Testing the response of cyanobacteria Synechocystis to PFOS using variable chlorophyll fluorescence and stable isotopes

Abstract

Polyfluoroalkyl substances (PFAS) constitute a widespread contaminant in the natural environment. Their resistance to degradation as a result of strong C–F bonds makes them largely unresponsive to conventional wastewater treatment methods. Bio-remediation, which uses organisms to break down contaminants, is an emerging approach that offers a cost-effective remediation technology with the potential for in situ treatment. In this study, we tested the potential of cyanobacteria Synechocystis for bio-remediation of perfluorooctanesulfonic acid (PFOS), which is one of the most common types of PFAS found in the environment. Our approach used (1) toxicology assays to determine the tolerance of Synechocystis to PFOS and (2) incubation experiments with 13C-labelled PFOS to assess its bio-accumulation potential. The toxicology assays revealed that over a period of 7 days, which corresponds to 5 generations, growth rates were not significantly affected by PFOS up to the maximum tested concentration of 8 mg L−1. The photosynthetic potential of Synechocystis across the exponential and stationary growth phases, measured by methods based on variable chlorophyll a fluorescence, was also unaffected within the tested range of PFOS concentrations. The bio-accumulation potential was tested at a PFOS concentration of 1 mg L−1. In contrast to the expected increase in δ13C as a result of 13C-PFOS accumulation by the cells, we observed a small but significant decrease, indicative of no PFOS accumulation. Overall, this study demonstrates that the growth of Synechocystis on short time scales is not affected by PFOS until concentrations that by far exceed those found in surface waters. However, further research is needed to determine why the 13C-PFOS based approach was insensitive to resolve the previously reported ability of this cyanobacteria species to bio-accumulate PFOS.