https://doi.org/10.5061/dryad.dfn2z359h

Analytical techniques

Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used at the Institute of Nuclear Physics to analyze the elemental composition of the liquid samples.

ICP-MS analysis was performed on an ELAN-9000 inductively coupled plasma quadrupole mass spectrometer (PerkinElmer SCIEX). The standard deviation of the output signal is no more than 6%, the resolution is from 0.6 atomic mass units (amu) to 0.8 amu. at a 10% peak height and mass ranging from 2 to 270 amu.

ICP-OES analysis was performed using an OPTIMA-8000 dual-view optical emission spectrometer with inductively coupled plasma (PerkinElmer Inc.), with an optical range of 166–900 nm and a peak half-maximum resolution of 0.008 nm at 200 nm.

Undiluted water samples were used for the elemental analysis.

The following drinking water quality hygiene criteria for the trace element group are recommended for use in the regulatory literature of the Republic of Kazakhstan [14]:

1. The heavy metal content of hazard classes 3 and 4 should not exceed the maximum acceptable concentration (MAC) for drinking water adopted in the Republic of Kazakhstan [14, 15].

2. The heavy metal index (HMI) was calculated for chemical elements belonging to hazard classes 1 and 2, and standardized according to the sanitary-toxicological hazard. The calculation was performed according to the formula [14]

                                                                                                                                 (1)

Where Сi – average seasonal concentration of the i-th chemical element, μg/L, MACi - maximum acceptable concentration of the i-th chemical element, μg/L, n– number of analyzed chemical elements of hazard classes 1 and 2, the average seasonal contents of which in water samples exceed the detection limit (DL) of the applied method. The HMI value should not exceed 1.

The elemental composition of drinking water samples collected at 26 selected points in Almaty in winter, summer, and autumn of 2023 was studied using ICP-MS and ICP-OES techniques. Thus, the chemical element contents As, Be, Co, Cd, Cu, Li, Mo, Ni, Pb, Se, U, Hg, Al, Ba, Cr, Fe, Mn, Sr, V, Zn, K, Mg, Na, and Ca were obtained. The average content for the three data samplings and the standard deviations for each sampling point were calculated based on the data obtained. The As, Be, Cd, Se and Hg element contents do not exceed the technique detection limit, which is 0.5 µg/L for As, 0.03 µg/L for Be, 0.05 µg/L for Cd, 3 µg/L for Se and 0.1 µg/L for Hg for all measured samples. Table 1 presents the average contents () and standard deviations (SD) for chemical elements whose contents exceeded the DL. The table also shows the MAC and hazard classes for each chemical element adopted in the Republic of Kazakhstan [14, 15]. The exceptions were U, Ca, and K, for which there was no MAC (U and K) or hazard class (K and Ca) in the regulatory literature. As shown in Table 1, uranium is an important chemical element for Almaty in assessing the degree of water suitability for drinking purposes. Therefore, uranium in drinking water standards adopted in other countries have been considered. Table 2 presents the MAC values of uranium used in the different countries. As shown in Table 2, the MACs for different countries varied greatly, ranging from 2 µg/L (Japan) to 964 µg/L (Czech Republic). We used the maximum acceptable concentration value adopted by the World Health Organization (WHO), 30 µg/L, to calculate the heavy metal contamination index of drinking water in the Almaty-HMI. HMIs were calculated for each sampling point using Equation (1). The values obtained are presented in the last column of Table 1.