**4. Results and discussion**

**Figure 1a** shows the correlation between As and Fe concentrations in the 35 groundwater samples taken in spring 2017. Results from analyses of samples collected autumn 2015 exhibit very similar trends and are therefore not included in this section. There is no visible correlation between As and Fe, and the correlation coefficient is only given for illustration. In contrast to the obvious decoupling between As and Fe, the concentration of As markedly and positively depends on the concentration of various lithophile elements (K shown as an example in **Figure 1b**). As is positively correlated with Na, Li, B, and Mo and negatively correlated with Ca, Mn, and As. Evidently, the reason for such a paradigm is mainly the derivation of As from silicates like clay minerals and feldspars and much less from Fe hydroxides and pyrite. Even though in [34] it is reported about a positive dependence of As on Fe in West Bengal and in [35] a positive correlation between As and Fe (r = 0.77) in the aquifer of the Nawalparasi district is also mentioned, a decoupling between aqueous As and Fe has also been observed in [13–15].

In [15] it is stated correctly that decoupling between Fe and As may result from sorption of Fe to other surfaces (i.e., clays) or precipitation of Fe(II) minerals, such as siderite. Anyways, the diagram in **Figure 1b** explicitly shows the correlation between As and the lithophile element K as an example. K as well as Na, Mg, and Sr (replacement of Na and K) can easily be dissolved from interlayers of clay minerals, Na, K, and Sr as well from alkali feldspars or the borosilicate tourmaline. Li, B, and Mo represent common trace elements found in micas; Li and B moreover are main components of tourmaline (general formula, (Ca,K,Na)

#### **Figure 1.**

*(a) Apparent decoupling between Fe (mg/l) and As (μg/l). The correlation coefficient (r) is included in the diagram for illustration though it is not significant. (b) Correlation between K (mg/l) and As (μg/l).*

**55**

in the Nepalese Himalaya.

*The Provenance of Arsenic in Southeast Asia Discovered by Trace Elements in Groundwater…*

(Al,Fe,Li,Mg, Mn)3(Al,Cr, Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F)4). Besides this said, tourmaline is one of the very rare minerals fitting a significant amount of boron in its structure. As reported in [36], authors found tourmaline-containing aquifers enriched in As in West Bengal, India; in [37] it is clearly described how trace elements of groundwater in the Terai of Nepal refer to the origin of the mentioned soil minerals being decomposed from tertiary leucogranites (rich in B) in the High Himalayas. As Fe is predominantly contained in the octahedral layer of clay minerals such as biotite (general formula, K(Mg,Fe2+,Mn2+)3[(OH,F)2|(Al,Fe3+,Ti3+) Si3O10]) and fits hardly in the interlayer, so it is not possible to exchange Fe against K or Na. However, the likely source of As due to the positive correlation between Na, K, and As points out to silicate minerals as As can be readily adsorbed on the surface and edges of these minerals. Muscovite KAl2[(OH,F)2|AlSi3O10] is another frequent clay mineral found in the sediments of Nawalparasi and is well known as

This obvious decoupling of As from Fe in the groundwater excludes Fe minerals like Fe hydroxides and pyrite being the source of arsenic in the alluvial sediments. Above all, several trace elements (Li, B, P, V, Cr, Mn, Cu, Zn, Se, Br, Sr, Mo, Cd, P, and U) analyzed in the groundwater samples of Nawalparasi boreholes are among the most prominent besides arsenic which could be found in relevant concentrations. Particularly the presence of the lithophile Li, B, P, Mn, Br, Sr, and U in the groundwater is a striking feature. Siderophile elements like Cu or Zn could be found in minor concentrations or in a few samples only. The immediate attention was attracted by boron as this element is rarely found in significant amounts in common minerals like silicates. Tourmaline is one of the very rare minerals incorporating a significant portion of boron in its structure. As already mentioned in [38], boron in spring waters in the Peshawar basin and surroundings in the Himalayan foreland of Pakistan is closely associated with igneous complexes (most probably with the tourmaline-rich tertiary leucogranites). Even boron is widely known to be present in salt water; such an influence can be neglected in landlocked Nepal having no link to the ocean. Thermal springs can be located in various areas of the Nepal Himalaya, but their influence is considered to be marginal taking the widespread occurrence of tertiary leucogranites besides metapelites and black shales into account. Above all, in [39], elevated boron in metasedimentary rocks of the lesser Himalaya (up to 322 ppm) as well as in the Manaslu leucogranite (up to 950 ppm) where tourmaline represents the boron-containing mineral is reported. Tourmaline-containing aquifers enriched in As in West Bengal, India were detected in [36]. These authors conclude therefore that the heavy mineral assemblage of these aquifers (opaque minerals, garnet, tourmaline, kyanite, rutile, and zircon) prove a mixed metamor-

phic and igneous provenance for the eroded and deposited materials.

