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| 14. |
- Ahlbom, Anders, et al.
(författare)
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Forskning om elöverkänslighet och andra effekter av elektromagnetiska fält; Åttonde årsrapporten
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Årets rapport diskuterar några forskningsområden där resultaten är av stor betydelse och som kan förväntas tilldra sig stor uppmärksamhet. Det första avser möjligheterna att skatta exponering och den relativa betydelsen av olika exponeringskällor. Viktigt arbete har där gjorts inom det Schweiziska nationella forskningsprogrammet. Vi har inkluderat en figur som på ett enkelt sätt sammanfattar viktiga och relevanta resultat avseende exponering i den allmänna miljön. Det framgår att basstationer, egen mobiltelefonanvändning och trådlösa hemtelefoner är de viktigaste källorna till exponering (om man bortser från lokal exponering till huvudet under samtal). Nästa område avser sömn och EEG-undersökningar. Det har där visat sig i ett antal undersökningar att elektromagnetiska fält tycks ha effekt på EEG under sömn. Effekterna är måttliga och kan storleksmässigt jämföras med vad som kan erhållas till exempel vid kaffe- eller alkoholintag. De tycks inte vara kopplade till subjektiv sömnkvalitet. Hur dessa effekter uppstår och vad de kan tänkas ha för betydelse är okänt. Men det är klart att det är angeläget att forskningen inom detta område fortsätter så att vi kan få denna effekt bekräftad om den är reell och ytterligare belyst och förstådd. Vi har också beskrivit en del ytterligare epidemiologisk forskning och framför allt slutrapporten från den så kallade Interphone-studien. Det har funnits förhoppningar om att denna studie skulle kunna ge definitivt besked i frågan om mobiltelefonanvändning och hjärntumörrisk. Men det stod redan efter publiceringen av de nationella rapporterna klart att så knappast skulle bli fallet. Rapporten har gett upphov till omfattande metodologiska diskussioner, vilka också varit orsaken till rapportens stora försening. Vår bedömning är att denna rapport inte ändrar våra tidigare bedömningar av risken för hjärntumör vid mobiltelefonanvändning, baserade bland annat på vad som framkommit i de nationella rapporterna. Däremot har denna rapport och andra rapporter från Interphone bidragit med viktiga metodologiska insikter. Vi diskuterar några ytterligare epidemiologiska undersökningar men inte heller de ändrar någonting i våra bedömningar. Slutligen presenterar vi nya riktlinjer för exponering från ”kraftfrekventa elektromagnetiska fält” från ICNIRP. De är baserade på en uppdaterad kunskapsgenomgång och på omfattande principdiskussioner. Bland annat har man nu bedömt att också fotofosfener (ljusblixtar) ska ingå bland kritiska effekter vilket i viss mån har påverkat gränsvärdena numeriskt. Detta har dock ingen praktisk betydelse för allmänhetens exponering därför att nivåerna ändå ligger flera storleksordningar över vad allmänheten normalt exponeras för. Det finns dock arbetsmiljöer där detta kan ha betydelse. En viktiga händelse under 2011 som redan nu kan förutses är att IARC (WHOs cancerforskningsinstitut) i maj ska ha ett så kallat monografimöte och ta ställning till hur sannolikt det är att radiofrekventa elektromagnetiska fält är cancerframkallande.
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| 15. |
- Ahlbom, Anders, 1993
(författare)
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Hydrothermal Depolymerisation of Kraft Lignin: The Influence of Capping Agents and Residence Time
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignin, the aromatic macromolecule found in wood and other lignocellulosic biomass, is envisioned as a future renewable source of aromatic compounds that can be used as, for example, chemicals, fuel additives and resins. A way in which this can be realised is by depolymerising the lignin once it has been isolated from the lignocellulosic biomass. Hydrothermal methods that employ water as a reaction medium are suggested as ways of accomplishing this. However, reactive fragments prone to repolymerisation, indeed char formation, are formed during depolymerisation, causing operational difficulties in the process as well as yield losses of the desired components. The suggestion has been made to add chemicals, i.e. capping agents, to scavenge the reactive components in order to mitigate these issues. Careful selection of reaction parameters, such as residence time and temperature, is also crucial for the process. In this work, the depolymerisation of softwood kraft lignin has been investigated under hydrothermal conditions, with additions isopropanol, glycerol and guaiacol, to investigate their potential of functioning as capping agents. A customised batch reactor (99 ml) enabling swift heating of the reaction mixture was employed at 290-335 °C and 250 bar with low residence times (1-12 min). The result of the hydrothermal depolymerisation of lignin was an aqueous suspension with a strong smoky odour. No apparent separate liquid organic phase was formed, although a char fraction precipitated. Characterisation of the products indicated a rapid depolymerisation of the lignin, since inter-unit ether linkages were cleaved, which was later followed by a slower repolymerisation. Additions of isopropanol, glycerol and guaiacol, reduced the weight average molecular weights (Mw) of the product fractions. Only isopropanol appeared to be able to reduce the amount of char formed from the lignin. Subsequent aftertreatment of the product would be required to obtain a usable product.
