Branching processes, Markov chains, and competing risks

This paper re-proves and generalizes results by Hardin and Sweet on the time to absorption in certain Markov chains by using a theorem on the time to extinction in multitype branching processes. Renaming “absorption” as “death” and “state immediately before absorption” as “cause of death” makes possible an interpretation in terms of competing risks. This is of very limited value, however, due to the rather severe mathematical restrictions on the Markov chains at hand.     

Consultative mechanisms in Sweden's environment protection policy

The institutional and legislative framework of Swedish environmental protection is presented with special reference to the role of consultation in the policy process. The functions and duties of the National Environment Protection Board, the Franchise Board for Environment Protection, the Environment Advisory Board, and the Product Control Board are outlined. The main thrust of the 1969 Environment Protection Act, the 1972 Hazardous Products Control Act, and the environmental impact assessment requirements of the Planning and Building Legislation is presented. The character of consultation within this framework is also discussed, with reference to the role of public participation and of organized regulated interests. It is found that the main functions of consultation in policy-making are “feeding back on former policy,” “foreseeing future policies,” and “canvassing for consensus.” In the stage of policy clarification, consultation is found to be a means of “catering for compliance” and “creating coherence.” In policy implementation, consultation is an important means of gathering information from parties possibly affected by implementative decisions.     

Assessment of the consequences of the radioactive contamination of aquatic media and biota for the Chernobyl NPP cooling pond: model testing using Chernobyl data

The ‘Cooling Pond’ scenario was designed to test models for radioactive contamination of aquatic ecosystems, based on data from the Chernobyl Nuclear Power Plant cooling pond, which was heavily contaminated in 1986 as a result of the reactor accident. The calculation tasks include (a) reconstruction of the dynamics of radionuclide transfer and bioaccumulation in aquatic media and biota following the accident; (b) assessment of doses to aquatic biota; and (c) assessment of potential doses and radiation risks to humans from consumption of contaminated fish. Calculations for the Scenario were performed by 19 participants using 6 different models: LAKECO-B (Netherlands); LAKEPOND (Romania); POSOD (USA); WATER, GIDRO and ECOMOD-W (Russia). For all endpoints, model predictions were compared with the test data, which were derived from the results of direct measurements and independent dose estimates based on measurements. Most of the models gave satisfactory agreement for some portions of the test data, although very few participants obtained good agreement with all criteria for model testing. The greatest level of difficulty was with the prediction of non-equilibrium radioecological processes in the first year after the accident (1986). The calculations 5 for this scenario gave modellers a unique opportunity to test their models using an independent data base and to analyse the advantages and weaknesses of different model approaches. The use of post-Chernobyl data in such a scenario is also recommended for use in training students in the field of radioecology and environmental protection.     

Electrostatic precipitator emission and opacity performance control through rapper strategy

The opacity and emission performance of two “identical” cold-side precipitators at a power plant utilizing a Western coal source was investigated through an extensive test program. The test program included establishment of outlet emission versus opacity correlations for the two “identical” units, correlation of rapper strategy (frequency and amplitude) with opacity, and correlation of power-off rapping strategy with opacity. Analysis of the test program data demonstrates that the opacity-emission correlations from the two “identical” units can be significantly different. The potential reasons for the differences between the two units are identified and examined in light of the test program data. Strong correlation of opacity with rapping strategy was developed from the test program. Results demonstrate that an automatic power-off rapping technique can significantly enhance precipitator performance on ash from Western coal.     

Derivation of a screening methodology for evaluating radiation dose to aquatic and terrestrial biota

The United States Department of Energy (DOE) currently has in place a radiation dose standard for the protection of aquatic animals, and is considering additional dose standards for terrestrial biota. These standards are: 10 mGy/d for aquatic animals, 10 mGy/d for terrestrial plants, and, 1 mGy/d for terrestrial animals. Guidance on suitable approaches to the implementation of these standards is needed. A screening methodology, developed through DOE's Biota Dose Assessment Committee (BDAC), serves as the principal element of DOE's graded approach for evaluating radiation doses to aquatic and terrestrial biota. Limiting concentrations of radionuclides in water, soil, and sediment were derived for 23 radionuclides. Four organism types (aquatic animals; riparian animals; terrestrial animals; and terrestrial plants) were selected as the basis for development of the screening method. Internal doses for each organism type were calculated as the product of contaminant concentration, bioaccumulation factor(s) and dose conversion factors. External doses were calculated based on the assumption of immersion of the organism in soil, sediment, or water. The assumptions and default parameters used provide for conservative screening values. The screening methodology within DOE's graded approach should prove useful in demonstrating compliance with biota dose limits and for conducting screening assessments of radioecological impact. It provides a needed evaluation tool that can be employed within a framework for protection of the environment.     

