Assessment of Total Mercury Levels Emitted from ASGM into Soil and Groundwater in Chami Town, Mauritania

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper reported the soil THg concentrations in Artisanal and Small-scale Gold Mining (ASGM) and surrounding regions. The results are clear with appropriate tables and figures, but some figure can be merged. I have a few minor comments, which may help improve clarity in some places.

1.        Line 10, describe the dispersion pattern in more detail.

2.        Line 11, the keywords should be a supplement for the title, whereas, most of the keyword had appeared in the title, so revise the keywords.

3.        Line 133, it is necessary to describe the analysis processes of soil and water, including the reproducibility. Why not use high temperature heating method to analyze soil mercury (e.g., DMA 80)?

4.        Lines 279, the THg was generally analyzed as the following method: BrCl solution was firstly added to 100 ml sample to oxidize all Hg species to Hg²⁺ followed by the addition of NH₂OH·HCl for the removal of excess BrCl, and SnCl₂ solution was finally added to the sample to reduce Hg²⁺ to Hg⁰, which was quantified by a cold vapor atomic fluorescence spectrometry (CVAFS, Model III, Brooks Rand, USA) using the two-stage gold amalgamation.

5.        Table 1, the classes are all 0 ?

6.        Line 503, delete the words: possibility and may

7.        Line 527, or is it possible that mercury is transported slowly in groundwater due to soil filtration? Yet it is necessary to focus on the release of Hg from soil to water in the future.

Comments on the Quality of English Language

well

Author Response

Reviewer #1

Comments and Suggestions for Authors

The paper reported the soil THg concentrations in Artisanal and Small-scale Gold Mining (ASGM) and surrounding regions. The results are clear with appropriate tables and figures, but some figure can be merged. I have a few minor comments, which may help improve clarity in some places.

1. Line 10, describe the dispersion pattern in more detail.

Response 1:

Thank you for highlighting such an important comment, the dispersion pattern is wide and requires a detailed explanation. Further study is underway to characterize the pattern. We have added more details explaining the mercury dispersion pattern to the manuscript "Our study emphasized the mercury dispersion patterns around Chami town, suggesting a gradual decrease in total Hg with increasing distance from ASGM sites, and a potential influence of the wind, accenting the need for further investigation."

2. Line 11, the keywords should be a supplement for the title, whereas, most of the keyword had appeared in the title, so revise the keywords.

Response 2:

Thank you for your comment.

We have replaced the keywords to be a supplement for the title: Soil and groundwater mercury pollution, Artisanal and Small-Scale Gold Mining (ASGM), Atomic Fluorescence Spectrometry (AFS), Cold Vapor Atomic Fluorescence Spectrometry (CVAAS), X-ray fluorescence (XRF), Banc d'Arguin National Park (PNBA).

3. Line 133, it is necessary to describe the analysis processes of soil and water, including the reproducibility. Why not use high temperature heating method to analyze soil mercury (e.g., DMA 80)?

Response 3:

Much appreciate your valuable suggestion and would like to reply as follows: 

We acknowledge the suggested method, as it is among the most advanced methods to measure total mercury in soil . In fact, DMA 80 is very efficient. However, our method provides the possibility to measure high range of total Hg in both soil and water sample. For instance, in the publication by Logar et al. (2001), titled "Determination of total mercury and monomethylmercury compound in water samples from Minamata Bay, Japan: an interlaboratory comparative study," it was demonstrated that our method's accuracy was validated through comparison with the ethylation method.

Furthermore, we would like to outline the primary reasons for not utilizing the high-temperature heating method:

• High-temperature heating analyzers, such as the DMA 80, are limited in their sample capacity when mercury concentrations are elevated. Consequently, if the concentration is low, a significant portion of the sample may fall below the detection limit, resulting in non-detectable (ND) outcomes. In the other hand, the Akagi method used in this study can completely decompose organic matter in soil/sediment due to thermal decomposition using three mixed pure and strong acids can decompose a large amount of sample (up to several grams) at a time, making it possible to easily handle samples with low mercury concentrations. However, it is difficult to dilute a sample using the high-temperature heating method, and weighing a small amount of mercury can result in a large error margin.
• High-temperature heating type mercury analyzers such as DMA80 cannot handle water samples. Since mercury in water samples is extremely low in concentration, only the mercury extraction and concentration method by adding dithizontoluene solution, such as the Akagi method used in this study, or the EPA's ethylation method can be used to accurately measure mercury.

