Pfas, or per- and polyfluoroalkyl substances, are a group of human-made chemicals found in everything from food packaging to firefighting foam. Often called "forever chemicals" due to their persistence in the environment, they can affect our health and disrupt our immune system.
Pfas cross the placenta, so that when a woman is pregnant, she shares some of the Pfas in her body with her unborn child . While most of us are routinely exposed to low levels of Pfas, some communities are exposed to far higher levels from nearby pollution sources, like factories and military fire training areas .
Our new study shows that in one of these at-risk communities, children were more likely to develop asthma if their mothers were exposed to very high Pfas levels during pregnancy.
In 2013, water testing in Ronneby, a town in the southern Swedish county of Blekinge, uncovered extremely high levels of Pfas in one of the town's two municipal water supplies - more than 200 times higher than the other supply .
The source of the contamination was a type of fire-fighting foam called aqueous film-forming foam. This chemical mixture containing Pfas is used to extinguish fuel fires . It had been used in firefighting training at a nearby military airbase since the 1980s. Contaminated runoff from the airbase had eventually reached the drinking water. This resulted in high concentrations of two forever chemicals known as PFOS (perfluorooctane sulphonic acid) and PFHxS, among other Pfas.
After that discovery, residents were switched to the town's other water source. But even though residents now had clean water, their past Pfas exposure could not be reversed. By measuring Pfas directly in the dried blood spots of newborn babies whose mothers had lived in Ronneby, we have shown that Pfas contamination was already present in these children in the mid-1980s . This exposure persisted, undetected, for over 30 years. When the mothers in our study were pregnant, they had no idea that they were exposed.
Connecting contamination to childhood asthma
In Sweden, all residents are given a unique personal identity number . This can be used to link government registry information like place of birth, residential history, annual income and family relations to hospital records. This enables population-level health research that might not be possible in most other countries.
Using Swedish national health and population registers, we followed 11,488 children who were born between 2006 and 2013 in Blekinge county through to the age of 12. We estimated whether and when children would develop asthma using a combination of medical diagnoses and prescription drug records. Healthcare is free of charge for children and easily accessible throughout Blekinge county, so most children with asthma receive treatment.
We didn't have a blood sample from all 11,488 children, so we couldn't measure their Pfas exposure directly. This lack of measured exposure usually limits how we can study Pfas health effects in children.
But because Pfas exposure in Ronneby depended so strongly on their drinking water source, we could link mothers' address history to the municipal water distribution records. This enabled us to identify which mothers received contaminated water at their home in the years before they had a child. Presumably, those women had higher Pfas in their body as a result.
We divided mothers into four groups, from background exposure (living outside of Ronneby) to very high exposure (living at a contaminated address continuously for the five years preceding delivery).
Next, we compared the rates of childhood asthma across the four prenatal exposure groups. We also accounted for other factors that could influence asthma risk, including maternal smoking during pregnancy, the child's birth order and several measurements of socioeconomic status.
We found that children whose mothers had very high Pfas exposure during pregnancy were about 40% more likely to develop asthma than children in the background exposure group. Children in the intermediate exposure groups did not have higher risk. We then directly compared very high-exposed children to a carefully matched group of similar background-exposed children. We found that 27% of the very high-exposed group developed asthma by age 12, compared to 16% of the background-exposed group.
This study is one of the first to identify a link between Pfas exposure and asthma in childhood. Unlike earlier research , we were able to include children with very high Pfas exposure before birth - and we only saw an effect in this very high group, which may explain the inconsistent results of previous studies.
One possibility is that the potentially harmful effects of Pfas on lung function only occur at very high exposure. Another possibility is that, even if Pfas has an effect at lower levels, it only becomes serious enough for a diagnosis at very high exposure.
Ronneby is not an anomaly. There are more than 13,000 sites across Europe where firefighting foam contamination is likely . Our research offers important insights into the potential health effects of this contamination in affected communities. Asthma is one of the most common chronic diseases in children . If high Pfas exposure contributes to this public health burden, it is a burden that has gone largely unrecognised until now.
Annelise Blomberg receives funding from European Union's Horizon Europe program under the Marie Skłodowska-Curie Postdoctoral Fellowships (grant number 101058697) and the Swedish Research Council for Health, Working Life and Welfare (FORTE, grant number 2024-00748). Views and opinions expressed are those of the authors only and do not necessarily reflect those of the European Union or the European Research Executive Agency (REA), and neither the European Union or the REA can be held responsible for them.
Anna Saxne Jöud receives funding from the Swedish Research Council for Health, Working Life and Welfare (grant number 2020-00112).
Christel Nielsen receives funding from Formas - the Swedish Research Council for Sustainable Development, the Jan Hain Foundation for Scientific Clinical Medical Research, the Crafoord Foundation, and the Royal Physiographic Society in Lund.
