A New Framework for the Management and Radiological Protection of Groundwater Resources: The Implementation of a Portuguese Action Plan for Radon in Drinking Water and Impacts on Human Health

Round 1

Reviewer 1 Report

The implementation of radon action plan is an actual and important task nowadays. This study is an accurate, huge research in this topic, however the understanding is very difficult thanks to its structure and language. There are a lot of Portuguese references, which is not meaningful for all reader. In some cases references should be improved, some of them should be deleted. Units should be indicate according to the format requirements. Description of measurement methods should be improved. Detailed review could be seen in the attachment.

Comments for author File: Comments.pdf

Author Response

Reviewer #1:

The implementation of radon action plan is an actual and important task nowadays. This study is an accurate, huge research in this topic, however the understanding is very difficult thanks to its structure and language. There are a lot of Portuguese references, which is not meaningful for all reader. In some cases references should be improved, some of them should be deleted. Units should be indicate according to the format requirements. Description of measurement methods should be improved. Detailed review could be seen in the attachment.

Thank you for recognizing the value of this work in the implementation of a Portuguese Action Plan for Radon in drinking water. The weaknesses raised are addressed below.

Ad1) line- 78, The cited references are not the best for this. The referenced behaviour and physical-chemical properties are general well-known facts, please cite mor relevant source. Reference 4 is a risk analyses, Reference 5 is a radon mappping teme, Reference 6 is a great article for exposure assessment.

Response 1. The sentence has been reformulated and new references have been added on the assessments of the effects of radon exposure.

Line 75: “Radon (222Rn) is a noble radioactive gas resulting from geogenic sources, with high mobility in natural systems due to its short half-life (3.8 days). Exposure to this colorless, odorless and tasteless gas can be a serious public health problem since it is responsible for approximately half of the radiation dose received by the human population [4–6]”

For the sake of clarification, we rephrased the sentence in the revised manuscript as follows:

“Radon (222Rn) is a noble radioactive gas resulting from geogenic sources, with high mobility in natural systems due to its short half-life (3.8 days). Exposure to this colorless, odorless and tasteless gas can be a serious public health problem since it is responsible for the radiation dose received by the human population [4–8].”

Ad2) Line 79- Please refer to the WHO report instead of / beside this reference

Response 2. As requested, the WHO report was placed beside this reference.

Ad3) Line 87 There are a lot of article deal with this theme, please cite referred one instead of conference proceedings.

Response 3. Following the recommendation of the reviewer, several references related to this theme have been added [12-20].

Ad4) Line 88: reputation (this is the 3rd time when the fact "radon is a gasous element" is mentioned...)

Response 4. The word “gas” was referred to several times throughout the manuscript. Currently, It is only mentioned in the revised manuscript twice: Line 90: to say that it is a noble gas; Line 103: because it is a gas, it can easily migrate in the geological substrate

Ad5) Line 168-189: (please be sure to use SI units in the same form accross all manuscript)

Response 5. As suggested by the reviewer, all SI units have been properly changed across all revised manuscript.

Ad6) Line 276: Obviously these reference is not related to this manuscript, these are for the map (ESRI, 2010)

Response 6. These references [37-53] are related to environmental studies that used ArcMap. The reference (ESRI, 2010) was also changed according to the format requirements

Ad7) Line 345: unnecessary, readers will see

Response 7. The sentence: “Additional explanation is provided in the text” was removed, as well suggested by the reviewer.

Ad8) Line 444: missing reference

Response 8. Added reference

Page 13 Line 1227: “It is worth mentioning that 4 springs reached the maximum levels of radon contamination above 1000 Bq.L^-1 and should be immediately subjected to mitigation measures in accordance with the European Directive [32] “

Ad9) Line 498: Please be sure these references are matched with the format requirements. 

Response 9. These references are now properly matched to the format requirements.

Reviewer 2 Report

Review of manuscript water-469335 “A new framework for the management and radiological protection of groundwater resources: the implementation of a national action plan for radon in drinking water and impacts on human health” by Martins et al.

