Researchers at Lund University in Sweden have investigated the link between exposure to PFAS and the development of asthma. The results show that among children whose mothers had very high levels of PFAS exposure during pregnancy, the risk of asthma was significantly higher than among children whose mothers had lower levels of PFAS exposure.
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.
More about the study
The 11,488 children in the study were divided into groups based on the level and duration of their mothers' exposure to PFAS in drinking water during the five years prior to the children's birth. The breakdown was as follows:
Very high exposure: 194 children (mothers who had lived at addresses with heavily contaminated drinking water for all five years) High exposure: 479 children (the mother had lived at such an address for at least one year prior to giving birth) Moderate: 1,591 children (the mother lived in Ronneby, but not at an address with heavily contaminated water) Control group: 9,224 children (the mother lived in Blekinge, but not in Ronneby)
The researchers on the study: "This study differs from previous epidemiological investigations in that it includes participants with very high exposure to PFAS. This provides a greater range of exposure than is usually observed in population-based studies. This makes it possible to assess potential health effects at high PFAS concentrations, which is relevant for highly exposed populations worldwide."
Regarding the study's limitations: "Although we used detailed Swedish registers to carefully adjust for important confounding factors such as the mother's age at delivery and smoking during pregnancy, we cannot rule out other sources of unmeasurable confounding, such as parents' smoking habits after the birth. Our study was unable to take into account the parents' own childhood asthma, but we adjusted for the presence of parental asthma during the study period."
"Prenatal PFAS exposure was estimated based on the mother's home address. This means that we were unable to take into account changes over time in PFAS levels in drinking water or individual differences in exposure. Nor can the study distinguish the effects of exposure during foetal development from exposure in early childhood, as many children continued to live at exposed addresses after birth."
Sources: Annelise Blomberg and Anna Saxne Jöud, Lund University.