Although two types of total mercury analyzers were used, the basic method is the reduction vaporization method using wet decomposition, so the methodology is unified.

 

The method we followed is also elaborated in the manual developed by the Ministry of the Environment in Japan. The analysis was conducted in the National Institute for Minamata Disease (NIMD) which belongs to the same ministry.

We also used recognized standards such as the European Certified Reference Materials (CRM 580) to maintain the accuracy and found high accuracy percentages in our analysis.

4. Lines 279, the THg was generally analyzed as the following method: BrCl solution was firstly added to 100 ml sample to oxidize all Hg species to Hg²⁺followed by the addition of NH₂OH·HCl for the removal of excess BrCl, and SnCl₂ solution was finally added to the sample to reduce Hg²⁺ to Hg⁰, which was quantified by a cold vapor atomic fluorescence spectrometry (CVAFS, Model III, Brooks Rand, USA) using the two-stage gold amalgamation.

Response 4: 

 

 

Thank you for the valuable comment. The methodology you addressed is well known and efficient to extract mercury from soil sample solution, although the procedure of total Hg analysis the NIMD includes the use of sulfuric acid (H2SO4), which is capable to extract 98% of mercury content, followed by the addition of potassium permanganate (KMnO4) which is also used to extract the mercury from the solution.

5. Table 1, the classes are all 0 ?

Response 5:

 

Thank you for the notice, it was a typing error as there are 7 classes for the Geoaccumulation Index (Igeo). The degree of contamination can be classified into seven categories based on the Igeo value for each soil sample.

• Class 1: Igeo ≤ 0 (unpoluuted),
• Class 2: 0 < Igeo ≤ 1 (unpoluuted to modrtately polluted),
• Class 2: 1 < Igeo ≤ 2 (moderately polluted),
• Class 3: 2<Igeo ≤ 3 (moderately to heavily polluted),
• Class 4: 3 < Igeo ≤ 4 (heavily polluted),
• Class 5: 4 < Igeo ≤ 5 (heavily to extremely polluted)
• Class 6: Igeo > 5 (Extremely polluted).

6. Line 503, delete the words: possibility and may

Response 6:

Thank you for the valuable recommendation. It is necessary to remove such words to make the manuscript more definitive and assertive.

The words were deleted accordingly:  "However, even at these sites, relatively high total Hg levels in soil were observed in the vicinity of the hotspots, indicating that ASGM activities have affected the surrounding soil."

7. Line 527, or is it possible that mercury is transported slowly in groundwater due to soil filtration? Yet it is necessary to focus on the release of Hg from soil to water in the future.

Response 7: 

Thank you for your feedback.

Your statement that mercury is possibly infiltrating slowly through the soil into the groundwater is a plausible explanation for the low total mercury concentrations found in the groundwater samples and yet the rarity of groundwater and the distance of groundwater wells from the ASGM sites are factors that should be put into consideration in future investigation.

 

References 

Logar, M.; Horvat, M.; Akagi, H.; Ando, T.; Tomiyasu, T.; Fajon, V. Determination of total mercury and monomethylmercury compounds in water samples from Minamata Bay, Japan: An interlaboratory comparative study of different analytical techniques. Applied Organometallic Chemistry 2001, 15, 515–526.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article is interesting and relevant. It is devoted to mercury pollution in artisanal gold mining. Mercury pollution is a serious threat, although the contribution of such facilities is local, as the study showed. Extensive material was used, selected at different sites. The methodical part is carefully prescribed. But there is no review of similar studies in other countries. For example, in Mongolia, this problem is acute – in artisanal gold mining, mercury from broken thermometers is used in the same arid climate due to the winter death of livestock. With a sufficiently large volume of the article, the results and discussion are not separated, which makes it much more difficult to understand the content. After the names of the authors there are incomprehensible crosses L. 5 – five water samples are insufficient according to the laws of statistics L. 77 and further - ng/g is not a commonly used measure of measurement, it is better to use the commonly used ppm L. 119 - what is the population of the city of Chami? Fig. 2 – the drawing needs to be redone – judging by the map, the surroundings of the city of Chami are located inside the contour of the city. It is necessary to mark the contours of the national park and specifically the city of Chami. Because in Fig. There is an inset in FIG. 1, they need to be swapped, It is desirable to use a geological basis or make a geological map additionally. l. 148 – it is desirable to provide photos of samples It is necessary to bring the bibliographic description of the sources to the standard, for example, 17, 20, 21

