Styrene is a liquid which is mainly used in the production of plastics, some of which ends up as food packaging. The German government's Federal Institute for Risk Assessment (BfR) last week said its research into the risks posed by the substance indicate that a human enzyme found in the lungs could convert styrene to styrene oxide, which is known to be tumorigenic, or a cancer-causing agent.
The preliminary research, if backed up by further research, could have implications for plant workers who are involved in making packaging and other products that use styrene.
Not enough evidence
However, a committee representing styrene manufacturers belonging to the European Chemical Industry Council, said the BfR's headline claim - that its research indicated that "styrene has a tumorigenic effect in humans” - is not supported by the overall scientific evidence.
"The chosen headline is therefore misleading and unnecessarily worrying," the committee stated.
The committee said it was concerned that the BfR press release on the issue might worry the public about the safety of styrene.
The committee noted that a draft risk assessment report on styrene prepared under the guidance of the European Chemicals Bureau states that lung tumours seen in mice "are unlikely to be of any relevance for human health".
"This conclusion was supported by the representatives of the BfR who are participating in this process as delegates from Germany," the committee stated in a position paper on the agency's research.
The committee noted that the BfR researchers caution that “the question whether the enzymes occur at a level which is sufficient for the formation of tumours cannot be definitively answered on the basis of the available data.”
Studies that show the opposite
The committee stated: "Studies covering more than 55 000 workers in the United States and Europe over a 45-year period in the glass reinforced industry (where exposure to styrene is higher than in the normal population) collectively show that exposure to styrene in the workplace does not increase the risk of cancer compared to other sites and compared to the general population."
The European Chemicals Bureau, an EU agency, is currently completing a risk assessment on styrene. The working group overseeing the risk assessment has maintained that so far styrene should not be reclassified as a potential cancer-causing agent.
The group did conclude that styrene can cause respiratory tract irritation, and has proposed an amendment to reflect the finding.
The BfR study notes that previous research into styrene has found that after inhalation of styrene, tumours form in the lungs of mice. The substance styrene oxid is formed in the cells of the lung tissue under the influence of specific enzymes. Up to now, these enzymes have not been detected in rats, nor has styrene oxide or the tumours described in mice, the BfR stated.
Assumption may be wrong
"So far it has been assumed that the enzymes required for the conversion of styrene to styrene oxide are not present in humans either or are not present in sufficient amounts to permit the formation of tumours," the BfR stated in a press release. "Results from experimental research at the Federal Institute for Risk Assessment (BfR) seem to indicate that this assumption may be wrong."
BfR claims its scientists have succeeded in detecting the enzymes involved in styrene conversion in human lung tissue, which have an effect comparable to that of the mouse.
"The tumorigenic styrene oxide could, therefore, also be formed in the human lung," the agency stated.
Styrene is classified as an “existing substance”, in wide use throughout the EU prior to the entry into force of the Chemicals Act. It is also used in many other countries. Because of a built-in exemption, industry was not required to include the necessary toxicological tests in registering the chemical for use under the act.
Such existing substances, including styrene, are currently being reviewed for safety at the European level. Whether or not a substance constitutes a risk to health depends on the degree of contact with that substance in addition to its harmfulness.
The chemical itself may not necessarily be toxic, the BfR noted. Its metabolites - substances formed during the conversion of the chemical in the body - may also trigger toxic effects, the agency suggests.
The BfR said its research was into the findings about why styrene leads to lung tumours in mice but not in rats and which of the effects should be taken as the basis for the assessment of the risk to consumers.
One major contributory factor to tumorigenic action in mice is the conversion of styrene to the toxicologically active degradation product styrene oxid in the lung. This is done with the help of two enzymes.
"The occurrence of the two enzymes responsible for the conversion of styrene to styrene oxid is an indication that a tumorigenic effect is also possible in humans," the BfR stated. - (Decision News Media, August 2006)
Styrene in packaging a cancer risk