Geochemical Patterns and Human Health Risks of Less-Regulated Metal(loid)s in Historical Urban and Industrial Topsoils from Alcalá de Henares, Spain

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a comprehensive geochemical and human health risk assessment of selected less-regulated, technology-related metal(loid)s (Ag, Co, Fe, Mo, Pt, Rh, Sb, Se and Y) in urban, industrial and garden topsoils from Alcalá de Henares (Spain). The topic is relevant to the scope of the Journal of Xenobiotics, particularly in the context of emerging contaminants, urban exposure pathways and regulatory gaps. The study is based on a relatively large dataset (137 samples), applies appropriate analytical techniques (ICP–MS), and combines descriptive statistics, enrichment indices, multivariate analysis and human health risk assessment. Overall, the manuscript is well structured, clearly written, and provides useful baseline information for urban soil contamination by less-studied elements.

However, several methodological, interpretative and conceptual issues should be addressed prior to publication of the manuscript. These are outlined below.

Major Comments

Use of historical samples (2001) and implications for relevance

The soil samples were collected in 2001 but analysed recently. While the authors justify this by the environmental persistence of metals, this issue deserves a more critical and transparent discussion. Urban environments, traffic composition (e.g., catalytic converter technology), industrial activities and regulatory frameworks have changed substantially over the past two decades.

• The authors should more clearly delineate whether the study aims to represent current exposure conditions or historical baselines.
• Conclusions and policy-relevant statements should be carefully framed to avoid implying present-day risk levels without contemporary validation.
• A short paragraph in the Discussion explicitly addressing how temporal changes may affect Pt, Rh and Ag inputs would strengthen the manuscript.

 

Choice and justification of reference elements for enrichment factors

The use of Mn as a normalising element for EF calculations is justified by data availability, but Mn can itself be influenced by anthropogenic and pedogenic processes in urban soils.

• The limitations of using Mn instead of more conventional conservative elements (e.g., Al, Ti, Sc) should be discussed more explicitly.
• For Y, a different EF approach based on Fe and upper continental crust values is used; this methodological inconsistency should be better justified and clearly signposted to the reader.

Human health risk assessment: scope and limitations

The human health risk assessment follows standard US EPA methodology and is clearly described. However, its scope is constrained by the lack of toxicological benchmarks for Pt, Rh and Y.

• The authors should avoid over-interpreting the “negligible risk” conclusion when key contaminants of interest cannot be quantitatively assessed.
• A clearer distinction should be made between assessed risk (Ag, Co, Mo, Sb) and unassessed or partially assessed risk (Pt, Rh, Y).
• The discussion could benefit from referencing emerging toxicological evidence or uncertainty-based approaches for platinum-group elements.

 

PCA interpretation and explained variance

PCA is used appropriately, but the first two components explain just over 50% of the variance, and Pt loads mainly on PC3.

• The authors should clarify the limitations of interpreting PC1–PC2 biplots when a key element (Pt) is largely represented in a separate component.
• Some source attributions (e.g., traffic-related inputs) would benefit from stronger linkage to spatial data or external emission evidence.

Minor Comments

1. Terminology and consistency
• Ensure consistent use of terms such as “metal(loid)s”, “PTEs” and “technology-related elements” throughout the manuscript.
• Clarify early in the Introduction whether Fe is treated primarily as a contaminant or as a reference/lithogenic element.
2. Detection limits and units
• Detection limits are sometimes reported as “limit on the attack solution”; this should be explained more clearly for non-specialist readers.
• Units for Pt and Rh (ng g⁻¹) should be reiterated in all relevant tables and figure captions to avoid confusion.
3. Regulatory context
• The manuscript cites regional Spanish guidance values (e.g., Aragón). A brief explanation of why these values are used in the absence of Madrid-specific thresholds would be helpful.
4. Figures and supplementary material
• Some figures (e.g., PCA plots and boxplots) are information-dense. Slightly enlarging axis labels and legends would improve readability.
5. Language and style
• The manuscript is generally well written; only minor grammatical and stylistic edits are needed.

Recommendation - Minor revision

The manuscript addresses an important and underexplored topic and has clear potential for publication in the Journal of Xenobiotics. However, the authors should address the comments above, particularly regarding the temporal relevance of the data, interpretation under high censoring, and limitations of the health risk assessment.

