PFAS fate using lysimeters during degraded soil reclamation using biosolids.

Carbon- and nutrient-rich biosolids are used in agriculture and land reclamation. However, per- and polyfluoroalkyl substances (PFAS) typically present in biosolids raise concerns of PFAS leaching to groundwater and plant uptake. Here, we investigated PFAS persistence and leaching from biosolids applied to a site constructed artificially to mimic degraded soils. Treatments included biosolids and biosolids blended with mulch applied at different rates to attain either one and five times the agronomic N rate for vegetable crops and a control treatment with synthetic urea and triple superphosphate fertilizer. Leachates were collected for a 2-year period from 15-cm depth zero-tension drainage lysimeters. Soils were analyzed post biosolids application. PFAS were quantified using isotope-dilution, solid-phase extraction and liquid chromatography tandem mass spectrometry. Leachate profiles exemplified an initial high total PFAS concentration, followed by a sharp decline and subsequent small fluctuations attributed to pre-existing soil conditions and rainfall patterns. Quantifiable PFAS in leachate were proportional to biosolids application rates. Short-chain perfluoroalkyl acids (CF2 < 6) were dominant in leachate, while the percentage of longer chains homologues was higher in soils. A 43% biosolids blend with mulch resulted in 21% lower PFAS leachate concentrations even with the blend application rate being 1.5 times higher than biosolids due to the blend's lower N-content. The blending effect was more pronounced for long-chain perfluoroalkyl sulfonic acids that have a greater retention by soils and the air-water interface. Biosolids blending as a pragmatic strategy for reducing PFAS leachate concentrations may aid in the sustainable beneficial reuse of biosolids.

Chronic Exposure to a PFAS Mixture Resembling AFFF-Impacted Surface Water Decreases Body Size in Northern Leopard Frogs (Rana pipiens).

Per- and polyfluoroalkyl substances (PFAS) occur in the environment as mixtures, yet mixture toxicity remains poorly understood. Aqueous film-forming foams (AFFFs) are a common source of PFAS. Our objective was to examine chronic effects of a complex PFAS mixture on amphibian growth and development. We tested toxicity of a five-chemical PFAS mixture summing to 10 µg/L and that accounts for >90% of the PFAS in AFFF-affected surface waters: perfluorooctane sulfonate (PFOS, 40%), perfluorohexane sulfonic acid (PFHxS, 30%), perflurooctanoic acid (PFOA, 12.5%), perfluorohexanoic acid (PFHxA, 12.5%), and perfluoropentanoic acid (PFPeA, 5%). We also included treatments to determine whether PFOS drove mixture toxicity and whether PFOS and mixture components act additively. We exposed Northern leopard frog (Rana pipiens) larvae through metamorphosis (∼130 d) in outdoor mesocosms. After 21 days of exposure, the larval body condition fell ∼5% relative to controls in the 4 µg/L PFOS treatment and mixtures lacking PFOS. At metamorphosis, the full 5-component 10 µg/L PFAS mixture reduced mass by 16% relative to controls. We did not observe effects on development. Our results indicate that toxicity of PFOS and other PFAS mixtures typical of AFFF sites act additively and that PFOS is not more inherently toxic than other mixture components.

Perfluoroalkyl acid transformation and mitigation by nNiFe-activated carbon nanocomposites in steady-state flow column studies.

