Anaerobic Microbial Dechlorination of 6:2 Chlorinated Polyfluorooctane Ether Sulfonate and the Underlying Mechanisms

The microbial transformation potential
of 6:2 chlorinated polyfluorooctane
ether sulfonate (6:2 Cl-PFESA) was explored in anaerobic microbial
systems. Microbial communities from anaerobic wastewater sludge, an
anaerobic digester, and anaerobic dechlorinating cultures enriched
from aquifer materials reductively dechlorinated 6:2 Cl-PFESA to 6:2
hydrogen-substituted polyfluorooctane ether sulfonate (6:2 H-PFESA),
which was identified as the sole metabolite by non-target analysis.
Rapid and complete reductive dechlorination of 6:2 Cl-PFESA was achieved
by the anaerobic dechlorinating cultures. The microbial community
of the anaerobic dechlorinating cultures was impacted by 6:2 Cl-PFESA
exposure. Organohalide-respiring bacteria originally present in the
anaerobic dechlorinating cultures, including Geobacter, Dehalobacter, and Dehalococcoides, decreased in relative abundance over time. As the relative abundance
of organohalide-respiring bacteria decreased, the rates of 6:2 Cl-PFESA
dechlorination decreased, suggesting that the most likely mechanism
for reductive dechlorination of 6:2 Cl-PFESA was co-metabolism rather
than organohalide respiration. Reductive defluorination of 6:2 Cl-PFESA
was not observed. Furthermore, 6:2 H-PFESA exhibited 5.5 times lower
sorption affinity to the suspended biosolids than 6:2 Cl-PFESA, with
the prospect of increased mobility in the environment. These results
show the susceptibility of 6:2 Cl-PFESA to microbially mediated reductive
dechlorination and the likely persistence of the product, 6:2 H-PFESA,
in anaerobic environments.