Assessment of Heavy Metal Contamination in Beach Sediments of Eastern St. Martin’s Island, Bangladesh: Implications for Environmental and Human Health Risks

Round 1

Reviewer 1 Report

Study description:
This study investigated heavy metal pollution in sediment samples from Eastern St. Martin's Island (SMI), Bangladesh. The concentrations of heavy metals were analyzed using Atomic Absorption Spectrometry (AAS). The measured metal concentrations were within permissible limits and lower compared to other studies. Risk assessments indicated a moderate risk to the aquatic ecosystem in the study area. However, sediment quality indices suggested that metal contamination levels were within acceptable boundaries and did not negatively affect sediment quality. The non-carcinogenic hazard index for different age groups indicated no significant risks, and the total carcinogenic risk was below the 10th percentile. The study highlights the importance of ongoing monitoring and stringent regulations to reduce heavy metal pollution and protect human and ecological health.
Comments:
Overall, this study provides a clear description of the research conducted on heavy metal pollution in sediments and its potential risks to the environment and human health. However, there are a few constructive comments to improve the manuscript:
1. It would be beneficial to briefly mention why heavy metal pollution is a pressing environmental issue and how it affects the marine resources. This would help readers understand the significance of the research.
2. Instead of just mentioning "Eastern St. Martin's Island (SMI), Bangladesh," provide a brief description of the study area, including its ecological importance or any specific characteristics that make it relevant to the research in the abstract.
3. While the manuscript mentions the use of Atomic Absorption Spectrometry (AAS) for evaluating heavy metals, it would be helpful to include a more description of the sampling and analysis methods employed. This would give readers a better understanding of the research process.
4. The manuscript mentions that the measured metal concentrations were within permissible limits and lower than those reported in other studies. It would be valuable to emphasize any unique or unexpected findings that contribute to the existing knowledge on heavy metal pollution in sediments. Provide more discussion regarding it.
5. While the manuscript mentions that the risk index results classified the study area as posing a moderate risk to the aquatic ecosystem, it would be useful to provide more details on the specific risks identified and their potential implications. This would add depth to the discussion of the research outcomes.
6. Although the manuscript describes that the non-carcinogenic hazard index and total carcinogenic risk were below certain thresholds, it would be beneficial to elaborate on the potential health implications for adults and children, even if the risks are considered low.
7. The manuscript mentions the need for continual monitoring and stringent regulations to reduce heavy metal pollution. It would be helpful to elaborate on the specific actions or strategies that could be implemented to achieve this, emphasizing the importance of the research findings in guiding environmental management decisions. Provide some policy recommendations.
By incorporating these suggestions, the manuscript will provide a more comprehensive overview of the research, its findings, and its implications for both the environment and human health.

Author Response

Reviewer 1:

Comments: Study description:

General Comment: This study investigated heavy metal pollution in sediment samples from Eastern St. Martin's Island (SMI), Bangladesh. The concentrations of heavy metals were analyzed using Atomic Absorption Spectrometry (AAS). The measured metal concentrations were within permissible limits and lower compared to other studies. Risk assessments indicated a moderate risk to the aquatic ecosystem in the study area. However, sediment quality indices suggested that metal contamination levels were within acceptable boundaries and did not negatively affect sediment quality. The non-carcinogenic hazard index for different age groups indicated no significant risks, and the total carcinogenic risk was below the 10th percentile. The study highlights the importance of ongoing monitoring and stringent regulations to reduce heavy metal pollution and protect human and ecological health.

Overall, this study provides a clear description of the research conducted on heavy metal pollution in sediments and its potential risks to the environment and human health. However, there are a few constructive comments to improve the manuscript:

Response: Thank you so much for your comments. We really appreciate your valuable insights on our manuscript. We have considered all of your comments and taken them positively in our revised manuscript.

Specific Comments 

Comment 1. It would be beneficial to briefly mention why heavy metal pollution is a pressing environmental issue and how it affects the marine resources. This would help readers understand the significance of the research.

