Interlaboratory Comparison of Extractable Organofluorine Measurements in Groundwater and Eel (Anguilla rostrata): Recommendations for Methods Standardization.

Research on per- and polyfluoroalkyl substances (PFAS) frequently incorporates organofluorine measurements, particularly because they could support a class-based approach to regulation. However, standardized methods for organofluorine analysis in a broad suite of matrices are currently unavailable, including a method for extractable organofluorine (EOF) measured using combustion ion chromatography (CIC). Here, we report the results of an international interlaboratory comparison. Seven laboratories representing academia, government, and the private sector measured paired EOF and PFAS concentrations in groundwater and eel (Anguilla rostrata) from a site contaminated by aqueous film-forming foam. Among all laboratories, targeted PFAS could not explain all EOF in groundwater but accounted for most EOF in eel. EOF results from all laboratories for at least one replicate extract fell within one standard deviation of the interlaboratory mean for groundwater and five out of seven laboratories for eel. PFAS spike mixture recoveries for EOF measurements in groundwater and eel were close to the criterion (±30%) for standardized targeted PFAS methods. Instrumental operation of the CIC such as replicate sample injections was a major source of measurement uncertainty. Blank contamination and incomplete inorganic fluorine removal may introduce additional uncertainties. To elucidate the presence of unknown organofluorine using paired EOF and PFAS measurements, we recommend that analysts carefully consider confounding methodological uncertainties such as differences in precision between measurements, data processing steps such as blank subtraction and replicate analyses, and the relative recoveries of PFAS and other fluorine compounds.

Reactions of α,ß-Unsaturated Carbonyls with Free Chlorine, Free Bromine, and Combined Chlorine.

Chemical disinfectants employed in water and wastewater treatment can produce a variety of transformation products, including carbonyl compounds (e.g., saturated and unsaturated aldehydes and ketones). Experiments conducted under conditions relevant to chlorination at drinking water treatment plants and residual chlorine application in distribution systems indicate that α,ß-unsaturated carbonyl compounds readily react with free chlorine and free bromine over a wide pH range but react slowly with combined chlorine (i.e., NH2Cl). For nearly all of the 11 α,ß-unsaturated carbonyl compounds studied, the apparent second-order rate constants for the reaction with free chlorine increased in a linear manner with hypochlorite (OCl-) concentrations, yielding species-specific second-order rate constants for the reaction with OCl- ranging from 0.21 to 12 M-1 s-1. Predictions based on the second-order rate constants indicate that a substantial fraction (i.e., >60%) of several of the more prominent α,ß-unsaturated carbonyls (e.g., acrolein, crotonaldehyde) will be transformed to an appreciable extent in distribution systems by free chlorine. Products from the reaction of chlorine with acrolein, crotonaldehyde, and methyl vinyl ketone were tentatively identified using nuclear magnetic resonance (NMR) and gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC-HRT-MS). These products lacked unsaturated carbons and, in some cases, contained multiple halogens.

Ring-Cleavage Products Produced during the Initial Phase of Oxidative Treatment of Alkyl-Substituted Aromatic Compounds.

Chemical oxidation with hydroxyl radical (HO•) and sulfate radical (SO4•-) is often used to treat water contaminated with aromatic compounds. Although oxidation of aromatics by these radicals has been studied for decades, the commonly accepted transformation pathway-sequential hydroxylation of the ring followed by ring cleavage and mineralization of the resulting products-does not account for the loss of the parent compound observed during the initial phase of the process. To assess the importance of pathways for aromatic compound oxidation that do not result in ring hydroxylation, we identified products formed after the initial reaction between HO• or SO4•- and benzene, toluene, ethylbenzene, and (BTEX) xylene isomers. We quantified products of ring hydroxylation and oxidation of alkyl substituents as well as a suite of ring-cleavage products, including acetaldehyde, formic acid, 6-, 7-, or 8-carbon oxoenals and oxodials. Other ring-cleavage products, which were most likely aldehydes and organic acids, were observed but not quantified. When SO4•- was used as the oxidant, aromatic organosulfates also were formed. Our results indicated that the initial phase of the oxidation process involves radical addition, hydrogen abstraction, or one-electron transfer to the ring followed by reaction with O2. The hydroxycyclohexadienylperoxy radical produced in this reaction can eliminate hydroperoxyl radical (HO2•) to produce a phenolic compound or it can rearrange to form a bicyclic peroxy intermediate that subsequently undergoes ring cleavage. Hydroxylation of the ring and oxidation of the alkyl substituent accounted for approximately 15-40% of the reacted mass of the parent compound. Ring-cleavage products for which quantification was possible accounted for approximately 2 to 10% of the reacted mass. Our results raise concerns about the formation of toxic ring-cleavage products during the initial stage of oxidation whenever HO• or SO4•- is used for the treatment of water containing benzene or alkylbenzenes.

