Review of 'Plastic agriculture using worms: Augmenting polystyrene consumption and using frass for plant growth towards a zero-waste circular economy.'

15 Sept 2020

Dear Editor,

We thank you and the reviewer for the helpful comments to our paper entitled “Plastic agriculture using worms: Augmenting polystyrene consumption and using frass for plant growth towards a zero-waste circular economy”.

            Please see below our responses to the reviewers’ comments in blue. We have done our best to incorporate the many helpful suggestions, and in the areas that we are unable to, we have given our responses in bold as below.

Thank you.

1. The main innovation of this research seemed to be the utilization of worm frass to enhance the growth of dragon fruit cacti and the circular zero waste economy. In Introduction section, the authors didn’t give the description of the previous researches on the worm frass utilization and the related information about circular economy. The authors may consider to supply the background of this part.

Response: While circular economy is an innovation aspect of our article, the use and characterization of condiments to augment the PS consumption is our focus, as that was something not previously performed. On the circular economy, we have cited Houben et al where their article used mealworm frass (not fed on plastic) to demonstrate a circular economy. The sentence with the citation is shown in tracked changes.

2. It is hard to recognize the difference between facilitation of rooting with several media from Figure 4, so it would be better to provide more pictures or data to illustrate the rooting situation. Besides, letter ‘b’ appeared twice in the caption of Figure 4A describing as “tea leaves (a,b), Bran (b,f)”. The authors may check and revise it.

Response: We thank the reviewer for the pointing this out and we have corrected Figure 4 as well as added more figures in supplementary.

3. Figure 1C showed the setup of the dragon fruit cacti with different media, but the size of these dragon fruit cacti seemed to be different. Were these the initial dragon fruit cacti? If so, then it would be more accurate if the initial dragon fruit cacti is similar in size while investigating the effect of the media on the growth of dragon fruit cacti.

Response: We have to the best of the available off-shoots, picked as similar as possible. Due to natural variability of the off-shoots, there will be natural variance in height. As we picked the off-shoots, all of them did not have lower roots, and are equally capable of rooting. All the dragon fruit cacti were from the same pot expanded over four years.  Since it was the change in height, we believe the original variance in height would have negligible impact. We have expanded the description of the plants in M&M.

4. Data supplied in the Table S1 showed the average change in worm weight in the unit of gram for control SW was 0, but the average change in worm weight in the unit of % for the same group was -0.04. This can cause confusion because if the average change in worm weight is 0 g, it should be 0 % as well. The author may check the data, or provide the explanations in detail.

Response: We note the confusion and have re-made the table to demonstrate the change in height. The p-values are based on comparison.

5. The heights of dragon fruit cacti for tea leaves group and bran group were different, however, the mean changes in height comparing the mealworm frass group to both tea leaves group and bran group were the same (-0.43 cm displayed in Table S2). It seems to be unreasonable. Superworm frass group was in the same situation. The authors may check the data, or provide the explanations.

Response: We note the confusion. The numbers -0.43 were the change in heights for cacti treated with Mealworm frass.  We have reformatted Table S2 to better reflect this and to avoid confusion.

6. The discussion was relatively comprehensive, but was a little verbose and not logically expressed. The authors may reorganize the discussion section by adding subtitles.

Response: We have re-written the discussion and added subtitles.

7. In the Results section of GC-MS analysis, there were a few sentences describing the goals of performing GC-MS and the experimental process (line 207-210), which would be better to move to the Materials and methods section.

Response: We have moved the sentences to the M&M section.

8. Further research on whether the bioaccumulation of plasticizers or other plastic-derived chemicals occurred is necessary and important to be verified before this circular zero waste strategy could be practically applied, as the authors mentioned in the Discussion section. Besides, the microplastics should also be considered since they may form when the PS balls were chewed by the worms. Microplastics may also accumulate in the worm body and frass, and cause negative effect on the plant growth or involve in the food chain. Only GC-MS were performed to verify that no toxic by-products formed in the frass seemed to be insufficient, and more characterizations were suggested to be performed.

Response: We have added a sentence pointing to a paper that showed that microplastics are indeed present in the frass, and that we did not detect by GC-MS. We have expanded the limitation of our characterization of the frass beyond GC-MS and acknowledged, as well as suggested possible remediation methods to get rid of microplastics when applied for wide-use, such as the tiered breeding method.

9. The sentence in line 280 was not expressed clearly, and the authors could reconsider the expression of this sentence.

Response: We have edited the sentence in question.

10. It is suggested that the detail citations should be supplied to the method of GC-MS analysis.

Response: We have added the citation to the “GC-MS analysis of superworm frass” methods section.

11. The retention time were overlapped in the Figure 5 which was difficult for the readers to recognize. The background of this figure was black. The authors could make some revisions to improve this figure.

Response: We have updated the figure.

Thank you for your comments.

Sincerely yours,

Samuel Ken-En Gan

On behalf of all the authors