Reducing the Gap Between Chemical and Biological Assessment of Petroleum-Contaminated Soils: An FTIR-Based Method Using Aqueous Dimethyl Sulfoxide Extraction
, Yuliya Yu. Petrova 1, Ruslan Ya. Bajbulatov 1 and Oleg S. Sutormin 1,2,*
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1: Soil sampling and characterization in Section 2.1 are adequately described, but key parameters like soil pH, cation exchange capacity, and exact organic matter content percentage are missing. These should be added to better contextualize the low sorption capacity of the sandy podzolic soil. In addition, The author needs to thoroughly correct language and sentence errors throughout the entire text, which can avoid excessive colloquialism and scientific rigor.
2: The preparation of model contaminated soils (Section 2.2) uses artificial contamination, which is suitable for controlled experiments. Nevertheless, the discussion should address potential differences in extraction efficiency between fresh and aged/weathered hydrocarbons, as noted in the limitations but not expanded upon. In addition, The extraction procedures (Section 2.3) are detailed, but the choice of 60-minute shaking time and room temperature (22-24°C) lacks justification.
3: Reservoir contamination caused by oil extraction is a problem that cannot be avoided in current energy extraction. The above discussion needs to be described in the introduction and reinforced with the following previous articles: ---Effect of Nanomaterials on Improving the Apparent Viscosity of Heavy Oil and the Environmental Evaluation of Reservoir Environment. ---Microscopic Analysis of Flow Resistance of Oil Displacement Fluid in Reservoir Fractures
4: In the FTIR spectroscopic analysis (Section 2.4), the adaptation from PND F 16.1:2.2.22-98 is mentioned, but instrumental details such as spectral resolution, number of scans per spectrum, and baseline correction methods are omitted. These should be included for methodological transparency. In addition, axis labels and peak assignments could be enlarged and more precisely annotated for better readability in Figure 1.
5: The selection of 75% DMSO (Section 3.2) is well-supported by the non-linear absorbance-concentration relationship in Figures 2 and 3. That said, the semi-logarithmic plot (Figure 3b) could benefit from a fitted exponential model equation to quantify the observed threshold behavior. Moreover, The comparison of water and aqueous DMSO extractions (Section 3.3) clearly shows DMSO's superiority, but the discussion of residual DMSO interference in spectra (Figure 4b) is underdeveloped.
6: Conclusions (Section 5) accurately summarize the findings but slightly overstate the method's immediate applicability to "comprehensive soil contamination and remediation frameworks." Tone this down and emphasize the need for validation in field conditions.
Author Response
Point 1: Soil sampling and characterization in Section 2.1 are adequately described, but key parameters like soil pH, cation exchange capacity, and exact organic matter content percentage are missing. These should be added to better contextualize the low sorption capacity of the sandy podzolic soil. In addition, The author needs to thoroughly correct language and sentence errors throughout the entire text, which can avoid excessive colloquialism and scientific rigor.
Answer 1: We thank the reviewer for this constructive comment. Section 2.1 has been revised to include the measured soil physicochemical parameters. Specifically, soil pH in water (1:2.5 soil-to-solution ratio) and soil organic carbon (SOC) content are now reported, with explicit indication of the analytical methods used (GOST 26423-85 and the Tyurin oxidation method, respectively). The measured pH value (6.24) and SOC value (0.40%) are now clearly stated in the manuscript (Lines 149-152).
Cation exchange capacity (CEC) was not directly determined in the present study. Because the primary objective of this work was methodological development of an FTIR-based extraction approach rather than comprehensive pedological characterization, we limited the reported parameters to those directly measured and analytically relevant. To avoid overinterpretation, statements implying quantified CEC values have been removed or reformulated accordingly.
In addition, the entire manuscript has undergone careful language editing to improve clarity, eliminate colloquial phrasing, and enhance scientific rigor. Numerous stylistic and grammatical corrections have been introduced throughout the text. All modifications are highlighted in the revised version of the manuscript.
Point 2: The preparation of model contaminated soils (Section 2.2) uses artificial contamination, which is suitable for controlled experiments. Nevertheless, the discussion should address potential differences in extraction efficiency between fresh and aged/weathered hydrocarbons, as noted in the limitations but not expanded upon. In addition, the extraction procedures (Section 2.3) are detailed, but the choice of 60-minute shaking time and room temperature (22-24°C) lacks justification.
