Review Reports - Adsorption Behavior and Residue Degradation of Triazine Herbicides in Soil Amended with Rice Straw Biochar

Round 1

Reviewer 1 Report

Dear authors,

After carrying out the review of the article entitled “Adsorption Behavior and Residue Degradation of Triazine Herbicides in Soil by Rice Biochar”, proposed for possible publication in Agriculture Journal would like to express that from my perspective the work is interesting, and the topic is relevant from the environmental point of view. However, I believe that some aspects should be considered and corrected before the work could be accepted. Next, I list some suggestions for improvement and details that I observed in it:

The first paragraph of the introduction should contain a reference that supports the mentioned information, if this is the corresponding one, it is suggested to join with the second paragraph. In addition, the authors should add a couple of background information that mention different types of biochard made from plant material and their uses for the absorption/desorption of pesticides.

Section 2.5.2. Sample Preparation

· Please change r/min for r.p.m.

· The authors mention “The organic phases were combined and evaporated to almost dryness.” Indicate the procedure under which they took the extract to almost dryness, rotary evaporator, or gentle flow of nitrogen, etc.

· The authors mention “The developed method's accuracy and precision were determined using spiked samples.” Indicate the procedure under which the accuracy and precision were calculated (recovery percentage?) and the validation guide followed, as well as the criteria established to affirm that the method is exact and precise.

2.6. Analytical Conditions

· Indicate the reference or references in the argument “Then the influence of the biochar amount on prometryn adsorption was investigated”. Apply the same to the rest of the document where this error appears (Error! Reference source not found).

3.1.1. Adsorption Test

• In the paragraph “The Freundlich model [23] was used to study the individual adsorption capacity of rice biochar prepared at different temperatures towards the studied herbicides. The rice biochar Kf value, 1/n, and correlation coefficient were calculated, as shown in Error! Reference source not found.” Complete the idea that you want to express.

• In the paragraph “Competitive adsorption when multiple pollutants were adsorbed by biochar has been reported [29]. Hence, the mixed adsorption behavior of three triazine herbicides with the rice biochar prepared at 600 °C was investigated (Error! Reference source not found)“. Complete the idea and add the missing reference.

3.1.2. Desorption Behavior of the Herbicides by Rice Biochar

• In the first and second paragraphs indicate the missing references.

3.2. Effect of Biochar on Residue Behavior of the Herbicides in Soil

• In the first and third paragraphs indicate the missing references.

The discussion needs to be improved, the authors limit themselves to discussing only the behavior of the observed results, however, comparison with other studies that use biochar from rice or other similar plant material for the absorption/desorption of pesticides is required. Preferible, herbicide pesticides with characteristics similar to those evaluated in this work.

Once the suggestions have been addressed, the work can be considered for publication.

Kind regards.

In general, the document handles good English writing and the ideas and expressions are clear and concise.

Author Response

Reviewer 1:

The first paragraph of the introduction should containa reference that supports the mentioned information, if this is the corresponding one, it is suggested to join with the second paragraph. In addition, the authors should add a couple of background information that mention different types of biochard made from plant material and their uses for the absorption/desorption of pesticides.

Response: The introduction was modified according the suggestion. The references are added into the first paragraph. Different types of biochard made from plant material and their applications for the absorption/desorption of pesticides was added into the third paragraph of the revised manuscript.

Revisions:

With the widespread use of pesticides, large amounts of the chemicals are directly or indirectly transferred into the environment, causing serious hazards to the soil, water, beneficial organisms, and plants [1-2].

Biochar is a carbonaceous material prepared by biomass waste under oxygen-limited conditions [11, 12]. Biochar's physicochemical characteristics and structure depend on the different raw biomass materials. In addition, the pyrolysis temperature significantly impacts biochar structure [13, 14]. In general, biochar with a large specific surface area presents a strong adsorption capacity for pollutants [15]. It has been reported that pesticide biodegradation in the soil was reduced due to adsorption mechanisms [16-18]. Adsorption of pesticides by biochar has been of growing concern, such as sugarcane bagasse-derived biochar as adsorbent for removal of chlorpyrifos from aqueous environments [19], cymoxanil adsorption by grape pomace-derived biochar [20], remediation of fipronil and its metabolites contamination in aquatic systems by biochar derived from corn stalks [21].

Section 2.5.2. Sample Preparation

Please change r/min for r.p.m.

Response: r/min in the revised manuscript was modified to r.p.m.

