GEOLOŠKI ANALI BALKANSKOGA POLUOSTRVA Volume 81 (2), December 2020, 33–48 – https://doi.org/10.2298/GABP200517007P Original scientific paper Оригинални научни рад

The occurrence and evolution of arsenic in aquifers of the volcanic complex (outskirts of , )

1 1 AjA 1oZNANović jiL1jANA oPovi ć ANjA 1ETrović MANTiPć Arko PA, hL ić oPrAN Ar, TiNkovi ćP P , D S & G M Abstract.

2 Avala Mountain is accommodated 15 km southward from the city of Belgrade and extends over the area of about 10 km . Avala Mountain is a cultural and historical heritage of Belgrade qualified by the Law on Environ - mental protection. The area is abundant with water springs that have been ex - ploited by tourist facilities and local population. By analyzing groundwater sampled from several springs and wells located in a vicinity of the Avala mag - matic entity here we study the occurrence, concentration and origin of arsenic pollutant. The investigated springs are accommodated within the faulted com - plex of Mesozoic carbonate and clastic sediments, serpentinite, further in - truded by the Tertiary magmatic rocks. By u sing the concentrations of the major and minor components(e.g. Cr, Ni, Fe, Mn) in groundwater, the relation - ship between groundwater and local lithostratigraphic units is outlined. Chemical analysis of the investigated waters shows that arsenic concentration in groundwater of the investigated area is in range from 3.0 to 102.0 μg/l. Ar - senic concentrations over the maximum allowed value in drinking water (10 Key words: μg/l) are detected in more than 55% cases. The occurrence of arsenic in arsenic, groundwater groundwater can be attributed to local igneous rocks, i.e. to the process of ox - aquifer, volcanic complex, Avala. idation of sulphide minerals with As (major or minor presence) – primarily arsenopyrite or pyrite. Groundwater with higher concentration of arsenic (above10 μg/l) is exploited as drinking water used by tourists and by local population. Along term use of the water with high concentration of arsenic im - Аpoпsсeт aр аmкaт jo. r health risk.

2 Планина Авала смештена је 15 km јужно од Београда и простире се на површини од око 10 km . На том простору се налазе неки од каптираних извора и бунара из којих воду употребљавају туристи и локално становништво. У овом раду анализирана је појава, концентра - ција и порекло арсена у подземној води аквифера вулканског комплекса Авале. Њега чини испуцали мезозојски офиолитски комлекс додатно испресецан терцијарним магматитима . Корелације између главних компонената (катјона и анјона ), као и микрокомпонената (као што су Cr, Zn, Ni, Fe, Mn и As) указала је на могућу везу између подземне воде и литостратиграфских јединица. Хемијском анализом утврђено је да је опсег концентрација Аѕ од 3.0–102.0 μg/l. Максимална довољена кон - центрација (10 μg/l) премашена је у 55% испитиваних узорака. 1 Geological Survey of Serbia, Rovinjska 12, 11000 Belgrade, Serbia. E-mail: [email protected]

33 Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

Кључне речи: арсен, подземна вода, Присуство арсена у испитиваним узорцима може бити пореклом из аквифер вулканског комплекса, локалних магматских стена, односно последица оксидације минерала у Авала . којима је Аѕ главна или споредна компонента (арсенопирит и пирит), чије је присуство доказано у испитиваној области. Дуготрајном свако - дневном употребом подземне воде у којој је доказано присуство Аѕ у концентрацијама изнад 10 μg/l може представљати висок ризик по здравље.

Introduction

presence and distribution of other elements, or -

th ganic mattEeTrr aunšEdv Smkiicrobiological activity in water

Arsenic is a chemical halcoth phile and siderophilte h and soil ( P , 2005). element which occupies 20 place in the abundance At moderate or high redox potentials As occurs in the Earth’s crust, being 14 in seawater and 12 as a series of pentavalent (arsenate) oxyanions. in human body. The concentration of As in unpol - however, under most reducing (ac3id– and mildly al - luted fresh waters typically ranges from 1–10 μg/l, kaline) conditions and lower red3ox potential the rising to 100–5000 μth gA/NlD iAnL areausZ uokfi sulfide minerali - trivAaNlDeAnL t arusZeunkiite specieAsr iN(AGEsr o )EpiLrLey dominate zation and mining ( M & S , 2002). With the (M & S , 2002; B & r , 2012). in beginning of the 20 century its concentration be - negative ion forms As adsorbs at positive-charged comes a very important topic, accounting its toxicity surface (e.ugx. TaomN orphous or crysuto al forms of Fe, Mn and carcinogenicity. Namely, a long term exposure oxides) (L et al., 2008; G et al., 2009) and and consummation of waters with the concentra - thus can be removed from aquatic systems. tions ranging > 5uo0 μg/l could be related to skin can - Generally, occurrence of a higher content of As in cer mortality ( G et al., 2009). For this reason, most groundwater is documented in specific geological countries have reduced maximum allowed concen - areas/conditions: in the areas of sulfide mineraliza - trations (MAC) in drinking water by decreasing the tion, geothermal areas, anaerobic aquifers, in arid recommenFdEeiFdE rvalue of Who (1999) from 50 μg/l to and semiarid areas with elevated ph values. in 10 μg/l (P et al., 2002). global scale, high concentration of arsenic in in nature arsenic constitutes many of Earth min - groundwater considers as the major environmental erals occurring either as a dominant or secondary issue. in South Asia (india, Bangla desh, China, viet - element . As a chalcophile element, arsenic occurs in nam, Taiwan), concentration reach es up to 3400 the form of sulphides, arsenides and sulpharsenides μg/l, whereas South America has documented con - of heavy metals. Arsenic2 als3o can occur in the form sidMeErDaLbEly y lower values 300 μg/l (Chile, Argentina) of oxides (arsenolite - As o ), prevalent in oxidizing (S , 2006). jELić zones sulfide-arsenide . As a siderophile ele - A clustero voAfN eićarlier TiAnNvieć stigations A(LeM.gA.C, iBA et ment, arsenic appears in the form of arsenopyrite al., 200E6T;r jović & S , 2006; D et al., and sulfides of iron (pyrite, marcasite). 2009; P et al., 2012) indicate that groundwa - The origin of arsenic in groundwater can be nat - ter of Serbia have rather a scattered irregular pat - ural (geological structure, volcanism, erosion) but tern of arsenic concentration. A special attention in also may originate from anthropogenic source (uti - the number of studies is reflecting onto the occur - lization of herbicidEeNs, pesticides, fungicides, fossil rence of arsenic in groundwater of ( sedi - fuels, mining, etc., r et al., 2007). Arsenic is redox- mentary) aquifers of Banat and Bačka admi nistrative sensitive element and its presence, distribution, areas. Another source of arsenic in Serbia could be form and mobility in groundwater is the result of a associated with the areas of considerable geother - 3c4omplex interaction of the several geochemical pa - mal potential, such as LGueokl.o avn.s Bkaalk .b paonlujoas .,s 2p0a20, ,j 8o1š (a2)n, 3ič3–k4a 8 rameters. These parameters include ph, Eh values, banja spa, Bujanovačka banja spa. These spas are The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

