the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Oct 2024
A quantitative assessment of the behavior of metallic elements in urban soils exposed to industrial dusts near Dunkirk (Northern France)
Abstract. In urban and industrialized areas, soil contamination and degradation caused by the deposition of industrial dusts may pose significant health and environmental risks. This problem relates to the vertical mobility and bioavailability of Potentially Toxic Elements (PTE). This study investigates the fate of PTE brought by industrial dusts in urban soils located in the Dunkerque agglomeration, one of the most industrialized areas of France. Four soil short cores were collected in the city of Gravelines (Dunkerque agglomeration) following a gradient from the industrial emitters to the deposition site. The soil cores were cut into discrete 1-cm-sections to study their PTE concentrations (using ICP-AES/MS analyses). Single HCl extraction was performed to evaluate the mobility of PTE in soils and to discuss their specific behavior according to the current soil parameters. For this purpose, the main soil parameters were identified (grain-size distribution, mineralogy, pH, CEC, TOC, calcium carbonates and water contents) in addition to the soil chemical composition (XRF, ICP-AES/MS analyses). The studied soils revealed globally low absorbent capacities for pollutants (CEC averaging 5.3 meq/100g), partially counterbalanced by the buffering effect of calcium carbonates (contents ranging from 8 % to 30 %). We highlighted minor (1<EF<3) to moderately severe (5<EF<10) Enrichment Factors in industrial PTE (Cr, Ni, Mo, Mn, Cd, Zn), in the first 3 centimeters of the soils located near the industrial emitters. The contamination profiles of these soils are concordant with atmospheric inputs of metallurgical dust. Using a relatively strong leaching reagent (HCl 1M), we estimated a low vertical mobility for Cr, Ni and Mo (average leached ratios <25 %) in soils, suggesting that these industrial PTE mainly occur in refractory phases (natural or anthropogenic). Mn, Cd and Zn, related to industrial and/or urban sources, present a higher mobility (average leached ratios > 60 % for Mn and Cd, and averaging 44 % for Zn). Our study points out the stability of industrial PTE in soils under current physicochemical conditions (calcareous soils with a slightly basic pH of 7.8). In this context, the monitoring of industrial PTE in these urban soils is highly recommended, considering (1) the presence of allotment gardens in the vicinity of the emitters and (2) the potential evolution of soil conditions as a result of increased flooding events.
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RC1: 'Comment on egusphere-2024-1875', Anonymous Referee #1, 18 Nov 2024
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In this paper, Casetta et al. present an in-depth study of four soil cores collected from an area predominantly contaminated by industrial dust deposition from the historic industrial seaport of Gravelines, located in the Dunkerque region. The study investigates the potential vertical mobility within the soil profile and the bioavailability of several Potentially Toxic Elements (PTEs) (e.g., Cr, Mn, Ni, Cu, Zn, Mo, Cd). This is achieved through a detailed analysis of the physico-chemical properties, organic matter content, and mineralogical and clay mineral composition at 1 cm intervals along the soil cores, providing a substantial amount of data.
While the soil properties are comprehensively presented in the results section, the information on PTEs is primarily addressed in the discussion. This creates a discussion section that is a mixture of both results and discussion. The authors seem to aim for a clear separation between a descriptive results section, focused on soil core characterization, and a result/discussion section that focuses into the study's main topic. However, this approach renders the discussion somewhat complex, as it includes extensive numerical data that can obscure the key findings (e.g., sections 4.1.1 and 4.1.2). In contrast, certain paragraphs that blend results and discussion more moderately, such as section 4.2.2, are effective. Reorganizing the discussion, by moving some to results section and to integrate findings more seamlessly could significantly enhance the paper's readability and the accessibility of its conclusions. A revised structure for the discussion section would better highlight the article's valuable insights.
Overall, this paper presents significant and timely findings regarding the management and future use of contaminated soils in the face of environmental pressures such as flooding and erosion. However, I recommend a ‘Major Revision’ to improve the article’s structure, thereby enhancing its clarity and its ability to engage the intended audience.
Specific comments:
Introduction
L61: “Contamination metals are generally…” - Contamination or contaminant metals?
L62: “Considering that sources of contamination are multiple, but that some PTE are characteristics of local and industrial dust, the main question concerns their vertical mobility” - Are the PTE coming from local industrial dust or are they both local and from industrial dust? Although I understand the logic and I agree with the above and the following, it's a bit rushed. In what way the local and industrial source of PTE are a reason to study their vertical distribution?
L70-71: “were established for better constrain” – to better constrain
L84-86: “According to the pedological classification of the French Association for Soils Study, the soils of Gravelines can be ascribed to “Thalassosols”, characteristic of a pedogenetic evolution on marine formations (Baize and Girard, 2009; GIS Sol and RMT Sols et Territoires, 2019).” - Perhaps you could add the WRB equivalent of the French classification if it is provided in the AFES 2008 Référentiel pédologique. By definition, Thalassosols develop on marine or fluvio-marine alluvial deposits which is a bit different from ‘marine formations’, is that what you meant?
L86: “In the highly populated studied area” – In the/this highly populated study area? I may not have understood
Results: From my understanding, conventionally, results are described using past. However, if no other reviewer has pointed this out, ignore my comment.
L.230-231: “Maxima CEC values are measured in the subsurface of cores 3 and 4 (7.3 and 7 meq/100 g, respectively) while minimum CEC is measured in core 2 [10-11cm] (3.5 meq/100 g).” – Could you indicate depths for both maximum and minimum CEC value to be more consistent.
Figure 2: It might be better to use two different colour scales between the total mineralogical composition and clay minerals composition since it could be confusing (same color for calcite and illite, quartz and smectite).
L255 “…as a global loamy texture…” – Maybe you could be more precise, one of the main features of Thalassosols is that they have a fine grain size (<50µm, as you mentioned: loamy) along the soil profile and continuous presence of carbonates.
Discussion
4.1.1 Reactivity of organic matter in the studied soils (L290-305) – Why are the results of the organic matter analysis presented in a Discussion? This paragraph is a Results/Discussion paragraph. To be consistent with the chemical and mineralogical description of the soil cores, it would be better to move the description of the Van Krevelen diagram to the Results section, even though it will be quite short, and leave its interpretation to the Discussion section. Perhaps you could spend more time introducing and discussing the differences between core 2 and the other three cores.
4.1.2 Discrimination of cores by the reactivity of their absorbent complex (LL. 311-331). Similar comment that for the previous sub-section. It is a mix between Results and Discussion sections.
4.2.1 Highlighting atmospheric PTE inputs in the soils of Gravelines (LL. 340-348). This paragraph is a more a result paragraph than a discusssion one.
L 397-408 - This could be covered first in the methodology and discussed again here, though it is a little surprising to present the entire methodological justification for discussion.
Table 5. As this table introduces the potential origin of elements and their mobility in soils, which is one of the main messages of this paper, it should be presented in the introduction or M&M section to justify the studied elements.
4.3.3 “relative immobility of these harmful elements” - I agree with the low bioavailability, but the introduction and conclusion list other risks such as increased frequency of flooding or use as a garden (children playing with soil, growing root vegetables). What about these risks? Perhaps these risks and potential pathways should be mentioned in the discussion, not just in the introduction and conclusion.
Citation: https://doi.org/10.5194/egusphere-2024-1875-RC1
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