Urs Berger, Senior Researcher at ITM and co-author of the article, says this was not the first time alarmingly high PFAA levels had been observed in otters. "Back in 2001 a study showed that otters had accumulated high levels PFOS (perfluorooctane sulfonate) which is one of the most studied PFAAs," he says. He continues: "This means that either otters are exposed to very high levels or the toxicokinetics of PFOS in otters makes them unable to get rid of the compound easily."
Anatomy of a PFAA
It was 2000 when the scientific community first became widely aware that PFAAs such as PFOS, then the key ingredient in 3M Company’s popular Scotchgard stain repellent, were being detected at low levels in the environment and in humans. Since then, environmental scientists and toxicologists have begun paying much more attention to PFAAs.
Perfluoroalkyl acids are surfactants, that is, they lower the surface tension of a liquid and so enhance the contact between the liquid and another substance. These properties make PFAAs ideal for use in a large number of industrial applications and consumer products ranging from the production of fluoropolymers such as Teflon to food packaging, to textile stain and soil repellents to fire fighting foams.
The widespread application of PFAAs is counterpoised by their extreme persistence in the environment. ”In terms of persistence, PFAAs are a new world for us. We don’t know of any natural process that can break down these compounds. The estimated environmental half-life of PFAAs is many decades,” says Urs Berger. Besides being extremely persistent, some PFAAs are also bioaccumulative and globally distributed. “PFAAs are found in both wildlife and humans and because they have been produced and used for more than 60 years now they have spread globally. However the concentrations we observe vary in a species-dependent manner,” says Urs Berger. He goes on to emphasise that even though the higher up in the trophic chain one is the higher the PFAA levels are, there is no linear relationship between tropic level of an organism and PFAA concentrations. “The mechanism of how PFAAs biomagnify are vastly unknown,” he says.
Upward trend
In the current study, the scientists measured the concentrations of 14 different PFAAs in liver samples from 140 Scandinavian otters collected between 1972 and 2011. They then used statistical methods to calculate how PFAA levels had changed over time.
The scientists were astonished to discover that not only were levels of most PFAAs very high in these otters but also that they were increasing. "The levels of PFOS we observe in Swedish otters today are comparable to the levels known to trigger toxicological responses in lab animals," says Urs Berger. He continues: "For the majority of compounds we investigated we found increasing time trends even between 2002 and 2011, despite the fact that some of these, like PFOA (perfluorooctanoic acid), have been phased out by the 3M Company in 2002. On the other hand, time trend studies of PFOA and PFOS in humans have shown that their levels have decreased since the phase-out. This supports the species-specific accumulation of PFAAs. We cannot really explain these differences."
Effects of PFAAs
A growing body of research is now focusing on the toxicological effects of PFAAs. "There are a lot of studies showing toxicological effects of these compounds on animals in the lab. However, it is very hard to extrapolate these findings to the low concentrations found in the environment," says Urs Berger. On that note, he mentions the growing evidence of subtle effects in humans coming from recent epidemiological studies.
If the effects themselves are difficult to define, deciphering the mechanisms that underlie these effects is even more challenging. "These compounds may be mistaken by the body as fatty acids, built into the fatty acid metabolism and go on to interfere with the function of cell membranes. That's one such mechanism proposed," says Urs Berger.
As for otters, there have been no toxicological studies of PFAAs thus far. Researchers do not know how otters respond to high levels of PFAAs, nor can they explain why PFAAs continue to accumulate in otter populations despite the reduction in emissions. Nevertheless, in Urs Berger's eyes we should prohibit the use of PFAAs completely. "What we've learned from this is that even though industry has voluntarily worked towards eliminating PFAA emissions, it has not been enough to protect every species from accumulating these compounds in increasing amounts. An encouraging trend in one species, like humans, doesn't imply the same trend in another, like otters," he says.
Text: Stella Papadopoulou