The Spatial Distribution, Contamination Status and Contributing Factors of Heavy Metals in Cropland Soils of Twelve Cities in Shandong Province, China

Round 1

Reviewer 1 Report

The paper report concentration levels of heavy metals in different cities of China.

The paper could be interesting if, besides the spatial distribution of the pollution, it would clarified the origin of pollution relating to number and type of industry or agriculture practice.

The authors classify the soil in brown, cinnamon and fluvoacquic. Please indicate on the basis of which soil classification criteria the soil was classified

Author Response

Dear Reviewer,
Thanks for your comments on our manuscript (ID: applsci-727812) “The distribution pattern and affecting factors of heavy metals in cropland soils of twelve cities in Shandong Province, China”, which was very helpful to improve our manuscript. We have carefully polished the English language, arranged the Abstract, rewrote the part of Introduction, enriched the part of Results and Discussion, and revised the manuscript accordingly.

We revised the manuscript with "Track Changes" function. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

Reviewer 2 Report

The paper deals with an important issue.

However it is necessary to develop it further and explicitly present novelty.
The abstract of the paper lacks a clear cut hypothesis and objectives.
The Introduction section needs to be re-written highlighting emphasis on the topic.

The results have been written to briefly, they need to be elaborated showing trends.

The authors seem to disregard or neglect some important global results that have been recently achieved in this specific field.

The discussion is not up to the mark and needs a drastic precise and focused approach.

I suggest improving the Discussion adding more recent related findings and explain each result properly.

The content is more a case study that original research work providing novel methods and or observation.

The results should be more conclusive and also generalised confirming if they have wide validity.

Otherwise the paper is more a technical report that original research work.

Author Response

Dear Reviewer,
We appreciate your work on our manuscript (ID: applsci-727812) “The distribution pattern and affecting factors of heavy metals in cropland soils of twelve cities in Shandong Province, China”, which was very helpful to improve our manuscript. We have carefully evaluated the comments and thoughtful suggestions, rewrote the part of Introduction, enriched the part of Results and Discussion, responded to the suggestions point-by-point, and revised the manuscript accordingly.

We revised the manuscript with "Track Changes" function. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

Your comments were divided into five questions, we responded to the suggestions point-by-point as below showed, specific revisions were showed in the revised manuscript.

1. The paper deals with an important issue. However it is necessary to develop it further and explicitly present novelty.

Answer: Thanks for your encouragement and suggestions which help us a lot. In the revised manuscript, the spatial distribution and contamination status of the six metals in cropland soils of different cities, soil types, and decade were presented. Meanwhile, the sources of the metals were explored by cluster analysis, Pearson correlation analysis, and the relations with economic indicators. We would be happy to do whatever is required if further revision is necessary.

2. The abstract of the paper lacks a clear cut hypothesis and objectives.

Answer: thanks for your comments, we revised the abstract:

To analyze the spatial distribution and contamination status of heavy metals in cropland areas, 55 agricultural soils were collected from 12 cities of Shandong Province, China, and concentrations of copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni) and zinc (Zn) were determined. Results showed that average contents of Cu, Pb, Cd, Cr, Ni and Zn were 24.13, 31.77, 0.16, 130.63, 22.13, and 71.19 mg·kg^-1, respectively, and contents of Cr, Pb, and Cd exceeded the background values in most cities. It showed that Cr in cities of Weifang, Weihai, Yantai, and Zibo were significantly higher than in other cities, Weihai and Zibo also had significantly high contents of Zn. Moreover, concentrations of Cr in brown soils and cinnamon soils were significantly higher than that in fluvo-aquic soils, while other metals showed no significant difference. Furthermore, the Cu, Pb and Zn showed the significant concentration decrease with respect to those measured in 2007. The significantly positive relationship between industrial added value and Cd may suggest the input of industrial waste. In addition, the significantly correlated Cu/Ni/Zn and Pb/Cd indicated the different input from human activities, while the accumulation of Cr was very complex. This study demonstrated that more attention should be paid to the contamination of Cr, Pb, and Cd, and industrial waste management is vitally imperative for safety of surrounding cropland soils.

