| 1. |
- Öberg, Tomas, 1956-, et al.
(författare)
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Different catalytic effects by copper and chromium on the formation and degradation of chlorinated aromatic compounds in fly ash.
- 2007
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Ingår i: Environmental Science and Technology. - Washington : American Chemical Society. - 0013-936X .- 1520-5851. ; 41:10, s. 3741-3746
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Tidskriftsartikel (refereegranskat)abstract
- Fly ash from municipal solid waste incineration may catalytically enhance the formation and degradation of chlorinated aromatic compounds. The activities of three Deacon catalysts in this process were investigated in a statistically designed experiment. Chlorides of copper, chromium, and nickel were added to fly ash samples and the resulting samples heated at 300 degrees C for 2 h in an air atmosphere. The addition of copper increases the formation of all chlorinated aromatic compounds except the low chlorinated congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans. The addition of chromium decreased the formation of most chlorinated aromatic compounds except the highest chlorinated species, where it was without effect. The addition of nickel did not show any significant effect. The outcome of the experiment can be interpreted as two competing processes: the chlorination of aromatic rings and the oxidation of carbon-carbon and carbon-oxygen bonds. The delicate balance between chlorination and oxidation could probably be further exploited to minimize both the emissions and the net production of chlorinated aromatic compounds from combustion.
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| 2. |
- Öberg, Tomas, 1956-, et al.
(författare)
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Metal catalyzed formation of chlorinated aromatic compounds : a study of the correlation pattern in incinerator fly ash.
- 2007
-
Ingår i: Chemosphere. - Oxford : Pergamon Press. - 0045-6535 .- 1879-1298. ; 67:9, s. S185-S190
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Tidskriftsartikel (refereegranskat)abstract
- Chlorinated aromatics are unintentionally formed and released from combustion and other thermal processes involving organic matter and chlorine. The catalytic activity of incinerator fly ash in the low-temperature formation of chlorinated aromatics has been demonstrated in both laboratory experiments and full-scale trials. Copper has been shown to be an effective catalyst, but several other transition metals possess a similar activity. Here results are reported from a series of full-scale combustion trials with different fractions of household and industrial wastes, with waste from forestry as a reference fuel. The composition of elements and chlorinated aromatics in the fly ash was evaluated with principal component analysis and partial least squares regression. The observed correlation pattern indicates that metals other than copper are of equal importance for the catalytic activity. Chromium and nickel are two of these metals, which may contribute to the de novo formation of chlorinated benzenes, phenols, PCDD and PCDF.
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| 3. |
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| 4. |
- Alriksson, Stina, et al.
(författare)
-
Conjoint analysis for environmental evaluation : a review of methods and applications.
- 2008
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Ingår i: Environmental Science and Pollution Research. - : Springer Berlin. - 0944-1344 .- 1614-7499. ; 15:3, s. 244-257
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND, AIM AND SCOPE: Conjoint analysis and the related choice-modelling methods have been used for many years in marketing research to evaluate consumer behaviour and preferences for different kinds of product attributes. Recently, the number of applications in environmental science and management has started to grow. Conjoint analysis is found in many different forms, and the environmental studies evaluated in this review display the same range of methods as in other fields. The key characteristic of all these methods is that trade-offs are evaluated by jointly considering a number of important attributes. MAIN FEATURES: This paper is a review of the literature on environmental applications of conjoint analysis and assesses in which environmental area conjoint analysis has been most successful. The method and the design of the studies are reviewed as well. RESULTS: A total of 84 studies were found, dealing with environmental issues that were evaluated by conjoint analysis. The studies concern agriculture, ecosystem management, energy, environmental evaluation, forestry, land management, pollution, products, recreation, environmental risk analysis and waste management. DISCUSSION: Choice experiments seem to have a comparatively stronger position in environmental studies than elsewhere. Most of the environmental applications are related to natural resource management. This is somewhat surprising, but a number of reports have appeared also on product evaluation, which could be a key application area in the future. CONCLUSIONS: Compared to marketing and transportation, the number of environmental conjoint studies is rather small but increasing, and the method has proven to work effectively in eliciting preferences on environmental issues. In environmental issues, experimenters often use choice experiments, especially concerning ecosystem management and environmental evaluations. When it comes to evaluating preferences concerning agriculture, forestry, energy and products, a more traditional approach of conjoint analysis is favoured. RECOMMENDATIONS AND PERSPECTIVES: Two new areas of application are identified in this review--environmental communication and expert elicitation. Conjoint analysis can thus be developed into a useful instrument for environmental risk analysis and communication, both of which are necessary for an efficient approach to risk governance.
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| 5. |
- Alriksson, Stina, 1971-, et al.
(författare)
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Towards a closed steel eco-cycle - cojoint analysis as a decision tool
- 2005
-
Ingår i: Proceedings Kalmar ECO-TECH´ 05. - Kalmar : Högskolan i Kalmar. ; , s. 27-36
-
Konferensbidrag (refereegranskat)abstract
- The Swedish steel industry has over the past 20 years made substantial efforts to promote energy efficiency and environment protection. However, the dominant part of these investments has been directed to the individual production sites, most of which today have 'solved' their own acute environmental problems. The focus has therefore switched to the properties and performance of the steel products where the evaluation of environmental performance is a complex task that often requires simultaneous consideration of many different attributes. Conjoint analysis is commonly used in marketing research, to evaluate how consumers appreciate specific attributes in products. It has also been widely used in health care, traffic planning and quality management. Conjoint analysis has also been applied to environmental issues such as energy, recreation, environmental valuation, ecosystem management, consumer preferences to products, public preferences to industrial projects, waste management, and environmental policy development. This previous research has shown that the method is well suited for evaluating environmental issues. Here we briefly present the methodology and review some papers on environmental applications. It is our intention to use this approach as a tool to integrate environmental considerations into both process and product development within the steel industry.