As the anion S was hardly detectable, the oxidation of pyrite in the sediments (suggested, e.g., by [40]) which would lead to an increased concentration of SO4

in the groundwater can be clearly ruled out as an mechanism of arsenic release into groundwater. Despite these convincing facts, ophiolites were seen as the initial source of arsenic contained in arsenopyrite (e.g., [6, 16]). But ophiolites do not exist

In conclusion, the diagram in **Figure 2** presents the most prominent trace elements in groundwater from Nawalparasi district in comparison with the few available data of the Macusani obsidian glass (peraluminous in composition, enriched in As-B-F-P). The data for comparison are taken from [41]. In [42], it was already declared that these volcanic rocks are compositionally and mineralogically equivalent to the Manaslu leucogranite. In article [41], it is reported for the first time that a significant accumulation of arsenic in a peraluminous glass from Macusani (SE Peru) which is representative of anatectic melts is derived from metasedimentary crustal

2−

*DOI: http://dx.doi.org/10.5772/intechopen.83014*

a carrier of K and Li, B, and Mo as trace elements.

#### *The Provenance of Arsenic in Southeast Asia Discovered by Trace Elements in Groundwater… DOI: http://dx.doi.org/10.5772/intechopen.83014*

(Al,Fe,Li,Mg, Mn)3(Al,Cr, Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F)4). Besides this said, tourmaline is one of the very rare minerals fitting a significant amount of boron in its structure. As reported in [36], authors found tourmaline-containing aquifers enriched in As in West Bengal, India; in [37] it is clearly described how trace elements of groundwater in the Terai of Nepal refer to the origin of the mentioned soil minerals being decomposed from tertiary leucogranites (rich in B) in the High Himalayas. As Fe is predominantly contained in the octahedral layer of clay minerals such as biotite (general formula, K(Mg,Fe2+,Mn2+)3[(OH,F)2|(Al,Fe3+,Ti3+) Si3O10]) and fits hardly in the interlayer, so it is not possible to exchange Fe against K or Na. However, the likely source of As due to the positive correlation between Na, K, and As points out to silicate minerals as As can be readily adsorbed on the surface and edges of these minerals. Muscovite KAl2[(OH,F)2|AlSi3O10] is another frequent clay mineral found in the sediments of Nawalparasi and is well known as a carrier of K and Li, B, and Mo as trace elements.

This obvious decoupling of As from Fe in the groundwater excludes Fe minerals like Fe hydroxides and pyrite being the source of arsenic in the alluvial sediments.

Above all, several trace elements (Li, B, P, V, Cr, Mn, Cu, Zn, Se, Br, Sr, Mo, Cd, P, and U) analyzed in the groundwater samples of Nawalparasi boreholes are among the most prominent besides arsenic which could be found in relevant concentrations. Particularly the presence of the lithophile Li, B, P, Mn, Br, Sr, and U in the groundwater is a striking feature. Siderophile elements like Cu or Zn could be found in minor concentrations or in a few samples only. The immediate attention was attracted by boron as this element is rarely found in significant amounts in common minerals like silicates. Tourmaline is one of the very rare minerals incorporating a significant portion of boron in its structure. As already mentioned in [38], boron in spring waters in the Peshawar basin and surroundings in the Himalayan foreland of Pakistan is closely associated with igneous complexes (most probably with the tourmaline-rich tertiary leucogranites). Even boron is widely known to be present in salt water; such an influence can be neglected in landlocked Nepal having no link to the ocean. Thermal springs can be located in various areas of the Nepal Himalaya, but their influence is considered to be marginal taking the widespread occurrence of tertiary leucogranites besides metapelites and black shales into account. Above all, in [39], elevated boron in metasedimentary rocks of the lesser Himalaya (up to 322 ppm) as well as in the Manaslu leucogranite (up to 950 ppm) where tourmaline represents the boron-containing mineral is reported. Tourmaline-containing aquifers enriched in As in West Bengal, India were detected in [36]. These authors conclude therefore that the heavy mineral assemblage of these aquifers (opaque minerals, garnet, tourmaline, kyanite, rutile, and zircon) prove a mixed metamorphic and igneous provenance for the eroded and deposited materials.