The ongoing contamination of groundwater with per- and polyfluoroalkyl substances (PFAS) has resulted in a global and rapidly growing interest in PFAS groundwater remediation. Preferred technologies that lead to PFAS destruction are often limited by not addressing all PFAS, being energy-intensive or not being suited for in-situ application. We developed nNiFe-activated carbon (AC) nanocomposites and demonstrated varying degrees of PFAS reduction and fluoride generation with these nanocomposites in batch reactors for several PFAS. Here we explore nNiFe-AC's effectiveness to transform perfluoroalkyl acid acids (PFAAs) under steady-state flow (0.0044 to 0.15 mL/min) in nNiFe-AC:sand packed columns. Column experiments included, two perfluorooctane sulfonate (PFOS) in deionized water and two PFAA mixtures in deionized water or bicarbonate buffer containing five perfluoroalkyl carboxylates (PFCAs, C5-C9) and three perfluoroalkyl sulfonates (PFSAs, C4, C6 and C8) at temperatures of 50 or 60°C were evaluated. PFOS transformation was similar in PFOS-only and PFAA mixture column experiments. Overall, % PFAA transformation under flow conditions exceeded what we observed previously in batch reactors with up to 53% transformation of a PFAA mixture with ∼ 8% defluorination. Longer chain PFAS dominated the PFAAs transformed and a bicarbonate matrix appeared to reduce overall transformation. PFAA breakthrough was slower than predicted from only sorption due to transformation; some longer chain PFAS like PFOS did not breakthrough. Here, nNiFe-AC technology with both in-situ and ex-situ potential application was shown to be a plausible part of a treatment train needed to address the ongoing challenge for cleaning up PFAS-contaminated waters.

Release of poly- and perfluoroalkyl substances from finished biosolids in soil mesocosms.

Finished biosolids were collected and characterized from seven municipal water resource recovery facilities. Poly- and perfluoroalkyl substances (PFAS) for the 54 quantified in the biosolids ranged from 323 ± 14.1 to 1100 ± 43.8 µg/kg (dry weight basis). For all biosolids, greater than 75% of the PFAS fluorine mass was associated with precursors. Di-substituted polyfluorinated phosphate esters (diPAPs) were the most abundant PFAS identified in the biosolids. The total oxidizable precursor assay on biosolids extracts generally failed to quantify the amount of precursors present, in large part due to the fact that diPAPS were not fully transformed during the TOP assay. Outdoor biosolids column leaching experiments intended to simulate biosolids land application showed sustained PFAS leaching over the 6-month study duration. Perfluoroalkyl acid (PFAA) concentrations in leachate, when detected, typically ranged in the 10 s to 100 s of ng/L; no diPAPs were detected in the leachate. The PFAA leaching from the biosolids exceeded the PFAA mass initially present in the biosolids (typically by greater than an order of magnitude), but the cumulative PFAA mass leached did not exceed the molar equivalents that could be explained by transformation of quantified precursors. These results highlight the importance of PFAA precursors initially present in biosolids and their contribution to long term leaching of PFAAs from land-applied biosolids.

Influence of dissolved organic matter on carbonyl sulfide and carbon disulfide formation from dimethyl sulfide during sunlight photolysis.

Carbonyl sulfide (COS) and carbon disulfide (CS2 ) are important atmospheric gases photochemically generated from organic sulfur precursors in sunlit natural waters. This study examined these processes by evaluating COS and CS2 photoproduction from dimethyl sulfide (DMS) in the presence of dissolved organic matter (DOM). DOM was added because it photochemically produces various reactive intermediates (3 CDOM*, • OH, 1 O2 , and H2 O2 ) potentially involved in these reaction pathways. DMS-amended synthetic waters at pH 8 were varied in terms of their DOM type and concentration, spiked with the 3 CDOM* quenching agent, phenol, in certain cases, and subsequently irradiated over varying exposure times. Results indicated that various DOM types ranging from freshwater to open-ocean DOM increased COS but did not alter CS2 , which remained at nondetect levels. DOM type influenced COS only at higher concentrations (20 mg/L), whereas increasing DOM concentrations proportionally increased COS concentrations for all DOM types. Phenol addition lowered COS formation for reasons that remained unclear because phenol likely quenched 3 CDOM* and DMS-derived sulfur-based radicals. Further comparisons with DMS-spiked natural waters and cysteine (CYS)-spiked synthetic and natural waters assessed previously indicated that COS formation from both precursors in natural waters was always greater than in waters containing DOM alone. PRACTITIONER POINTS: DMS- and DOM-spiked synthetic waters formed COS but did not form CS2 during sunlight photolysis. In DMS-spiked synthetic solutions, DOM type has a limited influence on COS formation whereas DOM concentration has a stronger influence on COS formation. COS formation in the DMS-spiked synthetic waters was fairly proportional to the DOC concentration but was generally lower than COS formation in DMS-spiked natural waters.