characterized by documeEnTtreodv imć odAeNrTai ćtely hLiogkho cLioCn A - Mesozoic agglomeration is a product of Late Meso - ceAnNtDraić tions of arsenic ( P -P & Z - zoic-Tertiary magmatic activity associated with the M , 2012). developing and closure of ancient vardar ocean The presence of arsenic within the investigated (NW Neotethys). The investigateodL jaićrea belongs to a, area was detected earlier, documented in several so-called, “Europe sub-basin” ( T et al., 2018). in water springs of Avala Mountain (springs “Sakinac”, the tectonic sense, the investigated segment is actu - “velika česma” and “vranovac”; Fig. 1). The measu - allPyA haicć commAuoDdEaNtyei d within the East vardar Zone red concentrations of arsenic exceed the limit of (S & G Aro,v2ić 019) or the segmCheMniDt of the maximum allowed concentrations (MAC) of arsenic “Sava Zone” ( M et al., 2007; S et al. , in water, according to botohZ,N tAhNeo dvoić mestoicP oavnidć foreign 2008). The oldest rock system outcropping is rep - regulations (10 μg/l) ( P & P , 2009). resented by the oopLjhićiolite-bearoiLnjigć system of jurassic in this study, the concentration fluctuations of As serpentinites ( T , 1995; T et al., 2018) scat - were observed during the period May–September tered over the eastern and southern section of this 2008. The results of the observations suggested that lower-latitude mountain (Fig. 1). The exposed there are almost insignificant variations in the mea - oceanic litho sphere of the Avala Mt. system is strati - sured concentrations. Therefore, a possible dilution graphically succeeded by the interchange of deep- due to the mixing of infiltrated atmospheric waters water flysch-like marine conditions of Lower in the short time has no effect on arsenic concentra - Cretaceous age. This sequence is succeeded by an - tions. in order to determine the oxidation state of other, this time dominant flysch-bearingo Lsjyićstems of arsenic of this groundwater, the samopZNleAs N woveićre ana - upper Cretaceous–Paleogene age ( T et al., lyzed by stripping voltammetry ( P et al., 2018). This pre- Tertiary Neotethyan tectonomag - 2009). The analysis corroborated that a dominant matic agglome ration is penetrated by numerous hy - form of arsenic is As (v) (90–98% concentration of drothermally altered magmavtiEcT kinovtrić usions of Late the total arsenic). The overall goal of this research Eocene–Early Miocene age ( C et al., 2004). is to provide a continuity of investigations depicting After the termination of magmatic activity and the distribution of the arsenic concentration in complete closure of this western segment of groundwater of available wells and springs; and to Neotethys ocean, the onset of a new extensional b) investigate the geological factors for the origin of phase during Early Miocene resulted in cuoNnDtinć ental- the arsenic occurrence in ground water of aquifer of lacustrine system of Lower Miocene ( r et al., tRhee gAivoanlaa Ml oguenotaloing vicolacla nainc dcomplex. 2019 ). Early Sarmatian resulted in a sea water in - hydrogeological setting flux and new transgressional stage (upper Mioce - ne). The former pre-Neogene paleorelief of displaced Avala Cretaceous magmatic ophiolite-bearing entity including newly developed local ancient paleo-valleys were overlaid by a well-d eveloped Neogene sedi - The Avala magmatic and sedimentary system is mentary (marine) veneer. This new sea-water in - a complex geological-geochemical entity with dis - gression and associated depositional system tinctive uplifted morphostructure (Fig. 1). The Avala “sealed” numerous magmatic intrusions exposed complex represents a mixture of different Mesozoic previously to erosion. The Middle Miocene marine and Cenozoic paleoenvironmental conditions char - and marine-brackish sediments are well developed acterized by different processes that yield a varietvy and represented by a sequenocLej ioć f conglomueNrDaićtes, koof vrioć cks with a different geochemical imprint ( i - sandstones and limestone ( T , 1995; r et et al. , 1971) . al., 2019 ). The post-rift subsidence stage (Middle to A geological entity of mountain Avala comprises upper Miocene) was likely affected by the uplifting a complex of Mesozoic volcano-sedimentary system of the entire Pannonian basin system, closed and in - Guenocl. oan. fBoarlkm. poalbuolsy., 2o0v2e0,r 8l1a (i2n), 3b3–y4 8 the highly complex of verted which is marked by the onset of Quaternar3y5 Miocene and Quaternary sequences (Fig. 1). The deposition. Ever since the Quaternary stage, the in - Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

Fig. 1. Simplified geological map of studied area (modified after Toljić , 1995) with the sampling localities.

