Occurrence of microplastics in Fish from Mendoza River: First Insights into Plastic Pollution in the Central Andes, Argentina

Round 1

Reviewer 1 Report

I have a few comments regarding the manuscript, which the authors may wish to address prior to its acceptance for publication (attached file).

Comments for author File: Comments.docx

Author Response

Response to Reviewer 1 Comments

Point 1: -General comment

The manuscript addresses the accumulation of microplastic particles in three fish species from freshwater environment in the area of Central Andes. The authors investigated the abundance and prevalence of MPs in gastrointestinal tract of fish samples. They also determine the shape of MPs as well as MPs color. Differences in abundance of MPs among different fish species as well as the potential correlation of MPs abundance with fish characteristics (body size and weight) have been discussed. It is a relevant and interesting manuscript providing insight into the levels of accumulated MPs in fish species important to local aquaculture and recreational fishing activities. It represents a first study of MPs accumulation in fish species in the investigated area and provides essential data for the development of future biomonitoring programs.

That being said, it is a very informative and relevant manuscript. It is well written and concise. Experimental work and methodological approach are original, with conclusions reflecting the presented experimental data. I have a few comments regarding the manuscript, which the authors may wish to address prior to its acceptance for publication (attached file).

-Abstract

The font of the Latin names of investigated fish species should be italic. Please correct this error

Response 1: Done, this mistake have been amended (see Abstract).

Point 2: -Introduction

You mentioned the biological effects of MPs pollution. I suggest adding a few sentences about the potential harmful effects stemming from adsorption of harmful contaminants (mainly organic pollutants, but also trace metals) to microplastic particles in order to emphasize the importance of studies focusing on MPs pollution and ingestion by aquatic organisms

Response 2: To provide more clarity and reinforce the pertinent paragraph of the Introduction, we have added a few sentences about the potential harmful effects stemming from adsorption of harmful contaminants to microplastic particles, as follows:

In addition, harmful contaminants may be adsorbed onto microplastics; thus, aquatic organisms potentially consume and accumulate these chemical compounds with microplastics (He et al., 2022). Furthermore, microplastics and harmful contaminants possibly accumulate in the food web as the lower trophic level organisms are consumed by fish (Chen et al., 2021). Therefore, the ecotoxicity of microplastics in aquatic organisms is now an important field of research.

Point 3: -Materials and methods

Sentence: “The regional climate can be defined as arid, of maximum continentally and...”

Comment: I suggest revising the sentence since it’s not quite clear what you meant by the phrase “maximum continentally”.

Response 3: To avoid confusion, we have decided to remove this sentence with not impact in the paragraph sense.

Point 4: --Results

Sentence: “Blue fibers (61%) were the most found, followed by black (20%), white (14%), red (5%), and yellow fibers (1%) in the analyzed specimens.”

Comment: If you add the percentages 61%, 20%, 14%, 5% and 1% you end up with 101%. I presume this is an effect of “rounding up” the number. If that is the case, I suggest rounding up the numbers to one decimal place (or two) to avoid the error mentioned above.

Table 1 and 2, Figures 2 and 3

Comment: There seems to be a discrepancy in number of fibers listed in tables and the number of MPs previously mentioned in the text. According to the numbers in the text, you assessed that 85% of the total of 115 MPs were in the shape of fibers. This would mean that approximately 98 MP particles were in the shape of fibers. However, according to tables 1 and 2, the total number of fibers was 71. This error is also reflected later on in figures 2 and 3. Please check the numbers in tables and figure values and correct the discrepancies.

Response 4:  We truly appreciate the reviewer's comment. Discrepancies between the text and the tables have been corrected. Since the values in the tables were correct, the error lay in the values that were mentioned in the text and that have now been corrected according to the original data. Since the total fiber content in fish GITs was 71, the percentages of fibers according to color are now mentioned in the text properly and included using two decimal places as suggested:

Overall, the analysis found that fibers were present in 65% of the samples, while fragments were found in 10% of the analyzed specimens. A total of 88 items of MPs were counted, corresponding to 80% fibers and 20% to fragments. Blue fibers (57.75%) were the most found, followed by black (26.76%), red (7.04%), white (5.63%), and yellow fibers (2.81%) in the analyzed specimens.

Regarding the values of the y axis of figures 2 and 3, these are correct, since they show the median in the abundance of microplastics in the GITs of fish. Since Kruskal-Wallis, used to test for possible significant differences among species, compares the medians values, Fig 2 and 3 are the graphic representation of these values.

Author Response File: Author Response.docx

Reviewer 2 Report

Please, see the attached file. 

Comments for author File: Comments.docx

Author Response

Response to Reviewer 2 Comments

Point 1: INTRODUCTION

Pag. 2 Line 13: it could be useful to specify also a dimensional classification of plastic debris into macro, meso, micro and nanoplatics.

Response 1:  Although there are several plastic litter classifications according to size, in the present study, we used the size classification according to GESAMP (2019). We agree with the reviewer suggestion and a brief sentence with dimensional classification of plastic debris into macro, meso, micro and nanoplatics was included in the Introduction as follows:

Plastic debris can be classified according to its size. According to GESAMP 2019 [6] , size classes typically attributed to the nomenclature of nano- (1<µm), micro- (<5mm), meso- (5-25mm), and macroplastics (25-1000mm). Particle size will be of major ecological relevance because it is one important factor determining the item’s interaction with biota and its environmental fate [7].

Point 2: MATERIALS AND METHODS

Pag. 2 Line 47: delete “middle” – insert “transport”

Response 2: This request is not applicable since “middle” refers to the basin section of the Mendoza River.

Point 3: DISCUSSIONS

Pag. 8 Line 31: it is advisable to discuss about the factors influencing MPs intake for mountain dwelling fish species also for other regions of the world, not only in Asia, Africa and America continents but also in european freshwaters with possible references.

Response 3: We agree with reviewer suggestion. To provide more clarity and reinforce the pertinent paragraph, we improve the beginning of the paragraph as follows:

Worldwide, there seems to be a trend that blue fibers are the most frequently plastic items found in the GITs of wild fish from freshwater systems including Southeast Asian [50], Africa [46], North America [22,51], South America [31,48], and Europe [23]. Factors such as shape and size [52], as well as the color [53,54] influence MPs intake for both marine and freshwater fish species.

Point 4: CONCLUSIONS

Pag. 9 Line 42: it is timely, to extend the final paragraph Conclusions suggesting, also, possible solutions to counteract this environmental problem. 

Response 3: To provide more clarity and reinforce the end of Conclusions, we include the following sentences:

It is important to highlight the joint effort of numerous scientific and governmental entities focused on mitigating the environmental problem generated by plastic pollution. The possible solutions to counteract the plastic dilemma can be summarized as follows: (i) implement the circular economy which encourages more responsible and sustainable consumption, (ii) implement the use of effective waste collection systems, (ii)  reduce waste generation, (iii) educate and sensitize consumers, and (iv) ensure that waste is properly managed and disposed of.

Author Response File: Author Response.docx