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Variations in Polycyclic Aromatic Hydrocarbon Contamination Values in Subtidal Surface Sediment via Oil Fingerprinting after an Accidental Oil Spill: A Case Study of the Wu Yi San Oil Spill, Yeosu, Korea

Water 2023, 15(2), 279; https://doi.org/10.3390/w15020279

by Byeongkyu Min¹, Huiho Jeong²

, Juhye Oh¹, Kyejin Paek¹, Woohyun Paeng¹, Jonghyeok Lee¹, Chonrae Cho³ and Hyeonseo Cho^1,*

Reviewer 1:

Weijun Guo

Reviewer 2:

Elvira De Rosa

Water 2023, 15(2), 279; https://doi.org/10.3390/w15020279

Submission received: 28 November 2022 / Revised: 5 January 2023 / Accepted: 6 January 2023 / Published: 9 January 2023

(This article belongs to the Special Issue Monitoring and Assessment of Pollutants in Coastal Waters, Sediments, and Biota)

Round 1

Reviewer 1 Report

I have read your paper and found it interesting and novel. Some advice will guide you through the minor corrections still needed at this stage in your submission. The suggested corrections include:

Point 1. Line 344 - it is concluded that alkyl PAHs showed different types of inflows, including combustion origins such as petrochemical plants located near the accident spot, vessel navigation, smoke and soot from surrounding cities. I think the author's conclusion is credible, however, the author should give the emission load of these sources in the discussion section. For example, the concentration of PAHs and alkyl PAHs in the local smoke and soot.

Point 2. In the end of this paper, it is concluded that the levels of polycyclic aromatic hydrocarbons before the accident were restored. I doubt this conclusion. As POPs, PAHs are unlikely to degrade so quickly. Personally, I think it is more likely that it will be transported to other sea areas under the action of sea currents. I hope the author can give a more reasonable explanation to the survey results.

Author Response

<A Cover Letter >

Journal: Water (ISSN 2073-4441)

Type: Article Manuscript ID: water-2094120

Title: Variations of Polycyclic Aromatic Hydrocarbons Contaminations in Subtidal Surface Sediment via Oil Fingerprinting After the Accidental Oil Spill: A Case Study of the Wu Yi San Oil Spill, Yeosu, Korea

Dear. Editors and Reviewers,

We are glad to resubmit the revised vision of the manuscript entitled ‘Variations of Polycyclic Aromatic Hydrocarbons Contaminations in Subtidal Surface Sediment via Oil Fingerprinting After the Accidental Oil Spill: A Case Study of the Wu Yi San Oil Spill, Yeosu, Korea’ to the Water (ISSN 2073-4441).

Before entering the second response, we would like to appreciate the reviewer's detailed comments. The authors believe that these comments will help us further improve the manuscript and have addressed the specific comments of each reviewer by providing a point-by-point response. Please take the time to consider reviewing again.

The revised parts were marked in red color with line numbers of the revised manuscript in this response. The "Track Changes" function in MS Word was used following the journal's guidelines.

Please see our attached response letter for each comment of the reviewers.

We appreciate your hard work, dedication, and cooperation.

Sincerely,

24 December 2022

Corresponding Author

<Reviewer 1 Comments>

Reviewer 1–Q1) Line 344 - it is concluded that alkyl PAHs showed different types of inflows, including combustion origins such as petrochemical plants located near the accident spot, vessel navigation, smoke and soot from surrounding cities. I think the author's conclusion is credible, however, the author should give the emission load of these sources in the discussion section. For example, the concentration of PAHs and alkyl PAHs in the local smoke and soot.

Reviewer 1–Q2). In the end of this paper, it is concluded that the levels of polycyclic aromatic hydrocarbons before the accident were restored. I doubt this conclusion. As POPs, PAHs are unlikely to degrade so quickly. Personally, I think it is more likely that it will be transported to other sea areas under the action of sea currents. I hope the author can give a more reasonable explanation to the survey results.

_{<Authors Response 1>}

Reviewer 1-Q1) Line 344 - it is concluded that alkyl PAHs showed different types of inflows, including combustion origins such as petrochemical plants located near the accident spot, vessel navigation, smoke and soot from surrounding cities. I think the author's conclusion is credible, however, the author should give the emission load of these sources in the discussion section. For example, the concentration of PAHs and alkyl PAHs in the local smoke and soot.