vestigated area underwent the exposure to terres - in contrast to a subdued surrounding, the hyp - trial conditions (land). The post-Miocene geomor - sometry and a cone shape of the mountain Avala 3p6 hological processes have shaped the mountain clearly (511 m) protrudGeosl. tahn.i sB aglke. opomluosr.p, 2h02o0l,o 8g1 i(c2)a, l3 3e–n 48- Avala and its immediate surrounding. tity (uplifted morphostructure). Numerous inherited The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

5 4 11 oLjić brittle (normal) faults are radially distributed across (Pb Sb S ), etc. ( T , 1995). The summary of the the investigated conoeL-jisć haped magmatic and sedi - investigated minerals at the area of Avala and the mentary complex ( T , 1995; Fig. 1). As the exten - surrounding, implicatesA tNhEaZti ć the mAaNični ć mineral of ar - sional fault system is penetrated by a dominant set of senic is arsenopyrite. j & T (2003) ana - sub-vertically emplaced intrusions of quartzlatite lyzed by x-ray diffraction method a sample of with basaltic and dacitic content (Fig. 1), it is to ex - arsenopyrite associated with pyrite (collected from pect that a relatively large segment of the investigated the vicinity of Crveni Breg mine). The authors con - magmatic entity is buried underneath a lower struc - firmed that the formation of minerals from this area tural level of the Avala complex. oHcycdurroegde uonldoegri chaylp soethtetirnmg al conditions. The average arsenic content in magmatic rocks in Serbia - andesite, AdNaGciić te, quAaNrGtizć latite is estimated to reach 2.6 ppm ( D & D , 2007). however, during generation of hydrothermal sulfide ore de - posits, arsenic in water-rock interaction becomes As mentioned earlier, the Avala Mountain system mobile and appears to be dispersed into the sur - geomorphologically differs from its rather subdued rounding rocks. As a product of progressive multi - surrounding. interestingly, the position of water- phase hydrothermal activity this alteredA NaGrieć as permeable tectonic discontinuities crosscutting coAnNtGaićin minerals enriched with arsenic ( D & Avala Mt. has differences relative to the both, D , 2007). Commonly, during the formation of regional drainage system (Topčiderska and Zavoj - hydrothermal and zinc deposits, arsenic con - nička rivers) and the local drainage system (inclu - centrates and deposits in the form of arsenopyrite, des smaller streams). and other sulphides of arsenic, arsenides of Ni and The position and configuration of the Avala Mt. Co, sulfarsenides Cu, Ag, Pb. hydrothermally altered allows intensive water exchange processes within rocks are indentified across the investigated area, the aquifer of the springs. Avala Mt. system is a encircling dominantly the exposed magmatic intru - segment of the documented hydrodynamic zone sions. The prominent examples of the hydrothermal characterized by intensive water exchange proces - activity are observed at the Crveni breg, Prečica ses, theoretically reaching a complete exchange of (southwestern mountainside of Avala), the areas of water in 100 years timeframe. The flow and lead-zinc mineralization. Another example is the šu - drainage of groundwater in the given conditions is plja stena area (Fig. 1), accommodated in the south - the consequence of gravitational forces. Within the eastern part of Avala-the area of hg mineralization comparable hydrody namic conditions, atmospheric (). The first example was form ed in sand - water infiltrates into local aquifers. higher content stone, marl and limestone of jurassic and Lower of oxygen and carbon dioxide makes these near- Cretaceous age, in which are embedded the veins of surface water systems aggressive. These gases boost quartzlatite, dacite and andesite. The ore deposits the ongoing weather ing of carrier-rocks, in šuplja stena appear in the zones of hydrothermally particular, carbonates and silicates (hydrolysis and altered serpentinite, which are partly silicified and dissolution of alumino silicates and carbonate) and dolomitizated . The impregnations of cinnabar are also oxidation of sulfides. accompanied with iron- sulfide ore minerals and are The aquifers in the narower area of Avala Mt. can associatoeLdji ć with the fracture zones trending East- be outlined as a rock assembly characterized by a West ( T , 1995). lower hydrogeological potential (reduced flow

in this particular area are recognized numero2us ability, water exchange and drainage of ground- minerals such as: sphalerite (ZnS), p4yrite (FeS ), water). Also, the entire system of captured springs pyrrhotite 2(FeS), arsenopyrite (FeAso ), c2halcopy - marks the local fault zones, which indicates that the rite (CuFeS ), gale2na (PbS), marcasite (FeS ) as well springs are controlled by the local tectonic discon- aGeso cl. hana.l Bcaolkc. iptoelu(2oCsu., S202)0, , c8o1 v(2e),l 3li3t–e48 (CuS3) accompanied by tinuities (faults). Consequently, the faults represen37t quartz (Sio ), calcite (CaCo ), boulangerite the permeable geological environment. Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

