| 1. |
- Backhaus, Thomas, 1967, et al.
(författare)
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Joint algal toxicity of phenylurea herbicides is equally predictable by concentration addition and independent action.
- 2004
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Ingår i: Environmental toxicology and chemistry / SETAC. - 0730-7268. ; 23:2, s. 258-64
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Backhaus, Thomas, 1967, et al.
(författare)
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Toxicity of a mixture of dissimilarly acting substances to natural algal communities: predictive power and limitations of independent action and concentration addition.
- 2004
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Ingår i: Environmental science & technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 38:23, s. 6363-70
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Tidskriftsartikel (refereegranskat)abstract
- Predictive studies of chemical mixtures are typically based on experiments with single species. To study the applicability of the concepts of independent action (IA) and concentration addition (CA) on a multispecies level, the carbon fixation of natural algal communities under toxicant exposure was studied. The presented study focused on a mixture of six dissimilarly acting substances. Conceptual reasoning as well as empirical evidence from single-species tests suggest that IA is more appropriate for this type of mixture. Nonetheless, the potential of CA was also investigated, to assess whether this concept may be applicable as a reasonable worst case prediction of mixture toxicities also on a community level. IA predicted the experimental EC50 precisely. CA underestimated the EC50 by a factor of only 1.4, although the shape of the predicted concentration-response curve was clearly different from experimental data. Hence, it can be concluded that the applicability of the concepts is not restricted to the level of single species. However, some limitations of both concepts became apparent, when stimulating (hormesis-like) effects were observed fo rtwo of the mixture components. These effects were also seen in the experimental mixture toxicity data but cannot be adequately modeled by either concept.
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| 3. |
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| 4. |
- Dave, Göran, 1945, et al.
(författare)
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The contribution of cobalt and manganese to the acute and chronic toxicity of sediments from Lake Molnbyggen and adjacent lakes around Leksand, Sweden.
- 2004
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Ingår i: Aquatic Ecosystem Health and Management. - : Michigan State University Press. - 1463-4988 .- 1539-4077. ; 7:3, s. 375-386.
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Tidskriftsartikel (refereegranskat)abstract
- A number of studies of pollutants and their effects on the fish fauna of Lake Molnbyggen outside Leksand, Sweden have been focused on leachate from the municipal landfill (Lindbodarna), which is located above the lake. The aim of the present study was to test the toxicity of sediment from Molnbyggen and some adjacent lakes, in order to see if this could explain the causes of the effects on the fish. The sampling sites were selected in co-operation with the project group at the Swedish Environmental Protection Agency to make the results more easily comparable with those from other studies on the fish fauna in the area. Both acute and chronic tests were made with the crustacean Ceriodaphnia dubia, and the sediment samples were equilibrated with standard reference water prior to exposure. The exposures were made under standard conditions in the laboratory to make them more readily comparable between the sampling locations and with previous studies. The effects on survival and reproduction were monitored during 8 days. After that a series of Toxicity Identification Evaluation manipulations of the tested waters were made in order to identify the cause(s) of the toxicity. The results from the Toxicity Identification Evaluation tests pointed towards heavy metals as the cause of toxicity, and the analytical results of heavy metals in the water phase showed that the concentrations of six metals (Cd, Co, Mn, Ni, Pb and Zn) were significantly correlated with toxicity. The concentrations of these metals were also correlated with each other making it hard to separate cause and effect among the metals. However, the concentrations of Cd, Ni, Pb and Zn were below the expected effect concentrations, but the measured concentrations of Co and Mn were high enough to be probable causes of the observed experimental toxicity. There was no indication that lipophilic compounds should have caused these effects. Therefore, the result of this study was rather surprising, showing that heavy metals like cobalt and/or manganese which are not generally considered as environmentally problematic may be of environmental concern. Potential effects of cobalt and manganese could be mediated through the olfactory system, because both these metals have been observed to affect this system in fish. However, the link between such effects and those observed on reproduction in Lake Molnbyggen is vague.
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| 5. |
- Hwang, G.S., et al.
