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PCDD/F formation on fly ashes, the effect of inhibitors was studied by this technique. While no inhibitory action was observed for triethylamine, ethanolamine was shown to act as a very efficient inhibitor, by blocking the active sites of copper surfaces. At this point it is important to draw attention to the differences between the carefully prepared surfaces investigated in this study, and the highly heterogeneous fly ash in the complex environment of an incinerator. Details of the phenomena observed in the laboratory cannot be transferred to the technical plant, and we cannot exclude the possiblity that other modes of inhibitory action are important in the incinerator environment. However, the relevant results on the inhibition of dioxin formation obtained in the pilot plant are consistent with the mechanisms proposed in this study.

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The EU-funded research project ALARM will develop and test methods and protocols for the assessment of large-scale environmental risks in order to minimise negative human impacts. Research focuses on the assessment and forecast of changes in biodiversity and in the structure, function, and dynamics of ecosystems. This includes the relationships between society, the economy and biodiversity.

Cr3+_28_Na^_14eluded to a large extent by the membrane, as shown by data collected when the test solution was dialyzed against distilled water (Table IV). The separation factors indicate that the transfer of species containing the solution cations does not significantly influence the transfer of N03~a cross the membrane in the acid solutions studied. The HF system behaved analogously. Summary and ConclusionsThis study investigated the chemical speciation and the dialysis behavior of concentrated acid solutions commonly used in industrial processes. A speciation model was developed that could predict measured F" concentrations with excellent accuracy (r2 = 0.94) over an ionic strength range of 0.5-6 M, a [F~] range of ^-"1 M, and in varied solution species matrices. An important component of that model was the calculation of the liquid junction potential, which must be taken into account if electrodes that have liquid junctions are used for collecting data in these systems.Based on the chemical speciation model results, transfer rates of acid are related via Fick's law to differences across the membrane in the HN03 or HF concentrations. Attempts to correlate the transfer rates to the concentration gradients of individual ionic species (e.g., H+, F~, or N03") were unsuccessful, indicating that the neutral acid species are the ones controlling transport through the membrane.Conventional wisdom has it that the type and number of charged groups in the membrane are critical variables that must be considered in evaluating the performance of ion-exchange membranes. It seems likely that membrane charge does affect the diffusion coefficients of individual species and hence the separation factors among species.However, once those coefficients are established, the performance of at least the membrane investigated can be interpreted on the basis of passive diffusion, without considering possible specific interactions between the ion-exchange sites in the membrane and the diffusing species. In other words, interactions in the membrane may affect the numerical values of the diffusion coefficients, but they do not require any change in the fundamental analysis.The products [H+] [N03~] and [H+][F~] are linearly related to [HN03] and [HF], respectively, via their stability constants, and with the appropriate transfer coefficients these products can also be used to model the experimental data in the framework of Donnan equilibrium.

Photosynthesis-inhibiting phenylurea derivatives, such as diuron, are widely used as herbicides. Diuron concentrations clearly exceeding the predicted-no-effect concentration have been regularly measured in European freshwater systems. The frequently observed exposure to mixtures of phenylureas additionally increases the hazard to aquatic primary producers. Fluctuating numbers and concentrations of individual toxicants make experimental testing of every potential mixture unfeasible. Thus, predictive approaches to the mixture hazard assessment are needed. For this purpose, two concepts are at hand, both of which make use of known toxicities of the individual components but are based on opposite mechanistic suppositions: Concentration addition is based on the idea of similar mechanisms of action, whereas independent action assumes dissimilarly acting mixture components. On the basis of pharmacological reasoning, it was therefore anticipated that the joint algal toxicity of phenylurea mixtures would be predictable by concentration addition. Indeed, we could demonstrate a high predictive power of concentration addition for these combinations. Surprisingly, however, the opposite concept of independent action proved to be equally valid, because both concepts predicted virtually identical mixture toxicities. This exceptional case has previously been derived from theoretical considerations. Now, the tested phenylurea mixtures serve as an example for the practical relevance of this situation for multicomponent mixtures.