Critical loads for Finnish lakes: comparison of three steady-state models

Three simple steady-state water-chemistry models are used to calculate critical loads of sulfur for lakes in Finland. Because of the high concentrations of organic matter in Finnish lakes, the influence of organic anions on the calculation of critical loads has been given special attention. The first two methods are well known ion-balance methods which have been used in many previous lake-acidification studies. The third method, developed for this study, includes the numerical solution of equilibrium equations for organic anions, inorganic carbon species and inorganic monomeric aluminum. The original pH and aluminum concentration of the lakes are estimated with this model, and a method to estimate the original acid neutralizing capacity (ANC) by simulating a Gran-titration is also tested on the lake data. Uncertainty in the predictions is estimated by varying the most critical model parameters.     

An introduction to critical loads

The critical loads approach to emission controls of gaseous pollutants is a concept with a short but eventful history. Despite difficulties with definitions and agreed values, its acceptance within the UN-ECE Convention on Long Range Transboundary Air Pollution has provided the impetus for developing methods to put critical loads to a practical use-the revision of the UNECE emission protocols for sulphur and nitrogen. Methodologies first focus upon quantifying a pollutant threshold at which harmful effects occur on particular sensitive receptors (usually biological species). This threshold is known as the critical load for deposited pollutants, and as the critical level for gaseous pollutants acting on receptors. To calculate a critical load, biological effects are usually 'translated' to critical chemical values, e.g. harmful effects on fish 'translate' to alkalinity or aluminium concentrations in water; thus, critical load calculations may be based upon the chemistry of a system. Such calculations may be performed using simple, steady-state models, whilst the use of more complex, dynamic models provides an insight into the past and future trends. Maps of critical loads can be drawn using calculated values, and maps of pollutant deposition data will then show geographical areas where critical loads are exceeded. Spatial emission-deposition models can identify sources contributing to areas of excess loads and quantify necessary emission reductions. Optimization procedures applied to such models can derive abatement strategies related to economic costs and critical load effects. The critical load calculations may also be used to underpin the setting of target loads; these are pollutant loads, determined by political agreement, which take account of social, economic and political considerations.     

Effect of nickel on some aspects of protein metabolism in the gill and kidney of the freshwater fish, Cyprinus carpio L

Nickel has an adverse effect on some aspects of protein metabolism of the freshwater fish, Cyprinus carpio. The main changes observed were: (a) Decrease in soluble, structural and total proteins, AlAT and AAT activities with an increase in the levels of free amino acids, protease and GDH activities and ammonia in the gill and kidney at 1, 2, 3, and 4 days of exposure to a lethal concentration, 40 mg litre(-1) of nickel; (b) Increase in soluble, structural and total proteins, free amino acids and the activities of protease, AlAT, AAT and GDH with a decrease in ammonia and urea in these organs at 1, 5, 10 and 15 days of exposure to sublethal concentration, 8 mg litre(-1); (c) The magnitude in these changes increased over time with both concentrations of the metal, and was more marked in gill than in kidney.     

Real-world vehicle emissions: a summary of the tenth coordinating research council on-road vehicle emissions workshop

The Coordinating Research Council (CRC) held its tenth workshop in March 2000, focusing on results from the most recent real-world vehicle emissions research. In this paper, we summarize the presentations from researchers who are engaged in improving our understanding of the contribution of mobile sources to emission inventories. Participants in the workshop discussed efforts to improve mobile source emission models and emission inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles, new methods for measuring mobile source emissions, improvements in vehicle emission control systems (ECSs), and evaluation of motor vehicle inspection/maintenance (I/M) programs, as well as topics for future research.     

Surfactant enhanced recovery of tetrachloroethylene from a porous medium containing low permeability lenses. 1. Experimental studies

A matrix of batch, column and two-dimensional (2-D) box experiments was conducted to investigate the coupled effects of rate-limited solubilization and layering on the entrapment and subsequent recovery of a representative dense NAPL, tetrachloroethylene (PCE), during surfactant flushing. Batch experiments were performed to determine the equilibrium solubilization capacity of the surfactant, polyoxyethylene (20) sorbitan monooleate (Tween 80), and to measure fluid viscosity, density and interfacial tension. Results of one-dimensional column studies indicated that micellar solubilization of residual PCE was rate-limited at Darcy velocities ranging from 0.8 to 8.2 cm/h and during periods of flow interruption. Effluent concentration data were used to develop effective mass transfer coefficient (Ke) expressions that were dependent upon the Darcy velocity and duration of flow interruption. To simulate subsurface heterogeneity, 2-D boxes were packed with layers of F-70 Ottawa sand and Wurtsmith aquifer material within 20-30 mesh Ottawa sand. A 4% Tween 80 solution was then flushed through PCE-contaminated boxes at several flow velocities, with periods of flow interruption. Effluent concentration data and visual observations indicated that both rate-limited solubilization and pooling of PCE above the fine layers reduced PCE recovery to levels below those anticipated from batch and column measurements. These experimental results demonstrate the potential impact of both mass transfer limitations and subsurface layering on the recovery of PCE during surfactant enhanced aquifer remediation.     

