Polycyclic Aromatic Hydrocarbons (PAHs) and Bis(2-ethylhexyl) Phthalate (BEHP) in the Soil of Teff-Acacia decurrens-Charcoal Production System in Northern Ethiopia

Round 1

Reviewer 1 Report

In this study the authors have determined PAH concentrations in soil over three rotations for plots where intercropping of Acacia decurrerns and Eragrostis tef took place. Concern over PAG concentrations in the soil arose due to the use of charcoal to improve the soil properties and reduce degedation. 13 EPA PAHs were determined, along with bis(2- ethylhexyl) phthalate, which is thought to arise from plastic bags used in the cropping process. BaP toxic and mutagenic equivalents were calculated. No significant differences in PAH concentrations were observed between rotations or between the intercropping plots and an adjacent mono-cropping plot.

I found this to be a very well written study that was carried out appropriately. The conclusions are reassuring for the continued cropping practices for this region and therefore provide a useful contribution to environmental health knowledge. 

I don't have many suggested corrections. Perhaps the authors could consider stating the use of the tef crop (for those not familiar). Also, perhaps a statement about how we know that the different rotations have not been treated differently - i.e. comparability between plots, given that a rotation is 4 to 5 years (is that correct - i.e. to the point where the two crops are planted again).

Author Response

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Reviewer 2 Report

The article examines the impact of the teff-Acacia decurrens charcoal production system on the content of PAHs and BEHP in soils and the potential danger of introducing PAH in charcoal compared to traditional TM technology. The application of charcoal is widely used to improve the physical and chemical properties of soils, including absorption and buffering capacity, which affects its fertility. At the same time, charcoal itself contains significant amounts of toxic organic substances (PAH), which negatively affect living organisms, including humans; some of these compounds have carcinogenic properties.

The research topic is certainly relevant.

The objects of the study were soils under the traditional cultivation technology teff, taken for comparison, and soils under the technology with the addition of charcoal (3 rotations).

The selected soils are homogeneous in granulometric composition (sandy-silty), light loamy, acidic; the content of organic matter and nitrogen, according to Table 1, depends on the addition of charcoal and by the third rotation decreases to control values.

The objects and methods of research fully correspond to the goal.

Table 2 shows the data for determining the content of 13 PAHs in soils. Unfortunately, the table does not contain data on the content of these substances in the original charcoal, and the doses in which they were added to the soil, which does not make it possible to calculate the predicted concentration and compare it with that measured during the analysis. In addition, the following data raises questions:

Fluorene is detected in the first two rotations, but is not detected in the third rotation. What happened to him? Judging by the change in concentration over two rotations (the concentration practically did not change), we are not talking about destruction. Does this mean that he migrated down the profile? How did the water regime of the sites change during the observation period?

Pyrene and Chrysene were not found in the first two rotations, but were present in the soil of the third rotation. What is it connected with?

Phenanthrene is present in all soils, including the control soil. If this is due to the fact that charcoal may have been added to the control soil at one time, then why are there no other PAHs there? Is the history of this site known, and can it be estimated when charcoal was last applied? Apparently, PAHs can accumulate in these soils and be transported to the underlying horizons (judging by the sandy-silty granulometric composition, possibly into groundwater).

In general, the data obtained can be assessed ambiguously

The work pays much attention to BEHP released into the soil from plastic bags when planting target crops. In my opinion, since this is not directly related to obtaining and depositing charcoal, research into BEHP behavior should be an independent separate work

Author Response

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Reviewer 3 Report

The article on 'Polycyclic Aromatic Hydrocarbons (PAHs) and Bis(2-ethylhexyl) Phthalate (BEHP) in the Soil of Teff-Acacia decurrens Charcoal Production System in Northern Ethiopia' is an interesting one and has the potential to get published in this journal. However, it needs some revisions as follows: 

1. L 16-17: Mention the rationale of this study in one sentence at the beginning of the abstract.

2. L 119: Include a novelty statement here.

3. L 149: Mention in details about the TACP process.

4. L 160: Why only 0-20 cm of soil depth was considered? The study should be up to 60 cm soil depth.

5. L 241: How did the authors use 2-way ANOVA? Mention the detailed statistical design of the study.

6. The results part is well written with proper depiction of tables.

7. I would suggest the authors separate the discussion part. 

8. The authors should rewrite the conclusion part focusing on the most relevant results and a possible recommendation and future scope of study.

Good luck!

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I still have some questions that I would like to get answers to in the article, but apparently I should study in more detail the earlier publications of the authors.

Just in case, I’ll repeat:

Table 2 shows the data for determining the content of 13 PAHs in soils. Unfortunately, the table does not contain data on the content of these substances in the original charcoal, and the doses in which they were added to the soil, which does not make it possible to calculate the predicted concentration and compare it with that measured during the analysis. In addition, the following data raises questions:

Fluorene is detected in the first two rotations, but is not detected in the third rotation. What happened to him? Judging by the change in concentration over two rotations (the concentration practically did not change), we are not talking about destruction. Does this mean that he migrated down the profile? How did the water regime of the sites change during the observation period?

Pyrene and Chrysene were not found in the first two rotations, but were present in the soil of the third rotation. What is it connected with?

Phenanthrene is present in all soils, including the control soil. If this is due to the fact that charcoal may have been added to the control soil at one time, then why are there no other PAHs there? Is the history of this site known, and can it be estimated when charcoal was last applied? Apparently, PAHs can accumulate in these soils and be transported to the underlying horizons (judging by the sandy-silty granulometric composition, possibly into groundwater).

In general, the data obtained can be assessed ambiguously

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors need to revise the article, especially in the methodology section. I have mentioned some points regarding the statistical design of the research work, however, the author did not follow the suggestions properly. Following are my comments for the further improvement of this article:

1. The depiction of TACP system is still not clear. You must provide details about the procedure of the TACP system. Only a figure and some shallow description of this would not be sufficient. 

2. Give a pictorial description of the layout of the study. The statistical design looks faulty. How many replications were there? Again a very casual depiction of design was made by the authors. 

3. Moreover, the authors did not follow some suggestions like separating results and discussion section. 

I would suggest some major corrections otherwise rejection. 

Author Response

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