Toxic Elements in Soil and Rice in Ecuador
Round 1
Reviewer 1 Report
General comments:
- Substitution of the term “Heavy metal”: this term is widely used in the manuscript. According to Pourret et al. (2020, ESPR), the use of the term heavy metal should be avoided, due to several causes. Thus, I would suggest to replace it by “toxic metal” or simply “metal” in the text (except in the references).
- Variation in metal transfer between cultivars: the accumulation of metals in plants depends on two factors: bioavailability of the metal in the soil and plant genotypes. Thus, some strategies for the reduction of metal accumulation in foodstuff are based in the selection of plant cultivars with reduced metal transfer to edible parts. After a brief search in the literature, I have seen several papers have found differences in Cd and in As accumulation between rice cultivars. In this manuscript, the authors indicate that soil and rice samples were collected from four rice-producing provinces in Ecuador. Do the authors know which rice cultivar they collected? It was the same cultivar in the four provinces or different cultivars? I think this information is important in order to interpret the results and even in the case of statistical analyses (for instance, if the rice samples came from different cultivars, the authors should include a new factor -cultivar- in the ANOVAs). The differences of metal(loid) uptake between rice cultivars is a factor that should be also considered in the interpretation of the (lack of) relation between plant uptake and soil metal concentrations (L 275-L309).
- Statistical analysis: this section needs to be enlarged. Currently, it is only indicated that ANOVA analyses were performed. However, we need to know which factors were compared with ANOVA (differences between 4 provinces? Were the data from the coastal provinces grouped together and compared with the inland province?). Moreover, it is necessary to explain which correlation coefficients were computed between soil parameters and bioconcentration factors.
- The subsection 3.3 (uptake of elements by plants) in results and discussion should be reorganised. Currently, I have the impression of two different texts put together. First a part discussing general results and interpretation of metals in soils and then a second part with more specific (and, in my opinion, more interesting) comments on the results dealing with differences in metal concentration between regions, plant parts...
Other comments:
- L 250-260: in this paragraph the authors present the results of metal concentration in plant parts. Cr concentration in several samples is above the national threshold (authors explain this was caused by the relatively high concentrations of this element in soils). Moreover, some rice grain samples show Cd, As and Pb concentrations above national thresholds. Authors didn’t comment it, but according to table S3, grains with Cd and As above thresholds came from the El Oro province, where only 5 samples were analysed. It is interesting that El Oro province also showed the highest bioavailability ratio for these elements. Could the authors explain the relevance of this information for the safety of rice consumption in that region?
- L 258: authors indicate that data showed an equal translocation coefficient from root to upper parts of the plant. However, the authors didn’t measure this parameter (they didn’t analyse roots). Please correct this sentence.
- L 475-476: the authors use again the term translocation factor referred to their own data, but they did not compute that parameter.
Minor modifications and typos
L 16-20: please indicate that you are referring to soil samples.
L104: Total metal contents in soils?
Figure 1: Please, modify the figure by increasing the size of the characters (or by increasing the resolution of the figure). I could not interpret what was the meaning of red squares and blue dots in the detail figures. Moreover, I don’t know which provinces are the dark green and the light green rectangles.
Figure 2B: I was not able to read any of the information included in the figure (the titles and scales of the axes, the modeling curves or the formulae, etc.). Please increase the resolution (or the size) of each chart.
Table 2: please align properly the numbers in each line. Please adjust the width of the columns to avoid partitioning of decimal values in different lines. What is the meaning of (TCr), (TZn) and so on in the section of the table presenting bioavailable concentrations? Please explain in the caption.
Supplementary material:
Table S3: why the authors did not analysed any rice grain sample from Orellana province? Were there any significant difference in the metal concentration in grains between the three coastal provinces?
Statistics 1 A to 1 D: which correlation coefficient was computed between parameters? Pearson’s? Spearman’s? What is the meaning of the correlation coefficients marked on bold type? Please indicate in the captions.
Author Response
We ppreciate the constructive review. Please find below our detailed answer to each of your remarks.
Substitution of the term “Heavy metal”: this term is widely used in the manuscript. According to Pourret et al. (2020, ESPR), the use of the term heavy metal should be avoided, due to several causes. Thus, I would suggest to replace it by “toxic metal” or simply “metal” in the text (except in the references).
We agree with the comment. All references to “heavy metal” were replaced by “metal(oid)”.
