Complete Hydrodehalogenation of Polyfluorinated and Other Polyhalogenated Benzenes under Mild Catalytic Conditions

Polyfluorinated arenes are increasingly used in industry and can be considered emerging contaminants. Environmentally applicable degradation methods leading to full defluorination are not reported in the literature. In this study, it is demonstrated that the heterogeneous catalyst Rh/Al₂O₃ is capable of fully defluorinating and hydrogenating polyfluorinated benzenes in water under mild conditions (1 atm H₂, ambient temperature) with degradation half-lives between 11 and 42 min. Analysis of the degradation rates of the 12 fluorobenzene congeners showed two trends: slower degradation with increasing number of fluorine substituents and increasing degradation rates with increasing number of adjacent fluorine substituents. The observed fluorinated intermediates indicated that adjacent fluorine substituents are preferably removed. Besides defluorination and hydrogenation, the scope of the catalyst includes dehalogenation of polychlorinated benzenes, bromobenzene, iodobenzene, and selected mixed dihalobenzenes. Polychlorobenzene degradation rates, like their fluorinated counterparts, decreased with increasing halogen substitution. In contrast to the polyfluorobenzenes though, removal of chlorine substituents was sterically driven. All monohalobenzenes were degraded at similar rates; however, when two carbon–halogen bonds were in direct intramolecular competition, the weaker bond was broken first. Differences in sorption affinities of the substrates are suggested to play a major role in determining the relative rates of transformation of halobenzenes by Rh/Al₂O₃ and H₂

Target and Suspect Screening Analysis Reveals Persistent Emerging Organic Contaminants in Soils and Sediments

An approach to identifying persistent organic contaminants in the environment was developed and executed for Switzerland as an example of an industrialized country. First, samples were screened with an in-house list using liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS) and gas chromatography tandem mass spectrometry (GC–MS/MS) in 13 samples from the Swiss National Soil Monitoring Network and three sediment cores of an urban and agricultural contaminated lake. To capture a broader range of organic contaminants, the analysis was extended with a suspect screening analysis by LC-HRMS/MS of >500 halogenated compounds obtained from a Swiss database that includes industrial and household chemicals identified, by means of fugacity modeling, as persistent substances in the selected matrices. In total, the confirmation of 96 compounds with an overlap of 34 in soil and sediment was achieved. The identified compounds consist generally of esters, tertiary amines, trifluoromethyls, organophosphates, azoles and aromatic azines, with azoles and triazines being the most common groups. Newly identified compounds include transformation products, pharmaceuticals such as the flukicide niclofolan, the antimicrobial cloflucarban, and the fungicide mandipropamid. The results indicate that agricultural and urban soils as well as sediments impacted by agriculture and wastewater treatment plants (WWTPs) are the most contaminated sites. The plausibility of this outcome confirms the combination of chemical inventory, modeling of partitioning and persistence, and HRMS-based screening as a successful approach to shed light on less frequently or not yet investigated environmental contaminants and emphasizes the need for more soil and sediment monitoring in the future