Response 1: We have provided description regarding this in the first paragraph of the manuscript. We have highlighted it in the revised manuscript. Thank you for your valuable suggestion.

Comment 2. Instead of just mentioning "Eastern St. Martin's Island (SMI), Bangladesh," provide a brief description of the study area, including its ecological importance or any specific characteristics that make it relevant to the research in the abstract.

Response 2: We have provided description regarding this in the first paragraph of the manuscript. We have highlighted it in the revised manuscript. Thank you for your valuable suggestion.

Comment 3. While the manuscript mentions the use of Atomic Absorption Spectrometry (AAS) for evaluating heavy metals, it would be helpful to include a more description of the sampling and analysis methods employed. This would give readers a better understanding of the research process.

Response 3: We have provided description regarding AAS of the manuscript. We have highlighted it in the revised manuscript in the materials and methods section. Thank you for your valuable suggestion.

Comment 4. The manuscript mentions that the measured metal concentrations were within permissible limits and lower than those reported in other studies. It would be valuable to emphasize any unique or unexpected findings that contribute to the existing knowledge on heavy metal pollution in sediments. Provide more discussion regarding it.

Response 5: Thanks for your nice observation. In St. Martin’s Island, pollution is increasing. We think the island sediment is polluted. But our findings are positive. It’s a good sign for SMI. So, I think there should not be unique or unexpected findings. This is very helpful for the community and policy makers.

Comment 5. While the manuscript mentions that the risk index results classified the study area as posing a moderate risk to the aquatic ecosystem, it would be useful to provide more details on the specific risks identified and their potential implications. This would add depth to the discussion of the research outcomes.

Response 5. There are detailed description of this in the index section. We have highlighted the revised sections in red font.

Comment 6. Although the manuscript describes that the non-carcinogenic hazard index and total carcinogenic risk were below certain thresholds, it would be beneficial to elaborate on the potential health implications for adults and children, even if the risks are considered low.

Response 6: There are detailed description of this in the index section. We have highlighted the revised sections in red font.

Comment 7. The manuscript mentions the need for continual monitoring and stringent regulations to reduce heavy metal pollution. It would be helpful to elaborate on the specific actions or strategies that could be implemented to achieve this, emphasizing the importance of the research findings in guiding environmental management decisions. Provide some policy recommendations.

Response 7:

Thank you for the insightful comment. I agree that it is imperative to elaborate on the specific actions or strategies needed to achieve continual monitoring and stringent regulations to mitigate heavy metal pollution. My recommendations, which are based on the research findings, aim to guide environmental management decisions as follows:

Firstly, it is crucial to regulate tourism activities in a more planned and systematic manner, particularly in ecologically sensitive areas, to minimize the environmental footprint. This could include implementing carrying capacity assessments to determine how many tourists an area can sustain without detrimental effects, and promoting eco-friendly tourism practices.

Secondly, the maritime sector, including ships and engine boats, plays a significant role in heavy metal pollution. It is necessary to enforce maintenance protocols that emphasize the use of cleaner fuels and technologies, and the proper management of ballast water and waste to reduce their environmental impact.

Thirdly, the construction of industries along the coast should be closely monitored and regulated. Environmental Impact Assessments (EIAs) should be mandatory, and approval should be contingent upon adherence to environmental best practices. Industries should also be required to have pollution control measures in place and ensure proper waste management.

Fourthly, shipbuilding and ship-breaking industries are known for their contribution to heavy metal pollution. These industries should be mandated to comply with national and international environmental regulations. This includes adopting cleaner production processes, proper waste management, and regular monitoring of their environmental impact.

            Lastly, agricultural activities, especially in areas such as SMI, must be conducted in an environmentally safe manner. This includes promoting the use of less toxic pesticides and fertilizers, implementing soil conservation practices, and educating farmers on sustainable agriculture. Overall, implementing these policy recommendations based on continual monitoring and research findings is essential for mitigating heavy metal pollution and safeguarding the marine and coastal environment. This will not only protect ecosystems but also ensure the sustainable development and well-being of communities that depend on these resources.