--
Variation in metal transfer between cultivars: the accumulation of metals in plants depends on two factors: bioavailability of the metal in the soil and plant genotypes. Thus, some strategies for the reduction of metal accumulation in foodstuff are based in the selection of plant cultivars with reduced metal transfer to edible parts. After a brief search in the literature, I have seen several papers have found differences in Cd and in As accumulation between rice cultivars. In this manuscript, the authors indicate that soil and rice samples were collected from four rice-producing provinces in Ecuador. Do the authors know which rice cultivar they collected? It was the same cultivar in the four provinces or different cultivars? I think this information is important in order to interpret the results and even in the case of statistical analyses (for instance, if the rice samples came from different cultivars, the authors should include a new factor -cultivar- in the ANOVAs). The differences of metal(loid) uptake between rice cultivars is a factor that should be also considered in the interpretation of the (lack of) relation between plant uptake and soil metal concentrations (L 275-L309).
In Ecuador about 10 varieties are planted, but the varieties INIAP 14, INIAP12, INIAP 17 are the dominant ones in the study area. However, we did not record the variety, which hinders the proposed analysis.
--
Statistical analysis: this section needs to be enlarged. Currently, it is only indicated that ANOVA analyses were performed. However, we need to know which factors were compared with ANOVA (differences between 4 provinces? Were the data from the coastal provinces grouped together and compared with the inland province?). Moreover, it is necessary to explain which correlation coefficients were computed between soil parameters and bioconcentration factors.
The description of the statistical methods was made clearer by indicating that the comparison of means was made only between the individual provinces, i.e, . It now states:
“Statistical and graphic analyses were performed using the statistical software R. Analysis of variance analysis (ANOVA) and Tukey test were performed to identify significant differences between means in the different individual provinces, and between Orellana province and the coastal provinces (remaining), at a significance level of 0.05. The Levene test was used to test homoscedasticity. The Pearson’s correlation coefficient was use to quantify the linear relationship between soil parameters, and between bio-concentration factors.”
The legends of tables in SM were also altered to identify clearly the use of the parametric measure of correlation: “Pearson’s correlation coefficients between (…)”.
--
The subsection 3.3 (uptake of elements by plants) in results and discussion should be reorganised. Currently, I have the impression of two different texts put together. First a part discussing general results and interpretation of metals in soils and then a second part with more specific (and, in my opinion, more interesting) comments on the results dealing with differences in metal concentration between regions, plant parts...
Indeed, the text follows the logic: contents and fractioning in soil, concentrations in the plants, and then the assessment of bioaccumulation. We believe that it makes the reading more intuitive like this, instead of having the analysis of soils separated from the analysis in plants.
--
Other comments:
L 250-260: in this paragraph the authors present the results of metal concentration in plant parts. Cr concentration in several samples is above the national threshold (authors explain this was caused by the relatively high concentrations of this element in soils). Moreover, some rice grain samples show Cd, As and Pb concentrations above national thresholds. Authors didn’t comment it, but according to table S3, grains with Cd and As above thresholds came from the El Oro province, where only 5 samples were analysed. It is interesting that El Oro province also showed the highest bioavailability ratio for these elements. Could the authors explain the relevance of this information for the safety of rice consumption in that region?
We added a coment about this observation in lines 264-266:
“Our results show the presence of abnormally high values of metal(oids) in rice in very specific areas of each province; but high toxic metal contents cannot be associated with a specific province (see also Otero et al. 2016)”
--
L 258: authors indicate that data showed an equal translocation coefficient from root to upper parts of the plant. However, the authors didn’t measure this parameter (they didn’t analyse roots). Please correct this sentence.
We corrected the sentence accordingly. It now states:
“(…) showing an equal translocation coefficient to the upper parts of the plant (…)”.
--
L 475-476: the authors use again the term translocation factor referred to their own data, but they did not compute that parameter.
We agree that the references to the translocation factors are misleading when referring to our data. As such, they were removed.
--
Minor modifications and typos
L 16-20: please indicate that you are referring to soil samples.
The sentence now states:
“Approximately 30% of soil samples (…)”
--
L104: Total metal contents in soils?
The heading was corrected. It states now:
“2.3. Total contents metal(oids)s content in soils”
--
Figure 1: Please, modify the figure by increasing the size of the characters (or by increasing the resolution of the figure). I could not interpret what was the meaning of red squares and blue dots in the detail figures. Moreover, I don’t know which provinces are the dark green and the light green rectangles.
