Are Water Filters Effective Against Microplastics?

Response to Reviewer Comments

1. Summary

Dear Editor and reviewers,

We would like to thank the reviewers for the positive feedback on the manuscript entitled “Are the water filters effective against microplastics?”. We are especially grateful for the thorough review that provided suggestions and contributed significantly to the improvement of the manuscript. We accepted almost all suggestions and also reformulated some paragraphs and sentences throughout the text. In this letter, we provided some point-to-point reply to some reviewer requests.

2. Questions for General Evaluation

Reviewer’s Evaluation

Does the introduction provide sufficient background and include all relevant references?

Yes

Are all the cited references relevant to the research?

Yes

Is the research design appropriate?

Yes

Are the methods adequately described?

Yes

Are the results clearly presented?

Yes

Are the conclusions supported by the results?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Reviewer 1

Comments 1: Affiliation should be in English.

Response 1: Thank you for pointing this out. We made the changes suggested by the reviewer (Lines 5 – 13).

Comments 2: Line 20 “A total of 9262 MPs” please specify the exact unit e.g. items of microplastics.

Response 2: Thank you for pointing this out. We made the changes suggested by the reviewer.

“A total of 9262 items of microplastics were identified in the water samples” (Line 20).

3.   Comments 3: Keywords: Environmental impact. I did not see the estimation of the environmental impact of microplastics in this study, however, I found only the discussion of result regarding the impact of microplastics. So, it should not be a keyword of this study.

Response 3: Thank you for pointing this out. We changed the keyword to "drinking water" (Line 29). 

4.   Comments 4: Figure 1 please specify for example fig.1A, 1B, 1C and describe caption for each three figures.

Response 4: We changed the figure and the figure caption.

“Figure 1. Map of the study area showing the Paraíba do Sul River basin (dark gray) (A) crossing three states (MG- Minas Gerais, SP- São Paulo and RJ- Rio de Janeiro) (B) and the sampling sites (red dashed circle = Santo Antônio de Pádua city, blue dashed circle = Cambuci city and green dashed circle = Campos dos Goytacazes city) (C) in the low portion of the basin” (Lines 103-107).

5.   Comments 5: Line 198 “nMDS” should be NMDS.

Response 5: Thank you for pointing this out. We made the changes suggested by the reviewer. “A non-metric multidimensional scaling analysis (NMDS) was used to examine multidimensional spatial variation in the abundance of each plastic item among ceramic filter, tap filter, and tap water” (Line 198).

6.   Comments 6: Line 200 “a unidirectional permutational analysis” change to “a unidirectional permutation analysis”.

Response 6: Thank you for pointing this out. We made the changes suggested by the reviewer. “We compared the scores of the first axis of the NMDS among treatments using a unidirectional permutation analysis of variance with the "lmp" function, available in the "lmPerm" package in R software [44]” (Line 200).

7.   Comments 7: Please check “MPs” and “MP” throughout the manuscript. I found in some sentences (Line 204, 227, 280, 325) use “MP” Please correct.

Response 7: Thank you for pointing this out. We made the changes suggested by the reviewer.

8.   Comments 8: Results, Line 207 “171 ± 123” is an average number? If so, please specify.

Response 8: Thank you for pointing this out. We made the changes suggested by the reviewer. The values ​​described refer to the mean and standard deviation.

“mean ± SD, 171 ± 123”.

9.   Comments 9: I suggest authors should identify the sub-section in the results. For example,

3.1 MPs abundance and concentration

3.2 MPs characteristics

3.3 The relationship between MPs morphotypes abundance and filter types

Response 9: Thank you for pointing this out. We made the changes suggested by the reviewer.

4. Response to Comments on the Quality of English Language

Point 1:

Response 1: We reviewed the English language again.

Response to Reviewer Comments

1. Summary

Dear Editor and reviewers,

We would like to thank the reviewers for the positive feedback on the manuscript entitled “Are the water filters effective against microplastics?”. We are especially grateful for the thorough review that provided suggestions and contributed significantly to the improvement of the manuscript. We accepted almost all suggestions and also reformulated some paragraphs and sentences throughout the text. In this letter, we provided some point-to-point reply to some reviewer requests.

2. Questions for General Evaluation

Reviewer’s Evaluation

Does the introduction provide sufficient background and include all relevant references?

Yes

Are all the cited references relevant to the research?

Yes

Is the research design appropriate?

Yes

Are the methods adequately described?

Yes

Are the results clearly presented?

