Displays

The organic matter is the most important component of soil material, which determines most soil properties. Among humic substances, humin fraction has been the least studied to date, although it usually constitutes over half of their composition. This is probably due to the fact, that humin fraction has highly hydrophobic properties and is insoluble at all pH values, which makes its isolation much more difficult, compared to humic (HA) and fulvic (FA) acid fractions. In addition, humin fraction forms very stable humic-clay complexes with mineral part of the soil (Stevenson 1994), which cannot be destructed during humic substances extraction. According to the literature, the methods of humin fraction isolation can be divided into two main groups: (1) extraction by different organic solvents, and (2) isolation by extraction of HA and FA followed by digestion of mineral soil components. Nevertheless, each of these methods has different limitations.

We investigated some modifications of the latter method, obtaining humin fraction from eight mollic horizons of Chernozems and Phaeozems, which differed in their physico-chemical properties.

The first step was to separate HA and FA according to IHSS method described by Swift (1996), however we adopted different shaking procedure. To asses differences, each supernatant obtained was analyzed for the carbon content concentration, which corresponded to HA and FA extracted.

HA and FA free residue was then digested to reduce the content of mineral components. We used several digestion with 10% HF/HCl , as higher concentrations of HF can result in structural alteration of the organic compounds (Hayes et al. 2017). To find the optimal time of the procedure, the ash content was determined following each digestion stage. After the HF/HCl treatment, the residue was rinsed with 10% HCl to eliminate secondary minerals. The residue was washed with distilled water until the neutral pH, then transferred to dialysis membranes and dialyzed with distilled water until a negative Cl⁻ test with AgNO₃. Afterwards the humin fraction was freeze dried. 

Finally, obtained humin fraction contained various ash content, ranged from 6 to 30%, depending on the soil. The conducted test indicated that: (1) the concentration of carbon in supernatant considerably increased as shaking time was extended to 20 hours, and (2) longer than 4 weeks digestion with HF/HCl did not affect the reduction of the ash content of the humin fraction obtained.    

Literature

Hayes M.H.B., Mylotte R., Swift R.S. 2017. Humin: Its Composition and Importance in Soil Organic Matter. In: Sparks D.L. (ed) Advances in Agronomy, Vol. 143, Academic Press, Burlington, 47–138.

Stevenson F.J. 1994. Humus Chemistry; Genesis, Composition, Reaction. 2nd ed. John Wiley & Sons., New York.

Swift R.S. 1996. Organic matter characterization. In: Sparks, D.L., et al. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods - Soil Science Society of America, Book Series no 5,  1011-1069.

Acknowledgements

This work was supported by the National Science Center (NCN) Poland (project No 2018/31/B/ST10/00677 “Chemical and spectroscopic properties of soil humin fraction in relation to their mutual interaction with pesticides").

How to cite: Weber, J., Jamroz, E., Kocowicz, A., Debicka, M., Ukalska-Jaruga, A., Mielnik, L., Bejger, R., Jerzykiewicz, M., Bekier, J., and Ćwieląg-Piasecka, I.: Isolation of the humin fraction from soil: preliminary comments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3110, https://doi.org/10.5194/egusphere-egu2020-3110, 2020.

The use of pesticides significantly influences the efficiency of agriculture production, but at the same time, their extensive and widespread use, raises serious concerns regarding the release of harmful substances into the environment [1,2]. The fate of pesticides in soil depends on many factors related mainly to the physico-chemical properties of these compounds as well as content and quality of organic matter [3]. Humin as the predominant fraction of organic matter, may significantly determine the behavior and transformations of pesticides in soil [5]. Therefore, the aim of this review was to present the state of the art of humin-pesticides mutual interactions.

Sorption-related studies showed that humin has dissimilar binding strengths with pesticides [4,5]. According to Pignatello [7], the sorption selectivity by humin has a number of potential causes: (1) preference for particular microdomains within fractions that are envisioned to segregate on the basis of functional group identity (aromatic, paraffinic, carbohydrate domains); (2) preference based on strong functional group interactions, such as hydrogen bonding and (3) preference based on the nature of the thermodynamic physical state of humin, namely the configurations and conformations of the molecules and strands at microstructural level.

Moreover, humin exhibits potentially different accumulation capacities for xenobiotics. Wang et al. [9] explained these relations with the limited accessibility to microporous domains of humin matrices for the larger-molecular-weight particles. The authors [9] observed a lower adsorbed mass of spatially developed compounds compared to compounds with small diameters. This process is probably most likely related to the structural rearrangement of the humin matrix under slow diffusion into microporous domains pronounced with the adsorption of large molecular weight compounds. Additionally, Pignatello [7] as well as Schaumann [4,5] indicated that the humin surface is covered with various polar and non-polar functionalities, which may efficiently interact with pesticides by van der Waals forces, hydrophobic attraction, hydrogen bonding, charge transfer or ligand exchange processes. Nevertheless, the chemical properties of pesticides as well as their coexistence with other chemical compounds i.e.: surfactants, coagulants, decomposition inhibitors and others [8] can modify the interactions of pesticides with humin in natural soil environment.

