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Article

Ecological State of Haplic Chernozem after Pollution by Oil at Different Levels and Remediation by Biochar

by
Anna Ruseva
1,
Tatyana Minnikova
1,*,
Sergey Kolesnikov
1,
Sofia Revina
1 and
Anatoly Trushkov
2
1
Academy of Biology and Biotechnology, Russian Academy of Sciences, Southern Federal University, Rostov-on-Don 344090, Russia
2
Azov-Black Sea Branch of the Federal State Budgetary Scientific Institution “All-Russian Research Institute of Fishing and Oceanography”, Rostov-on-Don 344002, Russia
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(18), 13375; https://doi.org/10.3390/su151813375
Submission received: 10 August 2023 / Revised: 29 August 2023 / Accepted: 5 September 2023 / Published: 6 September 2023
(This article belongs to the Special Issue Environmental Effects and Remediation of Soil Pollution)
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Abstract

:
One of the most modern and effective methods of soil restoration after pollution is the use of bioremediation. In recent years, special attention has been paid to the use of biochar. However, the ecological state after the introduction of biochar into petroleum-hydrocarbons-contaminated soils at different levels of pollution has been little studied. The work objective was to study the effect of biochar (10% of the soil mass) on the ecological statement of Haplic Chernozem contaminated with different levels of oil, from 0.1 to 50% of the soil mass. To assess the state of Haplic Chernozem after remediation with biochar, indicators of the biological activity of soils were studied. The maximum information content in the case of oil pollution and remediation with biochar was established by the activity of dehydrogenases (r = −0.90) and the total number of bacteria (r = −0.98). When applying biochar, the maximum stimulations of the integral indicator of the biological state (IIBS) relative to the background, by 62, 76, and 72%, were noted in samples with oil at concentrations of 0.5, 25, and 50%, respectively. The results of the study should be used for biodiagnostics and monitoring of the state of oil-contaminated Haplic Chernozem at different levels of contamination after remediation with biochar.