This manuscript presents the results of a study aimed at addressing the radiological contamination from a geogenic origin (i.e. by ²²²Rn) of groundwaters in northern Portugal. It also intends to provide the scientific background for the implementation of a national action plan that includes radon issues among all other contaminants. All this is suggested for the better management and protection of groundwaters as a resource for drinkable water in view of future climate changes.

Results show that: 1) physical-chemical properties of groundwater are crucial for radon transfer from rocks, even if the production is high, and 2) the vast majority of sampled sites have ²²²Rn values that are above the limit imposed by the Portuguese legislation.

General comment

In my opinion, the paper is very interesting and I really appreciate the effort of translating scientific results into ways to promote the better management of natural resources and their legal protection.

My biggest concern is relative to the data presented in the Supplementary Material that are either missing or incomplete. Indeed, authors write (lines 481-482) that Supplementary Materials “are available online at www.mdpi.com/xxx/s1, Figure S1: title, Table S1: title, Video S1: title” but the only file I could download at that address was a zipped folder including just an Excel file with the complete dataset. And also this dataset is somewhat problematic.

First of all, authors write that they sampled (lines 165-166) “A total of 56 representative rock samples …. in outcrops of metasedimentary (n = 11) and granitic units (n = 45)” but the table in the Supplementary Material reports data for porosity, PRn, and K₂O associated to 62 spring samples. I understand that rock samples have been associated to nearby spring samples (Am I right?) but this does not explain the discrepancy between the number of collected samples (56) and that of reported data (62). No repetitions are present in the dataset (that could result, for example, from the same rock sample being associated to multiple spring samples), then authors are requested to explain and fix this difference. Since rock and spring samples are presented with different symbols in Figure 1, I think it would be more correct to provide an additional dataset (i.e. Table S2) with data relative to rock samples separated from those obtained from spring samples.

The word “nascente” in Table S1 should be translated from Portuguese (I guess it means spring, am I correct?) and an explanatory legend should be provided to explain the acronyms related to the Geology column (i.e.  GPS, GTL, GLS, DCU, SUF, etc.).

In the main text, authors should also explain the reason for missing porosity data and, briefly, how they have calculated radon production potential (PRn, extracted from a MSc or PhD thesis, I suppose).

Specific comments

Please, refer to Portugal when referring to “national radon action plan” all along the manuscript.

In my opinion, Figure 1(a) is not necessary and could be deleted. I would also suggest to change  the colours with which Group III and Group IV are presented in Figure 1(e) because they are too similar in the present form and it is difficult to discriminate between these two crucial two litological units even on screen.

Please explain why data on annual precipitation refers on average values from 1960 just until 1991. Were more recent data unavailable? If so, this might be a problem because you assume that rain rates have remained unchanged in the last 20 years (up to 2014, the sampling year) a quite unrealistic assumption, in my opinion.

Please, shortly explain the reason why you determine K₂O in rocks and how you pass from gamma spectrometry measurements to % contents reported in Tables 1 and S1.

I think that a short description of the PCV procedure might be helpful to readers that are not well acquainted with this methodology, especially to explain what is reported on the y-axis of Figure 4.

Lines 373-374: please, provide the data interval of radon concentrations obtained in other countries to be compared with the study’s results.

Lines 397-398: please, refer to Table S1 to help identify the spring sample that produce an annual effective dose for ingestion that is higher than worldwide average.

Lines 408-410 area repetition of the immediately above sentence and should be erased.

The paper presents several typos and wrong or bad constructed sentences that could be detected also by a non-native speaker like me (e.g. lines 20, 36, 53, 95, 212, 229 among the others). Therefore, I think that a language and grammar check by a native English speaker or a skilled scientist is necessary.

Conclusive remark

I suggest to accept the paper after the suggested major revisions are provided.