Author Response

Reviewer #2

 

Comments and Suggestions for Authors

The article is interesting and relevant. It is devoted to mercury pollution in artisanal gold mining. Mercury pollution is a serious threat, although the contribution of such facilities is local, as the study showed. Extensive material was used, selected at different sites. The methodical part is carefully prescribed. But there is no review of similar studies in other countries. For example, in Mongolia, this problem is acute – in artisanal gold mining, mercury from broken thermometers is used in the same arid climate due to the winter death of livestock. With a sufficiently large volume of the article, the results and discussion are not separated, which makes it much more difficult to understand the content. After the names of the authors there are incomprehensible crosses L. 5 – five water samples are insufficient according to the laws of statistics L. 77 and further - ng/g is not a commonly used measure of measurement, it is better to use the commonly used ppm L. 119 - what is the population of the city of Chami? Fig. 2 – the drawing needs to be redone – judging by the map, the surroundings of the city of Chami are located inside the contour of the city. It is necessary to mark the contours of the national park and specifically the city of Chami. Because in Fig. There is an inset in FIG. 1, they need to be swapped, It is desirable to use a geological basis or make a geological map additionally. l. 148 – it is desirable to provide photos of samples It is necessary to bring the bibliographic description of the sources to the standard, for example, 17, 20, 21

 

Reply:

• Thank you for your relevant comments.

It is important to add a global aspect to the article because artisanal and small-scale gold mining is a worldwide issue, that extends across more than 80 nations, employs an estimated 15 million miners, and supports the livelihoods of nearly 100 million individuals.

We have added a global aspect to the introduction. We have also added to the manuscript the impact of artisanal gold mining in Mongolia where the total mercury levels exceeded 2 ppm in sediments to the introduction (Udodenko, Y.G.; Robinson, C.T.; Choijil, J.; Badrakh, R.; Munkhbat, J.; Ivanova, E.S.; Komov, V.T. Mercury levels in sediment, fish and macroinvertebrates of the Boroo River, northern Mongolia, under the legacy of gold mining. Ecotoxicology 2022, pp. 1–12.).

"Additionally, in Mongolia, the total Hg levels in the sediments of the upper Boroo have surpassed 2000 ng/g dry weight as a result of artisanal gold mining activities." Also added another study in Peru which highlights the effect of artisanal and small-scale gold mining on the increase of total Hg levels in soil, especially within the vicinity of artisanal gold mining sites "And in Peru the levels of mercury in soils exceeded the standard limit in Peru, with industrial areas exhibiting an average concentration of 72.6 ppm compared to the standard level of 24 ppm, meanwhile, residential areas revealed an average of 9.5 ppm against the standard limit in the residential area of 6.6 ppm (Aquino, R.Q.; Malone, A.; Smith, N.M.; Zúñiga, F.F.G. Perceptions and realities of mercury contamination in a Peruvian artisanal and small-scale gold mining (ASGM) community. Environmental Research 2022, 214, 114092)."

• Regarding separating results and discussion, we have created a discussion section with 8 subheadings.
• Fluctuating total Hg levels in soil
• Moisture Ratio
• Hg methylation
• Hg extraction
• Geo-Accumulation Index (Igeo)
• Implication of the study findings

We have added more comparisons to other studies and improved the English: “The geo-accumulation index analysis revealed that most samples, particularly those from PNBA and Chami Environs, were classified as class 0, indicating unpolluted conditions. However, samples HS2 and HS1 from the ASGM sites showed a stark contrast, falling into class 6, signifying extreme pollution. This disparity underscores the extensive impact of the sampling grid. Notably, the HS2 sample, classified as class 6 and indicating severe pollution, is situated in the central market of Chami town, thereby exposing the local population to significant Hg pollution risks. In this study, it is important to note that samples were not collected from tailings, despite the Igeo index results indicating a level of pollution comparable to that of the tailing samples in Darmali, Sudan.”