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| 6. |
- Bergius, Kristine, et al.
(författare)
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Initial screening of contaminated land : a comparison of US and Swedish methods.
- 2007
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Ingår i: Environmental Management. - : Springer Science and Business Media LLC. - 0364-152X .- 1432-1009. ; 39:2, s. 226-34
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Tidskriftsartikel (refereegranskat)abstract
- Preliminary surveys are used to prioritize between contaminated sites to select those to be investigated more thoroughly. The data-gathering steps are almost identical between countries; however, the assessment procedures differ significantly. In this study, we have investigated 21 contaminated sites assessed as belonging to the high-risk or the very high-risk class using the Swedish Methods for Inventories of Contaminated Sites (MICS). We then applied the US Preliminary Assessment (PA) method to the same sites and compared the results and conclusions from the two screening procedures. In both cases, all sites were recommended for further investigation and the two approaches seem to corroborate one another; however, the PA assessment scores and the preliminary MICS classifications did not correlate. The results obtained with the PA method were easier to explain than the final MICS classification. The PA method also seems more transparent and easier to standardize, although objections could be made regarding the weighting scheme, because the outcome in this study was entirely dependent on the surface exposure pathway. However, to examine this in greater detail, it is necessary to include sites with less contamination: The importance of preliminary surveys in the overall risk management process gives a strong motivation for such an evaluation. Generally, the lack of research and scientific support for the various assessment procedures in use suggests that there is a need for method development, standardization, and validation.
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| 7. |
- Cederqvist, Lars, et al.
(författare)
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Improved process stability during friction stir welding of 5 cm thick copper canisters through shoulder geometry and parameter studies
- 2009
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Ingår i: Science and technology of welding and joining. - London : Institute of Materials. - 1362-1718 .- 1743-2936. ; 14:2, s. 178-184
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Tidskriftsartikel (refereegranskat)abstract
- The spent nuclear fuel from Swedish power plants will be placed in copper canisters that are sealed with friction stir welding and the stability and robustness of this process is now being optimised in three steps: first, the shoulder geometry was identified that produced the most stable weld cycle, then the welding parameters were optimised for that geometry with regards to stability, and finally, the chosen geometry and welding parameters were verified and evaluated during multiple weld cycles. The shoulder study showed that stable welds could be produced repeatedly with a convex scroll geometry which proved more stable than various concave and flat scroll geometries. In the subsequent parameter study, not only were the most stable values for the welding parameters derived, but a clear relationship was shown between power input and tool temperature. This relationship can be used to more accurately control the process within the parameter windows, not only for this application but for other applications where the welding temperature needs to be kept within a specified range. Similarly, the potential of the convex scroll shoulder geometry for use in applications with other metals and thicknesses is evident.
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| 8. |
- Cederqvist, Lars, et al.
(författare)
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Reliability study of friction stir welded copper canisters containing Sweden's nuclear waste
- 2008
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Ingår i: Reliability Engineering & System Safety. - : Elsevier. - 0951-8320 .- 1879-0836. ; 93:10, s. 1491-1499
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Tidskriftsartikel (refereegranskat)abstract
- The plan for the final disposal of spent fuel from Swedish nuclear power plants is to place it in copper canisters that are sealed and stored in a deep repository. The canisters will be sealed by friction stir welding (FSW) and the reliability of this process has now been evaluated. The reliability study was performed in three steps: first an optimization experiment to identify optimal process settings and establish the process window; then a demonstration experiment with welding under production-like conditions; and finally a post-demonstration series to evaluate an adjustment in the welding equipment. A process window was defined around the optimal process setting, i.e., the limits within which the welding variables must lie in order for the process to produce the desired result. In the demonstration experiment, a series of 20 sealing welds was carried out under production-like conditions. The maximum discontinuity in each weld — detected by non-destructive testing — was fitted to a generalized extreme value distribution. The 95% confidence interval for the maximum discontinuity in a production series of 4500 canisters was estimated at 4.5–7.7 mm. The best estimate from the post-demonstration series suggests that the maximum size of a discontinuity will not exceed 2.3 mm. A main conclusion is that the FSW process produces reliable results, fulfilling the predetermined requirements for minimum copper thickness by a very good margin.
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| 9. |
- Filipsson, Monika, et al.
