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Article

The Effects of the Interaction of Pesticides with Humin Fraction as Influencing the Sustainable Development of Agroecosystems

by
Lilla Mielnik
1,
Jerzy Weber
2,*,
Aleksandra Ukalska-Jaruga
3,
Romualda Bejger
1,
Maria Jerzykiewicz
4,
Andrzej Kocowicz
2,
Irmina Ćwieląg-Piasecka
2,
Elżbieta Jamroz
2,
Magdalena Debicka
2 and
Jakub Bekier
2
1
Department of Bioengineering, West Pomeranian University of Technology in Szczecin, ul. P. Pawła VI 3, 71-459 Szczecin, Poland
2
Institute of Soil Science, Plant Nutrition and Environmental Protection, Wrocław University of Environmental and Life Sciences, ul. Grunwaldzka 53, 50-357 Wrocław, Poland
3
Department of Soil Science, Erosion and Land Conservation, Institute of Soil Science and Plant Cultivation, State Research Institute, ul. Czartoryskich 8, 24-100 Puławy, Poland
4
Faculty of Chemistry, University of Wroclaw, ul. Joliot-Curie 14, 50-383 Wroclaw, Poland
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(5), 1983; https://doi.org/10.3390/su16051983
Submission received: 29 January 2024 / Revised: 22 February 2024 / Accepted: 24 February 2024 / Published: 28 February 2024
(This article belongs to the Special Issue Interdisciplinary Research on Soil Sustainable Management in Different Agroecosystems: Management of Agriculture–Ecology–Land-Management-Planning Interactions)
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Abstract

:
Humin (HUM) is the most stable fraction of the soil organic matter, whose properties determine the soil health and sustainable development of agroecosystems. The aim of the paper was to determine changes in the properties of the HUM after interaction with selected pesticides, which can be visualized using photoluminescence methods. The HUM was isolated from the mollic horizon of Phaeozems arable soils derived from different parent materials in Poland. The isolated and purified HUM were saturated in a batch experiment with selected herbicides and insecticides, then analyzed for chemical composition and spectroscopic properties: Electron Paramagnetic Resonance, fluorescence, and delayed luminescence. The research showed that the interaction of the HUM with selected pesticides caused significant changes in the elemental composition of the HUM; however, no changes in their aromaticity/aliphaticity were found. The impact of pesticides was also marked by a reduction in the concentration of radicals, fluorescence and delayed luminescence intensity and properties. Changes in spectroscopic characteristics and their relationship with soil organic matter (SOM) structure properties require further research so that their results can be used in the management of agroecosystems in accordance with the principles of sustainable development.