Determination of source contributions to ambient PM2.5 in Kaohsiung, Taiwan, using a receptor model

Ambient particulates of PM2.5 were sampled at three sites in Kaohsiung, Taiwan, during February and March 1999. In addition, resuspended PM2.5 collected from traffic tunnels, paved roads, fly ash of a municipal solid waste (MSW) incinerator, and seawater was obtained. All the samples were analyzed for twenty constituents, including water-soluble ions, organic carbon (OC), elemental carbon (EC), and metallic elements. In conjunction with local source profiles and the source profiles in the model library SPECIATE EPA, the receptor model based on chemical mass balance (CMB) was then applied to determine the source contributions to ambient PM2.5. The mean concentration of ambient PM2.5 was 42.69-53.68 micrograms/m3 for the sampling period. The abundant species in ambient PM2.5 in the mass fraction for three sites were OC (12.7-14.2%), SO4(2-) (12.8-15.1%), NO3- (8.1-10.3%), NH4+ (6.7-7.5%), and EC (5.3-8.5%). Results of CMB modeling show that major pollution sources for ambient PM2.5 are traffic exhaust (18-54%), secondary aerosols (30-41% from SO4(2-) and NO3-), and outdoor burning of agriculture wastes (13-17%).     

ESF Workshop

Dioxin and PCB monitoring programs for food and feeding stuff in most countries of the world, including many European Countries are currently inadequate. Better control of food production lines and food processing procedures is needed to minimize entry of dioxin to the food chain and will help to avoid dioxin contamination accidents. This would also improve the ability to trace back a possible contamination to its source. European guidelines for monitoring programs should be established to ensure comparable and meaningful results. These guidelines should define the minimum requirements for the design of monitoring programs, analytical methods, and quality assurance. Though data from Northern Europe shows that the general population exposure to dioxin and PCB has decreased during the last ten years these compounds continue to be a risk of accidental contamination of the food chain. The most prominent recent example is the Belgian dioxin contamination of feeding stuff in 1999. The Belgian dioxin contamination was not detected due to dioxin monitoring programs but by their direct biological effects seen in animals. Four other cases of dioxin contamination have been detected in Europe since 1997 due to local monitoring programs. One of them (citrus pulp pellets 1998) was in a much larger scale than the Belgian dioxin contamination. The general population's exposure to dioxins and PCBs is still in the same range (1-4 pg WHO-TEQ/kg body weight and day) as the recently revised WHO tolerable daily intake (TDI). There is concern that short-term high level exposure to dioxins, furans, and PCB may cause biological effects on the human fetal development and further research is required. Further actions to control sources building on considerable advances already made in many countries may need to be supplemented by measures to prevent direct contamination of feeding stuff or food to reduce general population exposure further.     

Transport of volatile compounds in porous media in the presence of a trapped gas phase

The presence of an immobile gaseous phase in an otherwise-saturated porous medium affects the transport of volatile compounds. The linear theory of partitioning tracers suggests that a volatile tracer introduced into such a system should be retarded with a constant retardation factor. Using high concentrations, however, the saturation of the gaseous phase will change as an effect of the tracer test itself. Competitive gas transfer among all volatile compounds and the change of saturation may lead to tracer concentrations that are temporarily higher than those injected. We analyze the system in the framework of the coherence theory by Helfferich [Soc. Pet. Eng. J. 21 (1) (1981) 51]. The governing equations are formulated as functions of total concentration, i.e., the mass of solutes in all phases per pore volume. Neglecting dispersion and mass-transfer kinetics, we derive the characteristic form of the resulting system of hyperbolic equations. In a system with N volatile compounds, a variation of the concentrations splits up into N waves, each traveling with its own characteristic velocity. If the presence of a gaseous phase is sustained, one wave will be a standing one. We perform numerical model calculations for tracers with various Henry's law coefficients and show that the results agree with the semi-analytical solution obtained by coherence theory.     

Management, disposal and recycling of waste industrial organic solvents in Hong Kong.

An attempt has been made to establish a mass balance of industrial organic solvents in Hong Kong. It is estimated that only a small portion, less than 4%, of all the organic solvents consumed in Hong Kong are collected as waste solvents and properly treated, while the remainder are used either in the formulation of solvent containing products, or are lost to the environment through vapour emissions, leaks and spills, or dumped illegally. It was found that solvent recycling has been a common practice in some industries but the existing level of solvent recycling in Hong Kong is difficult to estimate. About 87.4% of all the waste organic solvents disposed of at the licensed facilities are potentially recyclable although whether they can be recycled in practice depends on many factors. Examples of existing waste organic solvent management and recycling practices from selected industries in Hong Kong are presented. The economic feasibility of current and future potential recycling systems is evaluated for a few selected cases. An integrated waste organic solvent management strategy is proposed to minimize adverse impacts of organic solvents to the environment and human health.