Major and trace elements in tap water from Italy

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Abstract

Tap water is a fundamental resource for everyday life, it is subjected to several routine controls and needs to fulfill many compliance scheme. Several elements are monitored on a regular basis, but many trace chemical elements are not usually analyzed, so there is the need to have some kind of indication about their concentration and variation ranges in order to better assess the water quality. An opportunity for such investigations has been provided by a project of the EuroGeoSurvey Geochemistry Expert Group aimed at the characterization of groundwater geochemistry using bottled mineral waters purchased in supermarkets all over Europe which included also the analysis for comparative purpose, of tap water. The initial tap water database of 24 sites has been subsequently increased to the final number of 157 distributed all over Italy and representative of end-user situations (either private houses and public places). In the samples, pH, conductivity and concentrations of 69 elements (Ag, Al, As, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, Tm, U, V, W, Y, Yb, Zn, Zr, Br, HCO3, Cl, F, NH4+, NO2, NO3, PO43−, SO42−,SiO2) were measured at the BGR geochemical laboratories. Some major elements (Ca, HCO3, Mg), the dominant water type, display limited range of variation whereas for others (Na, Cl) the scattering is wider (3 orders of magnitude). Only one sample for Cl and two samples for NO3 are above the recommended EU and Italian guidelines. Clear influence of bedrock geology and/aquifer composition is clear for some elements (e.g. As, F, Rb, V, U), other elements are indicator of mixing with deep formation water or sea-spray contribution (e.g. Br, I), others reflect also peculiar geographic area (e.g. B in Tuscany, Se in Emilia-Romagna). Factor analysis enabled the identification of a “corrosion” factor which includes Pb, Zn, Cd, Cu, Mn, Sn and Fe, all elements which are preferentially related to interaction with the distributing system pipelines.

Highlights

►157 tap water samples covering all Italy were analyzed for 69 chemical parameters analyzed at low detection limits. ► The study provided information about chemical elements not commonly analyzed in drinking water. ► Identification of natural sources (As, Rb, F, U, B, Br, I, Sr, Ba) controlled by geology, geography and hydrogeology. ► Discrimination of elements affected by contribution from the water distribution system (Pb, Zn, Cd, Cu, Mn, Sn, Fe). ► NO3, NH4+ and Fe, Al, Mn, As, Pb in few single samples are above Italian and EU drinking water directive.

Introduction

Potable or drinking water can be defined as the water delivered to the consumer that can be used for drinking, cooking and washing, a resource that required building of impressive waterworks even in ancient times such as the aqueducts of the Romans. Evidence of concern to water quality dates back to 2000 BC (Agardy et al., 2005). Drinking water quality is continuously monitored by health authorities and distributing companies since it must comply to physical, chemical, bacteriological and radiochemical guidelines before being introduced into the distributing system. Water used for potabilization has various sources: groundwater, spring water; water form rivers, streams, lakes, and artificial reservoirs. Any one of these sources can be present in a single area, particularly in large urban agglomerates where water can derive from local groundwater sources and/or, is possibly mixed with more distant, and chemically different, sources.

Supply from surface water is prone to air pollution, spillage and other occasional contaminants input in the watershed, change in weather conditions, while groundwater is generally less susceptible to occasional contamination inputs and more likely reflects the nature of the detrital material of the aquifer.

In any case, before being introduced into the distributing system, water needs some kind of treatment, generally stronger if the source is surface water. Treatment include some fundamental steps (De Zuane, 1997, Gray, 2008):

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    Disinfection, using Cl compounds or ozone and UV treatment, and possibly other compounds such as potassium iodide [KI] or B; disinfection takes place also at the end of the treatment plant and sometimes additional chlorination points are included in the distributing system if the distance from the source is high in order to keep the concentration of free reactive Cl high enough up to the end point;

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    removal of solid particles by sedimentation, generally required for surface water plants;

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    coagulation: chemicals are added to the raw water to remove colloids and improve physical properties before complete removal of solid particles. Among the coagulants there are Alum [Al2(SO4)3], sodium aluminate [Na2Al2O4], activated silica, ferrous sulfate [FeSO4 9H2O], soda ash [Na2CO3], quicklime [CaO]; possibly clays or limestone can be added in the treatment;

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    flocculation is the process of forming larger colloidal aggregate easier to settle and easily removed from water depending on amount of coagulant added, initial characteristics of the water, scale of the plant;

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    filtration, removal of remaining solid and flocculated particles through mechanical sieving on sand filters, possibly including also anthracite, or diatomaceous earth filters;

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    iron and Mn removal, particularly indicated for groundwater that could have high dissolved concentrations of these metals due to the reducing conditions in the aquifer, it is basically obtained by aeration, possibly with the addition of other oxidants such as potassium permanganate [KMnO4] or Cl. Solid oxy-hydroxides formed by aeration can remove also other elements by co-precipitation or adsorption (e.g., Cu, Zn, Ni, Co, As). Aeration will also remove volatile compounds (H2S, CH4, CO2 and other odor forming substances) possibly present in water.

The above treatments are meant to improve water quality for its aspect (e.g. turbidity removal), taste (e.g., removing or adding selected elements), odor (e.g., volatile compounds removal) or technical requirements (e.g., pH and hardness control to limit corrosion of the distributing system). These treatments are not designed to remove trace elements, but indirectly some water treatment as aeration, increase in pH, Fe and Mn removal can also affect the concentration of some elements sensitive to pH and Eh, and susceptible to adsorption and/or absorption reaction.