Authors 1-A1) The authors appreciate the reviewer's comment. It was supplemented in the revised manuscript.

Results and Discussions L.405-413. There was a report that the ∑16 PAHs levels in the atmosphere were 47.66 and 56.15 ng/m³ in the two local industrial facilities in the study area and 70.64 and 97.58 ng/m³ in two local residential areas surrounding the present study area, Yeosu and Gwangyang Cities, respectively [50]. Although there are no studies on PAHs contaminations derived from the shipping movement, the active movement that the number of vessel entries/departures was a total of 109,539 ships from January 2014 to May 2015 [51] was reported. These previous reports imply that the combustion origin from the industrial facilities, the residences, and the shipping movement played an essential role in PAHs contaminations in the study area.

Reviewer 1-Q2) In the end of this paper, it is concluded that the levels of polycyclic aromatic hydrocarbons before the accident were restored. I doubt this conclusion. As POPs, PAHs are unlikely to degrade so quickly. Personally, I think it is more likely that it will be transported to other sea areas under the action of sea currents. I hope the author can give a more reasonable explanation to the survey results.

Authors 1-A2) The authors appreciate the reviewer's comment and agreed with that the conclusion was not clear. It was supplemented in the revised manuscript.

Results and Discussions L.302-314. Notably, Jang et al. [23] determined the distributions of PAHs contamination derived from the Wu Yi San oil spill in the forty-surface sediment on the intertidal zone in the vicinity of the accident area. They highlighted the possibility that the fast tidal velocity and 82,880 volunteers for the purification made 16 PAHs levels considerably decrease four months after the oil spill, a similar tendency as the present results. In the subtidal zone, the Ministry of Oceans and Fisheries in Korea and The Korean Coast Guard were devoted to preventing and controlling the spreading of the oil spill, back then; The disaster prevention personnel 122,363 people, volunteers 7,873 people, 5,709 ships, 29 helicopters, 27,320 cm of the oil fences, 98,726 kg of the oil adsorbent, 3,651 the disaster prevention equipment [56]. This tendency can be found in the ∑Alkyl PAHs levels following the Hebei Spirit oil spill accident in Taean in December 2007, which decreased drastically from 3,800 ng/g on average immediately after the accident to the background level by September 2008 [24].
Results and Discussions L.354-369. The investigation in the present study was carried out one month after the oil spill on 31st January 2014. The spilled oil had light density resulting in a buoyant characteristic. This indicated that the oil was rapidly dispersed to the adjacent coasts rather than vertically deposited to the sediment via the fast velocity of tidal currents (the maximum velocity of 42.2 cm/s) because the accident area has a specific geographical characteristic, a relatively narrow channel.
The modeling results stated above [19] reported that, within three days after the oil spill, the PAHs distribution in the seawater was not found, but it accumulated on the adjacent coasts and beaches. Notably, ∑ 16PAHs and ∑ Alkyl PAHs in forty coasts and beaches in the previous study [23] were considerably higher than in the present study; the 16PAHs were ranged from 489-2,089 ng/g and accounted for 67% of the total PAHs (727-3,121 ng/g), implying that the previous modeling results [19] are persuasive. This sequence of results indicates that the spilled oil was not resident in the seawater and horizontally spread toward the adjacent coasts and beaches following the tidal current affected by the specific geographical and meteorological characteristics, resulting in no statistical significance in PAHs levels between surface seawater and sediment.
Conclusion L.490-506. The present study determined the variations of PAHs contamination in the subtidal surface sediment with oil fingerprinting and assessed its contaminations in the Wu Yi San oil spill in Yeosu City, Korea. The PAH levels in St.E and St.17, which have a short distance from the accident area, decreased considerably over time. Remarkably, the tendency was highlighted four months after the oil spill. This might be derived from the fast tidal current and effective prevention and control efforts by the Korean government. The PAHs contaminations were no statistical correlations between surface sediment and seawater. It indicates that the fate of PAHs in the surface seawater were rapidly spread toward the adjacent coasts and beaches rather than retained on the water column. The isomeric ratios of the 16 PAHs showed that the pyrogenic origin was dominant. Notably, there was no correlation between the 16 PAHs and the alkylated PAHs, and it indicates that alkylated PAHs were derived from the complex origins accompanying the combustion and oil spill sources. Notably, the double ratios of PAHs in this study were distinguished from the accident oil. The present study is the first to determine the Wu Yi San oil spill using oil fingerprinting in the subtidal surface sediment in the study area. The strategic research plan should be established to comprehensively assess the current PAHs contamination from the oil spill in the subtidal surface sediment based on this preliminary study as a cornerstone.

