Hunting for emerging polyfluorinated pollutants: from theoretical prediction to experimental detection

Abstract

A large number of chemicals are manufactured, used, and ultimately released to the environment every year, but only a few are regulated. Some chemicals are recognized as persistent organic pollutants (POPs) that are persistent, bioaccumulative, and can undergo long-range transport. Per- and poly-fluoroalkyl Substances (PFASs) have continued to attract attention since perfluorooctanoic acid and perfluorooctane sulfonate were first identified as POPs. However, the environmental behaviors of other polyfluorinated chemicals, such as longer chain (mixed) halogenated n-alkanes (PXAs), have never been investigated, although these chemicals are widely used. The lack of experimental data has hindered the assessment of these chemicals. We have developed two strategies to better estimate the environmental fate of an unknown compound without sufficient experimental data. The first strategy presented is an approach using quantitative structure-property relationships, density functional theory (DFT), chemical fate models, and partitioning space to prioritize all possible PXAs. The results suggest that PXAs with elemental compositions characterized by a more significant number of carbon and fluorine atoms but fewer chlorine and bromine atoms may pose a risk. These chemicals are likely constituents of substances used as lubricants, plasticizers, and flame retardants. In the second strategy, we analyzed the potential of conceptual DFT descriptors (global electronegativity, electrophilicity index, hardness, and polarizability) to predict a chemical's environmental behavior. The model shows that chemicals with POPs potential tend to possess a discrete zone in spaces defined by these descriptors from those with less or no POPs potential. Fluorinated chemicals tend to have a higher hardness than other compounds, which may explain their potential to bind with proteins. The results of PXA research also underline the urgent need to identify and monitor these suspected pollutants, most appropriately using mass spectrometry. We demonstrated that the novel cyclic ion mobility-mass spectrometer (cIMS-MS), coupled with gas chromatography atmospheric pressure chemical ionization (GC-APCI), can reveal the presence of unknown PFASs based on the ratio of their mass and collision cross section. PFASs compounds are revealed without prior knowledge of their occurrence in dust samples using cIMS-MS data. The method also indicates the presence of chlorofluoro n-alkanes as an emerging class of "forever chemicals" that contaminate the indoor environment.