Bioavailability, Sources, and Transfer Behavior of Heavy Metals in Soil–Crop Systems from a High Geological Background Area Impacted by Artisanal Zn Smelting in Guizhou Province, Southwest China

Round 1

Reviewer 1 Report

The manuscript is of interest due to of the study area - Emeishan basalt area, where the soils were subjected to anthropopression by artisanal Zn smelting. However, the manuscript requires major revisions, especially in the Materials and methods chapter.

Comments
1.    Keywords should be changed. I propose delete some keywords, such as: Emeishan basalt; Source apportionment and add new ones: farmland soil, soil contamination, soil-plant transfer factor.
2.    line 116-117: you wrote “…rhizosphere soil (0-20 cm depth) were collected with a stainless steel shovel”. It is not “rhizosphere soil” because the rhizosphere is the zone of soil surrounding a plant root where the biology and chemistry of the soil are influenced by the root. This zone is about 1 mm wide. The soil layer 0-20 cm is usually named as “topsoil layer”, “arable layer”, “surface layer soil” etc.
3.    line 118-119” you wrote: “Four subsamples (with an interval of 10 – 20m) from each site were mixed together to obtain a single composite sample”. Does this sentence apply to soil samples? If so, it should be moved to line 177, after the word "shovel".
4.    line 134-137: how were metals extracted from the soil for ICP-MS and AFS determinations?
5.    Line 141-144: add names for factions F1-F7
6.    Line 147-151: what reference material has been used? Give its name/symbol
7.    General comments to the Materials and Methods section: (1) the manuscript contains only soil pH and organic matter content, there are no other soil properties that significantly affect the mobility of heavy metals, such as soil texture, CEC, EC etc. (2) there is no methodology for the determination of heavy metals in plant material; (3) why in potato tubers heavy metals were determined in fresh weight and not in dry weight (see lines 129-130)? (4) Statistical analysis - you wrote: "...Shapiro-Wilk method was used to test the date for normal distribution". Where are the results of this statistical analysis?
8.    Table 2. (1) is the content of metals in plants in mg kg-1 dry matter or fresh matter? (see line 129-130); (2) explain why the n number is different for different elements; (3) the range of value for the tested elements should be given, and standard deviation or standard error should be placed with the mean value

Author Response

Response to Reviewer 1 Comments

Dear reviewer:

Thank you very much for providing insightful comments on this manuscript. These were helpful for enhancing the scientific rigor of the manuscript. Based on your suggestions, we have diligently undertaken revisions. The specific changes are as follows:

 

Point 1: Keywords should be changed. I propose delete some keywords, such as: Emeishan basalt; Source apportionment and add new ones: farmland soil, soil contamination, soil-plant transfer factor.

 

Response 1: Thank you for providing an excellent suggestion. Following the reviewer’s advice, we have revised the keywords for the manuscript to : Heavy metals；Farmland soil；Bioavailability；Soil contamination；Soil-plant transfer factor. (Line 35-36)

 

Point 2 : line 116-117: you wrote “…rhizosphere soil (0-20 cm depth) were collected with a stainless steel shovel”. It is not “rhizosphere soil” because the rhizosphere is the zone of soil surrounding a plant root where the biology and chemistry of the soil are influenced by the root. This zone is about 1 mm wide. The soil layer 0-20 cm is usually named as “topsoil layer”, “arable layer”, “surface layer soil” etc.

 

Response 2: Appreciate the reviewer for identifying this issue. We’ve now replaced all mentions of “rhizosphere soil” with “surface layer soil” throughout the manuscript. (Line 113 and 116)

 

Point 3 : line 118-119” you wrote: “Four subsamples (with an interval of 10 – 20m) from each site were mixed together to obtain a single composite sample”. Does this sentence apply to soil samples? If so, it should be moved to line 177, after the word "shovel".

 

Response 3: This sentence apply to soil samples collection. We have improved clarity by moving the sentence “Four subsamples (with an interval of 10 – 20m) from each site were mixed together to obtain a single composite sample” to after the word "shovel". （Line 117-118）

 

Point 4: line 134-137: how were metals extracted from the soil for ICP-MS and AFS determinations?

 

Response 4: We apologize for a brief introduction to the heavy metals extraction method was not provided in the original manuscript. We have added a concise introduction to the heavy metals extraction. “Cadmium, Co Cu, Ni and Pb were analyzed in the digested phase (0.1000g samples were put into a Teflon crucible and dissolved with a mixture of concentrated acid (HNO₃ + HF + HClO₄) ) by inductively coupled plasma mass spectrometry (ICP-MS; iCAP Qc, Thermo Scientific, USA).” (Line 136-137) “Arsenic and Hg were analyzed in the digested phase (0.1000g samples were digested with aqua regia (3:1 HCL/HNO₃) ) by atomic fluorescence spectrometry (AFS; AFS-3000, Beijing Haiguang Instrument Co, China).” (Line 139-140)

 

Point 5: Line 141-144: add names for factions F1-F7.