Answer 2: We appreciate this important remark. The Discussion section has been expanded to more thoroughly address differences between freshly spiked and aged/weathered petroleum hydrocarbons (Lines 387-396). We now explicitly discuss aging-related processes such as volatilization of lighter fractions, microbial transformation, and increasing association of heavier components with soil organic matter and mineral surfaces. The implications for extraction efficiency, concentration–response behavior, and potential recalibration for field-contaminated soils are described in greater detail.
Regarding extraction conditions, justification for the 60-minute shaking time and room temperature (22-24 °C) has been added to Section 2.3 (Lines 183-190). These parameters were selected as a practical compromise between sufficient mass transfer in batch extraction systems and procedural reproducibility, and were supported by preliminary optimization indicating that the FTIR C–H band response approached a stable spectral response under these conditions while maintaining consistency with commonly applied laboratory conditions for aqueous extract preparation in bioassay protocols.
Point 3: Reservoir contamination caused by oil extraction is a problem that cannot be avoided in current energy extraction. The above discussion needs to be described in the introduction and reinforced with the following previous articles: ---Effect of Nanomaterials on Improving the Apparent Viscosity of Heavy Oil and the Environmental Evaluation of Reservoir Environment. ---Microscopic Analysis of Flow Resistance of Oil Displacement Fluid in Reservoir Fractures
Answer 3: We thank the Reviewer for this suggestion. The Introduction has been revised to better contextualize petroleum-related environmental impacts beyond surface spills, including processes associated with extraction, reservoir stimulation, and fluid-rock interactions (Lines 57-62). The recommended references have been incorporated to strengthen the discussion of upstream processes contributing to environmental burdens across the production chain and to support the broader context motivating reliable soil assessment tools.
Point 4: In the FTIR spectroscopic analysis (Section 2.4), the adaptation from PND F 16.1:2.2.22-98 is mentioned, but instrumental details such as spectral resolution, number of scans per spectrum, and baseline correction methods are omitted. These should be included for methodological transparency. In addition, axis labels and peak assignments could be enlarged and more precisely annotated for better readability in Figure 1.
Answer 4: We thank the Reviewer for this important methodological comment. Section 2.4 has been expanded to include the necessary instrumental details (Lines 207-216), including spectral resolution, number of scans per spectrum, background subtraction, and spectral processing procedures as well as an explicit statement on baseline handling (no additional mathematical baseline correction; DMSO-related background variability controlled by identical spectral windows and peak positions across samples).
Figure 1 has been revised to improve readability, including enlarged axis labels and clearer annotation of characteristic absorption bands.
Point 5: The selection of 75% DMSO (Section 3.2) is well-supported by the non-linear absorbance-concentration relationship in Figures 2 and 3. That said, the semi-logarithmic plot (Figure 3b) could benefit from a fitted exponential model equation to quantify the observed threshold behavior. Moreover, The comparison of water and aqueous DMSO extractions (Section 3.3) clearly shows DMSO's superiority, but the discussion of residual DMSO interference in spectra (Figure 4b) is underdeveloped.
Answer 5: We appreciate this constructive suggestion. Figure 3b has been updated to include the fitted linear regression in semi-logarithmic coordinates (equation and R² shown on the plot). This semi-log fit corresponds to an exponential dependence of absorbance on DMSO concentration in the original scale, thereby quantifying the observed threshold-like behavior and providing a clearer mathematical description of the solvent-dependent enhancement of apparent hydrocarbon solubility.
In addition, the Discussion section has been expanded to more comprehensively address residual DMSO interference in FTIR spectra. We now discuss potential baseline effects, overlapping contributions, and strategies for minimizing solvent-related variability, including standardized baseline handling, solvent blank subtraction, and potential multivariate correction approaches for future quantitative refinement (Lines 357-374).
Point 6: Conclusions (Section 5) accurately summarize the findings but slightly overstate the method's immediate applicability to "comprehensive soil contamination and remediation frameworks." Tone this down and emphasize the need for validation in field conditions.
Answer 6: We thank the Reviewer for this important observation. The Conclusions section has been revised to moderate claims regarding immediate applicability. The wording now emphasizes that the method is currently best suited for coarse-textured sandy soils under controlled conditions and requires further validation using aged and field-contaminated soils and extension to other soil types (including finer-textured and higher-SOM soils). The need for broader soil-type testing and integration with biological assays is clearly highlighted (Lines 439-446).