With exception of the spring “Točak” (accom mo- denudation and extraction from the complex Avala dated within serpentinite) and „kraljeva česma ” other bedrock system, heavy components tent to perco - springs were formed in the upper Cretaceous sedi - late towards the nearest recharge area or in the di - ments- flysch (consists of layers of sandstone and clay, rection of a confined aquifer. The latter is, most and less often of marl and limestone). The ser pen - likely, comprised of the mixture connecting a frac - tinites, within solid rock body are chara cte rized by the tured magmatic body and surrounding sedimentary fracture-controlled porosity. Dacites, quartz latite, rocks. The essential processes, e.g., paleoprecipita - , and latites, do not have a signi ficant tion, secondary porosity and overall rock permeabil - influence on hydrogeological prope rties of the rocks. ity, have directly influenced the spatial mobility of however, these rocks and sulfide ore minerali zation heavy components, likewise arsenic. in addition, the cGaeno bleo ag iscoaulr ceev oefn atrss eannicd a gnedo octheerm heicavayl metals. timeframe of the second erosional phase (~3.6 Ma to evolution of arsenic in Avala`s aquifers present day) allowed a sufficient time for additional unroofing and removal of the overburden and the development of secondary porosity. removal of the overburden thus enabled a dissolution of durable principal arsenic sources – the arsenopyrite-bearing in addition to key geological processes likewise volcanic rocks. Extensional faulting and fracturing the local magmatic activity, and the circulation of hy - underpinned the solubility of arsenic-bearing mag - drothermal fluids among extensional fault conduits, matics, further allowing the development of second - it seems that another very important geological ary porosity. The secondary porosity further process have had certainly influenced the sampled facilitated a gravitational percolation of dissolved subsurface arsenic concentrations. This process is a heavy components moving these particles towards post-Pliocene – present-day erosion. Present-day re - a partially compartmentalized principal Avala’s lief is a function of different factors formed during the aquifers. The essential indicator of the proposed last terrestrial event. however, it is necessary to bear spatial subsurface hydrodynamic compartmental - in mind that there have been the two main erosional ization is a differential occurrence of the sampled stages differentiated during the geological evolution arsenic concentrations from the springs widespread of the investigated Avala complex. The initial ero - Macraotsesr tihael i navnedst imgaetetdh coodms plex. sional event was probably induced by a regional up - lift that was coeval with the magmatic emplacements Sample collection accommodated during the process of the vaCrhdMaiDr ocean closureP Aahnidć postAduaDtEiNnygi extension (e.g., S et al., 2008; S & G , 201 9). After the new post-collisional transgressive episodes lasting during Miocene ceased, weathering and denudation during Avala Mountain is abundant with springs char - the final post-Pliocene erosional stage exposed a acterized by a relatively low water production rate, large portion of the agglomerated flysch, volcanic and whereas several springs are additionally not acces - cap-rock Neogene sedimentary material. sible for water sampling or dried out. During the Au - After the local Pliocene lakes were drained away, gust and September of 2011, groundwater from the the sedimentary cover was exposed to the surface, springs named: “velika česma”, “Sakinac”, “vrano v ac”, atmospheric erosion led by the ancient paleo - “Točak”, “kraljeva česma”, “Ledenac”, “kamenac”, streams. A detailed analysis of the Quaternary con - “” and the wells “Avala” and “Zuce” were sam - tinental genetic formArsk hovigić hlights a dominance of pled. Location of the investigated area and the sam - fluvial processes ( M et al., 1985). After the pling points are presented in the Fig. 1. exposed sedimentary portion was gradually flushed The water samples were collected into acid- 3a8way, the deeper levels of a volcanic complex were wash ed polyethylene Gbeolt. talne. sBa alkn. pdo lusous.b, 2-0s2a0m, 81p (l2e),s 3 3f–o4r8 further exposed to the atmospheric influence. After arsenic analysis are immediately acidified with hCl The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

(1:1) solution (up to ph<2). The samples for detec - ological structure on the subsurface water compo - tion of heavy met3als (Cr, Ni, Pb, Zn, Fe, Mn, Cu) are sition, the main physicochemical parameters are an - treated with hNo (1:1) (up to ph<2), ph and elec - alyzed (Table 1). tro conductivity (EC) and temperature are addition - Groundwater around Avala structure exhibit ally analyzed on site. rather neutral ph values, low- to medium mineraliza -

The water from “Avala” well was re-sampled dur - tion wi3th lower temperatures. A predominant anion ing March 2012, because suspended compounds oc - is hCo with the mean value 392.6 mg/l, whereas curred during the pumping. This time the water predominant cations are Ca and Mg with the mean suspension was digested by acid . The applied me - values of 93.0 and 42.1 mg/l, respectively. Addition - thod here was used in order to consider the corre - ally, the mean value of one of the dominant ion - Cl is lation between As and the elements Fe, Mn 59.7 mg/l, and in samples “Sakinac” and “kamenac” (common for a solid residue appeared in subsurface is detected the highest value of As (Table 1). well waters). Thus, the concentration of the ele - Piper diagram (Fig. 2) is represented as a projec - mAnenatlsy tmiceaals mureetdh boedfsore and after the treatment tion of cation and anion ternary diagrams into HCO -Ca-Mg records variations/discrepancies. rhombic s3pace. According to dominant ions the investigated HCO -Cl-Ca-Mg groundwa3ter can be classified into the four types: • type: water from springs velika HCO -Mg- The total arsenic concentration is detected by česma, vranovac, Zuce and well Avala. 3 Ca using the AAS-hS technique (AAS-atomic absorp - • type: water from springs Saki - tion spectrophotometer-Perkin-Elmer 6500, with nac, kamenac, kraljeva česma and Ledenac. HCO -Mg MhS-15 hydride generation system, Perkin Elmer). • W3 ater of Točak spring belongs to the The limit of detection of this method is 0.5 μg/l. The type. samples, standard solutions and blank-samples are • Water from Zuce well can be classified as the prepared 24 hours before measuring, by treating type. the samples with 10% ki solution (10:1) with addi - The chemical composition of the studied waters tion of hCl conc. (10:3). seems to be a function of the geological setting i.e. The main cations: Ca, Na, k, Mg and Si are ana - geological (paleo) environment. Namely, the inves - lyzed by AAS-F (atomic absorption spectrophotom - tigated springs are mainly accommodated in the etry – flammable technique, Perkin Elmer 6500) fault zones that are crosscutting the Cretaceous sed - after direct aspiration of a4 no acidi3fied sample into iments and serpentinite (Fig. 1) The spring “velika the system. The anions So and No are determined česma” in the village originates from the by uv/viS spectrophotometer (Perki3n Elmer, contact of limestones, sandstones and marls (flysch Lambda 15), whereby anions Cl and hCo are ana - sediments) of the upper-Cretaceous age and sand, lyzed by the volumetric titration. sandstone, gravel and marly clay belonging the Mio- The concentrations of heavy metal Cr, Ni, Pb, Cu, Pliocene age. The springs “vranovac”, “Sakinac” and Zn, Fe, Mn are detected by iCP/oES spectrometry “Ledenac” are formed in limestones and marls of (CAP 6500 Duo, Thermo Scientific, uk), after direct upper-Cretaceous, which are tectonically damaged Rasepsirualtitosn a. nd discussion due to the magmatic intrusion of the eruptive veins, quartzlatites and latites; the spring “kraljeva česma” Physicochemical parameters appears from the fault zones in serpentinite, while the spring “Točak” is embedded in fractured serpen - tinite overlaid by the NeoogPeonveić conglomerates, gravel, sand and sandy clay ( P , 2007). The well “Zuce” located in the village of Zuce (35 m deep) is Geoli. nan o. Bradlke. pro tluoo sd.,e 2l0i2n0e, 8a1t (e2 ),t 3h3e–4 o8 rigin of arsenic in the drilled through serpentinites, whereas the sprin3g9 sampled waters, including the influence of local ge - “Zuce” itself, similarly likewise the spring “ka - Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

Table 1 . Physicochemical parameters of the groundwater samples.