We have added it as a separate policy recommendations section in the revised manuscript.

Reviewer 2 Report

Generally, the manuscript met the scope of this journal. However, there are still some questions which should be addressed carefully.  I would like to recommend editor to accept it with major revision.

1. Line 464, authors mentioned the CF for arsenic, but I can not find it in Fig.4, please explain.

2. Line 463 and 465, ‘lead ranges from 1.34to 1.59’ appeared twice in the text.

3. Line 462-466, The CF values for metals in the text seems not match with that in Fig.4, please check.

4. Considering that arsenic pollution is very prevail in Bangladesh, I recommend that authors should put arsenic in consideration in this text. Besides, arsenic has been considered in 2.6.1 and 2.6.2 part. I don not know why it was not appeared in '3. Results and discussion'. 

Author Response

Comment: Generally, the manuscript met the scope of this journal. However, there are still some questions which should be addressed carefully.  I would like to recommend editor to accept it with major revision.

Response: Thank you very much for your valuable suggestions. We have considered all your recommendations and revised the manuscript accordingly. Please find below the point by point response to the comments by the reviewer.

Comment 1: Line 464, authors mentioned the CF for arsenic, but I can not find it in Fig.4, please explain.

Response 1: It was a typo error; we have corrected it in the revised manuscript. Thank you so much for letting us know about the error.

Comment 2. Line 463 and 465, ‘lead ranges from 1.34 to 1.59’ appeared twice in the text.

Response 2: It was a typo error; we have corrected it in the revised manuscript. Thank you so much for letting us know about the error.

Comment 3. Line 462-466, The CF values for metals in the text seems not match with that in Fig.4, please check.

Response 3: It was a typo error; we have corrected it in the revised manuscript. Thank you so much for letting us know about the error.

Comment 4. Considering that arsenic pollution is very prevail in Bangladesh, I recommend that authors should put arsenic in consideration in this text. Besides, arsenic has been considered in 2.6.1 and 2.6.2 part. I dont not know why it was not appeared in '3. Results and discussion'.

Response 4: Dear worthy reviewer, thanks for your observation. We had no facility to estimate Arsenic, hence we have accordingly revised the section 2.6.1 and 2.6.2. Thank you so much for your valuable suggestion.

Reviewer 3 Report

Dear authors, I find your work innovative, interesting, meaningful and with practical applicability. My recommendation is that the paper could be considered for possible admission to publish in Water journal, after minor revisions.

The following modifications are suggested for improving the manuscript:

1. Introduction

Page 2, lines 56-57, after the sentence: While lower concentrations of HMs are essential for organism survival, bigger concentrations are harmful and negatively affect living things.

Comment: To support your point, I suggest you cite here a few works on the problem:

Dvorak P., Koushik R., Jaroslav A.Z, Dvorakova L., Mraz J., 2020. Vulnerability assessment of wild fish population to heavy metals in military training area: Synthesis of a framework with example from Czech Republic. Ecological Indicators, 110:105920. https://doi.org/10.1016/j.ecolind.2019.105920

Zhelev Zh.M, Arnaudova D.N., Popgeorgiev G.S., Tsonev S.V. (2020). In situ assessment of health status and heavy metal bioaccumulation of adult Pelophylax ridibundus (Anura: Ranidae) individuals inhabiting polluted area in southern Bulgaria. Ecological Indicators 115 (2020) 106413 https://doi.org/10.1016/j.ecolind.2020.106413

Bacchi E., Cammilleri G., Tortorici M., Galluzzo F.G., Pantano L., Calabrese V., Vella A., Macaluso A., Lo Dico G.M., Vincenzo Ferrantelli V. & Brunone M. (2022). First report on the presence of toxic metals and metalloids in East Asian Bullfrog (Hoplobatrachus rugulosus) legs. Foods 11: 3009. https://doi.org/10.3390/foods11193009

2. Materials and Methods

3.1. Study area

Page 3, lines 133-139: the whole passage.

