The quality of drinking water is one of the key factors defining the health of the population. In the developing countries, deviations in its qualitative composition mainly underpin epidemiological health risks, whereas in industrially developed areas, it is chemical safety indicators that are most important from the hygienic viewpoint [1–3]. According to the available data, 87% of the population are provided with high-quality drinking water, and the key goals of the Clean Water Federal Project have been fully achieved only in three quarters of the territory of the Russian Federation [4]. The common flaws of drinking water in centralized water supply systems that draw upon surface and underground sources are excessive hardness, high levels of iron, boron, cadmium, and lead [5–9]. The quality of drinking water is affected not only by the sanitary, hygienic and hydrological features of the source, but also by the water treatment methods; for example, chlorination of water contaminated with phenols translates into formation of chlorophenolic compounds [3].

One of the most effective approaches to the drinking water quality evaluation and control is risk assessment: it allows ranking chemical threats by their impact on public health, and helps identify and prioritize scientifically sound measures aimed at reducing health risks to acceptable levels [5, 10, 11].

In a capital of a subject of the Federation, it is particularly interesting to compare, district-wise, the chemical safety of drinking water from the centralized water supply system that draws upon different sources; such a comparison will allow identifying priorities among the efforts aimed at improvement of the quality of drinking water within given residential areas.

This study aimed to make a comparative integral assessment of the quality of drinking water from a centralized water supply system in residential areas of Ryazan based on chemical safety indicators.

METHODS

The study was conducted on the territory of Ryazan, the administrative center of the Ryazan region. The population there, as of January 1, 2024, was 520.5 thousand people. The population of the regional center receives water from a central ring-type water supply system, which draws upon the Oka River (55–60%) and the artesian waters of the Podolsk, Oka and Kashira aquifers (40–45%). Sanitary protection zones have been established for all water supply sources. In all districts of the city, the water in the system is a mixture from surface and artesian sources, with the exception of Solotcha, which receives water from the artesian wells only.

For this study, we used water quality assessments made at monitoring points of the supply network during the period from 2017 to 2022. There is one such point in each district of the city, with the exception of Oktyabrsky, where there are two monitoring points. The samples are taken monthly, i.e., 12 times a year. In total, the study relied on the results of 3,440 drinking water quality analyses that involved 720 samples. MR 2.1.4.0032-11 was the guiding document for the comparative integral assessment of chemical safety of drinking water from a centralized water supply system of the city of Ryazan [12]. To identify hazards, we specifically monitored the water quality indicators the values of which were above the relevant hygiene standards in 2017–2022. The confidence interval for the maximum values used in the calculation of organoleptic risks was set at 98%. Non-carcinogenic and carcinogenic risks were calculated based on the average long-term concentrations expressed as values with 95% confidence interval (non-threshold models) [12, 13]. The uncertainties inherent in the risk assessment stem from the limited list of indicators controlled in drinking water in the context of sanitary and hygienic monitoring.

Primary data were processed using the one factor analysis of variance with the target significance level p < 0.05; the software employed for the purpose was STADIA 8.0 (Informatics and Computers LLC; Russia).

RESULTS

In the considered districts of the city, the maximum values for drinking water smell and taste (98% CI) varied from 2.9–3.4 points, which is above the hygienic norm (tab. 1). The color of the water, however, was within the standard range (20°).

The given data show that the turbidity values (at p = 0.98) were maximum in Solotcha and Stroitel districts, where they exceeded the hygienic norm by 2.1 and 1.8 times, respectively; in other districts, this indicator was within the hygienic norm and ranged from 1.7–2.5 mg/l. The maximum concentration of iron (2⁺) in the drinking water was the greatest in Solotcha: it exceeded the maximum permissible concentration (0.3 mg/l) by 7.6 times. In Zheleznodorozhny, Stroitel and Oktyabrsky, this indicator was 3.5–5.2 times higher than the maximum permissible concentration, while in the remaining districts it was 1.1–2.8 times higher. Single concentrations of aluminum in the drinking water in Dyagilevo, Moskovsky, Solotcha, and Stroitel districts were below detection threshold (bdt), while its maximum concentrations in the remaining districts did not exceed the maximum permissible concentration (0.2 mg/l).

