Microplastic Pollution in the Surface Waters from Plain and Mountainous Lakes in Siberia, Russia

Round 1

Reviewer 1 Report

General comment

The manuscript water-1301898 entitled “Microplastic pollution in the surface waters from plain and mountainous lakes in Siberia, Russia” aimed to analyze for the first time the concentrations, composition, and spatial distribution of MPs in six lakes in southern Siberia. The study is interesting and fists well with the aim of Water. However, my main concern regards the size particle and the definition of MPs considered by the authors. “Microplastics are any synthetic solid particle or polymeric matrix, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water” (Friaa and Nash, 2019; https://doi.org/10.1016/j.marpolbul.2018.11.022). In the M&M section (line 162) the authors have affirmed to detect particles between 5 and 200 nanometres (0.05-0.2 micrometres). Why? Also, quality assurance/quality control are not reported. What was the LOQ of your method? Please, expand the section related to the MPs analysis. Did you compare the MPs among lakes? What kind of statistical tests did you use? A lot of key information are missed. Unfortunately, I cannot recommend publication of the study in Water. I am very sorry to disappoint the authors.

Other comments

The keywords of the paper should not contain any words already in the title, but can include abbreviated terms or location information not suitable for the title. Please, rewrite.

Line 57. I suggest to add other studies in remote lakes (i.e., Alps: https://doi.org/10.1016/j.chemosphere.2020.129121; North America: https://doi.org/10.3390/w13030264)

Table 1. I suggest to add the geographical coordinates of each site.

Line 186. “systematic differences”? What this meaning?

Author Response

Dear Reviewer!

Thank you very much for reviewing our paper and for your suggestions on how to improve it. In the first version of the paper, we focused only on small particles (below 300 nm) because the number of large particles (below 1000 nm) was small (less than 15%). According to your recommendation, we included all microplastic identification results in the current version. We expanded the explanation of the quality control in the methods section and performed a statistical analysis of the data. We compared the results, both in concentration and size of microplastics, with the recommended studies and other available data. In table 1, according to the recommendations, we entered the coordinates of the lakes. Keywords were partially corrected and added.

Thank you very much for the work done.

On behalf of all authors,

Dr. Natalia Malygina

 

Reviewer 2 Report

Lines 10-11: "essential elements in runoff formation" This is somewhat confusing because runoff enters lakes and does not occur from lakes.

Line 181: Please explain more clearly how concentration were dependent on watershed properties. You discuss the concentrations found in each lake and the characteristics of those lakes but do not discuss generally. If you have not studied enough lakes to draw general conclusions you probably cannot say that the concentrations are dependent on watershed properties, which is itself a general conclusion.

Overall: This work is needed because it is necessary to collect this type of data from a range of geographical sources. However, it is not particularly novel because it is primarily baseline data collection. The importance and interest of the article for scientists outside of this geographical location could be increased by drawing more comparisons to other regions. There are a few places in the article where concentrations are compared to Finland for example. Is it possible to draw further comparisons to a wider range of locations?

Author Response

Dear reviewer!

Thank you for your valuable suggestions. According to recommendations, we expanded the comparison of our data primarily with the data obtained by similar methods. In addition, we have corrected the text at lines 10-11 and 181 to make it clearer and more coherent. Indeed, we cannot yet draw general conclusions regarding the effect of watershed characteristics on concentrations and other characteristics of microplastic pollution in lakes.

Thank you very much for the work done.

On behalf of all authors,

Dr. Natalia Malygina

 

Reviewer 3 Report

The article presents the results of very interesting resarch abuot microplastic pollution in the surface waters from plain and mountainous lakes in Siberia, Russia. The article is well costructed and written. The introduction and the research part are well documented. The research method and results are briefly, but clearly described, supported by proper conclusions and reference to the results other authors. I recommend the publication of the work in the current form.

Author Response

Dear reviewer!

Thank you very much for your positive review.

Thank you very much for the work done.