• Regarding the incomprehensible crosses after the author's names, we have deleted them accordingly.
• Thank you for highlighting the significance of the number of groundwater samples collected, which totaled five. This limited number resulted from our meticulous coordination with local authorities and community members regarding the water sources for Chami town. Our investigation revealed that Chami is primarily supplied by just two wells. To enhance the comprehensiveness of our study, we subsequently collected samples from three additional underground water wells in proximity to Chami. This endeavor was made possible through the assistance of residents, who guided us in locating these wells, despite the inherent challenges posed by the desertic conditions of the area.
• L.77, thank you for your comment, we have changed all the units to ppm (mg/kg) in the manuscript and Figures 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, and Figure 10, accordingly.
• Thank you for highlighting the drawing complexity for Figure 2. In this regard, I redraw the figure and included Chami town, also added the population in the text accordingly (L119) now L.127. Figure 2 becomes Figure 1 because we deleted Figure 1 as it can be subjected to copyright restrictions and the owner does not reply. In the new figure, we can see the contour of Chami town and the border of the Banc d’Arguin National Park

Figure 1. Location of the sampling sites within the zone of study (in the attached pdf file).

⃰ Pictures of samples (in the attached pdf file).

• Improved English in the “Implication of the study findings.
• Added a picture of samples.
• Corrected the references.
• World Health Organization (WHO). Environmental and occupational health hazards associated with artisanal and small-scale gold mining. Available online: https://www.who.int/publications/i/item/9789241510271 (accessed on 13 May 2024).
• Pure Earth. GLOBAL MERCURY PROGRAM: STRATEGY AND APPROACH. Available online: https://www.pureearth.org/global-mercury-program/strategy-and-approach/ (accessed on 15 January 2024).
• UN Environment Programme (UNEP). Global Mercury Assessment 2013: Sources, emissions, releases, and environmental transport. Avilable online: https://www.unep.org/resources/report/global-mercury-assessment-2013-sources-emissions-releases-and-environmental (accessed on 25 April 2024).

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript is “Assessment of total mercury levels emitted from ASGM into soil and groundwater in Chami town, Mauritania”. Some detailed comments are as follows:

(1) The author of this manuscript only analyzed the mercury content in soil, but I believe that analyzing the trend of mercury content changes in soil is more important.

(2) Abstract: The research objectives and the problems to be solved are unclear.

(3) Introduction: The analysis of the research background is not comprehensive enough.

(4) Materials and Methods: The importance of the research area needs further clarification.

(5) The expression in Figure 1 is ambiguous. Additionally, this figure is from reference and requires permission.

(6) Results and Discussion: The difference in mercury content among soil samples in the region has not been revealed.

(7) Results and Discussion: The mechanism related to the influence of pollution sources on mercury content in soil is lacking in revelation.

(8) The research conclusion is only the research result, and there is a lack of important findings here.

(9) The format of the references does not meet the requirements of the journal.

(10) The English language of this manuscript needs improvement.

Comments on the Quality of English Language

The English language of this manuscript needs improvement.

Author Response

Reviewer #3

 

 

 

Comments and Suggestions for Authors

This manuscript is “Assessment of total mercury levels emitted from ASGM into soil and groundwater in Chami town, Mauritania”. Some detailed comments are as follows:

(1) The author of this manuscript only analyzed the mercury content in soil, but I believe that analyzing the trend of mercury content changes in soil is more important.

Reply (1):  

Thank you for your insightful comment and we acknowledge the importance of the analysis of trends in mercury content changes in soil. However, the present study is specifically structured to gain a fundamental knowledge and assess the mercury levels in a hyper-arid region whilst undertaking the case study of Chami town and its surrounding region. This investigation yields significant baseline data concerning the spatial distribution of mercury, which is vital for comprehending the immediate consequences of contamination on these delicate ecosystems.

Admittedly, the examination of mercury content trends in soil is of paramount significance. Nonetheless, the current research aims to quantify the extent of mercury contamination in the vicinity of Chami town and parts of the Banc d’Arguin National Park. This study provides essential baseline information regarding the spatial distribution of mercury and establishes a reference point for current mercury pollution levels. This foundational data will serve as the basis step towards future studies, and to build upon these findings for the analysis of the trends of mercury content in soil.

(2) Abstract: The research objectives and the problems to be solved are unclear.

Reply (2): Thank you for your relevant comment, problems and objectives must be addressed clearly.