1. Introduction

The intensive development of the globalization of the economy and trade over the past few decades has contributed to an increase in the consumption of petroleum hydrocarbons and petroleum products [1,2,3,4]. Global petroleum hydrocarbons consumption in the period from 2009 to 2019 increased by 0.83–3.19% per year [5,6]. In 2019 alone, the daily use of petroleum hydrocarbons reached a record level of 98.3 million barrels [7]. In the process of petroleum hydrocarbons extraction, transportation, and refining, their leakage inevitably occurs. Accidents with leakage of petroleum hydrocarbons can contribute to serious pollution of environmental components. Soil pollution is one of the main environmental problems in the world, hindering sustainable development [6,8,9,10]. Given the low decomposition rate, petroleum hydrocarbons can remain in contaminated soils for decades, creating a serious problem for the soil ecosystem and even for human health. Petroleum hydrocarbons change the structure and properties of the soil, violate its biological properties, and enter underground and surface waters, which significantly threatens the ecological situation [11,12].
Numerous studies have shown that bioremediation is a practical and environmentally friendly method of reclamation of petroleum-hydrocarbons-contaminated soils [7,10,13,14,15]. Soil restoration with the use of microorganisms or plants has a minimal number of negative side effects, but may depend on external conditions, such as weather events, and have a long recovery cycle compared to physical or chemical methods. To reduce the negative consequences, it is necessary to take more cost-effective measures or a combination of them, and the use of biochar can be the optimal solution to this problem [16].
Biochar is produced by burning biomass in an environment with a limited oxygen content and a relatively low temperature (300–700 °C). The average carbon content in the biochar is 70–80% [17]. In relation to oil, biochar acts as a potential sorbent. In addition, this ameliorant affects the activity and abundance of soil microorganisms, by creating additional space for their reproduction, as well as the transport and biodegradation of pollutants [18,19,20].
Different types of raw materials significantly affect such properties of biochar as ash content, content of elements and functional groups, aromaticity, porosity, specific surface area, etc. [21,22]. For example, biochar made of wood biomass has a higher specific surface area and porosity due to the thermal stability of lignin [17]. Recently, biochar has been attracting more and more attention due to its large specific surface area, high porosity of the material, strong adsorption capacity, and low cost. Considering the prospect of economic and environmental sustainability, high adsorption capacity, and chemical stability, biochar is considered the most promising carbon-containing material for use in the environment [23,24]. It can be used to improve the physical and chemical properties of the soil and stimulate microbial communities, providing the latter with nutrients and space for reproduction, by minimizing the external environmental impact [6,10,25,26]. Biochar has a significant positive effect on the soil, reduces the release of CO2, and improves soil porosity and pH. It also contributes to maintaining soil fertility: it has a higher cation exchange capacity than most other forms of organic matter, mobilizes nutrient reserves, in particular base cations, and is resistant to mineralization [27,28,29]. In addition, this sorbent contains a large amount of labile organic carbon and some elements important for plants (for example, N, K, P, S, Ca, and Mg) [30,31]. When applying the optimal amount of biochar to the soil, it can serve as a complex fertilizer for agricultural crops [32].
It is known that petroleum hydrocarbons pollution of up to 10% of the soil mass most often occurs in places of petroleum hydrocarbons production, its processing and transportation, production, and with the use of petroleum products [33]. Higher concentrations of petroleum hydrocarbons in the soil can also occur because of large spills. The maximum permissible concentration of petroleum hydrocarbons in the soil has not been developed to date; however, according to a Letter from the Ministry of Natural Resources of Russia (1993), five levels of soil contamination with petroleum products (in mg/kg) are allocated: I) acceptable (up to 1000); II) light (1000–2000); III) medium (2000–3000); IV) high (3000–5000); V) very high (from 5000) [34]. This classification does not consider regional features (background content) and the recovery potential of different soils [Bykova]. In the present study, the minimum concentration of petroleum hydrocarbons (0.1% of the soil mass), which polluted the Haplic Chernozem, corresponds to the II level of pollution. This level of soil contamination with oil is most often encountered during accidental oil spills [35].
The work objective is to assess the ecological statement of Haplic Chernozem after pollution by oil of different levels and remediation by biochar.

2. Materials and Methods

2.1. Study Object

Haplic Chernozem Loamic soil [36] was chosen as the study object. It was taken from the upper layer in horizon A (0–10 cm) on the arable land of the Botanical Garden of the Southern Federal University (Rostov on Done, Rostov Region, South of Russia) (47°14′17.54″ N; 39°38′33.22″ E) (Figure 1).
Haplic Chernozem is characterized by a neutral reaction of the medium (pH = 7.5), a soil organic matter content of 4.4%, and a content of easily soluble salts—141 ppm.

2.2. Petroleum Hydrocarbons Characteristics

Oil from the Novoshakhtinsky Petroleum Hydrocarbons Refinery (Novoshakhtinsk city, Rostov Region, Russia) was used to simulate petroleum hydrocarbons contamination of Haplic Chernozem. Oil characteristics are presented in Table 1.

2.3. Biochar Characteristics

Biochar is made from birch (Betula alba) grade A of GOST 7657–84 with a carbon content of at least 85% (LLC DianAGRO, Novosibirsk city, Russia) [37]. The sorbent is obtained by pyrolysis of wood (800 °C) in retort installations in an anoxic environment. The product has a high carbon content (85–90%) and lacks harmful or toxic impurities. The amount of carbon in 1 × 103 kg of biochar is equivalent to the content of 3 × 103 kg of carbon (C) in carbon dioxide (CO2).