Literature:

[1] FAO, ITPS Global Assessment of the Impact of Plant Protection Products on Soil Functions and Soil Ecosystems. FAO, Rome 2017, 40 pp.

[2] Silva, V.; Mol, H.; Zomer, P.; Tienstra, M.; Ritsema, C.J.; Geissena, V. Sci. Total. Environ.  2019, 653, 1532–1545.

[3] Stolte, J.; Tesfai, M.; Øygarden, L.; Kværnø, S.; Keizer, J.; Verheijen, F.; et al. Soil Threats in Europe: Status, Methods, Drivers and Effects on Ecosystem 4 Services, 2016, Report

[4] Stevenson F. 1994, John Wiley & Sons, New York

[5] Schaumann G. 2006a, J Plant Nutr Soil Sci 169:145–156

[6] Schaumann G. 2006b, J Plant Nutr Soil Sci 169:157–167

[7] Pignatello J. 2012,  J Soils Sediments 12:1241–1256

[8] Ehlers, G.; Loibner, A. 2006, Environ. Pollut. 141, 494-512

[9] Wang X, Guo X, Yang Y, Tao S, Xing B. 2011, Environ Sci Technol 45:2124–2130

Acknowledgement: The studies were supported from the National Science Centre project no. 2018/31/B/ST10/00677 “Chemical and spectroscopic properties of soil humin fraction in relation to their mutual interaction with pesticides”

How to cite: Ukalska-Jaruga, A., Bejger, R., Ćwieląg-Piasecka, I., Weber, J., Jamroz, E., Debicka, M., Mielnik, L., Jerzykiewicz, M., Bekier, J., and Kocowicz, A.: Interaction of soil humin fraction with pesticides - a review, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4609, https://doi.org/10.5194/egusphere-egu2020-4609, 2020.

Mining activities generate a great deal of particulate emissions and waste slag enriched in heavy metals that contaminate the surrounding, that is soil, water and air. Such effects are particularly serious and pose a severe ecological and human health risk, mainly if smelters are located in the proximity of urban areas. This is the case regarding the Kosovo, where from the 1930s the British company "Seltrust" founded Trepca Mining & Metallurgical Complex, causing a high level of pollution especially in the area of Mitrovicë, northern Kosovo. Two soils, A and B, have been sampled from two different sites in Mitrovicë municipality, showing a total content of Pb and Zn, respectively, of 2153 and 3087 mg kg^-1, and 3214 and 4619 mg kg^-1. A pot experiment was carried out aiming to understand the phytoremediation potential of two selected non-food crops (Sorghum bicolor L. Moench and Brassica napus cv. Westar) chosen for their economic importance and heavy metal accumulation capacities. Sorghum and canola plants were cultivated in polluted soils A and B. For both plant species, the accumulation of heavy metals proved to be higher in the roots. Indeed, in order to obtain an adequate phytoextraction, it is required that the metals be moved to the epigeal part of the plants, and plants with bioconcentration factor (BCF) and translocation factor (TF) values < 1 are not considered suitable for phytoextraction. The results obtained in this study indicate that, although canola was quite effective in translocating metals from roots to aerial parts, both sorghum and canola are not suitable for phytoextraction since their coefficient values were < 1. Anyway, both plants, especially canola ones, grew up in presence of high level of Pb and Zn pollution, thus they could be used for phytostabilisation process. Actually, the Tolerance Index (TI) values of the sorghum and canola clearly suggest, under the experimental conditions used in this study, a better performance of the canola in tolerating the presence of Pb and Zn in the soil, even if in soil B was not found the same efficiency shown by the same plants grown in soil A. Probably, since soil B has an absolute higher content of Pb and Zn and a lower pH, the availability of both metals is slightly higher, which may have induced in the plants that grow there a more intense condition of stress. This study shows that canola, unlike sorghum, can be an ideal choice for phytostabilization, and its breeding can represent an effective alternative to food crop. 

How to cite: Miano, T., Voca, H., Piscitelli, L., Malerba, A. D., Mondelli, D., and D'Orazio, V.: The phytoextraction potential of selected vegetable plants on Kosovo contaminated soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6844, https://doi.org/10.5194/egusphere-egu2020-6844, 2020.