Revisions:

30 mL methanol/water (1:1, v/v) was added to a 5 g (±0.001 g) sample, which was extracted by ultrasonication for 30 min, followed by centrifugation of the solution at 4000 r.p.m for 5 min.

The authors mention “The organic phases were combined and evaporated to almost dryness.” Indicate the procedure under which they took the extract to almost dryness, rotary evaporator, or gentle flow of nitrogen, etc.

Response: The evaporation procedure was added in the revised manuscript.

Revisions:

The organic phases were combined and evaporated to almost dryness at 40°C by rotary evaporator.

The authors mention “The developed method's accuracy and precision were determined using spiked samples.” Indicate the procedure under which the accuracy and precision were calculated (recovery percentage?) and the validation guide followed, as well as the criteria established to affirm that the method is exact and precise.

Response: The procedure under which the accuracy and precision were calculated was added in the revised manuscript.

Revisions:

The developed method's accuracy and precision were determined using spiked samples. The spiked sample concentrations were 0.064 mg/kg, 0.32 mg/kg, and 0.64 mg/kg, respectively. Accuracy and precision was determined by calculating the average recoveries and relative standard deviation (denoted as RSD, n=5) of the analytes at three spiked concentrations, respectively [33].

2.6. Analytical Conditions

Indicate the reference or references in the argument “Then the influence of the biochar amount on prometryn adsorption was investigated”. Apply the same to the rest of the document where this error appears (Error! Reference source not found).

Response: The manuscript was modified according to the suggestion.

Revisions:

Then the influence of the biochar amount on prometryn adsorption was investigated (Figure 1B). Prometryn adsorption by rice straw biochar increased with higher amounts of biochar [35].

3.1.1. Adsorption Test

In the paragraph “The Freundlich model [23] was used to study the individual adsorption capacity of rice biochar prepared at different temperatures towards the studied herbicides. The rice biochar Kf value, 1/n, and correlation coefficient were calculated, as shown in Error!Reference source not found.” Complete the idea that you want to express.

Response: The manuscript was modified according to the suggestion.

Revisions:

The Freundlich model [30] was used to study the individual adsorption capacity of rice biochar prepared at different temperatures towards the studied herbicides. The rice biochar K_f value, 1/n, and correlation coefficient were calculated [41], as shown in Table 2.

2) In the paragraph “Competitive adsorption when multiple pollutants were adsorbed by biochar has been reported [29]. Hence, the mixed adsorption behavior of three triazine herbicides with the rice biochar prepared at 600 °C was investigated (Error! Reference source not found)“. Complete the idea and add the missing reference.

Response: The manuscript was modified according to the suggestion.

Revisions:

Competitive adsorption when multiple pollutants were adsorbed by biochar has been reported [38]. Hence, the mixed adsorption behavior of three triazine herbicides with the rice biochar prepared at 600 °C was investigated (Figure 4, Table 3). The Freundlich isotherms of the herbicides on biochars were shown in Fig. S3 ~ Figure S5.

3.1.2. Desorption Behavior of the Herbicides by Rice Biochar

In the first and second paragraphs indicate the missing references.

Response: The manuscript was modified according to the suggestion.

Revisions:

The desorption amounts after single and mixed herbicide adsorption were measured [41], and the results are shown in Table 4 and Table 5, respectively.

According to Table 4 and Table 5, the desorption amount of the herbicides was much lower than their adsorption amount [41]. The desorption amount after the competitive adsorption of the triazine herbicides was lower than that of the individual herbicides.

3.2. Effect of Biochar on Residue Behavior of the Herbicides in Soil

1) In the first and third paragraphs indicate the missing references.

Response: There is no missing references in the first and third paragraph, and the relevant table is missing at the position. The discussion of the degradation behavior of the studied pesticides was modified according to the suggestion.

Revisions:

The rice biochar was added to the soil in the range of 0.1% ~ 1% (wt%) to study the effect of biochar on the degradation of the herbicides in the soil. The residue behavior of the herbicides in the soil is presented in Table 6.