On the Problem of Assessing the Resistance of Planktonic Community to Adverse Influences

An experimental-analytical method for assessing the vulnerability of aquatic ecosystems under conditions of anthropogenic pollution is considered. Such data are very important for estimating economic damage from accidental environmental pollution and determining the seasons in which industrial activities will be less hazardous in ecological terms. A feasible approach to this problem is based on the study of ecosystem behavior under critical conditions. Phytoplankton, being the main primary producer of organic matter in the aquatic ecosystem, is the key element providing for its stability.__________Translated from Ekologiya, No. 4, 2005, pp. 294–299.Original Russian Text Copyright © 2005 by Domnin, Korsak, Mosharov.     

Towards a coherent conceptual framework for emergency preparedness/response and rehabilitation – the application of the new ICRP recommendations given in ICRP 103

In the past, most emphasis in planning for and response to an emergency situation has been placed on selected protective measures in the early phase of an emergency to keep the doses received below levels where severe deterministic health effects can be excluded and/or where the risk of stochastic effects in the population is considered “acceptable”. Less emphasis has been placed on the development of comprehensive protection strategies which include considerations of the consequences of all exposure pathways and all phases, e.g. long-term rehabilitation. In its new publication 103, ICRP proposed a coherent conceptual framework for protection in all types of exposure situations including “emergency exposure situations” and “existing exposure situations”. In the context of developing protection strategies for these exposure situations, the Commission recommends that national authorities set reference levels between, typically, 20 mSv and 100 mSv annual effective dose (emergency exposure situation) and 1 mSv and 20 mSv (existing exposure situation). In order to optimise protection strategies, it is necessary to identify the dominant exposure pathways, the timescales over which the dose will be received, and the effectiveness of available protection options. The characteristics of the development and implementation of such protection strategies is described.     

Efficient ventilation in office rooms

Results from a two-box model for calculation of tracer gas concentrations in rooms are given and consequences of different definitions of “ventilation efficiency” are discussed. Results from three different series of experiments are presented. The first two series were dilution experiments; examples of the results are given and discussed. The third series of tests was performed with one person working at a desk in the test room. Above the person;s head, a tracer gas (N₂O) was injected into the convection plume, with as low momentum as possible. Starting with zero concentration, a test continued until steady-state conditions were established for the concentration levels in the different parts of the room. The tests included simulation of summer, autumn/spring, and winter daytime conditions. The results indicate a tendency towards lower tracer gas concentrations in the “breathing zone” when the supply air (typical flow rate equivalent to two air changes per hour) is brought into the room at a low level as compared to a high level close to the ceiling. The exhaust air terminal device in all tests was situated high in the “corridor” wall.     

Olfactory and chemical characterization of indoor air. Towards a psychophysical model for air quality

The relationship between the odor strength of total air samples and the odor strengths of the constituents was investigated in three field experiments in an office building and a new preschool. The odor strength was scaled by magnitude estimation according to a master scale principle which results in comparable values for the total and the constituent odors. Between 60 and 120 chemical components were detected by GC/FID in the indoor air samples (N = 66). Most (81%) of the detected components in an air sample were odorous, even though most of them were of the low concentrations. By a method of pattern analysis, chemical as well as odor patterns of indoor air were found to be characteristics of different buildings. From the odor patterns (POG), the “odor print” of the outdoor air associated with the buildings was also recognized in the indoor air. Thus, the “odor print” of an air sample is different from its “chemical print”. A model was found that predicts the overall odor strength of an air sample from the number of FID-detected components most frequently reported to have a strong odor.     

Challenges in radioecology

Today, radioecology covers a broad scientific field; from the source to long term environmental impact from ionizing radiation. To summarize key challenges within radioecology, the present paper focuses upon knowledge gaps related to processes, mechanisms and variables contributing most to the overall uncertainties in environmental impact assessments. A series of sources related to the nuclear weapon cycle and the civil nuclear cycle has contributed, is still contributing or can potentially contribute to release of radionuclides to the environment in the future. The speciation of most radionuclides depends on the source and release conditions, and will influence ecosystem transport, biological uptake, doses and effects in flora and fauna. Radionuclides may also co-occur in contaminant mixtures (e.g., metals, organics), which potentially could lead to synergisms or antagonisms. Thus, challenges associated with the links between the source or release term – radionuclide speciation – ecosystem transfer – exposure – response relationships are highlighted.     