Author Response

Reviewer 1

The manuscript presents a comprehensive geochemical and human health risk assessment of selected less-regulated, technology-related metal(loid)s (Ag, Co, Fe, Mo, Pt, Rh, Sb, Se and Y) in urban, industrial and garden topsoils from Alcalá de Henares (Spain). The topic is relevant to the scope of the Journal of Xenobiotics, particularly in the context of emerging contaminants, urban exposure pathways and regulatory gaps. The study is based on a relatively large dataset (137 samples), applies appropriate analytical techniques (ICP–MS), and combines descriptive statistics, enrichment indices, multivariate analysis and human health risk assessment. Overall, the manuscript is well structured, clearly written, and provides useful baseline information for urban soil contamination by less-studied elements.

However, several methodological, interpretative and conceptual issues should be addressed prior to publication of the manuscript. These are outlined below.

Major Comments

Use of historical samples (2001) and implications for relevance

The soil samples were collected in 2001 but analysed recently. While the authors justify this by the environmental persistence of metals, this issue deserves a more critical and transparent discussion. Urban environments, traffic composition (e.g., catalytic converter technology), industrial activities and regulatory frameworks have changed substantially over the past two decades.

• The authors should more clearly delineate whether the study aims to represent current exposure conditions or historical baselines.
• Conclusions and policy-relevant statements should be carefully framed to avoid implying present-day risk levels without contemporary validation.
• A short paragraph in the Discussion explicitly addressing how temporal changes may affect Pt, Rh and Ag inputs would strengthen the manuscript.

We agree and have revised the Abstract, Discussion, and Conclusions to frame the dataset explicitly as a historical (2001) baseline rather than as a direct representation of current exposure conditions. We also tempered policy-facing statements accordingly and added a short paragraph discussing how temporal changes since 2001 could affect inputs of Pt/Rh (vehicle fleet/catalyst evolution) and Ag (changes in consumer products and urban practices).

Choice and justification of reference elements for enrichment factors

The use of Mn as a normalising element for EF calculations is justified by data availability, but Mn can itself be influenced by anthropogenic and pedogenic processes in urban soils.

• The limitations of using Mn instead of more conventional conservative elements (e.g., Al, Ti, Sc) should be discussed more explicitly.
• For Y, a different EF approach based on Fe and upper continental crust values is used; this methodological inconsistency should be better justified and clearly signposted to the reader.

We have expanded Section 2.6 to acknowledge the limitations of Mn as a normalising element and to clarify that EF values should be interpreted as semi-quantitative indicators under this constraint. We also explicitly signposted that Y enrichment was evaluated using a separate Fe-normalised upper-continental-crust approach because local background values for Y were not available in the referenced regional unit; we clarified that Y enrichment results are therefore not directly comparable with the Mn-normalised EF values for Ag/Co/Mo/Sb.

Human health risk assessment: scope and limitations

The human health risk assessment follows standard US EPA methodology and is clearly described. However, its scope is constrained by the lack of toxicological benchmarks for Pt, Rh and Y.

• The authors should avoid over-interpreting the “negligible risk” conclusion when key contaminants of interest cannot be quantitatively assessed.
• A clearer distinction should be made between assessed risk (Ag, Co, Mo, Sb) and unassessed or partially assessed risk (Pt, Rh, Y).
• The discussion could benefit from referencing emerging toxicological evidence or uncertainty-based approaches for platinum-group elements.

We agree and have further clarified the scope of the risk assessment in the Discussion (section 3.5) and Conclusions. We now explicitly state that HQ/HI and cancer risk can only be calculated for elements with authoritative toxicological benchmarks, and that the absence of widely accepted reference values for Pt and Rh (and limited/less harmonised values for Y) precludes quantitative risk characterisation for these elements. We therefore clarify that the “low risk” conclusion applies only to elements with established benchmarks and should not be interpreted as evidence of no risk for Pt/Rh/Y, which remain priorities for future targeted assessment..

 

PCA interpretation and explained variance

PCA is used appropriately, but the first two components explain just over 50% of the variance, and Pt loads mainly on PC3.

• The authors should clarify the limitations of interpreting PC1–PC2 biplots when a key element (Pt) is largely represented in a separate component.
• Some source attributions (e.g., traffic-related inputs) would benefit from stronger linkage to spatial data or external emission evidence.

We clarified the limitations of interpreting PC1–PC2 biplots when Pt loads predominantly on PC3 and added an explicit statement that PCA identifies co-variation structures rather than proving causation. We aligned the source discussion more closely with the combined evidence from PCA loadings and spatial distribution patterns.

