Fibrous Ferrierite from Northern Italy: Mineralogical Characterization, Surface Properties, and Assessment of Potential Toxicity
, Paolo Ballirano 2, Alessandro Pacella 2, Michela Cangiotti 1, Fulvio Di Lorenzo 3, Laura Valentini 4, Maria Assunta Meli 4, Carla Roselli 4, Ivan Fagiolino 5 and Matteo Giordani 1Round 1
Reviewer 1 Report
Dear Authors,
your manuscript provides a valuable set of data on morphology, crystal structure, mineral-chemistry, and surface activity of fibrous ferrierite in filled vesicles within altered basalts, Tertiary in age, from Vicenza area (Veneto, Northern Italy). I can see that you used adequate analytical methods following Gualtieri et al. (2018: Am. Min. 103, 1044-1055). However, some of your conclusions are only working hypotheses. In general, concluding a given scientific research with one or more hypotheses is a normal circumstance, and should not weigh on the evaluation of the work. Nevertheless, the conclusions reported in this manuscript have implications in the social field as a potential cause of alarm and anxiety in the inhabitants of the Veneto or even of all of northern Italy. On this reason I suggest that only firm conclusions should be reported in this paper.
More precisely, the crucial point in your work is the evaluation of the toxicity of the samples. In this respect you considered fibrous zeolites of the erionite series, which have already been recognized as carcinogenic, as paradigm minerals. Please consider the following reasoning: Ferrierite displays physical-chemical aspects similar to those of the carcinogenic erionite therefore ferrierite has a carcinogenic behavior. This is only apparently correct, as carcinogenic mechanisms promoted by inhaled asbestos and other elongate mineral particles including fibrous erionite, still remain unknown (e.g. Berry et al. 2022, https:// doi.org/10.3390/ijerph1907403). In addition, you know that notable differences between the two minerals exist. For instance, wool-like fibers of erionite are different from needles of ferrierite. In fact, you may agree that the crystalline structure of erionite is more compatible with the development of the fibrous habit than that of ferrierite. Furthermore, synthetic erionite and ferrierite, both very reactive towards numerous organic compounds, are not interchangeable in industrial uses, each having specific functions. Therefore the toxicity of the two minerals may be very different both in nature and in power.
The presence of nanoscopic particles of minerals containing iron adhering to the walls of the fibers is another characteristics you adduced to support the carcinogenicity of your samples. You stated that "The surface reactivity of a mineral fiber is also conditioned by the presence of iron in the fiber surfaces (L 728) which "contribute to increasing the potential toxicity of the ferrierite fibers (L 731-733)". Moreover, you reported that "regarding the investigated ferrierite samples, iron has been detected in FER1 as iron-rich particles or nanoparticles (Fe-rich phyllosilicate and Fe-oxides) coating the crystal surface". In this respect I would say that the detection of about 2 wt% of iron in one of the samples analyzed by electron microprobe, and the XRD peaks compatible with an iron-bearing phyllosilicate, do not support the aforementioned statement (Please see detailed comments). You know that TEM/AFM observations are often necessary for evidencing nanoparticles stuck on mineral surfaces, especially in cases of fibrous minerals.
Provided that, in my opinion, the epidemiological evidence is necessary for an adequate assessing of the environmental hazard of Veneto ferrierite, I suggest you to conclude your paper with one or more sentences aimed at avoiding any premature alarmism among the population.
Detailed comments:
(L. 142-143)For comparison, ferrierite crystals from the FER1 sample were embedded in epoxy resin and analyzed by EMPA
Comment: I would ask about the electron beam diameter, as I can see that the fiber width is < 1 micrometer.
(L. 188-190) EMPA of FER1 indicated a FeO content of 1.97 wt.% arising from the Fe-rich phyllosilicate particles sticking at the surface. For this reason, iron was not included in the calculation of the crystal-chemical formula.
Comment: Up to this point you did not provide evidence of Fe-rich phyllosilicate "particles" sticking at the surface of the fibers. I agree that in the next pages, reporting on X-ray Powder Diffraction results, you state that " Preliminary analysis of the FER1 pattern revealed the occurrence of ..... an abundant 15 Å Fe-bearing phyllosilicate phase " and hence " the abundant presence of the phyllosilicate phase was approximated with two peaks located at ca. ......not related to any structure, whose position, intensity, and breadth were optimized during the least-squares procedure ......." (lines 247-250).
Provided that the two peaks really indicate a nontronite-like phase, you cannot affirm that this is certainly sticking on the surface of the ferrierite fibers. I agree that this is possible, even probable, and hence literature reports on nanoparticles containing iron sticking on fibrous zeolites , but you have yet to provide such an evidence. On the other hand, please consider that Fe-ferrierite with different Al/Si ratio were synthetized in hydrothermal conditions (e.g. Xu et al. 2020. doi: 10.3390/molecules25163722), therefore the presence of a few iron in natural samples (e.g. Fe3+ replacing Al3+) may be not a mineralogical oddity.