Assessing field-scale migration of radionuclides at the Nevada Test Site: “mobile” species

Many long-lived radionuclides are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. In conjunction with a comprehensive geochemical review of radionuclides (³H, ¹⁴C, ³⁶Cl, ⁹⁹Tc and ¹²⁹I) that are presumably mobile in the subsurface, we synthesized a body of radionuclide activity data measured from groundwater samples collected at 18 monitoring wells, to qualitatively assess their migration at the NTS over distances of hundreds of meters and over timescales of decades. Tritium and ³⁶Cl showed little evidence of retardation, while the transport of ¹⁴C may have been retarded by its isotopic exchange with carbonate minerals in the aquifer. Observed local reducing conditions (either natural or test-induced) will impact the mobility of certain redox-sensitive radionuclides (especially ⁹⁹Tc) that were otherwise soluble and readily transported under oxidizing conditions. Conversely, strongly oxidizing conditions may impact the mobility of ¹²⁹I which is mobile under reducing conditions. The effect of iodine speciation on its transport deserves further attention. Indication of delayed transport of some “mobile” radionuclides (especially ⁹⁹Tc) in the groundwater at the NTS suggested the importance of redox conditions of the natural system in controlling the fate and transport of radionuclides, which has implications in the enhanced performance of the potential Yucca Mountain repository, located adjacent to the NTS, to store high-level nuclear wastes as well as management of radionuclide contamination in legacy nuclear operations facilities.     

Pilot field study: Carbon monoxide exposure monitoring in the general population

A pilot field study was conducted with nine members of the general public to measure carbon monoxide exposure using personal monitors. The principal study objectives were to design and evaluate the research protocol and the instrumentation performance for application to the conduct of a large-scale personal monitoring program. Integrated carbon monoxide exposure was monitored and recorded according to type of activity such as “commuting” or “at work” for approximately 45 days by each subject. All subjects except one were able to handle both the equipment and data recording requirements with no significant problems. Actual data recording responsibilities consumed less than 10 min daily. The data consisted of 355 person-days each over 6-h duration, and weekdays only, from which 8-h average personal exposure levels could be computed. The 9 ppm (μL/L) ambient air quality standard was exceeded on 22 person-days. Elevated carbon monoxide concentrations during the commuting activity were frequently associated with the exceedences.     

Transport and fate of radionuclides in aquatic environments--the use of ecosystem modelling for exposure assessments of nuclear facilities

In safety assessments of nuclear facilities, a wide range of radioactive isotopes and their potential hazard to a large assortment of organisms and ecosystem types over long time scales need to be considered. Models used for these purposes have typically employed approaches based on generic reference organisms, stylised environments and transfer functions for biological uptake exclusively based on bioconcentration factors (BCFs). These models are of non-mechanistic nature and involve no understanding of uptake and transport processes in the environment, which is a severe limitation when assessing real ecosystems. In this paper, ecosystem models are suggested as a method to include site-specific data and to facilitate the modelling of dynamic systems. An aquatic ecosystem model for the environmental transport of radionuclides is presented and discussed. With this model, driven and constrained by site-specific carbon dynamics and three radionuclide specific mechanisms: (i) radionuclide uptake by plants, (ii) excretion by animals, and (iii) adsorption to organic surfaces, it was possible to estimate the radionuclide concentrations in all components of the modelled ecosystem with only two radionuclide specific input parameters (BCF for plants and Kd). The importance of radionuclide specific mechanisms for the exposure to organisms was examined, and probabilistic and sensitivity analyses to assess the uncertainties related to ecosystem input parameters were performed. Verification of the model suggests that this model produces analogous results to empirically derived data for more than 20 different radionuclides.     