Minor Comments

1. Terminology and consistency
• Ensure consistent use of terms such as “metal(loid)s”, “PTEs” and “technology-related elements” throughout the manuscript.
• Clarify early in the Introduction whether Fe is treated primarily as a contaminant or as a reference/lithogenic element.

We clarified early in the Introduction that Fe is treated in a dual way in this study: (i) as a predominantly lithogenic element supporting geochemical context and normalised interpretation, and (ii) as a screened metal because Fe can be anthropogenically enriched in industrial/urban soils and because guidance values are available for contextual comparison.

We also standardised the terminology by consistently using the inclusive term “metal(loid)s” throughout the manuscript (text, tables, and figure captions), thereby avoiding alternating expressions such as “metals and metalloids” and ensuring uniform wording across sections.

1. Detection limits and units
• Detection limits are sometimes reported as “limit on the attack solution”; this should be explained more clearly for non-specialist readers.
• Units for Pt and Rh (ng g⁻¹) should be reiterated in all relevant tables and figure captions to avoid confusion.

Thank you. We clarified the meaning of “limit on the attack solution” by explicitly defining it as the digestion-solution method detection limit (instrumental LoD propagated through digestion and dilution and back-calculated to soil concentration units). We implemented this clarification in the footnotes of Tables 1–3 (and Supplementary tables where applicable) to ensure non-specialist readers can interpret LoD consistently.

Units have been corrected/checked accordingly.

1. Regulatory context
• The manuscript cites regional Spanish guidance values (e.g., Aragón). A brief explanation of why these values are used in the absence of Madrid-specific thresholds would be helpful.

We added a brief clarification that regional Spanish guidance values are used only as contextual screening thresholds. Where Comunidad de Madrid guidance values were unavailable for a specific element (e.g., Fe), we included Aragón’s published value as a pragmatic Spanish comparator and clearly flagged this choice in the Methods.

1. Figures and supplementary material
• Some figures (e.g., PCA plots and boxplots) are information-dense. Slightly enlarging axis labels and legends would improve readability.

Thank you for this suggestion. We reviewed the information-dense figures (PCA and boxplots) for readability. The figures are already legible at journal resolution and include detailed captions/legends; therefore, we did not substantially redesign them to avoid unnecessary duplication or changes that would not improve interpretability. However, we have revised Figure 1 (sampling map) to more clearly display and distinguish the sampling locations by land-use category, improving visual clarity and facilitating interpretation of the spatial context.

1. Language and style
• The manuscript is generally well written; only minor grammatical and stylistic edits are needed.

Thank you. We completed a final proofreading pass across the manuscript to correct minor grammatical/stylistic issues and to ensure consistent use of abbreviations, units, and terminology (including element symbols and risk-assessment terms) throughout.

Recommendation - Minor revision

The manuscript addresses an important and underexplored topic and has clear potential for publication in the Journal of Xenobiotics. However, the authors should address the comments above, particularly regarding the temporal relevance of the data, interpretation under high censoring, and limitations of the health risk assessment.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript covers a relevant topic related to the spatial distribution and health risks associated with Ag, Co, Fe, Mo, Pt, Rh, Sb, Se and Y in urban, industrial and garden soils. The article is well structured, the dataset is large and carefully analysed, and suitable statistical methods, PCA, and enrichment and risk indicators are used. The work is a valuable contribution to the knowledge about urbanised areas in Spain in this context.

However, some important revisions are needed, which would strengthen the scientific contribution, improve the toxicological and ecological interpretation, and clarify several critical methodological points.

1. The time frame of the soil samples and the related interpretation are outdated. The samples were collected in 2001, but the results are interpreted as if they reflect current risk. A clear distinction is needed between a historical assessment of accumulation and their validity under present-day pollution scenarios. Without this clarification, there is a risk of overinterpretation.

2. The toxicological discussion is not sufficiently developed, and a deeper interpretation in this context is missing. It would be useful to explain why the absence of RfD/RfC for Pt, Rh and Y is critical. What are the known biological mechanisms of toxicity? How do the results fit into the broader framework of urban pollutants?

3. The sources of Ag and Mo are not sufficiently argued. There are no specific local data on activities in Alcalá de Henares, and stronger evidence is needed to support the proposed sources.

4. The discussion of garden soils is too limited. Garden soils show the highest Ag concentrations, the highest EF values, and potentially the greatest human contact. This part is underestimated and should be discussed in more detail regarding the risk for people who grow food, possible bioaccumulation pathways, and comparisons with other European cities.