Reviewer 2 Report
Comments and Suggestions for Authors1. Polluted soils are of great concern. The topic of this manuscript is in the line of the need of good methods to determine pollutants in a complex matrix like the soils. This paper entitled “Reducing the Gap between Chemical and Biological Assessment of Petroleum-Contaminated Soils: An FTIR-Based Method Using Aqueous Dimethyl Sulfoxide Extraction” add some information of interest regarding the soil pollution by petroleum.
2. I find the abstract quite good, as well as the keywords selected. However, some keywords appear in the title of the manuscript, so, if possible, it is better to use different words to facilitate the search in the database. We use to search by using title and keywords, so the possibilities of targeting researchers are great.
3. The introduction gives an adequate overview of the problem. I want to add that in all the countries, derived pollution from petroleum is presented close to petrol stations, so, the relevance of having a good method to determine the effects of the pollution can be greater considering this. Probably, future research can be centered in derived petroleum fuels.
4. I totally agree with “Despite their complementary roles, chemical and biological assessment approaches often yield results that are difficult to compare directly”. As a comment to improve the manuscript, I think that some mention about the complexity of the soils as a matrix with many different compounds and biota, including organic matter and some organic compounds that can react with petroleum, can be added in the introduction.
5. The section 2 is comprehensive and accurate. I think that the soil has a sandy-loam or sandy texture as it is a podzol. Additional information about soil properties can help to understand this experiment (only if they are available, minor comment). What it is necessary to justify is the reason of taking the soil sample from the middle horizon. In fact, the type of soil is a limiting factor of this experiment and for future research, it is necessary to use different types of soils.
6. The results are presented simply but are correct. They are, in fact, the results of an experimental procedure where there is little variability in the soil matrix, and it is an experiment similar to the fine-tuning of a new method. In this respect, everything is correct.
7. Regarding the discussion, the most important point, from my perspective, is that the authors address the experimental limitations and the future research to be conducted. In this respect, I refer to my previous comments.
8. Conclusions are supported by the results obtained
9. I believe that the references, although not extensive, seem sufficient. Probably in some way, they can be improved.
Author Response
Point 1: Polluted soils are of great concern. The topic of this manuscript is in the line of the need of good methods to determine pollutants in a complex matrix like the soils. This paper entitled “Reducing the Gap between Chemical and Biological Assessment of Petroleum-Contaminated Soils: An FTIR-Based Method Using Aqueous Dimethyl Sulfoxide Extraction” add some information of interest regarding the soil pollution by petroleum.
Answer 1: We thank the Reviewer for the positive evaluation. In the revised manuscript, we further refined the framing of the study as a method-development contribution aimed at improving comparability between solvent-based chemical FTIR monitoring and aqueous-extract-based biological assessment workflows, as explicitly stated in the Abstract and in the final paragraph of the Introduction (study aim and rationale).
Point 2: I find the abstract quite good, as well as the keywords selected. However, some keywords appear in the title of the manuscript, so, if possible, it is better to use different words to facilitate the search in the database. We use to search by using title and keywords, so the possibilities of targeting researchers are great.
Answer 2: We agree. The keyword list has been revised to reduce redundancy with the title and to improve discoverability in database searches by including related, search-relevant terms rather than direct repetitions. Specifically, we prioritized complementary indexing terms such as “cosolvency effect”, “water-miscible co-solvent”, “infrared screening”, and “soil extractability”, which are not direct repeats of the title wording.
Point 3: The introduction gives an adequate overview of the problem. I want to add that in all the countries, derived pollution from petroleum is presented close to petrol stations, so, the relevance of having a good method to determine the effects of the pollution can be greater considering this. Probably, future research can be centered in derived petroleum fuels.
Answer 3: We thank the Reviewer for this practical remark. A paragraph has been added to the Introduction highlighting chronic low-intensity leaks and runoff near petrol stations and fuel storage/distribution nodes as widespread sources of petroleum-derived soil contamination in urban and peri-urban environments. We also note that future validation should extend from crude oil to refined petroleum fuels (e.g., diesel and gasoline fractions) as a dedicated field-oriented validation direction (Lines 63-69).