1. Introduction

Humin (HUM) is the most stable fraction of the soil organic matter (SOM), which properties determine the soil health, food production and sustainable development of agroecosystems. Almost 60–70% of the soil in the European Union can be classified as unhealthy, of which 2.8 million are classified as potentially polluted sites as a direct result of current management practices. These facts were highlighted in the report of Horizon Europe as critical points for soil care [1]. One of the main identified environmental threats is soil pollution by pesticide residues due to agricultural intensification. This phenomenon leads to negative environmental effects, including the deterioration of a number of ecosystem services (food production, maintaining the proper circulation of nutrients and biodiversity, protecting soil health, etc.).
The properties of SOM in agricultural areas depend, among others, on the use of pesticides and other agrochemicals, which should support the increase in agricultural production but, above all, be consistent with sustainable development. It also leads to changes in chemical and biological parameters, which ultimately impact crop yield [2]. As a result, soil contamination by pesticide residues has become a global issue of increasing concern due to the high soil persistence of particular agrochemicals and their toxicity to non-target species [3]. In order to address the EU’s soil protection policies, including the EU biodiversity strategy for 2030 [4] and the EU soil strategy for 2030 [5], a new Soil Monitoring Law [6] has been proposed to ensure a high level of soil environment protection. However, large-scale studies on soil contamination by pesticide residues are scarce and limited mainly to one or only a few compounds [7,8,9,10,11,12]. Therefore, the real scale of pesticide residue contamination in agricultural soils and their aging processes are still unrecognized, which makes rational and sustainable soil management difficult. Therefore, in order to maintain healthy soils and reverse soil degradation processes, sustainable land use methods should be introduced using the principles of the ‘European Green Deal’ and ‘Sustainable Development Goals’. In order to effectively limit soil degradation due to excessive accumulation of pesticides in soil, it is necessary to first recognize the processes that accompany these phenomena.
In general, the behavior of pesticides and their persistence in soil are mainly determined by volatilization, uptake by plants, leaching and runoff, chemical degradation by hydrolysis, oxidation–reduction and photolysis, decomposition by soil microorganisms, sorption and binding by soil components [2,3]. Thus, the fate of pesticides in the soil depends on many interrelated factors. Numerous studies indicate that the main component that influences pesticide activity and behavior in the terrestrial system is the content of SOM, which ensures optimal physical and chemical properties of the soil and high agroecological potential. Chemodiversity of SOM, especially the content of radicals, hydroxyl and carboxyl groups, and the degree of humification as well as aromaticity may significantly modify their reactivity and sorption properties to pesticides [2,13,14,15,16,17,18]. One of the most important and resistant components of SOM is the HUM, whose properties have so far been relatively rarely studied. However, it has been shown that this fraction has a very significant impact on the retention and resistance of pesticides to degradation in soils [19]. This is due to the fact that HUM is more abundant in cross-linked, condensed spatial structures, resulting in a high sorption capacity for hydrophobic xenobiotics [20]. However, the impact of pesticide treatment on the properties of HUM has not been analyzed in more detail yet.
A constant challenge is finding precise methods for a comprehensive assessment of soil-pesticide interactions. The physical and chemical properties of HUM are investigated with different techniques, including ultraviolet-visible spectroscopy (UV-Vis), visible-near infrared spectroscopy (Vis-NIR), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma mass spectrometry (ICP-MS), pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS), as well as electrochemical methods (electrophoretic mobility) [21]. These methods have many advantages, but the tracking of changes in SOM properties is sometimes limited by their insufficient sensitivity. Complementary information on the properties of natural organic matter (NOM), including SOM, can be obtained using photoluminescence methods. These methods provide information about the processes of inter- and intramolecular energy transport and the structural changes that occur in the studied material under the influence of irradiation. This is due to the influence of light on the initiation of photochemical and photophysical reactions in the structures of the NOM. When exposed to light, NOM undergoes photochemical processes that are accompanied by the formation of long-lasting phosphors capable of producing electromagnetic radiation in the photoluminescence process. The basic requirement for photochemical reactions to occur is the absorption of light, with only some molecules of the system excited. This provides photochemical processes with high selectivity. The light absorption capacity of NOM is mainly caused by the presence of delocalized π electron systems in aromatic rings and conjugated double bonds responsible for energy charge transfer [22]. The method of π electron transfer additionally contributes to the durability of the molecule and at the same time determines reactions distinctive for the individual types of compounds, e.g., transfer of electronic excitation over longer distances or transfer of electrons and energy.
The phenomenon of light-induced luminescence (photoluminescence) includes fluorescence, phosphorescence and delayed luminescence. An important difference between these processes is related, among others, to their kinetics. Fluorescence is a fast photophysical process that occurs in ~10−8 s, while photoluminescence and delayed luminescence are characterized by a much longer lifetime, from 1 ms to many minutes. Fluorescence spectroscopy is more commonly used in NOM studies [23,24,25,26,27,28,29,30]. This is, among others, because it is an extremely sensitive method (it allows analysis of substances at low concentrations) and is also a non-destructive method. So far, the phenomenon of delayed luminescence in NOM research has not been used on a wider scale. This is related to the lack of suitable equipment on the market, which was the inspiration to develop the design of the measurement set and the delayed luminescence measurement conditions at the West Pomeranian University of Technology in Szczecin.
Previous research showed that under established excitation conditions, the ability of NOM to emit electromagnetic radiation that can be observed by delayed luminescence effects depends mainly on the origin of NOM, the conditions of its transformation, and the degree of its decomposition [31]. Therefore, photoluminescence methods can complement chemical methods and provide additional information about the conformations of organic bonds as well as the photoreactivity of the tested substances. For this reason, attempts to better determine the capabilities of photoluminescence methods used to study changes in SOM properties are important.
The aim of the research was to assess the changes in the properties of HUM after interaction with selected pesticides, which can be visualized using photoluminescence methods.