Biochar derived from biomass waste was widely applied for the removal or degradation of pesticides in soils. It is reported that biochar could reduce pesticide biodegradation in soil due to its adsorption capacity [16-18]. An alkali-modified biochar (BC_NaOH)/graphitic carbon nitride (g-C₃N₄) was used as the remediation agent to degrade atrazine residue in paddy soil. Excellent degradation performance (above 60%) of the herbicide was achieved due to the construction of an intact electron transfer pathway via the π-π stacking structure [46]. Cassava wastes-based biochars were added to an agriculture soil to attenuate the migration of atrazine in soil. It is indicated that the biochar significantly enhanced the sorption capacity of soil for atrazine [47]. Therefore, the biochar are promising sorbents for pesticides elimination and soil remediation. Conversely, the addition of biochar into the soil may induce higher microbial stimulation, thereby increasing the microbial degradation rate of pesticides [22, 23]. Therefore, the effect of biochar on pesticide degradation in soil depends on the combination of these two aspects and their interactions. According to the results, the addition of biochar into the soil enhanced the degradation of the herbicides (Table 6) because of the increasing biodegradation rate by the dominant microorganisms.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for author File: Comments.docx

English should be revised.

Author Response

Reviewer 2:

Title: Change to “…in soil amended with rice biochar”

Response: The title of the manuscript was modified according to the suggestion.

Revisions: Adsorption Behavior and Residue Degradation of Triazine Herbicides in Soil Amended with Rice Biochar.

Abstract: Not clear. It does not give enough details.

Response: Abstract was modified according to the suggestion.

Revisions:

Removal or decrease of pesticide residues in soil has attracted considerable attention, due to the serious pollution of pesticides in soil. The purpose of the study was to explore the adsorption behavior of biochar on pesticides and the impact on the degradation of pesticide residues in soil, providing a basis for the remediation of soil by biochar. Biochars were prepared by pyrolysis of rice straw at high temperature (300 °C, 400 °C, 500 °C, 600 °C). The individual and competitive adsorption of three triazine herbicides, prometryn, atrazine, and simazine, on biochar were investigated, and the degradation of the herbicide residues in biochar-added soil was determined. The selected herbicides presented similar adsorption characteristics to rice biochar, and the amount of the herbicides adsorbed increased with higher preparation temperature and the amount of the biochar. The rice biochar adsorbed the studied herbicides simultaneously, and the adsorption amount decreased as follows: simazine > atrazine > prometryn. The competition adsorption of the selected herbicides on the biochar presented a lower adsorption affinity than that when they are adsorbed individually. The adsorption isotherm were best fitted by the Freundlich model. The half-lives of prometryn, atrazine, and simazine were 9.8~12.6 d, 5.2~8.1 d, and 3.7~5.6 d, respectively. Biochar addition increased the degradation of the evaluated herbicides in soil. The rice straw biochar could be the potential sorbents that can be implemented for the removal of pesticides.

Introduction: Give dome information on behavior in soil of the selected herbicides

Response: The information was provided in the revised manuscript.

Revisions:

Triazine herbicides are extensively used as highly selective herbicides for controlling weeds in agricultural plants, mainly grasses [3]. However, they present the properties of good water solubility, a long half-life, relatively high mobility and persistence in soils [4, 5].

Objectives: Why notsorption studies in BC amended soil?

Response: Sorption of the selected herbicides was not studied in BC amended soil because soil also adsorbs the studied herbicides, which affected the adsorption behavior of the herbicides on biochar.

Materials and methods:

1) Why were the herbicide solutions prepared in MeOH?

Response: Methanol was used to prepare standard solutions of the studied herbicides due to the relatively high solubility of the analytes in methanol. In addition, methanol as a solvent is compatible with the mobile phase used in the analytical method.

4.1. Isothermsare not shown. Graphs presented are sorption kinetics

Response: Considering the page limit, isotherms of the herbicides are provided in the supplementary materials of the revised version according to the requirement.

Revisions:

Fig. S3 Freundlich isothermal of individual adsorption (open symbols) and competitive adsorption (filled symbols) of prometryn on rice biochars. 600℃ pyrolysis temperatures (p),and 500℃ (q), and 400℃ (˜), and 300℃ (¿).

Fig. S4 Freundlich isothermal of individual adsorption (open symbols) and competitive adsorption (filled symbols) of atrazine on rice biochars. 600℃ pyrolysis temperatures (p),and 500℃ (q), and 400℃ (˜), and 300℃ (¿).

Fig. S5 Freundlich isothermal of individual adsorption (open symbols) and competitive adsorption (filled symbols) of simazine on rice biochars. 600℃ pyrolysis temperatures (p),and 500℃ (q), and 400℃ (˜), and 300℃ (¿).