Yes

Are the conclusions supported by the results?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Reviewer 2

Comments 1: Row 113: What does 100 micro refer to?

Response 1: We appreciate the Reviewer's suggestion. The 100 micro mesh refers to two side openings in the aluminum collection cup. We have changed the sentence for better understanding.

“After the water passed through the meter, the water was directed into a 500 ml aluminum collection cup with two 4 cm diameter openings covered with 100 µ filters where the water was filtered and the MPs remained retained inside the collection cup” (Lines 115 – 118).

Comments 2: There is no reference in the text to Figure 2a and Figure 2b.

Response 2: We appreciate the Reviewer's suggestion. “For water sampling filtered with ceramic filters (candle filter = CF), two aluminum cans (35 cm height x 23 cm width) with a volume of 18L each were adapted, without epoxy varnish on the internal walls (Figure 2a-2b)” (Line 131).

Comments 3: Rows 116 - 129: Do you refer to the construction of the tap mounted filters and which are found in commerce (listed in the text row 114)? It is not clear to me if it is so, or refer to the equipment used to take samples.

Response 3: Yes, I am referring to the commercial filters that are attached to the taps.

We have modified the text for better understanding.

“Each commercial water purifier has filtering elements (activated carbon) included in the filter cartridge (candle) of the filter, a component located inside the water purifier (as described in [76]) (Figure 2d). The tap filters were: 10" high x 2.1/2" in diameter (33 cm high x 12 cm diameter); they were manufactured in pure polypropylene (non-toxic material, filter element durability = 3,000 liters of water or 6 months, maximum flow = 400 liters/hour, maximum working pressure = 7 Kgf/cm² and retention level of 5 microns). The water purifier cartridges belonged to class E of the National Institute of Metrology, Quality, and Technology (INMETRO), which indicates that the equipment retains particles between >30 and <50 µ.” (Lines 120 – 128).

Comments 4: In the case of figures 4c and 4d, different colors could be used instead of shades of gray, that cannot be distinguished between them.

Response 4: We appreciate the Reviewer's suggestion. We changed the graphics.

Comments 5: The text of the title from Figure 6 can be reduced by explaining the use of suffixes ”fi” (Fiber) and ”fr” (fragment) for each color, and not the enumeration of each type of microplastic and each color.

Response 5: We appreciate the Reviewer's suggestion. We changed the text.

“Figure 6. Mean abundance (bars) and relative contribution of MPs (circle) to the dissimilarity between CF (black bars), TF (grays bars) and TW (white bars) estimated through a SIMPER analysis. The denomination of each type of MP is given by its color, accompanied by the acronym "fi" for fibers and "fr" for fragments.” (Lines 276 – 279).

4.  Response to Comments on the Quality of English Language

Point 1:

Response 1: We appreciate the recommendation of the proofreader. We would like to point out that the English language has been revised.

Response to Reviewer Comments

1. Summary

Dear Editor and reviewers,

We would like to thank the reviewers for the positive feedback on the manuscript entitled “Are the water filters effective against microplastics?”. We are especially grateful for the thorough review that provided suggestions and contributed significantly to the improvement of the manuscript. We accepted almost all suggestions and also reformulated some paragraphs and sentences throughout the text. In this letter, we provided some point-to-point reply to some reviewer requests.

2. Questions for General Evaluation

Reviewer’s Evaluation

Does the introduction provide sufficient background and include all relevant references?

Yes

Are all the cited references relevant to the research?

Yes

Is the research design appropriate?

Yes

Are the methods adequately described?

Yes

Are the results clearly presented?

Yes

Are the conclusions supported by the results?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Reviewer 3

Comments 1: Sampling and testing of the microplastics should be clearly stated by using standard methods and approaches 

Response 1: We appreciate the Reviewer's suggestion. We have accepted the reviewer's suggestion and included the references used to perform the sampling and testing of microplastics in the recent scientific literature.

“Tap water (TW) samples were collected at each location using a metal pipe, with a small piece of latex hose attached to the upper end directly connected to the water outlet (as described in [75]), and a digital water volume meter (Joekol brand) attached to the lower end. After the water passed through the meter, it was directed into a 500 ml aluminum collection cup with two 4 cm diameter openings covered with 100 µ filters. Water samples from tap filters (TF), from brands “Ativi Filtro”, “Shop Ribeiro”, “Shophidraulica” and “Metais”, attached to faucets or pipes, followed the same water collection procedures as tap water treatment. Each water purifier has filtering elements (activated carbon) included in the filter cartridge (candle) of the filter, a component located inside the water purifier (as described in [76]) (Figure 2d).” (Line – 111).