3. The Introduction section needs to be re-written highlighting emphasis on the topic.

Answer: thanks for your suggestion, we rewrote the introduction part in the revised manuscript. It showed:

Introduction

Soil is a fundamental component of ecosystems and undertakes various human activities, among which, food production is an important function for the survival of mankind [1, 2]. However, industrial production and other producing activities usually discharge plenty of pollutants, which would pollute the surrounding cropland [3]. Owing to the rapid industrial and agricultural development, the accumulation of pollutants in agricultural soils in China has become increasingly serious [4, 5].

Shandong Province is situated in the eastern coast of China. Its total area is 155,800 square kilometers, and the total soil area is 121,100 square kilometers. It has a population of over 100.47 million and governs 16 cities (Figure 1). The topography of Shandong Province is complex and diverse, its eastern area belongs to the Shandong peninsula, the western and northern areas are parts of the North China Plain, and southern area has various mountains [6]. The Yellow River, Haihe River, Huaihe River and many tributaries are the dominant rivers that flow through Shandong Province from the east to the west and finally discharging into coastal zones. In addition, brown soils, cinnamon soils and fluvo-aquic soils are the three dominant soil types which account for 14.09 %, 14.66 %, and 38.53 % of the soil areas in Shandong Province, respectively [7, 8]. The cultivated rate and agricultural added value in Shandong Province ranked first in China, among which, corn and wheat are the main crops.

Since the Chinese reform and opening up, economic development in countryside has greatly increased by governmental effective measures, such as transferring industries from urban areas to the countryside, improving planting technology, and increasing employment, etc. [9]. Meanwhile, large quantities of wastewater and pollutants discharged from industries and domesticity into surrounding soils due to the lack of pollution management and controls in China [10, 11]. Industrial sewage, domestic wastewater and agrochemicals contains great deal of heavy metals, which have the characteristics of toxicity, abundance, and persistence [4, 12]. Thus, heavy metal contamination in soils has become a serious problem in the world [13]. Heavy metals can be bio-accumulated into vegetation and absorbed by contactee, and then directly or indirectly transferred into human bodies. Therefore, metal contamination in agricultural soils has threatened human health and should be given more attention [14].

In recent years, cropland soils in many areas of China are suffering from the contamination of chromium (Cr), copper (Cu), lead (Pb), zinc (Zn), nickel (Ni) and cadmium (Cd), etc. [5, 15, 16]. For example, Cd and Pb were excessively enriched in cropland soils near Pearl River Delta, South China [15]. Thus these metals were also determined in this study. Previous studies indicated that utilization of agrochemicals and discharge of industrial waste are the main factors causing the metal contamination in cropland soils [15, 16]. For example, industrial and agronomic practices, industrial fume, coal burning exhausts, and domestic waste were reportedly led to various degree of heavy metal accumulation to the local cropland soils in Northeast China [17]. Thus, accumulation and spatial distribution of heavy metals in different cropland areas may be affected by the surrounding industrial activities, which can be preliminarily confirmed by the correlations between heavy metals and local economic indicators. Meanwhile, the research on the spatial distribution of heavy metals in cropland soils of different cities is of important significance. Specifically, the similarity, differences and sources of the spatial distribution among different cities can be analyzed, thus cropland management can be improved while industrial producing. However, there are few relevant research focus on the horizontal comparison of heavy metal accumulation and spatial distribution in cropland soils of different cities. Shandong Province is a big province in industry and agriculture, which providing ideal research area to study the spatial distribution and contamination status of heavy metals in cropland soils of different cities and its relationships with economic growth.

In addition, the concentrations of heavy metals in cropland soils of Shandong Province in 2017 and in 2007 can also be compared to analyze the contamination differences by referring to the results of Zhang et al. [5]. Thus, the primary objectives of this study are: (1) to determine spatial variance and contamination status of heavy metals in agricultural soils in cities of Shandong Province, China; (2) to analyze the impacts of soil types on the metal accumulation; (3) to explore the accumulating changes of heavy metals from 2007 to 2017 and the possible relations between metal accumulation and economic indicators. The study on cropland soils of Shandong Province could provide essential and insightful information for other regions.

4. The results have been written to briefly, they need to be elaborated showing trends. The authors seem to disregard or neglect some important global results that have been recently achieved in this specific field. The discussion is not up to the mark and needs a drastic precise and focused approach. I suggest improving the Discussion adding more recent related findings and explain each result properly.

Answer: thanks for your suggestion, we enriched and revised the part of Results and Discussion. In the revised manuscript, the spatial distribution and contamination status of the six metals in cropland soils of different cities, soil types, and decade were presented. Meanwhile, the sources of the metals were explored by cluster analysis, Pearson correlation analysis, and the relations with economic indicators. Furthermore, we elaborated and discussed the results and added several references. The specific revision was showed in the manuscript.

