Nickel Binding Affinity with Size-Fractioned Sediment Dissolved and Particulate Organic Matter and Correlation with Optical Indicators

Round 1

Reviewer 1 Report

Review of applsci-10145887-peer-review-v1" Nickel binding affinity with size-fractioned sediment  dissolved and particulate organic matter and correlation with optical indicators"

This manuscript describes analysis and distribution of water-soluble and sediment bound Ni-containing industrial soil contaminants.

The general impression from reading the manuscript is that the manuscript is clear written, , the results are reliable and discussed correctly, the language is good.Conclusion: the manuscript can be accepted.

Comments for author File: Comments.pdf

Author Response

Comment #1-1

Review of applsci-10145887-peer-review-v1" Nickel binding affinity with size-fractioned sediment dissolved and particulate organic matter and correlation with optical indicators"

This manuscript describes analysis and distribution of water-soluble and sediment bound Ni-containing industrial soil contaminants.

The general impression from reading the manuscript is that the manuscript is clear written, the results are reliable and discussed correctly, the language is good.

Conclusion: the manuscript can be accepted.

Response comment #1-1

Thank you for your comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments for authors consideration are as follows:

1. The first half of the abstract is full of generality. Abstracts should be precise and indicate the summaries findings of the scientific literature related to the theme of the paper. It doesn't deduce the justification of the results obtained. Normally an abstract should state briefly the purpose of the study undertaken and meaningful conclusions based on the obtained results. Hence, this needs rewriting. I would expect a brief, yet concise, quantitative data description of the results in the abstract.
2. The term “biotoxicity” is more generic.
3. Section 2.1. Sampling site and samples collection – pre-processing of the collected samples should be given in detail.
4. L82 – “collected in” or “collected from”.
5. The real-time waste effluents are far more complex in terms of types and mix concentrations of contaminants. How this was avoided? The current findings are not enough to justify the claims more samples should be added from the real-time waste effluents containing complex/mix of contaminants.
6. L198 – Tables - What was the sample size? It needs to be clearly mentioned. Add a footnote explaining the coated values were taken from the duplicate/triplicate samples.
7. Figure 1 is badly constructed. Reconstruct is bar format with individual samples instead of putting all in one bar. Legends are overlapping with the last bar. Also, it is lacking error bars.
8. The conclusion section is superficial. What are the authors' own viewpoints? What are the major findings and how they are addressing the left behind research gaps and current challenges?

Author Response

Review #2

Comments for authors consideration are as follows:

Comment #2-1.

The first half of the abstract is full of generality. Abstracts should be precise and indicate the summaries findings of the scientific literature related to the theme of the paper. It doesn't deduce the justification of the results obtained. Normally an abstract should state briefly the purpose of the study undertaken and meaningful conclusions based on the obtained results. Hence, this needs rewriting. I would expect a brief, yet concise, quantitative data description of the results in the abstract.

Response comment #2-1

Thank you for the comments and suggestions.

The Abstract has been revised.

Abstract:

In rivers, the distribution and reactivity of heavy metals (HMs) are affected by their binding affinity with sediment dissolved organic matter (DOM) and particulate organic matter (POM). The HM-OM binding affinity affected by the interaction between DOM and POM is not well studied. This study investigated the Ni binding affinity to size-fractioned overlaying water DOM and alkaline extracted sediment POM solution (AEOM). The DOM/AEOM filtrates (<0.45 μm) were sequentially separated into five nominal molecular weight (MW) solutions. The AEOM optical indicators had lower autochthonous, higher terrestrial sources, and lower aromaticity than the DOM. The Ni mass (72.3±6.4%) was primarily distributed in the low molecular weight DOM (<1 kDa), whereas the Ni (93.5±0.4%) and organic carbon (OC) mass (85.3±1.0%) were predominantly distributed in the high molecular weight AEOM. The Ni and DOM binding affinity, ([Ni]/[DOC])_DOM ratio ranging from 0.76 to 27.32 μmol/g-C, was significantly higher than the ([Ni]/[DOC])_AEOM ratios, which ranged from 0.64 to 2.64μmol/g-C. The ([Ni]/[DOC])_AEOM ratio correlated significantly with the selected optical indicators (r = 0.87 – 0.92, p <0.001), but the ([Ni]/[DOC])_DOM ratio correlated weakly with the optical indicators (r = 0.13 – 0.40, p > 0.05). In the present study, the Ni binding affinity with size-fractioned DOM/AEOM agrees with the hypothesis of the DOM and POM exchange conceptual model in sediment. The POM underwent a hydrolysis/oxidation process; hence, AEOM had a high molecular weight and stable chemical composition and structure. The Ni mainly attached to the high molecular weight AEOM and the ([Ni]/[DOC])_AEOM ratios had a strong correlation with the AEOM optical indicators. In contrast, DOM had a high ([Ni]/[DOC])_DOM ratio in low molecular weight DOM.

Comment #2-2.

The term “biotoxicity” is more generic.

Response comment #2-2.

Thank you for your comment. We have replaced the word biotoxicity with the more meaningful word reactivity.

Comment #2-3.