2.4. Simulation Experiment

The prepared soil samples were dried and sieved through a sieve with a cell diameter of 3.2 mm. Haplic Chernozem was dried and was placed in the amount of 200 g in vegetative vessels, moistened, and polluted with petroleum hydrocarbons in various concentrations corresponding to II, III, IV (0.1, 0.25, 0.50% of the soil mass), and V (1, 2.5, 5, 10, 25, 50% from the mass of the soil) levels of oil pollution according to the classification of the Ministry of Natural Resources of Russia (1993) [34] (Table 2).
Then biochar (10% of the soil mass) was added to the oil-contaminated soil and thoroughly mixed with it. After applying petroleum hydrocarbons and biochar, soil samples were incubated for 30 days in laboratory conditions at a temperature of 20–25 °C and optimal moisture (40% of the soil mass).

2.5. Physical and Chemical Characteristics of Uncontaminated Soil

In Haplic Chernozem, before contamination oil and remediation of biochar, soil organic matter content (%) and pH were determined. The potassium dichromate method (NY 1121.6 2006) was employed to determine organic matter content in soil samples [38]. Soil pH was measured using an electrode potentiometer HANNA HI 2211 in distillate water, in the ratio of 1 part of soil to 2.5 parts of water (w/v) [39]. The content of easily soluble salts in soil was determined in the soil extract (soil:distilled water—1:5) using a conductometer, HANNA inst. Total Dissolved HI 9034 [40].

2.6. Biological Indicators

At the end of the model experiment, the following biological indicators were analyzed in Haplic Chernozem: the length of roots and shoots, the germination of radish seeds, catalase and dehydrogenase activity, and the total number of bacteria. The phytotoxicity of soils was assessed using a sensitive phytotest—seed of radish (Raphanus sativus L.) of the variety “Zhara”. The choice of the test object was made because radish seeds have a small supply of nutrients and, accordingly, are more susceptible to external influences [41,42,43]. In addition, this crop is cultivated on the Haplic Chernozems of the Rostov Region. The phytotoxic properties of Haplic Chernozem were determined by the intensity of initial growth (length of shoots and roots) and germination of radish (Raphanus Sativus var. Radicula) (Kolesnikov 2019, [44]. The activity of catalase (H2O2: H2O2—oxidoreductase) was determined by the gasometric method [45,46]. This is based on measuring the decomposition rate of hydrogen peroxide when it interacts with the soil by the volume of released oxygen. The widespread use of catalase activity in the biodiagnostics of soil cover occurs because the method of its determination is easy to use, it is characterized by reproduction fidelity, and it allows for a large variety of approaches. In addition, catalase is a sensitive enzyme to various types of anthropogenic impact [47]. To determine the activity of dehydrogenases (substrate: NAD (P)—oxidoreductase), 2,3,5-triphenyltetrazolium chloride (TTC) is used as a substrate in this method, which is reduced to a saturated red color by the formazan compound—triphenylformazan (TPF). In the soil, non-specific (carbohydrates, phenols, amino acids, fats, alcohols, etc.) and specific (humus substances) organic compounds can act as substrates [48,49]. Dehydrogenases act as catalysts for a wide range of oxidative reactions that are associated with the degradation of soil organic matter [50]. The total number of soil bacteria was determined by fluorescent microscopy in incident light [51]. The soil suspension was applied in a fixed volume to the slides in 2 repetitions (application area 2 cm2). Optimal for luminescent microscopy is this soil cultivation: water in the proportion of 1 g of soil per 100 mL of distilled water [52]. The preparations were placed in a solution of acridine orange to stain bacterial cells. This method is optimal for studying and quantifying bacteria in their natural environment.
According to the values of all biological indicators studied in this research, an integral indicator of the biological state (IIBS) of each soil was calculated [44]. For the IIBS of the soil, the data of control samples were taken for the maximum value of each indicator (100%). The relative values of this indicator for other options were calculated using Equation (1):
B 1   = B x B max × 100 %
where B1—relative score of the biological indicator; Bx—actual value of the biological indicator; Bmax—maximum value of the biological indicator (control).
Then, the relative values of the studied biological indicators were summed up, and for each option, the average score was calculated according to Equation (2):
B av = B 1 + B 2 + ... + B n N
where Bav—average score of biological indicators; B1 … Bn—relative score of biological indicator; N—number of biological indicators.
The final value of the IIBS was calculated using Equation (3):
IIBS = B av B ref × 100 %
where Bav—average score of a biological indicator; Bref—control value averaged over all biological indicators.