5. The content is more a case study that original research work providing novel methods and or observation. The results should be more conclusive and also generalized confirming if they have wide validity. Otherwise the paper is more a technical report that original research work.

Answer: thanks for your suggestion and comments. We have revised the whole manuscript. In the revised manuscript, heavy metals in cropland soils of twelve cities were determined, analyzed and discussed. We presented the spatial distribution pattern of the metals in Shandong Province, which may be similar with the metal distribution in other coastal province. We found the accumulation features of heavy metals in three typical soil types. We confirmed the significant reduction of heavy metals in farmland in 2017 with respect to that in 2007, and discussed the probable cause and the dominant sources of the metals. We believe the results in this manuscript can provide essential and insightful information for other regions. At last, this manuscript appeals to imperative waste management and technology improvement to protect agricultural soils.

We would be happy to do whatever is required if further revision is necessary.

Author Response File: Author Response.pdf

Reviewer 3 Report

First of all, I would have some doubts regarding the main hypothesis of this paper (lines 14-15), i.e., there is a link between the "spatial distribution of heavy metals in cropland areas and the association with economic development". If "... waste management and environmental protection are vitally imperative for ecological sustainable development." (lines 30-31) this links fails, i.e., it fails when a good enviromental protection policy is pursued.

Secondly, according to my understanding this paper needs a heavy English revision. For example, in line 25 "were non-significantly ordered as:..." does not mean anything to me. Lines 26-27 "... were significantly decreased than they showed in 2007." should be probably rewritten as " .. showed a concentration decrease with respect to those measured in 2007". I do not understand what the sentence "However ...metals" (lines 27-30) is supposed to mean, as well as the sentences "Soil is the limited ...human activities,.." (line 35) and "soil development produced plenty of pollutants" (line 37).

In line 47 please change "..which accounting for.." with "..which account for.." and in line 51 change "from urban to rural" with "from urban areas to the countrysides".

Rewrite lines 52-53: "..is significantly heavy discharged with .." which does not make any sense as well as lines 59-60: "...abundant enriched into human body, ..".

Similar remarks can be made for the whole rest of the paper.

Lines 84-89 have nothing to do with "soil sampling", they would have probably been more concerned with a "study area" paragraph.

As far as the "RESULTS", I do not agree with what is reported in lines 136-137: according to me it is not necessarily true that "The similar pattern indicates that anthropogenic industrial activities facilitated the metal accumulation in agricoltural soils". This statement might be a good working hypothesis which however would need further elements/data to be corroborated.

In lines 151-152 "It is notheworthy that contents of Ni ....background values": why is it notheworthy? What does it mean in terms of the link between spatial distribution of heavy metals and economic development?

While I liked lines 191-198 (because here the Authors try to argue some conclusions from their results), in my opinion this paper plod a little when exploring the link between economic development and spatial distribution of heavy metals with the exception of lines 228-236, however for Zn and Cd only. In the "CONCLUSIONS" (lines 249-250) the Authors resume these statements for Zn and Cd talking about the type of correlation (negative for Zn and positive for Cd) and "certain relationships between industrial and agricoltural activities" without specifying further details about these relationships: because in this sentence there is very little information for the reader, I would delete it.

In conclusion, with the exception of lines 191-198 this paper seems to miss one of its main goals, i.e., to "explore the relationship between economic growth indicators and heavy metal concentrations" as stated in lines 79-80 and thus to identify (at least partially) the pollution sources due to the economic growth.

Author Response

Dear Reviewer,
We appreciate your work on our manuscript (ID: applsci-727812) “The distribution pattern and affecting factors of heavy metals in cropland soils of twelve cities in Shandong Province, China”, which was very helpful to improve our manuscript. We have carefully evaluated the comments and thoughtful suggestions, rewrote the part of Introduction, enriched the part of Results and Discussion, responded to the suggestions point-by-point, and revised the manuscript accordingly.

We revised the manuscript with "Track Changes" function. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

We responded to your suggestions point-by-point as below showed, specific revisions were showed in the revised manuscript.