LANEy menac” appears at the upper-Cretaceous sediments. et al., 2009). During the Lower Miocene, the Water from the exploration well “Avala”, located on most part of the investigated area was overlaid by the western side of Avala Mt. is collected from the lacustrine / sea waters, and afterwards (Middle– fraAcrtukorevidć flysch sediments at the depth of 90 m Late Miocene) thereo Lwjiać s a deposuitNioDnić of clastic and (M , 2010). carbonate rocks (T , 1995; r et al., 2019). According to the published data and the results of During the very process of sedimentation, sea water analysis of studied samples it can be concluded that can be trapped in consolidated and poorly cemented in groundwater collected from the springs accommo - sediments, followed by the post-depositional circu - dated within the upper Creta3ceous sediments the lation of fluids. Circulation can cause their dissolu - dominant ions are Ca and hCo . A higher concentra - tion, removal and transport to the eventually tion of Mg and the detected presence of Cr in some overlaying geological entities. Considering the fact water samples (Table 1) can indicate the influence of that specific hydrogeological conditions are impor - serpentinite. Ni is detected in “kraljeva česma” spring tant for concentration level of the components, in and “Zuce” well, similarly marking the influence of particular principal ions, it is possible that Cl ions serpentinites. The other heavy metals such are Pb could be removed very rapidly with fast groundwa - and Cu were not detected in any of the samples. ter flow and accumulated in stagnant conditions. in general, chlorides can occur in association Nitrates appear in the springs of the north-east 4w0 ith sea water, evaporite sediments and often aurL e side of Avala Mt. ConsiGdeeolr. iann.g B atlhk.e p ofalucots .,t 2h0a2t0 , t8h1 e(2r)e, 3 3is–4 a 8 documented in a vicinity of active volcanoes (M - dense population and that there is an unprotected The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

Consequently, reductive dis - solution of Fe oxy-hydroxide to elevated concentra - tions of arsenic, because it can depend on releasing of aAbN - sDoErbZAeLdM arsenic forms (v - et al., 2010). in ad dition , redox condition in the environment (groundwa - ter) would reduce As (v) to As (iii) in the case of its presence, inducing a possible desorp - tion. The reason can be attrib - uted to a lower affinity of As (iii) for adsorption aAtr CoíxA y-háNy - dChrEoS xides surface ( G -S - et al., 2005). Mo reover, there are the other differences between the “Le denac” spring and the rest of water samples: minimum va lue of Ca, Mg and Fig. 2. Piper diagram of the studied groundwater samples. TDS. The main reason can be the fact that the spring is ac - commodated within a central part of the Avala volcanic dome, whereas other springs

3 are distributed along its mar - household septic system, the presence of No ions ginal area (Fig. 1). This area could be characterized by are likely to be related with local anthropogenic ac - more intensive dissolution of bedrocks and intensive tivities. dRrealianatigoen asnhdi tph ubse atcwcuemenul acthioenm inic nael arest aquifer. in the “Ledenac” spring, the concentrations of Fe parameters and bedrock and M4n have highest levels, along with the presence3 of Nh ions. however, the concentration of the No has lower values than in the other samples. Such composition can indicate reductive conditions con - sidering the fact that Mn is commonly present in The Pearson’s coefficients (Table 2) introduce groundwater, in partAicLuMlAaCri jiA n anaGeBrAoBbA ic or low oxi - possible correlations between the parameters, and dation conditions ( D & A , 2006 ). Such suggest similar or different behavior or the origin of conditions may also lead to the reduction of Fe (iii) elements in groundwater. Evident st rong positive re - to Fe (ii). in particular, the exposure to the atmo - lations (significantly corre3lations 0.63–1.0, p= 0.05) sphere influences (oxidative environment) dissolu - appear between3 Mg-hCo , Na-hCo , Mg-Cr, k-Fe, tion of ferrous iron that commonly oxidizes and k-Mn, TDS-hCo , and Zn-Si. relatively rapidly pEirMeAcNipN itateisr kiEn the form of ferric The highest correlation coefficient (0.996) is ob - oxy-hydroxides (r & B , 2010). The reduc - served between Fe and Mn indicating the similar tion of Fe and Mn in the lower oxidation states leads conditions and the mechanism of migration in the tGoeo tl.h aen.i rB aglkr. epaoltueors. ,s 2o02lu0,b 8i1l (i2t)y, 3 a3–n4d8 an increased concen - sampled groundwater. in addition, the concentr4a 1- tration. tion of k could be related to the adsorption-desorp - Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

Table 2 . Pearson’ s correlation of the parameters.