2. Materials and Methods

2.1. Soil Sampling and Characteristics

The research deals with the humin fraction isolated from soil samples collected from the mollic horizon of three Phaeozems located in Lower Silesia, Poland. They were developed from different parent materials and used as arable soils with different plants grown. According to the Köppen–Geiger climate classification [32], the area of soils under study has a warm temperate climate (Cfb). The average annual temperature is 9.3 °C and the annual rainfall is 600 mm. The basic properties of soils labeled 1Ps, 6M, and 8C are presented in Table 1.

2.2. Isolation of HUM and Saturation with Pesticides

The isolation of HUM was described in our previous publication [33]. Briefly, HA and FA were extracted with NaOH, and then the remaining soil was digested with the HF-HCl mixture to remove the mineral fraction. Finally, the material was neutralized, purified by dialysis, and freeze dried. The isolated HUM samples were saturated with four pesticide-active substances representing insecticides: acetamiprid and alfa-cypermethrin, as well as herbicides: flufenacet and metazachlor. The reference analytical standards for pesticide active substances with purity over 95% were provided by Merck (Darmstadt, Germany).
These compounds are characterized by a value of the octanol-water partition coefficient Log P between 0.8 and 5.8 due to their diversified chemical structure and binding potential, which allows for the prediction of their different adsorption behaviors by soil organic matter fractions. The physicochemical parameters of acetamiprid, alfa-cypermethrin, flufenacet and metazachlor were presented in a previous publication [18].
The HUM saturation experiment was performed according to OECD Guideline for the Testing of Chemicals No. 106. Flufenacet and alfa-cypermethrin were dissolved in hexane, while acetamiprid and metazachlor were dissolved in ethyl acetate and then added to HUM at a constant carbon concentration (CHUM = 0.5 g·dm−3). The conditions of the experiment chosen based on the values of the Koc coefficients of these compounds and their absorption potential on soil components (OECD Guidelines for the Testing of Chemicals No. 106) allowed for 100% pesticide saturation. The experiment was performed at 20 °C in dynamic conditions using a HUM/solution ratio: (1) 1:1—metazachlor and acetamiprid; (2) 1:5—flufenacet; (3) 1:100—alfa-cypermethrin. These solutions were shaken for 12 h, and then hexane and ethyl acetate were decanted and evaporated by 24 h and 96 h, respectively. The saturation procedure methodology was prepared based on an experiment presented in the previous publication [18].
Pesticides selected for research (flufenacet and metazachlor) are very common active substances in commercially produced herbicides due to their high effectiveness in crop protection. Similarly, acetamiprid and alfa-cypermethrin are widely used as insecticides in many commercial formulations.

2.3. Chemical Composition

The elemental composition of the HUM was analyzed with the CHNS Vario EL Cube analyzer (Elementar; Langenselbold, Germany) in three repetitions to obtain the highest precision of the results, which does not exceed 5% RSD between the same samples. The contents of C, H, N, and S were measured as percentages of the ash-free mass, while the oxygen concentration was calculated from the difference. The atomic ratios H/C, O/H, and N/C were calculated to show the relationship of the elements in the composition of HUM.

