# Plate tectonics influence on geogenic arsenic cycle: From primary source to global groundwater enrichment

Abhijit Mukherjee, Saibal Gupta, Poulomee Coomar, Alan Fryar, Stéphane Guillot, Swati Verma, Prosun Bhattacharya, Jochen Bundschuh, Laurent Charlet

<figure><img src="image_1.png" /></figure>

## To cite this version:

Abhijit Mukherjee, Saibal Gupta, Poulomee Coomar, Alan Fryar, Stéphane Guillot, et al. Plate tectonics influence on geogenic arsenic cycle: From primary source to global groundwater enrichment. Science of the Total Environment, 2019, 10.1016/j.scitotenv.2019.04.255. insu-02124508

HAL Id: insu-02124508

https://insu.hal.science/insu-02124508v1

Submitted on 11 Aug 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>
1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

# Plate tectonics influence on geogenic arsenic cycle: from primary source to global groundwater enrichment

Abhijit Mukherjee¹,*, Saibal Gupta¹, Poulomee Coomar¹, Alan E. Fryar², Stephane Guillot³, Swati Verma¹, Prosun Bhattacharya⁴, Jochen Bundschuh⁵, Laurent Charlet³

¹Department of Geology and Geophysics, and School of Environmental Science and Engineering, Indian Institute of Technology (IIT) - Kharagpur, West Bengal, 721302, India

²Department of Earth and Environmental Sciences, University of Kentucky, Lexington, KY 40506-0053 USA

³Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France

⁴Department of Land & Water Resources Engineering, Royal Institute of Technology (KTH) SE-100 44 Stockholm, Sweden

⁵University of Southern Queensland (USQ), Toowoomba, QLD, Australia

*Corresponding Author, abhijit@gg.iitkgp.ernet.in, amukh2@gmail.com

## Abstract:

More than 100 million people around the world are endangered by geogenic arsenic (As) in groundwater, residing in sedimentary aquifers. However, not all sedimentary aquifers are groundwater As enriched, and the ultimate source of As in enriched aquifer sediments is yet-unknown, globally. A reconnaissance of the major aquifers suggests that major As enriched aquifers are predictably systematic on a global scale, existing in sedimentary foreland basins in vicinity of modern or ancient orogenic systems. We demonstrate that the groundwater As comes
26 from magmatic arcs (primary source) in present (e.g. Andes) or ancient (e.g Himalaya)
27 continental convergent margins of some of the most prominent orogenic systems across the
28 globe, and ends up in sediments (secondary source) in adjoining foreland or related basins that
29 eventually act as aquifers. These arc magmatic cavenge As while rising through the deep
30 continental crust. Erosion of such orogens ultimately increases the bulk As content in sediments
31 of adjoining basins, leading to groundwater As enrichment in downstream aquifers. Such As-
32 polluted aquifers are eventually extensively used for groundwater exploitation, for drinking and
33 other human purposes. Surface geological and biogeochemical processes, like redox reaction,
34 conduces such groundwater As enrichment. We suggest this model by integrating our study of
35 long-time observations in Himalayan and Andean basin aquifers, and generalizing 63 major
36 aquifers across the globe, to demonstrate the source-to-sink transport of As, thereby delineating
37 it's geogenic cycling in the subsurface. This work outlines the specifics of the mechanism that
38 would drive the processes of groundwater As enrichment across the spatio-temporal scales, i.e.
39 tectonic-scale taking place over millions of years and in continental-scale and groundwater
40 pollution taking place at a human time-scale in village to household scale. Thus, in this work we
41 try to demonstrate a direct evidence of connectivity between global geological processes and
42 individual human health.
43

43
44 Keywords: tectonism; groundwater arsenic; health; hydrogeology

45
46 Introduction

47
48 Over the past few decades, aquifers in scores of global geological provinces with >100
million inhabitants have been identified as having toxic concentrations of groundwater As (>0.01
mg/L). Since the average crustal concentration of As (<1.8 mg/kg) (Henke, 2009), if leached, is sufficient to achieve these toxic levels, any lithological unit in the crust is potentially a source of As enrichment (Saunders et al., 2005). However, not all aquifers around the world are As-contaminated. While there is a broad consensus that As mobilization from the host aquifer sediments leads to its enrichment in groundwater (Smedley and Kinniburgh, 2002), the primary source of the As is not yet well understood (Mukherjee et al., 2009b). Clearly, elevated labile As concentrations in the source regions of the aquifer matrix would increase the probability of As enrichment in aquifer sediment and thus in associated groundwater. Global distributions of known groundwater As-enriched areas show a systematic pattern (Figure 1, Table 1), with most of the major As-polluted aquifers being hosted within extensive clastic sedimentary basins associated with young mountains (Ravenscroft et al., 2009) in or around active or ancient convergent tectonic settings (Mukherjee et al., 2014) (Figure 1). Examples of the association of As-enriched groundwater systems in aquifers hosted in such ancient or active convergent settings (Figure 1, Table 1) are prominent in the Indus-Ganges-Brahmaputra basin, the Mekong and Red river deltas in southeast Asia (Alpine-Himalayan orogenic system), the foreland basins of western USA and Canada (e.g., Western Canada Sedimentary Basin (Laramide-Nevadan-Sonoma orogenic system), the Appalachian foreland in New England and adjacent areas of the eastern USA (Appalachian-Ouachita orogenic system), and parts of Argentina, Bolivia, Chile and Peru in the Andean forelands of South America (Andean-Pampean-Tocoorogenic system), among many others. Since the allochthonous clastics in these polluted sedimentary aquifers are ultimately transported from up-stream provenances, the original source of As must be *ex-situ*. Thus, high groundwater As concentrations may be ultimately related to enhanced primary
solid-phase concentrations in major magmatic arcs and orogenic belts at convergent plate boundaries.

We propose that the groundwater arsenic comes from magmatic arcs (primary source) in present (e.g. Andes) or ancient (e.g. Himalaya) continental convergent margins of some of the most prominent orogenic systems across the globe, and ends up in sediments (secondary source) in adjoining foreland or related basins that eventually act as aquifers. We illustrate this by integrating observations from our long-time, ongoing studies in two of the largest orogenic systems (source), and the aquifers in their associated foreland basins (sink), located on opposite hemispheres of the globe. These include an active continental margin, the Andean orogenic system (e.g. Ramos Ramos et al., 2012; Ormachea Munoz et al., 2013, 2015, 2016; Raychowdhury et al., 2014), which is, in principle, a modern analogue of the older Himalayan orogenic system associated with the Indus-Ganges-Brahmaputra river systems in South Asia (e.g. Hattori and Guillot, 2003; Hattori et al., 2005; Guillot and Charlet, 2007; Mukherjee et al., 2009b, 2012; Verma et al., 2015, 2016).

## Link between groundwater arsenic content and convergent plate tectonics

A few previous studies have suggested that As-enriched sources can develop through complex interactions between tectonic, geochemical and biological processes (Saunders et al., 2005; Zheng, 2006, 2007; Nordstrom, 2009, 2012; Mukherjee et al., 2014). Nonetheless, a survey of the reported concentrations of As in various lithologies (Hattori and Guillot, 2003 and references therein) from around the world appears to suggest a closer association of primary-
source, solid-phase As with arc magma related to convergent plate boundaries, and thereby in turn with collision belts, which inevitably contain arc-derived components.

The high As content of arc magmas (Hattori and Gulliot, 2003; Hattori et al., 2005; Gulliot and Charlet, 2007) must have been ultimately derived from a) the subducting oceanic crust with its sedimentary veneer; b) the mantle component of the subducting slab; c) the mantle wedge component overlying the slab; or d) the overlying arc or continental crust through which the arc magma ascends to the surface. Nevertheless, ocean-floor basalts comprising the oceanic crust, which are formed by partial melting of the depleted mantle at the mid-oceanic ridge and subsequently hydrated (e.g. serpentinized) by hydrothermal circulation, are not known to be enriched in As. Indeed, samples of basalts from Iceland, located on the Mid-Atlantic Ridge, are reported to have extremely low concentrations of As (<0.01-0.24 mg/kg), with dacites fractionating from these basalts having As concentrations < 0.1 mg/kg (Arnorsson, 2003). A 'typical average' value of 1 mg/kg As from the oceanic spreading centers has been reported (Matschullat, 2000). This indicates that the As is unlikely to have been sourced directly from the convecting, depleted upper mantle, the source of mid-oceanic ridge basalts. Consequently, even if hydrothermal fluids are released by dehydration of hydrated ocean-floor basalts during subduction, they are unlikely to be particularly enriched in As. However, serpentinites in the mantle wedge that overlies the subducting slab can have As concentrations > 100 mg/kg, but As in serpentinites may not be mobile at temperatures < 300°C (Hattori and Guillot., 2003; Deschamps et al., 2013).

