Macroplastics Pollution in the Surma River in Bangladesh: A Threat to Fish Diversity and Freshwater Ecosystems

Round 1

Reviewer 1 Report

Dear Authors

Yours manuscript touches interesting and importatn environemtanl probelm especially on investigated area. I recommend publication after minor revision.

Additionally, I suggest to continue reaearch next years observing changes and degradation of macroplastics. Consider 3-4- even 5 years. Consider bigger area too - maybe not only river.

Material is realy good and should be publicated.

Comments for author File: Comments.pdf

Author Response

An attachment has been added as response letter

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript presents interesting and valuable results of research on the pollution of the Surma river with plastic waste against the background of selected parameters of water quality and its level in the river. The composition and abundance of this garbage at six sites of the river were also analyzed, as well as the results of fish catches at these points. The results of questionnaire studies revealing the sources of these pollutants as well as the social awareness of their existence and the threat they cause are also presented.

For these reasons, I believe that the manuscript deserves publication, but it certainly needs to be improved. I suggest you consider the following considerations:

Lines: 20-21: Since this is an abstract, and so far it has not been indicated what is Kazir Bazar and Beter Bazar, it does not seem correct to indicate them in this way as a place of particular water pollution. In my opinion, however, especially a foreign reader, should be introduced to the discussion of the results, giving, for example, what was the range of the analyzed parameters?

However, if these places are named with the names of these places, it would be advisable to describe these places very briefly.

Besides, in the "Material and methods" section, these places are marked with symbols only S followed by a number, eg S4 and S5 (lines 104-113). Also in the description of the map, the geographical names of these places do not appear. They were placed only in the last row of table 1, unfortunately without a relevant reference in the text and in the caption of figure 1 to this table.

Line 23-24: What does "No conspicuous conclusion ..." mean? The level was unchanged, did it show any constant tendency to change? Is there really nothing to write about it?

Lines 25-26: Is it really harmful to increase public awareness?

Line 30: Can plastics only be "regarded" as "as an emerging pollutant in aquatic environments".  Plastics are pollution.

Line 41: "1050 t" ????

Line 114-118: The description of these studies does not specify how many times the measurements of environmental parameters were carried out and at what times were they carried out? This is important information due to the results described in section “3.1. Water quality analysis ".

Line 122: "Three transects [...] were considered randomly in each sampling site to do triplicate." So how were these places in the field chosen? Perhaps, however, they were selected in such a way as to best (most faithfully) reflect the state of contamination in the visual assessment?

Line 142: The table shows the limits of the rating classes in the water pollution index.

Lines 143-144: The information on the method of fishing should be supplemented by providing a short technical description, especially the dimensions of the net used and the size of the mesh (from knot to knot) [mm]. The description of fishing also needs to be supplemented. As far as I understood, three catches with the net were carried out at each site (S1, S2, ....) (three times the net was cast), and these catches were carried out on a 1 km long section of the river?

Line 179: The table description does not include the number of measurements (n) on the basis of which the averages were calculated.

Line 180: Table 3. I guess values with the "±" sign are standard error. Does "0" at mean salinity values mean that no variation was observed?

Lines 180-183: Weren't the unit of electrolytic conductivity "mS/cm"?

Lines 215-217: Instead of "gm^-2" there should be "g m^-2".

Lines 225-226: I suggest "macroplastic concentration" instead of "abudance".

Lines 231-235: However, I would be more careful with formulating a water purity rating. First, the assessment is based on just a few parameters. Although the authors of the method assume that this is an acceptable procedure, one should take into account the possibility of influencing the results of the evaluation of the measured parameters, but of less importance in the evaluation. In my opinion, in the case of the analyzed parameters, it would be e.g. temperature. Second, I certainly disagree with the statement that 'S1, S2, and S6 were recognized as pollution-free sites'. Firstly, the WPI on these positions was only slightly smaller than on the S3 position, which in the text rated "as a moderately polluted site". Meanwhile, with each assessment there is an uncertainty of misclassification. This problem in the case of water quality assessment has already been described in a number of publications.

