Sampling Bay water is more challenging in part due to the complexity of what’s in the water—a chemistry soup filled with nutrients, ions, and organic compounds in flux from the creatures in the Bay. Unlike freshwater lakes or rivers, the Bay and its tributaries have a saltwater gradient that can affect how compounds like PFAS interact with suspended particles and the ions dissolved in the water.
The chain of carbon atoms bonded to fluorine atoms creates the PFAS "tail" containing the molecule's strongest bonds, the fluorine atoms bonded to carbon atoms. The molecule’s head, which includes oxygen and an alcohol group, allow that part of the molecule to interact with water. In the molecule, a C represents a carbon atom, an F represents a fluorine atom, an H represents a hydrogen atom, and an O represents an oxygen atom. The lines connecting the letters represent chemical bonds.
Although plants like marigolds can produce toxic pesticides naturally as a defense mechanism against deer and other predators, there’s a natural pathway for these molecules to break down. Then, the molecule’s components can be reassembled and recycled for other uses.
Active Sampling Provides a Snapshot of PFAS
Another benefit to sampling with Gionfriddo’s fibers is that they can be re-used and coated with different polymers to bind to specific PFAS from a sample. Gionfriddo painstakingly validated her method, cross-checking it against other measurement methods. Now, Gionfriddo’s lab members are using the method as an efficient way to measure low concentrations of PFAS in their water sampling.
Back in the lab, researchers use the corresponding chemical reactions to release PFAS from the sampler, measure PFAS levels, and back-calculate the PFAS concentrations in the water body where the sampler was deployed.
A member of Ghosh's laboratory installs a passive sampler for field testing in the Anacostia River.
Back in the Lab
A limiting factor in PFAS analysis is that there are thousands of variations of PFAS, but standards for only about 200 specific compounds. Although these standards include many of the PFAS that are known to affect human health, additional standards could help researchers gain a more holistic understanding of the compounds circulating in the water or sediment. Researchers can run the standards through their own instruments so they know exactly how each PFAS would appear in the readouts, adding additional certainty to their measurements.