The study showed that in all districts of the city, drinking water's smell (at 20 °C) and taste values, the organoleptic indicators, amounted to 0.5, which is five times higher than the acceptable value of 0.1 (tab. 2). In the city, the organoleptic risk associated with iron (2⁺) content in the drinking water was 2 to 8 times higher than the acceptable values, with the exception of Moskovsky and Sovetsky districts. The highest value, 0.821, was registered in Solotcha. In Oktyabrsky and Stroitel districts, iron content was six times higher, in other districts — 2-3 times higher than acceptable. It should be noted that organoleptic risks of drinking water associated with aluminum ion content and turbidity were insignificant in all the districts considered. In the overall assessment, the organoleptic risk of drinking water in Solotcha, Oktyabrsky, and Stroitel stemmed from the content of divalent iron, whereas in the remaining districts the factors shaping this risk were smell and taste, which could have various origins (increased iron content, corrosion of metal pipes, formation of microbial films of iron bacteria on the inner walls of water pipes, formation of chlorinated hydrocarbons, stagnation of water, etc.) [14–20].

The average long-term concentrations (95% CI) of the main contaminants in drinking water from Ryazan's centralized water supply system did not exceed the respective maximum permissible concentrations   (tab. 3). The total non-carcinogenic risk was below the threshold (0.05) in all the districts; it ranged between 0.013 (Moskovsky) and 0.021 (Stroitel).

Of the chemicals presented in tab. 3, only cadmium (Cd) and lead (Pb), which belong to IARC carcinogenicity groups 1 and 2B, respectively, have carcinogenic effects [15]. The study showed that only in Dashkovo-Pesochnya did the carcinogenic risk of drinking water exceed the acceptable value (1 × 10⁵) and amounted to 1.25E-05; in other districts, its values ranged between 3.19E-06 (Kanishchevo) and 6.09E-06 (Stroitel) (tab. 4). It should be noted that the main contributor to the total carcinogenic risk of drinking water was cadmium: in Dashkovo-Pesochnya, it supported the said risk by 93.2% (the highest), and in the Sovetsky district — by 66.8% (the smallest).

The results of the integrated assessment of hazards in the drinking water from centralized water supply system in residential districts of Ryazan are given in (tab. 5).

The study showed that in all residential districts of the city of Ryazan, the integral indicator (II) of the level of hazard of drinking water from the centralized water supply system exceeds the acceptable values, with the said level being the highest in Solotcha (II = 8.8) and Kanishchevo (II = 5.6). The greatest contribution to the II of hazard of drinking water is made by the organoleptic risk.

DISCUSSION

High maximum concentrations of iron in the drinking water in Solotcha, Stroitel, and Oktyabrsky create unacceptable organoleptic risks (0.6–0.8); they may stem from a higher proportion of artesian waters (Podolsk and Kasimov aquifers) in the supplied mixture, since this element is common therein [21, 22]. The content of iron in drinking water is known to grow with the time the water spends in the supply system due to pipe corrosion. The process also increases color and turbidity indicators, and the water acquires characteristic metallic taste. The organoleptic properties of water can also deteriorate due to the proliferation of iron bacteria inside water pipes [9, 14–17, 23]. Drinking water with a high iron content increases the risk of skin and subcutaneous fat diseases in children and adolescents [11]. Other studies have shown that elevated concentrations of iron in drinking water can have an adverse effect on the hematopoietic and immune systems [14, 15].

The identified high organoleptic risks of drinking water associated with the maximum values of smell and taste indicators may also be due to the formation of organochlorine compounds as a result of chlorination, which calls for preference of combined methods of disinfection [18–20]. However, the existing uncertainty stemming from the limited character of the list of substances the content f which in drinking water is controlled prevents us from confirming or disproving the above-mentioned reason in this study.

The individual carcinogenic risk above the acceptable threshold was registered in Kanishchevo only, and the reason behind this spike by 93.2% were cadmium ions, which may be related to anthropogenic pollution of the Oka River [24, 25]. The results of this study are generally consistent with the data reported by other authors, who underscore the unacceptable level of carcinogenic risk caused by the drinking water in Ryazan having lead and cadmium [26, 27].

CONCLUSIONS

The study showed that the total organoleptic risk of drinking water from the centralized water supply system of Ryazan was 5-8 times higher than acceptable in the Solotcha, Oktyabrsky, and Stroitel districts, the said risk created by the high content of divalent iron, while in other districts, the reasons behind the organoleptic risk were smell and taste.

The total non-carcinogenic risk did not exceed the acceptable values (0.05) in all the considered districts of the city; it ranged between 0.013 (Moskovsky) and 0.021 (Stroitel).

As for the carcinogenic risk, it was above the acceptable value (1 × 10⁵) in Dashkovo-Pesochnya only, where this risk amounted to 1.25E-05. Throughout the city, carcinogenicity of drinking water stemmed from the content of cadmium.

In all residential districts of Ryazan, the integral indicator of the hazard of drinking water from the centralized water supply system exceeded acceptable values, mainly due to the high organoleptic risk, which necessitates development and implementation of preventive measures aimed at reducing it.