114
The alternative possibility is that the elevated As content of subduction- zone volcanics at convergent plate boundaries is caused by the enhanced As content of the sediment veneer that overlies the ocean-floor basalts in the subducting slab. This As must ultimately be derived from terrigenous detritus, since the concentration of As in the continental crust is known to be at least two orders of magnitude higher than that in the depleted mantle, the source region for the mid-oceanic ridge basalts (McDonough, 2004; Salters and Stracke, 2004; Saunders, 2005; Matschullat, 2000, 2011). A perusal of As concentrations in subduction-zone magmas (also referred to as arc magmas) reveals that not all are necessarily enriched in As. A wide variability in the As content in arc volcanics is observed, ranging from very low to high values (e.g. <0.3 mg/kg to 70 mg/kg) (Smedley and Kinniburgh, 2002; Mandal and Suzuki, 2002; Henke, 2009, and references there-in). The arc magmas of some volcanoes in the southern part of Japan-Kurile volcanic chain have low As content comparable to normal depleted mantle-derived magmas. In contrast, several volcanoes in the northern part of the same region [e.g. Esan (Japan) and Onekotan (Kuriles)], whose extrusives have a significant component of melt derived from subducted sediments, unlike the volcanoes in the southern part of the arc, where the As content in the rocks is much lower (Ryan et al., 1995) and underlain by thick arc basement, have very high As values in their magmas (Noll et al., 1996; Henke, 2009). Similarly, medium to high As contents have been consistently reported from the arc extrusives of Cordilleran orogenic belts of British Columbia (Boyle et al., 1998), Alaska (Crock et al., 1999), Mexico (Armienta et al., 2001), Chile (Noll et al., 1996) and Peru (Noble et al., 1998), all of which are active continental margins.

136

137.
Based on this compilation, we generalize that the As content is variable in zones of
ocean-ocean convergence but, almost always high in As in magmatic settings, where the arc
magma ascends through an overlying continental crust (active continental margin), suggesting
that interaction of a volatile-enriched arc magma with continental crust is the most potent source
of primary As enrichment in contrast to other tectonic settings. However, this source and
processes of As cycling in the subsurface and extrusion may not have been uniform throughout
geological history. Comparisons of As concentrations of the present-day mantle with the
estimated As content for the primitive mantle suggest that As concentration in the present-day
mantle is far less than in the past (Palme and O'Neill, 2004; Saltersand Stracke, 2004).

147

148 The hypothesis: mobilization of arsenic from source to sink

149 a) Arc magmas as primary arsenic sources

150 Our proposed hypothesis is based on the following premises: (1)As is primarily
151 concentrated within continental crust, and therefore, in any tectonic regime, the continental crust
152 must represents the ultimate reservoir from which groundwater As may be derived; (2) As is
153 mobilized via hydrothermal action by neo-magmatic hydrous fluids generated by dehydration
154 and metasomatism and (3) As mobilization is enhanced in any situation that facilitates prolonged
155 interaction between continental crust and hot hydrous fluids or magmas.
156

156

157 Arsenic mobilization from the sediment veneer of the subducting plate to the fluid will be
158 most effective in continental domains with elevated geothermal gradients, such as near active
159 (e.g. Andes; Raychowdhury et al., 2014) or ancient centers of magmatic activity (e.g. Indus-
160 Tsangpo suture zone lithologies with As ~257 mg/kg of the Himalayas; Hattori et al., 2005).
Meteoric water in such domains can percolate to depth, become heated, and form hydrothermal systems (e.g. Costa Rican geothermal wells, As: ~25900 µg/L; Hammarlund et al., 2009; Mexican geothermal system, As ~24000µg/L, Chilean hot spring, As~28500 µg/L; Lopez et al., 2012 and references there-in) that can efficiently remove As and similar labile elements from the crust owing to their moderate volatility and high solubility (Noll et al., 1996; Webster and Nordstrom, 2003; Criaud and Fouillac, 1989; Stauffer and Thompson, 1984).

The limits of As mobilization by such fluids are defined by the extent of hot water-rock interaction, which in turn is constrained by the maximum depth to which water can penetrate from the surface (Gleeson and Inge Britsen, 2016). Arsenic can only be mobilized from deeper parts of the continental crust if an appropriate mechanism for introducing hot hydrous fluids can be identified. Our model argues that it is precisely this mechanism that is instrumental in As mobilization in active continental margins as shown in **Figure 2**: hot hydrous fluids that mobilize As are derived from the subducting slab (Tatsumi, 1989) (Figure 2, a), and may or may not be enriched in As at the time of slab dehydration. The As content of these fluids depends on the proportions of continental terrigenous detritus (Figure 2, c) and hydrated oceanic crust (Figure 2, d) associated with the subducted slab at the time of fluid release. The fluids may also be associated with slab-derived melts (Figure 2, b). It may subsequently metasomatically be depleted in continental lithospheric wedge (Figure 2, e), thereby lowering the mantle solidus and initiating the production of hydrous arc magmas. Such hydrous arc magmas are rich in As owing to its incompatible nature comparable to LREEs (Noll et al., 1996). Fractionation of these magmas leads to the generation of high-Al basalts/gabbros, andesites/diorites and dacites/granodiorites (Sisson and Grove, 1993) in active or ancient magmatic arcs, which are known to have high to
very high (up to 1500 mg/kg) solid-phase As (Henke, 2009). The chemistry of the arc magmas may also be influenced by sedimentary input into the trench (Plank and Langmuir, 1993)(Figure 2, c). Although the mechanism of magma generation is essentially similar for both ocean-ocean subduction zones and continental active margins, a major difference is that the ascending magma in the continental active margins would subsequently interact with the thick continental crust as it rises, whereas such interactions are very limited in an ocean-ocean setting. Since the magma is water-enriched, hydrous fluids may be expelled from the ascending magma if the water saturation levels in the magma are exceeded at any depth with decompression. This may lead to assimilation and fractional crystallization processes in the lower and middle continental crust around the ascending volcanic pipe (Figure 2, g), or in the vicinity of any deeper level magma chamber where the magma may pond on its way to the surface(Bebout and Barton, 1989). Thus, the rising hydrous magma is able to access and mobilize As from the lower continental and arc crust, in which the As content is in any case enhanced with respect to the mantle and oceanic crust. Thus, continental arc volcanics tend to have the highest primary As.

In such magmatic settings, the release of exsolving fluids from the rising magma or heating of percolating meteoric water sets a up deep hydrothermal circulation system (e.g. Turkish geothermal wells, As ~251 µg/L; Baba and Deniz, 2008, Baba and Sözbilir, 2012; Taiwanese geothermal system, As ~1456 µg/L; Maity et al., 2017)(Figure 2, h).