As the anion S was hardly detectable, the oxidation of pyrite in the sediments (suggested, e.g., by [40]) which would lead to an increased concentration of SO4 2− in the groundwater can be clearly ruled out as an mechanism of arsenic release into groundwater. Despite these convincing facts, ophiolites were seen as the initial source of arsenic contained in arsenopyrite (e.g., [6, 16]). But ophiolites do not exist in the Nepalese Himalaya.

In conclusion, the diagram in **Figure 2** presents the most prominent trace elements in groundwater from Nawalparasi district in comparison with the few available data of the Macusani obsidian glass (peraluminous in composition, enriched in As-B-F-P). The data for comparison are taken from [41]. In [42], it was already declared that these volcanic rocks are compositionally and mineralogically equivalent to the Manaslu leucogranite. In article [41], it is reported for the first time that a significant accumulation of arsenic in a peraluminous glass from Macusani (SE Peru) which is representative of anatectic melts is derived from metasedimentary crustal

*Trace Metals in the Environment - New Approaches and Recent Advances*

All trace elements in the groundwater samples were determined by ICP-MS (Agilent Technology, 7500 Series, Agilent Technologies, Waldbronn, Germany) at Eawag, Dübendorf, Switzerland, after 1:2 dilution with 0.5 M HNO3. Each measurement was conducted in triplicate. All ICP-MS determinations agreed to within 3–5%

**Figure 1a** shows the correlation between As and Fe concentrations in the 35 groundwater samples taken in spring 2017. Results from analyses of samples collected autumn 2015 exhibit very similar trends and are therefore not included in this section. There is no visible correlation between As and Fe, and the correlation coefficient is only given for illustration. In contrast to the obvious decoupling between As and Fe, the concentration of As markedly and positively depends on the concentration of various lithophile elements (K shown as an example in **Figure 1b**). As is positively correlated with Na, Li, B, and Mo and negatively correlated with Ca, Mn, and As. Evidently, the reason for such a paradigm is mainly the derivation of As from silicates like clay minerals and feldspars and much less from Fe hydroxides and pyrite. Even though in [34] it is reported about a positive dependence of As on Fe in West Bengal and in [35] a positive correlation between As and Fe (r = 0.77) in the aquifer of the Nawalparasi district is also mentioned, a decoupling between aqueous

In [15] it is stated correctly that decoupling between Fe and As may result from sorption of Fe to other surfaces (i.e., clays) or precipitation of Fe(II) minerals, such as siderite. Anyways, the diagram in **Figure 1b** explicitly shows the correlation between As and the lithophile element K as an example. K as well as Na, Mg, and Sr (replacement of Na and K) can easily be dissolved from interlayers of clay minerals, Na, K, and Sr as well from alkali feldspars or the borosilicate tourmaline. Li, B, and Mo represent common trace elements found in micas; Li and B moreover are main components of tourmaline (general formula, (Ca,K,Na)

*(a) Apparent decoupling between Fe (mg/l) and As (μg/l). The correlation coefficient (r) is included in the diagram for illustration though it is not significant. (b) Correlation between K (mg/l) and As (μg/l).*

**3.2 Trace element analysis**

standard deviation [33].

**4. Results and discussion**

As and Fe has also been observed in [13–15].

**54**

**Figure 1.**

#### **Figure 2.**

*The most noticeable trace elements in groundwater from Nawalparasi district (green triangles) compared with the few available data of the Macusani obsidian glass (peraluminous in composition, enriched in As-B-F-P). The data for comparison (purple stars) are taken from [41]. Note the logarithmic scale for comparison of concentrations.*

protoliths. In this glass, the authors of [41] found accumulations by factors of 10–100 for As, compared with the mean continental crust values and other incompatible trace elements (e.g., Be, B, Rb, Sn, Sb, and Ta), and by factors of 100–200 for Li, Cd, and Cs. In a second article [43], the authors of reference [41] state that remarkable concentrations of Cd (up to ~300 ppm) could be found in quartz-hosted fluid and melt inclusions in hydrous peraluminous systems (pegmatites and leucogranites) for the first time ever. A distinct number of the groundwater samples used for this study show detectable concentrations of Cd. Significant amounts of Li, B, Zn, As, and Pb were also found in quartz-hosted fluid inclusions from the Huanuni tin deposit in Bolivia (hosted in peraluminous granites with ASI ≥ 1.1) [44]. The indicative trace elements of leucogranites (Li, B, P, Mn, Zn, As, Sr, Pb, and U) are similarly detected in the ground water in Nawalparasi. The high concentration of Sr in groundwater can be based by the frequent occurrence of calcium carbonates in the soil hosting the groundwater. In study [45], the authors mentioned lithologies like rhyolite and shale (greywackes) representing a greater risk of elevated As in groundwaters.