(författare)
-
Exponeringsfaktorer vid riskbedömning : Inventering av dataunderlag
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Exponering definieras som kontakten mellan ett kemiskt, fysikaliskt eller biologiskt agens och den yttre avgränsningen för en organism. Människors exponering för kemiska ämnen i miljön styrs inte bara av förekomsten av en förorening, utan även av beteende, fysiologiska egenskaper och olika yttre faktorer. De mätbara variabler som används i exponeringsmodeller för att beskriva detta benämns exponeringsfaktorer. Den mest omfattande sammanställningen av data för olika exponeringsfaktorer härrör från USA, men det finns även ett par europeiska sammanställningar. Beteenden, fysiologiska egenskaper och yttre miljöfaktorer skiljer dock mellan olika länder. Det finns därför skäl att sammanställa sådana data även för svenskt vidkommande. En sammanställning kan även bidra till en viss standardisering av riskbedömningar. I föreliggande rapport redovisas exponeringsfaktorer för olika områden och i stora stycken överensstämmer urvalet med de tidigare nämnda internationella sammanställningarna. Redovisningen och dess omfattning påverkas även i hög grad av tillgången på data. Det innebär exempelvis att variabilitet (naturlig variation) och osäkerhet inte kan anges för alla faktorer. Dessa databrister är särskilt påtagliga vad gäller konsumtion av dricksvatten och hemodlade vegetabilier samt tidsanvändning. Dataunderlaget är däremot gott för fysiologiska parametrar som kroppsvikt och hudyta liksom den allmänna konsumtionen av livsmedel. För dessa exponeringsfaktorer redovisas statistiska parametrar som medelvärde, standardavvikelse, skevhet och kurtosis. Dessutom anges osäkerhetsintervall för dessa parametrar. Percentiler utgör ett användbart alternativ för presentera variabilitet (naturlig variation) och även sådana redovisas tillsammans med tillhörande osäkerhetsintervall. Ytterligare exponeringsfaktorer som behandlas i rapporten är åldersfördelning och flyttningsfrekvens, boende och byggnader, kontakt med mark och damm och markegenskaper. Förutom tabellerade värden återfinns även referenser till de primära datakällorna så att det är möjligt att själv gå vidare och fördjupa sig i underlaget. I rapporten jämförs även insamlade data med remissversionen av den svenska beräkningsmodellen för riktvärden för mark. Jämförelsen med denna modell visar att valda värden för exponeringsfaktorerna ibland motsvarar en bästa skattning (medelvärde/median), ofta en konservativ skattning och ibland en mycket konservativ skattning. Det går inte att utifrån dessa jämförelser dra några säkra slutsatser om dess inverkan på den slutliga riskbedömningen och beslut avseende åtgärder. Det är rapportförfattarnas förhoppning att föreliggande sammanställning ska underlätta och påskynda en övergång till riskbedömningsmetoder där variabilitet och osäkerhet kan uppskattas och redovisas kvantitativt.
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| 10. |
- Filipsson, Monika, et al.
(författare)
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Exposure to contaminated sediments during recreational activities at a public bathing place
- 2009
-
Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 171:1-3, s. 200-207
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Tidskriftsartikel (refereegranskat)abstract
- More and more time is spent on recreational activities, but few risk assessments focus specifically on these situations and exposure factor data are often scarce. To assess exposure to contaminants at a public bathing place in an urban environment, we have compiled literature data, conducted observation studies, and analyzed water and sediment samples. The levels of anthropogenic contaminants are high in urban environments and traffic frequently plays an important role. In this study, to characterize variability and uncertainty, the deterministic exposure calculations for metal pollutants were supplemented by a probability bounds analysis for the polycyclic aromatic hydrocarbons (PAH). The results from these calculations show that oral intake is the major exposure route for metals, while skin absorption, with present assumptions, is more important for the PAH. The presently measured levels of contaminants, at this public bathing place, cannot be anticipated to cause any significant adverse influence on public health.
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| 11. |
- Filipsson, Monika, et al.
(författare)
-
Undersökning och riskbedömning av Trekantens badplats : Riskkarakterisering
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Trekanten är en av Stockholms mer förorenade sjöar. Sedimenten i sjöns djupare delar innehåller höga halter tungmetaller och polycykliska aromatiska kolväten (PAH). Frågan om det kan vara hälsofarligt att komma i kontakt med sedimenten har uppkommit och oron har främst gällt bad vid badplatsen. Det har därför funnits skäl för att närmare utreda föroreningshalterna i anslutning till badplatsen och fastställa om någon hälsofara kan förekomma vid bad. I föreliggande rapport redovisas de exponeringsberäkningar och den riskbedömning som har gjorts utifrån de undersökningar som genomfördes under sommaren 2006 och 2007. Undersökningarna har omfattat dels en studie av badvanor, dels provtagning och analys av föroreningar i sediment och ytvatten. Exponeringsberäkningarna baseras även på sammanställningar av modeller och exponeringsfaktorer från den vetenskapliga litteraturen liksom svenska undersökningar. Ett informationsutbyte har även skett med tjänstemän vid det amerikanska naturvårdsverket (U.S. EPA). Undersökningarna har visat att föroreningshalterna i sand vid badplatsen och i ytvatten är låga. Halterna av PAH och metaller i sanden var lägre än de generella riktvärdena för förorenad mark som avser känslig markanvändning. Halterna av PAH och metaller (med undantag för krom) i ytvatten var lägre än normerna för dricksvatten. Exponeringsberäkningarna har genomförts separat för barn och vuxna. Huvudsakligen avser beräkningarna punktskattningar, dels en bästa skattning, dels en skattning av rimlig maximal exponering. För PAH-föreningar har utvärderingen även kompletterats med en sannolikhetsberäkning för att beskriva variabilitet och osäkerheter i dataunderlaget. Den beräknade exponeringen är i de flesta fall under de toxikologiska referensvärden som har använts. Slutsatsen från de genomförda undersökningarna är att exponeringen för PAH och metaller vid bad i sjön Trekanten, vid nu uppmätta halter, inte kan förutses medföra någon ogynnsam påverkan av betydelse för befolkningens hälsa.
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| 12. |
- Liu, Tao, et al.
(författare)
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Modelling of partition constants : Linear solvation energy relationships or PLS regression?
- 2009
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Ingår i: Journal of Chemometrics. - New York : Wiley. - 0886-9383 .- 1099-128X. ; 23:5, s. 254-262
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Tidskriftsartikel (refereegranskat)abstract
- Estimation methods for partition constants are needed in many fields of engineering and science. The partitioning between phases is determined by the free energy of the transfer and all estimation methods must therefore describe the same entity. Linear solvation energy relationships (LSERs) try to split the contributions to van der Waals and polar interactions into directly interpretable solute descriptors, while projection-based regression methods can accomplish a similar dimensionality reduction from a set of theoretical descriptors. Here, we use the partitioning between octanol and water (Kow) and water solubility (Sw) to investigate similarities and differences between LSER and partial least squares regression (PLSR) models. The similarities in model structure are described, and shown to transform into a comparable prediction performance. We also demonstrate the opportunity to accomplish an analogous chemical interpretation of a PLSR model - either directly or through a linear transformation of the PLS factors - as with an LSER model. Much of the alleged difference between the mechanistic or semi-empirical LSER and the statistical PLSR models will then disappear. The choice of a modelling approach should therefore primarily be driven by the availability of data and predictive performance.