2.4. Electron Paramagnetic Resonance (EPR) Method

The X-band EPR spectra were obtained with a Bruker Elexsys E500 spectrometer (Bruker, Karlsruhe, Germany) at room temperature using the double rectangular cavity resonator devoted to quantitative measurements. The Pahokee peat HA standard (1S103H) and Leonardite HA standard (1S104H) extracted and distributed by the International Humic Substances Society, in addition to the Bruker alanine pill, were used as quantitative standards. To quantitatively analyze the spectra of the HUM radicals, we performed a double integration of the signals using WinEPR from Bruker.

2.5. Fluorescence Method

Fluorescence emission spectra were recorded at three selected wavelengths of excitation light λex: 254 nm, 310 nm, and 460 nm, using the Hitachi F 7000 spectrofluorometer (Hitachi, Tokyo, Japan). Before analysis, the HUM samples were dissolved in DMSO:H2SO4 solution (v:v 94%:6%), while maintaining a constant carbon content of HUM at 10 mg·dm−3. The mixtures obtained were pre-exposed to ultrasound twice for 10 min to obtain homogeneous solutions and then shaken on a horizontal shaker for 24 h. Each solution was prefiltered through a pleated paper filter with a pore size of 0.2 mm, and then through a syringe filter with a pore size of 0.45 μm. The solutions were placed in a nonfluorescent quartz cuvette with a path length of 1 cm and thermostated at 20 °C. The slit width of the monochromators for the excitation and emission bands was 5 and 10 nm, respectively, and the scanning speed was 240 nm·min−1. Spectra correction was performed according to the procedure recommended in the Hitachi F-7000 user manual.

2.6. Delayed Luminescence Method

Delayed luminescence was analyzed in solutions prepared similarly to those for UV-Vis and fluorescence analysis. Excitation and recording of delayed luminescence intensity were carried out using a flow measurement device designed and constructed at the Department of Bioengineering of the West Pomeranian University of Technology in Szczecin. The density of the excitation light photon flux was 1500 µmol·m−2·s−1. Two monochromatic light sources with different wavelengths were used: 465–485 nm (blue light, DL-Blue) and 620–630 nm (red light, DL-Red). The delayed luminescence intensity was recorded at 0.10–0.35 s after excitation. The flow rate was 800 cm3·min−1.

2.7. Statistical Analysis

Statistical analysis was performed using Statistica Software (Version 13, StatSoft Inc., Toolsa, OK, USA, 2011). The significance of differences was analyzed with both ANOVA and post hoc with p = 0.05 Tukey tests when preliminary ANOVA assumptions met. Person’s correlation coefficients were calculated for the parameters characterizing chemical and photoluminescence parameters from the studied HUM.

3. Results

3.1. Chemical Composition

The analysis of the tested HUM revealed differences in their elemental composition (Table 2). Saturation of HUM with selected pesticides resulted in a decrease in the content of C, H, and N and an increase in the content of O in their structure.
Changes in the elemental composition were accompanied by changes in the values of atomic ratios. These proportions are related to the degree of condensation of aromatic rings and the content of oxygen functional groups, respectively [34,35]. The calculated values of the H/C ratio did not vary significantly, and their average values ranged from 0.88 to 1.26, which corresponds to aromatic systems coupled with an aliphatic chain containing up to 10 carbon atoms. For samples, 1Ps and 6M saturation with flufenacet and metazachlor resulted in a slight increase in H/C, while in 8C, visible changes occurred after saturation with acetamiprid and metazachlor. Saturation with selected pesticides also caused changes in the values of atomic ratios. In most cases, pesticide saturation contributed to a slight reduction in the C/N ratio. The exception is the saturation of sample 8C with alfa-cypermethrin and metazachlor, leading to an increase in the C/N ratio.