We have edited the abstract accordingly: “Artisanal and small-scale gold mining (ASGM) is a serious growing concern in Sub-Saharan Africa. In Mauritania, recent gold discoveries in the north and northwest have led to a boost in ASGM centers, reflecting trends across the region and posing considerable risks of mercury (Hg) contamination. Notwithstanding this fact, the extent of mercury contamination in the region remains unclear due to insufficient knowledge on the mechanisms of Hg dispersion in hyper-arid regions. In light of this, the present study aims to acquire fundamental knowledge to elucidate the mercury dispersion mechanism by conducting soil and groundwater sampling in and around Chami town, Mauritania, where ASGM activities have intensified. We analyzed 180 soil samples and five groundwater samples for total mercury (total Hg) using cold vapor atomic absorption spectrometry (CVAAS) and atomic fluorescence spectrometry (AFS) methods. The total Hg levels in soil samples ranged from 0.002 to 9.3 mg/kg, with the highest concentrations found at ASGM sites. Groundwater samples exhibited low total Hg levels (0.25–1.25 ng/L). The total Hg content in soil and groundwater samples was below Japanese standards, yet soil samples from hotspot points exceeded other international standards. Our study emphasizes the Hg dispersion patterns around Chami town, suggesting a gradual decrease in total Hg with increasing distance from ASGM sites and a potential influence of wind dynamics. The knowledge accumulated in this study provides essential insights into the Hg dispersion mechanisms in Chami town, laying a foundation for establishing a predictive model of Hg contamination in hyper-arid regions.”

(3) Introduction: The analysis of the research background is not comprehensive enough.

Reply (3): Thank you for your comment.
We have added more texts to the introduction and more references from location with similar climate to Mauritania in order to improve the comprehension of the analysis of the research background. For example, we have added to the manuscript the impact of artisanal gold mining in Mongolia where the total mercury levels exceeded 2 ppm in sediments, and in Peru where total Hg exceeded the standard limit: "Additionally, in Mongolia, the total Hg levels in the sediments of the upper Boroo have surpassed 2000 ng/g dry weight as a result of artisanal gold mining activities (Udodenko, Y.G.; Robinson, C.T.; Choijil, J.; Badrakh, R.; Munkhbat, J.; Ivanova, E.S.; Komov, V.T. Mercury levels in sediment, fish and macroinvertebrates of the Boroo River, northern Mongolia, under the legacy of gold mining. Ecotoxicology 2022, pp. 1–12.). And in Peru the levels of mercury in soils exceeded the standard limit in Peru, with industrial areas exhibiting an average concentration of 72.6 ppm compared to the standard level of 24 ppm, meanwhile, residential areas revealed an average of 9.5 ppm against the standard limit in the residential area of 6.6 ppm (Aquino, R.Q.; Malone, A.; Smith, N.M.; Zúñiga, F.F.G. Perceptions and realities of mercury contamination in a Peruvian artisanal and small-scale gold mining (ASGM) community. Environmental Research 2022, 214, 114092).

In addition to relevant studies above, we have added the following motivation of this study. As the previous studies mentioned above were conducted in different continents and did not investigate the extent of mercury contamination dispersion over large distances in hyper-arid regions. Hence, it is of paramount importance to conduct a relevant study in Mauritania marked with the specific climate and gain insights on the dispersion mechanism of mercury from ASGM activities.

(4) Materials and Methods: The importance of the research area needs further clarification.

Reply (4): Thank you for your comment.
The Introduction and Materials and Methods sections outline the significance of the research area which includes the ASGM sites and located nearby a national park as well as the Atlantic Ocean, which encompasses Chami town and the surrounding Banc d’Arguin National Park. This park is recognized for its sensitive ecosystem and is the largest protected area in the country. It is noted that 53% of the 233 bird species associated with the park demonstrate a significant dependency on its coastal and marine ecosystems for their life cycle. Consequently, it can be inferred that migratory birds may be impacted by mercury contamination, potentially transporting mercury to other bird’s migration sites globally. The research encompassed Chami town as a significant source of mercury contamination. This contamination arises from ASGM centers in the town, in addition to semi-industrial gold mining areas.

(5) The expression in Figure 1 is ambiguous. Additionally, this figure is from reference and requires permission.

Reply (5): Thank you for your comment.
We have deleted the figure accordingly to avoid any copyright issues and improved Figure 2 to ensure that the main idea is clear.

(6) Results and Discussion: The difference in mercury content among soil samples in the region has not been revealed.