Author Response

Reviewer #2:

This manuscript presents the results of a study aimed at addressing the radiological contamination from a geogenic origin (i.e. by 222Rn) of groundwaters in northern Portugal. It also intends to provide the scientific background for the implementation of a national action plan that includes radon issues among all other contaminants. All this is suggested for the better management and protection of groundwaters as a resource for drinkable water in view of future climate changes.

Results show that: 1) physical-chemical properties of groundwater are crucial for radon transfer from rocks, even if the production is high, and 2) the vast majority of sampled sites have 222Rn values that are above the limit imposed by the Portuguese legislation.

General comment

In my opinion, the paper is very interesting and I really appreciate the effort of translating scientific results into ways to promote the better management of natural resources and their legal protection.

We thank your kind words for our original manuscript. In the revised manuscript, even considering the requested major changes, we did the utmost to improve the text making it leaner and stronger, also considering the comments and suggestions of other reviewers.

Ad1) My biggest concern is relative to the data presented in the Supplementary Material that are either missing or incomplete. Indeed, authors write (lines 481-482) that Supplementary Materials “are available online at www.mdpi.com/xxx/s1, Figure S1: title, Table S1: title, Video S1: title” but the only file I could download at that address was a zipped folder including just an Excel file with the complete dataset. And also this dataset is somewhat problematic.

Response 1. Page 14, Lines 1364-1368: In the revised manuscript, the two tables of the supplementary material (table S1 and table S2) was properly mentioned in the sentence.

Ad2) First of all, authors write that they sampled (lines 165-166) “A total of 56 representative rock samples in outcrops of metasedimentary (n = 11) and granitic units (n = 45)” but the table in the Supplementary Material reports data for porosity, PRn, and K2O associated to 62 spring samples. I understand that rock samples have been associated to nearby spring samples (Am I right?) but this does not explain the discrepancy between the number of collected samples (56) and that of reported data (62). No repetitions are present in the dataset (that could result, for example, from the same rock sample being associated to multiple spring samples), then authors are requested to explain and fix this difference. Since rock and spring samples are presented with different symbols in Figure 1, I think it would be more correct to provide an additional dataset (i.e. Table S2) with data relative to rock samples separated from those obtained from spring samples.

Response 2. In the PhD thesis of Martins, (2017) a total of 119 rock samples were used to carry out PRn measurements. Since it was not possible the rock sampling at each spring, we chose to use these pre-existing data and carry out other measurements of K2O and porosity only on 56 rock samples that were located near to the springs. Subsequently, the interpolation of these parameters was performed using the Arcgis "Topo to raster" tool and at each point of springs collection, the corresponding value was extracted using the Arcgis tool "Extract multivalues to points" These discrepancies well mentioned by the reviewer are now properly explained in the text, and sampling points can be seen in Figure 3a-c. As can be seen in this previous figure, there are some springs (n = 7) that are located outside the raster boundary generated through interpolation. A brief description of the existing discrepancy is given in the text.

Line 285 of the original version stated: “Since some features are unknown in the groundwater sampling sites, the use of this interpolate tool in concomitance with the Extract Multi Values to Points tool becomes crucial for a consistent dataset preparation for the projection on PCV plot (Figures 3d-f).”

Now is:

“Since it was not possible to sample rocks in areas near of the springs, it was decided to use measurements of PRn obtained by Martins [17], being carried out analysis of porosity and K2O in these same rocks. For a consistent dataset preparation, the used of an interpolation tool (Topo to raster) in concomitance with the Extract Multi Values to Points tool becomes crucial for dataset projection on PCV plot. For these three parameters, there are missing values in Table S1 of the supplementary material because some springs (n = 7; Figure 3a-c) are located in the outside of the raster boundary generated through the performed interpolations.”

Ad3) The word “nascente” in Table S1 should be translated from Portuguese (I guess it means spring, am I correct?) and an explanatory legend should be provided to explain the acronyms related to the Geology column (i.e.  GPS, GTL, GLS, DCU, SUF, etc.).

Response 3. The word “nascente” has already been changed by “spring” in Table S2. The acronyms of lithologies in Geology column were removed because no further study was carried out for each lithological variety, not even mentioned throughout the manuscript.