 

Response 5: The name of faction F1-F7 was added according to reviewer comments. “Heavy metals in the soils were successively extracted as the following seven fractions: water soluble fraction (F1), ion-exchangeable fraction (F2), fraction bound to carbonates (F3), fraction bound to humic acid (F4), fraction bound to Fe-Mn oxides (F5), fraction bound to organic matter (F6) and residual fraction (F7).” (Line 151-154)

 

Point 6: Line 147-151: what reference material has been used? Give its name/symbol

 

Response 6:  The names of reference materials were added to the manuscript. “The quality of chemical analysis (the accuracy and precision of data) was checked with blank samples, repetitive samples and standard reference materials (GSS30, GSS31, GSS33 and GSS34 for soil samples, and GBW10011, GBW10012, GBW10021 and GBW10043 for plant samples from IGGE, China) during the analytical process.”(Line 158-160)

 

Point 7: General comments to the Materials and Methods section: (1) the manuscript contains only soil pH and organic matter content, there are no other soil properties that significantly affect the mobility of heavy metals, such as soil texture, CEC, EC etc. (2) there is no methodology for the determination of heavy metals in plant material; (3) why in potato tubers heavy metals were determined in fresh weight and not in dry weight (see lines 129-130)? (4) Statistical analysis - you wrote: "...Shapiro-Wilk method was used to test the date for normal distribution". Where are the results of this statistical analysis?

 

Response 7: (1) Appreciate the valuable input from the reviewer. Unfortunately, this study did not include testing for soil texture, CEC, and EC indicators. Future research will incorporate these parameters to explore their impact on heavy metals activity and migration in soil.

(2) We supplemented the methodology for the determination of heavy metals in plant samples. “The concentrations of As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn in the plant samples were analyzed by ICP-MS, and Hg was analyzed by AFS (used microwave digestion process).”(Line 143-146)

(3) The testing method for biological samples follows the "National Food Safety Standard Determination of Multielements in Foods" (GB 5009.268-2016). According to the national standard, for high-water content samples like vegetables and fruits, they should be thoroughly washed, dried, and the edible portion should be homogenized before conducting further analysis and testing. Therefore, this test focuses on determining the content of heavy metals in fresh potato samples.

(4) We have incorporated the results of the normality test into 2.6 Statistical analysis. “The results indicated that the total concentrations of Cd, Co, Ni, Pb, V, Zn and Zr in the soils conform to a normal distribution, while As, Cr and Cu follow a log-normal distribution. However, Hg did not conform to either a normal or log-normal distribution.”（Line 189-191）

 

Point 8: Table 2. (1) is the content of metals in plants in mg kg^-1 dry matter or fresh matter? (see line 129-130); (2) explain why the n number is different for different elements; (3) the range of value for the tested elements should be given, and standard deviation or standard error should be placed with the mean value

 

Response 8: (1) We have carefully cross-checked the issues you raised. As described in the line 126-130, maize grains were dried before analysis, and the measurements were taken on dry matter, while potato samples were directly mashed into a paste for analysis. The testing method for biological samples follows the "National Food Safety Standard Determination of Multielements in Foods" (GB 5009.268-2016).

(2)"n" represents the number of samples that were above the detection limit. We have provided an explanation of "n" in Table 2 and supplemented the detection limits for plant sample elements. “The detection limits of As, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, and Zn were 0.01、0.002、0.002、0.05、0.003、0.01、0.2、0.02、0.001 and 0.05 mg·kg^-1, respectively.” (Line 145-146)

(3) Based on your suggestion, we have added the minimum, maximum, and standard deviation of the element content in Table 2.

 

 

Thank you for your valuable time invested in this manuscript.

Yours sincerely

Honghong Ma

Reviewer 2 Report

This manuscript presented an interesting study about the effect of anthropogenic activities in soil-crop systems. The work has potential. However, some points listed below need to be improved.

 

Section 2.2: I suggest add the month (or months) when the samples were collected.

 

Section 2.3.1: please better describe how the samples were prepared for XRF, ICP-MS, and AFS.

 

Section 3.1: I suggest expand the discussion in this section. The authors may compare their results with others locations were anthropogenic activities might cause changes in the soil.

