Monitoring of Respiratory Health Risks Caused by Biomass Storage in Urban-Type Heating Plants

Round 1

Reviewer 1 Report (New Reviewer)

Dear Authors

The study aimed to monitor the concentration and identify phytopathogens in wood chip storages at urban heating plants. The research was conducted between 2017 and 2022 at three municipal heating plants in Slovakia's central region. These heating plants store biomass in large piles. The study involved taking samples annually from the pile surface and a depth of 0.5 m. An accredited laboratory tested the samples for moisture and microbial content. The authors analyzed these data. The average number of phytopathogen colonies did not differ significantly between the years. The most frequently recorded species in terms of occurrence in individual years and samples were Mycelia Sterilia, Penicillium sp., Aspergillus brasiliensis, Aspergillus unguis, and Yeasts, and the species of Penicillium and Aspergillus had the highest number of colony-forming units per gram. Based on the study's results, the authors postulate establishing legislative frameworks and work procedures for individual activities to mitigate these risks.

After reading the article, I have some minor comments for consideration by the authors:

1.       I propose to shorten the title, removing the "smaller urban-type" phrase. Instead, "Monitoring of respiratory health risks during biomass storage in smaller urban-type heating plants" better: "Monitoring of respiratory health risks caused by biomass storage in heating plants". I leave this issue to the authors' decision.

2.       The study aim is "The goal of our work was long-term monitoring of the concentration and identification of phytopathogens in wood chip storage piles, in urban-type heating plants. Based on the obtained results, the aim was also to determine the potential health risks for the workers of the plants and residents in the vicinity of these facilities. The results should contribute to the introduction of effective countermeasures and proposals for possible changes in legislation.". I propose to rephrase, according to the SMART methodology. In my opinion, "the long-term monitoring" and "identification of phytopathogens" is not the aim, but the method. Maybe "The study aims to identify health risks and propose effective countermeasures and legislative changes related to wood chip storage at urban heating plants for workers and residents." I leave this issue to the authors' decision.

3.       Lines 101-103: The sentences "Samples from the given place were always taken in 2 specimens. One specimen was used for microbiological analysis and the other specimen for determination of relative moisture content" are generally correct, but I propose "Two specimens were always collected from each sampling location, with one specimen used for microbiological analysis and the other for determining the relative moisture content." as more specific. I leave this issue to the authors' decision.

4.       Line 105: References to literature nos. 18 and 19 seem to be cited incorrectly (in the wrong place). None of these publications describe the method or results of moisture content measurement (references to the appropriate literature are given in ref. 18)).

5.       I propose unifying the vertical axes' descriptions in Figures 3, 4, 5, 6 and 7. (Additionally, I propose to correct "Nr."; an example Figure 5 "Storage Nr."? correctly "Storage No.")

Despite my reservations in the comments, the article is very interesting, presents original research results, and will potentially interest other researchers. It is worth publishing after making corrections to the content.

Sincerely,

Author Response

I propose to shorten the title, removing the "smaller urban-type" phrase. Instead, "Monitoring of respiratory health risks during biomass storage in smaller urban-type heating plants" better: "Monitoring of respiratory health risks caused by biomass storage in heating plants". I leave this issue to the authors' decision.

We have partially modified the title. In our opinion, the urban-type connection is important in terms of the impact of risks on potential urban built-up near the heating plants and the negative impact on residents.

2. The study aim is "The goal of our work was long-term monitoring of the concentration and identification of phytopathogens in wood chip storage piles, in urban-type heating plants. Based on the obtained results, the aim was also to determine the potential health risks for the workers of the plants and residents in the vicinity of these facilities. The results should contribute to the introduction of effective countermeasures and proposals for possible changes in legislation.". I propose to rephrase, according to the SMART methodology. In my opinion, "the long-term monitoring" and "identification of phytopathogens" is not the aim, but the method. Maybe "The study aims to identify health risks and propose effective countermeasures and legislative changes related to wood chip storage at urban heating plants for workers and residents." I leave this issue to the authors' decision.

Thank you for the valuable suggestion. We change the work aim according to your recommendation.

3. Lines 101-103: The sentences "Samples from the given place were always taken in 2 specimens. One specimen was used for microbiological analysis and the other specimen for determination of relative moisture content" are generally correct, but I propose "Two specimens were always collected from each sampling location, with one specimen used for microbiological analysis and the other for determining the relative moisture content." as more specific. I leave this issue to the authors' decision.

Was changed, according to your recommendation.

4. Line 105: References to literature nos. 18 and 19 seem to be cited incorrectly (in the wrong place). None of these publications describe the method or results of moisture content measurement (references to the appropriate literature are given in ref. 18)).

The reference numbers were corrected.

5. I propose unifying the vertical axes' descriptions in Figures 3, 4, 5, 6 and 7. (Additionally, I propose to correct "Nr."; an example Figure 5 "Storage Nr."? correctly "Storage No.")

The figure axis descriptions were modified.

