Environmental Impacts on Soil and Groundwater of Informal E-Waste Recycling Processes in Ghana

Reviewer comment

Authors response

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1.     The authors nicely summarized the literature. However, several important articles on the topic are missed. E.g. (1) Science of the Total Environment 2024, 917, 170219. (2) Applied Surface Science 2023,636, 157827. These references should be cited in the introduction of revised version.

Thank you very much for drawing our attention to this literature, we have included it accordingly.

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2.     There are some grammar mistakes and typos remained in the manuscript, a thorough polish is requested.

Thank you for bringing this to our attention. We have carefully reviewed the manuscript and made the necessary corrections to address the grammar mistakes and typos.

Whole manuscript

3.     There were many format issues in the references. Please check carefully in the paper.

Thank you for this comment, we have thoroughly reviewed the references and addressed the format issues identified. Corrections have been made to ensure consistency and accuracy throughout the paper.

References

4.     The authors should further improve the quality of figures and tables for this manuscript.

Thank you for your feedback regarding the figures and tables in our manuscript. We have made enhancements to improve the quality, including increasing the resolution for better clarity and readability. Additionally, we have revised the axis descriptions of figure 2 to ensure accuracy and comprehension.

Figures and tables

5.     The language needs to be further polished

Thank you for your feedback, we have done proof reading through the native speakers of our authors and improved the language.

Whole manuscript

Reviewer comment

Authors response

Line numbers modified

According to the Reviewer, the article should also include an extended description of natural conditions.

There is a lack of coherent characteristics of the geological structure, hydrogeological conditions (especially the characteristics of the permeability of the subsoil), and hydrological conditions in terms of the migration of pollutants, e.g., in flood conditions.

Thank you for your valuable feedback. We acknowledge the importance of providing a comprehensive description of natural conditions in the article, particularly concerning the geological, hydrogeological, and hydrological aspects and appreciate your constructive feedback, which will contribute to improving the scientific quality and relevance of the article.

We have revised the geological aspects in the methods chapter “Study area and geology”. We also added this important point in the discussion chapter to address the relations between soil and groundwater pollution and the migration of pollutants in flood conditions.

We have added the description of the grain size and geological structure, the permeability and the hydrological soil group according to the infiltration rate.

201-226 and  Discussion

1/ The natural characteristics of the article should be completed.

The description of the geological structure should include a cross-section indicating subsequent layers' permeability.

Information about annual precipitation is provided, and what is the amount of effective infiltration?

From the point of view of environmental risk, important information would be whether the tested groundwater represents a usable aquifer used for drinking purposes.

Thank you for your feedback. We have addressed it in the Discussion section of the article. The groundwater is indeed unusable for drinking according to our data. Furthermore, we added to the discussion how the infiltration and geological conditions relate to the groundwater quality. We have also added this important information to the conclusion section.

Discussion

What is the volume of the e-waste recycling site Agbogbloshie Scrapyard, and is it located on a geological base impermeable to percolating rainwater?

Thank you for your feedback. Regarding the volume of e-waste at Agbogbloshie Scrapyard, it was already provided in the article at line 183, indicating that it amounts to 15,092 tons per year, however, we have added the constitution of the e-waste respectively.

In terms of the geological base's characteristics with respect to percolating rainwater, we have revised and added information in lines 204-227 of the manuscript. We describe the area's low permeability and poor drainage characteristics, which contribute to the challenges associated with rainwater percolation.

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2/ Methodological remarks. The number of samples taken is not very representative of the statistical sample.

Thank you for your insightful comment. We acknowledge that a larger sample size would ideally be desirable for more robust estimates. However, we faced limitations in achieving this due to financial constraints, project budget considerations, and the high costs associated with shipping polluted soil abroad, where suitable laboratory facilities are available. In Ghana, especially, the analysis of organic pollutants is challenging due to the unavailability of suitable analysing devices. Therefore, careful consideration was given to sample collection, as adding samples quickly and cheaply is not feasible.

Furthermore, the informal nature of the setting posed challenges in obtaining samples, as actors were often hesitant to allow researchers to conduct drilling activities on their premises. This challenge is well-documented in the literature, and we have addressed it by discussing the constraints on sample size in our study, aligning with existing research practices. Other studies also point to these problems, such as the work by Adanu, S.K.; Gbedemah, S.F.; Attah, M.K. on the challenges of adopting sustainable technologies in e-waste management at Agbogbloshie, Ghana.