Influence of dissolved organic matter on carbonyl sulfide and carbon disulfide formation from cysteine during sunlight photolysis.

Carbonyl sulfide (COS) and carbon disulfide (CS2) are important atmospheric gases that are formed from organic sulfur precursors present in natural waters when exposed to sunlight. However, it remains unclear how specific water constituents, such as dissolved organic matter (DOM), affect COS and CS2 formation. To better understand the role of DOM, irradiation experiments were conducted in O2-free synthetic waters containing four different DOM isolates, acquired from freshwater to open ocean sources, and the sulfur-based amino acid, cysteine (CYS). CYS is a known natural precursor of COS and CS2. Results indicated that COS formation did not vary strongly with DOM type, although small impacts were observed on the kinetic patterns. COS formation also increased with increasing CYS concentration but decreased with increasing DOM concentration. Quenching experiments indicated that ˙OH was not involved in the rate-limiting step of COS formation, whereas excited triplet states of DOM (3CDOM*) were plausibly involved, although the quenching agents used to remove 3CDOM* may have reacted with the CYS-derived intermediates as well. CS2 was not formed under any of the experimental conditions. Overall, DOM-containing synthetic waters had a limited to no effect towards forming COS and CS2, especially when compared to the higher concentrations formed in sunlit natural waters, as examined previously. The reasons behind this limited effect need to be explored further but may be due to the additional water quality constituents present in these natural waters. The findings of this study imply that multiple variables beyond DOM govern COS and CS2 photoproduction when moving from freshwaters to open ocean waters.

Reductive transformation of perfluorooctanesulfonate by nNiFe0-Activated carbon.

Degradation of linear (L) and branched (Br) perfluorooctanesulfonate (PFOS) using nNiFe° particles supported on activated carbon (AC) and heat is demonstrated for the first time and with several lines of evidence. At 60 °C, PFOS degradation plateaued at 50 ± 6%, while at 50 °C, 94 ± 4.1 % PFOS transformed. The accelerated iron corrosion at the higher temperature is attributed to the lower PFOS transformation at 60 °C. However, at both temperatures, ≥ 97 % of the PFOS transformed was accounted for by the moles of fluoride generated. At 60 °C, PFOS degradation rates were estimated at 0.028 ± 0.003 h-1 and fluoride and sulfite generation rates of 0.70 ± 0.165 h-1 and 0.62 ± 0.157 h-1, respectively, with no differences between L-PFOS and total Br-PFOS. Using time-of-flight mass spectrometry, some organic products were identified in the particle extracts from the 60 °C reaction. Products included single-bonded C8 polyfluoroalkyl sulfonates (F16 to F7) and alkyl acids (PFCAs, C4-C8) and one perfluorinated C8 desulfonated product supporting both defluorination and desulfonation pathways. Most of the organic products were gone after the first 25 h. High PFOS mineralization using nNiFe°-AC technology warrants further investigation for its use in permeable reactive barriers.

Indirect Photochemical Formation of Carbonyl Sulfide and Carbon Disulfide in Natural Waters: Role of Organic Sulfur Precursors, Water Quality Constituents, and Temperature.

Carbonyl sulfide (COS) and carbon disulfide (CS2) are volatile sulfur compounds that are critical precursors to sulfate aerosols, which enable climate cooling. COS and CS2 stem from the indirect photolysis of organic sulfur precursors in natural waters, but currently the chemistry behind how this occurs remains unclear. This study evaluated how different organic sulfur precursors, water quality constituents, which can form important reactive intermediates (RIs), and temperature affected COS and CS2 formation. Nine natural waters ranging in salinity were spiked with cysteine, cystine, dimethylsulfide (DMS), or methionine and exposed to simulated sunlight over varying times and water quality conditions. Results indicated that COS and CS2 formation increased up to 11× and 4×, respectively, after 12 h of sunlight, while diurnal cycling exhibited varied effects. COS and CS2 formation was also strongly affected by the DOC concentration, organic sulfur precursor type, O2 concentration, and temperature, while salinity differences and CO addition did not play a significant role. Overall, important factors in forming COS and CS2 were identified, which may ultimately impact their atmospheric concentrations.