3.2. Electron Paramagnetic Resonance (EPR)

When considering the structure of humic substances (HS), the issue of radicals cannot be omitted. Their concentration is related to the degree of HS transformation. The saturation of HUM with all pesticides investigated caused a lowering of the concentration of radicals measured by EPR spectroscopy (Table 2). Active compounds of pesticides can act as photoinducers in interactions with HUM. The interaction of pesticides with HUM may lead to a modification of the basic characteristics of radicals, namely their durability and reactivity. In the case of analyzed substances, only differences in radical concentrations were observed, while the structure remained unchanged (no differences in g parameters).

3.3. Fluorescence

The fluorescence emission spectra presented in this work clearly reflect changes in HUM properties occurring under the influence of selected pesticides. The structure of the presented spectra, their shape, location, and intensity of the maxima may indicate the presence of an effective energy-transfer system in HUM macromolecules.
The investigated HUM showed a very weak fluorescence when excited with light at a wavelength of 254 nm. However, the obtained spectra illustrated changes in the structure of the HUM analyzed as a result of their reaction with the pesticides used (Figure 1). The saturation of HUM samples with alfa-cypermethrin resulted in a decrease in fluorescence intensity in sample 6M. While the addition of acetamiprid to samples 1Ps and 8C caused an increase in fluorescence intensity in the short-wave part of the spectrum, shifting the main maximum to the wavelength region λem = 340–390 nm. In the case of the herbicides tested, changes in the fluorescence spectra were different. For samples in 1Ps and 6M, the addition of metazachlor resulted in a slight increase in fluorescence intensity, while the addition of flufenacet caused a strong quenching of fluorescence for the sample 1Ps, and for 6M, a decrease in fluorescence intensity together with a hypsochromic shift of the main maximum. In the case of sample 8C, the reaction to herbicide saturation was the opposite—metazachlor saturation evoked a slight decrease in the intensity of fluorescence, while flufenacet caused a significant increase in the wavelength range of 350–400 nm.
The strongest fluorescence was observed when excitation of HUM with light of wavelength λex = 310 nm. The shape of the fluorescence spectra obtained was very similar (Figure 2). The most important differences were related to the fluorescence intensity of the main maxima that occurred in the spectra analyzed. In the pure HUM spectrum for sample 8C, the maximum intensity of fluorescence occurred at λem = 415 nm, while for samples 1Ps and 6M, the main maximum was the peak at λem = 380 nm.
The saturation with the insecticide group caused only a slight decrease in fluorescence intensity but did not influence the formation of characteristic peaks. Metazachlor saturation, as in the case of insecticides, caused only slight changes in fluorescence intensity. Only in the case of the 1Ps sample this action did result in an enhancement of the maximum at λem = 415 nm. The situation was different in the case of interaction with flufenacet, the saturation of which resulted in almost complete quenching of fluorescence. Changes in the spectra of short-wave excited fluorescence observed in HUM saturated with pesticides are probably the result of conformational and structural changes in the tested preparations.
Long-wave excited fluorescence (λex = 460 nm) is characteristic of a more stable internal structure [36,37]. The similar shape of the fluorescence spectra obtained may indicate a strongly shaped aromatic core of the HUM molecule tested (Figure 3). Saturation with active substances did not significantly affect changes in the long-wave-induced fluorescence, except for the 1Ps sample, where a significant increase in its intensity was observed.

3.4. Delayed Luminescence

Numerous studies provide evidence that HS enhances the photodegradation of substances polluting the natural environment (pesticides, herbicides, and other organic pollutants), acting as sensitizers or precursors of reactive species [38,39]. Analysis carried out using the delayed luminescence method showed that the saturation of HUM with the pesticides used has a significant impact on HUM, especially the kinetics and efficiency of the delayed luminescence process. Figure 4a,b show the delayed luminescence intensity values before and after saturation of HUM with pesticides.
As a result of the excitation of HUM solutions with blue light (λex = 465 ÷ 485 nm), which is the most energetic, the highest values of delayed luminescence intensity were obtained, while the lowest delayed luminescence intensity was observed with the excitation of HUM solutions with red light (λex = 620 ÷ 630 nm). Saturation of the 1Ps sample with acetamiprid, alfa-cypermethrin, and metazachlor caused a decrease in the intensity of DL-Blue, except for flufenacet, whose saturation caused a strong increase in delayed luminescence intensity (Figure 4a). In the case of sample 6M, saturation with the four active pesticide substances resulted in a decrease in DL-Blue intensity. In the case of sample 8C, saturation with all pesticides tested resulted in a statistically significant increase in DL-Blue (Figure 4b). The lack of correlation between DL-Red and DL-Blue may indicate that the mechanisms leading to delayed luminescence emission during red light excitation are completely different from those observed during blue light excitation.