Lines 235-239: Perhaps these statements should be expanded a bit, in the end individual indicators assess the differentiation differently, e.g. the Simpson index determines the probability of drawing two individuals belonging to the same species, and the Dominance indicates the quantitative share of a given species in the analyzed ecosystem.

Lines 246-250: Figure 7A shows that the "Salinity" and "Total plastic" values ​​were (even very) poorly correlated with the other parameters. These, in turn, formed two clearly correlated groups of “pH” and “DO” as well as “Temperature”, “TDS” and “Conductivity”, while the parameter values ​​in these two groups changed inversely, i.e. when DO and pH increased, those in the second group decreased. Second: component one ordered (explained) the variability caused by "Total plastic". The remaining variables slightly influenced the location of points S1-S6 in relation to the first axis, and (in order) “Conduvtivity”, “DO”, “TDS”, “pH” and “Temperature” influenced the arrangement of points S1-S6 along the second axis. Consequently, the lowest values ​​of “DO” and “pH” were found in S4, S3 and S1, and the highest in S5. On the other hand, S2 was characterized by values ​​close to the mean values ​​of these parameters. This was evidenced by the location of the S2 point near the zero value on axis 2.

Lines 250-253: The right angle between the vectors representing "Total plastic" and most of the variation indices (except Evenness and Berger-Parker) shows that there is no correlation between them. Similarly to the above, the location of points along axis 1 was mainly determined by "Total plastic", and to a lesser extent by Evenness and Berger-Parker. The graph also clearly shows that the other indicators were very weakly correlated with Total plastic, and the dominance changed in the opposite way than the "Fisher's alpha - Simpson" group.

Line 282: Figure 12 is not in the text.

Lines 290-298: It is very difficult to respond to the statement "many people are totally unaware of plastic pollution". There is no mention in the paper informing about the wording of the question / questions on the basis of which this conclusion was drawn. In turn, the presented photos, e.g. in Figure 9, indicate that even one visit to the river should not leave any doubts related to the presence of numerous plastic waste in the water and on the banks. However, the question of whether people can properly name the state of the river (its pollution) remains open in this situation. It does not follow from the text whether people perceive garbage by the water and whether, when they see it, they can determine that it is pollution, or whether in their consciousness it is a "normal" state (eg. "Because it has always been like this").

Line 307: If the names of the authors of a publication are mentioned on lines 318 and 319, then it should be done here as well. Similarly in line 349.

Line 346: Information on hydrotechnical structures in the Surma River should be included in the Material and Methods section, especially when it is relevant to the evaluation of the results obtained.

Lines 353: Please correct as suggested earlier. Notes to lines 246-250 and 250-253.

Lines 361-362: There was no such hypothesis in the "Introduction" section, but nothing of the sort in the "Results" section either.

Author Response

An attachment has been added as a response letter. 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Although the Authors of the cover letter assured that they took my suggestions into account, in the "revised" version of the manuscript they left not only unfortunate phrases, but also obvious errors, often gross errors. Take the sentence in verses 41-42 as an example. The original text (in lines 40-41) read: "The production of various plastic wastes has drastically expanded between 1050 t 2015 on a global scale [7]." In my first review with regard to the content in line 41, I asked the question: „"1050 t"????”, which should have suggested the need to check the compliance of the given data/statements with the quoted publication. Admittedly, the Authors have changed this sentence, stating that: "The production of various plastic wastes has drastically expanded between 1050 - 2015 MT on a global 42 scale [7]." However, in the cited publication Almeshal et all. (2020) the number 2015 only appears 6 times and 1050 does not appear at all. Additionally, the number 2015 is the upper limit of the period in which the global production of plastic waste was estimated, and I quote: “According to United Nations Environment Programme (UNEP), the world produces more than 400 Mt of plastics every year. Fig. 1 show the global plastic wastes generation between 1950 and 2015 [3].” However, later Almeshal et all. (2020) reports that “8300 million metric tons (Mt) as of virgin plastics have been produced to date. Until 2015, approximately 6300 Mt of plastic wiaste had been generated ....”. Additionally, the Authors of the mauncript do not provide in the sentence changed in this way what the unit Mt means - million metric tons. I omit that the notation "MT" is inconsistent with the International System of Units (SI).