Interactions between diesel emissions and gaseous copollutants in photochemical air pollution: Some health implications

A complete assessment of the health effects of diesel emissions must take into account the possible chemical transformations (and associated biological impacts) of particulate organic matter (POM) due to reactions with the many gaseous copollutants which have now been unambiguously demonstrated to be present in atmospheres burdened by photochemical air pollution. These copollutants include the “trace” species, nitric (HNO₃) and nitrous (HONO) acids, the nitrate radical (NO₃), formaldehyde (H₂CO) and formic acid (HCOOH), as well as the criteria pollutants, ozone (O₃) and nitrogen dioxide (NO₂). Techniques for establishing the atmospheric concentrations of the trace pollutants (and their spatial and temporal variations) are briefly described, and we present results of investigations into the reactions of polycyclic aromatic hydrocarbons (PAH) coated on filters and exposed to ambient concentrations of O₃ and NO₂. Environmental health implications of these results are discussed and include the potential for sampling “artifacts” and their possible effects on the correlation (or lack thereof) between ambient PAH levels and urban lung cancer rates, as well as the problems associated with understanding the appropriate POM “dose” to be employed in animal testing and assessments of impacts on human health.     

Improving the efficiency of free-jet scrubbers

A free-jet scrubber is an innovative gas cleaner in which the primary liquid/gas contacting takes place in the turbulent mixing zone emanating from a jet nozzle. The first such devices, powered by supersonic steam or air ejectors, were exceptionally effective cleaners but were criticized as being high-energy users. A great reduction in the energy consumption of free-jet scrubbers has been accomplished in the last four years, a feat which may seem in contradiction to the “contacting power rule.” An explanation of what is happening in these devices must take into account the effectiveness with which energy and water are utilized. thereby leading one to a somewhat circular definition of “effective contacting power.” The theoretical implication of this analysis is primarily to remind us that there are many paths between two states and some are more energy efficient than others. The practical value is that such analysis generates information which aids in choosing between several design options, a direct benefit of the various free-jet configurations.     

Selection of (bio) indicators to assess effects of freshwater use in wetlands: a case study of s’Albufera de Mallorca, Spain

Parc Natural sAlbufera de Mallorca is an internationally recognised resting area for a wide array of migratory birds, and like most wetlands it has many other ecological functions and socio-economic values. In the catchment, in which the wetland is situated, expanding tourism and intensification of agriculture place much pressure on a limited amount of freshwater. The freshwater supply to the wetland decreased due to water-extraction mainly driven by intensification of agriculture in the catchment. As a result saltwater intrusion increased since 1983–1985. This had considerable impacts on the ecological integrity of the wetland as reflected by changes in the state of the aquatic ecosystem. The distribution of submerged plants, less tolerant of salinity, declined or disappeared, while the distribution of species, known to prefer high salinity increased. As a contribution to the development of monitoring programs and management strategies that address both socio-economic and natural water demand, this article will formulate ecological criteria to assess the natural water demand by selection of (bio)indicators within the aquatic ecosystem.     

Impact of European legislation on marketed pesticides — A view from the standpoint of health impact assessment studies

The very significant impact of European legislation (Directive 91/414/EEC) on the authorization of plant protection products is reviewed herein, which has resulted in withdrawal of 704 active substances (AS) out of 889 assessed so far. The list of currently approved 276 AS includes 194 AS “existing” in the market before 1993 and 82 “new” AS introduced during the last 15 years. Results of toxicity characterization of the approved AS are also summarized, utilizing several well-known databases. Although significant data gaps exist for a rather large part of the approved AS, it is found that 84 AS are positive for at least one health effect (after chronic and/or acute exposure) including carcinogenicity, reproductive and neuro-developmental disorders, as well as endocrine disruption. The toxicity characterization results of this study are compared to those of recent assessments by other organizations (KemI, the Swedish Chemicals Agency, and the Pesticide Safety Directorate of the UK), where interpretation and use is made of AS “cut-off” criteria foreseen in new EU legislation. These studies report a comparatively smaller AS number with positive toxicity characterization. The possibility of some additional AS withdrawal in the near future, combined with the rather small rate of new AS introduction (approx. 5 per year) suggest that the list of approved AS over the next 10–15 years may not change very drastically. Consideration of the above trends is necessary and instructive in evaluating results of existing health impact assessment (HIA) studies, as well as in planning new ones. Due to the very drastic change in the number and type of marketed AS, that took place within the past 8–9 years, it is suggested that new HIA studies (based on epidemiological data after year 2000) should focus on a rather short time frame and, therefore, on appropriate cohort groups, e.g. young children. For the same reason, results of epidemiological studies of the past (involving banned AS) should be carefully interpreted and used with caution.