Ad4) In the main text, authors should also explain the reason for missing porosity data and, briefly, how they have calculated radon production potential (PRn, extracted from a MSc or PhD thesis, I suppose).

Response 4. The reason for missing porosity was now widely explained in the manuscript.

Line 313: “For these three parameters, there are missing values in Table S1 of the supplementary material because some springs (n = 7) are located in the outside of the raster boundary generated through the performed interpolations (Figure 3a-c).”

The radon production rate (PRn, in Bq.m-3.h-1) was calculated using the following equation portrayed in (Pereira et al., (2017).

PRn = ARa x E x d x λ where, ARa is the radium activity, E is the emanation coefficient, d is the apparent density and λ is the decay rate of ²²²Rn.

Pacheco, F.A.L., Van der Weijden, C.H., 2014. Role of hydraulic diffusivity in the decrease of weathering rates over time. J. Hydrol. 512, 87–106. https://doi.org/https://doi.org/10.1016/j.jhydrol.2014.02.041

Page 7, Line 732: To strengthen this point we added the following sentence to the revised manuscript:

“A brief description of radon production methodology is portrayed in Pereira et al. [34].”

Ad5) Please, refer to Portugal when referring to “national radon action plan” all along the manuscript.

Response 5. As suggested by the reviewer the “national radon action plan” was changed by “Portuguese Action Plan for Radon” all along the manuscript.

Ad6) In my opinion, Figure 1(a) is not necessary and could be deleted. I would also suggest to change the colours with which Group III and Group IV are presented in Figure 1(e) because they are too similar in the present form and it is difficult to discriminate between these two crucial two litological units even on screen.

Response 6. The Figure 1(a) was deleted as recommended by the reviewer and the colors of the groups of two-mica granites were also changed to more contrasting colors, so the geological map becomes clearer. Now, we believe it easy to identify the various lithological unites looking to the contrasting colors.

Ad7) Please explain why data on annual precipitation refers on average values from 1960 just until 1991. Were more recent data unavailable? If so, this might be a problem because you assume that rain rates have remained unchanged in the last 20 years (up to 2014, the sampling year) a quite unrealistic assumption, in my opinion.

Response 7. In fact, the annual rainfall rate for the period 1960-1991 was used because there is no gathering of data to compute the annual rainfall for a recent period. The average rainfall rate for the period 1960-1991 was taken from the Water Atlas developed by the National Water Resources Information System (SNIRH). On the other hand, to develop a study about annual rainfall rate for a recent period is out of the scope of this study.

However, according to Pacheco and Van der Weijden, (2014) for this region the turnover time in the fractured aquifer estimated from baseflow discharge, is on the order of several decades (1.5 – 67.6 years). This means that rainwater can circulate for decades from infiltrating subsoil to the aquifer system. As such, the rainwater infiltrated in the 1960s may only emerge recently at some springs, reflecting the hydraulic discharge from the precipitation of previous decades. In the absence of more recent data, it appeared to be the only option to study the effect of the rainwater rate on radon concentration using only these pre-existing data.

Pacheco, F.A.L., Van der Weijden, C.H., 2014. Role of hydraulic diffusivity in the decrease of weathering rates over time. J. Hydrol. 512, 87–106. https://doi.org/https://doi.org/10.1016/j.jhydrol.2014.02.041

Ad8) Please, shortly explain the reason why you determine K2O in rocks and how you pass from gamma spectrometry measurements to % contents reported in Tables 1 and S1.

Response 8. The K₂O was determined to understand the possible relationship between this parameter and the porosity. Some considerations about this possible relation are described in the manuscript in the lines 332-335.

“In addition, K2O content is very noticeable in this type of granites mainly due to the high-muscovite amount in comparison to the biotite granites. On the other hand, it can be verified that in the NE of VPA territory outcrops Parautochthonous metasediments with low-K2O content but with higher porosity (Figure 3a-b).”