Point 4: I totally agree with “Despite their complementary roles, chemical and biological assessment approaches often yield results that are difficult to compare directly”. As a comment to improve the manuscript, I think that some mention about the complexity of the soils as a matrix with many different compounds and biota, including organic matter and some organic compounds that can react with petroleum, can be added in the introduction.
Answer 4: We agree. The Introduction has been expanded to better reflect soil as a heterogeneous reactive matrix including minerals, organic matter, pore water, and biota, and to emphasize that partitioning, sorption, and transformation processes complicate extraction and interpretation. This addition directly supports the rationale for comparing extraction media (Lines 80-85).
Point 5: The section 2 is comprehensive and accurate. I think that the soil has a sandy-loam or sandy texture as it is a podzol. Additional information about soil properties can help to understand this experiment (only if they are available, minor comment). What it is necessary to justify is the reason of taking the soil sample from the middle horizon. In fact, the type of soil is a limiting factor of this experiment and for future research, it is necessary to use different types of soils.
Answer 5: We clarified in Section 2.1 that the 30-50 cm mineral horizon was selected to minimize variability associated with fresh litter and heterogeneous surface organic layers while still representing a matrix relevant to potential downward migration of petroleum hydrocarbons (Lines 139-143). We also added the key soil properties requested by the Reviewer, confirming a predominantly sandy texture (>97% fine sand; negligible silt/clay), low SOC (0.40%), and supporting parameter (pH) (Lines 149-153), to better contextualize the low sorption capacity of the selected Podzol horizon. We also explicitly acknowledge in the Discussion that soil type represents a limitation and that validation on finer-textured and higher-organic-matter soils is required (Lines 398-406).
Point 6: The results are presented simply but are correct. They are, in fact, the results of an experimental procedure where there is little variability in the soil matrix, and it is an experiment similar to the fine-tuning of a new method. In this respect, everything is correct.
Answer 6: We thank the Reviewer for this constructive interpretation. The Results section was intentionally kept focused and concise to reflect the method-development nature of the study. To support transparency and repeatability, all extractions and FTIR measurements were performed in triplicate and results are reported as mean ± SD, consistent with the controlled-matrix optimization scope.
Point 7: Regarding the discussion, the most important point, from my perspective, is that the authors address the experimental limitations and the future research to be conducted. In this respect, I refer to my previous comments.
Answer 7: Following the Reviewer’s recommendation, we strengthened the Discussion to explicitly address (i) differences between freshly spiked and aged/weathered contamination (Lines 387-396), (ii) the limitation of using a single coarse-textured low-SOC soil, and (iii) the need for validation using field-contaminated soils, aged residues, and different soil textures and organic matter levels (Lines 398-406). We also highlight integration with aqueous-extract-based bioassays as a key future direction to improve chemical–biological comparability (Conclusion section).
Point 8: Conclusions are supported by the results obtained
Answer 8: We thank the Reviewer for this assessment.
Point 9: I believe that the references, although not extensive, seem sufficient. Probably in some way, they can be improved.
Answer 9: We reviewed and refined the reference list to ensure consistency and direct alignment with the revised narrative, particularly in the Introduction and Discussion sections. In particular, we added and (or) updated references supporting: upstream (reservoir-related) environmental context; DMSO (co-solvent) use in analytical and toxicity-testing settings; and methodological guidance relevant to aqueous (co-solvent) approaches, thereby improving the breadth and traceability of the revised arguments.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors, I congratulate you on your interesting manuscript. I think that with my suggestions and comments, the work will be even better.
My suggestions:
- The last author (Oleg S. Sutormin) of the manuscript has the numbers 1 and 2 next to his last name. Does he work in two places or did you write one number by mistake?
- Throughout the manuscript, two terms are mixed up, crude oil on one side and petroleum hydrocarbons on the other. They are not the same at all. Crude oil is raw unrefined fossile fuel from underground very deep geologic faormations. Petroleum hydrocarbons are a broad group of thousands of organic compounds made primarily of hydrogen and carbon, derived from crude oil, bitumen, and coal. They are the main components of fuels (gasoline, diesel, jet fuel), lubricants, and asphalt. These compounds, often referred to as Total Petroleum Hydrocarbons (TPH), are categorized by their molecular size, boiling point, and behavior in the environment. The authors need to clarify what they used in experiment in laboratory?