1. First of all, I would have some doubts regarding the main hypothesis of this paper (lines 14-15), i.e., there is a link between the "spatial distribution of heavy metals in cropland areas and the association with economic development". If "... waste management and environmental protection are vitally imperative for ecological sustainable development." (lines 30-31) this links fails, i.e., it fails when a good enviromental protection policy is pursued.

Answer: thanks for your detailed comments and suggestion. We agreed with your opinion about the overmuch mention of the relationships between heavy metals in cropland soils and the economic development, but had no sufficient data and description in part of results and discussion. Moreover, this phenomenon may not exist in other countries. Thus, we rearranged the key points. In the revised manuscript, the spatial distribution and contamination status of the six metals in cropland soils of the twelve cities were presented. Then, the impacts of soil types, economic indicators, and temporal changes on the heavy metals were discussed. Meanwhile, the sources of the metals were explored by cluster analysis and Pearson correlation analysis. We would be happy to do whatever is required if further revision is necessary.

2. Secondly, according to my understanding this paper needs a heavy English revision. For example, in line 25 "were non-significantly ordered as:..." does not mean anything to me. Lines 26-27 "... were significantly decreased than they showed in 2007." should be probably rewritten as " .. showed a concentration decrease with respect to those measured in 2007". I do not understand what the sentence "However ...metals" (lines 27-30) is supposed to mean, as well as the sentences "Soil is the limited ...human activities,.." (line 35) and "soil development produced plenty of pollutants" (line 37).

Answer: thanks for your detailed comments and suggestion. We agreed with you about the incorrect statement of the results. For example, we revised the Lines 26-27 "... were significantly decreased than they showed in 2007." into “Furthermore, the Cu, Pb and Zn showed the significant concentration decrease with respect to those measured in 2007.” So we rewrote the abstract and introduction, revised and polished the manuscript, and checked again. The revised abstract was showed below:

Abstract: To analyze the spatial distribution and contamination status of heavy metals in cropland areas, 55 agricultural soils were collected from 12 cities of Shandong Province, China, and concentrations of copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni) and zinc (Zn) were determined. Results showed that average contents of Cu, Pb, Cd, Cr, Ni and Zn were 24.13, 31.77, 0.16, 130.63, 22.13, and 71.19 mg·kg^-1, respectively, and contents of Cr, Pb, and Cd exceeded the background values in most cities. It showed that Cr in cities of Weifang, Weihai, Yantai, and Zibo were significantly higher than in other cities, Weihai and Zibo also had significantly high contents of Zn. Moreover, concentrations of Cr in brown soils and cinnamon soils were significantly higher than that in fluvo-aquic soils, while other metals showed no significant difference. Furthermore, the Cu, Pb and Zn showed the significant concentration decrease with respect to those measured in 2007. The significantly positive relationship between industrial added value and Cd may suggest the input of industrial waste. In addition, the significantly correlated Cu/Ni/Zn and Pb/Cd indicated the different input from human activities, while the accumulation of Cr was very complex. This study demonstrated that more attention should be paid to the contamination of Cr, Pb, and Cd, and industrial waste management is vitally imperative for safety of surrounding cropland soils.

3. In line 47 please change "..which accounting for.." with "..which account for.." and in line 51 change "from urban to rural" with "from urban areas to the countrysides".

Answer: thanks for your detailed comments and suggestion. We revised the “..which accounting for..” into “..which account for..”. in line 51, we revised  "from urban to rural" with "from urban areas to the countrysides". More revisions were showed in the revised manuscript.

4. Rewrite lines 52-53: "..is significantly heavy discharged with .." which does not make any sense as well as lines 59-60: "...abundant enriched into human body, ..". Similar remarks can be made for the whole rest of the paper.

Answer: thanks for your detailed comments and suggestion. We have rewritten the two sentences and the introduction. That paragraph was revised into:

Since the Chinese reform and opening up, economic development in countrysides has greatly increased by governmental effective measures, such as transferring industries from urban areas to the countrysides, improving planting technology, and increasing employment, etc. [9]. Meanwhile, large quantities of wastewater and pollutants discharged from industries and domesticity into surrounding soils due to the lack of pollution management and controls in China [10, 11]. Industrial sewage, domestic wastewater and agrochemicals contains great deal of heavy metals, which have the characteristics of toxicity, abundance, and persistence [4, 12]. Thus, heavy metal contamination in soils has become a serious problem in China and even in the world [13]. Heavy metals can be bio-accumulated into vegetation and absorbed by contactee, and transferred into human bodies then directly or indirectly [14]. Therefore, metal contamination in agricultural soils has threatened human health and should be given more attention [14].