4. Discussion

The research carried out showed that the saturation of the tested HUM with selected pesticides caused significant changes in the elemental composition of the HUM. This process caused a decrease in the content of C, H and N and, consequently, an increase in the content of O. However, no change in the H/C and N/C ratios was found, indicating no changes in the aromaticity or aliphaticity of the analyzed HUM [40,41,42]. The impact of pesticide saturation was also marked by a reduction in the concentration of radicals, which confirmed previous findings known from the literature [21,42].
The presence of carbonyl groups and quinone rings, which exhibit significant photochemical reactivity, plays a significant role in the development of the photoluminescence phenomenon. The excited carbonyl chromophores easily transform into the triplet state, initiating radical decomposition processes of the carbonyl group bond with the rest of the carbon chain [43]. Processes of non-radical disintegration of neighboring bonds can also be observed. In turn, excited quinones may play the role of sensitizers for neighboring fragments of SOM biopolymers. HUM is equipped with numerous sites capable of selective adsorption of pesticide molecules [44]. Our previous research shows that the pesticides analyzed were characterized by different sorption dynamics by HUM [18]. Acetamiprid and metazachlor had the highest degree of saturation, while alfa-cypermethrin and flufenacet were sorbed much slower, with much lower sorption efficiency, which is also reflected in the photoluminescent properties of HUM.
The process of pesticide absorption is accompanied by changes in the structure of HUM molecules, leading to changes in fluorescence in their photoluminescent properties. The addition of acetamiprid and metazachlor did not significantly affect the short-wave-induced fluorescence emission (λex = 310 nm). However, saturation with alfa-cypermethrin caused a decrease in fluorescence, which was practically quenched after saturation with flufenacet. A decrease in fluorescence intensity was also observed after saturation in the case of fluorescence induced in the long wave (λex = 460 nm). The exception was sample 1Ps, in which a strong increase in fluorescence intensity after HUM saturation with flufenacet would be associated with a particularly marked reduction in the concentration of radicals in this sample.
The analyses performed showed that pesticide saturation causes changes in delayed luminescence intensity. This may be associated with a reduction in the reactivity of radicals, which may result from the delocalization of an unpaired electron in the aromatic ring system. As a result, some radicals can be maintained in a stable, non-reactive form for a long time. It can be assumed that delayed luminescence excited by blue light is related to the induction of charge-transfer complexes with a complete transfer of charge from the donor to the acceptor with an extensive system of double bonds [31]. The analyzed changes in DL-Blue differed in non-saturated samples, which showed a varied intensity for the samples. This indicates differences in their structure, which determines their different abilities to bind individual pesticides. In the case of 6M sample, saturation with all analyzed active substances resulted in a decrease in the concentration of DL-Blue, while in tha case of 1Ps sample, the decrease occurred after saturation with acetamiprid, alfa-cypermethrin and metazachlor. The opposite reaction was observed in the latter sample after saturation with flufenacet. An increase in DL-Blue was also observed in the 8M sample as a result of saturation with all pesticides analyzed.
Saturation of HUM with the pesticides analyzed resulted in an increase in the intensity of DL-Red for all the samples analyzed. This may be related to reducing radical concentration, which is confirmed by a statistically significant negative correlation between DL-Red and RC (r = −0.83). On the other hand, a significant relationship was obtained between DL-Red and the elemental analysis parameters: %H and %N (r = −0.52 and r = −0.64, respectively). The observed trend is opposite to that in the case of previously studied lake sediments [31], but those results refer to humic acids, not HUM. Among the processes leading to delayed luminescence emission, the formation of excimers and exciplexes cannot be ruled out [31].
Many possible photophysical and photochemical processes make it difficult to draw conclusions regarding changes in HUM properties as a result of pesticide saturation. The research carried out provided additional information on changes in the properties of the HUM analyzed, but the interpretation of these properties is difficult at the up-to-date stage of identification. Given the current state of knowledge about the delayed luminescence of organic substances, it is difficult to clearly state what changes in chemical properties were caused by the saturation with active substances of pesticides. Such conclusions will be possible after conducting more experiments on delayed luminescence changes in NOM samples, which will be supported by analyses using other analytical methods.
Results suggested that pesticides exhibit high binding affinity to humin. Pignatello et al. [45] reviewed the various binding mechanisms between these particles, specifying the nature and strength of chemical intermolecular interactions. Hydrogen bonding, van der Waals forces, ligand exchange, and charge transfer complexes represent weak binding energies, whereas covalent linkages lead to the formation of chemically stable bonds [46]. The covalent bonding causes the incorporation of the compound into the humin structure and the formation of a new molecule with a different conformation. These behaviors are the result of pesticide aging processes, leading to the formation of a stable balance between the attractive and repulsive forces of pesticides and HUM [47,48].