On behalf of all authors,

Dr. Natalia Malygina

 

Round 2

Reviewer 1 Report

The authors have addressed most of my concerns. However, I did not understand if the Authors have determined the chemical composition of the microplastics. Indeed, they reported the concentration and the shape. What was the chemical composition of your particles? How can you say that i.e., a retrieved fibre is a plastic and not a cellulose? Please, clarify. 

I recommended to check the English language in the revised version.

 

 

Author Response

Dear Reviewer!

 

Thank you very much for reviewing our paper and for your suggestions on how to improve it.

 

In the paper (methods section), we have made small additions concerning determining the elemental composition of microplastics (using SEM/EDS).

 

The principle of microplastics determination by SEM/EDS was described in detail in Marianna Gniadeka and Agnieszka Dąbrowskab "The marine nano- and microplastics characterisation by SEM-EDX: The potential of the method in comparison with various physical and chemical approaches" (Marine Pollution Bulletin 148 (2019) 210-216). Below we summarize some details from that work:

 

«Scanning electron microscopy (SEM) can give fast information of morphology, ageing, and origin of the examined samples as it provides the high-resolution data of surface state and the qualitative information about the chemical composition (by EDS). SEM provides high-magnified, high-resolution images of the surface of the investigated particles. SEM microscopes are equipped with various detectors which generated images based on different collected electrons types. For example, a detailed secondary electron image helps distinguish the nature of the objects – fish leftovers, parts of shells. Backscattered electron detector provides information on topography and material contrast based on atomic number (Z). Samples with elements composed of a higher atomic number (Z) yield more backscattered electrons than lower Z elements. This phenomenon can be used to distinguish differences in the composition of the samples. Moreover, most of the SEMs are equipped with an EDS detector, which enables a fast elemental analysis of the particles. EDS provides qualitative and quantitative information on the composition of the sample. This technique is very useful for discrimination of organic (rich in Ca/Mg/Sr) and inorganic (minerals, salts) and microplastics (rich in C/Cl/S/Ti). The SEM-EDS is often considered as an expensive technique which requires substantial time and effort for sample preparation and examination. As far as microscopes are costly, samples preparation and investigation can be done quite fast, easy and low-costly. Most of the researchers focused on microplastics debris characterisation are using environmental SEMs (Wagner et al., 2017). Those systems use to minimise sample charging under the electron beam injection of water vapour or other gases (like air, nitrogen, oxygen, argon) into the SEM chamber (so-called: wet-mode imagining). In other cases, when using conventional SEM microscope researches are covering samples with conducting layers by sputtering Au, AuPd or carbon on the non-conducting microplastics scraps (Mahon et al., 2017). Energy Dispersive X-ray spectroscopy (EDS) cannot be considered as a separate technique form SEM. It requires an electron beam generated by an electron microscope cathode. Primary electron beam when hitting the sample surface generates different interactions (among others – X-ray). EDS is a very powerful method of analysis of the composition of microplastics. EDS can provide qualitative information about elements and their spatial distribution within the sample. The combined use of electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) provides detailed information on the elemental composition of microplastics with additional information on the inorganic additives they contain. The utilisation of SEM-EDS aids in the further differentiating natural materials forms microplastics due to simultaneously collected images and elemental mapping. EDS elemental analysis can also provide indirect information. Strong nitrogen peaks appearing on the surface of polypropylene, polyethylene and polystyrene debris can be a proxy for biomass (Pan et al., 2019). The intense occurrence of nitrogen in the MPs samples is an indicator of bioaccumulation which revealed strong interactions between MPs and biota. The presence of the chlorinated microplastics (for instance the PCV) is easily confirmed as well as the direct observation of the environmental weathering of the surface.»

 

 

Thank you very much for the work done.

On behalf of all authors,

 

Dr. Natalia Malygina

 

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

The authors have addressed my main concern.

I recommended the authors to follow the authors guidelines. Citations and references are not well reported. In the text, reference numbers should be placed in square brackets [ ], and placed before the punctuation; for example [1], [1–3] or [1,3]. For this reason, the MS can be accepted for publication in Water after minor revision.

Author Response

Dear Reviewer!

Thank you very much for reviewing our paper and for your suggestions on how to improve citations and references

Dr. Natalia Malygina

Author Response File: Author Response.docx