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| 13. |
- Sander, Per, et al.
(författare)
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Comparing deterministic and probabilistic risk assessments : A case study at a closed steel mill in southern Sweden
- 2006
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Ingår i: Journal of Soils and Sediments. - Landsberg : Ecomed Pub.. - 1439-0108 .- 1614-7480. ; 6:1, s. 55-61
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Tidskriftsartikel (refereegranskat)abstract
- Background, Aims and Scope. Contaminated land is a high priority environmental problem in most of Europe and North-America. Sweden is no exception and generic guideline values have been developed for the initial assessment, but site-specific assessments are also needed. The generic guideline values are not applicable when the exposure conditions are different from the typical Swedish conditions or when the site contains a particularly sensitive ecosystem. The Swedish guideline values have, like in many other countries, been set by using deterministic point estimates for all variables and constants in the used multimedia model. The same approach is common also for site-specific assessments, and a limitation is that it fails to quantify variability and uncertainty. Probabilistic risk assessment provided a method to deal with this problem. Variability and uncertainty in the input parameters (variables or constants) are described by probability distributions, and likewise the output (risk or exposure) is presented as a probability distribution. A substantial number of probabilistic risk assessments for contaminated land at sites in North America, Europe and Asia have been published. However, an extensive review of the literature did not identify any study where probabilistic risk assessment was applied to a site contaminated by an iron or steel industry. Here we will describe such a case, where we have compared a deterministic point estimate with a probabilistic risk assessment for six elements and benzo[a]pyrene. Methods. The site had different metallurgical plants in operation for more than 100 years. Most parts of the steel mill were closed by the mid 1980s, and today the site is used by small-sized enterprises. The soil is contaminated with metals from the previous industrial operations. The present owner plans to develop the site and has therefore initiated extensive investigations of soil contamination. Sixty-two soil samples collected between 1997 and 2000 provided a good coverage of the whole site, and were analyzed for the content of different elements and polycyclic aromatic hydrocarbons (PAH). The exposure assessments were focused on six elements with high concentrations compared to the generic guideline values; arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn). In addition, benzo[a]pyrene was included due to the high toxicity and comparatively high concentrations. Variability and uncertainty were characterized in a Monte Carlo simulation of exposures (10 000 iterations), and the exposures were evaluated with two land use scenarios; less sensitive use and sensitive use. Results and Discussion. The deterministic point estimates and the probabilistic estimates of the 95th percentile are in approximately the same ranges in the scenario of less sensitive land use. It is only the exposure for arsenic that is slightly above the toxicological reference value (TRV) in the deterministic assessment. In the probabilistic assessment, the exposure for all elements is below the TRV. The results for sensitive land use are applicable to a scenario where the site is developed for general housing. The deterministic point estimates and the probabilistic estimates of the 95th percentile are also here in approximately the same ranges, but the exposure exceeds the TRV for arsenic, cadmium and lead. Drinking water, vegetables grown on site and soil ingestion are the major exposure pathways for this scenario. In this assessment, the estimated intake distributions are applicable to a randomly selected individual. The probability distributions used here to characterize the different soil parameters are typically representing both variability and uncertainty, and the same is true the majority of the exposure variables. We therefore decided not to attempt to separate variability and uncertainty at this stage, but with additional data from a more in-depth site investigation it might be possible to achieve this. Conclusions and Outlook. To the best of our knowledge, this study is the first report on a probabilistic risk assessment on a former iron and steel works site. The materials handled by this industry were less toxic than for many other metallurgical operations, but contaminants may still severely limit the options for future land use. This case study shows that probabilistic exposure estimates for a set of soil contaminants can be quite similar to deterministic point estimates. The main difference is instead to be found in the additional information obtained with the probabilistic assessment. The sensitivity analyses show pathways and input variables that contribute most to variations in the total intake of each contaminant, e.g. dermal contact and ingestion of soil, vegetables and drinking water. This information can be used both in the planning of future land use and for active measures to reduce current exposure. The probabilistic assessment also provides information on the magnitude of exposure and the margin of safety. This information may facilitate risk communication between decision-makers and stakeholders. The presentation of results from probabilistic risk assessments is only briefly discussed in the literature and here we see a need for research and opportunities for enhancement. The choice of data analytical tools may then be of importance, since more complex multimedia models are rather difficult to decipher when implemented within traditional spreadsheet software. Some of the research needs are identified here and in a previous review article in this journal.
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| 14. |
- Sander, Per, et al.
(författare)
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Uncertain numbers and uncertainty in the selection of input distributions--consequences for a probabilistic risk assessment of contaminated land.
- 2006
-
Ingår i: Risk Analysis. - New York : Plenum Press. - 0272-4332 .- 1539-6924. ; 26:5, s. 1363-1375
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Tidskriftsartikel (refereegranskat)abstract
- Risks from exposure to contaminated land are often assessed with the aid of mathematical models. The current probabilistic approach is a considerable improvement on previous deterministic risk assessment practices, in that it attempts to characterize uncertainty and variability. However, some inputs continue to be assigned as precise numbers, while others are characterized as precise probability distributions. Such precision is hard to justify, and we show in this article how rounding errors and distribution assumptions can affect an exposure assessment. The outcome of traditional deterministic point estimates and Monte Carlo simulations were compared to probability bounds analyses. Assigning all scalars as imprecise numbers (intervals prescribed by significant digits) added uncertainty to the deterministic point estimate of about one order of magnitude. Similarly, representing probability distributions as probability boxes added several orders of magnitude to the uncertainty of the probabilistic estimate. This indicates that the size of the uncertainty in such assessments is actually much greater than currently reported. The article suggests that full disclosure of the uncertainty may facilitate decision making in opening up a negotiation window. In the risk analysis process, it is also an ethical obligation to clarify the boundary between the scientific and social domains.