Author Response File: Author Response.docx

Reviewer 2 Report

In the manuscript titled “Variations of Polycyclic Aromatic Hydrocarbons Contaminations in Subtidal Surface Sediment via Oil Fingerprinting After the Accidental Oil Spill: A Case Study of the Wu Yi San Oil 5 Spill, Yeosu, Korea” the authors determine the PAHs concentrations and the presence or absence of oil after the Wu Yi San oil spill in and around the spill zone, 16 PAHs and alkylated PAHs were analyzed. This work is interesting but limited to a single event, therefore more suitable for a regional investigation, moreover, the mere evaluation of the concentrations present in the sediment does not make the paper complete from a scientific point of view.

The authors to publish this study must improve it in several aspects. Therefore, my final opinion is to accept the paper with major revision.

Major points:

1) Abstract: In the abstract authors should provide to include immediate information on the data obtained and information on the risk assessment or origin of the PAHs found in the study area. Add a sentence about these information for immediate feedback.

2) Introduction Section: In the Introduction the authors do not explain what the objectives of the work are. I suggest including them

3) In particular, an important issue regarding this manuscript is the total lack of analysis on Suspended particulate matter and Dissolved phase. Yet, it would be essential to carry out analyses also on these matrices. In fact, to correctly analyse the PAHs behaviour it is very important to understand how they move through the water column, also to understand what kind of pollution it is. Analyse the distribution between sediment, SPM and dissolved phase, allows readers to understand if PAHs input in this study area is a fresh or an historical input. This information is very important to accurately study the type of pollution and to allow readers to have consistent data with which to compare.

4) Results: Isomeric ratios are widely used to estimate the origin of PAHs. In the literature there are many papers that talk about it. I suggest the authors to add the statistical analysis that can enrich and confirm their thesis (for example a PCA).

5) Results: To make the paper complete, the authors should have also evaluated the fugacity, in fact water-sediment partitioning is an important environmental process that can be used to evaluate the equilibrium partition behaviour of PAHs in aquatic environments. This further underlines the importance of evaluating the concentrations of these compounds in the three different phases (dissolved phase, SPM and sediment).

6) Results: I suggest the authors also evaluate the toxicity of the increasingly emerging PAHs in aquatic environment.

7) Figure 1: improve the resolution of this image

Minor points:

1) Add bibliographic references, furthermore a single reference added at the end of the sentences is not enough and it is necessary to add more than one to support the concepts expressed.

Author Response

<A Cover Letter >

Journal: Water (ISSN 2073-4441)

Type: Article Manuscript ID: water-2094120

Dear. Editors and Reviewers,

The revised parts were marked in red color with line numbers of the revised manuscript in this response. The "Track Changes" function in MS Word was used following the journal's guidelines.

Please see our attached response letter for each comment of the reviewers.

We appreciate your hard work, dedication, and cooperation.

Sincerely,

24 December 2022

Corresponding Author

<Reviewer 2 Comments>

Reviewer 2–Q1) Abstract: In the abstract authors should provide to include immediate information on the data obtained and information on the risk assessment or origin of the PAHs found in the study area. Add a sentence about these information for immediate feedback.

Reviewer 2–Q2) Introduction Section: In the Introduction the authors do not explain what the objectives of the work are. I suggest including them

Reviewer 2–Q3) In particular, an important issue regarding this manuscript is the total lack of analysis on Suspended particulate matter and Dissolved phase. Yet, it would be essential to carry out analyses also on these matrices. In fact, to correctly analyse the PAHs behaviour it is very important to understand how they move through the water column, also to understand what kind of pollution it is. Analyse the distribution between sediment, SPM and dissolved phase, allows readers to understand if PAHs input in this study area is a fresh or an historical input. This information is very important to accurately study the type of pollution and to allow readers to have consistent data with which to compare.