Bacterial dealkylation of benzalkonium chlorides in wastewater produces benzyldimethylamine, a potent N-nitrosodimethylamine precursor.

N-nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct that forms during chloramine disinfection of municipal wastewater effluents which are increasingly used to augment drinking water supplies due to growing water scarcity. Knowledge of wastewater NDMA precursors is limited and the known pool of NDMA precursors has not closed the mass balance between precursor loading, precursor NDMA yield, and formed NDMA. Benzalkonium chlorides (BACs) are the most prevalent quaternary ammonium surfactants and have antimicrobial properties. The extensive utilization of BACs in household, commercial and industrial products has resulted in their detection in wastewater at elevated concentrations. We report the formation of a potent NDMA precursor, benzyldimethylamine (BDMA) from the biodegradation of BACs during activated sludge treatment. BDMA formation and NDMA formation potential (FP) were functions of BAC and mixed liquor suspended solids concentration at circumneutral pH, and the microbial community source. Sustained exposure to microorganisms reduced NDMA FP through successive dealkylation of BDMA to less potent precursors. BAC alkyl chain length (C8 - C16) had little impact on NDMA FP and BDMA formation because chain cleavage occurred at the C-N bond. Wastewater effluents collected from three facilities contained BDMA from 15 to 106 ng/L, accounting for an estimated 4 to 38 % of the NDMA precursor pool.

Ubiquitous Production of Organosulfates During Treatment of Organic Contaminants with Sulfate Radicals.

Oxidation of organic contaminants by sulfate radical (SO4 •-) is becoming more popular for the treatment of hazardous waste sites by in situ chemical oxidation (ISCO) and industrial wastewater by advanced oxidation processes (AOPs). It is well documented that SO4 •- can produce similar oxygen-containing transformation products as hydroxyl radical-based treatment processes, but SO4 •- also has the potential to produce organosulfates by radical addition. Experiments conducted with a suite of 23 aromatic and 5 aliphatic compounds, including several contaminants typically detected at hazardous waste sites, demonstrated the formation of at least one stable sulfate-containing product for 25 of the compounds. These compounds likely exhibit higher mobility in the subsurface due to a lower affinity for surfaces (e.g., aquifer solids, activated carbon) than most other transformation products. Although the health risks associated with organosulfates are still uncertain, some aromatic organosulfates produced in this study (i.e. phenyl sulfate and p-cresyl sulfate) are known to be harmful uremic toxins. Further study of organosulfate formation, fate, and toxicity is needed before SO4 •--based treatment processes are more widely employed.

Elucidating the redox cycle of environmental phosphorus using ion chromatography.

Historically, it was assumed that reactive, inorganic phosphorus present in pristine environments was solely in the form of orthophosphate. However, this assumption contradicts theories of biogenesis and the observed metabolic behavior of select microorganisms. This paper discusses the role of ion chromatography (IC) in elucidating the oxidation-reduction cycle of environmental phosphorus. These methods employ suppressed-IC, coupled with tandem conductivity and electrospray mass spectrometry detectors to identify and quantify phosphorus oxyanions in natural water, synthetic cosmochemical, and biological samples. These techniques have been used to detect phosphite and orthophosphate in geothermal hot springs. Hypophosphite, phosphite, and orthophosphate have been detected in synthetic schreibersite corrosion samples, and termite extract supernatant. Synthetic schreibersite corrosion samples were also analyzed for two poly-phosphorus compounds, hypophosphate and pyrophosphate, and results show these samples did not contain concentrations above the 1.3 and 2.0 µM respective 3σ limit of detection. These methods are readily adaptable to a variety of matrices, and contribute to the elucidation of the oxidation-reduction cycle of phosphorus oxyanions in the environment. In contrast to most studies, these techniques have been used to show that phosphorus actively participates in redox processes in both the biological and geological world.