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- Kärrman, Anna
(författare)
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Analysis and human levels of persistent perfluorinated chemicals
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An extensive use of perfluorinated chemicals (PFCs) in the last 50 years has resulted in a worldwide spread of these persistent chemicals. Human populations are subjected to a large number of PFCs in ways that are not yet fully explained. The aims of this thesis are to develop and assure the quality of analytical methods in order to collect information on human levels and to facilitate the assessment of human exposure of PFCs. Solid-phase extraction (SPE) methods for human blood and milk using two sorbents, octadecyl (C18) and a weak anion exchange polymer (WAX), were developed. Perfluorinated alkyl sulfonates (PFSAs) and perfluorinated alkyl carboxylic acids (PFCAs) with carbon chain lengths between four and fourteen together with perfluorooctane sulfonamide (PFOSA) could be extracted from human matrices. These extraction procedures enable selective and sensitive analysis of PFCs in human matrices using single quadrupole mass spectrometry (SQMS). The accuracy and reliability of the methods are discussed in the context of intralaboratory as well as interlaboratory quality assurance. Further improvements of the analysis are discussed including the evaluation of ultra performance liquid chromatography (UPLC). Human whole blood, plasma and serum from Sweden, Australia and the United Kingdom have been analysed. The blood matrix selection in the assessment and comparisons of human exposure to PFCs is crucial. Human plasma contains a high percentage of PFSAs and PFCAs. On the contrary, only about 20% of the total PFOSA content is present in plasma after removal of the red blood cells. Up to eleven persistent PFCs are detected in human blood, with detection levels between 0.1-0.5 ng/mL. A gender difference with higher serum levels for males is apparent. An age trend was observed for perfluorooctane sulfonate (PFOS) levels in serum from Australia. The levels found in Australian serum indicate that emissions from the PFC production facilities are of less importance for human exposure. Matched human milk and serum samples from Sweden show that milk levels of PFCs are about 1% of the maternal serum level. Up to five persistent PFCs are found in human milk from Sweden, with detection limits between 0.005-0.1 ng/mL, and the levels in Swedish pooled milk samples have remained constant between 1996 and 2004. A linear relationship between the maternal serum level and milk level was seen for PFOS and its shorter homologue perfluorohexane sulfonate (PFHxS). The daily intake of PFOS for a nursing infant in Sweden is estimated to be 121 ng/day if the maternal serum level is 20 ng/mL. Lactation is therefore a major exposure source for breast-fed infants. Monomethyl- and dimethyl-branched isomers of PFOS could be separated in human blood using high performance liquid chromatography (HPLC). Human plasma contains a smaller percentage of the linear PFOS compared to commercially available PFOS standard materials, which indicate isomer specific uptake and/or elimination. A difference in the isomer composition is also seen between the countries studied. Human blood from the UK and Australia have significantly lower amount of linear PFOS (59-60%) compared to Swedish blood (68%). This geographical variation suggests different human exposure sources and pathways.