Reply (6): Thank you so much for your comment. First of all, please note that the primary purpose of this study is to acquire a general trend of mercury contamination levels in a hyper-arid region, based on the case study of Chami town and its surroundings, in order to form the basic foundation for elucidating mercury dispersion mechanisms in hyper-arid regions. A further study is being conducted whilst narrowing down the region of soil sampling based on the contamination map derived from this study. Nonetheless, we believe that the present study has provided valuable information and suggestions regarding the extent and mechanism of mercury contamination in hyper-arid regions as shown in the results and discussions (revised).

Considering the primary purpose of this study described above, we have added more texts to the results, especially the soil samples to explain the total mercury results based on the different sampling locations, in order to clarify the difference in mercury content among soil samples. More specifically, we have done adjustment to the manuscript to clarify the difference in mercury content among soil samples in the region and adjusted Figure 5 (now Figure 4) for better understanding of total Hg distribution within the different sampling locations as below.

Figure 4: Distribution map of the total Hg content in soil samples (in the pdf file).

More editing has been done for many other figures for better understanding of the differences in mercury content in different soil sampling locations.

(7) Results and Discussion: The mechanism related to the influence of pollution sources on mercury content in soil is lacking in revelation.

Reply (7): Thank you for your insightful comment.

Research findings from Senegal provide insights into the mercury destination and raise the concern of the necessity to conduct further research to model the mercury dispersion and possible deposition sites (Niane, B., Guédron, S., Feder, F., Legros, S., Ngom, P. M., & Moritz, R. (2019). Impact of recent artisanal small-scale gold mining in Senegal: Mercury and methylmercury contamination of terrestrial and aquatic ecosystems. Science of the Total Environment, 669, 185-193). In addition, other studies provide a clear effect of ASGM on the distribution of total Hg within soil and Nile river, case of ASGM near Nile Valley in Egypt and Sudan (ABDELAAL, Ahmed, et al. Emerging mercury and methylmercury contamination from new artisanal and small-scale gold mining along the Nile Valley, Egypt. Environmental Science and Pollution Research, 2023, 30.18: 52514-52534, and ELWALEED, Ahmed, et al. Assessment of Mercury Contamination in Water and Soil from Informal Artisanal Gold Mining: Implications for Environmental and Human Health in Darmali Area, Sudan. Sustainability, 2024, 16.10: 3931).

Comparing to the above-mentioned research findings our study provides comprehensive knowledge about the mercury contamination in desertic regions and the possibility of contamination over large distance enhanced by the wind dynamics and the dunes movements. Our research covered larger distance compared to other research and we found that mercury contamination can be extended to wide areas. Furthermore, our study suggests the immediate influence of the hyper-arid climate on mercury dispersion as well as the slow infiltration of mercury released of ASGM into the subsoil and thus the groundwater despite the high leachability of mercury in soil within the ASGM sites.

The discussion above including references has been added to the discussion section in the revised manuscript.

 

(8) The research conclusion is only the research result, and there is a lack of important findings here.

Reply (8): thank you for highlighting this issue. According to your suggestion, we rewrote the conclusion as below:

“This study investigates the environmental impacts of ASGM activities, with a specific focus on developing a predictive model for mercury contamination in hyper-arid regions. The research was conducted in Chami town, Mauritania, a region characterized by a hyper-arid climate. The analysis revealed elevated total Hg content in local soils, particularly within identified ASGM hotspots. Meanwhile, groundwater samples exhibited relatively low mercury concentrations, suggesting the limited and slow Hg infiltration to the groundwater due to the distance from ASGM sites. However, the study of soil mineralogy and organic matter composition indicated conditions that could facilitate the methylation of mercury, posing additional environmental and health risks. The extreme pollution levels detected within ASGM sites, as evidenced by the geo-accumulation index, underscored the urgency for further investigations.

Furthermore, the findings in the Hotspot 3 suggest that the transport of waste tailings from ASGM operations to semi-industrial mining locations is a significant contributor to the widespread mercury contamination, which could be potentially affected and enhanced by the strong wind dynamics known within the area. The significant use of Hg(0) in the amalgamation process, coupled with uncertainties regarding its environmental fate, highlighted the need for a detailed mercury dispersion model tailored to hyper-arid regions. The study provides important insights into the mechanisms driving mercury contamination in hyper-arid environments, which can be useful in the development of predictive models and guide targeted interventions to mitigate the environmental and health impacts of ASGM activities in Chami town, similar regions, and worldwide.”.

