Biomedical subjects

Tomas Oberg

Publications and source records attributed to Tomas Oberg.

7 recordsLinked to original sources

PubMed2006

Initial screening of contaminated land: a comparison of US and Swedish methods.

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.

Environmental Monitoring↗

PubMed2006

Uncertain numbers and uncertainty in the selection of input distributions--consequences for a probabilistic risk assessment of contaminated land.

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.

Body Weight↗

PubMed2006

Virtual screening for environmental pollutants: structure-activity relationships applied to a database of industrial chemicals.

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.

Chemical Industry↗

PubMed2004

Halogenated aromatics from steel production: results of a pilot-scale investigation.

The potential environmental impact of emissions of halogenated aromatics from the steel industry is of growing concern. It has been suggested that electric arc furnaces are the only industrial source with constant or increasing emissions of dioxins to air. Here the results are reported from a pilot plant study on how scrap composition and various treatment alternatives affect the formation and release of chlorinated and brominated aromatics. The experiments were conducted with a statistical mixture design, and it is shown that scrap composition has a significant impact on the outcome. In contrast, the various treatment schemes examined--shredding, disassembly, and briquetting--did not affect the formation and release of halogenated aromatics. Parallel experiments with injection of adsorbents showed that it is possible to reduce emissions without substantial investments, and this option is recommended as a low-cost solution.

Air Pollution↗

PubMed2004

A QSAR for baseline toxicity: validation, domain of application, and prediction.

The interest in modeling and application of structure-activity relationships has steadily increased in recent decades. 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 baseline toxicity for a large database. A large number of theoretical descriptors (867) were generated from two-dimensional molecular structures for compounds present in the U.S. EPA's Fathead Minnow Database (611) and the Syracuse Research Corporation's PhysProp Database (25,000+). A quantitative structure-activity relationship model was developed for baseline toxicity (narcosis) toward the fathead minnow (Pimephales promelas) 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 were related to size/shape and polar interactions. The prediction error was comparable to, or slightly better than, the ECOSAR procedures. A set of 16,805 compounds, drawn from the PhysProp Database, was projected onto the PLSR model. More than 90% (15,597) of the compounds fall within the valid model domain, defined by the residual standard deviation and the leverage. The predicted baseline toxicity indicates an acute hazard for two-thirds of these compounds, classes I-III in the OECD Globally Harmonized Classification System (LC50 < or = 100 mg L(-1)). Finally, the mode of action assigned in the U.S. EPA Fathead Minnow Database was investigated. Reclassification to narcosis as the mode of action is suggested for 92 compounds, mostly from the groups "unsure" and "mixed". The present classification into specific modes of action seems to be further strengthened by the findings in this investigation.

Animals↗

PubMed2002

Distribution and levels of brominated flame retardants in sewage sludge.

One hundred and sixteen sewage sludge samples from 22 municipal wastewater treatment plants in Sweden were analysed for brominated flame retardants. Polybrominated diphenyl ethers (PBDEs) were in the range n.d.-450 ng/g wet weight, tetrabromobisphenol A (TBBPA) varied between n.d. and 220 ng/g wet weight, 2,4,6-tribromophenol was in the range n.d.-0.9 ng/g wet weight and polybrominated biphenyls were not detected (except for a possible analytical interference). There was a significant variation in the samples among plants. Influence from industries and other local sources can therefore be assumed. The correlation pattern indicated contribution from three different types of technical products; composed of either low-brominated PBDEs, decaBDE or TBBPA.

Bromine Compounds↗

PubMedDate not supplied

Boiling points of halogenated aliphatic compounds: a quantitative structure-property relationship for prediction and validation.

Halogenated aliphatic compounds have many technical uses, but substances within this group are also ubiquitous environmental pollutants that can affect the ozone layer and contribute to global warming. The establishment of quantitative structure-property relationships is of interest not only to fill in gaps in the available database but also to validate experimental data already acquired. The three-dimensional structures of 240 compounds were modeled with molecular mechanics prior to the generation of empirical descriptors. Two bilinear projection methods, principal component analysis (PCA) and partial-least-squares regression (PLSR), were used to identify outliers. PLSR was subsequently used to build a multivariate calibration model by extracting the latent variables that describe most of the covariation between the molecular structure and the boiling point. Boiling points were also estimated with an extension of the group contribution method of Stein and Brown.

Journal Article↗