5. Lines 84-89 have nothing to do with "soil sampling", they would have probably been more concerned with a "study area" paragraph.

Answer: thanks for your detailed suggestion. We added the 2.1. study area for this paragraph. The specific revision was showed in the manuscript.

6. As far as the "RESULTS", I do not agree with what is reported in lines 136-137: according to me it is not necessarily true that "The similar pattern indicates that anthropogenic industrial activities facilitated the metal accumulation in agricoltural soils". This statement might be a good working hypothesis which however would need further elements/data to be corroborated.

Answer: thanks for your detailed comments and suggestion. We agreed with your opinion with this sentence. Based on the high contents of Cr and industrial added values in the four cities than other cities, we presented the results and speculation as below in the revised manuscript.

Moreover, cluster analysis of Cr among the twelves cities showed that three coastal cities (Weifang, Weihai, and Yantai) and one inland city (Zibo) were gathered into one cluster, with the significantly high concentrations of 181.13, 177.8, 161.62, and 172.78 mg·kg^-1, respectively (Figures 2 and 3). Similarly, the gross value of industrial output of Weifang, Yantai, and Zibo were 230.75, 330.94, 218.31 billon in 2017, which were also significantly higher than other cities except Qingdao (tourism dominated the gross product). The higher accumulation of Cr and gross value of industrial output in the cities than in other cities may indicated that industrial producing can aggravate the accumulation of Cr in the agricultural soils, and the specific relations need further research.

7. In lines 151-152 "It is notheworthy that contents of Ni ....background values": why is it notheworthy? What does it mean in terms of the link between spatial distribution of heavy metals and economic development?

Answer: thanks for your detailed comments and suggestion. The sentence of "It is notheworthy that contents of Ni ....background values" was revised into “Though the contents of Ni in Zibo and Heze (28.65 and 27.8 mg·kg^-1) were approaching the background values, the contamination of Ni was the slightest comparing to other metals.” In addition, we try to find the relations between concentrations of heavy metals and economic indicators in Shandong Province, China, so as to analyze impact of economic producing on the metal contamination in cropland soils in this manuscript. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

8. While I liked lines 191-198 (because here the Authors try to argue some conclusions from their results), in my opinion this paper plod a little when exploring the link between economic development and spatial distribution of heavy metals with the exception of lines 228-236, however for Zn and Cd only. In the "CONCLUSIONS" (lines 249-250) the Authors resume these statements for Zn and Cd talking about the type of correlation (negative for Zn and positive for Cd) and "certain relationships between industrial and agricultural activities" without specifying further details about these relationships: because in this sentence there is very little information for the reader, I would delete it.

Answer: thanks for your encouragement and suggestion. We agreed with your views about the redundant expression on relations between heavy metals and economic indicators but had no sufficient and particular data to verify. Thus, we lessened the relevant sentences in the parts of Abstract and Introduction. Based on your advices, we argued the relations between metals and economic indicators and explored the cause of it. The details were showed in the revised manuscript and below:

The development of industry, agriculture, tourism and services brings about rapid growth of economy and living standards [42, 43]. Meanwhile, the damage to ecological environment is also profound and lasting, which include soil contamination around the industries, reduction of grain yield, destruction of natural habitat, etc. [44, 45]. Thus, the relationship between economic indicators and heavy metals in agricultural soils should be researched.

Concentrations of heavy metals presented certain relations with some economic indicators. Specifically, the primary industrial added value showed significant and negative correlation with concentration of Zn, while industrial added values indicated significant and positive relationship with the contents of Cd (Table 3). It may suggest that industrial production aggravated the accumulation of Cd, which can also be confirmed by the high accumulation of Cd in this study [29, 30]. The closely related Zn and the primary industrial added value may attribute to the bio-accumulation as primary industry was mainly involved to biological yield [46]. With the crop growth, Bhatti et al. [47] showed high bioaccumulation of Zn in the crops while Xu et al. [30] indicated the high enrichment of Cd in the soils. Thus, the high primary industrial added value simultaneously boosted the bio-accumulation of Zn into aboveground vegetation and the enrichment of Cd into rhizospheric soils [48, 49].

9. In conclusion, with the exception of lines 191-198 this paper seems to miss one of its main goals, i.e., to "explore the relationship between economic growth indicators and heavy metal concentrations" as stated in lines 79-80 and thus to identify (at least partially) the pollution sources due to the economic growth.

