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- Sander, Per, et al.
(author)
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Uncertain numbers and uncertainty in the selection of input distributions--consequences for a probabilistic risk assessment of contaminated land.
- 2006
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In: Risk Analysis. - New York : Plenum Press. - 0272-4332 .- 1539-6924. ; 26:5, s. 1363-1375
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Journal article (peer-reviewed)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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| 2. |
- Öberg, Tomas, 1956-, et al.
(author)
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A review of probabilistic risk assessment of contaminated land
- 2005
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In: Journal of Soils and Sediments. - Springer : Berlin. - 1439-0108 .- 1614-7480. ; 5:4, s. 213-224
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Journal article (peer-reviewed)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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| 3. |
- Öberg, Tomas, 1956-, et al.
(author)
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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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In: Chemosphere. - Oxford : Pergamnon Press. - 0045-6535 .- 1879-1298. ; 71:6, s. 1135-43
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Journal article (peer-reviewed)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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| 4. |
- Öberg, Tomas, 1956-, et al.
(author)
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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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In: Environmental Science and Technology. - Washington : American Chemical Society. - 0013-936X .- 1520-5851. ; 41:10, s. 3741-3746
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Journal article (peer-reviewed)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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| 5. |
- Filipsson, Monika, et al.
(author)
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Exponeringsfaktorer vid riskbedömning : Inventering av dataunderlag
- 2008
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Reports (other academic/artistic)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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