Styrene, a common ingredient in many plastic items, now deemed to be “probably carcinogenic” by WHO

The World Health Organization’s International Agency for Research on Cancer (IARC) has now upgraded the cancer-causing status of the common plastic ingredient styrene. The move came in response to the results of a comprehensive study carried out by researchers from Aarhus University, along with new animal evidence.

More than 70,000 people were included in the register-based research. The scientists looked at the incidence of acute myeloid leukemia, which is a rare form of leukemia that has been associated with styrene exposure. In a population of this size, the researchers would statistically expect 10 patients to have the disease. Instead, they found 25 cases of the illness, leading them to conclude that the ingredient is even riskier than once believed.

They also found a fivefold higher risk for a specific type of nasal cancer among those who have been exposed to styrene.

In response, the IARC has upgraded styrene from being “possibly carcinogenic” to being “probably carcinogenic” to humans. The announcement will be published as a monograph – a special type of impartial research report that countries can use as a basis for legislation – written by 23 researchers from all over the world. These researchers reviewed and reevaluated the chemical’s risk in light of the latest research on exposure to styrene, including human epidemiological studies, mechanism studies, and experiments with animals.

You can find styrene in synthetic rubber, disposable tableware, fiberglass plastic, Styrofoam and some other types of packaging, and insulation materials.

The IARC has been looking into the dangers of styrene ever since the 1970s, when there was a spike in leukemia among those working in the synthetic rubber industry in the United States. At the time, it wasn’t possible to determine whether the workers developed leukemia because of their exposure to styrene itself or from another chemical used with the styrene in producing synthetic rubber known as butadiene.

Therefore, the researchers decided to look at the reinforced plastics industry, where styrene is used without butadiene. After examining the cancer incidence for workers in this industry from 1968 to 2011, they discovered that it was indeed the styrene that was problematic.

They followed more than 73,000 people who worked in Danish companies that used styrene to produce goods like yachts and wind turbines. They looked at company registers, patient registers, the Danish Cancer register and other data to compare the workers’ incidence of cancer to that of the general population.

One of the study’s authors, Occupational Medicine Professor Henrik Kolstad, expressed his disappointment that Danish companies that analyze styrene exposure among their workers were unwilling to share their data with the research team, not even in an anonymized form. However, the measurements supplied by the Danish Working Environment Authority were enough to help them reach their conclusions. He added that while the Danish reinforced plastics industry has made noteworthy improvements in the past few years, exposure to styrene remains a big problem overall around the world.

U.S. government admitted styrene’s link to cancer

In 2011, the U.S. government warned that styrene may cause cancer, but they downplayed the risks to most consumers while conceding that those who work with the chemical in manufacturing plants were at risk.

They identified building material fumes, tobacco smoke, and photocopiers as avenues of exposure for consumers. They said that those most at risk, however, were workers responsible for building bathtubs, shower stalls, car parts, and boats. They said at the time that workers who were exposed to the chemical had high risks of lymphoma and leukemia, along with genetic white blood cell damage and a higher risk of pancreatic and esophageal cancer.

It remains to be seen whether the new research and upgraded status will prompt legislative action to protect people from toxic styrene.

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