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Humic Material (humic + material)
Selected AbstractsEffect of humic material on the bacterioplankton community composition in boreal lakes and mesocosmsENVIRONMENTAL MICROBIOLOGY, Issue 5 2005Kaisa Haukka Summary The bacterioplankton community composition in two Finnish forest lakes with different content of humic substances was studied by denaturing gradient gel electrophoresis (DGGE) and sequencing of the major bands. The same dominant bacterial phylotypes were detected in the bacterioplankton communities of clear-water Lake Ahvenlammi and humic Lake Sammalisto. For 4 years, in every water layer, Actinobacteria was the dominant and Verrucomicrobia the second most common phylum. In the hypolimnion, other dominant phyla were also found. We set up a mesocosm experiment to assess the effect of a sudden load of allochthonous humus extract to the bacterioplankton community composition. Changes in the bacterial communities were followed in four control and four humus extract-added mesocosms for 50 days. In the humic mesocosms the phylotypes of allochthonous Proteobacteria arriving with the humus extract were initially prevalent but disappeared during the first weeks. After this the Actinobacteria -dominated communities resembled the bacterioplankton communities of the control mesocosms and Lake Ahvenlammi. Towards the end of the experiment the community patterns in all the mesocosms started to change slightly because of erratic occurrence of new proteobacterial phylotypes. Thus the effects of a sudden load of allochthonous humic material and bacteria to the bacterioplankton community composition were transient. [source] Citrate-mediated increase in the uptake of weathered 2,2-bis(p -chlorophenyl)1,1-dichloroethylene residues by plantsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2002Jason C. White Abstract Experiments were conducted to determine the ability of citrate to enhance the plant uptake of weathered 2,2-bis(p -chlorophenyl) 1,1-dichloroethylene (p,p,-DDE) from soil. Plots containing three rows of clover, mustard, hairy vetch, or rye grass were constructed in soils containing p,p,-DDE. On 11 occasions, the rows of each crop received water or sodium citrate (0.005 or 0.05 M). For each crop, there were significant reductions in p,p,-DDE concentration in the soil fractions (near root and rhizosphere) closely associated with the plant versus bulk soil. The roots of each crop accumulated 2 to 5 times more of the weathered contaminant (dry wt) than present in the bulk soil. Citrate (0.05 M) increased the concentration of p,p,-DDE in the roots of clover, mustard, and hairy vetch by 39% compared with vegetation that received water. In batch desorption studies, the release of weathered p,p,-DDE was significantly greater in the presence of 0.05 M citrate than in water. Citrate increased the extracted aqueous concentrations of five metal ions (Al, Fe, Ca, K, Mn) from soil by five- to 23-fold over distilled water. We hypothesize that citrate physically disrupts the soil through chelation of structural metal ions and release of bound humic material, facilitating p,p,-DDE availability and uptake by plants. [source] Phase distribution of synthetic pyrethroids in runoff and stream waterENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2004Weiping Liu Abstract Synthetic pyrethroids (SPs) are a group of hydrophobic compounds with significant aquatic toxicity. Their strong affinity to suspended solids and humic materials suggests that SPs in natural surface water are distributed in solid-adsorbed, dissolved organic matter (DOM)-adsorbed, and freely dissolved phases. The freely dissolved phase is of particular importance because of its mobility and bioavailability. In the present study, we used solid-phase microextraction to detect the freely dissolved phase, and we evaluated the phase distribution of bifenthrin and permethrin in stream and runoff waters. In stream water, most SPs were associated with the suspended solids and, to a lesser extent, with DOM. The freely dissolved phase contributed only 0.4% to 1.0%. In runoff effluents, the freely dissolved concentration was 10% to 27% of the overall concentration. The predominant partitioning into the adsorbed phases implies that the toxicity of SPs in surface water is reduced because of decreased bioavailability. This also suggests that monitoring protocols that do not selectively define the freely dissolved phase can lead to significant overestimation of toxicity or water-quality impacts by SPs. [source] Modeling pentachlorophenol bioavailability and bioaccumulation by the freshwater fingernail clam Sphaerium corneum using artificial particles and humic acidsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Noemi R. Verrengia Guerrero Abstract The uptake of anthropogenic chemicals by benthic bivalves may occur through the water phase and also by the ingestion of particles from both the suspended matter and bottom sediments. Many chemicals sorb to sediments and, subsequently, are released in the digestive tract of animals. The assessment of sediment-bound chemicals has been difficult because of the complexity of the association between these chemicals and natural particles. To simplify this complexity, we previously devised a test system using artificial particles with known chemical structures. In the present work, we improved this experimental design by adding humic materials as a source of organic matter. Bioassays were conducted by exposing the fingernail clam Sphaerium corneum to sublethal levels of pentachlorophenol (PCP) in the presence or absence of the artificial particles, treated with or without a commercial preparation of humic acids. The results showed that the bioavailability and bioaccumulation could be explained on the basis of the interactions of PCP with the active groups and/or the backbone of the resins, both in systems with or without humic acids. This model may constitute a useful approach to modeling and predicting the uptake and accumulation of chemicals bound to natural sediments. [source] Free radicals, antioxidants, and soil organic matter recalcitranceEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2006D. L. Rimmer Summary Highly reactive, and potentially damaging, free radicals are readily generated in our oxygen-rich environment, and are ubiquitous in biological systems. However, plants and animals have evolved protection against them with a range of antioxidant molecules, such as vitamins C and E, many of which are phenolic compounds. These stop the destructive chain reaction of free radical formation by being transformed into unreactive, stable free radicals. The biodegradation of food involves oxidation by free radicals, and is retarded by antioxidants. Similarly, the biodegradation of plant residues in soils involves free radicals; so the questions arise: (i) do soils have antioxidants, and (ii) what function might they have? The evidence suggests that they probably do have antioxidants. First, plant and animal remains added to soils will contain antioxidants. These are likely to persist for a time, particularly tannins, which are polyphenolic compounds with known antioxidant properties and which are relatively resistant to degradation. Second, studies using electron spin resonance spectroscopy have shown that humic materials contain stable semiquinone free radicals, and that their concentration increases as humification progresses. These semiquinone species are most likely to be derived from the reaction of phenolic compounds with reactive radicals. If this is the case, the phenolics are acting as antioxidants, because they are scavenging the reactive free radicals and terminating the oxidative chain reaction responsible for soil organic matter (SOM) degradation. Thus the soil's antioxidant capacity could control the rate of breakdown of organic matter in the more labile pools and could provide a chemical mechanism for the recalcitrance of SOM. Current available evidence for the nature of the recalcitrant pool in SOM is discussed in the light of this hypothesis, and the experimental approaches necessary for testing it are outlined. [source] | ||||||||||