However the exact mechanism by which As is partitioned between the volcanic fluids and magma is not very well understood due to lack of data in melt and gaseous phase (Lopez et al., 2012). Experimental and theoretical work by Pokrovski et al., 2002 on the stoichiometry and
stability of As gaseous complexes in the system As-H₂O-NaCl-H₂S at P-T conditions of 6×10⁷ Pa and 500°C points towards As(OH)₃, as the predominant As complex responsible for the transport and fractionation of As in volcanic gages and boiling hydrothermal systems. In contrast the sources and behavior of As in liquid dominated hydrothermal systems is better apprehended (Bundschuh and Maity, 2015). High temperature, pressure, and residence time along with moderate solubility and volatility of As, and undersaturation with respect to arsenopyrite and other arsenic minerals in hydrothermal fluids results in extraction of As from hot subsurface rocks (Ballantyne, and Moore, 1988; Webster and Nordstrom, 2003) under specific Eh-pH conditions (Figure 3). A plethora of other elements/phases such as B, F, Cr, Sr, Ba, Sb, Li, Se, Tl, Hg, and H₂S are leached along with As. Together with As this element assemblage is a good indicators of interaction of such fluids with native groundwater (Webster and Nordstrom, 2003; Bundschuh and Maity, 2015). More As may be acquired by mixing with other enriched hydrothermal fluids of non-volcanic origin (Noll et al., 1996; Webster and Nordstrom, 2003; Criaud and Fouillac, 1989; Stauffer and Thompson, 1984), which are commonly detectable in hydrothermally sourced groundwater discharge (e.g. hot springs observed in orogenic systems). Redox processes play a vital role in influencing this fluid chemistry. Typically, the hydrothermal fluids originate in reducing redox conditions, and with pH values of 4–8. H₃AsO₃⁰ª is the dominant As species (Figure 3) (Ballantyne and Moore, 1988; Pokrovskiet al., 1996; Lopez, et al., 2012). H₃AsO₃⁰ª is considered to be a dissolution product of both As oxide (As₄O₆) and orpiment (As₂S₃) in reduced fluids which persists over a wide temperature range and acidic to neutral pH conditions (Ballantyne, and Moore, 1988). Arsenic can also occur in hydrothermal fluids as thioarsenates/thioarsenites and methylated As compounds under strongly sulphidic and microbially mediated anoxic conditions respectively (Planer-Friedrich et al., 2006, 2007). Upon
230 dissolution As can either remain in the liquid phase and emerge via hot springs or partition into
231 the gas/vapour phase, emerging through fumaroles and steam fields. Upon cooling, such fluids
232 precipitate common As-bearing minerals (e.g. arsenopyrite, realgar, orpiment, and pyrite), which
233 contain a suite of chalcophile elements (Smedley and Kinniburgh, 2002), including gold (Reich
234 et al., 2005; Arehart, 1996) along their flow paths (Goldhaber et al., 2001) (Figure 2, i) thereby
235 further enhancing the As content of the continental crust.
236

237 Owing to its volatile nature As is also a common component in volcanic gases with
238 enrichment factors of 100 to 1000 to magma (Symonds, 1990; Mambo et al., 1991; Symonds et
239 al., 1987; Quisefit et al., 1989). The subsequent separation in vapor phase leads to selective
240 dissemination of Asinto the aquatic system and atmosphere during magmatism. Thus, volcanoes
241 are significant sources of arsenic emissions to the atmosphere (Signorelli, 1997; Nriagu, 1989).
242

## b) Surface expression of tectonics on arsenic distribution

244 Arc volcanism in Andes has led to deposition of As-laden volcanic ash and detritus
245 (Figure 2,j) that can be carried to downstream basins. Arsenic enriched rhyolitic glass, volcanic
246 ash, and associated silicates in sediments and metamorphic deposits (Asupto 10 mg/kg;
247 Raychowdhury et al., 2014) undergo hydrolytic dissolution and produce an influx of major (e.g.,
248 Na, K, Si, and HCO₃⁻) and minor (e.g., oxyanions of As, V, and Mo) solutes to groundwater,
249 which leads to precipitation of clays (Mukherjee et al., 2014; Raychowdhury et al., 2014), under
250 conducive climatic conditions. Himalayan-arc-derived lithologies also comprise significant
251 proportions of mafic and intermediate rocks (predominantly andesites), all of which are enriched
252 in As compared to their non-arc equivalents, owing to interaction with subduction-zone fluids
253 (Hattori et al., 2005; Guillot and Charlet, 2007).
254

255 Our study suggests that chemical weathering and leaching of more soluble and labile,
256 physio-sorbedsolid-phase As from the meta-stable, high-temperature arc-sourced mafic minerals
257 (e.g. olivine, pyroxenes or even serpentine) in these rocks (As~19 mg/kg; Verma et al., 2016)
258 facilitates release of this As into the hydrological system (As up to 4100 µg/L; Mukherjee et al.,
259 2009b). Some circulating As-laden hydrothermal fluids may also discharge as geothermal waters
260 (As up to 25900 µg/L; Hammarlund et al., 2009). Subsequently, with the initiation of orogeny at
261 active continental margins, the As-laden magmatic arcs coalesce with sediments and rocks of the
262 rising orogen. With continuing convergence, slices of serpentinizedand, therefore, As-enriched
263 mantle rock (As~275mg/kg; Hattori et al., 2005) are also incorporated into the orogen by
264 thrusting (Hattori and Guillot, 2003). Sediments derived from the rapidly rising orogenic belt by
265 weathering of the exhumed As-laden magmatic arc and obducted, serpentinized mantle rocks are
266 subsequently deposited in adjacent foreland and even back-arc basins (Verma et al., 2016).
267 During protracted convergence over geologic time, several generations of foreland basins can
268 form and coalesce with the main orogenic belt (e.g. the Siwaliks in the Himalayas, with As~10
269 mg/kg; Guillot et al., 2015).
270

271 As rivers or glaciers cut through the orogenicbelt, they erode the foreland sediments
272 (Guillot and Charlet, 2007; Verma et al., 2016) and any further exhumed, arc-derived magmatic
273 rocks, and deposit the weathered As-rich sediments in the most recent foreland basins(e.g., Terai,
274 Nepal; Asup to 27 mg/kg; Guillot et al., 2015). Proximity to these orogenic sources results in the
possibility of enhanced chemical weathering and leaching (Verma et al., 2016) of more soluble and labile, physi-sorbed, solid-phase primary As from meta-stable, high-temperature arc-sourced lithologies (primary As source). With increasing distance from these sources, primary As is likely to reside in more recalcitrant or more strongly-bonded phases (e.g. low-temperature/late-phase silicates) (Onishi and Sandell, 1955), which are less prone to chemical weathering (Henke, 2009). Conversely, with distance, the released As become strapped in physi-sorbed, more labile, secondary solidphases, which act as immediate (secondary) source of groundwater As in adjoining foreland basin aquifers by redox-dominated reactions (Mukherjee et al., 2014). This liberated As, can co-precipitate with or adsorb onto secondary Fe (III) (oxyhydr) oxides (Smedley and Kinniburgh, 2002) or can be re-sequestered by re-sorption or by co-precipitation with authigenic Fe (II) sulfides under sulfate-reducing conditions (i.e. aquifer sediment sink) (Lowers et al., 2007; Mukherjee and Fryar, 2008; Mukherjee et al., 2008b) (Figure 4). Ultimately, this As-laden groundwater is abstracted for drinking purposes and other human activities like irrigation for food crop production. Thus the geogenic-sourced As eventually ends up in a glass of drinking water. Similarly, the soil As, deposited from the abstracted irrigation water, is taken up by crops and vegetable-growing plants, eventually bio-accumulating in the human body by ingestion. The outcome of such ingestion results in serious health hazards, including arsenicosis and allied health issues that have been considered to be the “largest mass poisoning in human history” (Smith et al., 2000). On the other hand, these As-enriched aquifer sediments are eventually re-worked by terrigenous erosional processes and subsequently transported back to ocean basin, thus closing the geogenic As cycle.

296

297 Evidence across the globe
In addition to integrating the knowledge of orogen-sourced sediments and groundwater
chemistry of ancient (Himalayan) and modern (Andean) orogen, we compiled the tectonic
settings and groundwater As-enrichment data from 63 major aquifers across the world
(convergent (34), non-convergent (27), and mixed (2) setting **Table 2**). As visible from **Figure 5**, a remarkably high proportion of As-affected aquifers are located in convergent settings (90%,
n = 28 of 31), particularly magmatic arc settings (9 of 9). In comparison, a far lower proportion
(5%, n = 1 of 19) of basins in other tectonic settings (e.g. passive margin or intracratonic) are
affected by As. Exceptions to this generalization can be observed in aquifers within several rift-
related settings (n=7), that are found to have enriched As in groundwater, e.g. the Basin and
Range Province, the Newark basin, the Rhine graben, the Albuquerque basin/Middle Rio Grande
rift basin, the Song-Liao basin, Hetao basin and the Gettysburg basin. Interestingly, all these rift
basins have a provenance that supplies arc detritus, commonly andesite (see **Table 2**). While
most have a primary source, the Newark basin appears to have undergone As-enrichment in two
stages – a primary source in the Avalon terrane was initially deposited in the Appalachian
foreland, from which the As enriched phases were where eventually deposited in the Newark
basin(Peters, 2008; Blake and Peters, 2015). This two-stage process may represent an ancient
analog to the present-day As enrichment in the Ganges-Brahmaputra river basin. Similarly,
aquifers in two basins (e.g. Red River and Mekong), which are also As-polluted, have a mixed
convergent/non-convergent setting, with sediment sources from ancient Qamdo-Simao arc rocks
(Stanger, 2005).

