New Approach to the Assessment of Insecticide Losses from Paddy Fields Based on Frequent Sampling Post Application

Comments of Reviewer 1:

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Title

1. Line 2 and 3: The title should be modified. For example, “New approach to the assessment of insecticide losses from paddy fields based on frequent sampling post application”.

Thanks for this suggestion. The title was revised as suggested.

Abstract

2. Line 20: chlorpyrifos and abamectin loads were “exported” within merely 1 h after application. Change “exported” for “detected”.

Revised as suggested.

Introduction

3. Line 55 (Lines 63-64): “export process”, please, specify. Is it pesticide loss/loss of pesticide? For example, it maybe the loss via evaporation, volatilization, runoff and etc.

It is pesticide loss via surface runoff. Revised as suggested.

4. Line 55 (Lines 56-64): please, clarify why existing studies are limited. It is unclear how your work advanced the field, in theory and practically. Please explicitly clarify.

Pesticide monitoring is a costly campaign. Limited existing studies prefer to conduct high-frequency monitoring of pesticides at larger scales. We thoroughly rewrote this paragraph pointing out the the limitations of the conventional infrequent monitoring

5. Lines 64-65 (Lines 72-73): The one of objectives is “to identify the key factors that affect insecticide behavior and establish a kinetic model that can better describe the edge-of-field insecticide concentration variations….” So this reason you should give the short description of existing models in the introduction. Benefits and limitations of such models should be presented.

We added a short description of existing first-order kinetic model in Lines 56-57. Its benefits and potential limitations were introduced in Lines 60-61.

Materials and Methods

6. Line 80 (Line 89): please, specify the source of the equations

The source of the equation has been added.

7. Line 102-104 (Lines 111-114): please, repeat again chlorpyrifos (CPF), abamectin (ABM) and thiamethoxam (THM) like in line 60. And it will be cool if you write the company which produced these pesticides. Is it a pesticide formulation? If yes, please write the concentration of active substances in such formulations.

Revised as suggested.

The active ingredient was mentioned in Lines 116-117.

8. Line 110 (Line 120): “to assess the pesticide residues of…”

Revised as suggested.

9. Line 112 (Line 122): In the table 1. The parameter is K_ow (20 ℃, pH 7). But there are values of logarithm of octanol/water partitioning coefficient in the column. Please, also check the value of DT₅₀ for CPF (27.6 days in field not 27.3).

“Log P” has been added. The value of DT₅₀ for CPF was corrected.

10. Line 113 (Line 123): please add the link (http://sitem.herts.ac.uk/aeru/footprint/index2.htm) in the reference [21].

Revised as suggested.

11. Line 129 (Line 139): How water samples were collected and what was the volume?

They were grab water samples. The volume was 500 mL.

Added as suggested.

12. Lines 150-151 (Lines 161-162): The detection limits of CPF, ABM and THM were 0.0126, 0.0050, and 0.0500 mg L^-1, respectively. The detection limits are quite low for analytical quality assurance. µg L^-1 will be better.

We finally chose to apply the unit mg L^-1 throughout the paper, so we still used mg L^-1 here.

The detection limit here have been modified. Please see the reply of Suggestion 17.

13. Line 163 (Line 174): Specify the source of the equation.

Revised as suggested.

Results

14. Line 201: I do not understand the meaning of this sentence: “The recoveries of CPF, THM and ABM were 81.2%-137.8%, 91.6%-148.4% and 56.9%-149.1%, respectively”. Please, clarify.

In the method establishment process of pesticide analysis, the recovery is the ratio of the measured concentration of a pesticide (after pretreatment) to the original actual concentration. The more the recovery of a pesticide is close to 100%, the more applicable the method is.

15. Line 213 (Line 212): C_CPF-g is the concentration of chlorpyrifos in groundwater?

Yes, it is.

16. Line 215 (Line 214): Measured insecticide concentrations are depicted in Fig.3, but the concentration of CPF is in mg per L, the concentrations of ABM and THM - in µg per L. The y-axis dimensions should be the same. And please, add the error bars which represent standard deviations.

The y-axis dimension was uniformly changed to mg L^-1 as suggested. We could evaluate the reliability of the measured concentration according to the recovery of three insecticides. Since the recovery was well enough, the error bars might not be needed.

17. Lines 222-223 (Lines 221-222): please, add the dimension of measured chlorpyrifos concentrations (mg per L or µg per L). And as mentioned above the detection limit for CPF was 0.0126 mg per L. Concentration values below the detection limit (nd) should be set to zero.