Reviewer 2–Q5) Results: To make the paper complete, the authors should have also evaluated the fugacity, in fact water-sediment partitioning is an important environmental process that can be used to evaluate the equilibrium partition behaviour of PAHs in aquatic environments. This further underlines the importance of evaluating the concentrations of these compounds in the three different phases (dissolved phase, SPM and sediment).

Reviewer 2–Q6) Results: I suggest the authors also evaluate the toxicity of the increasingly emerging PAHs in aquatic environment.

Reviewer 2–Q7) Figure 1: improve the resolution of this image

_{<Authors Response 2>}

Authors 2-A1) The authors appreciate the reviewer's comment. It was supplemented in the revised manuscript.

Abstract L.15-26. This study aimed to determine the variations of PAHs contamination in the subtidal surface sediment with oil fingerprinting in the Wu Yi San oil spill in Yeosu, Korea, in January 2014. The ∑16PAHs and ∑alkyl PAHs were investigated in surface sediment and seawater one month after the oil spill for one year with three months intervals in the accident (St.A-F) and adjacent areas (St.1-20). The averaged ∑16 PAHs and ∑Alkyl PAHs concentrations ranges in the five samplings were 42.2-171.7 ng/g and 211.5-221.8 ng/g, respectively. Comparing the PAHs levels in St.E and St.17 indicated a decreased tendency, from 357.9 to 31.1 ng/g dw. in ∑16 PAHs, from 1,900.9 to 211.5 ng/g dw. in ∑Alkyl PAHs. The PAHs were not statically correlated between the surface sediment and seawater (p>0.05), implying the PAHs fate was rapidly dispersed toward adjacent coasts and beaches. Pyrogenic origin was predominant in 16-PAHs and petrogenic origin in alkylated PAHs. Notably, C2-D/C2-P and C3-D/C3-P ratios in the accident area in the first sampling were similar to accident oil, but the similarity was not shown in other samplings. Only the C2-naphthalene (St.A), C1- (St.A and St.B), and C2-phenanthrenes (the entire accident area points) were higher than the ERL SQG.

Reviewer 2–Q2) Introduction Section: In the Introduction the authors do not explain what the objectives of the work are. I suggest including them

Authors 2-A2) The authors appreciate the reviewer's comment. It was supplemented in the revised manuscript.

Introduction L.72-82. Therefore, monitoring the oil contamination is essential in the study area. The present study investigated the 16 PAHs and alkylated PAHs levels in the surface sediment and seawater in Gwangyang Bay and Yeosu Strait five times one month after the accident in three-month intervals. This study aims to determine the variations of the PAHs contamination in subtidal surface sediment using oil fingerprinting after the oil spill and assessing the biological effects via sediment quality guidelines (SQGs). It is a preliminary study as a cornerstone to assess the current PAHs contamination derived from the oil spill in the surface sediment ten years after the accident. To the best of our knowledge, this is the first report to determine the Wu Yi San oil spill using oil fingerprinting in the subtidal surface sediment in the study area. This will provide insight into monitoring other oil spills and preventing and controlling the possibility of accidental ones.

Authors 2-A3) The authors appreciate the reviewer's comment. Herein, the PAHs levels in seawater and the discussion on the fate of PAHs derived from the oil spill were additionally supplemented in the revised manuscript, including the point that should be improved in future work.