(9) The format of the references does not meet the requirements of the journal.

Reply (9): Thank you for your comment.
We have edited the references accordingly to match the journal specifications.
We have also compared the reference style of my paper with the original papers to avoid any mistakes.

(10) The English language of this manuscript needs improvement.

Reply (10):

• Thank you for your relevant comment.
  
  We have carefully improved the English of the manuscript by rewriting many paragraphs of the articles.

 

References:

1. Logar, M.; Horvat, M.; Akagi, H.; Ando, T.; Tomiyasu, T.; Fajon, V. Determination of total mercury and monomethylmercury compounds in water samples from Minamata Bay, Japan: An interlaboratory comparative study of different analytical techniques. Applied Organometallic Chemistry 2001, 15, 515–526.

1. Udodenko, Y.G.; Robinson, C.T.; Choijil, J.; Badrakh, R.; Munkhbat, J.; Ivanova, E.S.; Komov, V.T. Mercury levels in sediment, fish and macroinvertebrates of the Boroo River, northern Mongolia, under the legacy of gold mining. Ecotoxicology 2022, pp. 1–12. 
2. Radio France Internationale (RFI). Mauritanie: Les orpailleurs de Chami confrontés au VIH (2/4). Available online: https://www.rfi.fr/fr/podcasts/reportage-afrique/20211206-mauritanie-les-orpailleurs-de-chami-confront%C3%A9s-au-vih-2-4 (accessed 23 August 2024).
3. Aquino, R.Q.; Malone, A.; Smith, N.M.; Zúñiga, F.F.G. Perceptions and realities of mercury contamination in a Peruvian artisanal and small-scale gold mining (ASGM) community. Environmental Research 2022, 214, 114092.
4. Elwaleed, A.; Jeong, H.; Abdelbagi, A.H.; Thi Quynh, N.; Nugraha, W.C.; Agusa, T.; Ishibashi, Y.; Arizono, K. Assessment of Mercury Contamination in Water and Soil from Informal Artisanal Gold Mining: Implications for Environmental and Human 694
   Health in Darmali Area, Sudan. Sustainability 2024, 16, 3931. 695
5. Thiombane, M.; De Vivo, B.; Niane, B.; Watts, M.J.; Marriott, A.L.; Di Bonito, M. A new hazard assessment workflow to assess soil contamination from large and artisanal scale gold mining. Environmental Geochemistry and Health 2023, 45, 5067–5091.
6. Kodamatani, H.; Maeda, C.; Balogh, S.J.; Nollet, Y.H.; Kanzaki, R.; Tomiyasu, T. The influence of sample drying and storage conditions on methylmercury determination in soils and sediments. Chemosphere 2017, 173, 380–386.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors mostly took into account the comments and made the necessary amendments or provided exhaustive explanations. It is confusing that in Figure 1 the square is located on the territory of Western Sahara, not Mauritania, and that the ppm dimension is still not used

Author Response

Round 2

Reviewer #2

Comment: The authors mostly took into account the comments and made the necessary amendments or provided exhaustive explanations. It is confusing that in Figure 1 the square is located on the territory of Western Sahara, not Mauritania, and that the ppm dimension is still not used.

 

Response:

Dear reviewer, your feedback is greatly valued, and revisions have been made accordingly. Specifically, the map presented in Figure 1 has been revised to ensure that the square is now accurately positioned within the designated study area. In accordance with your suggestion to utilize parts per million (ppm), we have substituted mg/kg for ng/kg in the first revision round. Furthermore, the mg/kg unit within the manuscript has been changed and used ppm throughout the text.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Before publication, the author still needs to review and revise this manuscript.

Comments on the Quality of English Language

Before publication, the English language of this manuscript still needs to be revised.

Author Response

Round 2

Reviewer #3

Comment: Before publication, the author still needs to review and revise this manuscript.

 

Response:

Dear Reviewer, your feedback is highly valued. 

The process of reviewing the manuscript is essential in order to identify and rectify any potential errors, as even minor inaccuracies can significantly impact the overall quality of the paper. Accordingly, we have carefully examined the manuscript on a line-by-line basis to ensure that all identified errors have been addressed and corrected.

Additionally, we engaged the services of MDPI's English editing service (See attachment) to enhance the linguistic quality of our manuscript, ensuring that it aligns with the standards expected by your esteemed journal.

Author Response File: Author Response.pdf