5. Conclusions

The research revealed a new perspective on the properties of HUM as a stable organic matter fraction, thus expanding the complex and hypothetical picture of the processes of transformation of these substances in the environment. The results obtained showed that the interaction of the HUM with selected pesticides caused changes in the elemental composition of the HUM; however, no changes in their aromaticity/aliphaticity were found. The impact of pesticides was also marked by a reduction in the concentration of radicals, which confirmed previous findings known from the literature. This is probably one of the main reasons for the changes in photoluminescent properties. The addition of acetamiprid and metazachlor did not significantly affect the short-wave-induced fluorescence emission. However, saturation with flufenacet caused a decrease in fluorescence, which was practically quenched after saturation with flufenacet. A decrease in fluorescence intensity after saturation with pesticides was also observed after long-wave-induced fluorescence.
The analyses performed showed that the interaction of HUM with pesticides causes changes in the intensity of the delayed luminescence. This provided additional information about changes in their properties, but its interpretation is difficult at the current stage of knowledge. The research results collected so far do not allow us to explain the mechanisms leading to changes in delayed luminescence emissions. The range of possible photoreactions is so extensive that determining the mechanism of transformation is a task that requires significant effort from large research teams. The applied methods allow us to identify changes in the quality of organic matter as a result of interactions with pesticides. Despite limited research, the results can be used to adapt the presented methods to monitor and control changes in soil organic matter resulting from the accumulation of pollutants, especially in agricultural lands.

Author Contributions

L.M.—photoluminescence analyses, original draft preparation, J.W.—writing and editing, A.U.-J.—writing review, R.B.—humin saturation, M.J.—chemical and EPR analyses, A.K.—soil sampling and humin isolation, graphical abstract, I.Ć.-P.—review and editing, M.D.—humin isolation, E.J.—humin isolation, preparation of references, J.B.—humin isolation. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Science Centre, Poland (Grant number 2018/31/B/ST10/00677).

