Arsenic in aquifers extensively used in circum-Himalayan Asia for drinking, cooking and irrigation gives rise to high exposures to over 100,000,000 people resulting in avoidable premature deaths on the order of 100,000 per annum. Although the arsenic in these aquifers is largely thought to be of geogenic origin, it has been hypothesized by Harvey et al (2002) that extensive abstraction of groundwater has given rise to accelerated rates of mobilization from solid-phase aquifer materials into groundwater. This hypothesis has given rise to extensive debates over the last 20 years (e.g. Polya and Charlet, 2009) in part because of the complexity of the arsenic mobilization processes and in part because of the profound impact that resolution of the hypothesis might have on groundwater resource management policies in the impacted countries. The theoretical basis of the hypothesis is that labile young surface derived organic carbon is drawn down into shallow aquifers by massive groundwater abstraction and that this organic carbon is oxidized in an arsenic-mobilising process coupled with the reduction of arsenic bearing Fe-O-H phases (cf. Islam et al., 2004).  A key piece of evidence supporting the hypothesis is that dissolved inorganic carbon, which in part arises from the oxidation of reduced organic carbon moieties, has ¹⁴C model ages that are significantly younger than the ¹⁴C model ages of dissolved organic carbon in the same aquifers (Harvey et al., 2002). 

Using a novel ⁸⁷Sr/⁸⁶Sr based mixing model (Magnone et al., 2019) to isolate the isotopic characteristics of dissolved inorganic carbon arising from the oxidation of organic carbon, we demonstrate that these isotopic characteristics are not only distinctly different from those of bulk dissolved inorganic carbon, but that once other sources of dissolved inorganic carbon are quantitatively  accounted for, the determined isotopic characteristics are no longer supportive of Harvey et al’s (2002) model. We conclude, therefore, massive groundwater abstraction in arsenic-prone circum-Himalayan aquifers has not been demonstrated to be caused or accelerated by the introduction of surface-derived organic matter, although such abstraction might give rise to arsenic mobilization through other processes. 

Biographical Sketch:

Dave Polya has 30+ years’ research experience on the (bio)geochemical behaviour and modelled health impacts of metals and metalloids in surface and low temperature and hydrothermal/geothermal sub-surface systems, and involving field, laboratory, spectroscopic & computer modelling approaches. The research has primarily been funded/supported (> ￡10M; with >￡5M as PI) by the European Commission, NERC, EPSRC, TSB (now Innovate UK) & British Council as well as from commercial and/or regulatory organisations in the instrumentation, mining, water & environmental sectors.   

His research output (100+ publications; 9147 citations; h-index = 50; 2023) includes on the biogeochemistry of arsenic in groundwater (Islam et al., 2004, https://www.nature.com/articles/nature02638 ), AI models of groundwater arsenic distribution in India (Podgorski et al., 2020,  https://www.mdpi.com/1660-4601/17/19/7119 ) and environment-health interactions, including studies of the genotoxicity of inorganic arsenic in rice (Banerjee et al., 2013, https://www.nature.com/articles/srep02195 ) and  modelling the distribution of groundwater arsenic attributable cardiovascular disease related mortality (Wu et al., 2021, https://www.mdpi.com/2073-4441/13/16/2232 ). Polya co-edited the IWA Best Practice Guide for the Control of Arsenic in Drinking Water (Bhattacharya et al (Eds), 2017,  https://doi.org/10.2166/9781780404929 ). Polya’s work addresses UN SDG 6 (https://www.manchester.ac.uk/research/impact/sdgs/health/groundwater-arsenic-sdg-6/) with awareness, policy change and mitigation impacts, in part, summarised in a UK REF2021 impact case (https://www.manchester.ac.uk/research/impact/ref-2021/case-studies/ )

Polya is an Associate Director of the Williamson Research Centre for Molecular Environmental Science & Head of MAGU (Manchester Analytical Geochemistry Unit). He has coordinated pan-European (AquaTRAIN Marie Curie Research Training Network), Europe-Asia (EU ASIA-LINK CALIBRE) & UK-India (UKIERI PRAMA, FAR-GANGA, www.farganga.org ) research training networks. Prof Polya’s role as FSE (Faculty of Science and Engineering) Associate Dean for Internationalisation involves the promotion of research, teaching and social responsibility/knowledge transfer/business engagement opportunities between FSE and key organizations across the globe for mutual benefit & positive social impact.