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| 16. |
- Ahlbom, Anders, 1993
(författare)
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Hydrothermal Liquefaction of Kraft Lignin - The influence of capping agents and residence time
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the context of exploring alternatives to replace fossil resources, lignin has been acknowledged as a renewable source of various aromatic compounds that have the potential of being precursors to chemicals as well as fuel additives. Originating from lignocellulosic biomass such as wood, lignin is an amorphous polymer with a high content of aromatic units and, in order to harness these units, it must be depolymerised. A major problem with current depolymerisation techniques, however, is that lignin repolymerises after being depolymerised, and forms an undesirable char fraction. The addition of capping agents and fine-tuning the reaction conditions can be used to mitigate such formation of char. This work has investigated the depolymerisation of kraft lignin in hydrothermal conditions under varying temperatures (290-335 °C), residence times (1-12 min) and charges of isopropanol (IPA/dry lignin, 0-4.9) which, aside from being a co-solvent, was hypothesised as acting as a capping agent. The influence of these reaction parameters on the molecular weights, yields and elemental compositions of the products was studied, along with changes in the molecular structure compared to the starting lignin. The product is a suspension of solid material, i.e. char, in an aqueous phase and thus any desired organic liquid phase requires extraction from the aqueous product. While the yield of char increased with temperature and residence time, it decreased with increasing isopropanol loading, suggesting that the isopropanol does in fact act as a capping agent. Most of the lignin forms a water-soluble fraction that precipitates when the aqueous product phase is acidified, thereby forming the precipitated solids fraction (PS). The components remaining dissolved after acidification of the product phase are known as acid soluble organics (ASO). A portion of the ASO fraction was aromatic monomers, with guaiacol dominating: this result was expected since the lignin was sourced from softwood. The amount of such monomers increased with residence time in the reactor. Molecular weight analyses showed a rapid depolymerisation of the lignin within 1 min of hydrothermal liquefaction (HTL) treatment via a significant decrease in the molecular weight of all product fractions: char, PS and ASO. Moreover, the carbon-oxygen inter-unit linkages were found to break in this timeframe as well. The repolymerisation reactions started to exceed depolymerisation between residence times of 4 and 12 min, causing the weight average molecular weight (Mw) to increase again. Although minimising the residence time allows the char yield and Mw to be kept low, more monomers were formed at longer residence times. This calls for careful tuning of the residence time in the HTL of kraft lignin.
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| 17. |
- Ahlbom, Anders, et al.
(författare)
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Occupational magnetic field exposure and myocardial infarction incidence.
- 2004
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Ingår i: Epidemiology. - : Ovid Technologies (Wolters Kluwer Health). - 1044-3983 .- 1531-5487. ; 15:4, s. 403-8
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Studies on healthy volunteers have seen reduced heart rate variability after exposure to extremely low-frequency electric and magnetic fields (EMF). Because reduced heart rate variability has been linked to cardiovascular disease risk, it has been hypothesized that exposure to EMF might increase the risk of cardiovascular disease. One epidemiologic study has shown increased mortality from cardiovascular conditions in utility workers with elevated exposure to magnetic fields, but several other epidemiologic studies have failed to confirm this result. We tested the hypothesis that occupational EMF exposure increases the risk of myocardial infarction in a large population-based case-control study of myocardial infarction, with detailed information on potential confounders. METHODS: We used data from the SHEEP study, which is a population-based case-control study of acute myocardial infarction in Stockholm. Occupational EMF exposure was based on job titles 1, 5, and 10 years before diagnosis. We used 2 approaches to classify exposure: first, specific individual job titles with presumed elevated EMF exposure, and second, classification of subjects according to a job-exposure matrix. RESULTS: We found no increased risk of myocardial infarction in subjects classified as having elevated EMF exposure. For the highest exposure category of > or = 0.3 microT according to the job-exposure matrix, the adjusted relative risk was = 0.57 (95% confidence interval = 0.36-0.89). CONCLUSIONS: The results of this study do not support the hypothesis that occupational EMF exposure increases the risk of myocardial infarction.
