Potential of Adsorption of Diverse Environmental Contaminants onto Microplastics
Round 1
Reviewer 1 Report
The submitted manuscript refers to the very important topic of microplastics, which not only pollute the environment, but also can be a carrier for other dangerous contaminants. Although the scope of the research is undoubtfully up to date and worth investigating, the obtained results should be better discussed. For example, why the adsorption mechanism (physical or chemical) is so important. Also the pH adjustment is not justified sufficiently, i.e. I doubt if the pH as low as 3 (or around) is relevant for aquatic environment.
The obtained adsorption capacity of heavy metals is indeed very high – I think it was estimated from the concentration change in the aqueous solution. Good sorbents designed for heavy metals removal from water reach only slightly higher values, but the MP are not modified (functionalized) for the process. These values are very surprising, but I cannot discuss with experimental data. If so, a very interesting would be to carry out the desorption and verify how robust the sorption is (i.e. if the metals can be leached out using a hot water) and then verify again how much metals can be regained (to confirm the high capacity).
Detailed remarks and comments are listed below:
- Title suggests that MP can be adsorbed onto something, but the studied process refers to adsorption on the polymers – the syntax should be corrected.
- Abstract lines 9-10: “chemical damage to microplastics” – this is not correct notion to the studied adsorption process.
- Abstract lines 17: “Adsorption amount” – adsorption is the process (cannot be quantified).
- Abstract lines 17-18: “The main adsorption mechanism of heavy metals was found to be through physical and chemical adsorption” – I do not know any other option, adding “both” or saying that “in contrast to dyes” will clarify, what Authors wanted to say.
- Abstract lines 20-21: “…creating a manual that recognizes environments where contact with plastics should be avoided” – a very general sentence, which does not provide any useful information (here and in conclusions the same sentence is embedded).
- Line 66: capital letter in “However” (beginning of a new sentence).
- Line 68: “there were few effects in various sizes” – not clear.
- Line 96: size distributions shown in Fig. 1 do not correspond to provided ranges (for example in group 1 there are many particles larger than 20 micron etc. – only group 2 for PS looks consistent with the definitions provided by Authors).
- Line 105: dosage (???)
- Line 114: what reactions???
- Line 133: “…, the sample 133 should measure quickly.” (incorrect English).
- Line 145: “It was also confirmed that it was distributed in a micro-sized morphology” -not clear (English).
- Line 146-…: Please discuss if (or how) the zeta potential affected the aggregation tendency of small particles. How “zeta” was measured for such large objects??? Please, clarify the methodology.
- Chapter 3: Please comment the relevance of experiments carried out at low pH values.
- Line 182: The range is usually defined from lower to upper limit (small to large particles). The sentence in this line is not clear (“of large size”???).
- Line 210: If the sorption depends on the particle size, the adsorption is on the outer surface only. Then obtaining so high sorption capacities (mentioned above in my comments) is even more surprising, because the specific surface area of the particles is not very high. To give an impression about figures I made a quick rough assumption assuming that the small PS fraction (1) is represented by the average size 10 micron – this gives the spec. surf. area of only 0.6 m2/g!! Of course, the surface is rough with cracks or defect due to weathering or other process. Anyway, this will not provide extension of the surface to approach similar value as a proper sorbent activation process for other sorbents does. Even “bad sorbents” have much more surface available. I would recommend to verify the results very carefully, because such high sorption in my opinion seems to be overestimated.
- Line 218-219: Do you have any evidence for these listed interaction forces to support your “conclusion” or it is just taken from the theory, what interactions can occur?
- Line 238-239: “In general, it was reported that the adsorption performance of cationic metal adsorption increases with the increase in pH” – English syntax should be corrected.
- Line 244: “high adsorption amounts at the smallest size and 30 day(Figure 5)” – amount (not amounts), days (not day) of what?, a space missing before the bracket.
- Line 294: Information about thiol groups is not relevant for the research.
- Line 310: How important is it that the sorption process is physical? Why do you study and verify this mechanism, what useful information it provides?
There are some important deficiencies in the submitted manuscript, which are pointed out above. If Authors address them all, the revised manuscript (major revision recommended) it can be considered for publication in the journal.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this article, the authors present an evaluation of the adsorption performance of different types of MPs of the same size and the possibility of adsorption of inorganic and organic pollutants by MPs under the same conditions.
The results are very interesting and can be used in the identification of potential accumulated chemical contamination for each type of plastic.
The conclusions are relevant and drawn from the study.
The authors may refer to the following suggestions:
1.Try to identify more comparations of your results wit the results of other authors and present in the section 3. Results and Discussion.
2. I recommend checking the text to eliminate eventually spelling mistakes.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I acknowledge Autor's comments and explanations provided in the coverletter. The paper is significantly improved now. My only remark is with regards to the distributions and description of the size. Author's indicate that the mode value (the size which appaears most frequently in the distribution = maximum on the distribution curve) is less than indicated size. In fact for example for MP-1 the modal value equal to16.9 micron is less than 20 micron, but there are also particles 40 or close to 50 micron (where the distribution curve drops to zero) in this "group". Hence, saying that the MP-1 contains particles <=20 micron is not correct.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
