| 1. |
- Arsenie, Irina, et al.
(författare)
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Effects of Gamma Irradiation on an Aquatic Fulvic Acid
- 1991
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Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 233-241
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Bokkapitel (refereegranskat)abstract
- An aquatic fulvic acid was irradiated with gamma radiation from a 60Co-source (dose range 0-48 Mrad), as part of a larger study of the transformation and decomposition of humic substances in natura! aquatic systems. Experiments were performed at two concentrations (1000 mg/l and 100 mg/l) and at various pH-values (2-10). The fulvic acid transformation was studied by monitoring optical density (UV-spectroscopy ), molecular weight distribution (GPC-technique) and total dissolved organic carbon (TOC). A general decrease in TOC with increasing radiation dose was observed: the initial G-value of about 5 decreased with the increasing dose to a minimum value of 0.2-0.3. A simultaneous increase in molecular weight (Mn rose from approximately 2000 to a maximum of about 4000) was observed in the acidic samples (pH 2-4) at a dose below 10 Mrad. Natural background radiation can significantly contribute to the degradation of dissolved humic substances in deep groundwaters, considering the observed G-value for low doses (about 5) and the otherwise high chemical stability of the fulvic acid fraction even after long residence times (103-104 y) in the ground.
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| 2. |
- Asplund, Gunilla, et al.
(författare)
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Soil Peroxidase-Mediated Chlorination of Fulvic Acid
- 1991
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Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 474-483
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Bokkapitel (refereegranskat)abstract
- Humic matter has recently been shown to contain considerable quantities of naturally produced organohalogens. The present study investigated the possibility of a non-specific, enzymatically mediated halogenation of organic matter in soil. The results showed that, in the presence of chloride and hydrogen peroxide, the enzyme chloroperox1dase (CPO) from the fungus Caldariomyces fumago catalyzes chlorination of fulvic acid. At pH 2.5 - 6.0, the chlorine to fulvic acid ratio in the tested sample was elevated from 12 mg/g to approximately 40-50 mg/g. It was also shown that this reaction can take place at chloride and hydrogen peroxide concentrations found in the environment. An extract from spruce forest soil was shown to have a measurable chlorinating capacity. The activity of an extract of 0.5 kg soil corresponded to approximately 0.3 enzyme units, measured as CPO activity. Enzymatically mediated halogenation of humic substances may be one of the mechanisms explaining the w1despread occurrence of adsorbable organic halogens (AOX) in soil and water.
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| 3. |
- Grimvall, Anders, et al.
(författare)
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Phytotoxic Substances in Runoff from Forested Catchment Areas
- 1991
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Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 397-406
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Bokkapitel (refereegranskat)abstract
- Runoff from different catchment areas in southem Sweden was tested in a root bioassay based on solution cultures of cucumber seedlings. Water samples from agricultural catchment areas produced no signs at all or only weak signs of inhibited root growth, whereas several water samples from catchmcnt areas dominated by mires or coniferous forests produced visible root injuries. The most severe root injuries (very short roots, discolouration, swelling of root tips and lack of root hairs) were caused by samples from a catchment area without local emissions and dominated by old stands of spruce. Fractionation by ultrafiltration showed that the phytotoxic effect of these samples could be attributed to organic matter with a nominal molecular-weight exceeding 1000 or to substances associated with organic macromolecules. Experiments aimed at concentrating phytotoxic compounds from surface water indicated that the observed growth inhibition was caused by strongly hydrophilic substances. Previous reports on phytotoxic, organic substances of natura! origin have emphasized interaction between plants growing close together. The presence of phytotoxic substances in runoff indicates that there is also a large-scale dispersion of such compounds.
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| 4. |
- Nordén, Maria, et al.
(författare)
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Interaction of Strontium and Europium with an Aquatic Fulvic Acid Studied by Ultrafiltration and lon Exchange Techniques
- 1991
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Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 297-303
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Bokkapitel (refereegranskat)abstract
- The complexation of an aquatic fulvic acid, FA, with Sr2+ and Eu3+ was studied using an ultrafiltration technique and an ion exchange distribution method. The total amount of bound metal (Sr2+ and Eu3+) was measured as a function of pH at low meta! concentrations (trace levels) and constant FA concentration. In the Sr-FA system the bound meta! fraction increased slightly with pH, and the values obtained from the two experimental techniques were comparable. For Eu-FA, according to the ultrafiltration data, the fraction of bound meta! ion was relatively insensitive to pH changes, whereas values from the ion exchange measurements showed a strong and positive dependence on pH. The results are discussed in the light of possible intrinsic problems of the two methods.
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| 5. |
- Pettersson, Catharina, et al.
(författare)
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Dating of groundwaters by ¹⁴C-analysis of dissolved humic substances
- 1991
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Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidleberg New York : Springer. - 3540537023 ; , s. 135-141
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Bokkapitel (refereegranskat)abstract
- Fulvic acids of the DOC of five deep (139-409 m) groundwaters were recovered (adsorption on DEAE-cellulose) and used for age determination (14C determined by accelerator mass spectrometry), and compared with fulvic acids recovered from a shallow groundwater and a surface water. The composition of the seven different fulvic acids was similar, despite variations in hydrochemical conditions and residence times, indicating a high stability of this molecular weight fraction. The ages calculated from the 14C-content of the fulvic acid fraction (600 to 10000 y) are less than the ages indicated from analyses of the dissolved carbonate (data available for three sites). Using a fraction of the DOC with high stability (like the fulvic acid fraction) as a 14C-source when assessing the ages of subsurface waters, appears to be superior to using dissolved carbonate.
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