Speciation and Mobility of Cr and Ni in Serpentine Rocks and Derived Sediments (Tuscany, Italy)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The research is relevant and important and I see it's significance. I have a few questions I hope the author can clarify:

The abstract mentions "significant differences in availability and mobility" of chromium and nickel, but doesn’t provide any actual numbers. Could the author include specific concentration ranges or percentage data?

In the methods, it says the extractions were done in triplicate and that the precision was "below 20%." This seems like a high level of uncertainty for geochemical work. Can the author explain how they ensured the results are still reliable?

Aqua regia digestion is used to estimate total metal content, but it doesn't break down silicate minerals well. How does this affect interpretation of the results, especially for chromium in silicate-bound forms?

Figure 2 shows a noticeable gap in nickel concentrations between sediments and serpentinites. This is said to be due to sampling bias, but doesn’t that suggest a bigger issue with the data that might impact the study’s conclusions?

The sequential extraction results are only shown for a small number of samples. How do the authors know these few samples represent the full range of geochemical conditions across the site?

There is no statistical analysis showing how extraction results relate to pH, redox potential (Eh), or mineralogy. Shouldn’t these relationships be explored and quantified to support the risk assessment?

The study doesn’t include statistical comparisons between different sample types or locations. How can environmental risks be evaluated without that kind of analysis?

The paper claims to offer a way to assess Cr(VI) risk in groundwater but doesn’t provide clear risk levels or thresholds. What counts as "high risk" versus "low risk," and how is that decided?

If the author says there are “significant differences” in metal mobility, shouldn’t they include proper statistical tests to support that?

Author Response

All changes have been incorporated into the revised manuscript

- Abstract: Added quantitative data to support statements on significant differences in Cr and Ni mobility (ranges and concentrations included).

- Methods: Clarified why precision below 20% is acceptable for sequential extraction studies and explained the limitations of aqua regia digestion regarding silicate-bound metals.
- Results: Justified the representativeness of selected samples and addressed the observed gap in Ni concentrations between sediments and serpentinites.
- Discussion: Included a note on the need for statistical analysis to explore relationships between extraction results and soil parameters (pH, Eh, mineralogy).
- Conclusions: Defined risk thresholds for Cr and Ni based on Italian soil quality standards.

Reviewer 2 Report

Comments and Suggestions for Authors

It is an interesting and thorough investigation on the transformations that can occur in natural rocks and soils, my two recommendations are:

1) check English in figures (i.e. Nichel is Nickel)

2) it will be interesting to add in the introduction information on a global estimate or presence of serpentinite rocks, how common they are? are regions in the world with high serpentinite?

3) for discussion: if the soil around it can affect the speciation, this would imply that if acid rain is a problem, there could be an increase in Cr(VI) ? this could be relevant for regions that have both serpentinite and acid rain 

Comments on the Quality of English Language

 

1) check English in figures (i.e. Nichel is Nickel)

 

Author Response

All changes have been incorporated into the revised manuscript.

- Introduction: Added global context on serpentinite rocks, including their distribution and environmental relevance.
- Figures: Corrected English errors (e.g., 'Nichel' changed to 'Nickel') and improved captions for clarity.
- Discussion: Added a paragraph discussing the potential effect of acid rain on Cr(VI) formation and environmental risk.

Reviewer 3 Report

Comments and Suggestions for Authors

The article "Speciation and Mobility of Cr and Ni in Serpentine Rocks and Derived Sediments (Tuscany, Italy)", describes an environmental process where the eroded ophiolites compose a serpentine terrestrial.

The abstract is well structured and the introduction introduces the reader to the meaning of the article.

The material and method part is clearly explained.

The results are understandable.

And the disscusion topic is supported by the the results.

The article must be presented in the appropriate way.

The references have to be provided according to the form of the journal and some figures and tables should be presented in a better way.

Author Response

All changes have been incorporated into the revised manuscript.

- Formatting: Improved figure and table presentation and ensured references comply with journal style.
- Language: Revised the manuscript for clarity and conciseness, correcting minor typos and improving readability.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have answered the queries and made necessary edits to the manuscript. It can be published , my only issue now is the quality of figures and table. For example table 1 is so blurry that it is hard to read the datapoints.  The quality of figure1 and 2 is also very blurry. Is this something that can be rectified? 

Author Response

 

Thank you for your positive feedback and for pointing out the issue regarding the quality of Table 1 and Figures 1. I appreciate your attention to detail.

I will replace the current versions with high-resolution images and tables (pdf and xlsx) to ensure clarity and readability of all data points.