2.7. Statistical Processing

Statistical data processing was carried out using the Statistica 13.3 package and MS Excel (2016). The significance was tested at * p < 0.05, ** p < 0.001, *** p < 0.0001. Statistical data (average values and variance) were determined, and the reliability of various samples was established using a variance analysis (Student’s t-test).

3. Results

3.1. Indicators of the Intensity of Initial Growth and Germination of Radish Seeds

Oil in all concentrations significantly reduced the germination of radish seeds by 30–73%; concentrations of 0.25 and 50% were the most toxic (Figure 2a).
The use of biochar as an ameliorant proved to be effective at all concentrations of the pollutant, except for 5 and 10% of the soil mass, where germination was unreliably reduced. The maximum increase in seed germination relative to samples with only a contaminant was noted at oil concentrations of 0.25 and 50% of the soil mass—by 105 and 145%, respectively. At the same time, only at low concentrations of oil (from 0.1 to 1%), the values of the indicator in the Haplic Chernozem after remediation are close to the control. The study showed that in Haplic Chernozem without a contaminant, biochar contributes to an increase in the length of radish roots by 77%, the length of green seedlings by 27%, and germination by 18% relative to the control (Figure 2b).
Contamination of the studied soil with oil in all concentrations led to a decrease in root length values from 41 to 92% compared to the control. The highest concentrations of oil turned out to be the most toxic—10, 25, and 50% of the soil mass—in that decreases of 83, 84, and 92%, respectively, were observed (Figure 2c).
The introduction of biochar into the oil-contaminated Haplic Chernozem led to an increase in the length of the roots in all options. This increase was significant in all samples, except those containing the maximum concentrations of oil—25 and 50% of the soil mass. The greatest effectiveness of the ameliorant was noted at an oil concentration of 0.25%, where the root length values were two times higher than those of the sample without biochar at the same concentration. At concentrations of the pollutant from 0.1 to 1% in the soil with biochar, there was also an increase in values relative to the control, by 11–48%. The study of the length of green seedlings showed that the introduction of oil into the soil helped to reduce the indicator by 45–83% relative to the control. Oil concentrations of 10, 25, and 50% also had the greatest suppressive effect on the length of radish seedlings, reducing the indicator by 69, 70, and 83%.
The addition of biochar to polluted soil increased the length of green seedlings in all concentrations of oil. The maximum increase in the length of green seedlings was observed at oil concentrations of 2.5 and 5% by 120 and 190%, respectively, relative to samples with oil only (background).
Phytotoxic indicators had the greatest sensitivity to oil contamination after biochar application: the length of radish roots at a dose of 0.25% oil was 200%, the lengths of green seedlings at concentrations of 2.5 and 5% were 120 and 190%, and germination values at concentrations of 0.25 and 50% were 105 and 145%, respectively.

3.2. Activity of Soil Enzymes

Enzymatic activity is a sensitive indicator of the state of the soil environment. Soil enzymes such as dehydrogenases, catalase, and urease are widely used to monitor the decomposition of hydrocarbons [53,54]. In this study, the activity of catalase and dehydrogenases was studied.
The study of catalase activity in Haplic Chernozem allowed us to establish that the introduction of biochar improperly stimulated enzymatic activity (Figure 3a). In the case of oil contamination, the enzymatic activity was inhibited in all studied options, while a significant decrease in activity was observed at higher concentrations of oil (from 0.5 to 50%), and the maximum decrease, by 77% relative to the control, occurred when the largest dose of the pollutant was applied—50% of the soil mass.
The use of biochar in petroleum-hydrocarbons-contaminated soil stimulated the activity of the enzyme at oil concentrations of 0.1, 0.5, 1, 2.5, 25, and 50% of the soil mass. The most effective was the use of an ameliorant at a dose of 2.5% oil, where the activity value significantly increased, by 81% relative to Haplic Chernozem with oil.
The study of dehydrogenase activity showed that biochar inhibited dehydrogenase activity in soil without contamination (Figure 3b). The introduction of oil into Haplic Chernozem also led to the inhibition of enzymatic activity by 20–71% in all concentrations of oil, except for at a dose of 0.1% of the soil mass. The latter activated dehydrogenases by 5% relative to the control. The introduction of biochar into contaminated Haplic Chernozem led to the stimulation of dehydrogenase activity in all options. The maximum increases of 124 and 72% relative to contaminated samples were found in options with oil concentrations of 2.5 and 10%.

