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In Sweden, around 18,000 workers are exposed to hexavalent chromium in their workplace. Hexavalent chromium is a powerful carcinogen that is released, for example, during welding of stainless steel or the manufacture of paints and rustproofing. Thirty years ago, the limit for hexavalent chromium in Sweden was set at 5 micrograms per cubic meter of air.
It is a technically calculated value that was determined based on what industry was considered to be able to handle at the time, rather than medical studies examining the level at which people start developing cancer . That level is actually five hundred times higher than what we normally accept for carcinogens outdoors, so a reduction of the limit is necessary, says Karin Broberg, professor of occupational and environmental medicine at Lund University. Researchers from Lund University collected breath, blood and urine samples from workers who had been exposed to the substance.
The study, published in the Journal of Hazardous Materials , showed that many workers are exposed to carcinogens unnecessarily and that the limit should be lowered. The current study included 89 people who were exposed to hexavalent chromium at work, and a control group of 47 people. The results show that workers experience significant changes in their cells long before disease develops, even though exposure is well below the Swedish limit.
In this study, more than 90% of workers were exposed to levels below the current limit and the majority (80%) were exposed at levels lower than the new proposed limit of 1 microgram per cubic meter of air. Nevertheless, the workers have subtle but significant changes in their cells' microRNAs that are linked to lung cancer development. Our bodily fluids contain small molecules, known as microRNAs, which regulate gene activity and are strongly linked to cancer development.
They are also important for signaling between tissues and are particularly interesting to study as biomarkers of disease progression. These early biological changes are warning signals, which can help us recognize how serious diseases, such as lung cancer, develop. By identifying these molecular signals and understanding how they can predict risks, health surveillance can be strengthened for exposed workers and stricter safety regulations put in place.
However, more studies are needed to confirm whether these changes can be used to predict the risk of cancer and determine whether the changes may be reversible. "The study is particularly relevant given the Swedish Work Environment Authority's recent proposal to lower the limit for exposure to hexavalent chromium from 5 to 1 microgram per cubic meter of air. The current limit in Sweden is higher than in several other countries, including Denmark, which lowered its limit a few years ago following an alarming report.
Denmark has now lowered its limit again to 0.25 micrograms, due in no small part to learning of our study last year. It is crucial that the Swedish authorities continue to act by further reducing the limit," concludes Broberg.
More information: Zheshun Jiang et al, Integrative analyses of circulating microRNA expression profile in hexavalent chromium exposed workers—A cross-sectional study within the SafeChrom project, Journal of Hazardous Materials (2025). DOI: 10.1016/j.
jhazmat.2025.137367.