318

319 Limitations of the model?

320
While many aquifers in foreland sedimentary basins adjacent to major orogenic belts have highly As-enriched groundwater (e.g. Himalayas, Andes, southern parts of Western Cordillera), others do not (e.g. Alps, northern parts of Western Cordillera, Pyrenees). We speculate that this depends on the extent of heating of the orogen required to release deep, As-enriched hydrothermal fluids. Orogens can be labeled as “hot” or “cold” based on the heat generated during their formation (Collins, 2002; Beaumont et al., 2006) (Figure 6). In cold orogens, temperatures generally do not exceed 500°C, while hot orogens are characterized by much higher maximum temperatures (Beaumont, 2013), which may go up to 1000°C (Brown et al., 2007). Cold orogens (e.g. Southern Alps of New Zealand, Pyrenees, and the Alps) are generally smaller and lack the magnitude of crustal thickening and related thermal relaxation that are necessary to achieve high temperatures. In larger, hot orogens (e.g., Himalayas, Tibet, and the Andes), there is higher radiogenic heat production and/or tectonic switching during accretionary orogenesis, when lithospheric extension or slab breakoff is punctuated by intermittent, short-term contractions.

## Conclusion

Based on the average crustal concentration of As, any aquifer is susceptible to hosting As-enriched groundwater. However, most major occurrences of As-enriched groundwater are within basins located near active or ancient magmatic arcs that formed in continental convergent zones. Consistency in such occurrences, from Asia to the Americas, cannot be a random observation, nor can it be explained away as manifestations of heterogeneous As-mobilizing (bio)geochemical conditions. Instead, it must be related to underlying geodynamic processes that have regional-scale predictability. Our extensive studies for more than three decades in ancient
344 (Himalayan) and modern (Andean) orogenic-sourced aquifers, and observations from 63
345 aquifers, globally suggest that As enrichment of aquifer matrix and groundwater is related to
346 surficial extrusion and subsequent dispersal of particulate or dissolved As by hot, metasomatic
347 fluids. These fluids are generated from deep crustal processes in subduction zones, which
348 scavenge As along their path to the surface through thick continental crustal sequences by
349 extensive water-rock interaction. Weathering of volcanic glasses and subduction-fluid hydrated
350 mafic phases of arc-derived lithologies subsequently transfer As into the drainage networks of
351 the foreland-basin aquifers that receive arc-derived detritus. The surface geological processes
352 like chemical weathering and biogeochemical processes like redox cycling of Fe-S-C plays a
353 pivotal role in this final phase, where As is eventually introduced to groundwater systems. This
354 As-laden groundwater is abstracted for drinking water, domestic uses and crop production. This
355 As in the drinking water or food crop eventually bio-accumulates in human body, potentially
356 causing arsenicosis and allied health issues that have been considered to be the "largest mass
357 poisoning in human history". On the other hand, these As-enriched aquifer sediments are
358 eventually re-worked by terrigenous erosional and denudation processes, and subsequently
359 transported back to ocean basin, thus closing the geogenic As cycle.
360

361 This work outlines the specifics of the mechanism that would drive the processes of
362 groundwater As enrichment across the spatio-temporal scales, i.e. tectonic-scale taking place
363 over millions of years and in continental-scale and groundwater pollution taking place at a
364 human time-scale in village to household scale. Thus, as a corollary, we provide a model to
365 demonstrate the connectivity between global geological processes and individual human health,
366 where tectonism can eventually be related to arsenicosis, across the spatio-temporal scale.
367 Exceptions to this general observation are seen in several rift basins, which also appear to have
368 sediment provenances from nearby magmatic arcs.

369

370 Acknowledgements

371 The authors thank C. Beaumont (Dalhousie University), D. Kirk Nordstrom (USGS), Kevin
372 Henke (University of Kentucky), Yan Zheng (Southern University of Science and Technology,
373 China), and Tapas Bhattacharya (University of Calcutta) for helpful comments and inspiration,
374 and PalashDebnath and SoumendraNathBhanja (IIT Kharagpur) for assistance with figures. AM
375 acknowledges the time and resources available from his employer to write the manuscript. No
376 external funding was available and used for this work.
377

378 **References**

379

380 Andriashek, L.D., 2000, Geochemistry of selected glacial and bedrock geologic units, Cold Lake
381 Area, Alberta. Alberta Geological Survey Earth Sciences Report, 2000-10.

382

383 Arehart, G.B., 1996. Characteristics and origin of sediment-hosted disseminated gold deposits: a
384 review. Ore Geology Reviews,11(6), 383-403.

385

386 Armienta, M.A., Villaseñor, G., Rodríguez, R., Ongley, L.K., Mango, H., 2001, The role of
387 arsenic-bearing rocks in groundwater pollution at Zimapan Valley, México. Environmental
388 Geology, 40(4-5), 571-581.doi:10.1007/s002540000220

389

390 Arnorssón, S., 2003. Arsenic in surface- and up to 90°C ground waters in a basalt area, N-
391 Iceland: processes controlling its mobility. Applied Geochemistry, 18, 1297-
392 1312.doi:10.1016/S0883-2927(03)00052-0

393

394 Ayotte, J.D., Montgomery, D.L., Flanagan, S.M., Robinson, K.W., 2003. Arsenic in groundwater
395 in eastern New England: occurrence, controls, and human health implications. Environmental
396 Science and Technology, 37(10), 2075-2083.

397

398 Baba, A., Deniz, O., 2008. Potential, Determination of Applicability and Evaluation of
399 Environmental Effects of Geothermal Source in the Biga Peninsula, TÜBİTAK
400 Project.CAYDAG-104Y082, 349 [in Turkish].

401 Baba, A., Sözbilir, H., 2012. Source of arsenic based on geological and
402 hydrogeochemical properties of geothermal systems in Western Turkey. *Chemical Geology*,
403 334, 364-377.

404

405 Ballantyne, J.M., Moore, J.N., 1988. Arsenic geochemistry in geothermal
406 systems. Geochimica et Cosmochimica Acta, 52, 475-483.

407
408 Bauder, J.W., 1995, Written Communication, June, Bozeman, Montana.

409
410 Beaumont, C., Nguyen, M., Jamieson, R., Ellis, S., 2006. Crustal flow modes in large hot
411 orogens. Geological Society, London, Special Publications, 268, 91-145.
412 doi:10.1144/GSL.SP.2006.268.01.05

413
414 Beaumont, C., 2013. Personal communication.

415
416 Bebout, G.E., Barton, M.D, 1989. Fluid flow and metasomatism in a subduction zone
417 hydrothermal system: Catalina Schist terrane, California. Geology, 17, 976-980.
418 doi:10.1130/0091-7613(1989)017<0976:FFAMIA>2.3.CO;2

419
420 Berg, M., Tran, H.C., Nguyen, T.C.,Pham, H.V., Schertenleib,R., Giger,W., 2001. Arsenic
421 contamination of groundwater and drinking water in Vietnam: a human health threat.
422 Environmental Science and Technology, 35(13), 2621-2626.

423
424 Bhattacharya, P., Claesson, M., Bundschuh, J., Sracek, O., Fagerberg, J., Jacks, G., Martin, R.A.,
425 Storniolo, A. del R., Thir, M., 2006. Distribution and mobility of arsenic in the Río Dulce
426 alluvial aquifers in Santiago del Estero Province Argentina. Science of Total Environment, 358,
427 97-120.

428
429 Bexfield, L.M., Plummer, L.N., 2003. Occurrence of arsenic in ground water of the Middle Rio
430 Grande Basin, central New Mexico. In: Welch, A.H., Stollenwerk, K.G. (Eds), Arsenic in
431 Groundwater: Geochemistry and Occurrence. New York: Springer-Verlag, pp. 295-327.

432
433 Bi, R.L., 1994. A Preliminary Study on the Arsenic Enrichment of Groundwater in Chianan
434 Area, Taiwan.Department of Geosciences, National Taiwan University, Taipei.