 

Section 3.3.2:  if possible comment about the season (month) when the soil samples were collected, because a rainy season may influenced in the heavy metal lixiviation.

Author Response

Response to Reviewer 2 Comments

Dear reviewer:

Thank you very much for providing insightful comments on this manuscript. These were helpful for enhancing the scientific rigor of the manuscript. Based on your suggestions, we have diligently undertaken revisions. The specific changes are as follows:

Point 1: Section 2.2: I suggest add the month (or months) when the samples were collected.

Response 1: Follow the reviewer’s suggestion, we have added the collection time of the samples. During the maize and potatoes maturity period (September to October), the plants were uprooted and the corresponding surface layer soil (0 – 20cm depth) were collected with a stainless steel shovel. (Line 115-117)

Point 2: Section 2.3.1: please better describe how the samples were prepared for XRF, ICP-MS, and AFS.

Response 2: We apologize for a brief introduction to the heavy metals prepared method was not provided in the original manuscript. We have added a concise introduction to the heavy metals extraction. “The total concentrations of Cr, V, Zn, and Zr in the soil powder samples were analyzed by X-ray fluorescence spectrometry (XRF; Advant XP, ARL, Switzerland). Cadmium, Co Cu, Ni and Pb were analyzed in the digested phase (0.1000g samples were put into a Teflon crucible and dissolved with a mixture of concentrated acid (HNO₃ + HF + HClO₄) ) by inductively coupled plasma mass spectrometry (ICP-MS; iCAP Qc, Thermo Scientific, USA). Arsenic and Hg were analyzed in the digested phase (0.1000g samples were digested with aqua regia (3:1 HCL/HNO₃) ) by atomic fluorescence spectrometry (AFS; AFS-3000, Beijing Haiguang Instrument Co, China).”(Line133-140)

Point 3: Section 3.1: I suggest expand the discussion in this section. The authors may compare their results with others locations were anthropogenic activities might cause changes in the soil.

Response 3: According to the reviewer's suggestion, we added the comparison and discussion of heavy metal concentration in soil with other metal smelting areas in section 3.1. “Compared the concentration of heavy metals in soil in the study area to other lead-zinc mining and smelting regions. According to Peng et al.'s 2015 survey in this area, the average concentrations of As, Cd, Cr, Cu, Hg, Pb, and Zn in the soil were 14.07, 2.04, 160.17, 125.67, 0.12, 62.83, and 260.00 mg·kg^-1, respectively. The current survey revealed higher average Cd and Cu levels compared to previous research. The investigation of heavy metals in the soil around Jinding Zn-Pb mining field in Yunnan exhibited median concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn at 29.4, 3.52, 57.3, 31.8, 0.18, 22.3, 115.3, and 233.1 mg·kg^-1, respectively. In contrast, this study's soil exhibited significantly higher concentrations of Cr, Cu, and Ni, similar Cd levels, and comparatively lower levels of As, Pb, and Zn. Du et al.'s observations indicated that soil in mining-affected areas near Changsha had higher As (15.1 ± 4.1 mg·kg^-1) and Pb (51.2 ± 15.0 mg·kg^-1) concentrations than this study area, while displaying lower levels of the other 7 heavy metals (excluding Hg). Furthermore, compared to findings in the nonferrous metal smelting area of Baiyin City, this study found higher concentrations of Co, Cr, Ni, and V, while Cd, Cu, Pb, and Zn concentrations were notably lower.”(Line 213-227)

Point 4: Section 3.3.2:  if possible comment about the season (month) when the soil samples were collected, because a rainy season may influenced in the heavy metal lixiviation.

Response 4: Thank you for the excellent suggestion. The harvest season for potatoes and maize in Weining County, Guizhou, often coincides with continuous rainy weather. The rainy season could potentially impact the lixiviation of heavy metals. We will be mindful of this issue and try to avoid rainy days as much as possible, focusing on collecting samples during more favorable weather conditions.

 

 

Thank you for your valuable time invested in this manuscript.

 

Yours sincerely

Honghong Ma

Round 2

Reviewer 1 Report

Dear Authors, I accept your changes to the manuscript. However, I suggest moving the sentence from lines 202-205 to the chapter Results and discussion for examle after Table 1.

Author Response

Dear reviewer:

Thank you for accepting the first round of revisions and providing valuable feedback once again. However, it seems that we didn't quite understand your point. Lines 202 to 205 are already in the chapter of 'Results and Discussion'. Could you please provide a more precise identification of this point? We are committed to making through revisions based on your suggestions.

Thank you very much for your dedicated efforts on this manuscript.

Yours sincerely

Honghong Ma