Impact of Microplastic Fibers from the Degradation of Nonwoven Synthetic Textiles to the Magdalena River Water Column and River Sediments by the City of Neiva, Huila (Colombia)

Round 1

Reviewer 1 Report

Review of the manuscript Water 774115

The manuscript presents an interesting dataset and an important study on microplastics amount, shapes and materials in river water and sediments of a urban environment. In the studied area, the input of industrial manufacturing processes is neglectable, thereby providing an opportunity to characterize the load of microplastics in the Magdalena River produced from rural (upstream) and urban areas derived by agricultural practices and household activities. The main finding of the manuscript is the abundance of fibers derived from non-woven synthetic textiles, having a different origin from the washing of woven synthetic textiles so far thought to be the main responsible for microplastic fibers. This provides an important advancement in the field, especially for our understanding of the main sources of microplastics contamination of waterways.  

The manuscript is well written and the reasoning well discussed. I only have minor comments.

Line 99: and all throughout the text, please check as the µ sign is missing in many parts when referring to µm size (lines 173, 182, 200, 263-265, 278-279, 285, 341)

Line 104-106: more details on the tests performed to check the efficiency of density separation could be added in the methods or in supplementary information

Line 135: I think you refer to ImageJ – not J Image?

Line 155: How do you explain in sediment samples the lower values found in site 2?It does not seem that fragments really increase with downstream distance. I suggest to add an explanation to this observation in the discussion.

Line 195-196: please use µm instead of microns throughout the text

Line 262: is it possible that fibers from woven synthetic textiles are retained in sediments more downstream than site 3?

Line 304-311: I found this part no so clear. What do you mean by minimal difference? It seems that rural area are very much responsible for fibers concentration 4-to-5 times more than in urban areas, as you stated. So perhaps agricultural practices are likely the source? And a major source compared to urban environments or at least, to the city of Neiva? These high theoretical outflow of fibers from rural areas could be explained by increasing concentration in downstream sediments (e.g. site 3)? Maybe you could rephrase some concepts in this paragraph making it more clear.

Line 330- Conclusions: can your data be compared to other similar regions worldwide in terms of population density and number, and economic activities / landscape? Just a thought.

Author Response

Please see attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

General Comments

The manuscript deals with the measurement of the microplastic concentrations in the river water and sediments (Magdalena River that flows through Neiva, Colombia). Characterization of the origins of these particles was also performed. This is an extensive research challenge the authors have attempted to tackle. It is important work to be undertaken, as the authors stated well in the introduction.

In general, the article is logically constructed and written and gives adequate references to related work. Methods and statistical analysis are well performed and formulated. Findings are described in detail and are compared with data from the open literature. Overall, the research question is interesting, and this represents a significant global scale study likely of interest to a wide range of readers. The results highlight the importance of origin, transport and fate of microplastic particles in rivers. The findings indicate the impact of microplastic fibers originating from nonwoven synthetic textiles and bring new information in the open literature. Figures are helpful to resume the text.

Consequently, I think that the paper merits to be published in Water journal if major revisions are carried out.

I hope the comments below will help you to clarify the manuscript.

Specific comments

• Microplastic analysis: The authors should more clearly state which aspects of the sampling and analysis of microplastics in both matrices (water and sediments) are meaningful. In addition, there is a lack of information regarding possible contamination of fibers in the air. How the authors avoid the contamination of fibers floating in the air in both the field and laboratory?

• Lines 101-104: Please specify the known concentrations of polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalates (PET) microplastic particles in the aqueous solution.
• Lines 104-106: Did the authors correct their results taking into consideration the efficiency of the extraction method for high density microplastics (PVC and PET) (79%) or not? Please specify. In addition, please provide standard deviation values for the three repetitions.
• Lines 136-138: Please add some data to support the statistical analysis performed for the quantity of microplastics and their geometry among sampling sites.
• Lines 225-245: It would be of interest to see a correlation analysis with these data in order to further support the statements in this paragraph providing us a general idea of which factor is more important regarding the origins of the microplastic particles. For example, correlation between microplastic concentrations in the sampling areas and population density.
• Lines 259-262: Please justify further this statement.
• Lines 287-291: Please provide details regarding the constant hydrological flow of the Magdalena River during the sampling period.
• Lines 289-290: “…and assuming the concentration of microplastic particles in the surface water is representative of the average annual surface water concentration,..” Please justify further this statement.
• Please add in the manuscript some representative Raman spectra used for polymer identification by comparing the Raman spectra of pure polymers (PP, PE, PS, PVC, and Nylon) with those of water and sediment samples.

Minor comments

• Line 52: “in sediments [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 y 36]”. Please revise as follows; “in sediments [16-36]”. Please revise accordingly in the whole text.
• Line 135: Please add the relative citation for the J Image software.
• Line 341: “..Fiber widths of < 20 m,”.  Please check.
• I would suggest the authors to use the same format for all figures.

Author Response

Please see attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The manuscript was improved and merits publication