5. The authors treat the PCA loadings as direct evidence for anthropogenic/geogenic sources. Clarifications are needed that PCA does not prove causation and that additional isotopic or mineralogical data would be necessary.

6. The text needs stylistic smoothing. It is too long, contains repetitions, and often retells information already described.

7. In the figures, some units are missing in the legends, and Pt and Rh are shown in ng/g, but sometimes discussed in mg/kg in the text — full unification is needed.

8. The references should be expanded with more recent publications after 2020, especially for PGEs and REEs.

9. The tables are too large, and it may be appropriate to move some of them to the Supplementary Material.

Author Response

Reviewer 2

The manuscript covers a relevant topic related to the spatial distribution and health risks associated with Ag, Co, Fe, Mo, Pt, Rh, Sb, Se and Y in urban, industrial and garden soils. The article is well structured, the dataset is large and carefully analysed, and suitable statistical methods, PCA, and enrichment and risk indicators are used. The work is a valuable contribution to the knowledge about urbanised areas in Spain in this context.

However, some important revisions are needed, which would strengthen the scientific contribution, improve the toxicological and ecological interpretation, and clarify several critical methodological points.

1. The time frame of the soil samples and the related interpretation are outdated. The samples were collected in 2001, but the results are interpreted as if they reflect current risk. A clear distinction is needed between a historical assessment of accumulation and their validity under present-day pollution scenarios. Without this clarification, there is a risk of overinterpretation.

We agree and revised the manuscript to present the study as a historical baseline (2001) with explicit limitations regarding present-day applicability. Risk statements were reworded to apply to the 2001 concentrations under the stated scenarios, and we added a short discussion of how changes in traffic/catalyst technology and urban practices may affect current inputs.

Moreover, we have explicitly situated our findings within the broader framework of urban soil pollution by adding a short synthesis statement linking the observed land-use contrasts and enrichment patterns to the main urban drivers (traffic-related non-exhaust inputs and resuspension, industrial/urban legacy deposition and localised hotspots, and managed-soil inputs in gardens) superimposed on lithogenic background contributions.

1. The toxicological discussion is not sufficiently developed, and a deeper interpretation in this context is missing. It would be useful to explain why the absence of RfD/RfC for Pt, Rh and Y is critical. What are the known biological mechanisms of toxicity? How do the results fit into the broader framework of urban pollutants?

We agree and have strengthened the toxicological interpretation and its integration with the risk assessment. First, in Section 3.5 we now explicitly explain why the absence of route-specific benchmark values (RfD/RfC and, where applicable, IUR) for Pt and Rh—and the limited/less harmonised benchmark coverage for Y—is critical: without authoritative toxicity benchmarks, standard quantitative screening metrics (HQ/HI and cancer risk) cannot be computed, so risk characterisation for these technology-related elements must remain qualitative and is presented as a recognised uncertainty rather than interpreted as “no risk.”

Second, we expanded the mechanistic toxicology context by summarising available evidence that traffic-related PGEs can elicit oxidative-stress and pro-inflammatory responses, with hazard strongly dependent on chemical form and bioaccessibility, and we note the established sensitisation potential of soluble Pt salts in occupational settings. We also added a synthesis for REEs/Y indicating recurring mechanistic themes in recent reviews (ROS generation/oxidative stress, inflammatory signalling, mitochondrial dysfunction, DNA damage and apoptosis/autophagy-related pathways), while emphasising that dose–response evidence remains insufficiently mature for widely accepted soil-exposure benchmarks.

Third, we explicitly place our results within the broader framework of urban pollutant mixtures by highlighting that observed land-use contrasts reflect combined influences of non-exhaust traffic inputs/resuspension, industrial/legacy deposition and managed-soil inputs (e.g., amendments in gardens) superimposed on lithogenic background, and we argue that inclusion of PGEs and Y complements conventional urban-metal assessments by identifying less-regulated, technology-related indicators.

These additions are found in the revised Abstract (benchmark gaps for Pt/Rh/Y), Introduction (knowledge gaps and lack of regulatory/toxicological coverage), and Section 3.5 (benchmark limitation statement + mechanistic paragraphs + urban-mixture framing).

1. The sources of Ag and Mo are not sufficiently argued. There are no specific local data on activities in Alcalá de Henares, and stronger evidence is needed to support the proposed sources.