Despite these constraints, we remain confident that our results are sufficiently robust to address the research questions and contribute to closing a knowledge gap in this field. Additionally, our study provides an important starting point for subsequent research by identifying the pollution effects of individual processes, which, to our knowledge, are not directly available in the literature. Furthermore, we have provided an outlook on future research directions to further explore and refine our findings.

Limitations

Write in which laboratory the tests were performed.

Thank you for your feedback. We have addressed your suggestion by including information about the laboratory where the tests were performed in the Methods section of the paper.

287-291

Describe why the concentrations of the same metals in the soil - the upper and lower layers - were not tested. If the concentrations of the same metals were tested, it would be possible to trace a decreasing or increasing trend in metal concentrations determined by local factors.

Thank you for your comment. We acknowledge the importance of testing the concentrations of the same metals in both upper and lower soil layers to trace potential trends influenced by local factors.

Indeed, it would have been advantageous to conduct such analysis. However, due to budget constraints and logistical challenges, researchers faced limitations in performing all analyses in a single laboratory. Despite intending to include this aspect in our research planning, practical constraints hindered the execution as desired.

Justify why environmental pollution indicators were used. For example, referring to the permissible concentration levels of metals and other components in soils and groundwater was possible according to applicable standards.

Thank you for this comment.

We employed pollution indices as useful tools for evaluating the degree of soil contamination by metals. These indices are widely utilized and facilitate comparisons not only within our study but also across other research efforts internationally. Pollution indices provide a relative assessment by comparing pollution against background values, offering insight into pollution levels relative to expected baseline conditions.

Furthermore, considering ecological risk is advantageous as it accounts for individual elements' biological toxicity responses, providing a more comprehensive understanding of environmental health.

The flexibility in interpretation offered by contamination factors allows for their application to various pollutants and environmental media. This enables researchers to assess multiple pollutants simultaneously and evaluate their combined impact on environmental quality.

Additionally, contamination factors reflect cumulative effects, providing a holistic view of overall pollution burdens rather than focusing on individual pollutant concentrations. This approach is crucial for understanding the true environmental impact.

Another advantage is the possibility to monitoring trends in contamination factors over time allows researchers and policymakers to identify areas requiring targeted intervention and implement timely mitigation measures. For example, the utilization of the Geoaccumulation Index (Igeo) is particularly valuable, as it is one of the most accurate pollution indices and has been widely used for decades to evaluate contamination levels. According to Kowalska, among individual pollution indices, Igeo and Enrichment Factor (EF) are considered the most useful and universal, while the Risk Index (RI) is crucial among complex pollution indices.

We have revised and added this to the methods chapter 2.4 Contamination indices and data processing accordingly

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I did not find a citation to item no. 56 in the text

We apologize for this inconvenience, however in our manuscript the citation of Nyarku et al. is in line 187 of the unrevised version.

Figure 2. Describe the vertical axis

Thank you, we have revised it accordingly

Figure 2

Title of the article

The title should be supplemented with the location of the research

Thank you for your suggestion regarding the title of the paper. We have taken this feedback into consideration and have supplemented the title with the location of the research, providing readers with a clearer understanding of the geographical context of our study.

Title

Reviewer comment

Authors response

Line numbers modified

Realistically the article is a technical report with no scientific aspect to it.

Thank you for your feedback. While we understand your viewpoint, we respectfully disagree. Our article presents findings based on systematic data collection and analysis, adhering to scientific methodologies. We believe the results contribute valuable insights to the field, addressing significant environmental concerns.

We thought about what might have led the reviewer to this assumption and in response, we have thoroughly revised the discussion section of our paper to enhance its scientific aspects. We have restructured the discussion of the results according to the research questions posed in the study, aiming to provide a clearer and more cohesive understanding of our research findings. This restructuring ensures that our discussion aligns closely with the objectives of the study, facilitating a more systematic and coherent presentation of our results and their implications.

Discussion

Enumerated  by the authors 4 questions in their study (page 4) are very doubtful in the presented subject of the paper without the temporal analysis of behavior in dynamics .

We appreciate your feedback regarding the research questions presented in the study.

While we acknowledge your concerns about the absence of temporal analysis of behaviour in dynamics, we would like to clarify that the primary aim of our study was not to investigate temporal dynamics. Instead, our focus was on examining the environmental impacts of informal e-waste recycling practices, particularly in relation to soil and groundwater quality at a specific point in time.

We have taken your feedback into consideration and made adjustments accordingly. Specifically, we have revised research questions and reordered the discussion section to better align with the sharpened research questions. Additionally, we have improved the discussion on the relationship between soil and natural conditions to provide a more comprehensive analysis of the study findings.