Author Response
Reviewer#1
Dear Authors,
your manuscript provides a valuable set of data on morphology, crystal structure, mineral-chemistry, and surface activity of fibrous ferrierite in filled vesicles within altered basalts, Tertiary in age, from Vicenza area (Veneto, Northern Italy). I can see that you used adequate analytical methods following Gualtieri et al. (2018: Am. Min. 103, 1044-1055).
Answer 1: we are grateful to Reviewer#1 for the positive comment about the paper, and we appreciate its detailed and constructive suggestions.
However, some of your conclusions are only working hypotheses. In general, concluding a given scientific research with one or more hypotheses is a normal circumstance, and should not weigh on the evaluation of the work. Nevertheless, the conclusions reported in this manuscript have implications in the social field as a potential cause of alarm and anxiety in the inhabitants of the Veneto or even of all of northern Italy. On this reason I suggest that only firm conclusions should be reported in this paper.
Answer 2: Reviewer#1 is correct, and we thank her/him for pointing out this weakness. Some confusion has been made in the manuscript between what the firm conclusions are and what may be working assumptions and/or implications. According to this suggestion, and also in agreement with the indications of Reviewer#2, the abstract (Lines 17-27 of the “untracked changes version of the revised manuscript), discussion (Lines 629-643 and 727-731), and conclusions (Lines 742-747 and 756-763) have been redrawn in the revised text.
More precisely, the crucial point in your work is the evaluation of the toxicity of the samples. In this respect you considered fibrous zeolites of the erionite series, which have already been recognized as carcinogenic, as paradigm minerals. Please consider the following reasoning: Ferrierite displays physical-chemical aspects similar to those of the carcinogenic erionite therefore ferrierite has a carcinogenic behavior. This is only apparently correct, as carcinogenic mechanisms promoted by inhaled asbestos and other elongate mineral particles including fibrous erionite, still remain unknown (e.g. Berry et al. 2022, https:// doi.org/10.3390/ijerph1907403). In addition, you know that notable differences between the two minerals exist. For instance, wool-like fibers of erionite are different from needles of ferrierite. In fact, you may agree that the crystalline structure of erionite is more compatible with the development of the fibrous habit than that of ferrierite. Furthermore, synthetic erionite and ferrierite, both very reactive towards numerous organic compounds, are not interchangeable in industrial uses, each having specific functions. Therefore the toxicity of the two minerals may be very different both in nature and in power.
Answer 3: yes, we agree entirely with these considerations, but this was probably not clear in the manuscript. We modified the revised manuscript to underline that ferrierite is only suspected to be toxic based on the collected data such as fibrous habit, morphometry, surface properties, and interacting abilities, which can be connected with their potential toxicity. See abstract (Lines 17-27), discussion (Lines 629-643 and 727-731), and conclusions (Lines 742-747 and 756-763) of the revised manuscript.
The presence of nanoscopic particles of minerals containing iron adhering to the walls of the fibers is another characteristics you adduced to support the carcinogenicity of your samples. You stated that "The surface reactivity of a mineral fiber is also conditioned by the presence of iron in the fiber surfaces (L 728) which contribute to increasing the potential toxicity of the ferrierite fibers (L 731-733)". Moreover, you reported that "regarding the investigated ferrierite samples, iron has been detected in FER1 as iron-rich particles or nanoparticles (Fe-rich phyllosilicate and Fe-oxides) coating the crystal surface". In this respect I would say that the detection of about 2 wt% of iron in one of the samples analyzed by electron microprobe, and the XRD peaks compatible with an iron-bearing phyllosilicate, do not support the aforementioned statement (Please see detailed comments). You know that TEM/AFM observations are often necessary for evidencing nanoparticles stuck on mineral surfaces, especially in cases of fibrous minerals.
Answer 4: That of iron is a very intriguing question, as evidenced by the number of contributions in the literature on this subject (e.g., Turci et al., 2011, Chem. Eur. J. 2011, 17, 350-358; Gualtieri et al., 2016, Sci. Rep. 2016, 6, 37981; Ballirano et al., 2015, Microporous Mesoporous Mater. 2015, 211, 49-63; Pacella et al., 2017, Sci. Rep. 2017, 7, 1319; Pacella et al., 2018, Minerals 2018, 8, 36).