3.3. Total Number of Bacteria

The activity of soil microorganisms, along with enzymatic activity, is the best indicator of the stability and fertility of soil ecosystems. Oil pollution has a negative impact on the populations of soil bacteria. Even in the first stages of oil pollution, changes occur in the composition, abundance, and metabolism of microorganisms [55,56].
During the study of the total number of bacteria, it was revealed that biochar led to an unreliable decrease in their number (Figure 4). Oil reduced the number of bacteria from 15 to 84% relative to the control, while the higher the concentration of the pollutant was, the lower the number of microorganisms.
When biochar was introduced into contaminated Haplic Chernozem, the total number of bacteria increased in all options; the greatest increases, by 95 and 86%, were observed at oil concentrations of 25 and 50%, respectively, relative to samples with only oil in the same concentrations (Figure 3).

3.4. Integral Indicator of the Biological State of Soils

To assess changes in the properties of Haplic Chernozem based on all studied biological indicators (catalase and dehydrogenase activity, total number of bacteria, root length, green seedlings, and germination of radish seeds), a method developed at the Department of Ecology and Nature Management of the Southern Federal University was used to calculate the IIBS. This technique acts as an informative parameter of the violation of the ecological functions of the soil due to chemical pollution [33].
The results of the present study showed that biochar contributed to an increase in the IIBS of Haplic Chernozem without a contaminant by 19% relative to the control. The introduction of oil reduced the integral indicator in all options, from 24 to 80%, depending on the pollutant dose (Figure 5).
The integral indicator of the biological state of oil-contaminated Haplic Chernozem with the introduction of biochar increased significantly at any of the studied pollution levels. The maximum stimulation values of biological indicators, by 62, 76, and 72%, were observed in samples with oil concentrations of 0.5, 25, and 50%, respectively, relative to similar samples but without the addition of ameliorant (Figure 4).
The results of the correlation analysis showed that in petroleum-hydrocarbons-contaminated samples, the studied indicators had an inverse relationship with the oil concentration. Strong reliable feedback was noted for the length of roots, green seedlings, and activity of catalase and dehydrogenases, as well as the total number of bacteria (Table 3).
When adding biochar to contaminated soil, there was strong reliable feedback of all studied biological indicators with the dose of the pollutant.
The introduction of the sorbent contributed to an increase in the correlation ratio for indicators of soil toxicity: the length of roots and green seedlings and germination of radish seeds. At the same time, there were decreases in the correlation ratios for catalase activity, dehydrogenases, and the number of bacteria. In the latter case, the changes were insignificant.

