PONE-D-22-05415Fragmentation of hunting bullets observed with synchrotron radiation: Lighting up the source of a lesser-known lead exposure pathwayPLOS ONE

Dear Dr. Leontowich,

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Please specifically focus on the comments from Reviewer #1 which request expansion of the discussion of the limitations of the study. Also, please note an important potential correction identified by Reviewer #2 in equation 1. 

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: N/A

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: The authors used synchrotron K edge subtraction imaging to investigate the fragmentation of a traditional lead-core bullet after impact on ballistic gelatin and compared it with the fragmentation of a copper bullet. The synchrotron K edge subtraction imaging method was applied the first time on this subject and allowed to image specifically the lead fragments. A statistical analysis of the size distribution of the lead particles down to particle sizes of a few micrometer showed for the first time that the vast majority of particles is smaller than detectable by visual inspection.

The study is very clearly and carefully written, technically sound and the topic is of relevance for human health and environment.

However, the study has some limitations in my view, which the authors should comment on:

1. The study is based only on four impacts: two with a lead-core bullet (with and without bone), and two with a copper bullet (with and without bone).

a. It is not clear whether the results of this particular lead-core bullet can be generalized to all or other popular types of lead-core bullets.

b. It is not clear whether this single impact is representative for this bullet type.

c. It is not clear whether the fragmentation is the same for ballistic gelatin, which is used in the study, and for a real big game animal.

2. The synchrotron K edge subtraction imaging method is standard at synchrotrons. The novelty of this study lies therefore exclusively in its application. Would the method also work with similar sensitivity on real big game animals? Please comment on expected limitations.

3. What is the market share of lead-core bullets compared to nonlead-core bullets today? Are lead-core bullets still relevant?

4. In line 346 ff you reason about the maximum extent that fragments may be distributed in a harvested big game animal. I suggest to use your data to compile a size dependent radial distribution of the fragments (of cause you only have the measurement of the projection of the distribution, estimate the effect).

In conclusion, the publication of the study is recommended. The comments should be considered. In the best case it helps to expulse lead-core bullets worldwide. Whether PLoS ONE is the appropriate journal is to be assessed by the editor.

Reviewer #2: In the paper, KES imaging is used to identify lead bullet fragments in animal remains among other metal (copper) and bone fragments. High resolution capabilities of the technique is also evaluated. A comparison with the widely diffused medical radiography imaging shows the advantages of the synchrotron KES imaging.

Material and methods are well discussed and results fully reproducible. Bibliography is up-to-date and pertinent. Text is clear, logical and well written.

Just a few remarks: in eq.1 line 206, “t” where (line 208) “t is thickness (cm)” makes no sense. It should be lambda, i.e. mass thickness in g/cm2.

I would move line from 266 to 292 in the Introduction (it’s basically bibliography) The same for lines from 324 to 333 and from 338 to 345.

ImageJ software needs to be described in the Methods.

Is the last paragraph “Alternatives to traditional rifle ammunition” really required in a research paper like this? I feel it’s redundant.

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Reviewer #1: No

Reviewer #2: Yes: Matteo Donghi

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Fragmentation of hunting bullets observed with synchrotron radiation: Lighting up the source of a lesser-known lead exposure pathway

PONE-D-22-05415R1

Dear Dr. Leontowich,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Christopher James Johnson, Ph.D.

Section Editor

PLOS ONE

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