Fluorinated alkyls (PFAS) are considered forever chemicals: they are extremely persistent and accumulate in the food chain. So far, however, little research has been carried out into where the hotspots of PFAS contamination are, because analyzing them using soil samples is very time-consuming. In the future, a bioindicator could come to the rescue: wild boars. Due to their lifestyle and mobility, they come into contact with a particularly large amount of PFAS, which accumulate in their liver. Analyzes of liver samples thus reflect the environmental pollution well, as a study has now shown.
Fluorine-containing hydrocarbons such as per-/polyfluorinated alkyl substances (PFAS) are mostly water and grease repellent and are used in many everyday objects, including outdoor clothing, non-stick pans and other coatings. Because they are chemically very stable, they are hardly degraded in nature and therefore accumulate in the environment. In the meantime, PFAS can be detected even in remote polar regions, in the tissue of numerous animals and also in us humans – with potentially negative consequences. Many PFAS are suspected to be harmful, some have been shown to be toxic.
Wild boar as a pollutant sniffer
It is therefore correspondingly important to monitor exposure to PFAS and to find out where, for example, particularly high concentrations of these pollutants are found. The problem, however, is that the PFAS used by industry alone contain more than 10,000 different compounds. Collecting them all in individual analyzes is extremely time-consuming and hardly feasible. Many local pollution hotspots in Germany are therefore still undiscovered because the analytical effort for soil samples is too high. That is why Jana Rupp from the Helmholtz Center for Environmental Research (UFZ) in Leipzig and her colleagues have now developed and tested a different method of monitoring: they use wild boar as bioindicators to determine the PFAS contamination in a habitat or at a site.
“The wild boar is widespread and hunted everywhere. From the animal species you can therefore get a very good overview of where the hotspots for the spread of PFAS are in Germany,” explains Rupp. Since the wild boar is also very mobile and occupies an area of several square kilometers, it also reflects the contamination over a larger area – an advantage over soil samples, with which it is much more difficult to make statements about the PFAS contamination of larger areas. In addition, the wild boar is an omnivore and is relatively high up in the food chain, because it eats mice, frogs, snails or worms, which in turn are contaminated. It also digs a lot in the ground and also absorbs PFAS from it.
Liver samples reveal PFAS burden
The researchers chose the liver of the wild boar as a suitable sample for monitoring, because it is often not used for consumption in animals killed and because it should contain a particularly large amount of PFAS: “PFAS do not accumulate in the fatty tissue like most environmental pollutants, but bind tend to stick to proteins. That’s why they circulate in the blood and are very easy to detect in the liver,” explains Rupp.
To find out whether wild boar liver is really suitable as a biological indicator, the research team examined the livers of wild boar from three locations for 66 different PFAS. The sites were an industrial area, an area where PFAS-contaminated paper sludge was spread on the fields until the 2000s, and a control area where the background exposure to PFAS could be determined. Complementary environmental samples from these sites served as benchmarks.
The analyzes confirmed that wild boar liver is a good bioindicator of PFAS exposure. “We were able to detect significantly increased levels in regions with a known increased PFAS load,” says senior author Thorsten Reemtsma from the UFZ. For example, the PFAS concentration at the industrial site was almost twice as high as on those areas where PFAS-contaminated paper sludge was used in agriculture – and almost eight times higher than the concentrations on the control areas. From the liver analyses, the team was also able to determine which PFAS groups were predominant at the different sites. “The comparison of the PFAS contamination of wild boar and soil shows that wild boar liver is suitable as a bioindicator for PFAS contamination,” summarizes Reemtsma. “With the liver of the wild boar, the contaminated areas can be located and delimited much more easily.”
Source: Helmholtz Center for Environmental Research (UFZ); Specialist article: Science of the Total Environment, doi: 10.1016/j.scitotenv.2023.162028