PFAS (perfluoroalkyl and polyfluoroalkyl substances) are a large group of synthetic substances that can be found in many products and foods, including firefighting foam. These substances are highly persistent, and certain types of PFAS remain in the body for a long time.

Background and exposure in Blekinge

In the current study, researchers have investigated the prevalence of asthma among over 11,000 children born in the county of Blekinge, Sweden, between 2006 and 2013. This follows the discovery in 2013 of high levels of PFAS in the drinking water in Ronneby municipality in Blekinge. Following fire drills at the F17 regiment, a third of the town’s residents had been exposed to drinking water contaminated by firefighting foam. The contamination had been ongoing for over 30 years, but when the women became pregnant, it was not yet known that the drinking water in parts of Blekinge was contaminated. PFAS can cross the placenta, which means that the mother’s exposure during pregnancy also results in exposure for the foetus.

But we saw a clear link between very high PFAS exposure and a higher incidence of asthma. The risk of developing asthma was around 40 per cent higher among children of mothers with very high PFAS exposure.

To estimate the foetuses’ exposure, the researchers used the mothers’ residential addresses during the five years prior to the child’s birth. This data was then linked to the municipality’s information on water supply. The women were divided into different groups, ranging from low exposure to very high exposure. “Very high exposure” was defined as the mother having lived at an address with heavily PFAS-contaminated drinking water for all five years. “High exposure” meant having lived at such an address for at least one of the five years prior to giving birth.

Study results and asthma risk

The children in the study were followed from birth up to the age of 12. The results show that no increased incidence of asthma was observed in children whose mothers had been exposed to intermediate levels of PFAS during pregnancy.

“But we saw a clear link between very high PFAS exposure and a higher incidence of asthma. The risk of developing asthma was around 40 per cent higher among children of mothers with very high PFAS exposure,” says Annelise Blomberg, a researcher in occupational and environmental medicine at Lund University.

The researchers took into account other factors that might influence the link between mothers’ PFAS exposure and their children’s asthma. They compared children with very high exposure to children with low exposure who had similar backgrounds, for example in terms of socio-economic status and smoking during pregnancy. During the follow-up period, 16 per cent of the children with low exposure developed asthma, compared with 27 per cent in the group with very high PFAS exposure.

Interpretation and future research

“We can only observe this link. We cannot say for certain that the increase is specifically due to PFAS, but we have done our best to rule out other factors that might influence the results,” says researcher Anna Saxne Jöud, associate professor of epidemiology at Lund University.

She says that we are all exposed to PFAS to some extent, through a wide range of products and foods. It is important to note that the current study found an increased incidence of asthma only at very high levels of exposure. Previous studies, which have mainly examined populations with lower exposure, have produced mixed results.

Further research is now needed, note Annelise Blomberg and Anna Saxne Jöud. It is important to investigate whether similar results can be observed in other populations with very high PFAS exposure. According to the researchers, it is also urgent to clarify whether PFAS can affect lung function, even at lower exposure levels.

“We will also refine our exposure models for Ronneby in order to pinpoint the timing and intensity of PFAS exposure even more accurately. This would improve our ability to analyse how exposure at different stages of development can affect children’s health,” says Annelise Blomberg.