Data Availability Statement

Data available on request from the authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 254 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
Figure 1. The fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 254 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
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Figure 2. The Fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 310 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
Figure 2. The Fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 310 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
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Figure 3. The fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 460 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
Figure 3. The fluorescence emission spectra of non-saturated and saturated HUM with selected pesticides obtained at 460 nm excitation wavelength. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
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Figure 4. DL-Blue (a) and DL-Red (b) of non-saturated and saturated HUM with different pesticides. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
Figure 4. DL-Blue (a) and DL-Red (b) of non-saturated and saturated HUM with different pesticides. -AC—saturated with acetamiprid; -CY—saturated with alfa-cypermethrin; -FL—saturated with flufenacet; -ME—saturated with metazachlor.
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Table 1. Basic properties of Mollic horizon of investigated soils.
Table 1. Basic properties of Mollic horizon of investigated soils.
SoilpH (KCl)CaCO3TOCTNTOC/TNCEC 1HA 2FA 3HUM 4USDA
Textural Class
g kg−1% of C
1Ps7.7114.613.31.0612.528.345.2017.7237.09sandy loam
6M7.5215.321.21.6013.233.435.6418.7945.57loam
8C7.3910.326.12.0312.821.627.3229.7442.94silt loam
1 cation exchange capacity [cmol(+) kg−1]; 2 humic acids; 3 fulvic acids; 4 humin.
Table 2. Elemental composition, radical concentration (RC) and g-parameter of non-saturated and saturated HUM.
Table 2. Elemental composition, radical concentration (RC) and g-parameter of non-saturated and saturated HUM.
SampleCNHOH/CO/HC/NRC·10−16 [Spins g−1]g-Paramater
Atomic % of Ash Free Mass
1Ps41.261.8741.8218.170.930.4422.048.322.0030
1Ps-AC *133.711.6131.1733.390.921.0720.984.032.0028
1Ps-CY *233.011.5430.8934.250.941.0421.506.572.0030
1Ps-FL *328.981.5036.5732.151.260.8819.363.822.0030
1Ps-ME *432.641.7233.1631.011.020.9418.944.542.0028
6M38.981.9941.8320.360.970.5219.6212.402.0030
6M-AC *136.061.7536.9724.251.030.6620.585.062.0030
6M-CY *237.751.8335.0123.800.930.6320.633.202.0030
6M-FL *334.111.7538.4625.281.130.6619.513.492.0030
6M-ME *435.621.9739.2519.731.100.5018.043.592.0030
8C42.842.3040.8115.920.880.3718.6511.702.0030
8C-AC *128.571.4829.4340.011.031.3619.365.602.0030
8C-CY *238.461.6233.9125.150.880.6523.687.032.0030
8C-FL *338.901.7734.2022.690.880.5821.923.692.0030
8C-ME *440.861.5439.0617.660.960.4526.555.482.0030
*1—saturated with acetamiprid; *2—saturated with alfa-cypermethrin; *3—saturated with flufenacet; *4—saturated with metazachlor.
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Mielnik, L.; Weber, J.; Ukalska-Jaruga, A.; Bejger, R.; Jerzykiewicz, M.; Kocowicz, A.; Ćwieląg-Piasecka, I.; Jamroz, E.; Debicka, M.; Bekier, J. The Effects of the Interaction of Pesticides with Humin Fraction as Influencing the Sustainable Development of Agroecosystems. Sustainability 2024, 16, 1983. https://doi.org/10.3390/su16051983

AMA Style

Mielnik L, Weber J, Ukalska-Jaruga A, Bejger R, Jerzykiewicz M, Kocowicz A, Ćwieląg-Piasecka I, Jamroz E, Debicka M, Bekier J. The Effects of the Interaction of Pesticides with Humin Fraction as Influencing the Sustainable Development of Agroecosystems. Sustainability. 2024; 16(5):1983. https://doi.org/10.3390/su16051983

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Mielnik, Lilla, Jerzy Weber, Aleksandra Ukalska-Jaruga, Romualda Bejger, Maria Jerzykiewicz, Andrzej Kocowicz, Irmina Ćwieląg-Piasecka, Elżbieta Jamroz, Magdalena Debicka, and Jakub Bekier. 2024. "The Effects of the Interaction of Pesticides with Humin Fraction as Influencing the Sustainable Development of Agroecosystems" Sustainability 16, no. 5: 1983. https://doi.org/10.3390/su16051983

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