Methods and Materials L.169-186. The liquid-liquid extraction method was employed to analyze PAHs in the surface seawater. The 2 mg/L of the surrogate internal standard (naphthalene-d₈, acenapthalene-d₁₀, phenanthrene-d₁₀, chrysene-d₁₂, perylene-d₈; internal standard mix, Supelco, Bellefonte, PA, USA) was spiked in the 2 L of a seawater sample, and 100 mL of dichloromethane was added to the sample. The solution was shaken intensely for 1 hour (RS-1, JEIO TECH, Korea) and left for 1 hour. The extracted solution was filtered with the anhydrous sodium sulfate put on the filter paper using a glass funnel to remove moisture. This extraction process was repeated twice. The solvent was substituted with the hexane using a rotary evaporator, and the filtered sample was concentrated to approximately 1-2 mL. The silica gel column was used to purify the concentrated solution. After injecting the solution, 25 mL of hexane was poured, and the flowed hexane through the column was discarded. After purification, 25 mL of dichloromethane: hexane (2:3 v/v) was poured to elute the target materials. The solvent in the extracted solution was substituted with the hexane and was concentrated to approximately 1-2 mL. This concentrated sample was transferred to 10 mL of a glass centrifuge tube, and 100 µL of the gas chromatograph internal standard (terphenyl-d₁₄, Supelco, Bellefonte, PA, USA) was spiked. The sample was concentrated into 1.0 mL using nitrogen gas (99.99%) and used as a sample for GC analysis.
Results and Discussions L.339-377.
3.2. Distribution of the PAHs concentrations in surface Seawater
Table 6 shows the results of the total of 16 priority management PAHs (∑16PAHs) in the surface seawater in the twenty sampling points. The concentration ranges of ∑16PAHs were 2.2–3 ng/L (average 20.9±10.9ng/L), 18.8–167.9 ng/L (average 59.7±46.0 ng/L), 2.9–103.9 ng/L (average 38.5±31.8 ng/L), 9.0–56.3 ng/L (average 29.9±14.2 ng/L), and 5.1–12.5 ng/L (average 8.4±2.2 ng/L ) in the first (May 2014), second (August 2014), third (November 2014), fourth (February 2015), fifth samplings (May 2015), respectively. The concentration was a tendency to decrease over time.
In the previous study, higher PAHs concentrations in surface seawater and suspended particulate matter (SPM) were reported than in sediment [50]. Contrary to this, ∑ 16PAHs levels in the surface seawater (average 31.5 ng/L) showed four orders of magnitude lower than the level in the surface sediment (average 107.9 ng/g dw.). The levels of seawater and sediment were not shown a statistically significant correlation in each sampling time (p-value > 0.50, Pearson correlation analysis)(Fig.3).
The investigation in the present study was carried out one month after the oil spill on 31st January 2014. The spilled oil had light density resulting in a buoyant characteristic. This indicated that the oil was rapidly dispersed to the adjacent coasts rather than vertically deposited to the sediment via the fast velocity of tidal currents (the maximum velocity of 42.2 cm/s) because the accident area has a specific geographical characteristic, a relatively narrow channel.
The modeling results stated above [19] reported that, within three days after the oil spill, the PAHs distribution in the seawater was not found, but it accumulated on the adjacent coasts and beaches. Notably, ∑ 16PAHs and ∑ Alkyl PAHs in forty coasts and beaches in the previous study [23] were considerably higher than in the present study; the 16PAHs were ranged from 489-2,089 ng/g and accounted for 67% of the total PAHs (727-3,121 ng/g), implying that the previous modeling results [19] are persuasive. This sequence of results indicates that the spilled oil was not resident in the seawater and horizontally spread toward the adjacent coasts and beaches following the tidal current affected by the specific geographical and meteorological characteristics, resulting in no statistical significance in PAHs levels between surface seawater and sediment.
However, the present study analyzed the PAHs in the surface seawater regardless of the PAHs present types. The SPM acts as the essential carrier for pollutants in the marine environment [47-48] because the hydrophobic property makes PAHs in surface seawater adsorb to the SPM in the water column. The SPM is, therefore, one of the primary factors in the transportation and weathering of PAHs [49]. Furthermore, the PAHs fugacity in the seawater-surface sediment is also the primary point on the fate of PAHs [52]. Since many researchers highlighted these significant roles of PAHs contamination in sediment, suspended particulate matter, and dissolved phases [49, 52], this perspective should be implemented in future work to understand the detailed current fate of PAHs.

Table 6. Total concentrations of 16 PAHs and alkylated PAHs concentrations in surface seawater in Gwangyang Bay and the Yeosu Channel

