Extensive arsenic contamination in high-pH unconfined aquifers in the Indus Valley

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Science Advances  23 Aug 2017:
Vol. 3, no. 8, e1700935
DOI: 10.1126/sciadv.1700935

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  • RE: Answer to the comments of E-letter (by Nabeel Niazi)

    Dear Editor,

    I am writing this letter with regards to the concerns by the local researcher (E-letter published in Science Advances on 29 August in response to our report). As a (second) author of the arsenic study recently published in Science Advances, we take strong exception to the many uninformed points and misleading statements made. While going through certain statements in the response to the report, I got the impression that they did not (yet) read the publication in detail or are lacking the updated knowledge about statistical modeling and its application in the field of hydrology. This could be one of the possible reasons why country wide dataset/hazard risk maps of arsenic contamination have not been generated previously. An undeclared conflict of interest and/or jealously with fellow researchers is also very common in developing countries. I have read a few misleading statements by a fellow researcher in the field (who has also already reported the severe arsenic contamination in fewer areas of Punjab). In any case, we would plead that anyone publicly commenting on our study make the effort to first fully understand it, so as to avoid unfounded, and sometimes illogical, criticism as contained in the recently published E-letter.

    Below we briefly respond to some of the incorrect statements made:

    • The study referred to in the E-letter recently sent to the editor of Science Advances, is conducted by a very good Pakistani research group working...

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    Competing Interests: None declared.
  • Response to eLetter by Nabeel Khan Niazi from 29 August 2017
    • Joel Edwin Podgorski, Project Coordinator, EAWAG Swiss Federal Institute of Aquatic Science and Technology
    • Other Contributors:
      • Michael Berg, Head of Department, EAWAG Swiss Federal Institute of Aquatic Science and Technology

    Dear Editor,

    We would like to respond to the eLetter by Nabeel Khan Niazi from 29 August 2017.

    We would first like to emphasize that the point of our modelling approach is to remove the need to densely sample all of a study area in order to obtain an approximation of the overall state of contamination. As opposed to interpolation/extrapolation, such as regression kriging or nearest neighbor spatial analysis that is based only on arsenic measurements, our modelling finds statistical relationships between arsenic concentrations and various geospatial parameters of geology, soil properties, climate and hydrology related to the natural biogeochemical process of arsenic accumulation in groundwater. The resulting arsenic hazard maps show areas where the probability of contamination is above a certain threshold (also see the Supplementary Information). However, these maps are unable to capture the fine heterogeneity of aquifer systems that can result in contaminated wells existing in close proximity to uncontaminated ones.

    The success of modeling is strongly dependent on the variability and resolution of the predictor variables, since a larger number of samples will not necessarily produce a better hazard map. Compared to our group’s previous hazard maps for China (Rodríguez-Lado et al., 2013), Southeast Asia (Winkel et al., 2008), the Red River Delta (Winkel et al., 2011), or even the world (Amini et al., 2008), the number of samples used for the Pakistan mo...

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    Competing Interests: None declared.
  • RE: Comment on the “Extensive arsenic contamination in high-pH unconfined aquifers in the Indus Valley”
    • Nabeel Khan Niazi, Assistant Professor/Research Scientist, University of Agriculture Faisalabad and University of Bremen

    Dear Editor,

    This is an interesting study which indicates about arsenic contamination issue in groundwater wells in different areas of Pakistan. Arsenic contamination of groundwater in Pakistan is an emerging issue and needs an attention to develop suitable management and remediation measures in arsenic-affected areas.

    However, this report, about prediction of arsenic-induced population risk (50 to 60 million people), appears to be too much ‘exaggerated and overestimated’.
    There are some critically-important points that authors should have considered before claiming that ’50 million to 60 million are at high risk of arsenic poisoning in the Indus Valley of Pakistan’.

    1. Firstly, it is not mentioned in paper which areas of Punjab and Sindh provinces in Pakistan were exactly targeted for groundwater sampling. This is crucial to know and indicate arsenic contamination extent and trend in groundwater from geologically different settings, and compare with previous studies in those areas. For example, arsenic in majority of groundwater wells from areas around central Punjab (e.g., Gujranwala, Hafizabad, Faisalabad (our own unpublished data) is well below the WHO safe limit (10 μg/L) of arsenic in drinking water – the problem mainly exists in southern Punjab (e.g., Vehari, Multan, Bahawalpur) (1), and near Lahore (2) with number of safe wells exist in the same area (3).
    2. A total of 1184 groundwater samples were taken in this study, of which 39...

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    Competing Interests: None declared.