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| 2. |
- Näsström, Gunilla, 1968-
(författare)
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Measurement of alignment between standards and assessment
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many educational systems of today are standards-based and aim at for alignment, i.e. consistency, among the components of the educational system: standards, teaching and assessment. To conclude whether the alignment is sufficiently high, analyses with a useful model are needed. This thesis investigates the usefulness of models for analyzing alignment between standards and assessments, with emphasis on one method: Bloom’s revised taxonomy. The thesis comprises an introduction and five articles that empirically investigate the usefulness of methods for alignment analyses.In the first article, the usefulness of different models for analyzing alignment between standards and assessment is theoretically and empirically compared based on a number of criteria. The results show that Bloom’s revised taxonomy is the most useful model. The second article investigates the usefulness of Bloom’s revised taxonomy for interpretation of standards in mathematics with two differently composed panels of judges. One panel consisted of teachers and the other panel of assessment experts. The results show that Bloom’s revised taxonomy is useful for interpretation of standards, but that many standards are multi-categorized (placed in more than one category). The results also show higher levels of intra- and inter-judge consistency for assessment experts than for teachers. The third article further investigates the usefulness of Bloom’s revised taxonomy for analyses of alignment between standards and assessment. The results show that Bloom’s revised taxonomy is useful for analyses of both standards and assessments. The fourth article studies whether vague and general standards can explain the large proportion of multi-categorized standards in mathematics. The strategy was to divide a set of standards into smaller substandards and then compare the usefulness and inter-judge consistency for categorization with Bloom’s revised taxonomy for undivided and divided standards. The results show that vague and general standards do not explain the large proportion of multi-categorized standards. Another explanation is related to the nature of mathematics that often intertwines conceptual and procedural knowledge. This was also studied in the article and the results indicate that this is a probable explanation. The fifth article focuses on another aspect of alignment between standards and assessment, namely the alignment between performance standards and cut-scores for a specific assessment. The validity of two standard-setting methods, the Angoff method and the borderline-group method, was investigated. The results show that both methods derived reasonable and trustworthy cut-scores, but also that there are potential problems with these methods.In the introductory part of the thesis, the empirical studies are summarized, contextualized and discussed. The discussion relates alignment to validity issues for assessments and relates the obtained empirical results to theoretical assumptions and applied implications. One conclusion of the thesis is that Bloom’s revised taxonomy is useful for analyses of alignment between standards and assessments. Another conclusion is that the two standard setting methods derive reasonable and trustworthy results. It is preferable if an alignment model can be used both for alignment analyses and in ongoing practice for increasing alignment. Bloom’s revised taxonomy has the potential for being such an alignment model. This thesis has found this taxonomy useful for alignment analyses, but its’ usefulness for increasing alignment in ongoing practice has to be investigated.
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| 3. |
- Hagström, Katja, 1975-
(författare)
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Occupational exposure during production of wood pellets in Sweden
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aims of the studies underlying this thesis were to assess workers’ air exposure to wood dust and various chemicals, and to evaluate the variability in exposure and occupational dermal exposure to resin acids during the production of wood pellets in Sweden. Personal air measurements of wood dust, monoterpenes, resin acids and nitrogen dioxide (as a marker of diesel exhaust), accompanied by area measurements of these substances, VOCs and carbon monoxide, were performed at up to ten plants. Repeated measurements were also performed to evaluate within- and between-worker variability, determinants of exposure, the probability that a worker’s mean exposure exceeded the occupational exposure limit, OEL (overexposure), and the bias in the exposure-response relationship (attenuation).Dermal exposure was measured at the forehead, neck, forearm and hand using a tape-stripping method, in which a strip of adhesive tape is applied to the skin and then removed along with the outermost layer of the skin and chemicals adsorbed to this layer. The workers’ exposure to wood dust was high (mean: 2.4 mg/m3), with 35−42 % of the measurements above the Swedish OEL of 2 mg/m3. The exposure is also classified as unacceptable due to the calculated levels of overexposure. Exposure to resin acids like 7-oxodehydroabietic acid and dehydroabietic acid was identified, which has not been previously observed in the wood industry, with mean sum levels of 2.4 _g/m3. Levels of monoterpenes, nitrogen dioxide, VOCs and carbon monoxide were all below their Swedish OELs. A factor that influenced the level of exposure to wood dust and resin acids was the nature of the work done, notably cleaning operations, like sweeping, which increased the exposure slightly. The attenuation was high for the individual-based model, and at least 12 repeated measurements were needed to yield a bias in the exposureresponse relationship of _10 %. The results also showed that dermal exposure to resin acids occurs in these plants, which has not been shown before, and provided indications of both increased exposure during a work shift and diffusion into the skin. The main conclusion is that wood dust exposure at these levels is likely to have implications for the workers’ health in the long run, and, therefore, it is important to reduce exposure to wood dust in this industry.
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