tion process with Fe-Mn oxy-hydroxide surface. The could be associated with deeper thermal waters ac - weak negative correlation between Mg and Ca sug - tively flowing along the contact between eruptive gests that these elements generally do not have the veins and Cretaceous sediments. Furthermore, the same origin, despite these coexist and occur to - negative correlation between TDS-As can be related gether in carb3onates. The s3trong correlation be - to the water exchange pro cesses. Namely, in the tween Mg-hCo and Na-hCo indicates that erosion springs accommodated within the aquifer of the of carbonate 3is not ther eAxZocvluACsive soojiuNrocvei C of thiLeo rdAoDcouv - hypsometrically elevated area, the lower TDS mented hCo ions ( M & v 3 -M , contents and higher concentrations of arsenic are 2011). in general, occurrence of hCo , Ca, Mg, k, Na observed. Moreover, such negative cor relation in waters could be the result of hydrolysis of alumi - implies that more intensive water exchange nosilicates, in particular of fieMldiTsrpijaErv (ić orthoclaseo, uprlAa S- processes exist as the higher concentrations of As gioclase, albite, anortite; D , 1988; k are. in support of the previous, there is a strong et al., 2007). The presence of the aforementioned inverse correlation between As and TDS. minerals is documented in the Tertiary volcanic The lack of good correlation between Fe-As rocks of Avala. Therefore, Na, Ca and Mg in the sam - (Table 2) can be explained by a different behavior ples partially were derived due to mineral decom - of the final products of decay, arsenopyrite and position. on the other hand, the correlation between pyrite (Equation 2.). Whereas the iron is deposited Cr-Mg, Mg-Si and Mg-Na suggests possible weather - in the form of insoluble limonite or amorphous ing of other minerals such as serpentinites (ultra - Feooh, the arsenic which is in the form of arsenate mafic rocks). becomes mobile. A high correlation factor between

The negative c3orrelations coefficient, registered Si-Zn (0.7857) corroborates a hypothesis of adsorp - between As-hCo (r3= –0.62) and As-TDS (r= –0.66) tion barriers. Elevated concentrations of dissolved indicates that hCo and arsenic do not have the Si4, foll4owed by decomposition of silicate (in form of 2+ same origin, whereas the highest presence is de - h Sio at ph=7) result in an increase of the Zn con - tected in the water samples with lower mineraliza - centration (due to adsorption of cations Zn 2to ne2g - 4ti2 on (mild weathering driven dissolution of ative particles of clay, cGoelollo. aind. aBla lpk.a protluicolse., s20 x2S0,i 8o 1 (*2)y, 3h 3–4o8 car bonates or alumosilicates). The probable origin or other negative charged Si-particles). The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

Sulfates are not well4-correlated with the elements, process could be explained by the following mecha - with exception4 of Ca-So (0,599). This correlation sug - nism: gests that So could have mo4re than one source. 2 2 4 2 2 4 hence, the concentration of So ions in water is not 2FeAsS+7o +6h o→2FeAso ×h o+2h So , (1) proportional to the quantity of sulphide which can be regarded as one of the potential sources (in the case by oxidation arsenopyrite is transformed to the of the presence of sulfide ore - deposits rocks) neAirthCíeA r scorodite. wáiNthCh AEsS . The same conclusion is underlined by G - This mineral is stable in dry and oxidative condi - S et al. (2005). Furthermore, the concentrations tions. however, in contact with fluids (water) sco - are influenced by (a) surrounding rocks, (b) the extent rodite can be transformed into a mobile arsenic form of the oxidation zone and a (c) groundwater regime. and insoluble limonite as deposit:

Groundwater fluctuations and changes of an oxida - 4 2 2 3 3 4 tion-reductive layer cause the concentration fluctua - FeAso ×h o+2h o→Fe(oh) +h Aso , ( 2 ) Dtioisnt orfi bthuet siuolnp houfr ae/rsuelnphica taens.d definition of its origin in the area of Avala Mt., scorodite has not been de - tected, whereas limonite is documented. Similarly, arsenic can be transformed to the mo - bile form from pyrite (in the structure of pyrite, As changes the sulfur atom), which may be initiated by The range of concentration of inorganic arsenic in spontaneous oxidation. it occurs especially because Avala´s groundwater is 3.0–102.3 μg/l. The arsenic pyrite undergoes to oxidation, (due to iron`s affinity concentrations are discussed with respect to the do - to an oxygen): 2 + mestic and internal regulations: regulation on Qual - 2 2 2 4 ity and other requirements for Natural Mineral 2FeS +7o +5/2h o→Fe ooh+2So +2h , (3) Water, Spring Water and Bottled Drinking Water (Službeni list SCG, 2005) as well as regulation of The final product is limonite or amorphous Fe Who and Eu Directive 1998/83/EC Drinking Water. oxy-hydroxide. Sulfur is oxidized to sulfate, which The MAC of arsenic in drinking water defined by the then has a capabiMiliiTtryi jtEov mić igrate or remains in the ox - standards is 10 μg/l. idation zone ( D et al., 2002). A comparison of the results with the reference on the other hand, the lowest concentrations, as value for As, yields that the studied waters (excluding well as the concentrations below a detection limit are the waters from “Točak” spring and the wells “Avala” in the waters formed in the zones of fractured ser - and “Zuce”) are enriched by this element. pentinite (oldest ophiolite-bearing complex of the in order to understand the highest arsenic content Avala Mt.). The similar conclusion can be derived from the “vranovac” spring, the surrounding geology from the results of analyses of the water sample col - is analyzedo mLjoić re in detail. According to the geological lected from the investigated well drilled in 2008 map of T (1995), the vicinity of vranovac (Zavojnička river,i ZPkuocvei)ć . The concentration of arsenic stream/creak can be characterized by hydrothermally was 3.0 mg/l ( T , 2008). altered quartzlatite veins. A similar observation was The results of detected concentrations of arsenic confirmed on the sampling site during the field trip. A in the aquatic environment are not the results of the significant presence of hydrothermally altered rocks weathering processes only. Their presence and mo - and the occurrence of arsenopyrite could explain a bility of arsenic forms is a function of chemical envi - highest concentration of arsenic in the sampled water ronment within the aquifer. Following the arsenic of “vranovac” spring. release through the process of pyrite oxidation, a The result of chemical weathering of arsenopyrite newly formed amorphous Fe ooh plays an impor -