Thanks for this suggestion.

We have added the dimension. Unfortunately, we did not consider the effect of concentration process on the detection limit before. Since the CPF, ABM and THM water samples were concentrated to 1/25, 1/50 and 1/50, respectively, we have updated the detection limits of the three insecticides considering the concentration process in Lines 157. The low CPF concentrations exhibited in Table 2 are actually detectable.

18. Line 254 (Line 253): Please provide the analysis of dependence of the real values on the predicted values and analysis of dependence of error distribution on the predicted value. This would allow a better understanding. You can find it in the article [1] which was cited by you.

Thanks for this suggestion. The analysis results have been added in Lines 269-280.

19. Lines: 255-258 (Lines 254-258): a brief mention justifying the model’ choice should be added.

Added as suggested.

20. Lines: 267-268 how did the kinetic model predict the concentrations of THM and ABM?

We stated it in Lines 274-276.

Discussion

21. Line 296: you mentioned the substance group Neonicotinoid, but previously it is not shown. Please, add the column called “substance/chemical group” in Table 1.

Revised as suggested.

22. Line 302 (Line 323): Please, specify that THM has a low value of K_oc (mobile) and thus has high leachability to groundwater… or modify the sentence: “The leachability to groundwater significantly increases with increasing water solubility and with decreasing octanol–water partition coefficient”.

Revised as suggested.

23. Line 349 (Line 377): specify, did you calculate the pesticide concentration of CPF? Where is PEC for THM and ABM?

The concentrations were derived in Figure 3a. We have explained it. We just took the case of CPF for an example to illustrate the benefits and necessity of high-frequency monitoring and added this presentation in Line 377.

24. Line 366 (Line 395): the high-frequency monitoring results of ABM concentration has not been mentioned.

Revised as suggested in Lines 395-397.

Conclusions

25. Line 393 (Line 424): Please, address explicitly the limitations of this kinetic model.

Revised as suggested.

Comments of Reviewer 2:

Reply

Abstract

1. L10 What do you mean by the word “pulse”. This word is used several times in the manuscript. Please check the meaning and correct if necessary!

Thanks for this suggestion. The word “pulse” is a vivid description of the phenomenon that the concentration of insecticides may increase rapidly to the peak and then decrease to the low level after spray application. We have explained it in Lines 42-43.

2. L14 Pesticide. Do you mean insecticide? Please avoid using many words for the same thing!

Revised as suggested. We have changed almost all the “pesticide” throughout the text to “insecticide” except for some situations when “pesticide” is more suitable.

3. L20 Replace “elevated” by “high”

Revised as suggested.

Introduction

4. L34-35 Suggestion: reword as “Such practice, however, creates a high potential of pesticide losses through drainage

Revised as suggested.

5. L58-61 (L62-64): paragraph is too long. It need to be reworded

The paragraph has been rewritten according to the suggestion of another reviewer.

Revised as suggested. We deleted the latter part of the long sentence.

6. What are the hypotheses tested in this study? Would be good to indicate them at the end of the introduction

Revised as suggested (L65).

Methodology

7. L69 (L77) Reword the subtitle “site description” or make another subtitle as the information given go beyond a description of the site.

Revised as suggested.

“Site description” was changed to “Study area”.

8. L70-71 (L78-79) Indicate the coordinates of the study sites

Revised as suggested.

9. L101 (L110) “two insecticide applications were conducted for the control of Cnaphalocrocis medinalis and other potential insects.” Reword as “two insecticides were applied for the control of Cnaphalocrocis medinalis and other potential insects”

Revised as suggested.

10. L110 (L120) What do you mean by “sampling well”? Need to be reworded probably

A sampling well is a well artificially drilled into a certain depth of soil layer for collecting groundwater samples as exhibited below:

11. L118 (L128) insecticide or pesticide? Please use the same word for the same thing

Revised as suggested.

Results

12. L178-197 (L190-196) Stick to the presentation of the results ie. comment on the figure and keep the interpretations for discussion

Thanks for this suggestion. Revised as suggested and we removed the interpretations to the new discussion section 4.1.

13. L209 (L207) you mean “of” a certain pesticide

Yes. Revised as suggested.

14. L202-210 (L201-209). Which figure or table do you comment? Please stick to what is shown

The contents in L202-210 are not related to any tables or figures. We reorganized the paragraphs to avoid misunderstanding.

Discussion

15. L349 (L376) citation is not in the right format

Revised as suggested.