We agree that source attribution must be evidence-proportionate and that our original wording risked over-specificity. We therefore revised the Discussion to frame Ag and Mo sources as plausible, non-exclusive hypotheses consistent with (i) the pronounced hotspot behaviour (high CV, right-skewness, elevated upper percentiles) and (ii) well-established urban source profiles reported in the literature. For Ag, we now cite evidence that wastewater treatment can concentrate Ag in sewage sludge and that land application of biosolids can increase Ag in amended soils, making biosolids/compost inputs a plausible pathway in managed soils (e.g., gardens), alongside other diffuse urban inputs. For Mo, we strengthened the discussion by citing evidence that traffic-related materials and non-exhaust emissions (including brake-pad/brake-dust composition and associated mineral phases) can contribute trace metals to urban environments, supporting traffic/urban activity as a plausible contributor in addition to any local industrial influences. We also explicitly state that definitive attribution would require complementary tracers (e.g., isotopes, mineralogy/speciation, source sampling) not available in this study, and therefore our interpretations remain hypothesis-based.

1. The discussion of garden soils is too limited. Garden soils show the highest Ag concentrations, the highest EF values, and potentially the greatest human contact. This part is underestimated and should be discussed in more detail regarding the risk for people who grow food, possible bioaccumulation pathways, and comparisons with other European cities.

We agree and expanded the garden-soil discussion to reflect (i) the substantially higher enrichment observed for Ag, (ii) the higher likelihood of direct contact through gardening activity and soil disturbance, and (iii) the relevance of gardens as food-growing settings, introducing a potential additional pathway via consumption of home-grown produce. We clarify that our current assessment is based on total concentrations, not bioaccessibility or plant uptake, and therefore we frame these as potential exposure considerations and recommend follow-up work prioritising Ag speciation/bioaccessibility and soil-to-crop transfer. We also added comparison to recent urban garden studies and risk-focused discussions in other European contexts to contextualise why enrichment in this land use warrants attention even when conventional thresholds are not exceeded.

1. The authors treat the PCA loadings as direct evidence for anthropogenic/geogenic sources. Clarifications are needed that PCA does not prove causation and that additional isotopic or mineralogical data would be necessary.

We agree and have strengthened the wording throughout the PCA interpretation to avoid implying proof of source causation. We now state explicitly that PCA is an exploratory method that identifies co-variation structure (shared variance) and therefore can suggest hypotheses about common controls or potential sources, but it does not demonstrate causation or uniquely resolve sources without additional evidence. We further note that confirmatory source apportionment would require complementary lines of evidence (e.g., mineralogical/speciation analyses, isotopic tracers, and/or direct source profile measurements and receptor modelling), which were beyond the scope of this baseline study.

1. The text needs stylistic smoothing. It is too long, contains repetitions, and often retells information already described.

We undertook targeted language tightening to improve flow and reduce repetition, particularly where numerical results were restated across multiple sections. The Results section is now more concise and factual, while interpretative statements are consolidated in the Discussion. We also harmonised terminology and removed redundant summaries that duplicated content already provided in Tables 1–3 and the supplementary figures.

1. In the figures, some units are missing in the legends, and Pt and Rh are shown in ng/g, but sometimes discussed in mg/kg in the text — full unification is needed.

Thank you for seeing this. We corrected and harmonised Pt and Rh units throughout the manuscript (text, tables, and figure captions), consistently reporting Pt/Rh in ng g⁻¹ and all other elements in mg kg⁻¹.

1. The references should be expanded with more recent publications after 2020, especially for PGEs and REEs.

We expanded the bibliography with additional recent (post-2020) publications on platinum-group elements and Y, including recent reviews and toxicology-focused syntheses that summarise emerging evidence and highlight benchmark gaps relevant to risk assessment and standard setting.

1. The tables are too large, and it may be appropriate to move some of them to the Supplementary Material.

We appreciate the reviewer’s concern regarding table length. We respectfully prefer to retain Tables 1–3 in the main text because they provide the core quantitative evidence needed to interpret this study’s primary contribution: a land-use resolved baseline for less-regulated technology-related metal(loid)s, including descriptive statistics, censoring information, local backgrounds, pollution indices, and the applicable screening benchmarks in one place. These tables contain information that is not readily available for the study area and elements considered and is required for transparency, reproducibility, and comparison by readers who may use the dataset as a reference baseline. To improve readability without removing content, we have ensured consistent abbreviations and footnoting and tightened the table notes and cross-references so that the narrative text does not duplicate the numerical summaries presented in the tables.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript analyzes the soil contamination results. A large number of samples were used for the analysis. The article is basically prepared correctly, but corrections are needed:

1) Introduction. It is necessary to emphasize the novelty of the article. What is the main difference from other soil contamination studies?