Once the water enters the distributing system it can be subject to losses, deterioration of the microbial quality; it can corrode the pipeline becoming enriched in trace metals and to control this aspect pH and water hardness are key parameters (De Zuane, 1997, Gray, 2008). Acidic waters are much corrosive than neutral or basic waters and a “soft” water is more “corrosive” or “aggressive” than hard water for plumbing systems. In plumbing systems brass, Cu, galvanized Fe, or Pb solders are present and so a soft water could contain higher levels of dissolved elements such as Pb, Cu, Zn, Cd, Ni, Cr and Fe. Key issues are the composition of the material of the distributing system, the age of the distributing system, although the variation trends can vary for the different metals (Veschetti et al., 2010) and basically depend on interaction time.

Italian tap water derives for about 70% by groundwater (11000 million of m3 per year in 2007) and for the 30% by depurated surface waters (Acquavita et al., 2007). Only in Puglia and Sardinia the amount of depurated surface water exceeds groundwater (Acquavita et al., 2007). Additionally, since Puglia does not have sufficient water supply, receives a large portion of tap water from aqueducts of the neighboring regions of Campania and Basilicata. These waters originate in a geological context very different from the Puglia one. This is the only case of important water interregional distribution occurring in Italy.

This study started in the framework of the EuroGeoSurvey Geochemical Expert Group project aimed at the geochemical characterization of groundwater all over Europe by the analysis of bottled mineral water (Birke et al., 2010a, Reimann and Birke, 2010) which included also analysis of tap water samples for comparison all over Europe (24 from Italy). This first group, collected in 2009, was integrated in 2010 to reach the total number of 157 sampling sites (Fig. 1, Table 1) covering almost all the Italian territory (only 6 provincial towns out of 111 were not sampled) and analyzed for their inorganic chemical composition. The sampling strategy was directed to the end-consumers, so the data reflect what the people is actually exposed to. We are aware that this introduces some unpredictable factors in the data interpretation, mostly related to interaction with the distributing system. These will be highlighted and discussed, but the main focus of the work will be on the description of the major chemical features of the tap water and to the evaluation of the distribution of some key trace element, focusing basically on the relation with the geological–geochemical features of source areas. Additionally, results will be compared to thresholds set by Italian and EU regulations, and US-EPA, WHO and FAO guideline values, to evaluate their quality. Tap water chemical features will be compared with the Italy bottled mineral waters ones (Cicchella et al., 2010, Dinelli et al., 2010, Lima et al., 2010) in a separate detailed paper in press (Dinelli et al., submitted for publication).

Section snippets

Health related guidelines

Italian drinking water supply is generally of excellent quality. However, water in nature is never “pure”. It picks up parts of everything it comes into contact with, including minerals, silt, vegetation, and agricultural run-off. While most of these substances are harmless, some may pose a health risk especially some trace elements. To address the latter risk, the World Health Organization (WHO) has developed guidelines that set out the maximum acceptable concentrations of these substances in

Geological and hydrogeological outline

The Italian territory (Fig. 2) is dominated by two important mountain belts, the Alps and the Apennines, originating by the orogenic processes related to the Eurasian and African plate collision and the closing of the Tethyan ocean (Carminati and Doglioni, 2005, Pfiffner, 2005 and references therein). The Pre-Alpine basement crops out in Sardinia, Calabria and locally in the Alps. It is composed of metamorphosed sedimentary successions and Caledonian and Variscan magmatic rocks. Post-Variscan

Materials and methods

A total of 157 tap waters was sampled in private or public distributing system all over Italy (list in Table 1, location in Fig. 1) between 2009 and 2010. Samples represent the present end-user tap water composition, so it is the one we drink every day. Samples were taken at private houses and in public places (bars, restaurants, offices, public fountains), although no systematic recording of the source was carried out. Samples were collected from ordinarily used taps, stored in PET

Results and discussion

The summary statistic presented in Table 3 and graphical dispersion of the data in Fig. 3 indicate that many elements like Ba, Zn, Mn, Cr, Cu, Pb, U and NO3 display wide ranges of concentrations spanning several orders of magnitude (104–103). Te, Ta, Sc, Hf, Bi and NO2 show instead narrow range of variation, of about one order of magnitude, Hg has only one value above detection limit. Chemical elements and compounds, expressed as mg/L, like HCO3, Ca, SO42−, Cl, Mg, Na, NO3 and Si, have the

Concluding remarks

The large tap water database available enabled us the definition of the following main conclusions:

  • The analysis of 69 chemical parameters on 157 samples of tap water from domestic and public points shows a very homogeneous composition as concerns EC (88% of the samples of low mineral concentration). The dominating water type is Ca–Mg–HCO3, which has a nationwide distribution. Na–Cl waters are frequent in Sardinia and Sicily, where the weight of supply from treated artificial reservoir water is

Acknowledgments

The authors are grateful to Clemens Reimann for the inspiration of the wider project on the geochemistry of European bottled mineral waters within the EuroGeoSurvey Geochemistry Expert Group, from which this research stemmed. Many thanks to friends and colleagues which enthusiastically helped in the sample collection in the Italian territory.

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