Another significant problem is the results of measurements of electrolytic conductivity in the tested water of the Surma River. In Table 3 (lines 191-193 in the current version of the text, and in lines 179-180 in the previous version), the Authors report that the average conductivity values ​​at the six test stations were in the range 225-289 mS/cm, and the standard values ​​are 200 -500 mS/cm. In my review I indicated that the mS/cm unit used is not correct and should be corrected to μS/cm. In response to the reviews, the Authors stated: “We used YSI multiprobe parameter to measure different physicochemical parameters. Conductivity was calculated as mS/cm. Consequently, they left these values ​​unchanged. I believe that the Authors did not provide a substantive justification for such a decision, because reading the results with a gross error on the scale of the measuring instrument cannot be considered an argument for publishing them. This position of the Authors forced me to look at the literature cited in the header („Table 3. Physicochemical properties of water at different sampling locations with standard values 191 [46,47]”). In the publication, number 46 - Uddin et all. (2014) - I found completely different values ​​given as possible standards (p. 252: „Table 1. Comparison the physical parameters of Jamuna River water during dry and wet season”):

Standard (DOE, 2001) 300 (μS/cm)

Bangladesh Standard for Fisheries (EQS,1997) - 800-1000 (μS/cm)

Irrigation standard (Ayers and Westcot 1976) – 750 (μS/cm).

And in the description of this parameter on page 253 the following comment: „Specific conductance of most natural water generally ranges from about 50 to 1500 µS/cm.The Electric Conductivity in the study area ranged between 135 to 141 µS/cm in dry season and 104 to 109 µS/cm in wet season (Table 01) most of which is lying within standard level of EC of most natural waters.” The above proves (similarly to the first example) that the authors treat the quoted sources with great nonchalance and give completely different values ​​than the cited Authors.

The issue has very serious consequences in the case of the analysis presented in the manuscript. In general, the electrolytic conductivity of polluted water (waste water) is typically in the range 1000-10000 µS/cm (1-10 mS/cm); salt (sea) water from 100 to 10,000 μS/cm (0.1 - 10 mS/cm); industrial water in the range 1-100 mS / cm; while in concentrated acids and bases it ranges from 100 - 1000 mS/cm. It follows from the above that, according to the results presented in the manuscript, it is not water that flows in the Surma River, but a solution with the content of dissolved ions corresponding to the content in concentrated acids or bases. Recognizing the values ​​given by the Authors would mean that we are dealing with a gutter, not a river, and the problem of „water quality" cannot be limited solely to the presence of plastic. In this context, determining this "water quality" with only the six parameters taken into account by the Authors of the manuscript could not actually reflect the actual state. The more that one of them is temperature, and the description of the river does not suggest that it could be changed by any anthropogenic heat sources. It would also have a significant impact on the social awareness studied by the Authors of the manuscript - one of the main issues of this manuscript. It should be expected that in a completely different way, people will refer to plastic waste pollution (a specific) „landfill", which would undoubtedly be the „river" of Surna, in which the liquid would flow completely unsuitable for any use, and completely different to the pollution of the river with water that is fit for use.

Another problem is associated with the above. In my previous review, I drew attention to an important issue in the description of the survey conducted - failure to provide the wording of the question or questions, on the basis of which the „categorization of awareness towards plastic pollution among local people at different study areas", given in Figure 12, was established. There is no description of the method, how is it proved that someone is “totally not aware”, “aware but careless”, “aware and trying to maintain” and “totally conscious and maintaining”? The Authors in the original and revised version of the manuscript (lines 169-171) and in the cover letter invariably limit themselves to the following statement: „A field survey was conducted by preparing a standard questionnaire to identify the possible major sources of riverine plastic pollutants and to categorize the level of consciousness among the common people towards plastic pollution. A total of 300 adult people from diverse professions (50 from each site) participated in the survey (section 2.7).“

The lack of presentation of this form (questions asked) not only makes it impossible for the reader to verify the results presented in Figure 12, but also constitutes a serious gap in the description of research methods, which makes it impossible to repeat the research and conduct research showing possible changes in social awareness in the future.