In our ferrierite samples, EMP data indicate a considerable variability of the FeO content, ranging from ca. 1.3 to as much as 5 wt.% (locally to ca. 54 wt% in the case of particles of iron oxides/hydroxides). Among the positive analyses, the FeO content ranges from 1.63 to 2.60 wt.%. It is worth noting that the inclusion of FeO in the analysis leads to E% values in the -20 range suggesting very improbable the possible incorporation of Fe within the structure of ferrierite. The two options of incorporating:
- a) Fe as an extra-framework cation increases the total extra-framework site scattering to more than 80 e- which would be double respect to the values reported for ferrierite;
- b) Fe as a framework cation (ca. 0.75 apfu Fe). Calculating the empirical formula based on 36(Si+Al+Fe) results in ca. 71.2 apfu O as compared to the expected 72 apfu (and as in case a) an E% of ca -18).
Moreover, the idealized chemical composition of nontronite contains ca. 32 wt.% Fe2O3 and therefore, a small amount of this phyllosilicate is easily detected by EMP. We believe that the detected iron could be mainly related to nanoscopic particles on the fiber surface for all these reasons. Of course, TEM/AFM observations would have made a significant (maybe resolutive) contribution to solving this problem. In any case, in agreement with what was correctly suggested by Reviewer#1, having no reliable data to support this, we have modified the revised manuscript presenting this as a working hypothesis (Lines 358-362 and 727-731).
Provided that, in my opinion, the epidemiological evidence is necessary for an adequate assessing of the environmental hazard of Veneto ferrierite, I suggest you to conclude your paper with one or more sentences aimed at avoiding any premature alarmism among the population.
Answer 5: yes, we agree that the epidemiological evidence is necessary for an adequate assessment of the environmental hazard of Veneto ferrierite. We certainly do not want to generate premature and uncontrolled alarmism. The final task of the conclusion section has been rewritten accordingly (Lines 756-763 of the revised manuscript).
Detailed comments:
(L. 142-143) For comparison, ferrierite crystals from the FER1 sample were embedded in epoxy resin and analyzed by EMPA
Comment: I would ask about the electron beam diameter, as I can see that the fiber width is < 1 micrometer.
Answer 6: the EMP analyses were carried out in the largest crystals (2-3 microns), using the smallest electron beam diameter (1 micron). This has been added to the revised manuscript (Line 143).
(L. 188-190) EMPA of FER1 indicated a FeO content of 1.97 wt.% arising from the Fe-rich phyllosilicate particles sticking at the surface. For this reason, iron was not included in the calculation of the crystal-chemical formula.
Comment: Up to this point you did not provide evidence of Fe-rich phyllosilicate "particles" sticking at the surface of the fibers. I agree that in the next pages, reporting on X-ray Powder Diffraction results, you state that " Preliminary analysis of the FER1 pattern revealed the occurrence of ..... an abundant 15 Å Fe-bearing phyllosilicate phase " and hence " the abundant presence of the phyllosilicate phase was approximated with two peaks located at ca. ......not related to any structure, whose position, intensity, and breadth were optimized during the least-squares procedure ......." (lines 247-250).
Provided that the two peaks really indicate a nontronite-like phase, you cannot affirm that this is certainly sticking on the surface of the ferrierite fibers. I agree that this is possible, even probable, and hence literature reports on nanoparticles containing iron sticking on fibrous zeolites, but you have yet to provide such an evidence. On the other hand, please consider that Fe-ferrierite with different Al/Si ratio were synthetized in hydrothermal conditions (e.g. Xu et al. 2020. doi: 10.3390/molecules25163722), therefore the presence of a few iron in natural samples (e.g. Fe3+ replacing Al3+) may be not a mineralogical oddity.
Answer 7: see answer 4, which is related to the same observation. In agreement with Reviewer#1, having no reliable data to support the presence of Fe-rich nanoparticles, we have modified the revised manuscript presenting this as a working hypothesis (Lines 358-362 and 727-731).
Reviewer 2 Report
The authors applied a wide range of instrumental methods and carried out a detailed crystal-chemical characterization of fibrous ferrierite from Northern Italy. They compared the obtained characteristics with those available for other fibrous zeolites, primarily with erionite, and concluded that “fibrous ferrierite has all the credentials to be considered a potential health hazard, and the notable similarities that exist between ferrierite and erionite strongly support the hypothesis that both fibrous zeolites may have a high toxicity/pathogenicity potential.”
However, the data they obtained cannot unequivocally answer the question whether fibrous ferrierite can represent a potential health hazard. As the authors themselves write, these results only provide "background knowledge for upcoming experiments on the biological activity of ferrierite". It turns out that the results obtained at this stage only confirm the previously made reasonable assumptions as a possible risk of ferrierite to human health (Gualtieri et al 2018; Zoboli et al 2019) The authors themselves provide these references in the introduction.