(författare)
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Sediment Toxicity Assessment in the Intertidal Flat Zone of the Middle West Coast of Korea
- 2004
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Ingår i: Kor. J. Env. Hlth.. ; 30:4, s. 347-351
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Tidskriftsartikel (refereegranskat)abstract
- A battery of sediment bioassays was performed for the sediments from the intertidal flat zone along the middle west coast of Korea to assess their potential toxicity. In the bioassayss, three crustaceans, Daphnia magna, Nitocra spinipes, and Hyalella azteca were exposed to 16% sediments (we weight) collected from 14 sites. Immobility (%) was checked as an endpoint after 24- and 48-h exposures to Daphnia magna and after 69-h exposure of Hyalella azteca and Nitocra spinipes. Among the three bioassays, the 48-h Daphnia bioassay showed the most distinct differential sensitivity in relation to sediment contamination, while the Notocra and the Hyalella bioassays failed to show the differential sensitivity properly among the sites classified as polluted. Significantly different levels of immobility (%) were obtained between the sites classified as chemical/nutrient poluted and the sites classified as non-polluted in the Daphnia bioassays, but not in the Nitocra bioassay and the Hyalella bioassay. Some differences of toxic response to the same sediments among bioassays were observed, suggesting that there may be a chemical specificity of response sensitivity to sediment toxicity, due to differences in bioavailability of sediment toxicants among test species.
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| 6. |
- Willander, Magnus, 1948, et al.
(författare)
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Modelling living fluids with the subdivision into the components in terms of probability distributions
- 2004
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Ingår i: Math. Models Methods Appl. Sci.. - : World Scientific. - 0218-2025. ; 14:10, s. 1495-1520
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Tidskriftsartikel (refereegranskat)abstract
- As it follows from the results of C. H. Waddigton, F. E. Yates, A. S. Iberall, and other well-known bio-physicists, living fluids cannot be modelled within the frames of the fundamental assumptions of the statistical-mechanics formalism. One has to go beyond them. The present work does it by means of the generalized kinetics (GK), the theory enabling one to allow for the complex stochasticity of internal properties and parameters of the fluid particles. This is one of the key features which distinguish living fluids from the nonliving ones. It creates the disparity of the particles and hence breaks the each-fluid-component-uniformity requirement underlying statistical mechanics. The work deals with the corresponding modification of common kinetic equations which is in line with the GK theory and is the complement to the latter. This complement allows a subdivision of a fluid into the fluid components in terms of nondiscrete probability distributions. The treatment leads to one more equationthat describes the above internal parameters. The resulting model is the system of these two equations. It appears to be always nonlinear in case of living fluids. In case of nonliving fluids, the model can be linear. Moreover, the living-fluid model, as a whole, cannot have the thermodynamic equilibrium, only partial equilibriums (such as the motional one) are possible. In contrast to this, in case of nonliving fluids, the thermodynamic equilibrium is, of course, possible. The number of the fluid components is treated as the number of the modes of the particle-characteristic probability density. In so doing, a fairly general extension of the notion of the mode from the one-dimensional case to the multidimensional case is proposed. The work also discusses the variety of the time-scales in a living fluid, the simplest quantum-mechanical equation relevant to living fluids, and the non-equilibrium nonlinear stochastic hydrodynamics option. The latter is simpler than, but conceptually comparable to, stochastickinetic equations. A few directions for future research are suggested. The work notes a cohesion of mathematical physics and fluid mechanics with the living-fluid-related fields as a complex interdisciplinary problem.
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| 9. |
- Bockgård, Niclas, et al.
(författare)
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Accuracy of CFC groundwater dating in a crystalline bedrock aquifer: Data from a site in southern Sweden
- 2004
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 12:2, s. 171-183
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium were determined in groundwater in fractured crystalline bedrock at Finnsjon, Sweden. The specific goal was to investigate the accuracy of CFC dating in such an environment, taking potential degradation and mixing of water into consideration. The water was sampled to a depth of 42 m in three boreholes along an 800-m transect, from a recharge area to a local discharge area. The CFC-113 concentration was at the detection limit in most samples. The apparent recharge date obtained from CFC-11 was earlier than from CFC-12 for all samples, with a difference of over 20 years for some samples. The difference was probably caused by degradation of CFC-11. The CFC-12 dating of the samples ranged from before 1945 to 1975, with the exception of a sample from the water table, which had a present-day concentration. Conclusions about flow paths or groundwater velocity could not be drawn from the CFCs. The comparison between CFC-12 and tritium concentrations showed that most samples could be unmixed or mixtures of waters with different ages, and the binary mixtures that matched the measured concentrations were determined. The mixing model approach can be extended with additional tracers.
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