435
436 Blake, J.M., Peters, S.C., 2015. The occurrence and dominant controls on arsenic in the Newark
437 and Gettysburg Basins. Science of the Total Environment, 505, 1340-1349.

438 dx:10.1016/j.scitotenv.2014.02.013
439
440 Blake, J.M., Peters, S.C., Johannesson, K., 2017. Application of REE geochemical signatures for
441 Mesozoic sediment provenance to the Gettysburg Basin, Pennsylvania. Sedimentary Geology,
442 349, 103–111.

443
444 Boyle, D.R., Turner, R.J.W., Hall, G.E.M., 1998. Anomalous arsenic concentrations in
445 groundwaters of an island community, Bowen Island, British Columbia. Environmental
446 Geochemistry and Health, 20, 199–212.

447 doi:10.1023/A:1006597311909

448
449 Brown, M., 2007. Metamorphism, plate tectonics, and the supercontinent cycle. Earth Science
450 Frontiers, 14, 1–18

451
452 Bundschuh, J., Farias, B., Martin, R., Storniolo, R., Bhattacharya, P., Cortes, J., Albouy,
453 B.R.,2004. Groundwater arsenic in the Chaco–Pampean Plain, Argentina: case study from Robles
454 County, Santiago del Estero Province. Applied Geochemistry, 19 (2), 231-243.

455
456 Bundschuh, J., Maity, J.P., 2015. Geothermal arsenic: Occurrence, mobility and environmental
457 implications. Renewable and Sustainable Energy Reviews, 42, 1214–1222.

458
459 Chery, L., Barbier, J., Arnaud, C., 1998. High heavy metal (Sb, As, Ba, Ni, Pb and
460 Zn)Concentrations in drinking-water supplies: Relationship with the natural geochemical
461 background and an aid in sanitary control: Hydrogeologie,4, 57–62 [in French].

462
463 Choudhury, R., Nath, B., Khan, M.R., Mahanta, C., Ellis, T., Geen, A., 2018. Impact of aquifer
464 flushing across a 35Km transect perpendicular to the upper Brahmaputra river in Assam, India.
465 Water Resources Research.doi:10.1029/2017WR022485

466
467 Collins, W.J., 2002. Hot orogens, tectonic switching, and creation of continental
468 crust. Geology, 30(6), 535-538.

469
Cook, S.J., Levson, V.M., Giles, T.R., Jackaman, W., 1995. A comparison of regional lake sediment and till geochemistry surveys—a case-study from the Fawnie Creek area, Central British Columbia: Exploration Mining Geology, 4, 93–110.

Criaud, A., Fouillac, C., 1989, The distribution of arsenic (III) and arsenic (V) in geothermal waters: examples from the Massif Central of France, the island of Dominica in the Leeward islands of the Caribbean, the Valles Caldera of New Mexico, USA, and southwest Bulgaria. Chemical Geology, 76(3-4), 259–269.

Crock, J.G., Gough, L.P., Wanty, R.B., Day, D.C., Wang, B., Gamble, B.M., Henning, M., Brown, Z.A., Meier, A.L., 1999. Regional Geochemical Results from the Analyses of Rock, Water, Soil, Stream Sediment, and Vegetation Samples — Fortymile River Watershed, East-Central Alaska, 1998 Sampling, U.S. Geological Survey, Reston, Virginia, Open-File Report 00-511. http://pubs.er.usgs.gov/publication/ofr9933

Dasher, G.H., Lomax, T., and Jewett, S.C., 2012, AKMAP 2006 - 2007 Aleutian Islands Coastal Survey - Statistical Summary. Alaska Department of Environmental Conservation Division of Water, Water Quality Standards, Assessment and Restoration Program, Alaska Monitoring and Assessment Program 555 Cordova St., Anchorage, AK 99501.

Deschamps, F., Godard, M., Guillot, S., Hattori, K., 2013. Geochemistry of subduction zone serpentinites: A review. Lithos, 178, 96-127. doi:10.1016/j.lithos.2013.05.019

Ellis, A.J., Mahon, W.A.J., 1977. Chemistry and Geothermal Systems. Academic Press, New York.

Fitzgerald, D., Chanasyk, D.S., Neilson, R.D., Kiely, D., Audette, R., 2001. Farm well water quality in Alberta. Water Quality Resources Journal Canada, 36, 565–588.
499 Gamaletos, P., Godelitssas, A., Dotsika, E., Tzamos, E., Gottliche, J., Fillipidis, A., 2013.

500 Geological sources of As in the environment of Greece: A review. In: Scozzari, A., Dotsika, E., (Eds.), The Handbook of Environmental Chemistry. Springer, Berlin, pp. 1-37.

501
502
503 Glass, R.L., 1996. Ground-water conditions and quality in the western part of Kenai Peninsula, south-central Alaska. U.S. Geological Survey Open-File Report 96-466, 66.

505
506 Gleeson, T., Ingebritsen, S.E. (Eds.), 2016. Crustal permeability. Wiley-Blackwell, 472 p. ISBN:
507 978-1-119-16656-6

508
509 Goldhaber, M.B., Irwin, E., Atkins, B., Lee, L., Black, D.D., Zappia, H., Hatch, J., Pashin, J.,
510 Barwick, L.H., Cartwright, W.E., Sanzolone, R., Rupert, L., Kolker, A., Finkelman, R., 2001.
511 Arsenic in Stream Sediments of Northern Alabama, U.S. Geological Survey Miscellaneous Field
512 Studies Map, Reston, VA.

513
514 Grimmett, R.E.R., McIntosh, I.G., 1939. Occurrence of arsenic in soils and waters in the
515 Waiotapu Valley, and its relation to stock health. New Zealand Journal of Science and
516 Technology, 21, 138-150.

517
518 Grossier, P., Ledrans, M., 1999. Arsenic in drinking water: a primary approach to assess exposure
519 of the French population: Techniques Sciences Methodes. GenieUrbain-Genie Rural, 2, 27-32
520 [in French].

521
522 Guillot, S., Charlet, L., 2007. Bengal arsenic, an archive of Himalaya orogeny and
523 paleohydrology. Journal of Environmental Science and Health Part A 42, 1785-1794.
524 doi:10.1080/10934520701566702

525
526 Guillot, S., Garcon, M., Weinman, B., Gajurel, A., Tisserand, D., France-Lanord, C., van Geen,
527 A., Chakraborty, S., Huyghe, P., Upteri, B.N., Charlet, L., 2015. Origin of arsenic in Late
528 Pleistocene to Holocene sediments in the Nawalparasi district (Terai, Nepal). Environmental
529 Earth Sciences, 74, 2571-2593.
doi:10.1007/s12665-015-4277-y

Gurung, J.K., Ishiga, H., Khadka, M.S., 2005, Geological and geochemical examination of arsenic contamination in groundwater in the Holocene Terai Basin, Nepal: Environmental Geology, 49(1), 98–113.

Guo, H., Yang, S., Tang, X., Li, Y., Shen, Z., 2008, Groundwater geochemistry and its implications for arsenic mobilization in shallow aquifers of the Hetao Basin, Inner Mongolia: Science of the Total Environment, 393, 131–144.

Hammarlund, L., Pionens, J., Bhattacharya, P., Mukherjee, A., Nordstrom, D.K., Bundschuh, J., Alvarado, G.E., 2009. Study of geothermal water-groundwater interaction and evolution in thermal fields of Costa Rica. Geological Society of America Abstracts with Programs 41 (7), 219.

Hammarlund, L., 2009. Arsenic in geothermal waters of Costa Rica—A minor field study. Stockholm, Sweden: MSc Thesis, Department of Land and Water Resources Engineering, Royal Institute of Technology.

Hattori, K.H., Guillot, S., 2003. Volcanic fronts form as a consequence of serpentinite dehydration in the forearc mantle wedge. Geology, 31(6), 525–528.

doi:10.1130/0091-7613(2003)031<0525:VFFAAC>2.0.CO;2

Hattori, K., Takahashi, Y., Guillot, S., Johanson, B., 2005. Occurrence of arsenic (V) in forearc mantle serpentinites based on X-ray absorption spectroscopy study. Geochimica et Cosmochimica Acta, 69(23), 5585–5596. doi:10.1016/j.gca.2005.07.009

Heinrich, C. A., Eadington, P. E., 1986. Thermodynamic predictions of the hydrothermal chemistry of arsenic, and their significance for the paragenetic sequence of some cassiterite- atsenopyrite-base metal sulfide deposits. Economic Geology, 81, 511–529
561 Henke, K.R., 2009. Arsenic in natural environments. In Henke, K.R., and ed., Arsenic — Environmental Chemistry, Health Threats and Waste Treatment: Chichester, U.K., John Wiley & Sons, p. 69–236.