In connection with the above, the authors can be advised to rethink the scientific novelty of the presented work and carry out its substantial revision:
- To correct the name (for example, it is not clear why the chemical characterization is not considered mineralogical, and the EPR method is taken out separately);
- To reform tasks (task 1 is not consistent with the results, tasks 2 and 3 contradict each other);
- To rewrite the abstract (in particular, to enter there new data on the characteristic features of ferrierite from Northern Italy);
- To significantly rework the "Discussion" section.
Author Response
Reviewer#2
The authors applied a wide range of instrumental methods and carried out a detailed crystal-chemical characterization of fibrous ferrierite from Northern Italy. They compared the obtained characteristics with those available for other fibrous zeolites, primarily with erionite, and concluded that “fibrous ferrierite has all the credentials to be considered a potential health hazard, and the notable similarities that exist between ferrierite and erionite strongly support the hypothesis that both fibrous zeolites may have a high toxicity/pathogenicity potential.”
However, the data they obtained cannot unequivocally answer the question whether fibrous ferrierite can represent a potential health hazard. As the authors themselves write, these results only provide "background knowledge for upcoming experiments on the biological activity of ferrierite". It turns out that the results obtained at this stage only confirm the previously made reasonable assumptions as a possible risk of ferrierite to human health (Gualtieri et al 2018; Zoboli et al2019) The authors themselves provide these references in the introduction.
Answer 1: we thank Reviewer#2 for the positive comment about the paper. Her/him well understood the purpose of the work and highlighted the same weakness that was also emphasized by Reviewer#1. The revised manuscript has been corrected to underline that ferrierite is only suspected to be toxic based on the collected data such as fibrous habit, morphometry, surface properties, and interacting abilities, which can be connected with their potential toxicity (see abstract, Lines 17-27; discussion, Lines 629-643 and 727-731; conclusions, Lines 742-747 and 756-763). We also clarify that our data cannot unequivocally answer whether fibrous ferrierite can represent a real potential health hazard (Lines 756-763 of the revised manuscript).
In connection with the above, the authors can be advised to rethink the scientific novelty of the presented work and carry out its substantial revision:
- To correct the name (for example, it is not clear why the chemical characterization is not considered mineralogical, and the EPR method is taken out separately);
Answer 2: yes, the title of the manuscript has been modified accordingly to these suggestions.
- To reform tasks (task 1 is not consistent with the results, tasks 2 and 3 contradict each other);
Answer 3: regarding task1, reviewer#2 is correct, and we are sorry about this incongruence. The values reported in brackets were those relating to the parameters of “breathable” fibers and not those of the studied fibers. Here is the discrepancy. The task1 has been modified in the revised manuscript (Lines 736-741) according to the results.
About the observation that tasks 2 and 3 contradict each other, it is unclear what Reviewer#2 means. From our point of view, the only connecting element between these two tasks is the Si/Al ratio. The higher the Si content, the more hydrophobic the zeolite is and has a greater affinity for hydrocarbons. In contrast, with high Al contents, the number of exchangeable cations is more significant and the affinity with water increases. Hence, having a high Si/Al ratio, ferrierite has a higher affinity with similar CAT8 species. And this is also demonstrated in fig. 8. The polar interactions are linked to the aqueous component coordinated at the surface level and are mediated with electrostatic interactions in outer-sphere bonding. Undoubtedly, having not measured the permanent structural charge, we can only assume these mechanisms. However, we tried to simplify these points in the revised manuscript to make them clearer (Lines 742 to 755).
- To rewrite the abstract (in particular, to enter there new data on the characteristic features of ferrierite from Northern Italy);
Answer 4: yes, accordingly to this comment, the abstract has been rewritten with the addition of new data on the features of ferrierite from Northern Italy (Lines 17-27).
- To significantly rework the "Discussion" section.
Answer 5: the discussion section has been modified in the revised manuscript.
Round 2
Reviewer 1 Report
Lines 361-363
Comment: I may agree that "Crystal-chemical data and formula calculations" suggest that iron is not in the (ferrierite) crystalline structure. Nevertheless, this information cannot indicate where and in what form the iron is. In fact you correctly use the dubitative form that iron "could be mainly related to Fe-rich particles or nanoparticles on the fiber surface". Due to the considerable implications of this occurrence for assessing the toxicity of the mineral, all doubts should be removed. Microscopic evidence is absolutely necessary for confirmation.
Line 737 (Conclusions)
General comment on your conclusions: If future epidemiological investigation will confirm that the inhabitants of those areas have never had health problems attributable to fibrous ferrierite, the results of your study, as well as results of future investigations on the same topic, including bio-medical experiments, should remain in the academic field in order not to create anxiety in the population. Please consider that anxiety can be correlated with various diseases, even fatal ones.
Reviewer 2 Report
The authors carefully considered the reviewer's comments and improved the quality of the manuscript by correcting it.
