 

If there are genotoxic effects, doesn't that mean that antimony is a carcinogen or should be treated as one?

Although the data from in vitro studies indicate antimony cations to have mutagenic properties the data following exposure to very high doses in vivo do not.  This indicates the body may be doing something to it to prevent this effect.  Data have shown that antimony trioxide is not well absorbed from the gastrointestinal tract.  The available chronic exposure data showing no excess tumors provides evidence that antimony is not a carcinogen by ingestion.

How can antimony or antimony trioxide be a carcinogen by inhalation but not by ingestion?

There are many types of poorly soluble particles that overwhelm the lungs' ability to clear the material after exposure to high concentrations of the particulates by inhalation.  This sets up an inflammatory reaction that leads to tumor formation.  This is essentially a rat-specific phenomenon and has not been observed in mice or hamsters after exposure to the same materials. When tumors are seen only in the lungs and airways, this is evidence that they result from inhalation-specific mechanisms of tumor formation and there is not a systemic concern of significance. If tumors were seen in other parts of the body, then there would be reason to suspect carcinogenicity by other routes of exposure.  In the animal studies where tumors were seen after exposure to antimony trioxide, the tumors were found only in locations that were consistent with inhalation-specific mechanisms.

What about exposure to workers in the PET industry?

Standard engineering controls and good industrial hygiene practices prevent hazardous exposures to personnel. These controls include adequate ventilation, avoidance of dust generation, appropriate storage conditions, and use of appropriate protective equipment.  The most recent chronic inhalation study in rats showed no evidence of tumors after a daily exposure to a level 10 fold higher than what workers may be exposed to under the current TLV (threshold limit value).  Air monitoring of workplace exposures has shown that workers are exposed to levels much less than the TLV, and exposures only occur on an infrequent basis whereas the inhalation studies involved chronic (continuous or frequent intermittent?) exposure.

What about after use of the PET bottle? Does antimony trioxide present a hazard to the environment?

There is no evidence to indicate that antimony trioxide as used in PET presents a risk to the environment. There is little opportunity for the antimony in PET to enter into the environment. Migration occurs only at very low levels that are safe. When incinerated, studies have shown that antimony generally either ends up in the bottom ash or in the fly ash that is trapped by electrostatic precipitators.

The European Chemicals Bureau is currently carrying out a risk assessment on this substance. The second draft of the environmental risk assessment section (March 2006) does not include any proposals to classify it as Dangerous for the Environment (symbol N) or as a bioaccumulative material.  According to the Organization for Economic Co-operation and Development (OECD) guidelines, because of the low solubility of antimony trioxide no acute or chronic ecotoxicity classification is required either. Hence, the risk of bioaccumulation is negligible.