Human activities are negatively affecting ecosystems through the erosion and impoverishment of natural resources. Considering soil, global warming and unsustainable agricultural practices are reducing soil organic matter with consequent loss of fertility. An issue of major concern is also the soil pollution by organic and inorganic compounds affecting soil ability to generate ecosystem services. Polycyclic aromatic hydrocarbons are a large group of pollutants, made of two or more aromatic rings, widespread in the environment, soil included, and extremely toxicity for human and environmental health. Polycyclic aromatic hydrocarbons persistence in soil is an issue great concern that could be effectively faced by microbial remediation techniques.

In this work we studied the remediation of pyrene polluted soil through two parallel tests: bioremediation and biostimulatin techniques. The first involves inoculation into soil of exogenous microorganisms, in our case Trichoderma harzianum, whereas the latter was aimed at promoting the degrading ability of endogenous microorganisms. Moreover, in order to sustain microorganisms growth, we incorporated olive husk biochar in the two tested bioremediation systems.

Biochar is currently considered an excellent soil conditioner and its incorporation into soil seems to promote PAHs adsorption and to interact positively with soil microorganisms. Biochar is a carbonaceous matrix produced through thermal processing of organic biomasses at high temperature and at very low oxygen partial pressure. Here we converted olive husks, that is a potentially toxic by-product of olive oil extraction, by slow pyrolysis process with the aim of deprived this waste biomass of its noxious characteristics.

Soil samples were spiked with 50 ppm of pyrene, biochar was incorporated at a concentration of 13 g·kg^–1 d.w. of soil and endogenous microbial growth, T. harzianum growth and microbial pyrene-degradation activity were measured weekly up to 28 days.

Pyrene concentration was reduced of approximately 70% in 28 days in both bioaugmentation and biostimulation remediation systems. T. harzianum did not display a distinctive ability in degrading pyrene and partially inhibited the endogenous soil microflora from degrading pyrene. Olive husks biochar application did not limited pyrene bioavailability or neither affected microbial pyrene degrading activity. However, our results underline that olive husks biochar increases T. harzianum growth and stimulates soil endogenous microorganisms.

How to cite: Piscitelli, L., Malerba, A. D., Mezzapesa, G. N., Dumontet, S., Mondelli, D., Miano, T., and Bruno, G. L.: Olive husks biochar application in microbial remediation of pyrene polluted soil: a possible win-win solution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7044, https://doi.org/10.5194/egusphere-egu2020-7044, 2020.

Soil contamination with arsenic in historical mining sites is a matter of considerable environmental concern, as the concentrations of As in those soils are locally as high as thousands mg/kg. Some of soils, particularly those affected in the past by tailings that were released from impoundments, are located in floodplains and used as grasslands. Those lands are periodically flooded, and the frequency and duration of flooding will probably increase in the future with changing climatic conditions. Reducing environment that develops upon soil flooding can cause a release of As from soil solid phase. This is an inherent effect of reductive dissolution of amorphous and crystalline iron hydroxides that are the main hosting components for metalloids. Changing redox conditions affect also the speciation of As in pore water, influencing its toxicity to soil biota. Moreover, soil fertilization with inorganic fertilizers that contain phosphates, or with organic fertilizers such as cattle manure, can accelerate As release from iron hydroxides, mainly via competitive desorption. The effects of all those processes are highly dependent on soil properties and still require a close examination.

Three kinds of soil material, containing up to 8000 mg/kg As, were collected from the tailings-affected floodplain of the Tująca river in Złoty Stok, a historical As mining centre. A laboratory incubation experiment with fertilized and non-fertilized soils was carried out to examine the changes in As concentrations in soil pore water, as well as to assess pore water ecotoxicity, determined in standard bioassays, including Microtox and Phytotox. Soil flooding resulted in a rapid release of As from soil solid phase. As concentrations in soil pore water in all samples exceeded 10 mg/L after a 2-day incubation, and tended to increase slowly with time. In some cases, after the 270-day incubation, As concentrations in pore water reached several hundred mg/L. Those effects resulted in a very high ecotoxicity of pore water, caused lethal effects to bacteria and springtails, and impeded plant germination. Soil amendment with manure was a factor that significantly enhanced those effects. The factors responsible for various effects that were reported from three soils were discussed.

How to cite: Szopka, K., Karczewska, A., Dradrach, A., and Gałka, B.: The effects of waterlogging on the solubility of arsenic and ecotoxicity of soil pore water in non-fertilized and fertilized soils in historical mining sites., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10576, https://doi.org/10.5194/egusphere-egu2020-10576, 2020.