Answer: thanks for your detailed comments and suggestion. We agreed with your opinions, and basically revised the whole manuscript. In the revised manuscript, we aimed to analyze the spatial distribution and contamination status of heavy metals in different cities, soil types and decade, as well as sources analysis. We presented the spatial distribution pattern of the metals in Shandong Province, which may be similar with the metal distribution in other coastal province. We found the accumulation features of heavy metals in three typical soil types. We confirmed the significant reduction of heavy metals in the cropland soils with respect to that in 2007, and discussed the probable cause and the dominant sources of the metals. We believe the results in this manuscript can provide essential and insightful information for other regions. At last, this manuscript appeals to imperative waste management and technology improvement to protect agricultural soils.

We would be happy to do whatever is required if further revision is necessary.

Round 2

Reviewer 1 Report

The objective of the study is not well defined. 

I strongly suggest to include in the data analysis data (quantitative or qualitative) and not text regarding the source of pollution ant typology, consequently try to correlate data.

Author Response

Dear Reviewer,
We appreciate your work on our manuscript (ID: applsci-727812) “The Spatial Distribution and, Contamination Status and Affecting Factors of Heavy Metals in Cropland Soils of Twelve Cities in Shandong Province, China”, which was very helpful to improve our manuscript. We have carefully evaluated the comments and thoughtful suggestions, revised and polished the language, rearranged the introduction for defining our objectives, added the factor analysis between economic data and heavy metals and a Table 4 to ensure their connections, and revised the conclusions to extract main conclusions that corresponding to our objectives. Specific revisions were showed in the revised manuscript.

We revised the manuscript with "Track Changes" and “highlight” functions. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

Reviewer 2 Report

The “Introduction” section of the manuscript requires extensive revision. First of

all, the authors need to expand the review of word literature that is relevant to their study.

Second, and probably most importantly, the aim of the study needs to be properly

highlighted and justified. I would suggest that the authors attempt

to present the key objectives of their study with regards to what is currently known

(i.e. literature), thus highlighting the added value of the paper.

The authors state: “The study on cropland soils of Shandong Province could provide essential and insightful information for other regions”, but in my opinion it is too local. What about cropland soil pollution in other regions of the world?

Author Response

Dear Reviewer,
We appreciate your work on our manuscript (ID: applsci-727812) “The Spatial Distribution and, Contamination Status and Affecting Factors of Heavy Metals in Cropland Soils of Twelve Cities in Shandong Province, China”, which was very helpful to improve our manuscript. We have carefully evaluated the comments and thoughtful suggestions, revised and polished the language, rearranged the introduction for defining our objectives, added the factor analysis between economic data and heavy metals and a Table 4 to ensure their connections, and revised the conclusions to extract main conclusions that corresponding to our objectives.

We revised the manuscript with "Track Changes" and “highlight” functions. We hope that our revision and answers will enable our manuscript to win your satisfaction. And we would be happy to do whatever is required if further revision is necessary.

We responded to the suggestions point-by-point as below showed, specific revisions were showed in the revised manuscript.

1. The “Introduction” section of the manuscript requires extensive revision. First of all, the authors need to expand the review of word literature that is relevant to their study.

Answer: Thanks for your suggestions very much, we really lacked this section before. Thus, we added relevant literature retrieval in the Introduction part to support our research purpose and objectives.

2. Second, and probably most importantly, the aim of the study needs to be properly highlighted and justified. I would suggest that the authors attempt to present the key objectives of their study with regards to what is currently known (i.e. literature), thus highlighting the added value of the paper.

Answer: Thanks for your suggestions, we added the description about current research results, the research insufficient, and why we carried out this study, thus highlighted our research objectives. Specific changes can be showed in the revised version.

3. The authors’ state: “The study on cropland soils of Shandong Province could provide essential and insightful information for other regions”, but in my opinion it is too local. What about cropland soil pollution in other regions of the world?

Answer: Thanks for your comments. In previous manuscript version, we did not clearly expound the research significance. In the revised manuscript, we added the research significance in the introduction. And changed the sentence into: We believe the study on cropland soils of Shandong Province could provide essential information for relevant research.

Round 3

Reviewer 1 Report

The manuscript have been extensively revised. It could be accepted as such

Reviewer 2 Report

The authors improved the manuscript