4.2. Why only 1 cycle of desorption?

Response: In order to compare the adsorption and desorption behavior of the herbicides on biochar, the desorption was performed only one cylce.

5.1. Incubation for 1 week? How were dissipation studies performed? Soil characteristics?

Response: The purpose of cultivation for one week is to activate the microbial environment in the soil. Soil characteristics was provided in the revised manuscript. The procedure of dissipation studies was described in the section of 2.5.1. After the Biochar was mixed with the soil, the studied pesticide was sprayed to the soil. The soil samples were collected at different time after herbicides application. The residue of the herbicides was detected, and the degradation half-lives of the herbicides were determined.

Revisions:

Rice biochar prepared at 600°C was selected to investigate the analytes degradation in soil. Brown soil used in the study was collected from the top layer of local lawn. It has a pH of 7.2, organic matter content of 2.5 % with moderate fertility.

Percentages of recoveries should be given yM&M section.

Response: Percentages of recoveries were provided in the first paragraph of results and discussion.

Results and Discussion:

1) Figures 1,2 and 3. These figures are not sorption isotherms, they are sopriton kinetics. Some symbols are missing.

Response: The related parameters of isothermal adsorption were provided in tables in the manuscript. In order to avoid repetitive information and page limitation, the isothermal graphs were not provided. Sorption isothermal graphs are provided in the supplementary materials of the revised version (as mentioned above).

2) How were sorption coefficients determined from sorption kinetics? Give standard deviation about mean values.

Response: Sorption coefficients were determined from isothermal graphs which were provided in the supplementary materials of the revised version (as mentioned above).

3) Give sorption coefficients values when herbicides are coapplied in order to compare with single pesticide application.

Response: The sorption coefficients values when herbicides are coapplied were provided in the revised manuscript.

Revisions:

Table 3. Isothermal adsorption model of mixed adsorption of the studied herbicides by rice biochar.

Parameter	Analyte	Prepared temperature(°C)
Parameter	Analyte	300	400	500	600
K_f	Prometryn	2.38	2.44	2.48	2.91
	Atrazine	3.10	3.22	3.41	3.63
	Simazine	2.27	2.32	2.34	2.39
1/n	Prometryn	0.028	0.026	0.022	0.017
	Atrazine	0.062	0.055	0.049	0.043
	Simazine	0.022	0.018	0.017	0.012
R²	Prometryn	0.91	0.90	0.94	0.96
	Atrazine	0.93	0.94	0.94	0.94
	Simazine	0.90	0.95	0.94	0.96

Reference 29. Give referencefor competitive sorption of organic pollutants, not inorganic and organic.

Response: The new reference for competitive sorption of organic pollutants was provided in the revised manuscript.

Revisions:

Competitive adsorption when multiple pollutants were adsorbed by biochar has been reported[38]. Hence, the mixed adsorption behavior of three triazine herbicides with the rice biochar prepared at 600 °C was investigated (Figure 4, Table 3).

Tables 3 and 4 not clear. Repetitive paragraphs.

Response: Repetitive paragraphs were deleted in the revised manuscript.

Revisions:

The desorption amounts after single and mixed herbicide adsorption were measured [41], and the results are shown in Table 4 and Table 5, respectively.

Conclusions: Repetitive paragraphs.

Response: Repetitive paragraphs were modified in the revised manuscript.

Revisions:

The Adsorption behavior of three triazine-group herbicides on rice straw-derived biochar was studied. The herbicides' individual adsorption behavior was similar to that when they were present in a mixture, which increased with the higher preparation temperature and the increasing amount of rice biochar. Freundlich isotherm adsorption model was the best fit for the selected herbicides adsorption. The rice biochar exhibited a strong desorption hysteresis effect on the studied herbicides.

The dissipation rate of the herbicides in the soil after biochar addition increased significantly and was positively associated with the amount of biochar added. The half-lives of prometryn, atrazine, and simazine were 9.8~11.9 d, 5.2~7.5 d, and 3.7~5.2 d, respectively, at rice biochar concentration in the range of 0.1%~1% in the soil.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear authors,

Thank you for taking my suggestions/comments into account, I hope I have contributed to improving the document.

I consider that it already has the quality to be accepted for publication.

Best Regards

With an English edition by the person in charge of the journal, the work will be ready for publication.

Reviewer 2 Report

Changes incorporated in manuscript have improve it and in my opinion is suitable for publication.