Humic substances (HS) represent fascinating heterogeneous mixture of natural molecules, which possess a high potential to interact with various substances e.g. metals, surfactants, dyes, pesticides. This beneficial property allows their further utilization as the reactive part of sorbents with possible applications in remediation processes of soils and waste waters treatment plants. Surfactants represent a group of substances, which are artificially introduced in the nature by human driven applications causing the undesirable foaming of waters and enhancing the solubility of hydrophobic organic pollutants such as highly toxic polycyclic aromatic hydrocarbons. The present work is focused on the study of colloidal aspects of interactions between selected representatives of surfactants and humic substances, as the example of a promising sorbent and flocculant. For purposes of present work Hexadecyltrimethylammonium bromide, Tetradecyltrimethylammonium bromide, and Carbethoxypendecinium bromide were used as selected cationic surfactants, Sodium dodecyl sulphate as anionic and TWEEN-20 as a non-ionic. The interactions between the individual components were studied by using a combination of dynamic light scattering (determination of the changes in particle size distributions), electrophoretic light scattering (zeta potential – stability investigation) and isothermic titration calorimetry (thermodynamic parameters of interactions) in titration mode of measurement. This set-up provided us the determination of the critical aggregation concentrations of the surfactant-humic system, which corresponded to its phase separation. Moreover, the interactions between the components were confirmed also by routine physico-chemical methods (e.g. thermogravimetry and Fourier transform infrared spectroscopy).  We believe that the outcomes of our work will help to shed a new light on the phenomenon of the formation of the interaction between surfactants and humic substances and will provide the crucial insight in the broader utilization of specific fractions humic substances as the universal sorbent for surfactants mainly from the waste waters.

How to cite: Kalina, M., Duchacek, T., Krouska, J., Sedlacek, P., and Smilek, J.: Colloidal Aspects of the Formation of the Interactions between Humic Substances and Surfactants, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17042, https://doi.org/10.5194/egusphere-egu2020-17042, 2020.

In aquatic environments, Hg(II) is strongly reactive with the dissolved organic matter (DOM) and form complexes with acidic functional groups like carboxylic acids, phenols, ammonia, alcohol, and reduced sulfur ligands (S_red). It has been suggested, however, that both the concentration of Hg(II) and the composition of the DOM influence the potential for the removal of Hg(II) in water treatment.

Jar test experiments were performed at optimum coagulation conditions of pH and alum dose, using unfractionated DOM, humic substances (humic acids and fulvic acids) and different Hg(II) concentrations. Samples used in this work were obtained from the International Humic Substances Society (IHSS) and were selected based on the differences in aromatic carbon, reduced sulfur content, acidic functional groups concentration, geographical location, and commercial availability.

Results showed that good removal of Hg(II) can be achieved by alum coagulation under two circumstances: (1) when the DOM is low in S_red ligands but rich in aromatic content and (2) when the DOM is rich in Sred ligands and low in aromaticity. At low Hg/DOM ratio (0.05 μg Hg/mg DOM), Hg(II) removal can be as high as 95%, while at high Hg/DOM ratio (1.0 μg Hg/mg DOM) Hg removal can be as high as 73%. The aromaticity of the DOM and the presence of Hg(II)-binding ligands in the fraction of carbon that adsorbs to aluminum hydroxide flocs were the key variables that control the removal of mercury. All the same, the character of DOM determines the extent of the removal of carbon and the minimum amount of Hg(II) that can be removed from solution.

How to cite: Diaz, F., Katz, L., and Lawler, D.: Hg(II)-Dissolved Organic Matter (DOM) Interactions in Freshwater and their Removal in Conventional Water Treatment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20727, https://doi.org/10.5194/egusphere-egu2020-20727, 2020.

The humic substances, the major and the most important part of soil organic matter, are responsible for the immobilization of organic compounds (e.g. heavy metal ions, organic dyes, surface active agents, etc.) in the soil. Unfortunately, there are a lot of gaps in the knowledge in the complex mechanism of binding of organic charged compounds by humic substances.

The unconventional diffusion and dialysis (transport) techniques have been developed for the purpose of study on the interactions between humic substances and organic charged substances.  In our contribution we are focusing on one fraction of humic substances – humic acids. The binding between humic acids with/without selectively blocking of carboxylic functional groups (methylation by –CH3) with organic charged compounds (e.g. organic dyes, surface active agents) has been studied by diffusion and dialysis approach using the spectroscopic techniques as analytical method. The strong impact of methylation on the positive affinity of humic acids towards organic compounds has been expected. These expectations were not confirmed by diffusion and dialysis techniques. The role of carboxyls in the structure of humic acids is not so essential as was expected and mentioned in the literature. The other effects (e.g. hydrophobic interactions, pi-pi stacking, etc.) are more important in the binding of organic compounds as was expected. The positive binding as well as kinetics of this process is also strongly depending on the physico-chemical circumstances of the system (e.g. pH, ionic strength, temperature, etc.).

How to cite: Smilek, J., Belusova, A., Kalina, M., and Sedlacek, P.: The function of carboxyls in the structure of humic acids to binding of organic substances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21642, https://doi.org/10.5194/egusphere-egu2020-21642, 2020.