As frequently described in the literature, low-grade metapelites are often considered as protoliths of peraluminous granites (see, e.g., [22, 46, 47]) where concentrations of As, Sb, Be, B, Ba, and Rb by a factor of 5–10 higher than their average crustal abundances (2–5 ppm) [48–50] were not unusual. The leucogranites (two-mica or muscovite-tourmaline mica) found in the Himalayas of Nepal are undoubtedly peraluminous in composition (see, e.g., [22, 51, 52]) and coherently a comparison with the findings from [41] is warranted. Most of the leucogranites analyzed in [51] are peraluminous (ASI > 1.1) to strongly peraluminous (ASI ≥ 1.1). According to Ref. [53], lead represents one of the rare elements usually behaving incompatible during crustal melting. Pb can be significantly enriched in low T S-type granite melts, especially if the proportion of partial melting remains low. Moreover, muscovite, known as being a major mineral of metapelitic sources, can exhibit relatively high Pb contents. The leucogranites in the Nepal Himalayas are widely described to be of crustal origin and are derived from vapor-absent muscovite-dehydration melting of pelitic and psammitic protoliths during the Late Miocene (see, e.g., [47, 54–59]).

**57**

**Author details**

**Conflict of interest**

No conflict of interest.

Barbara Mueller

provided the original work is properly cited.

Bamugeobiochem, Ettenhausen, Switzerland

\*Address all correspondence to: barbara.mueller@erdw.ethz.ch

guide in Nepal and responsible for all logistics over many years.

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*The Provenance of Arsenic in Southeast Asia Discovered by Trace Elements in Groundwater…*

leucogranites as the original source of the arsenic is evidently warranted.

As described above, arsenic is primarily dissolved from micas as a major constituent of sediment hosting the groundwater in Nawalparasi. Keeping in mind that the Manaslu area is the watershed of the Nawalparasi water system, assuming the

So far it was considered that As is mainly released from iron (hydr)oxides, but a major host for sorption and release of As are alumosilicates such as clay minerals (including micas) into groundwater. The apparent decoupling of the concentrations of Fe and As and the positive correlation between concentrations of Na, K, and As in the groundwater are a significant evidence that As cannot be released from Fe minerals predominantly—so silicates represent the fundamental source of As in sediments. Clay minerals preferentially lose Na and K from their interlayers during chemical weathering and hence become enriched in immobile elements such as Fe and Al. Moreover, the trace elements detected in the groundwater samples of Nawalparasi are well known to be contained in peraluminous obsidian glasses from Peru enriched in As-B-F-P. These glasses equal the leucogranites in the Manaslu area North of Nawalparasi in their geochemistry and represent the original host rocks of

I am grateful for the help and analytical skills of Dr. Stephan Hug, Eawag, Dübendorf, Switzerland, and I thank Thomas Ruettimann, Eawag, for analysis of the samples by ICP-MS. My gratitude for support and valuable discussions is expressed to Tommy Ngai and Candice Young-Rojanschi from CAWST, Calgary, Canada; Bipin Dangol and Hari Boudhatoki from ENPHO, Kathmandu, Nepal; Gyan Prakash Yadav, Parasi, and to Som Rai, my loyal expedition and trekking

*DOI: http://dx.doi.org/10.5772/intechopen.83014*

**5. Conclusions**

arsenic.

**Acknowledgements**

*The Provenance of Arsenic in Southeast Asia Discovered by Trace Elements in Groundwater… DOI: http://dx.doi.org/10.5772/intechopen.83014*

As described above, arsenic is primarily dissolved from micas as a major constituent of sediment hosting the groundwater in Nawalparasi. Keeping in mind that the Manaslu area is the watershed of the Nawalparasi water system, assuming the leucogranites as the original source of the arsenic is evidently warranted.
