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Method development of total oxidizable precursor assay for perfluoroalkyl acid precursors in domestic sludgeSöderlund, Lydia January 2018 (has links)
Per- and polyfluoroalkyl substances (PFASs) are persistent organic pollutants used in industrial applications and are globally distributed in the environment. A group of PFASs that are difficult to measure with today’s method are perfluoroalkyl acid precursors (PFAA precursors) that, when degraded, serves as indirect sources of PFAAs. This study has optimized a previously developed method for quantification of PFAA precursors in soil; through total oxidizable precursor assay (TOP assay) under alkaline conditions, to be applicable on sewage sludge. To achieve and maintain an alkaline environment during the entire oxidative treatment, several parameters were tested: concentrations of NaOH, persulfate and sample; additional clean-up with graphitized non-porous carbon and reaction time. Solid phase extraction-weak anion exchange (SPE-WAX) was used for clean-up and separation of analytes, and LC-MS/MS was used for quantification. The optimal conditions with the highest levels of PFAAs detected was obtained with 1.33 M NaOH, 60 mM persulfate, 3.57 g/L sludge with a reaction time of 6 hours. The use of graphitized non-porous carbon reduced matrix effects on oxidative conversion resulting in a higher pH as well as a higher degree of oxidation, but with some analyte loss.
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The study of organofluorine analysis applied to totaloxidizable precursor (TOP) assay to understand perandpolyfluoroalkyl substances (PFASs)Ho, Crystal January 2018 (has links)
Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals which are used in a wide range of applications such as aqueous film forming foam (AFFF) for firefighting, paint, coating and cosmetics. For almost a decade, PFASs have received worldwide attention because of the ubiquitous detection of PFAS in the environment and their bioaccumulative, persistent and give toxic effects on animals and humans. A number of study have shown many unknown organofluorine present in environmental samples. The total oxidizable precursor (TOP) method is an oxidation method to convert any precursor compounds of PFASs into measurable perfluorinated carboxylic acids (PFCAs) or sulfonic acids (PFSAs). The aims of this project are to evaluate if the use of total oxidizable precursor (TOP) assay may help improve the mass balance analysis between the quantifiable PFASs and extractable organofluorine in samples. In this study, three water samples: landfill leachate water, contaminated groundwater and adiluted Sthamex AFFF with tap water were undergone TOP assay to reveal the present of any unidentified precursor compounds. To obtain the extractable organofluorine and quantifiable PFAS levels in the samples, combustion ion chromatography (CIC) and liquid chromatography – tandem mass spectrometry (LC-MS/MS) were used, respectively. Results suggested the presence of unidentified precursor compounds in the samples with the aid of TOP assay reaction. Although after the oxidative conversion, a large portion of unidentified PFASs compounds were still present in the samples. The quantifiable PFASs in the samples were up to 7 % of the EOF; in other word, there were still around 93 % of unidentified compounds present in the samples. Further development of analytical method for characterization or identification of these unknown PFAS compounds is needed.
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Characteristics and Management Implications of Mollic Soils in Forest Versus Grassland Settings in Central CaliforniaClark, Brian Charles 01 March 2021 (has links) (PDF)
Efforts to sequester soil carbon (C) should consider soils intrinsically capable at C retention. Of the mineral soil orders, Mollisols have minimum requirements for soil organic C (SOC; over 0.06 %) and basic saturation (over 50 %). In the U.S., grasslands comprise 93% of the vegetation mapped above Mollisols. Soils beneath the southern extent of Sequoia sempervirens (redwood) forests in central California are mapped as Molliols. It widely accepted that redwood forests harbor considerable biomass C, but the extent to which aboveground C is retained in the soil is not well understood. This study aimed to: (i) to gather baseline soils data (bulk density, pH, basic saturation, cation exchange capacity, SOC, total nitrogen, structure, depth) for an iconic and understudied ecosystem, the southern extent of coast redwood forests and to compare said properties to those in adjacent grasslands, (ii) to identify taxonomic classifications of said soils, (iii) to investigate the influence of vegetative gradation on soil properties between these ecosystems using auger sampling, (iv) to compare levels of basic cations between the forest floor and mineral horizons and, (v) to characterize the total C and active C pools within these ecosystems and to explore interpretations of these pools.
In sites randomly selected across two regions, Swanton Pacific Ranch (SPR) and Landels-Hill Big Creek Reserve (LHBCR), soil was collected and described in 24 profiles beneath redwoods and compared to 19 profiles in nearby grasslands. Auger samples at fixed depths were collected in a complimentary study from 5 randomized transects that transitioned through mixed-evergreen forest (and across ecotones) between redwoods and coastal grasslands at SPR. Mineral soil samples were analyzed for SOC, permanganate oxidizable C (POXC), C/N ratio, pH, extractable basic cations, and cation exchange capacity. Samples of forest litter were analyzed for basic cation composition.
Multivariate regression models of profile data found higher values of pH, C/N, and CEC in redwoods than in grasslands, and lower values of bulk density in redwoods than in grasslands. Redwood soils were conducive to mollic epipedon formation (21 of 24 profiles in the redwoods as Mollisols) and generally had high base levels, for which extractable calcium from the forest floor was the main driver. Along the transects, multivariate regression returned generally consistent and graded patterns for C/N ratios, POXC/SOC ratios, and pH; these variables were generally highest in the redwood forest and decreased sequentially across mixed-evergreen forest and into the grassland
Our look at soil C pools focused on the fraction of SOC that was POXC. Observed higher ratios of POXC/SOC in redwoods than in the grasslands at SPR was corroborated by the transect study; at LHBCR, the regression model provided no evidence for a significant difference in POXC/SOC ratios between communities. Differences in POXC fractions across plant communities and localities were postulated as the result (and combination) of contrasting ecologies, and different management strategies and disturbance histories. The data collected in this study does not provide clear mechanisms to explain these discrepancies, and further research is needed; disharmonious interpretations of POXC across the literature suggested that the replacement of operationally defined C fractions with pools tied to a particular stabilization mechanism would provide clearer insights across ecosystems to land managers.
Our estimates of SOC in the top 1 m of soil showed redwood soils stored as much or more C than soils in the neighboring grasslands, at SPR, 144 (± 21) and 123 (± 25) tons SOC per ha in the top 1 m of redwoods and grasslands, respectively, and at LHBCR, 221 (± 23) and 126 (± 24) tons SOC per ha in the top 1 m of redwoods and grasslands, respectively. The carbon densities provided in this study can be used as a baseline to measure changes to SOC and POXC pools in response to future activities to sequester C in our study regions and/or to assess losses from recent 2020 wildfires.
We are curious to see how the breadth of information gathered in this study can provide refinement for following questions that will hopefully one day, direct considerate and conscientious management in response to the environmental challenges ahead.
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Sustainable Bioenergy Feedstock Production Using Long-Term (1999-2014) Conservation Reserve Program LandRaut, Yogendra Y. 08 August 2017 (has links)
No description available.
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