4. Discussion

During the study of the ecotoxicity of soils, it was noted that oil contributed to a significant decrease in all phytotoxic parameters of radish, and biochar contributed to the stimulation of these indicators. Among the indicators of the intensity of initial growth, the length of the roots was more susceptible to change. Significant changes in the length of the roots when the soil is contaminated with petroleum hydrocarbons, as well as when applying biochar, can be explained by the fact that this part of the plant is in the soil, directly in contact with the introduced substances, and is more susceptible to their effects than other parts of the plant. A.S. Cherdakova and S.V. Galchenko (2020), in the study of the phytotoxicity of soils during microbiological remediation, noted a similar situation, but on other crops [57]. Oats (Avena sativa L.) and mustard (Brassica rapa L.) were used as test objects in this work. If the petroleum-hydrocarbons-contaminated soil is slightly humus, as in the Far North of Russia (Murmansk Region), the use of biochar should be replaced by its lighter and saturated-with-organic-matter analogue—peat [58]. After the reclamation, the germination of sorrel (Rumex acetosa L.) increased by 1.6–3.7 times. In the samples, where the complete death of seeds was initially noted, after reclamation, the germination rate of sorrel was 11–17%. Soil containing 100 g/kg of oil is toxic to watercress [59]. The most sensitive parameters of watercress (Lepidium Sativum L.) are the length of roots and shoots; therefore, for their growth and development, it is necessary to dilute the analyzed soil by 24 times. Technical treatment of alfalfa (Medicago sativa L.), ryegrass (Lolium perenne L.), nitrogen fertilizers, and 10 soil sites polluted with oil at an average concentration of 13.7 g/kg were cleaned up by agrotechnical treatment [60]. At the same time, annual soil cleaning resulted in an improvement of 72–90%, whereas with natural phytoremediation, soil cleaning reached the same level only after 5 years. This combined approach to assess the toxicity of oil-contaminated soil allows us to create a series of plant susceptibility: Zea mays < Cucumis sativus < Lactuca sativa L. [61]. It is known that enzymes are sensitive indicators of soil pollution. With their help, it is possible to assess the level of pollution and the general condition of soils before, after, and during their restoration, which makes it possible to develop measures for the remediation of anthropogenically disturbed ecosystems [62,63,64]. The biodegradation of oil involves redox enzymes—catalase, phenoloxidase, peroxidase, polyphenoloxidase, and dehydrogenases [55,65]. The most sensitive bioindicator of petroleum hydrocarbons’ pollution of soils is the activity of dehydrogenases [54,66,67]. The main reason for the inhibition of enzymatic activity is the accumulated degradation products of petroleum hydrocarbons in soils. The degree of inhibition of dehydrogenases and other soil enzymes is influenced by the pollutant concentration. Thus, low concentrations of petroleum hydrocarbons (0.5–1.0%) stimulate the activity of sulfiteoxidase and sulfitereductase, while higher concentrations reduce the activity of enzymes [55]. In the present study, only the lowest dose of petroleum hydrocarbons (0.1% of the soil mass) contributed to a slight increase in the activity of dehydrogenases, which can be explained by the stimulating effect of small concentrations (hormesis). In other options, an inverse relationship was observed between the concentration of petroleum hydrocarbons and the enzymatic activity: the higher the dose, the lower the value of the indicator. Petroleum hydrocarbons also reduced the activity of catalase. At the same time, the introduction of biochar into contaminated Haplic Chernozem had a greater stimulating effect on the activity of dehydrogenases, which may be due to their greater sensitivity to the concentration of petroleum hydrocarbons, which decreases due to its sorption and degradation when using ameliorant. An increase in the activity of dehydrogenases of petroleum-hydrocarbons-contaminated soils with the addition of biochar was also noted in several studies [6,17,68].
It was also found that oil pollution at all studied concentrations contributed to a decrease in the total number of bacteria of Haplic Chernozem. Biochar increased the number of bacteria in all options, and the greatest differences between the values of the indicator in contaminated samples and in samples after remediation were observed at maximum concentrations (25 and 50%). The increase in the number of bacteria in oil-contaminated Haplic Chernozem with the addition of biochar may be due to several reasons. Due to the oil sorption, the toxic effect of the pollutant on the soil biota is reduced. In addition, the feedstock for the biochar contains mineral biogenic elements that remain in it even after pyrolysis. Biochar can also absorb and retain biogenic elements from the soil due to surface structure. These elements (initially present and absorbed) are available to soil microorganisms and can stimulate their abundance [6,69,70,71].
According to previous studies [44], it was found that the soil performs its ecological functions normally if the IIBS decreases by no more than 5%. If the integral indicator decreases by 5–10%, then there is a violation of the information ecosystem functions of the soil. With a decrease in IIBS from 10 to 25%, in addition to information, biochemical, chemical, physicochemical, and holistic ecosystem functions are also disrupted. A decrease in the IIBS by more than 25% leads to a violation of all the above functions and, in addition, physical ecosystem functions. During this study, it was found out that oil contributed to a decrease in the integral indicator by 24–80%, depending on the dose of the pollutant, which corresponds to the level at which all functions of the soil are disrupted. In the case of adding biochar to the contaminated Haplic Chernozem, the maximum stimulation of biological parameters was noted in samples with oil concentrations of 0.5, 25, and 50%. When comparing the values with the control, only at a 0.5% oil dose was the IIBS value at the level at which the soil normally performs its functions. In addition, after remediation, samples with lower concentrations of the pollutant—0.1 and 0.25%—were at the same level. In the work of M.V. Bykova (2019), we find a comparison of the permissible concentrations of oil products, including with reference to the document dated 27 December 1993: “The procedure for determining the amount of damage from land pollution by chemicals” [72]. The document states that the permissible level of pollution varies from 0.1 to 0.2%. With an increase in the value of the permissible oil content of more than 0.2% of pollution, the level of impact on the soil increases. The obtained results make it possible to use biological indicators as a diagnostic criterion for the condition of petroleum-hydrocarbons-contaminated soil after the use of ameliorants acting as adsorbents of the pollutant or biostimulators of the number of native bacteria oil destructors. The results obtained in the article can be used to develop the maximum permissible levels regarding the impact of petroleum hydrocarbons’ contamination of soil before and after remediation.

