Documents determination of concentration 17 results

"Ground-level ozone is formed in complex atmospheric photochemical reactions between nitrogen oxides and hydrocarbons. The levels are highest in summertime and outside city centers. Elevated concentrations of ground-level ozone is mainly due to chemical reactions of emissions of volatile organic compounds and nitrogen oxides. The average concentrations of ground-level ozone occurring in nonurban areas in western Europe range from 40 to 70 µg m3. One-hour maximum values may reach 300 µg m3 in central Europe and 200 µg m3 in Sweden. Numerous studies, ranging from experimental studies with laboratory animals to controlled studies with humans to epidemiologic studies, have been performed on the health effects of ozone. In animal experiments, morphological effects on lung tissue, effects on host defense mechanisms, inflammation, fibrosis and tumors have all been induced by the inhalation of ozone. The lowest concentration tested that has given rise to these effects is 200 µg m3. It led to hyperplastic changes, proinflammatory changes, and sensitization to allergens.

In chamber exposure studies of 1- to 6-h duration, respiratory symptoms and pulmonary effects such as lung function decrements, increased airway responsiveness, and inflammatory reactions have all been demonstrated in humans. These effects have occurred even at the lowest concentration tested, 160 µg m3 for 6 h. Reduced lung function at 1-h maximum daily values of 160 µg m3 has also been found in epidemiologic studies, and some reports indicate effects at even lower levels. Other effects of ozone seen in epidemiologic studies include respiratory symptoms, hospital admissions, and emergency room visits for respiratory conditions, all of which correlated with daily 1-h maximum values of 240 µg m3 and lower. From these data on humans, and with the use of a safety factor of 2, a 1-h guideline value of 80 µg m3 is recommended. This level is also intended to protect against health effects in the most sensitive sections of the population. The proposed guideline level is currently exceeded and should be regarded as a goal for action to avoid adverse health effects in the future.

The experimental and epidemiologic basis for a risk assessment concerning long-term exposure is much weaker than for short-term exposure, and no explicit long-term guideline value is recommended. However, the proposed short-term guideline would probably offer some protection against potential effects of ozone following long-term exposure."

"A general model to take into account the distribution of persistent organic pollutants (POPs) in the water column as well as POPs interaction with the atmosphere and sediments has been developed. The model has been adapted to deal with several families of POPs, including PCBs (Polychlorinated Biphenyls), PAHs (Polycyclic Aromatic Hydrocarbons), PBDEs (Polybrominated Dyphenyl Ethers) and PCDD/Fs (Polychlorinated dibenzo-p-dioxins and dibenzofurans). The simulated time series concentrations for one year are in general in good agreement with experimental observations from literature for these families of contaminants. However, specific designed campaigns still need to be performed to validate the model with a set of homogenous forcings concerning air and historical sediment concentrations as well as data on evolution of concentrations in the water column and in the surficial sediment layer. The model is being coupled with a biogeochemical model to assess the influence of phytoplankton, zooplankton and bacteria on the dynamics of POPs. In a further step, the model will be used to analyze the data obtained from different experimental campaigns carried out in Thresholds as well as mesocosm experiments."

"As workplace air measurements of manufactured nanoparticles are relatively expensive to conduct, models can be helpful for a first tier assessment of exposure. A conceptual model was developed to give a framework for such models. The basis for the model is an analysis of the fate and underlying mechanisms of nanoparticles emitted by a source during transport to a receptor. Four source domains are distinguished; that is, production, handling of bulk product, dispersion of ready-to-use nanoproducts, fracturing and abrasion of end products. These domains represent different generation mechanisms that determine particle emission characteristics; for example, emission rate, particle size distribution, and source location. During transport, homogeneous coagulation, scavenging, and surface deposition will determine the fate of the particles and cause changes in both particle size distributions and number concentrations. The degree of impact of these processes will be determined by a variety of factors including the concentration and size mode of the emitted nanoparticles and background aerosols, source to receptor distance, and ventilation characteristics. The second part of the paper focuses on to what extent the conceptual model could be fit into an existing mechanistic predictive model for ''conventional'' exposures. The model should be seen as a framework for characterization of exposure to (manufactured) nanoparticles and future exposure modeling."

"In potential nano-objects can be released into the workplace air during production, during the handling of nanopowders and during the treatment of end-products that contain manufactured nanomaterials. Experimental studies that could mimic the exposure processes revealed the formation of larger agglomerates after release. Studies conducted in workplaces confirmed this assumption, however, the data are still very scarce and not easily to compare due to differences in the format of reporting the data. Number-, mass-, and surface area concentrations are reported, however, currently an estimate of the potential for worker exposure is not possible. It is recommended that future workplace exposure studies will be conducted according to a more harmonized approach for analyzing and reporting of the results."

"En raison des fluctuations environnementales d'un jour à l'autre de la concentration au poste de travail (dues à la variabilité du process), les aspects statistiques de l'exposition professionnelle sont examinés sur la base d'une distribution log-normale des expositions. Différentes techniques de diagnostic (sous ou sur exposition par rapport à la valeur limite) sont décrites à partir d'une approche probabiliste en prenant en compte les estimations de l'écart-type géométrique et de la moyenne géométrique de la distribution. L'influence de la fidélité et du biais de la méthode de mesure prélèvement analyse est examinée à partir du modèle log-normal. L'incertitude de la méthode n'a pas d'influence devant l'incertitude liée aux fluctuations environnementales sauf dans le cas du biais qui peut altérer le diagnostic. Une attention particulière devra donc être portée sur le biais de la méthode de mesure et comme cela a déjà été montré, plusieurs mesurages au cours de l'année devraient être effectués pour obtenir suffisamment d'informations pour porter un diagnostic fiable sur l'exposition."(Résumé des auteurs)

"La contaminación humana por compuestos tóxicos persistentes es una de las características más definitorias y sin embargo ignoradas de nuestra sociedad. Hoy la exposición a estos compuestos -fundamentalmente, plaguicidas y residuos industriales- empieza en el vientre materno y se prolonga durante toda la vida. Las personas nos exponemos a ellos prácticamente sin advertirlo, apenas los podemos eliminar y la acumulación corporal aumenta paulatinamente con la edad.
Esta obra servirá de referencia a todo ciudadano interesado, y en especial a los profesionales de la salud, el medio ambiente y las otras ciencias de la vida y la sociedad (desde la educación, la alimentación y la sociología hasta el derecho, la química y la ingeniería ambientales). Su propósito es también ayudar a dinamizar las políticas públicas y privadas que pueden disminuir la exposición de las personas a estos contaminantes y, por tanto, disminuir la carga de muerte, enfermedad y sufrimiento que actualmente contribuyen a causar. "