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| 18. |
- Ahlbom, Anders, 1993, et al.
(författare)
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On the hydrothermal depolymerisation of kraft lignin using glycerol as a capping agent
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:3, s. 159-169
-
Tidskriftsartikel (refereegranskat)abstract
- Depolymerisation of kraft lignin under hydrothermal conditions was investigated at short residence times (1–12 min) with glycerol being used as a capping agent. The weight average molecular weight (M w) of the products decreased within the first minute of residence time, with the inter-unit ether linkages breaking accordingly. Furthermore, the M w of the product fractions decreased at increasing residence times, while the char yield increased. Short residence times thus appear to be beneficial for mitigating the formation of char. Also, addition of NaOH reduced the yield of char. Although the addition of glycerol caused a decrease in the M w of the products, it seemed to increase the yield of char and therefore might not be a suitable capping agent for kraft lignin depolymerisation.
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| 19. |
- Ahlbom, Anders, et al.
(författare)
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Radiofrequency electromagnetic fields and risk of disease and ill health - Research during the last ten years
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this report is electromagnetic fields of the type that occur in connection with mobile telephony, so called radio frequency (RF) fields and the possibility that exposure to such fields poses a risk of disease or ill health. The purpose is to describe what was known ten years ago, what we have learned during the past decade, and where we stand today. TEN YEARS AGOThe mechanism of interaction between RF fields and the human body was established long ago and is increased temperature of exposed tissue (compare microwave ovens). Methods for measurements of the fields in the air were developed early but the data on distribution of the absorbed energy in the human body was still restricted. Data regarding sources and levels of exposure to the population was limited because systematic measurements had not been conducted. A considerable number of provocation studies on exposure to fields of lower frequencies (related to electric power and computer screens) had already been conducted and had not found any evidence of an association to symptoms (headache, vertigo, dizziness, concentration difficulties, insomnia) but the corresponding information about RF fields and occurrence of symptoms was scarce. Few and methodologically limited epidemiological studies had been conducted on RF field exposure and cancer.WHAT WAS LEARNED DURING THE PAST TEN YEARSExtensive research on various aspects of RF fields has been conducted during the last ten years and the knowledge database has increased considerably. Simulation models have improved our knowledge about how the fields and the energy are distributed in the body. Mobile, so called, exposimeters have been developed for use in epidemiological studies. Many more measurements have been conducted to increase our knowledge about sources and level of exposure to the population. More than 15 provocation studies (single or double blind) have been conducted on symptoms attributed to exposure to RF fields. These studies have not been able to demonstrate that people experience symptoms or sensations more often when the fields are turned on than when they are turned off. One longitudinal study has looked at frequency of symptoms in relation to environmental exposure and this study found no association between exposure and symptoms. A considerable number of studies on cancer, and in particular brain tumor, were presented. As a consequence there exist now very useful data including methodological results that can be used in the interpretation of this research. With a small number of exceptions the available results are all negative and taken together with new methodological understandings the overall interpretation is that these do not provide support for an association between mobile telephony and brain tumor risk. In addition, national cancer statistics are very useful sources of information because mobile phone usage has increased so quickly. Had mobile phone use and brain cancer risk been associated it would have been visible as an increasing trend in national cancer statistics. But brain cancer rates are not increasing. WHERE WE STAND TODAYWe now know much more about measurements and absorption of RF fields and also about sources of exposure to the population and levels of exposure. A considerable number of provocation studies on RF exposure and symptoms have been unable to show any association. Overall, the data on brain tumor and mobile telephony do not support an effect of mobile phone use on tumor risk, in particular when taken together with national cancer trend statistics throughout the world. Research on mobile telephony and health started without a biologically or epidemiologically based hypothesis about possible health risks. Instead the inducement was an unspecific concern related to a new and rapidly spreading technology. Extensive research for more than a decade has not detected anything new regarding interaction mechanisms between radiofrequency fields and the human body and has found no evidence for health risks below current exposure guidelines. While absolute certainty can never be achieved, nothing has appeared to suggest that the since long established interaction mechanism of heating would not suffice as basis for health protection.
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| 20. |
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