564 doi:10.1002/9780470741122.ch3

565 Katsoyiannis, I.A., Mitrakas, M., Zouboulis, A.I., 2015. Arsenic occurrence in Europe: emphasis in Greece and description of the applied full-scale treatment plants. Desalination and Water Treatment, 54(8), 2100-2107.

569 Klinchuch, L.A., Delfino, T.A., Jefferson, J.L., Waldron, J.M., 1999. Does biodegradation of petroleum hydrocarbons affect the occurrence or mobility of dissolved arsenic in groundwater? Environmental Geosciences, 6(1), 9–24.

573 Lopez, D.L., Bundschuh, J., Birkle, P., Armienta, M.A., Cumbal, L., Sracek, O., Cornejo, L., Ormachea, M., 2012. Arsenic in volcanic geothermal fluids of Latin America. Science of the Total Environment, 429, 57–75.

577 Lowers, H.A., Breit, G.N., Foster, A.L., Whitney, J., Yount, J., Uddin, M.N., Muneem, A.A., 2007. Arsenic incorporation into authigenic pyrite, Bengal Basin sediment, Bangladesh. Geochimica et Cosmochimica Acta, 71 (11), 2699–2717.

581 Maity, J.P., Chen C-Y., Bundschuh, J., Bhattacharya, P., Mukherjee, A., Chang, Y-F., 2017. Hydrogeochemical reconnaissance of arsenic cycling and possible environmental risk in hydrothermal systems of Taiwan. Groundwater for Sustainable Development, 1-13.

585 doi: 10.1016/j.gsd.2017.03.0011

586 Mandal, B.K., Suzuki, K.T., 2002. Arsenic round the world: a review. Talanta, 58 (1), 201–235.

588 Mambo, V. S., Yoshida, M., Matsuo, S., 1991. Partition of arsenic and phosphorus between volcanic gases and rock. Part I: Analytical data and magmatic conditions of Mt. Usu, Japan. Journal of Volcanology and Geothermal Research, 46, 37–47.
592
593 Margat, J., 2008. Great aquifer systems of the world. In: Cherry, L., Marsily, G.(eds), Aquifer
594 systems management – Darcy’s legacy in a world of impeding water shortage. Taylor & Francis
595 Group, London, UK, pp. 105–116.

596
597 Matschullat, J., 2000. Arsenic in the geosphere-a review. Science of the Total Environment.
598 249(1-3), 297-312.doi:10.1016/S0048-9697(99)00524-0

599
600 Matschullat, J., 2011. The global arsenic cycle revisited. In: Deschamps E., Matschullat, J. (eds),
601 Arsenic: Natural and Anthropogenic. CRC Press, London, pp. 3 – 26.

602
603 McArthur, J.M., Banerjee, D.M., Hudson-Edwards, K.A., Mishra, R., Purohit, R., Ravenscroft,
604 P., Cronin, A., Howarth, R.J., Chatterjee, A., Talukder, T., Lowry, D., Houghton, S., Chadha,
605 D.K., 2004. Natural organic matter in sedimentary basins and its relation to arsenic in anoxic
606 groundwater: the example of West Bengal and its worldwide implications: Applied
607 Geochemistry, 19, 1255-1293.

608
609 McDonough, W.F., 2004. Composition model for the Earth's core. In: Carlson, R.W., Holland,
610 H.D., Turekian, K.K. (eds.), Treatise on Geochemistry: Volume 2: The Mantle and Core.
611 Elsevier Science, pp. 547–568. doi:10.1016/B0-08-043751-6/02015-6

612
613 Mukherjee, A., Fryar, A.E., 2008. Deeper groundwater chemistry and geochemical modeling of
614 the arsenic affected western Bengal basin, West Bengal, India. Applied Geochemistry, 23, 863–
615 892.

616
617 Mukherjee, A., Bhattacharya, P., Savage, K., Foster, A., Bundschuh, J., 2008a. Distribution of
618 geogenic arsenic in hydrologic systems: Controls and challenges. Journal of Contaminant
619 Hydrology, 99, 1–7. doi:10.1016/j.jconhyd.2008.04.002

620
621 Mukherjee, A., von Brömssen, M., Scanlon, B.R., Bhattacharya, P., Fryar, A.E., Hasan, M.A.,
622 Ahmed, K.M., Jacks, G., Chatterjee, D., Sracek, O., 2008b. Hydrogeochemical comparison and
effects of overlapping redox zones on groundwater arsenic near the western (Bhagirathi sub-basin, India) and eastern (Meghna sub-basin, Bangladesh) of the Bengal basin. Journal of Contaminant Hydrology, 99, 31–48.

Mukherjee, A., Fryar, A.E., and O’Shea, B.M., 2009a. Major Occurrences of Elevated Arsenic in Groundwater and Other Natural Waters. In: Henke, K.R. (ed.), Arsenic—Environmental Chemistry, Health Threats and Waste Treatment. John Wiley& Sons, Chichester, UK, pp. 303–350.

Mukherjee, A., Fryar, A.E., Thomas, W.A., 2009b. Geologic, geomorphic and hydrologic framework and evolution of the Bengal basin, India and Bangladesh. Journal of Asian Earth sciences, 34(3), 227–244.

doi:10.1016/j.jseaes.2008.05.011

Mukherjee, A., Scanlon, B.R., Fryar, A.E., Saha, D., Ghosh, A., Chowdhuri, S., Mishra, R., 2012. Solute chemistry and arsenic fate in aquifers between the Himalayan foothills and Indian craton (including central Gangetic plain): Influence of geology and geomorphology. Geochimica et Cosmochimica Acta, 90, 283–302.

Mukherjee, A., Verma, S., Gupta, S., Henke, K.R., Bhattacharya, P., 2014. Influence of tectonics, sedimentation and aqueous flow cycles on the origin of global groundwater arsenic: paradigms from three continents. Journal of Hydrology, 518, 284–299.

doi:10.1016/j.earscirev.2005.04.004

Muloin, T., Dudas, M.J., 2005. Aqueous phase arsenic in weathered shale enriched in native arsenic. Journal of Environmental Engineering and Science, 4(6), 461–468.

Nath, B., Jean, J., Lee, M., Liu, C., 2008. Geochemistry of high arsenic groundwater in Chia-Nan plain, Southwestern Taiwan: Possible sources and reactive transport of arsenic. Journal of Contaminant Hydrology, 99, 85–96.
654 Nimick, D.A., 1998, Arsenic hydrogeochemistry in an irrigated river valley - A re-
655 evaluation. Ground Water, 36(5), 743-735.

656
657 Nimick, D.A., Moore, J.N., Dalby, C.E., Savka, M.W., 1998. The fate of geothermal arsenic in
658 the Madison and Missouri Rivers, Montana and Wyoming. Water Resources Research, 34(11),
659 3051-3067.

660
661 Noble, D.C., Ressel, M.W., Connors, K.A., 1998. Magmatic As, Sb, Cs and other volatile
662 elements in glassy silicic rocks. Geological Society of America, Abstracts with Programs,30(7),
663 377.

664
665 Noll, P.D. Jr., Newsom, H.E., Leeman, W.P., Ryan, J.G., 1996. The role of hydrothermal fluids
666 in the production of subduction zone magmas: Evidence from siderophile and chalcophile trace
667 elements and boron. Geochimica et Cosmochimica Acta, 60, 587-611. doi:10.1016/0016-
668 7037%2895%2900405-X

669
670 Nordstrom, D.K., 2009. Natural arsenic enrichment: effects of diagenetic-tectonic-hydrothermal
671 cycle. Geological Society of America, Abstracts with Programs 41(7), 217.
672 https://gsa.confex.com/gsa/2009AM/finalprogram/abstract_164767.htm

673
674 Nordstrom, D.K., 2012. Arsenic in the geosphere meets the anthroposphere. In: Ng, Noller,
675 Naidu, Bundschuh, Bhattacharya (eds.), Understanding the Geological and Medical Interface of
676 Arsenic. Taylor and Francis, pp. 15-19.