In order to convert the values of the 40K activity in Bq. Kg-1 to K in percentage, the activity of 40K is divided by the value of the specific activity of K (312.5 Bq / kg / 1%). It means, therefore, that for conversion purposes, 1% of K corresponds to 312.5 Bq and as such for the final conversion of K2O (%), multiplies by 1.205. This methodology described for the conversion of gamma spectrometry measurements to % contents obtained recently an accreditation of the international standard ISO 17025 for the standardization of tests and calibration. Currently, the Laboratory of Natural Radioactivity of Coimbra University is the first laboratory in the Iberian Peninsula to obtain this accreditation for the evaluation of all radiological parameters, responding to the overall requirements imposed by the European Union regarding protection against the hazards of exposure to natural radioactive substances.

Ad9) I think that a short description of the PCV procedure might be helpful to readers that are not well acquainted with this methodology, especially to explain what is reported on the y-axis of Figure 4.

Response 9. The following PCV procedure is extremely helpful to readers and explains what is reported on the Y-axis of Figure 4 (mean lines). In the PCV procedure of XLSTAT software, when mean lines are activated, this option let XLSTAT display for each lithological group, a line that corresponds to the mean of the quantitative variables and to the mode of the nominal variables (geology groups). When the rescale option is activated, this option allows comparing how the data are distributed for multivariate quantitative variables (geogenic, radiological, climatic and physical-chemical properties) and facilitates the visualization.

As such, the following sentence was inserted in the revised manuscript:

Page 7 Line 745:“In the PCV procedure, when mean lines are activated, this option let XLSTAT display for each lithological group, a line that corresponds to the mean of the measured variables (222Rn, altitude, rainfall, electric conductivity, temperature, pH, porosity, K2O and PRn) for each nominal variable (geology group). When the rescale option is activated, it allows comparing how the data are distributed for multivariate measured variables and facilitates the visualization.”

Ad10) Lines 373-374: please, provide the data interval of radon concentrations obtained in other countries to be compared with the study’s results.

Response 10. We thank the reviewer for this comment. We provide the data interval of radon concentrations in drinking water for several countries.  

Ad11) Lines 397-398: please, refer to Table S1 to help identify the spring sample that produce an annual effective dose for ingestion that is higher than worldwide average.

Response 11. This reference to Table S2 clearly helps to identify the spring sample that produces an annual effective dose for ingestion that is higher than the worldwide average.

Ad12) Lines 408-410 area repetition of the immediately above sentence and should be erased.

Response 12. The area repetition of the immediate sentence mentioned above was erased.

Ad13) The paper presents several typos and wrong or bad constructed sentences that could be detected also by a non-native speaker like me (e.g. lines 20, 36, 53, 95, 212, 229 among the others). Therefore, I think that a language and grammar check by a native English speaker or a skilled scientist is necessary.

Response 13

We thank to the reviewer for this comment about several wrongs or badly constructed sentences. The revised manuscript has checked by a skilled scientist in response to your previous comment.

Round 2

Reviewer 1 Report

Most of my suggestion have been implemented in the manuscript, thank you for the cooperation, I propose to accept it.

Author Response

Ve very much appreciate the recognition of our effort in improving the manuscript according to the reviewer comments and suggestions

Reviewer 2 Report

The authors answered to all issues I raised and I think they improved sensibly their work. I am happy to suggest its publication on Water. Nevertheless, I still think that the colors with which Group III and Group IV are presented in Figure 1(d) are too similar (even if the authors have indeed changed the color for Group III). I think they can do better than that.

Author Response

Reviewer comment

The authors answered to all issues I raised and I think they improved sensibly their work. I am happy to suggest its publication on Water.

Authors answer

We very much appreciate the kind words about our effort to improve the manuscript

Reviewer comment

Nevertheless, I still think that the colors with which Group III and Group IV are presented in Figure 1(d) are too similar (even if the authors have indeed changed the color for Group III). I think they can do better than that.

Authors answer

The figure was improved according with the reviewer suggestion