Gise oel.x apnl. aBnalka. tpioluno so.,f 2 t0h20e, 8p1r (2e)s, 3e3n–4c48 e of mig4rative form and tant role in controlling the mobility of arsenic in th4e3 oxidation state As v (h Aso /hAso , at ph=7). This storage zone. Fe ooh may accommodate a subse - Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

quent removal of arsenic, prior its recovery (predo- 1) Spanning the Late Cretaceous – present-day geo - minantly aAtNtrDiEbruZtAeLdM to sorption under favorable con - logical timeframe, the investigated area repre - Table 3. The results of analysis of the water sample from well “Avala”- before and after acid ditions; v et al., 2011). This conclusion sents the system with favorable conditions for digestion. corroborates the experiment presented in the Table 3. arsenic subsurface development. initially, there is a documented presence of hydrothermally altered mag - ma tic rocks including the oc - currence of mineralizations, followed by a protracted weathering and atmospheric impact o n the particular ar - senic-bearing rocks. Secondly, being crosscut by rock dis - continuities and deformati - Detection of the concentration of As, Mn, Fe be - ons, the fractured Avala volcanic complex fore and after acid digestion of the water suspension fa cilitated a protracted interaction of water per - sample “Avala” well (water with the solid residue the colating throughout these subsurface discontinu - results) indicates an increase in the total concentra - ities; tions of arsenic and Fe (sum of the concentrations in 2) The occurrence of arsenic in groundwater of the water and solid residue). The result suggests that ar - investigated area is of natural origin. its presence senic is deposited along with Fe and Mn. More pre - within the detected concentration range could be cisely, it is adsorbed at the surface of ferry a result of the two controlling processes: a) oxy-hydroxide particles. Namely, arsenate as a stable expected chemical weathering of minerals such form in aerobic conditions can become less mobile. as arsenopirite-pyrite and b) mechanisms such as Thus, the As could be removed by the several pro - sorption/desorption commonly associated with cesses, precipitation or adsorption onto hydrous iron the surface or occlusions by amorphous Fe ooh oxides. The fact that hydrous iron oxide has a positive (or limonite) ; surface charge in most geological environments and 3) The range of the concentration of inorganic ar - preferentially adsorbs anions, whereas manganese senic in Avala´s groundwater is 3.0–102.3 μg/l. oxide is negatively charged and adsorbs cations, pro - The spring with maximum detected concentra - vidueBrs AtMheAN siuANitable explanation of a such distribution tion of arsenic is “vranovac”, emplaced within the (S at al., 2002). Moreover, the example of geological domain characterized by hydrother - this equilibrium could be water of “Ledenac” spring mally altered quartzlatite veins. The lowest con - (explained earlier in the text). centrations, along with the concentrations below in contrast to the “Avala” well, the concentration the detection limit are documented within the of arsenic in other springs and other well are ele - waters formed in the zone of fractured serpenti - vated because arsenic from ferric oxy-hydroxides nite (in the Avala’s oldest rock complex). Addi - particle surface desorbs to the investigated ground - tionally, the highest concentrations of As were Cwoatnecr leunsviroon nment. documented in the area of the intense water ex - change.

The concentrations of arsenic measured in seven samples exhibit the levels which are above the max - The study documents the presence of arsenic, its imum-allowed values for drinking water (according distribution, and the origin in groundwater of the to the domestic and foreign regulations). A continu - 4A4 vala volcanic complex. This research leads to the ous ongoing exploitatioGneo ol. fa nw. Baatlek.r p ofrluooms., 2t0h2e0,s 8e1 s(2u), p33p–l4y 8 following conclusions: sources may impose a risk to human health. Never - The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

iMCiThreijmEvicić al induNstTroy NijEvić iMiTrijEvić j theless, the health risk is rather low considering the D , M., A , M. & D , L . v. 2002. fact that the spring waters have just occasionally oxidation of pyrite-consequence and significance. bAeceknn uosewdl beyd tgoeurmisetsn at nd local population. , 56 (7–8): 299–316 [in Serbian]. EC. 1998. Directive related to the quality of wateErn ivn i -

ArrtCeoíAndmeáedNn CfthoaErlS Gheuomloagnoyy ,cAoNno sumptioAyno, r9G8A /83/EC G -S , A., M , A. & M , P. 2005. high ar - senic contents on groundwater of central Spain.

This research did not receive any specific grant from uo TüBEN ErNE4r 7: 847–u854. . Applied Geo - funding agencies in the public, commercial or not-for- G c, hhe.,m S istry , D., B , Z. & y , Q. 2009. Characteristics profits sectors. We would like to thank anonymous re - of arsenic adsorption from aqueous solution: effect of viewers in their efforts to improve an earlier version of arsenic species and natural adsorbents thEev mENaknA uscEriipć t. Also, we thank to Editor in Chief Prof. Dr. vković u,k 2ov4i:ć 657–6ik6o3L. ić ovAčEvić ALAvESTrić N Đ for guidance throughout the manuscript i j , AET., rv ović , Ao.v, AN Nović B, aj.,s ik cr GiFeuoNlovgiić,c Da.l, mP api BoiNf oFvoir ć -, mer 1: 100 000, sheet Pančevo Rreevifeewr pernoceess. Lj., P , v., j , L ., T , r. & S , L . 1971. osnovna geološka karta SFr jugoslavije 1:100 000, list Pančevo [ – in SBerubllieatni]n ,