Despite my reservations in the comments, the article is very interesting, presents original research results, and will potentially interest other researchers. It is worth publishing after making corrections to the content.

Author Response File: Author Response.docx

Reviewer 2 Report (New Reviewer)

The paper submitted for review presents the results of monitoring the presence of phytopathogens in wood chip storage facilities located in various parts of Slovakia. Monitoring was carried out over several years. In the process of monitoring the state of mold in the composition of wood chips, mold fungi were identified, e.g. such as Aspergillus sp. or Penicillum sp., which produce spores with a respilable fraction - i.e. dangerous for the respiratory tract.

In the discussion of the work, I miss the reference to the normative guidelines (if they exist in Slovakia), which indicate what level of microbiological contamination is safe and what is already a threat to health.

In some countries such guidelines exist, e.g. regulations of the Minister of Health. If there are no such guidelines, it can refer to global guidelines.

The work also lacked important results of monitoring the microbiological quality of air, confirming that the presence of fungus in the biomass of wood chips has a clear impact on air quality (or exclude it).

Author Response

The paper submitted for review presents the results of monitoring the presence of phytopathogens in wood chip storage facilities located in various parts of Slovakia. Monitoring was carried out over several years. In the process of monitoring the state of mold in the composition of wood chips, mold fungi were identified, e.g. such as Aspergillus sp. or Penicillum sp., which produce spores with a respilable fraction - i.e. dangerous for the respiratory tract.

In the discussion of the work, I miss the reference to the normative guidelines (if they exist in Slovakia), which indicate what level of microbiological contamination is safe and what is already a threat to health.

These guidelines and legislation are characterized in the introductory part of the manuscript. In general, there are currently no legislatively defined levels of these phytopathogens when storing biomass. For phytopathogens, most species are classified in group no. 2: groups that can cause disease in humans and could pose a hazard to workers but are not likely to spread in the population, where effective prophylaxis or treatment is usually available. Most of the species occurring during biomass storage are also indicated for the development of allergic diseases. However, permissible values and levels of exposure to these harmful factors are not specified in the legislation.

In some countries such guidelines exist, e.g. regulations of the Minister of Health. If there are no such guidelines, it can refer to global guidelines.

Some guidelines used in the world have been added to the discussion section.

The work also lacked important results of monitoring the microbiological quality of air, confirming that the presence of fungus in the biomass of wood chips has a clear impact on air quality (or exclude it).

The level of airborne spore concentration was not investigated. As outlined in the final part, this research is planned in the next steps, as long as the research projects are successful. We do not yet have accreditation or equipment for such monitoring. Similar research was carried out in the cited work.

Barontini, M.; Crognale, S.; Scarfone, A.; Gallo, P.; Gallucci, F.; Petruccioli, M.; Pasciaroli, L.; Pari, L. Airborne fungi in biofuel wood chip storage sites. Int. Biodeter. Biodegr. 2014, 90, 17-22. doi: 10.1016/j.ibiod.2013.12.020.

 This research demonstrated that spore concentrations are much lower in the air than in stored material.

Author Response File: Author Response.docx

Reviewer 3 Report (New Reviewer)

1.       The background statement in the ‘Introduction’ should focus the problems and latest research related to goal of this study all over the world.

2.       Line 78.  Why the heating plants were selected in the central part of Slovakia? There will be more meaning if the distribution of the heating plants is wider in the country?

3.       Line 87. Why the samples are different from the pile surface and a depth of 0.5m?

4.       Line 90. The sampling locations should be fixed to obtain the accurate results.

5.       Line 105. The moisture content of the samples are the average value, did you measured the moisture content of each or several ships to judge the deviation of moisture content in chips?

6.       Line 110, why did you calculate the relative moisture content, but not absolute moisture content (based on oven-dry weight of samples)?

7.       Please adjust the format of all Figures.

8.       Line 153, herein you just analyze the effect of moisture content, do you consider the number of phytopathogens is affected by other possible factors?

9.       Line 158, the orange bar in Figure 4 in 2018 is quite long compared with others, did you analyze the possible reasons for the significant difference？

10.   Line167, symbol a and b should be attached in Figure 5 to be more readable. And did you compare the date in Figure 5 (left)?  Are there significate differences between them?

11.   Did you analyze or find the change rule of the date in Figure 4, 6 and 7?

12.   Try to explain reasons in all discussion sections corresponding to the results obtained.

Author Response

1. The background statement in the ‘Introduction’ should focus the problems andlatest research related to goal of this study all over the world.

In the Introduction, we focused primarily on the problems related to the storage of biomass, especially in the European context (works from Hungary, Croatia, Germany, Italy, and the Nordic countries are cited). Examples of solutions from Canada and Kuwait are also presented. Based on this, we dare to say that the overview at this level can be considered global. Greater emphasis is placed primarily on European conditions, mainly because of similar legislation, business conditions, and the like.

2. Line 78.  Why the heating plants were selected in the central part of Slovakia? There will be more meaning if the distribution of the heating plants is wider in the country?

The explanation was added to the methodology part.

