The quality of drinking water is a worldwide concern. It is important to monitor its quality prior to any further precautions [20
]. This study presents and reports the concentration levels of metals in the drinking water and/or groundwater samples by analyzing the four different sources of water samples from Kosovo.
Trace elemental concentration of NIST 1643e SRM reference water solution is often used to validate the analytical techniques during measurements. The quality control results of the certified and measured values of NIST 1643e SRM reference water, n = 7, are presented in . The measured values agree well with the certified values.
Values of certified and calculated NIST 1643e SRM reference water analyzed by ICPMS and internal standard used for correction.
The main statistical parameters (mean, min, max, median, and 25th and 75th percentile) of the elemental concentrations (μg/L) for the four sources of drinking water are summarized in . also shows the percentage ≤ LOQ as well as the EU and/or WHO limit of drinking water guidelines. From 951 samples, 68.0% are private-bored well samples, 21.1%, naturally flowing artesian water, 7.4% pumped-drilled well, and 3.5% from public water source. Private-bored well drinking water sources are the main water supplier for the majority of the Kosovo's population and therefore it needs greater attention.
Summary of concentrations for the water sources in Kosovo and EU and WHO guidelines.
The drinking water analyzed was compared to the limits and recommendations of the EU and WHO drinking water standards (). presents the number of samples that surpass the levels of EU and WHO guidelines in drinking water, respectively. It can be clearly ascertained that the samples exceeding the limits were mostly from the private-bored wells, then naturally flowing artesian water, pumped-drilled well, and public water source, respectively. Of the 14 (U excluded) regulated elements by either EU and/or WHO, the elements that surpassed the set levels most often, when compared to the total samples for that element, were Mn, Fe, Al, Ni, and As.
Total samples exceeding the EU and WHO drinking water guidelines.
From it can be clearly determined that there is a large variation for the elemental concentrations and a similar situation for elemental concentrations of different sources. Moreover, for most of the minor elements analyzed, we encountered a wide range (2 to 4 orders of magnitude) of elemental concentrations. This span is not as evident for the major elements (Na, Mg, K, Ca), yet the median concentration differs between the sources for the major elements and some minor elements, respectively (). Mn mean concentrations vary significantly between the sources, with the highest concentrations in the private-bored wells. Similar patterns are seen for Fe, Cr, Co, Zn, Cd, and Sb. These variations cannot be explained due to the lack of geological and environmental studies in Kosovo. However, one can postulate that the elements that show higher orders of magnitude could have no solubility controls if present in an oxidizing environment; they could be redox and pH sensitive or they could have various concentrations in rocks [21
]. Further, with ANOVA analysis we tested the source variation on whether the means are equal. Hence, we determined that the concentrations between groups are significantly different for the following elements: Li, Na, Mg, K, Ca, As, Rb, Sr, Mo, Sb, and Ba. Additionally, we tested the differences in variance between different sources of water using Bartlett's test for equal variances with P
value less than 0.05 showing that the variances are not the same across groups. In this case, we determined that the only element with the same variance across different sources of water was Mg.
In our study we found 792 samples to exceed at least one or more elements of either EU and/or WHO drinking water concentration guidelines. These samples are not significantly different between the sources. If we set the criteria to consider four or more elements surpassing any of the guidelines, we found only 57 sample points exceeding the set concentration guidelines, from which we can note that most of these sample points are private-bored well (43.9%), followed by naturally flowing artesian water (38.6%), pumped-drilled well (10.5%), and public water source (7.0%), respectively. Private-bored well drinking water source dominates within the highest number of samples surpassing the concentration guidelines.
We also performed some linear regression analysis testing the effect of depth (1–150
m) and age (up to 250 years) of the water source and latitude and longitude on the risk of the drinking water. Neither the depth nor the age showed a correlation with the concentration of the contaminants. After elimination of the variables with the highest P
values we found the latitude and longitude as significant variables. Regression analysis showed that as the latitude of the water source increased, the risk for higher elemental concentration in the water increased. A similar regression analysis showed a similar pattern with longitude: an increase in longitude of the water source showed an increase in the risk for higher elemental concentration. This implies that the northeast area of Kosovo should have a higher number of contaminated samples. In , we show the distribution of the Mn concentration.