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| 15. |
- Tetko, Igor V, et al.
(författare)
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Critical assessment of QSAR models of environmental toxicity against Tetrahymena pyriformis : focusing on applicability domain and overfitting by variable selection.
- 2008
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Ingår i: Journal of chemical information and modeling. - : American Chemical Society. - 1549-9596 .- 1549-960X. ; 48:9, s. 1733-46
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Tidskriftsartikel (refereegranskat)abstract
- The estimation of the accuracy of predictions is a critical problem in QSAR modeling. The "distance to model" can be defined as a metric that defines the similarity between the training set molecules and the test set compound for the given property in the context of a specific model. It could be expressed in many different ways, e.g., using Tanimoto coefficient, leverage, correlation in space of models, etc. In this paper we have used mixtures of Gaussian distributions as well as statistical tests to evaluate six types of distances to models with respect to their ability to discriminate compounds with small and large prediction errors. The analysis was performed for twelve QSAR models of aqueous toxicity against T. pyriformis obtained with different machine-learning methods and various types of descriptors. The distances to model based on standard deviation of predicted toxicity calculated from the ensemble of models afforded the best results. This distance also successfully discriminated molecules with low and large prediction errors for a mechanism-based model developed using log P and the Maximum Acceptor Superdelocalizability descriptors. Thus, the distance to model metric could also be used to augment mechanistic QSAR models by estimating their prediction errors. Moreover, the accuracy of prediction is mainly determined by the training set data distribution in the chemistry and activity spaces but not by QSAR approaches used to develop the models. We have shown that incorrect validation of a model may result in the wrong estimation of its performance and suggested how this problem could be circumvented. The toxicity of 3182 and 48774 molecules from the EPA High Production Volume (HPV) Challenge Program and EINECS (European chemical Substances Information System), respectively, was predicted, and the accuracy of prediction was estimated. The developed models are available online at http://www.qspr.org site.
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| 16. |
- Zhu, Hao, et al.
(författare)
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Combinatorial QSAR modeling of chemical toxicants tested against Tetrahymena pyriformis
- 2008
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Ingår i: Journal of chemical information and modeling. - : American Chemical Society. - 1549-9596 .- 1549-960X. ; 48:4, s. 766-784
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Tidskriftsartikel (refereegranskat)abstract
- Selecting most rigorous quantitative structure-activity relationship (QSAR) approaches is of great importance in the development of robust and predictive models of chemical toxicity. To address this issue in a systematic way, we have formed an international virtual collaboratory consisting of six independent groups with shared interests in computational chemical toxicology. We have compiled an aqueous toxicity data set containing 983 unique compounds tested in the same laboratory over a decade against Tetrahymena pyriformis. A modeling set including 644 compounds was selected randomly from the original set and distributed to all groups that used their own QSAR tools for model development. The remaining 339 compounds in the original set (external set I) as well as 110 additional compounds (external set II) published recently by the same laboratory (after this computational study was already in progress) were used as two independent validation sets to assess the external predictive power of individual models. In total, our virtual collaboratory has developed 15 different types of QSAR models of aquatic toxicity for the training set. The internal prediction accuracy for the modeling set ranged from 0.76 to 0.93 as measured by the leave-one-out cross-validation correlation coefficient ( Q abs2). The prediction accuracy for the external validation sets I and II ranged from 0.71 to 0.85 (linear regression coefficient R absI2) and from 0.38 to 0.83 (linear regression coefficient R absII2), respectively. The use of an applicability domain threshold implemented in most models generally improved the external prediction accuracy but at the same time led to a decrease in chemical space coverage. Finally, several consensus models were developed by averaging the predicted aquatic toxicity for every compound using all 15 models, with or without taking into account their respective applicability domains. We find that consensus models afford higher prediction accuracy for the external validation data sets with the highest space coverage as compared to individual constituent models. Our studies prove the power of a collaborative and consensual approach to QSAR model development. The best validated models of aquatic toxicity developed by our collaboratory (both individual and consensus) can be used as reliable computational predictors of aquatic toxicity and are available from any of the participating laboratories.
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| 17. |
- Öberg, Tomas, 1956-
(författare)
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A general structure-property relationship to predict the enthalpy of vaporisation at ambient temperatures.
- 2007
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Ingår i: SAR and QSAR in environmental research (Print). - Reading, Berkshire, Great Britain : Gordon and Breach Science Publishers. - 1062-936X .- 1029-046X. ; 18:1-2, s. 127-139
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Tidskriftsartikel (refereegranskat)abstract
- The vapour pressure is the most important property of an anthropogenic organic compound in determining its partitioning between the atmosphere and the other environmental media. The enthalpy of vaporisation quantifies the temperature dependence of the vapour pressure and its value around 298 K is needed for environmental modelling. The enthalpy of vaporisation can be determined by different experimental methods, but estimation methods are needed to extend the current database and several approaches are available from the literature. However, these methods have limitations, such as a need for other experimental results as input data, a limited applicability domain, a lack of domain definition, and a lack of predictive validation. Here we have attempted to develop a quantitative structure-property relationship (QSPR) that has general applicability and is thoroughly validated. Enthalpies of vaporisation at 298 K were collected from the literature for 1835 pure compounds. The three-dimensional (3D) structures were optimised and each compound was described by a set of computationally derived descriptors. The compounds were randomly assigned into a calibration set and a prediction set. Partial least squares regression (PLSR) was used to estimate a low-dimensional QSPR model with 12 latent variables. The predictive performance of this model, within the domain of application, was estimated at n=560, q2Ext=0.968 and s=0.028 (log transformed values). The QSPR model was subsequently applied to a database of 100,000+ structures, after a similar 3D optimisation and descriptor generation. Reliable predictions can be reported for compounds within the previously defined applicability domain.