- Line 114. Soil properties are extremely important in such research. Please explain the soil properties (texture, pH, organic matter percentage) in more detail. Also state the depth from which the soil samples were taken. You wrote: ...low organic matter....,
- It is mandatory to determine the soil type according to the WRB classification
https://wrb.isric.org/documents/ or https://isric.org/explore/wrb
- Line 151 - you wrote PND F 16.1:2.2.22-98
- Instead of the letter "A" in the all Figures, write the full name
- Line 307. In several places in the manuscript you use low humus level or high humus level. Please express this in numbers: 2% or 5%
English is not my native language, so I can't judge it.
Author Response
Point 1: The last author (Oleg S. Sutormin) of the manuscript has the numbers 1 and 2 next to his last name. Does he work in two places or did you write one number by mistake?
Answer 1: The indication of affiliations “1,2” is correct. Dr. Oleg S. Sutormin holds a primary position at Surgut State University (Affiliation 1) and an additional appointment at the Department of Biophysics, School of Fundamental Biology and Biotechnology, Siberian Federal University (Affiliation 2). This is not a typographical error.
Point 2: Throughout the manuscript, two terms are mixed up, crude oil on one side and petroleum hydrocarbons on the other. They are not the same at all. Crude oil is raw unrefined fossile fuel from underground very deep geologic faormations. Petroleum hydrocarbons are a broad group of thousands of organic compounds made primarily of hydrogen and carbon, derived from crude oil, bitumen, and coal. They are the main components of fuels (gasoline, diesel, jet fuel), lubricants, and asphalt. These compounds, often referred to as Total Petroleum Hydrocarbons (TPH), are categorized by their molecular size, boiling point, and behavior in the environment. The authors need to clarify what they used in experiment in laboratory?
Answer 2: We appreciate this important clarification request. The revised manuscript now clearly distinguishes between crude oil, which was used in the laboratory as a multicomponent unrefined petroleum mixture for artificial soil contamination (Section 2.2, Lines 159-164), and petroleum hydrocarbons, which refer to the operationally defined hydrocarbon fraction extracted from the soil–oil system and quantified by FTIR in the 2800–3100 cm⁻¹ region (i.e., an operationally defined TPH-like fraction, as stated in Section 2.2). This clarification has been explicitly introduced in the Abstract, Section 2.2, and the Results section.
Point 3: Line 114. Soil properties are extremely important in such research. Please explain the soil properties (texture, pH, organic matter percentage) in more detail. Also state the depth from which the soil samples were taken. You wrote: ...low organic matter....,
Answer 3: Section 2.1 has been expanded to provide detailed soil characterization, including sampling depth, particle-size distribution, soil pH, and soil organic carbon (SOC) content. Cation exchange capacity (CEC) was not measured in the present study and therefore is not reported; we have avoided statements implying quantified CEC values. These additions contextualize the low sorption capacity typical of quartz-dominated sandy Podzols.
Point 4: It is mandatory to determine the soil type according to the WRB classification https://wrb.isric.org/documents/ or https://isric.org/explore/wrb
Answer 4: The WRB classification has been added in Section 2.1. According to the World Reference Base for Soil Resources (WRB, 2022), the investigated soil corresponds to a Podzol (Lines 135-137). The WRB reference has been included in the reference list and cited appropriately.
Point 5: Line 151 - you wrote PND F 16.1:2.2.22-98
Answer 5: The citation has been verified and correctly formatted in the revised manuscript.
Point 6: Instead of the letter "A" in the all Figures, write the full name
Answer 6: All figures have been revised to replace single-letter notation with the full term “Absorbance,” improving clarity and consistency. For the semi-log plot (Figure 3b), the y-axis denotes a log-transformed absorbance and is labeled accordingly (e.g., log(Absorbance)) rather than a standalone “A”.
Point 7: Line 307. In several places in the manuscript you use low humus level or high humus level. Please express this in numbers: 2% or 5%
Answer 7: Qualitative expressions have been replaced with numerical values where applicable. The investigated soil is now explicitly reported as SOC = 0.40%. When discussing broader applicability, numerical example thresholds (e.g., >4-5% SOM) are provided instead of qualitative descriptors.
Round 2
Reviewer 1 Report
Comments and Suggestions for Authorsaccepted