Station	∑16PAHs (ng/L)
Station	May 2014	Aug. 2014	Nov. 2014	Feb. 2015	May 2015
st. 1	38.9	21.2	86.0	14.5	10.4
st. 2	24.9	54.9	74.4	37.5	9.3
st. 3	38.6	45.3	75.6	43.9	7.4
st. 4	39.8	46.6	81.6	46.0	6.5
st. 5	40.3	28.7	82.0	29.5	8.9
st. 6	25.7	40.0	2.9	32.0	10.2
st. 7	14.0	40.0	44.2	55.9	5.1
st. 8	17.8	46.0	11.0	9.0	6.5
st. 9	18.3	18.8	8.4	19.0	5.5
st.10	15.4	19.7	13.1	56.3	8.2
st.11	14.6	107.5	11.3	17.0	11.4
st.12	14.6	97.0	18.5	17.1	8.2
st.13	10.9	20.8	21.2	24.6	12.5
st.14	11.8	-	17.7	26.5	11.4
st.15	19.4	90.1	20.9	23.8	10.9
st.16	16.2	21.4	34.1	9.7	6.7
st.17	30.3	19.0	38.8	43.4	5.2
st.18	11.2	82.5	12.7	40.4	6.2
st.19	13.9	167.9	103.9	36.2	8.0
st.20	2.2	167.9	11.0	15.9	9.1
Min	272	18.8	2.9	9.0	5.1
Max	40.3	167.9	103.9	56.3	12.5
Mean	20.9	59.7	38.5	29.9	8.4
SD	10.9	46.0	31.8	14.2	2.2
Median	17.0	45.3	21.0	28.0	8.2

Reviewer 2–Q4) Results: Isomeric ratios are widely used to estimate the origin of PAHs. In the literature there are many papers that talk about it. I suggest the authors to add the statistical analysis that can enrich and confirm their thesis (for example a PCA).

Authors 2-A4) The authors appreciate the reviewer's suggestion. To the best of our knowledge, PCA is also frequently used to estimate the origin of PAHs and the isomeric ratios. The originality of the present study is that this is the first report to determine the Wu Yi San oil spill using oil fingerprinting in the subtidal surface sediment in the study area. The authors believe that the isomeric ratios in this study sufficiently and validly represent the PAHs origins, as shown in much previous research.

Notably, the present manuscript is just a preliminary study, and we will establish strategic research on the current PAHs distribution in the study area based on the manuscript. The reviewer's suggestion is obviously appropriate to complete future strategic research. The authors will positively consider using PCA in the next step. Once again, we are grateful for the reviewer's suggestion to improve our research.

Authors 2-A5) The authors appreciate the reviewer's comment and strongly agree with the suggestion to understand the status of the PAHs equilibrium in sediments. This comment is connected with previous comments.

To understand the PAHs equilibrium state, the input flux toward surface sediment (i.e., positive flux) and out flux from the sediment (i.e., negative flux) should be determined. The examples of the positive and negative fluxes in surface sediment in our study area are below;

Positive flux: the PAHs in deposited SPM
Negative flux: the PAHs in resuspended SPM, the diffusion of dissolved PAHs in the sediment (fugacity).

Although fugacity can be estimated using the Kow portion, there are still remaining limitations in the SPM fluxes from the water column toward the surface sediment. Furthermore, our results represent the total PAHs concentration in the seawater regardless of the PAHs phase (SPM, dissolved).

Our research group is specialized in monitoring pollution in the marine environment. We also had accomplishments in determining the SPM flux between seawater and surface sediment using strategically manufactured sediment traps. The traps can provide both the deposited and resuspended SPM flux. Therefore, the authors believe that we can determine the PAHs equilibrium states in the study area in the future, both (1) particle-phase PAHs and (2) diffusion of dissolved PAHs (fugacity). The present manuscript is just a preliminary study. Using the present manuscript as a cornerstone, we will establish and develop the research on the current PAHs contamination and equilibrium state in the study area 10 years after the oil spill to complete this study.

However, the limitation that the reviewer pointed out is clearly stated in the revised manuscript.

Results and Discussions L.369-377. However, the present study analyzed the PAHs in the surface seawater regardless of the PAHs present types. The SPM acts as the essential carrier for pollutants in the marine environment [47-48] because the hydrophobic property makes PAHs in surface seawater adsorb to the SPM in the water column. The SPM is, therefore, one of the primary factors in the transportation and weathering of PAHs [49]. Furthermore, the PAHs fugacity in the seawater-surface sediment is also the primary point on the fate of PAHs [52]. Since many researchers highlighted these significant roles of PAHs contamination in sediment, suspended particulate matter, and dissolved phases [49, 52], this perspective should be implemented in future work to understand the detailed current fate of PAHs.