3. Line 87. Why the samples are different from the pile surface and a depth of 0.5m?

The explanation was added. “We chose two sampling height levels because the temperature and moisture characteristics of the stored biomass change fundamentally just below the surface and we wanted to verify the effect of these different conditions on the number of phytopathogen spores produced.”

4. Line 90. The sampling locations should be fixed to obtain the accurate results.

Fixed sampling points would not be of practical importance, mainly because the volume, shape, and location of biomass continuously change over time with the continuous intake and consumption of wood chips for use. Therefore, we chose rather place the sampling points so that they cover the entire area of the stored pile evenly.

5. Line 105. The moisture content of the samples are the average value, did you measured the moisture content of each or several ships to judge the deviation of moisture content in chips?

The moisture content was measured for each sample taken exactly according to the laboratory procedure established by the standard

6. Line 110, why did you calculate the relative moisture content, but not absolute moisture content (based on oven-dry weight of samples)?

Relative moisture content is an important parameter in terms of evaluating the energy properties of fuel (biomass). Absolute moisture content is used in the wood processing industry for other uses of wood such as energy purposes. And it is based on valid legislation - standards.

7. Please adjust the format of all Figures.

The figure format has been modified (axis names, scales). Some graphs are a specific output of the statistics software and have a different graphic output than graphs from MS Excel.

8. Line 153, herein you just analyze the effect of moisture content, do you consider the number of phytopathogens is affected by other possible factors?

Analysis of the causative factors of a number of phytopathogens was not the goal of our work. However, we have already dealt with such an analysis in our previous works and did not want to repeat the findings. See works:

1. Lieskovský, M.; Gejdoš, M.; Messingerová, V.; Němec, M.; Danihelová, Z.; Moravčíková, V. Biological Risks from Long-Term Storage of Wood Chips. J. Environ. Stud. 2017, 26(6), 2633-2641. doi: 10.15244/pjoes/70630.
2. Gejdoš, M.; Lieskovský, M. Wood Chip Storage in Small Scale Piles as a Tool to Eliminate Selected Risks. Forests 2021, 12(3), 289. doi: 10.3390/f12030289.
3. Suchomel, J.; Belanová, K.; Gejdoš, M.; Němec, M.; Danihelová, A.; Mašková, Z. Analysis of fungi in wood chip storage piles. Bioresources 2014, 9, 4410–4420.
4. Gejdoš, M.; Lieskovský, M.; Slančík, M.; Němec, M.; Danihelová Z. Storage and Fuel Quality of Coniferous Wood Chips. Bioresources 2015, 10(3), 5544-5553.

9. Line 158, the orange bar in Figure 4 in 2018 is quite long compared with others, did you analyze the possible reasons for the significant difference？

There is no logical reason for this significant difference. It may have been sample contamination, which is highly unlikely given the way the samples were collected and analyzed. It was probably a very specific material from a certain production location, where other technologies and methods of transportation and storage could have been used. However, we cannot obtain or verify this information from the company.

10. Line167, symbol a and b should be attached in Figure 5 to be more readable. And did you compare the date in Figure 5 (left)?  Are there significate differences between them?

Figure 5 was divided into two figures 5 and 6. and a comment in the text was added

11. Did you analyze or find the change rule of the date in Figure 4, 6 and 7?

Figure 4 evaluates the development of the number of phytopathogens at individual landfills during individual years. Figures 6, and 7 evaluated the identified amount of individual phytopathogen species during the entire monitored period. From the point of view of the effect of permanent health risks, this statement seemed to us to be the most appropriate. We could also add pictures of the development of the number of specific phytopathogens in individual years. However, the number of images in the manuscript would fundamentally have to increase, and we are concerned about the subsequent clarity and comprehensibility.

12. Try to explain reasons in all discussion sections corresponding to the results obtained.

In some cases, the explanations would be pure speculation, not based on scientific evidence. In some cases, the directly discussed works explain the reasons. The goal was to demonstrate whether such threats persist in the long term even with the constant circulation of biomass in storage.

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear Authors,

I read your article and with great interest.

The subject of research is very interesting and extremely important in the foreign energy transformation.

I got the impression that you paid a lot of attention to the analysis of the collected data, very good.

Nevertheless, I recommend performing and adding deeper statistical analyzes of the collected data. The use of statistical tests to highlight the relationship between individual factors would increase the substantive value of the article.

In my opinion, the article is well and professionally written and I have no further comments.

Best regards,

Reviewer.

Author Response

Dear reviewer,
thanks for your general review. However, the character of the results and the aim of the manuscript was not to point out the influence of individual factors on the occurrence and number of colonies of individual fungi species (we have already published several works in this area that sufficiently analyzed these causal connections). The aim of the article was to verify whether increased concentrations of phytopathogens are found in piles for a long time (even if there is a continuous supply and removal of biomass) and especially which types of phytopathogens prevail in these piles for a long time. We would be grateful if you could advise us on how to statistically analyze these results since it is only a question of revealing the causal relationship between time versus content and type of phytopathogens.