The article “Mercury contamination in staple crops impacted by Artisanal Small-scale Gold Mining (ASGM): Stable Hg isotopes demonstrate dominance of atmospheric uptake pathway for Hg in crops” examines Hg in soil, crop, and atmosphere in the vicinity of ASGM operations. Authors measure THg and MeHg concentrations, as well as isotopic measurements of Hg. The paper is well written and data is clearly presented and discussed.

General comments:

The sampling design is well-structured, with multiple environmental sample types. The samples themselves are very valuable, as ASGM sites are understudied in the context of the global Hg cycle. The drawback of the study is that the number of samples per environmental sample type (soil, air, crop) is quite low, as the authors themselves state. Nonetheless, the authors used multiple analytical approaches to make the best use of these samples and the study is valuable for readers of Biogeosciences and researchers in the field, with minor corrections needed.

Specific comments:

Section 2.5.2. In the best practices for the analysis of Hg isotopes (e.g., as outlined in Blum et al., 2017: https://doi.org/10.2138/rmg.2017.82.17), the importance of using Tl internal standard is well explained. The authors do not report using Tl internal standard for their Hg isotope analysis. What is the reasoning behind not using it? In published syntheses of Hg isotopic work, studies conducted without the use of Tl internal standard are often excluded from data analysis.

Line 297:  The d202Hg value of 0.29 ± 0.98 ‰ for Farm 1 does not indicate low variability as the authors state, ~1 ‰ SD is quite high for Hg isotopes. Please rephrase this discussion accordingly.

Lines 319-324: This paragraph seems out of place, fitting more to the introduction part into the justification for the chosen experimental design/methods (or somewhere else, but not here).

Lines 397-398: The subtraction of MDF for the soil-to-shallow roots (from Yuan et al 2022) is explained in supplementary material section S4. But until carefully reading the supplementary section, this subtraction is quite unclear to the reader, disturbing the reading flow. The authors should add a succinct explanation for this subtraction in the main text in lines 397-398.

Lines 221-225, 392-395: The PTD analysis for Hg is not very robust. Therefore, authors should note that the conclusions they draw from these analyses are speculative (also in the discussion of the results, lines 392-395). Additionally, the term “speciation” is used too loosely, as speciation is, by definition, qualitative or quantitative measurement of chemical species, while in this case, there is no information about what the measured species are. Please replace “speciation” with “analysis” or “PTD analysis” in places where referred to PTD analysis, throughout the text.

Lines 484-488: Would it make sense for future research to include some livestock near ASGM farms? Hg isotopic signatures in the livestock tissues could tell a very interesting story too. It could be worth mentioning in the text.

Section S3 and Figure S8: Authors mention certain reference standards were used for PTD analysis. Where can the reader see these desorption results for reference standards? The point of using these standards is to see if the desorption peaks of samples overlap with some desorption peaks of Hg standards. Why are the standards not shown then?

Table S7.3: It would be clearer if authors wrote “Peanut soil 1, Peanut soil 2, …” to make it clear that these are soil analyses and not crop analyses.

Technical corrections:

Line 31: “significantly high” should be “higher”

Line 40: “soil derived” should be “soil-derived”

The manuscript describes a study on the distribution of Hg in soil, plants and the atmosphere near a ASGM mining site in Nigeria. The authors determined total and methyl Hg as well as stable Hg isotopes in soil, the atmosphere (by passive samplers (MerPas) as well as different parts of three types of edible plants with the aim to evaluate Hg levels in the plant and to track pathways of Hg uptake by the plants. Samples were taken near the mining site and at two farm sites (one reference site) situated at different distances from the mining site. The authors can show that the atmosphere, soil, and all edible plants are clearly affected by GEM emissions from the ASGM site. However, total and methyl Hg concentrations in all plant tissues were below reference dose thresholds.

Hg isotope analyses coupled with a two-endmember mixing model reveal that most Hg in plants are derived from atmospheric GEM uptake via foliage although crop roots appear to be to a larger extent influenced by Hg uptake from soil.

ASGM is seen as the most important todays anthropogenic Hg emission source to the environment. Besides its role in the global Hg cycle, investigations on the exposure of local people to ASGM Hg emissions, especially through crops, has been rarely investigated. Thus, the presented study is timely and important.

The study presents a comprehensive data set. I like such multi-proxy approaches as they offer deeper insights into the local biogeochemical cycling of Hg and disperion pathways. The manuscript is well written although I think that some parts esp. the abstract and the introduction could be shortened.

The authors mentioned that Hg isotopes are used for both, evaluation of Hg species transformation processes and for tracking contamination or uptake pathways. In this sense, I believe that the interpretation of the Hg isotope data is probably not as robust as it seems. Especially because there is actually only a single Hg source which is GEM and Hg isotope fractionation proceeses in soils and plants are far from beeing completely known/understood. May be the authors could address this point in their discussion, although I don’t think that this will change the overall message of the study.

The manuscript entitled "Mercury contamination in staple crops impacted by Artisanal Small-scale Gold Mining (ASGM): Stable Hg isotopes demonstrate dominance of atmospheric uptake pathway for Hg in crops" by Eboigbe et al. examines the biogeochemical cycling of mercury and uptake mechanisms in selected crops in areas contaminated with mercury due to ASGM. In light of the fact that ASGM represents the largest anthropogenic source of Hg today, and that due to the illegal nature of the ASGM activities, such areas are understudied, this contribution is very welcome and provides new valuable insights for scientific community.

Overall, the manuscript is very well and clearly written and logically structured. Appropriate complementary analytical methods are used, and the data are appropriately and adequately interpreted and evaluated in light of previous related studies. Therefore, I consider the article suitable for publication in the journal Biogeosciences. Regarding the content, I have only one general suggestion, namely that a section on the limitations of the studies be added to the discussion, where the aforementioned restrictions during sampling are critically evaluated and, on this basis, appropriate recommendations for future studies are made.