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| 18. |
- Öberg, Tomas, 1956-
(författare)
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A QSAR for the hydroxyl radical reaction rate constant : Validation, domain of application, and prediction
- 2005
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 39:12, s. 2189-2200
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Tidskriftsartikel (refereegranskat)abstract
- A large number of anthropogenic organic chemicals are emitted into the troposphere. Reactions with the hydroxyl radical are a dominant removal pathway for most organic compounds, but experimentally determined gas-phase reaction rate constants are only available for about 750 compounds. The lack of experimental data increases the importance of applying structure-activity relationships (QSAR) to evaluate and predict reactivities. It is generally acknowledged that these empirical relationships are valid only within the same domain for which they were developed. However, model validation is sometimes neglected and the application domain is not always well defined. The purpose of this paper is to outline how validation and domain definition can facilitate the modeling and prediction of the hydroxyl radical reaction rates for a large database. A substantial number of theoretical descriptors (867) were generated from 2D molecular structures for compounds present in the Syracuse Research Corporationﾒs PhysProp Database. A QSAR model was developed for the hydroxyl radical reaction rate constant using a projection-based regression technique, PLSR (partial least squares regression). The PLSR model was subsequently validated with an external test set. The main factors of variation could be attributed to two reaction pathways, hydrogen atom abstraction and addition to double bonds or aromatic systems. A set of 17 293 compounds, drawn from the PhysProp Database, was projected onto the PLSR model and 74% were inside the applicability domain. The predicted hydroxyl reaction rates for 25% of these compounds were slow or negligible, with atmospheric half-lives in the range from days to years. Finally, the list of persistent organic compounds was matched against the OECD list of High Production Volume Chemicals (HPVC). Together with the experimental data, nearly three hundred compounds were identified as both persistent and in high volume production.
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| 19. |
- Öberg, Tomas, 1956-, et al.
(författare)
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A review of probabilistic risk assessment of contaminated land
- 2005
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Ingår i: Journal of Soils and Sediments. - Springer : Berlin. - 1439-0108 .- 1614-7480. ; 5:4, s. 213-224
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Tidskriftsartikel (refereegranskat)abstract
- Background, Aims and Scope. The management and decisions concerning restoration of contaminated land often require in-depth risk analyses. An environmental risk assessment is generally described as proceeding in four separate steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. The risk assessment should acknowledge and quantify the uncertainty in risk predictions. This can be achieved by applying probabilistic methods which, although they have been available for many years, are still not generally used. Risk assessment of contaminated land is an area where probabilistic methods have proved particularly useful. Many reports have appeared in the literature, mostly by North American researchers. The aim of this review is to summarize the experience gained so far, provide a number of useful examples, and suggest what may be done to promote probabilistic methods in Europe and the rest of the world. Methods. The available literature has been explored through searches in the major scientific and technical databases, WWW resources, textbooks and direct contacts with active researchers. A calculation example was created using standard simulation software. Results and Discussion. Uncertainty and variability are part of every risk assessment. Much work on risks from contaminated soil has focussed on exposure, and choice and structure of the exposure model is then a basic uncertainty factor. Other factors, e.g. parameter uncertainty, are easier to characterize. Variability can be separated into inter-individual, spatial and temporal components. Both uncertainty and variability in the exposure variables can be investigated using Monte Carlo simulation methods. These simulations enable not only the estimation of the probability for a given risk or exposure, but also add information on the sensitivity of the various input variables. This will assist the assessor in further refining the risk analysis. The large number of applications published encompasses soil contamination by lead, arsenic, chromium, uranium, polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), hexachlorobenzene, pentachlorophenol and chlorinated solvents. Probabilistic risk assessments have been used in widely different settings, such as the metallurgical industry (mining and smelting operations), manufacturing, gas plants, wood impregnation, infrastructure, and waste landfills. Site-specific remediation goals can be specified using probabilistic methods, and a guideline document has been issued within the US Superfund programme. The usability of probabilistic risk assessment is illustrated by a calculation example. The current Swedish generic guideline value for benzo[a]pyrene in contaminated soil, with ingestion of vegetables as the major route of exposure, is compared with a probabilistic estimate. The toxicological reference value corresponds well with the upper 95th percentile of the estimated variability in intake, but does not account for uncertainty in the partition coefficients. Conclusions and Outlook. The probabilistic approach to risk assessment has proved its value in characterizing variability and uncertainty, and thereby contributing to a more informed and transparent decision-making process. The management of contaminated land is a major environmental application for probabilistic risk assessments. A substantial number of studies have been published and the method is now well established in the scientific community. This development has progressed further in the United States than elsewhere, but similar applications are now being reported from Europe and Asia. Probabilistic risk assessment is used to derive soil guideline values in the United Kingdom, and other countries may be anticipated to follow. However, efficient use of probabilistic methods for risk assessment of contaminated land requires certain components. There is a requirement for quality assurance and transparency that can be met by guidelines specifying data requirements and which items to report on. Both federal and state governments in the United States have issued such guidelines, and we see a similar need from a European perspective. A second component, necessary for a successful implementation of probabilistic methods, is education. We have ourselves developed undergraduate curricula, but we also see a need for continuous education of risk assessors and decision makers. The third component required is case studies, showing how probabilistic risk assessment can be implemented successfully in the cleanup of contaminated land. Most published studies originate from the United States, so here too there is a need for the rest of the world to catch up. In addition to the three components mentioned, there is an obvious need to develop and improve methods and practice of risk communication.
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| 20. |
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| 21. |
- Öberg, Tomas, 1956-, et al.