677
678 Nriagu, J.O., 1989. A global assessment of natural sources of atmospheric trace metals. Nature,
679 338(6210), 47-49.

680
681 O'Shea, B., Jankowski, J., Sammut, J., 2007. The source of naturally occurring arsenic in a
682 coastal sand aquifer of eastern Australia. Science of the Total Environment, 379(2-3), 151-166.

683
684 Onishi, H., Sandell, E.B., 1955. Geochemistry of arsenic. *GeochemicaetCosmochimicaActa*, 7, 1-
685 33.doi:https://doi.org/10.1016/0016-7037(55)90042-9

686
687 Ormachea Muñoz, M., Wern, H., Johnsson, F., Bhattacharya, P., Sracek, O., Thunvik, R.,
688 Quintanilla, J., Bundschuh, J., 2013. Geogenic arsenic and other trace elements in the shallow
689 hydrogeologic system of Southern Poopó Basin, Bolivian Altiplano. Journal of Hazardous
690 Materials, 262, 924-940.

691
692 Ormachea Muñoz, M., Bhattacharya, P., Sracek, O., Ramos Ramos, O., Quintanilla Agurre, J.,
693 Bundschuh, J., Maity, J.P., 2015. Arsenic and other trace elements in thermal springs and in cold
694 waters from drinking water wells on the Bolivian Altiplano. Journal of South American Earth
695 Sciences, 60, 10 – 20.doi:10.1016/j.jsames.2015.02.006

696
697 Ormachea Muñoz, M., Aróstegui, J.L.G., Bhattacharya, P., Sracek, O., Moreno, M.E.G.,
698 Kohfahl, C., Aguirre, J.Q., Diaz, J.H., Bundschuh, J., 2016. Geochemistry of naturally occurring
699 arsenic in groundwater and surface-water in the southern part of the Poopó Lake basin, Bolivian
700 Altiplano. Groundwater for Sustainable Development, 2-3, 104-116.

701
702 Palme, H., O'Neill, H.S.C., 2004. Cosmochemical estimates of mantle composition. In: Carlson,
703 R.W., Holland, H.D., Turekian, K.K. (eds), Treatise on Geochemistry: Volume 2: The Mantle
704 and Core. Elsevier Science, pp. 1-38.

705
706 Pawley, A.R., Holloway, J.R., 1993. Water sources for subduction zone volcanism: New
707 experimental constraints. *Science*, 260, 664-667.
708 doi:10.1126/science.260.5108.664

709
710 Peters, S.C., Blum, J.D., Klaue, B., Karagas, M.R., 1999. Arsenic occurrence in New Hampshire
711 drinking water. *Environmental Science and Technology*, 33(9), 1328-1333.

712
713 Peters, S.C., 2008. Arsenic in groundwaters in the Northern Appalachian Mountain belt: A
714 review of patterns and processes. *Journal of Contaminant Hydrology*, 99, 8-21.
doi:10.1016/j.jconhyd.2008.04.001

Plank, T., Langmuir, C.H., 1993. Tracing trace-elements from sediment input to volcanic output at subduction zones. Nature, 362(6422), 739-743.

doi:10.1038/362739a0

Planer-Friedrich, B., Lehr, C., Matschullat, J., Merkel, B.J., Nordstrom, D.K., Sand-strom, M.W., 2006.Speciation of volatile arsenic at geothermal features in yellow-stone nationalpark. GeochimicaetCosmochimicaActa, 70, 2480-2491.

Planer-Friedrich, B., London, J., McCleskey, R.B., Nordstrom, D. K., Wallschläger, D., 2007.Thioarsenates in geothermal waters of Yellowstone National Park: determination, preservation and geochemical importance. Environmental Science and Technology, 41, 5245-5251.

Piper, J., Kim, N., 2006.Arsenic in Groundwater of the Waikato Region. Environment Waikato Technical Report. Report No.2006/14.

Pokrovski, G., Gout, R., Schott, J. Zotov, A., Harrichoury, J-C., 1996.Thermodynamic properties and stoichiometry of As(III) hydroxide complexes at hydrothermal conditions. GeochimicaetCosmochimicaActa, 60(5), 737-49.

Pokrovski, G.S., Zakirov, I.V., Roux, J., Testemale, D., Hazemann, J.L., Bychkov, A.Y., Golikova, G.V., 2002. Experimental study of arsenic speciation in vapor phase to 500 °C: implications for As transport and fractionation in low-density crustal fluids and volcanic gases. GeochimicaetCosmochimicaActa, 66, 3453-3480.

Price, R.E., Pichler, T., 2007.Elevated arsenic concentrations in Hot Springs Creek, Akutan Island, Aleutian Islands: a natural lab to study point-source pollution of the coastal ocean. Geological Society of America Abstracts with Programs 39 (6), 219.
746 Quisefit, J. P., Toutain, J. P., Bergametti, G., Javoy, M., Cheynet, B., Person, A., 1989. Evolution
747 versus cooling of gaseous volcanic emissions from Momotombo Volcano, Nicaragua:
748 Thermochemical model and observations. GeochimicaetCosmochimicaActa, 53, 2591-2608.

749 Ramos Ramos, O.E., Cáceres, L.F., Ormachea Muñoz, M.R., Bhattacharya, P., Quino, I.,
750 Quintanilla, J., Sracek, O., Thunvik, R., Bundschuh, J., García, M.E., 2012. Sources and
751 behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake
752 Basin, Bolivian Altiplano. Environmental Earth Sciences, 66 (3), 793-807.
753 doi:10.1007/s12665-011-1288-1

754 Ravenscroft, P., Brammer, H., Richards, K.S., 2009. Arsenic Pollution: a Global Synthesis.
755 Wiley-Blackwell Publication, p.588.
756 doi:10.1002/9781444308785

757
758 Raychowdhury, N., Mukherjee, A., Bhattacharya, P., Johanesson, K., Bundschuh, J., Sifunetes,
759 G., Nordberg, E., Martin, R., Storniolo, R., 2014. Provenance and fate of arsenic and other
760 solutes in the Chaco-Pampean Plain of the Andean foreland, Argentina: from perspectives of
761 hydrogeochemical modeling and regional tectonic setup. Journal of Hydrology, 518, 300-316.
762 doi:10.1016/j.jhydrol.2013.07.003

763
764 Reich, M., Kesler, S.E., Utsunomiya, S., Palenik, C.S., Chryssoulis, S.L., Ewing, R.C., 2005.
765 Solubility of gold in arsenian pyrite. GeochimicaetCosmochimicaActa, 69(11), 2781-2796

766
767 Robertson, F.N., 1989, Arsenic in groundwater under oxidizing conditions, south-west United
768 States. Environmental Geochemistry and Health, 11(3-4), 1711-1785.

769
770 Romero, L., Alonso, H., Campano, P., Fanfani, L., Cidu, R., Dadea, C., Keegan, T., Thornton, I.,
771 and Farago, M., 2003. Arsenic enrichment in waters and sediments of the Rio Loa (second
772 region, Chile). Applied Geochemistry, 18(9), 1399-1416.

773
774 Rott, U., Friedle, M., 1999. Subterranean removal of arsenic from groundwater. In: Chappell, W.R., Abernathy, C.O., Calderon, R.L. (Eds), Arsenic Exposure and Health Effects III. Elsevier, Oxford, pp. 389-396.

777 Ryan, J.G., Morris, J., Tera, F., Leeman, W. P., Tsvetkov, A., 1995. Cross-arc geochemical variations in the Kurile arc as a function of slab depth. Science, 270, 625-627. doi:10.1126/science.270.5236.625

781 Salters, V.J.M., Stracke, A., 2004. Composition of the depleted mantle. Geochemistry, Geophysics, Geosystems, 5, Q05B07.

784 doi:10.1029/2003GC000597

785 Saunders, J.A., Lee, M.K., Mohammad, S., 2005. Natural arsenic contamination of Holocene alluvial aquifers by linked tectonic, weathering, and microbial processes. Geochemistry, Geophysics, Geosystems, 6(4), Q04006.

789 doi:10.1029/2004GC000803.