5. Conclusions

Contamination of Haplic Chernozem by oil at moderate and very high levels of oil pollution contributed to a significant decrease in all biological indicators. Remediation of Haplic Chernozem by biochar at any level of oil led to the restoration of biological parameters relative to oil-contaminated soils. Phytotoxic indicators had the greatest sensitivity to oil contamination after biochar application. The maximum information content in the case of oil pollution after remediation by biochar was established by the activity of dehydrogenases and the total number of bacteria. The results of the study should be used for biodiagnostics and monitoring of the health of oil-contaminated soils at different levels after remediation with biochar. The use of the most informative and sensitive biological indicators will make it possible to correctly organize measures to control the cleanup of soils contaminated with oil after the application of ameliorants. The results obtained in the article can be used to develop the maximum permissible levels regarding the impact of oil on soil before and after remediation.

Author Contributions

Conceptualization, T.M. and A.R.; methodology, S.K.; software, T.M.; formal analysis, A.R.; investigation, A.R., T.M. and S.R.; resources, T.M.; data curation, T.M.; writing—original draft preparation, A.R., T.M. and S.R.; writing—review and editing, A.R., A.T. and T.M.; visualization, A.R.; supervision, T.M.; project administration, T.M.; funding acquisition, T.M. and S.K. All authors have read and agreed to the published version of the manuscript.