(författare)
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Catalytic effects by metal oxides on the formation and degradation of chlorinated aromatic compounds in fly ash.
- 2008
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Ingår i: Chemosphere. - Oxford : Pergamnon Press. - 0045-6535 .- 1879-1298. ; 71:6, s. 1135-43
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Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated benzenes, dibenzo-p-dioxins (PCDD), and dibenzofurans (PCDF) may be formed below the combustion temperature in fly ash from municipal solid waste incinerators (MSWI). Copper catalyzes this formation, possibly by the Deacon reaction. Many other elements are also Deacon catalysts or promoters, and here we report results from a statistically designed experiment with 15 metal oxides added to fly ash and heated at 300 degrees C for 2h in an air atmosphere. A resolution IV fractional factorial design with four replicates was completed in 36 runs with the oxides of magnesium, yttrium, titanium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, and tin. All samples were analyzed for chlorinated benzenes and the results were evaluated by analysis of variance. The addition of copper significantly increased the amounts of the chlorinated benzenes, while cobalt, chromium and vanadium decreased the net formation. The oxides of zinc and iron seemed to have a slightly positive and negative effect respectively. The findings in this study seem to corroborate our previously reported results regarding the different catalytic effects of copper and chromium, and lack of a significant effect by nickel. Besides chromium, it also identifies cobalt and vanadium as potent catalysts for oxidative degradation of the chlorinated aromatic compounds found in MSWI fly ash.
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| 22. |
- Öberg, Tomas, 1956-
(författare)
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Chemicals in Statistics - Method Development
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Statistics on import, manufacture, and export of chemicals can be an important information source to follow up the results of environmental policy and management decisions. In this pilot study we evaluate the use of the official trade and manufacture statistics for the purpose of screening for bioaccumulating and persistent compounds of a particular environmental relevance. An impact index to measure these properties is applied to chemical groupings in the trade statistics. Furthermore, data from the trade statistics for selected chemicals is compared to corresponding data from the Swedish Products Register, at the Swedish Chemical Agency. The results show that the level of detail in the trade statistics does not permit estimation on the impact index using a compound specific index for environmental impact. In the trade statistics, a substantial number of chemicals with different properties are often grouped with the same identifier. However, this study shows that it is possible to use the same index to identify the groups containing the most problematic chemicals. The 100 chemicals identified to rank highest with regard to the potential environmental impact index belong to several groups, but 94 of these were halogenated. The two dominating groups in the trade statistics were halogenated aromatics and hydrochlorofluorocarbons (HCFC), with 25 and 20 members, respectively. A more detailed study of the trade statistics for these high-impact groups revealed substantial deviations between data from Statistics Sweden and Swedish Chemical Agency. Anomalies and an outlier were also observed and some misclassifications discovered. The self-reported statistics thus seems to need further validation to improve their usability for chemical policy purposes. Suggestions are made for further comparisons of databases, but tracing back to primary sources may also prove necessary to ensure relevance and good quality.
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| 23. |
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| 24. |
- Öberg, Tomas, 1956-
(författare)
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Introducing chemometrics to graduate students
- 2006
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Ingår i: Journal of Chemical Education. - Bellmarw : American Chemical Society. Division of Chemical Education. - 0021-9584 .- 1938-1328. ; 83, s. 1178-1181
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Tidskriftsartikel (refereegranskat)abstract
- Chemometric methods enjoy an ever-increasing popularity, and there is a need to introduce more graduate students to these research tools. This article describes an introductory course covering design of experiments, pattern recognition, and multivariate calibration. The course was composed of a series of formal lectures, seminars, and practical computer exercises followed by a project assignment tailored to each participant's own research. The teaching was focused to a few statistical methods, selected for their usefulness in solving chemical research problems. The mathematics was kept to a minimum, practical aspects and conceptual understanding were highlighted, and the exercises confronted the students with a diverse set of applications. The use of a ready-made training package—from one of the developers of chemometrics software—facilitated the course preparations and also provided the senior researchers with an opportunity for self-study. The challenge that now lay ahead at our university is to create an environment that can stimulate and support the future use of these rational methods for chemical research.
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| 25. |
- Öberg, Tomas, 1956-
(författare)
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Low-temperature formation and degradation of chlorinated benzenes, PCDD and PCDF in dust from steel production.
- 2007
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Ingår i: Science of the Total Environment. - Amsterdam : Elsevier. - 0048-9697 .- 1879-1026. ; 382:1, s. 153-158
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Tidskriftsartikel (refereegranskat)abstract
- Dust from thermal processes may catalytically enhance the formation of chlorinated aromatic compounds under oxygen-rich conditions. The activities of two dust samples from electric arc furnaces and one from iron ore-based steelmaking (oxygen converter) were investigated in a laboratory experiment. The dust samples were heated at 300 degrees C for 2 h in an air atmosphere. The concentrations of chlorinated benzenes did not change greatly upon heating, while the concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans decreased. The addition of copper in parallel runs resulted in a substantial increase in the concentration of chlorinated benzenes, thus indicating that the experimental setup was suitable for the evaluation of low-temperature catalysis. The outcome of the experiment seems to suggest that results cannot easily be extrapolated between different thermal and metallurgical processes. Some measures to reduce emissions, such as inhibition of catalytic activity and rapid cooling, could possibly be counterproductive when applied to off-gases from the steelmaking processes investigated here.