Section 2.1. Sampling site and samples collection – pre-processing of the collected samples should be given in detail.

Response comment #2-3.

Thank you for your comment and suggestion. Section 2.1. for pre-processing of the collected samples is given in detail.

2.1. Sampling site and samples collection

The sampling site (22°37'50.2"N 120°32'12.1"E) was downstream from a food industrial park in Pingtung County, Taiwan. The wastewaters from the individual manufacture were collected in a central wastewater treatment plant. The water quality in the effluent of the treatment plant wastewater agreed with the wastewater standard of the Taiwan Environmental Protection Administration (BOD < 30 mg/L, COD < 100 mg/L, and SS < 30 mg/L). The sampling location was about 1000 m downstream of the effluent outlet of the wastewater treatment plant. The samples were collected in triplicate in October 2016. The DOM and POM samples were collected from the surface sediment with a grab method.  5 L samples (including liquid and solid phases) were collected in each capture group. The samples were taken back to laboratory within 4 h. In the laboratory, sediment samples were centrifuged at 4500 rpm for 30 min. The liquid sample was filtered (< 0.45μm) to collect the DOM sample and was stored at 4 ℃ for further separation. The solid phase was air dried for two weeks and then passed through a 2 mm sieve to collect the POM. The POM was stored in a 4 ℃ for further extraction.

Comment #2-4.

L82 – “collected in” or “collected from”.

Response comment #2-4.

Thank you for the comment.

Line 82 “collected in” has been replaced with “collected from”

Comment #2-5.

The real-time waste effluents are far more complex in terms of types and mix concentrations of contaminants. How this was avoided? The current findings are not enough to justify the claims more samples should be added from the real-time waste effluents containing complex/mix of contaminants.

Response comment #2-5.

Thank you for the comments and suggestions.

We agree that the real-time waste effluent is far more complex in terms of types and mix concentrations of contaminants.

One of the methods used to avoid the deviation was to analyze enough samples and to analyze with different instruments. Another way was to prove the possible results with reference data and a possible mechanism.

In the present study, the overlaying water was flowing and the source might have been complex and mixed as the reviewer has stated.  One hypothesis (Burdige and Komada, 2015) asserts that the chemical properties of the sediment are more stable compared to the liquid phase. The results in the present study agreed with this hypothesis and we used the DOM/POM exchange hypothesis to deduce the difference and interaction between Ni and DOM/POM. In addition, we used size-fractioned DOM/AEOM to analyze the chemical property differences among the size-fractioned DOM/AEOM. We obtained the results confirming the hypothesis mechanism. In a future study, more types of heavy metals and samples need to investigated. The chemical properties in the present study were low aromaticity and autochthonous sources. Therefore, the different chemical properties in another area also needs to be studied in order to verify that the DOM/POM affects the heavy metal and organic matter binding affinity.

Comment #2-6.

L198 – Tables - What was the sample size? It needs to be clearly mentioned. Add a footnote explaining the coated values were taken from the duplicate/triplicate samples.

Response comment #2-6.

Table 1 adds the sample number; the standard deviation is for triplicate samples.

Table 1. The measured DOC and Ni concentrations for size-fractioned DOM and AEOM*

*Separation volume ratios for each size-fractioned solution are MW-A (0.1), MW-B (0.09), MW-C (0.081), MW-D (0.0729), and MW-E (0.6561). ^a the standard deviation value for n=3.

Comment #2-7.

Figure 1 is badly constructed. Reconstruct is bar format with individual samples instead of putting all in one bar. Legends are overlapping with the last bar. Also, it is lacking error bars.

Response Comment #2-7.

Thank you for the comment and suggestion.

Figure 1 has been reconstructed. The mass percentages of Ni (Fig. 1a) organic carbon (Fig.1b) and for size-fractioned DOM and AEOC have been plotted with a group bar chart. The error bars have been added.

Figure 1a. Ni percentages for size-fractioned DOM/AEOM

Figure 1b. Organic carbon percentages for size-fractioned DOM/AEOM

Comment #2-8.

The conclusion section is superficial. What are the authors' own viewpoints? What are the major findings and how they are addressing the left behind research gaps and current challenges?

Response Comment #2-8.

Thank you for your comments and suggestion.

The conclusion has been revised. The significant findings and the meaning of the research gap are emphasized according to the reviewer's comment and suggestion.

Conclusion

In this study, we studied OC and Ni distribution and Ni binding affinity on size-fractioned DOM/AEOM. The Ni and OC mass distribution in the DOM and AEOM was significantly different. The HMW AEOM had higher [Ni]/[DOC] ratios than the LMW AEOM, but the LWM DOM had higher ratios than the HMW DOM. The ([Ni]/[DOC])_AEOM ratios had a significant correlation with the optical indicators, but the ([Ni]/[DOC])_DOM ratios correlated weakly with the optical indicators. These results are in agreement with the exchange process between the DOM and POM in sediment. The present study suggests the exchange between the DOM and POM might play an essential role in understanding Ni and organic matter binding affinity in sediment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revised version reads well. Authors have addressed all the comments raised in the last review. This manuscript can now be accepted for publication.