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Persistent Pollutants


April 30, 2021 | A version of this story appeared in Volume 99, Issue 16


Letters to the editor

Microbes and PFAS

The cover of C&EN's March 22, 2021, issue, which shows cartoons of microbes.
Credit: Illustration by Rick Smith

This discussion of current remediation research on per- and polyfluoroalkyl substances (PFAS) (C&EN, March 22, 2021, page 30) brings to mind some of the details of General Electric’s failed efforts several decades ago to recruit microbes to “naturally” degrade some thousands of metric tons of polychlorinated biphenyls (PCBs) it had dumped into the upper Hudson River and surrounding area in New York State from plants in Hudson Falls and Fort Edward, destroying a thriving commercial fishery.

The PCBs were produced in the US by Monsanto and were a class of highly toxic oily liquids comprising 209 congeners. They were used primarily as dielectric fluids for capacitors and transformers rather than as solvents, as implied in the article. After initial lab studies, GE scientists attempted to demonstrate an in situ proof of concept in the river using caissons loaded with preferred microbe strains and measuring the kinetics of the dechlorination process. The microbes did not fare well and had to be repeatedly replenished, according to data published in Science and in the American Chemical Society magazine Chemtech. Various estimates ranged up to hundreds of years for this type of cleanup effort in the Hudson River.

Some years after this failure, GE was judicially compelled to enter into a consent decree, and it committed to a multiyear dredging effort with a 10-digit dollar cost to partially remove the PCBs from the river. Sadly, the effort has been judged woefully incomplete, the commercial fishery has remained closed, and recreational and subsistence fishing has remained severely limited.

Carbon-fluorine bonds are even stronger than carbon-chlorine bonds and are expected to be even more difficult to degrade. Thus, professor Rolf U. Halden states in the article that he is “very, very skeptical” of practical microbe deployment for PFAS, and he correctly notes the real and urgent need to cut back on PFAS uses, many of which are not critically needed. Remediation of such widely used and unfortunately also widely dispersed fluorinated compounds will be complex and expensive. The chemistry and engineering effort might be challenging, but the economics will be even more so, as was amply noted in the published article. It’s time we adopted the European precautionary principle and asked ourselves beforehand what kind of Pandora’s box we are opening.

William H. Flank
Silver Spring, Maryland



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