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| 26. |
- Öberg, Tomas, 1956-
(författare)
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Miljöriskanalys
- 2009. - 1
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Miljöriskanalys omfattar, riskbedömning, riskkommunikation och riskhantering.I boken introduceras den teori och de metoder som är grundläggande för att hantera risk- och beslutsproblem inom miljöområdet. Olika nyckelbegrepp förklaras ingående och terminologin har anpassats till de senaste harmoniseringsförslagen. Bokens fokus är på praktisk problemlösning och dess struktur följer innehållet i riskanalysprocessen. I separata kapitel avhandlas faroidentifiering, farokarakterisering, exponeringsbedömning och riskkarakterisering. I denna del ingår även ett kapitel om sannolikhet och statistik samt ett kapitel som introducerar de senaste sannolikhetsbaserade metoderna för att beskriva osäkerheter och naturlig variation. Kapitlen därefter behandlar riskkommunikation och riskhantering av miljöproblem. Samtliga av bokens nio ämneskapitel innehåller olika tillämpningsexempel liksom instuderingsfrågor och problem att lösa själv.Bokens syfte är att förmedla och utveckla kunskaper om riskanalytiska metoder och dessas tillämpning inom miljöområdet, med en tyngdpunkt på kvantitativ miljöriskbedömning.Boken vänder sig både till universitetsstuderande, med en naturvetenskaplig eller teknisk inriktning, och till yrkesverksamma inom områdena miljö och hälsa.
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| 27. |
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| 28. |
- Öberg, Tomas, 1956-
(författare)
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Probabilistisk riskbedömning fas 1. : Sannolikhetsbaserad uppskattning av miljö- och hälsorisker i förorenade markområden – en litteraturöversikt.
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Förorenad mark medför risker för hälsa och miljö. Litteraturöversikten redovisar hur nuvarande metodik för kvantitativa riskbedömningar kan kompletteras med en sannolikhetsbaserad – probabilistisk – ansats. Den probabilistiska metoden innebär att variabilitet (naturlig variation) och osäkerhet (okunskap) kan karakteriseras och därmed erhålls både ett bättre beslutsunderlag och kunskap om hur bedömningen ytterligare kan förfinas. Den probabilistiska metodiken har fått stor användning i USA och nu börjar den även tillämpas i flera europeiska länder. Probabilistiska riskbedömningar baseras i allmänhet på simuleringar av utfall från ett stort antal möjliga val av värden för ingångsvariabler och modellparametrar. Beräkningarna kan numer utföras med en vanlig persondator, men kräver en grundläggande kunskap om både teknikens möjligheter och begränsningar. Förorenad mark är vid sidan av kärnkraftsindustrin den viktigaste miljötillämpningen av probabilistisk riskbedömning och ett stort antal studier har publicerats för specifika objekt i Nordamerika, Europa och Asien. De avser exempelvis förorening med bly, arsenik, krom, uran, PCB, PAH, hexaklorbensen, pentaklorfenol, dioxiner och klorerade lösningsmedel. Dessa probabilistiska riskbedömningar täcker in olika exponeringssituationer inom vitt skilda verksamheter, däribland tidigare metallurgisk industri (smältverk och gruvor), tillverkningsindustri, gasverkstomter, träimpregnering, infrastruktur och deponier. En övergång till probabilistisk riskbedömning ställer krav på kvalitetssäkring, både avseende arbetsgången och redovisningsrutinerna. Det amerikanska naturvårdsverket (U. S. EPA) har gett ut relativt detaljerade anvisningar som i stort överensstämmer med vad som idag utgör vetenskapligt konsensus. Liknande behov av riktlinjer finns även i Europa. Behovet av att karakterisera variabilitet, osäkerhet och känslighet i riskbedömningsmodeller är inte annorlunda i Sverige än i Nordamerika. Dessutom behöver säkerhetsmarginalernas storlek klart kunna anges. Probabilistisk metodik kan enkelt integreras med nuvarande svenska riskbedömningsmodeller och rapporten redovisar ett beräkningsexempel för benso[a]pyren. Probabilistisk riskbedömning har ofta använts för att etablera platsspecifika riktvärden och det är här som en framtida användning i Sverige främst kan förutses. Rapporten pekar på behovet av ramar för att underlätta tolkning och jämförbarhet och rekommenderar att ett vägledningsdokument utarbetas. Likaså krävs utbildningsinsatser. Kurser i probabilistiska metoder finns i det ordinarie utbildningsprogrammet vid ett par högskolor, men ett behov finns även av kurser för fortbildning av redan yrkesverksamma, både som distansutbildning och kortare problembaserade kurser.
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| 29. |
- Öberg, Tomas, 1956-
(författare)
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Virtual screening for environmental pollutants : structure-activity relationships applied to a database of industrial chemicals
- 2006
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Ingår i: Environmental Toxicology and Chemistry. - 0730-7268 .- 1552-8618. ; 25:4, s. 1178-1183
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Tidskriftsartikel (refereegranskat)abstract
- The current risk paradigm calls for individual consideration and evaluation of each separate environmental pollutant, but this does not reflect accurately the cumulative impact of anthropogenic chemicals. In the present study, previously validated structure-activity relationships were used to estimate simultaneously the baseline toxicity and atmospheric persistence of approximately 50,000 compounds. The results from this virtual screening indicate fairly stable statistical distributions among small anthropogenic compounds. The baseline toxicity was not changed much by halogen substitution, but a distinct increase seemed to occur in the environmental persistence with increased halogenation. The ratio of the atmospheric half-lives to the median lethal concentrations provides a continuous scale with which to rank and summarize the incremental environmental impacts in a mixture-exposure situation. Halogenated compounds as a group obtained a high ranking in this data set, with well-known pollutants at the very top: DDT metabolites and derivatives, polychlorinated biphenyls, diphenyl ethers and dibenzofurans, chlorinated paraffins, chlorinated benzenes and derivatives, hydrochlorofluorocarbons, and dichlorononylphenol. Environmentally friendly chemicals that obtained the lowest rank are nearly all hydroxylated and water-soluble. Virtual screening can assist with "green chemistry" in designing safe and degradable products and enable assessment of the efficiency in chemicals risk management.
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