Comment: Remove this passage!

Page 3, lines 140-144: the whole passage.

Comment: Remove this passage!

Page 3, lines 145-147: the whole passage.

Comment: Remove this passage!

2.3. Sample digestion, analysis, and quality control

Page 5, lines, in the sentence: All samples were examined for Cr, Ni, Cu, Pb, Mn, Zn, and Fe utilizing an Atomic absorption spectrophotometer (AAS, Model No. ZEEnit700P#150Z7P0110 from Analytikjena, Germany) in air/acetylene flame.

Comment: Indicate on what basis the focus of the research is placed precisely on these metals.

2.6.2. Assessing Carcinogenic risk

Pages 7-8, in the sentence: By employing the cancer slope factor (CSF) for the specific metal content for each pathway, the lifetime cancer risk (CR) exposure was evaluated (USEPA, 2000). As per USEPA (2002), the CSF values are 1.5 mg/kg/day for arsenic (As), 0.5 mg/kg/day for chromium (Cr), and 15 mg/kg/day for cadmium (Cd)[36]. To determine the CR, utilize the following formula:

Comment: Cadmium and arsenic were not analyzed in this study!

3. Results and discussion

3.1. Heavy metals concentrations in sediment

Pages 8-9, lines 306-315: the whole passage.

Comment: All this is known and there is no need to explain it at length. Please recite the passage in 2-3 short sentences!

Pages 12-13, Lines 339-400: the whole passage.

Comment: Optimize this passage!

3.5. Identification of sources of heavy metals in sediment

Page 18, lines 563-564, in the sentence: The high loading of Zn (0.703) in PC3 showed a total variance (17.32%), which was related to battery manufacture and other industrial issues.

Comment: Either be specific or don't say it.

Author Response

Reviewer 3:

Comments: Dear authors, I find your work innovative, interesting, meaningful and with practical applicability. My recommendation is that the paper could be considered for possible admission to publish in Water journal, after minor revisions.

The following modifications are suggested for improving the manuscript:

1. Introduction

Page 2, lines 56-57, after the sentence: While lower concentrations of HMs are essential for organism survival, bigger concentrations are harmful and negatively affect living things.

Comment 1: To support your point, I suggest you cite here a few works on the problem:

Dvorak P., Koushik R., Jaroslav A.Z, Dvorakova L., Mraz J., 2020. Vulnerability assessment of wild fish population to heavy metals in military training area: Synthesis of a framework with example from Czech Republic. Ecological Indicators, 110:105920. https://doi.org/10.1016/j.ecolind.2019.105920

Zhelev Zh.M, Arnaudova D.N., Popgeorgiev G.S., Tsonev S.V. (2020). In situ assessment of health status and heavy metal bioaccumulation of adult Pelophylax ridibundus (Anura: Ranidae) individuals inhabiting polluted area in southern Bulgaria. Ecological Indicators 115 (2020) 106413 https://doi.org/10.1016/j.ecolind.2020.106413

Bacchi E., Cammilleri G., Tortorici M., Galluzzo F.G., Pantano L., Calabrese V., Vella A., Macaluso A., Lo Dico G.M., Vincenzo Ferrantelli V. & Brunone M. (2022). First report on the presence of toxic metals and metalloids in East Asian Bullfrog (Hoplobatrachus rugulosus) legs. Foods 11: 3009. https://doi.org/10.3390/foods11193009

Response 1: We have cited these references to support our point. The inserted references are 6-8

2. Materials and Methods

3.1. Study area

Page 3, lines 133-139: the whole passage.

Comment 2: Remove this passage!

Response 2: Thank you very much for helping us to revise our manuscript. We have now deleted this passage as suggested.

Page 3, lines 140-144: the whole passage.

Comment 3: Remove this passage!

Response 3: Thank you very much for helping us to revise our manuscript. We have now deleted this passage as suggested.