2) Chapter 2.1. There is a lack of description of the main potential sources of pollution.

3) Fig. 1. It is not clear which sample points are from urban, which are from industrial, which are from garden areas. It is better to mark the sample points with different colors or different symbols.

4) L. 160. If samples are taken from the 0-3 cm layer, I doubt whether that is enough to analyze historical pollution. But the text further discusses historical pollution.

5) Chapter 2.2. Why are city green areas divided into urban parks and gardens? These areas need to be explained in more detail.

6) Chapter 3. There is a lack of detailed analysis between the concentrations of toxic elements in soil and possible sources of pollution. This could be presented in table form. 

Author Response

Reviewer 3

The manuscript analyzes the soil contamination results. A large number of samples were used for the analysis. The article is basically prepared correctly, but corrections are needed:

1) Introduction. It is necessary to emphasize the novelty of the article. What is the main difference from other soil contamination studies?

We agree that the novelty should be stated more explicitly. Accordingly, we revised the Introduction to include a clear contribution statement emphasising that this study provides a land-use-resolved assessment of less-regulated, technology-related metal(loid)s (including Pt and Rh) in urban topsoils, and that the 2001 dataset constitutes a baseline supporting source-informed interpretation and future temporal comparisons. Moreover we have highlighted that we combined land-use stratification with multivariate and enrichment metrics, including appropriate treatment of censored data, to clarify spatial patterns and plausible controls in an urban European setting. The revised text has been added to the paragraph beginning in line 115.

2) Chapter 2.1. There is a lack of description of the main potential sources of pollution.

We agree. We have expanded Section 2.1 by adding a short paragraph describing the main plausible anthropogenic sources relevant to the monitored metal(loid)s in Alcalá de Henares (traffic-related deposition and resuspension, industrial estates/legacy inputs, construction and urban materials, and managed-soil inputs in gardens/landscaped areas). We also clarify that these categories provide contextual support for interpretation, while definitive source attribution would require targeted source sampling and/or additional tracers.

3) Fig. 1. It is not clear which sample points are from urban, which are from industrial, which are from garden areas. It is better to mark the sample points with different colors or different symbols.

We revised Figure 1 so that sampling locations are explicitly coded by land-use category (urban parks, industrial areas and gardens) using distinct symbols and colours, and we updated the legend accordingly. This makes it immediately clear which points correspond to each sampling group.

4) L. 160. If samples are taken from the 0-3 cm layer, I doubt whether that is enough to analyze historical pollution. But the text further discusses historical pollution.

We agree that sampling the 0–3 cm layer is not intended to reconstruct stratigraphic “historical pollution” in a time-resolved sense (which would require deeper soil profiles/cores). In this study, the shallow surface horizon was deliberately selected because it concentrates atmospheric deposition and is the soil layer most relevant to human contact and exposure assessment, which is central to the risk characterisation component of the manuscript. We clarify that “historical” refers to the baseline surface-soil concentrations as of the sampling year (2001), rather than to a depth-resolved reconstruction of older legacy inputs. We also note explicitly in Section 2.2 that, although the soils were collected in 2001, they were preserved under standard protocols and processed and analysed recently using current instrumentation, and that the reported total concentrations remain valid indicators of baseline surface contamination for persistent metal(loid)s.

5) Chapter 2.2. Why are city green areas divided into urban parks and gardens? These areas need to be explained in more detail.

We added a short clarification in Section 2.2 defining ‘urban parks’ versus ‘gardens’ in the study context, noting differences in management intensity, likelihood of soil/amendment inputs, and potential direct contact, which supports interpretation of the observed Ag enrichment hotspots.

6) Chapter 3. There is a lack of detailed analysis between the concentrations of toxic elements in soil and possible sources of pollution. This could be presented in table form. 

We agree that a concise synthesis of element–source interpretation can improve readability. However, to avoid expanding the main text and in light of the reviewer’s separate concern about table size, we have added a compact synthesis table as Supplementary material (Supplementary Table S1). This table summarises, for each element, the main observed land-use pattern and the primary lines of evidence used in the manuscript (land-use contrasts, EF/PI behaviour, PCA structure and hotspot mapping), together with appropriately cautious, hypothesis-based interpretations of plausible sources/controls.

 

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The scientific content is very good, the analyses are sound, and the manuscript is solid and suitable for publication in the journal.