Reviewer 2–Q6) Results: I suggest the authors also evaluate the toxicity of the increasingly emerging PAHs in aquatic environment.

Authors 2-A6) The authors appreciate the reviewer's comment. We also agree that the ecological risk assessment should be supplemented to assess the oil spill synthetically.

However, the present study conducted the final sampling seven years ago. It doubts whether risk assessment can represent current situations because the oil spill is a single event, not continuously acting, and the PAHs levels were dramatically decreased over time. It implies that the risk assessment using past results has minor significance. Rather than that, the current risk assessment should be urgent in the study area. The shipping activities, petrochemical plants, and the equilibrium state of PAH contamination derived from the oil spill will be the primary factors in assessing the environmental risk assessment for the current PAHs contamination. These works should be established in the future plan based on this manuscript.

Notably, authors believe that the effect range-low (ERL) and effect range-median (ERM) are validly employed to assess the biological effects of PAHs contamination, as shown in much previous research.

These points were additionally supplemented in the revised manuscript.

Results and Discussions L.461-477. The 16-PAHs and Alkyl PAHs levels in the twenty adjacent surface sediment (St.1- St.20) from the accident area were considerably lower than the ERM and ERL. As stated above, the previous modeling [19], PAHs levels in the intertidal zone [44], and the present study results indicate that the spilled oil was rapidly dispersed and accumulated in the adjacent coasts and beaches rather than in the accident area. This may result in the PAHs level being below the ERL.
Contrary to this, the C2-naphthalene, C1- and C2- phenanthrenes concentrations in the accident area showed higher than the ERL. The three PAHs levels in St A, where the distance is approximately 100 m from the accident point, were highlighted. Notably, C2- phenanthrenes in the entire accident area were higher than the ERL because these sediment samples were collected one month after the oil spill nearby the accident point.
In much previous research, the ERL and ERM were validly employed to assess the biological effects of PAHs contamination. However, the final sampling in the present study was implemented seven years ago, and it is challenging to represent the current situation. It is necessary to comprehensively assess the recent PAHs contamination using additional environmental risk assessment (e.g., the risk quotient (RQ) [52-55]), not only the sediment guideline, in the study area by establishing a strategic research plan to overcome the limitations of the present study mentioned earlier.

Reviewer 2–Q7) Figure 1: improve the resolution of this image

Authors-A7) Thank you for your detailed comments. The resolution of figure 1 was improved in the revised manuscript.

Methods and Materials L.113-114. Figure 1. Sampling locations for surface sediment collection in the Wu Yi San oil spill site , the straits of Yeosu and Gwangyang Bay, Korea.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have made the corrections I have suggested. I haven’t remarks to make. The content of this manuscript is appropriate for WATER, therefore, my final opinion is to accept the paper in the present form.

Author Response

<자기소개서 >

저널: 물 (ISSN 2073-4441)

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원고의 질을 높이기 위해 헌신한 편집자와 익명의 검토자에게 진심으로 감사드립니다. 의견과 제안은 적절했으며 향후 작업에서이 원고의 한계를 개선하기 위해 최선을 다할 것입니다. 본 원고는 다음과 같은 연구를 확립하는 데 필수적인 역할을 할 것입니다.

두 번째 개정판의 주요 요점은 본문의 영어 수정이었습니다. 여기에서는 MDPI 영어 수정 서비스 (송장 ID English-57867)에 수정을 요청했으며 원고의 최종 수정 버전을보고하고 있습니다. 변경 사항은 저널의 지침에 따라 MS Word의 "변경 내용 추적"기능을 사용하여 이루어졌습니다.

특히, 서비스의 제안을 수락하여 제목은 "우발적 인 기름 유출 후 기름 지문을 통한 조간대 표면 퇴적물의 다환 방향족 탄화수소 오염 값의 변화 : Wu Yi San 기름 유출 사례 연구, 여수, 한국"으로 수정되었습니다.

다시 한 번 여러분의 헌신과 협조에 감사드립니다.

솔직히

05 1월 2023

교신저자

Author Response File: Author Response.docx

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Variations in Polycyclic Aromatic Hydrocarbon Contamination Values in Subtidal Surface Sediment via Oil Fingerprinting after an Accidental Oil Spill: A Case Study of the Wu Yi San Oil Spill, Yeosu, Korea

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