Background:

Per-Polyfluoroalkyl substances (PFAS) are known as “forever chemicals” because of their persistence in the environment. The C-F bonds in the compound result in very long breakdown times because of low reactivity, and thus have very high bioaccumulation. PFAS are used in packaging, non-stick materials, and firefighting foam.

Recent studies have linked PFAS to kidney disease and certain cancers, and many industries are substituting long-chain PFAS for short-chain PFAS in the false belief that they would not accumulate in the environment as much or as long. Short-chain PFAS are smaller and more soluble in water compared to long-chain PFAS, which allows them to disperse farther from their release point. A team of scientists even found higher than expected concentrations of PFAS on Mount Everest, showing their high spreading potential in the environment. Methods that were developed for removing long-chain PFAS from water, such as activated coal filters, are not effective on short-chain PFAS, and there are no reliable methods for the removal of short-chain PFAS from the environment at this time.

Hypothesis and Methods:

In San Diego, PFAS concentration over time has not been extensively studied. If we know the amount that PFAS has risen over time, it can help us predict the rise in the future. To accomplish this, we tested for PFAS in sediment samples from Tecolote Canyon in 2014 and 2021. We extracted the PFAS from the samples and used mass spectrometry to identify the most common PFAS compounds that were likely to be present. We hypothesized that the 2021 concentrations of both long and short-chain PFAS would be double the concentrations found in the 2014 sample.

Results:

After testing the samples, we found that while the average concentration of short-chain PFAS was the same between both years, the average concentration of long-chain PFAS seemed to be higher in the sediment from 2021. In addition, we found some PFAS compounds in the 2021 samples that was not present in the 2014 sample, suggesting that while the average concentrations may not have changed much, the composition of the PFAS have changed (Table 1).

Figure 1. PFAS concentrations in Tecolote sediment from 2014 and from 2021. Error bars represent  ± 1SE.

Table 1. PFAS compounds found in Tecolote Canyon samples. Asterisks represent short-chain PFAS.

While further tests are required to get closer to the true concentration of PFAS in 2021 Tecolote Canyon, it is clear that the number of different PFAS has increased, which may point to new sources in PFAS or the further spread of existing PFAS through the environment. It is important to do everything we can to prevent the entrance of PFAS into the environment, so if you are able to, ask companies to cease use of PFAS compounds in any of their products.