Funding

The study was supported by a grant from the President (MK-175.2022.5), with the financial support of the project of the Strategic Academic Leadership Program of the Southern Federal University (“Priority 2030”) for the creation of a youth laboratory of ecobiotechnologies for diagnosing and protecting soil health (No. SP-12-23-01), the Ministry of Science and Higher Education of the Russian Federation in the Soil Health laboratory of the Southern Federal University (agreement No. 075-15-2022-1122), the project of the Ministry of Science and Higher Education of Russia in the Young Scientist Laboratory within the framework of the Interregional scientific and educational center of the South of Russia (no. LabNOTs-21-01AB, FENW-2021-0014).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Map of soil site on the Botanical Garden of the Southern Federal University (Rostov on Done, Rostov Region, South of Russia).
Figure 1. Map of soil site on the Botanical Garden of the Southern Federal University (Rostov on Done, Rostov Region, South of Russia).
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Figure 2. Changes in the intensity of initial growth and development of radish seeds when contaminated with various concentrations of oil. contaminated Haplic Chernozem after remediation by biochar, % of control: (a) germination; (b) the length of shoots; (c) length of roots. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
Figure 2. Changes in the intensity of initial growth and development of radish seeds when contaminated with various concentrations of oil. contaminated Haplic Chernozem after remediation by biochar, % of control: (a) germination; (b) the length of shoots; (c) length of roots. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
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Figure 3. Changes in enzymatic activity in Haplic Chernozem when contaminated with various concentrations of oil and remediation by biochar, % of control: (a) activity of catalase; (b) activity of dehydrogenases. Note *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
Figure 3. Changes in enzymatic activity in Haplic Chernozem when contaminated with various concentrations of oil and remediation by biochar, % of control: (a) activity of catalase; (b) activity of dehydrogenases. Note *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
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Figure 4. Change in the total number of bacteria in Haplic Chernozem when contaminated with different concentrations of oil and remediation by biochar, % of control. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
Figure 4. Change in the total number of bacteria in Haplic Chernozem when contaminated with different concentrations of oil and remediation by biochar, % of control. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
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Figure 5. Change in the integral indicator of the biological state of Haplic Chernozem when contaminated with different concentrations of oil and remediation by biochar, % of control. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
Figure 5. Change in the integral indicator of the biological state of Haplic Chernozem when contaminated with different concentrations of oil and remediation by biochar, % of control. Note: *—according to the Letter of the Ministry of Natural Resources of Russia (1993) [34].
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Table 1. Characteristics of some physical and chemical properties of oil.
Table 1. Characteristics of some physical and chemical properties of oil.
Physical and Chemical PropertiesContent
Density, g/m30.818
Mass fraction of water, %0.270
Mass fraction of sulfur, %0.430
Mass fraction of mechanical impurities, %0.0028
Table 2. Levels of soil pollution by oil according to a Letter from the Ministry of Natural Resources [34].
Table 2. Levels of soil pollution by oil according to a Letter from the Ministry of Natural Resources [34].
LevelConcentrations,
% of Oil of the Soil Mass		Conversion of Oil, in mg of PHC in 1 kg of SoilLevel of Pollution of Soil
I<0.10<1000acceptable
II0.101000light pollution
III0.252500light pollution
IV0.505000medium pollution
V1.0010,000medium pollution
V2.5025,000medium pollution
V5.0050,000heavy pollution
V10.00100,000heavy pollution
V25.00250,000heavy pollution
V50.00500,000heavy pollution
Table 3. The value of the Spearman’s rank correlation coefficient between the biological parameters of Haplic Chernozem and the concentration of oil before and after remediation by biochar.
Table 3. The value of the Spearman’s rank correlation coefficient between the biological parameters of Haplic Chernozem and the concentration of oil before and after remediation by biochar.
Biological IndicatorsIntroduction of Biochar
BeforeAfter
Length of roots−0.79 *−0.95 *
Length of shoots−0.82 *−0.93 *
Germination−0.49−0.86 *
Activity of catalase−0.98 *−0.79 *
Activity of dehydrogenases −0.98 *−0.90 *
The number of bacteria−0.99 *−0.98 *
* Noted correlations are significant at p < 0.05.
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Ruseva, A.; Minnikova, T.; Kolesnikov, S.; Revina, S.; Trushkov, A. Ecological State of Haplic Chernozem after Pollution by Oil at Different Levels and Remediation by Biochar. Sustainability 2023, 15, 13375. https://doi.org/10.3390/su151813375

AMA Style

Ruseva A, Minnikova T, Kolesnikov S, Revina S, Trushkov A. Ecological State of Haplic Chernozem after Pollution by Oil at Different Levels and Remediation by Biochar. Sustainability. 2023; 15(18):13375. https://doi.org/10.3390/su151813375

Chicago/Turabian Style

Ruseva, Anna, Tatyana Minnikova, Sergey Kolesnikov, Sofia Revina, and Anatoly Trushkov. 2023. "Ecological State of Haplic Chernozem after Pollution by Oil at Different Levels and Remediation by Biochar" Sustainability 15, no. 18: 13375. https://doi.org/10.3390/su151813375

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