“MPs were categorized based on color and morphotypes, with the latter divided into fibers and fragments [38]. A total of 1,472 (16%) MPs were randomly selected for polymer composition identification. MPs were analyzed using Fourier-transform infrared spectroscopy (FTIR) (detailed information in Frias et al. [39]).” (Line – 163).

Comments 2: although some filters (such as ceramic filter, PP filters) were compared, basic information about the filters (like flux, pore size, rejection rate, cleaning or lifespan, ect.,) should be clearly stated.

Response 2: We appreciate the Reviewer's suggestion. We have accepted the reviewer's suggestion.

“The tap filters were: 10" high x 2.1/2" in diameter (33 cm high x 12 cm diameter); they were manufactured in pure polypropylene (non-toxic material, filter element durability = 3,000 liters of water or 6 months, maximum flow = 400 liters/hour, maximum working pressure = 7 Kgf/cm² and retention level of 5 microns). The water purifier cartridges belonged to class E of the National Institute of Metrology, Quality, and Technology (INMETRO), which indicates that the equipment retains particles between >30 and <50 µ. For water sampling filtered with ceramic filters (candle filter = CF), two aluminum cans (35 cm height x 23 cm width) with a volume of 18L each were adapted, without epoxy varnish on the internal walls (Figure 2a-2b).” (Lines 122 – 131).

Comments 3: The measurement of various plastics should be clearly stated to as compared to the size of particles and other properties 

Response 3: We appreciated and accepted the Reviewer's suggestion.

“All particles were measured in millimeters. The MPs are normally defined as plastic particles that are less than 5 mm in their longest dimension [77], the size of the particles was measured based on the longest side of the observed particles using a scale connected to the stereomicroscope. The size of each particle was directly measured and recorded.” (Lines 156 – 159).

Comments 4: Similar performance comparison with other studies should be conducted by citing other references. 

Response 4: We appreciate the Reviewer's recommendation. However, we would like to point out that comparison between our results and those of other studies are cited throughout the entire discussion of the manuscript.

For example:

“All water samples analyzed in this study contained MPs. The average concentration of plastic items was 1.0 ± 0.45 MPs/L, with higher values observed for TW and TF compared to CF. Among all studied systems, lower MPs concentration were noted in tap water in Denmark (0.31 MPs/L) [45] and Iran (0.11 MPs/L) [17]. However, studies in Brazil have found much higher MP concentration in drinking water (~100 MPs/L, Sinos River, [19]; Paranoá lake [18].”

“The composition and concentration of MPs differed among the analyzed treatments, rejecting the null hypothesis. Lower concentration and richness of MPs were observed in CF water compared to TW and TF, respectively. Sturm et al. [50] describe that such purification systems are generally made of plastic materials, and that over time and due to the lack of maintenance of internal parts, the degradation of plastic components produces MPs that are incorporated into the water flow [50]. Drinking water treatment plants (DWTPs) present an important contribution in retaining MPs from raw water (water captured from rivers and streams) [51]. Studies conducted in three DWTPs in the Czech Republic demonstrated the removal of 70 to 83% of MPs (>100 μm to 1 μm) with water treatment comprising coagulation/flocculation, sedimentation or flotation, as well as sand and activated carbon filtration [15], revealing the presence of up to 628 ± 28 MPs/L of treated water, of which 95% of the MPs were smaller than 10 μm [15].”

“The higher presence of smaller-sized MPs (< 500 µm to 1 mm) in our results can be explained by the presence of grooves in the external wall of the ceramic filters. We observed the presence of recesses between the base of the ceramic structure and the plastic disc that supports this structure, which is still attached to the overall filter structure by plastic nuts, washers, and threads, allowing the passage of smaller MPs. However, Ingram [54] highlights that the Brazilian clay filter is the most effective purification system on the planet, considering that the composition of the filtration chamber and ceramic candles are effective in retaining chlorine, pesticides, iron, aluminum, in addition to retaining 95% of lead in the water and 99% of the protozoan Cryptosporidium, which causes diarrhea and intestinal infections [54]. Thus, ceramic filters seems also an excellent option for home MPs filtration, however they require regular maintenance and cleaning to maintain working quality.”

4.  Response to Comments on the Quality of English Language

Point 1: The English could be improved to more clearly express the research.

Response 1: We appreciate the recommendation of the proofreader. We would like to point out that the English language has been revised.