The distribution of Mn concentration.
3.1. Health Implications
The importance and the health implications of selected elements are discussed. Particular attention is given to elements exceeding the EU and WHO guidelines, yet some unregulated elements with noted health implications are also discussed.
Previously, we singled out Mn, Fe, Ni, As, and Al as the elements surpassing the EU and WHO guidelines in the largest number of samples tested. According to WHO, when high concentrations of Mn and Fe are observed, the iron bacteria may cause deposits in the drinking water source and, therefore, may compromise the acceptability of the drinking water [7
Manganese (Mn) is an essential element in small quantities mainly for bone development and the metabolism of amino acids, lipids, and carbohydrates. In excess amounts, however, Mn has been shown to be toxic causing hyperactive behavior in infants and neurotoxin effects. Additionally, areas with a high concentration of Mn in drinking water report higher infant mortality [23
]. In the brain, high doses of Mn can cause Parkinson syndrome [22
]. A high concentration of Mn in drinking water also causes an unpleasant taste [22
]. The moderate presence of manganese in drinking water has no direct health effects, but the precipitated manganese in water can lead to aesthetic and infrastructure problems. A precipitate of manganese is usually black [22
]. In our analyses, a total of 74 samples exceeded the drinking water limit of 50μ
g/L set by the EU and only 20 samples exceeded the limit of 400μ
g/L set by WHO. The highest concentrations of Mn were observed in private wells.
Iron (Fe) is a necessary element for the biological functions of the human body, yet in excess can lead to acute Fe poisoning [21
]. The EU guideline for Fe in drinking water is 200μ
g/L, which was exceeded by 62 samples.
Nickel (Ni) is an essential element in small quantities, yet in high concentrations can cause heart and liver damage and skin irritation [21
]. The EU guideline for Ni in drinking water (20μ
g/L) was surpassed in 23 samples and only 5 samples surpassed the WHO guidelines (70μ
g/L). As for the other elements (), private well water source had the most number of samples exceeding the recommended values.
Arsenic (As) is an essential element in ultratrace quantities and higher concentrations of As in drinking water are a worldwide concern. Countries such as Hungary, India, and Bangladesh have coped with severe health problems caused by high concentrations of As in drinking water. It has been documented that As is carcinogen and highly toxic. Chronic poisoning has led to skin lesions and vascular disease [21
]. In Kosovo, As concentration levels in drinking water were higher in private wells than in other sources. Maximum acceptable concentration of 10μ
g/L (EU and WHO) was exceeded in 29 samples of which 23 were from private wells.
Aluminum (Al) is considered to be less toxic [21
]. Yet, studies have shown that Al in drinking water has been related epidemiologically to Alzheimer's disease [28
]. WHO does not have regulated limits for Al in drinking water. The 200μ
g/L limit set by the EU for Al in drinking water was exceeded in 36 samples of which 18 were from private wells.
Boron (B) has been recognized as a toxic element and is known to accumulate in the human body and damage the nervous system [21
]. The drinking water samples analyzed in this study surpassed the WHO regulated value of 500μ
g/L in 20 samples of which 16 came from private wells.
3.2. Water Quality
As most of the samples of the four sources were sampled directly from a pipeline system (a common household water distribution system), or other sampling devices (e.g., buckets and electronic pumps), one could argue that contamination occurred from the infrastructure or transport methods. Yet, our goal is to present the elemental analyses using a realistic method of how drinking water is distributed and consumed by the Kosovar population. Furthermore, research has shown that when water is run for at least five minutes before sampling, the water's elemental profile is similar to the natural groundwater structure [29
The elemental concentration results show that the drinking water is reasonably acceptable with a few exceptions in which some elements were significantly above EU and WHO guidelines. We believe that the high number of drinking water and/or groundwater samples with depth ranging from 1 to 150 meters is a good representation of the quality of water in Kosovo. The surrounding countries of Kosovo lack similar studies and further judgment on the water quality of the region could not be assessed. In the future, our study could be used to evaluate and correlate the contamination caused by different environmental factors.