Quaternary ammonium compounds (QACs) are increasingly used to enhance the removal of per- and polyfluoroalkyl substances (PFAS), particularly short-chain compounds, through hydrophobic ion pairing (HIP). Here, we investigated how HIP with cetyltrimethylammonium chloride (CTAC) influences the interfacial and colloidal behavior of selected PFAS at low-micromolar concentrations below reported critical micelle concentrations (CMCs) and across varying solution chemistries (pH, ionic strength, and natural organic matter) using surface tension measurements, dynamic light scattering (DLS), ζ-potential analysis, and transmission electron microscopy (TEM). Relative to the corresponding PFAS-only controls, CTAC (6.66 μM) reduced the surface tension of PFBA, PFBS, and PFOA solutions (3.33 μM each) by 24.64, 45.71, and 70.17%, respectively. PFOS exhibited little additional surface-tension response to CTAC but responded strongly to a shorter-chain QAC (C12), indicating that interfacial behavior depends on fluorocarbon–hydrocarbon chain-length compatibility. Targeted DLS, ζ-potential, and TEM characterization identified detectable bulk coassembly in selected PFAS–QAC systems at concentrations of 3.33–33.30 μM. Electrolyte addition produced PFAS-dependent changes in interfacial behavior, while NOM reduced the interfacial activity of several mixtures. These findings provide mechanistic insight into PFAS–QAC behavior relevant to the development of QAC-assisted PFAS separation processes.
B. Pandey, Ligaya Manalastas, Afaq Ahmad et al.· ACS ES&T Water· 0 citations
The US Environmental Protection Agency (EPA) draft sewage sludge risk assessment indicates that land application of biosolids containing as little as 1 ng/g of perfluorooctanoate (PFOA) or perfluorooctane sulfonate (PFOS) may exceed human health risk thresholds. This study provides updated measurements of per- and polyfluoroalkyl substances (PFAS) in US biosolids. Twenty-seven biosolid samples from 15 states were analyzed using EPA Method 1633 and the total oxidizable precursor (TOP) assay. Dominant PFAS included 5:3 fluorotelomer carboxylic acid (FTCA) (70.2 ± 84.7 ng/g), 7:3 FTCA (23.7 ± 43.7 ng/g), and PFOS (22.1 ± 45.2 ng/g), with total PFAS ranging from 2 to 807 ng/g, showing no correlation with sewer-shed population or industrial inputs. At one facility, PFAS increased from 17.3 ng/g in primary sludge to 150 ng/g in centrifuge cake, consistent with precursor transformation. TOP assay did not increase total PFAS levels but shifted the profile, with perfluoroalkyl carboxylic acids increasing and FTCAs and other precursors decreasing, likely reflecting incomplete transformation of precursors during wastewater and sludge treatment. These findings suggest that regulated PFAS will increase following land application due to transformation of precursors over time. Compared to the 2001 national sewage sludge survey samples, PFOA and PFOS declined by > 80%, yet remain at least one order of magnitude above 1 ng/g. Current study supports EPA’s conclusion that land application of biosolids continues to pose potential human health risks.
Xia-Yan Ye, A. Maroli, Santhoshi Chitthaluri et al.· Environmental science and po...· 1 citation
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