We have further elaborated the temporal dynamics in the limitation of the study.

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The classification of different levels are not representative in real conditions of both for soil and groundwater (presented in Table 2).

Thank you for your insightful comment regarding the classification of soil layers presented in Table 2.

We appreciate the opportunity to provide further clarification and improvements in this aspect. It's essential to understand that soil classification is based on various factors, including the proportion of organic matter, mineral content, and physical and chemical properties. In our study, we classified the soil layers based on established criteria in literature, with the A horizon representing the topsoil and the B horizon representing the subsoil.

To enhance the representation of soil characteristics, we have added additional information such as grain size distribution, permeability, infiltration rate, and bulk density for each soil layer. These parameters provide valuable insights into the mobility and adsorption of pollutants within the soil matrix, improving the comprehensiveness of our analysis.

Furthermore, we have incorporated discussions on these soil characteristics into the discussion section of the paper. This allows for a more thorough examination of how soil properties influence the transport and fate of pollutants, contributing to a deeper understanding of the environmental implications of our study findings.

We believe that these enhancements better reflect the real conditions of soil and groundwater and provide a more comprehensive analysis of the environmental impacts of informal e-waste recycling practices. We appreciate your feedback, which has helped us improve the quality and relevance of our research.

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Supposedly introduced statistical analysis, is primitive for both soil and groundwater parameters with ecological risks (Table 3). This is just formal simulation without any explanations.

Thank you for your feedback on the statistical analysis presented in Table 3. We understand your concern regarding the perceived simplicity of the statistical method employed. You are correct in noting that the term "statistical analysis" may be overly broad for our study. We revised the terminology to more accurately reflect the specific analytical methods employed in our research.

It's important to note that our primary aim was to show the impact of e-waste treatment techniques on soil and groundwater, rather than to establish comprehensive statistical relationships. We have clarified this point in the chapter 3.3 by explaining that our aim was to draw conclusions about the source of the pollution. Therefore, it is descriptive and we have used the Pearson correlation for this purpose

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(1)    How much electronics waste is generated in the Republic of Ghana and how much is imported from other countries?

Thank you for your question. According to data from the Global E-waste Monitor, the estimated e-waste generation in Ghana for the year 2023 was approximately 72,000 tons per year, we have added this information in the introduction.

We already addressed the issue of importation, which can be found in line 72, in the unrevised version. (150,000 tons of used electronics).

Additionally, we have added literature on how much if these imports are waste at arrival which varies between studies from 15-30 % (see e.g.  SBC (2011) Where are WEee in Africa? Findings from the Basel Convention E-waste Africa Programme; Odeyingbo O, Nnorom IC, Deubzer O (2017) Person in the Port Project: assessing import of used electrical and electronic equip- ment into Nigeria. UNU-ViE SCYCLE and BCCC Africa, Bonn)

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(2)    What are the volumes of electronics waste stored at the Agbogbloshie landfill site in Akre, and what is the composition of this waste?

Thank you for your question. In our study, we have provided information on the volume of e-waste stored at the Agbogbloshie landfill site, which is approximately 15,092 tons per year, as indicated in line 182 of the unrevised version.

Additionally, we have included data on the composition of this waste in the same section, offering insights into the types of e-waste materials present at the site.

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(3)    Is the sample size sufficient to make such estimates?

Thank you for your comment regarding the sample size in our study. We acknowledge that a larger sample size would ideally be desirable for more robust estimates. However, we faced several constraints that limited our ability to increase the sample size.

Financial constraints and project budget considerations posed challenges in obtaining a larger sample size, particularly given the high costs associated with shipping polluted soil abroad for analysis, especially considering the lack of available analytical devices for organic pollutants in Ghana. As such, we had to carefully consider the feasibility and cost-effectiveness of sample collection, prioritizing the most critical areas for analysis.

Additionally, the informal nature of the setting presented challenges in obtaining samples, as stakeholders were often reluctant to allow researchers to conduct drilling activities on their premises. This issue is well-recognized in the literature, and we have addressed it by discussing the constraints on sample size in our study.

Despite these limitations, we believe that our results are sufficiently robust to address the research questions and contribute to closing a knowledge gap in this field. Furthermore, our study serves as an important starting point for subsequent research, as there is currently limited data available in the literature on pollution resulting from individual e-waste recycling processes.

We have acknowledged the limitations regarding sample size in our study in the limitations section and have provided an outlook on future research directions to further explore and refine our findings. We remain committed to advancing our understanding of the environmental impacts of informal e-waste recycling processes and welcome further research in this area.

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