Page 3, lines 145-147: the whole passage.

Comment 4: Remove this passage!

Response 4: Thank you very much for helping us to revise our manuscript. We have now deleted this passage as suggested.

2.3. Sample digestion, analysis, and quality control

Page 5, lines, in the sentence: All samples were examined for Cr, Ni, Cu, Pb, Mn, Zn, and Fe utilizing an Atomic absorption spectrophotometer (AAS, Model No. ZEEnit700P#150Z7P0110 from Analytikjena, Germany) in air/acetylene flame.

Comment 5: Indicate on what basis the focus of the research is placed precisely on these metals.

Response 5: Thank you for raising this important query. The selection of the metals, namely Chromium (Cr), Nickel (Ni), Copper (Cu), Lead (Pb), Manganese (Mn), Zinc (Zn), and Iron (Fe), for analysis in this study was based on several criteria. First, these metals are widely recognized as common pollutants in marine environments, often originating from various anthropogenic sources such as industrial discharges, agricultural runoff, and shipping activities. As such, monitoring these specific metals is crucial for evaluating the general state of heavy metal pollution in marine sediments. Second, some of these metals, such as Lead and Chromium, are known for their potential toxicity to aquatic life and humans. Monitoring these metals helps in assessing the potential ecological risks and human health hazards associated with their presence in marine sediments. Third, Copper, Zinc, Manganese, and Iron are essential trace elements for aquatic organisms but can be toxic at elevated concentrations. Assessing the levels of these metals is essential to understand their role in the ecosystem and to ensure that their concentrations remain within ranges that are beneficial rather than harmful. Further, the selection was also influenced by the existing literature and global standards. Monitoring these metals is consistent with international protocols and guidelines for assessing heavy metal pollution, allowing for meaningful comparisons with other studies and contributing to a broader understanding of global trends in marine pollution. In light of these considerations, the inclusion of these specific metals was deemed critical for achieving a comprehensive understanding of the heavy metal pollution and its potential implications on Eastern St. Martin's Island.

We have added this information according to the suggestions of the worthy reviewer. Thank you very much for helping us to improve our manuscript.

2.6.2. Assessing Carcinogenic risk

Pages 7-8, in the sentence: By employing the cancer slope factor (CSF) for the specific metal content for each pathway, the lifetime cancer risk (CR) exposure was evaluated (USEPA, 2000). As per USEPA (2002), the CSF values are 1.5 mg/kg/day for arsenic (As), 0.5 mg/kg/day for chromium (Cr), and 15 mg/kg/day for cadmium (Cd)[36]. To determine the CR, utilize the following formula:

Comment 6: Cadmium and arsenic were not analyzed in this study!

Response 6: Thank you for letting us know this error. We have deleted it now.

3. Results and discussion

3.1. Heavy metals concentrations in sediment

Pages 8-9, lines 306-315: the whole passage.

Comment 7: All this is known and there is no need to explain it at length. Please recite the passage in 2-3 short sentences!

Response 7: We have deleted it and revised it accordingly.  

Pages 12-13, Lines 339-400: the whole passage.

Comment 8: Optimize this passage!

Response 8: We have made this section very concise now as per the suggestions of the worthy reviewer. Thank you very much for your suggestions

3.5. Identification of sources of heavy metals in sediment

Page 18, lines 563-564, in the sentence: The high loading of Zn (0.703) in PC3 showed a total variance (17.32%), which was related to battery manufacture and other industrial issues.

Comment 9: Either be specific or don't say it.

Response 9: Thank you very for much pointing out this issue. We have now deleted it. Thank you once again

Round 2

Reviewer 2 Report

The revised manuscript has been well addressed according to reviewer's comments, I woulf like to recommend it for publication in this journal.

1.Line 118, "3.1" should be "2.1";

2.Line 283, "2.8" should be "2.7"

Author Response

Thank you very much for letting us know about these typo issues. We have rectified them now and the same are highlighted for easy reference.

Thank you once again