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oZuNAnNpouvbić l. StudioeP, oGveićological iAnNsotijtLuotveić of Serbia, Belgrade. oLGjićeology, AuTnEiNvCeo rsity oTfo BjAeDligNroavdić e. iLLiNGShoFEr P , M., P P,r Lojc.e &e dM ings of the, 3D8. t2h0 C0o9n. fDeoremnecset oic f T ju, BMov.,i ćM BrADo, vLić., S , uG., lW obal and Plane, tEa. r& y aSenrdb iinatne wrnaatteiro npaoll lruetgiounla qtiuoanlsit oy fc coonntrcoeln storactieiotyn, l“eWvealt eorf Lchange, -o , D. 2018. understanding fossil fore- a2r0s0e9n” ic in drinking water taken from spring Sakinac, arc basins inferences from Cretaceous Adria-Europe Mt. Avala, Serbia. convergence in the NE DinaridesH. ydrogeological inves - th Proceedings of the 30 Con - riPtkigoavtićions1 7of1 t: h1e6r7m–a1l8 w4a. ter in the Zavojnička reka area oZfNeArNeonvci,eć 4 o6f 7th–e4 U7o2nP i[oivni ćESnegrbiniaener] s and Technicians of Serbia T , M. 2008. hidrogeološka istraživanja termalne P “Water ,a Mnd. & w Pater sup, Lpjl.y 2” 009. Arsenic in groundwater vode u oblasti Zavojnička reka [ of Avala’s springs (Serbia). – in Serbian]. unpubl. report, Geological institute of 46 Geol. an. Balk. poluos., 2020, 81 (2), 33–48 , 63–67 [in Serbian]. Serbia, Belgrade. The occurrence and evolution of arsenic in aquifers of the Avala volcanic complex (outskirts of Belgrade, Serbia)

Guidelines for drinking water quality

Who 2004. , 3rd ed. групу мало до средње минерализованих,, при ANWDEhrZoA,L GM eneva.iLLoN Arry ioTLiNSki irBy чему су н3ајдоминантнији катјони Ca и Mg и ан - v ,E j.GLA. L D LA A,L PL.E j., B , k.E., M , k., k , јони hCo и Cl.. Хемијски са став одражава гео - Applied Geochemistry , j.k., & L S , C. 2011. Arsenic mobility and лошке кара ктеристике испи тиване области, јер impact on recovered water quality during aquifer су извори смештени у оквиру испуцалих зона тј. storage and recovery using reclaimed water in a car - локално развијених пукотина које пресецају Реbзoиnмatеe. 26: 1946 –1955. Авалски офиолитски комплекс (серпентинити) . Прису ство Ni, Cr и Mg, као и значајна корелација Појава и еволуција арсена у из међу Cr и Mg указује на вероватан утицај извориштима вулканског комплекса серпен тинита на састав воде . С друге стране, Авала (периферија Београда, Србија) одсуство значајне позитивне коре лације Аѕ са наведеним компонентама, може сугерисати на другачије порекло овог елемента. Оно је најве - роватније везано за дубље цирку лисање тер - малних вода на контакту магматских интрузија Арсен је хемијски елемент који, у животној које пробијају сам офиолитски ком плекс укљу- средини , као загађивач може бити присутан из чујући и околни седиментни пакет кредне природних и антропогених извора. Иако по старости . заступљености у Земљиној кори заузима дваде- Резултати хемијских анализа су показали да сето место, због своје токсичности проучавање опсег концентрација Аѕ у испитиваним узор - присуства и садржаја арсена, посебно у пијаћој цима износи од 3.0 –102.3 μg/l. Најниже концен - води све више добија на значају. Томе доприноси трације или одсуство Аѕ карактеристично је за податак да дуготрајно уношење арсена у воде формиране у испуцалим серпентинитима количи ни од 30 –60 μg изазива канцер коже. које припадају најстаријем офиолитском ком- Природно порекло арсена у водама везано је плексу источне Вардарске зоне . Максимална за специфичне области-сулфидне минерализа - концентрација регистрована је у извору сме - ције, геотермалне, семиаридне-аридне са висо - штеном у области хидротермално измењених ким рН, као и области анаеробних аквифера. стена уз присуство арсенопирита , односно Обзиром да су у испитиваној области вул- пирита . Додатно, резултати хемијске анализе канско -офиолитског комплекса Авале реги - суспендованог узорка воде бунара „Авала”, пре и строване појаве сулфидних минерализација, после киселинске дигестије на садржај еле - прет ходна иницијална истраживања указала су мената Аѕ, Fe и Mn указали су на могућ процес на појаву арсена у води појединих каптираних адсорпције-копреципитације Аѕ услед таложења извора, највише посећених од стране туриста . У Fe- и Mn- оксихидроксида . њима су регистроване појаве садржаја арсена Сумирано, појава арсена у подземним водама изнад максималне дозвољене ( 10 μg/l). Стога, Авале је природног порекла јер су постојали ово истраживање представља : 1.) потврђивање геолошки предуслови за његово присуство. Они датих вредности садржаја Аѕ у испитиваним су везани за хидротермалне измене магматских водама; 2.) утврђивање појаве и концентрације стена и појаве сулфидне минерализације пра - у води других доступних извора или бунара; 3.) ћене хемијском алтерацијом минерала. Додатно, порекла арсена у подземној води аквифера вул - томе доприносе екстензионе деформације као и канског комплекса Авале. Такође , у овом раду ис пуцалост стена магматског комплекса Авале дефинисан је катјонско -анјонски састав вода и која омогућава циркулацију подземних вода . корелација између главних компонената/ми - Опсег концентрација детектованих у изворима крокомпонената. Сходно томе, доведен је у везу и бу нарима последица је равнотеже између про - састав подземне воде и литостратиграфских цеса хемијске алтерације минерала типа ар– сено - Gјеeдolи. aнn.и Bцalаk. кpoоluјеos .с, у20 п20р, 8и1с (у2)т, 3н3е–4 8на површини. пи рита и пирита, као и процеса ад сор пци4је7 Испитивани узорци подземних вода спадају у де сорпције-копреципитације арсена са Fe окси - Maja PoznanoVić , L jiLjana PoPoVi ć, Tanja PETRoVić PanTić , D aRko SPahić & G oRan MaRinkoVi ć

Manuscript received May 17, 2020 хи дроксидима (у кристалном - лимонит или може представљати висок ризик по људско Revised manuscript accepted September 23, 2020 аморфном облику ). здравље. Свакодневном дуготрајном употребом под - земне воде са извора у којој је доказано при - суство Аѕ у концентрацијама изнад 10 μg/l

48 Geol. an. Balk. poluos., 2020, 81 (2), 33–48