790 Serfes, M., Herman, G., Spayd, S., Reinfelder, J., 2010. Sources, mobilization and transport of arsenic in groundwater in the Passaic and Lockatong Formations of the Newark basin, New Jersey: New Jersey Geologic Society Bulletin, v. 77, Chapter E, E1-E40.

794 Shah, B. A., 2015. Arsenic Contamination in Groundwater in the Middle Gangetic Plain, India: Its Relations to Fluvial Geomorphology and Quaternary Stratigraphy. In: Ramanathan, A., Johnston, S., Mukherjee, A., Nath, B. (Eds.), Safe and sustainable use of arsenic contaminated aquifers in the Gangetic plain. Springer, pp. 33-53.

799 Shimada, N., 1996, Geochemical conditions enhancing the solubilisation of arsenic into groundwater in Japan. Applied Organometallic Chemistry, 10, 667-674.

802 Sims, K.W.W., Newsom, H.E., Gladney, E.S., 1990. Chemical fractionation during formation of the Earth's core and continental crust: clues from As, Sb, W, and Mo. In: Newsom, H.E., Jones,
805 J.H. (eds), Origin of the Earth. Oxford University Press, New York; Lunar and Planetary Institute, Houston, pp. 291–317.

807 Signorelli, S., 1997. Arsenic in volcanic gases. Environmental Geology, 32(4), 239–244.

809 Sisson, T.W., Grove, T.L., 1993. Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism. Contributions to Mineralogy and Petrology, 113, 143–166.

813 doi:10.1007/BF00283225

814 Smedley, P., 2005. Towards a more effective operational response: Arsenic contamination of groundwater in south and east Asian countries II, Technical Report, World Bank, Report No. 31303.

815 Smedley, P.L., Kinniburgh, D.G., 2002. A review of the source, behavior and distribution of arsenic in natural waters. Applied Geochemistry, 17(5), 517–568.

821 doi: 10.1016/S0883-2927(02)00018-5

822 Smith, A.H., Lingas, E.O., Rahman, M., 2000. Contamination of drinking-water by arsenic in Bangladesh: a public health emergency. Bulletin of the World Health Organization, 78 (9), 1093–103.

826 Smith, J.V.S., Jankowski, J., Sammut, J., 2003. Vertical distribution of As(III) and As(V) in a coastal sandy aquifer: Factors controlling the concentration and speciation of arsenic in the Stuarts Point groundwater system, northern New South Wales, Australia. Applied Geochemistry, 18(9), 1479–1496.

831 Stanger, G., 2005. A palaeo-hydrogeological model for arsenic contamination in southern and south-east Asia. Environmental Geochemistry and Health, 27, 359–367.

834
835 Stanton, M.R., Sanzolone, R.E., Sutley, S.J., Grimes, D. J., Meier, A.M., Lamothe, P.J. 2001,
836 Abundance, residence, and mobility of arsenic in Santa Fe Group sediments, Albuquerque Basin,
837 New Mexico. Geological Society of America, Abstracts with Programs 33(5), 2.

838
839 Stauffer, R. E., Thompson, J., 1984. Arsenic and antimony in geothermal waters of Yellowstone
840 National Park, Wyoming, USA. Geochimica et Cosmochimica Acta, 48, 2547-2561.

841
842 Symonds, R. B., Rose, W. I., Reed, M. H., Lichte, F. E., Finnegan, D. L., 1987. Volatilization
843 transport and sublimation of metallic and non-metallic elements in high-temperature gases at
844 Merapi Volcano, Indonesia. Geochimica et Cosmochimica Acta, 51, 2083-2101.

845
846 Symonds, R.B., 1990. Applications of multicomponent chemical equilibria to volcanic gases at
847 Augustine Volcano, volcanic halogen emissions, and volcanological studies of gas-phase
848 transport. Ph.D. thesis. Michigan Technological University.

849
850 Tatsumi, Y., 1989. Migration of fluid phases and genesis of basalt magmas in subduction
851 zones. Journal of Geophysical Research, 94(B4), 4697-4707.
852 doi:10.1029/JB094iB04p04697

853
854 Thompson, T.S., Le, M.D., Kasick, A.R., Macaulay, T.J., 1999. Arsenic in well water supplies in
855 Saskatchewan. Bulletin of Environmental Contamination and Toxicology, 63, 478-483.

856
857 Varnavas, S.P., Cronan, D.S., 1991. Hydrothermal metallogenic processes off the islands of
858 Nisiros and Kos in the Hellenic Volcanic Arc. Marine Geology, 9, 109-133.

859
860 Verma, S., Mukherjee, A., Choudhury, R., Mahanta, C., 2015. Brahmaputra river basin
861 groundwater: Solute distribution, chemical evolution and arsenic occurrences in different
862 geomorphic settings. Journal of Hydrology: Regional Studies, 4, 131-153.
863 http://10.1016/j.ejrh.2015.03.001

864
865 Verma, S., Mukherjee, A., Mahanta, C., Choudhury, R., Mitra, K., 2016. Influence of geology on groundwater-sediment interactions in arsenic enriched tectono-morphic aquifers of the Himalayan Brahmaputra river basin. Journal of Hydrology, 540, 176-195.

868 doi:10.1016/j.jhydrol.2016.05.041

869 Webster, J.G., Nordstrom, D.K., 2003. Geothermal arsenic. In: Welch, A.H., Stollenwerk, K.G. (Eds), Arsenic in Groundwater: Geochemistry and Occurrence. Springer, New York, pp. 101-126.

873 Welch, A.H., Lico, M.S., Hughes, J.L., 1988. Arsenic in groundwater of the Western United States: Ground Water, 26, 333-347.

876 Welch, A.H., Lico, M.S., 1998. Factors controlling As and U in shallow ground water, southern Carson Desert, Nevada. Applied Geochemistry, 13(4), 521-539.

879 Winkel, L.H.E., Casentini, B., Bardelli, F., Voegelin, A., Nikolaidis, N.P., Charlet, L., 2013. Speciation of As in Greek travertines: co-precipitation of arsenate with calcite. Geochimica et Cosmochimica Acta, 106, 99-110.

883 Xia, Y., Liu, J., 2004. An overview on chronic arsenism via drinking water in PR China. Toxicology, 198(1-3), 25-29.

886 Zheng, Y., 2006. The heterogeneity of arsenic in the crust: a linkage to occurrence in groundwater. Geological Society of America Abstracts with Programs 38 (7), 179.

889 Zheng, Y., 2007. The heterogeneity of arsenic in the crust: A linkage to occurrence in groundwater. Quaternary Sciences, 27, 1-15.

892
893
894
895
List of Figures

**Figure 1:** Major aquifers across the world and their tectonic settings, orogenic belts (redrawn from http://earthquake.usgs.gov; http://whymap.org; Margat, 2008) along with areas known for naturally occurring As-enriched groundwater and geothermal water (following Smedley and Kinniburgh, 2002, Mukherjee et al, 2008a, 2014 and Ravenscroft, 2009). The number marked in the figure denotes the serial number in Table 1.

**Figure 2:** Schematic diagram depicting the proposed process of As enrichment in arc magmas, and its transfer into sedimentary foreland-basin aquifers. Numbers refer to locations on Figure 1 and Table 1.

**Figure 3:** Bivariate plot of pH and log $pO_2$, showing calculated predominance fields for arsenic species in equilibrium with a sulfur-bearing aqueous fluid in the system Fe-As-S-O-H with excess Fe at 250°C. The shaded box represents the general pH and redox condition of geothermal systems (modified after Ballantyne and Moore, 1988 and Heinrich and Eadington, 1986).

**Figure 4:** Flow chart demonstrating As mobilization from source (arc magma) to sink (groundwater and aquifer matrix).

**Figure 5:** Histogram showing the frequency of major aquifers (n=63) across the globe, classed by their tectonic settings [i.e. convergent (n = 34), non-convergent (n=27) and mixed setting (n=2)] and known presence of As-enriched groundwater. The details of these aquifers are provided in Table 2.

**Figure 6:** Conceptual bivariate plot of magnitude versus temperature for hot and cold orogens (modified from Beaumont et al., 2006), classified by the presence (dark grey) and absence (light grey) of known major locations of natural As-enriched groundwater in the region. Large/hot and small/cold domains are marked by dashed lines.