The above remarks, resulting from reading the Authors' cover letter and reading the relevant fragments of the text of the „revised” manuscript, made me consider a detailed reading of the entire manuscript pointless. At the same time, I believe that they disqualify the manuscript.

I find that the current version of the manuscript cannot be printed in Water. In addition, the method of correcting the text by the Authors does not guarantee the correct correction of the manuscript authorizing me to change my position.

Author Response

Dear reviewer, Please check the response letter in the attachment. 
Thank you.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Although the authors corrected the content of lines 40-42 of the manuscript (water-1917804-peer-review-v2.pdf), however, the other two issues in the previous review were not satisfactorily changed:

-          "The standard limits in the freshwater systems" according to the entry in line 147 were to be determined on the basis of two items of literature, i.e. 47 and 48. Meanwhile, table 3 already mentions three items - [47–49]. Additionally, in the quoted publication by Uddin et al. (2014) published in J. Environ. Sci. & Natural Resources, 7 (1): 249 - 256. There is no information about such limit values, as I indicated in the previous review, and according to the version available in Google Scolar, this publication was published in 2014, and not in 2015 as this provide the authors in the list. This table can be effectively corrected by marking each cited range of values ​​with a symbol and in the explanations specify which publication these values ​​are quoted from, e.g. 20 - 30 * and under the table: * - after .....

-          - I also see an attempt to more precisely describe the manner in which the questionnaire was carried out. The authors indicated that the questionnaires included closed and open-ended questions. They indicated that 300 people were examined, indicating that they represented various professions and places of residence, and the research was carried out at homes or in nearby markets area. The authors also mentioned that: "Participants were questioned about whether they consider plastics as pollution, and their consent and recommendations for the management, disposal, and reduction of this pollutant in river water were used as criterion tools to categorize them in different levels of awareness. . " Nevertheless, I believe that these additions still imprecisely describe the method and results of the research. The quoted fragment shows that the assessment of consciousness or its lack was categorized on the basis of "their consent and recommendations for ...". Still, the reader does not know what the criterion for distinguishing between the state of eg "Conscious but careless" and "Conscious and trying to hold on" was. How are "fully aware and maintaining" people distinguished from the latter?

-          The subjects were defined as "key informants". How do the authors know about this? The description of the results does not contain any information about the number of correctly completed questionnaires, the number of possibly rejected questionnaires and the reasons for their rejection, as well as the structure of the surveyed people (% of women,% of men), about the distance of their places of residence and / and workplace from the river, the intensity of using the river's "values" (including water for domestic, maybe recreational purposes?), and whether the respondents answered all the questions in the survey?

-          I have the impression that the survey lacked general questions, such as closed ones: "Is plastic waste, compared to other urgent issues to be solved, a problem?" (along with possible answers: "They are not a problem", "Rather unimportant", "Rather important", "Important", "Most important") and more detailed questions illustrating the negative impact of plastic waste pollution of the river on the lives of the respondents. Moreover, the results lack graphs illustrating the types of answers to open-ended questions about the reasons for throwing plastics into the river (with variants classifying, for example, "No well-functioning ...", "Excessive attachment to ...") along with the percentage of responses, e.g. " No impact ”,“ Probably not influencing ”,“ Neither influences nor influences / hard to say ”,“ Rather does not affect ”.

Perhaps, as a consequence, the relation (in my opinion) of very important survey research results comes down to a single chart (Figure 12), which, together with the imprecise description of the method of preparing the survey and conducting it, makes it impossible to repeat them in the future or to obtain results comparable with the same method by another research team on another river. It is a widely accepted testing standard that is also included in the guidelines for authors of the journal Water. This has a negative impact on the assessment of the importance of research and its importance for science.

Therefore, I cannot still recommend the manuscript for publication.

Author Response

Dear Reviewer,

Please check the response letter in the attachment.

Regards.

Hossain MA.

Author Response File: Author Response.pdf