Figure 1 was replaced by a new one showing the provinces where sampling was made. The number of samples is provided in tables 1 and 2 so not necessary in the figure. The caption was also altered to:
“Location of the provinces of Ecuador where the sampling was carried out”
--
Figure 2B: I was not able to read any of the information included in the figure (the titles and scales of the axes, the modeling curves or the formulae, etc.). Please increase the resolution (or the size) of each chart.
The contrast and definition of the graphs was improved.
--
Table 2: please align properly the numbers in each line. Please adjust the width of the columns to avoid partitioning of decimal values in different lines.
The formatting of the tables was made by the editorial office, so we assume those details are going to be corrected before publication (if that is the case).
--
What is the meaning of (TCr), (TZn) and so on in the section of the table presenting bioavailable concentrations? Please explain in the caption.
They are typo errors and were removed. So were other references to TAs and FeT in the text.
--
Supplementary material:
Table S3: why the authors did not analysed any rice grain sample from Orellana province?
Because at the time of sampling the plants were in the vegetative stage. We added a footnote to Table S3 indicating this:
“*: at the time of sampling the crop was in the vegetative stage.”
--
Were there any significant difference in the metal concentration in grains between the three coastal provinces?
The analysis comparing the different provinces was made throughout the text.
--
Statistics 1 A to 1 D: which correlation coefficient was computed between parameters? Pearson’s? Spearman’s? What is the meaning of the correlation coefficients marked on bold type? Please indicate in the captions.
To clarify the headings and contents the caption now states:
“Pearson’s correlation coefficients between (…). Larger correlations are indicated in bold.”
Reviewer 2 Report
The paper presents very interesting and sophisticated issues related to the presence and bioavailability of toxic metals in soil. Methodological description and obtained results are clear. The work needs small corrections as it has mistakes in the form of double or missing spaces, errors in spelling of units, etc. Latin plant names should be written in italics.
Please clarify and include the abbreviation "TAs" in the text.
The sentence on page 13, lines 453-454, should be read and corrected as it contains an error. It seems to me that the authors meant the difference between Zn content in roots and shoots.
Author Response
We appreciate the constructive remarks. Please find below our response to your comments.
The work needs small corrections as it has mistakes in the form of double or missing spaces, errors in spelling of units, etc. Latin plant names should be written in italics.
Please clarify and include the abbreviation "TAs" in the text.
The corrections were made. The abbreviation “TAs” was substituted by “As” when referring to total arsenic content.
--
The sentence on page 13, lines 453-454, should be read and corrected as it contains an error. It seems to me that the authors meant the difference between Zn content in roots and shoots.
In fact, the sentence should indicate the difference between roots and shoots. It now states.
“At low Zn concentration in soils, the translocation factor between roots and shoots is therefore close to one (Safarzadeh et al., 2013).”
Reviewer 3 Report
The manuscript titled „TOXIC ELEMENTS IN SOIL AND RICE PLANT IN ECUADOR” describes the results of experiments examining the content of heavy metals in soil and rice grains grown in countries with high production and consumption of this grain. The research was carried out in great detail. The experiments were well planned and well described. With the exception of a few comments below, the manuscript deserves to be published in the Agronomy journal.
Introduction:
In the following sentence a name of the country should be delivered: „This paper studies the content of As and toxic metals in the three main rice-producing 75 provinces (Guayas, Los Ríos, and El Oro) located in the coastal area, as well as in the Orel- 76 lana province, located in the Eastern part of the country. „
The heading of subsection 2.3. „Total contents metals in soils” shall be changed into „Total contents of metals in soils”
The manuscript needs revision in terms of typo mistakes.
Figure 2 quality is insufficient. It should be delivered in much higher resolution.
Author Response
We appreciate the constructive comments. Please find below the response to the remarks.
Introduction:
In the following sentence a name of the country should be delivered: „This paper studies the content of As and toxic metals in the three main rice-producing 75 provinces (Guayas, Los Ríos, and El Oro) located in the coastal area, as well as in the Orel- 76 lana province, located in the Eastern part of the country. „
We agree that the indication of the country is missing. The sentence now states:
“This paper studies the content of As and toxic metals in the three main rice-producing provinces in Ecuador (…)”.
--
The heading of subsection 2.3. „Total contents metals in soils” shall be changed into „Total contents of metals in soils”
The heading now states:
“2.3. Total contents metal(oids)s content in soils”
--
The manuscript needs revision in terms of typo mistakes.
The text was reviewed for typo errors.
--
Figure 2 quality is insufficient. It should be delivered in much higher resolution.
Caption size and other graphic elements were made larger to increase readability.
