Problems of the safe use of modern cement materials in the practice of drinking water supply

Abstract

Introduction. Recently, there have been increasing changes in the technology of preparation of cement mixtures and concrete, the use of new components in their composition, since traditional materials are not quite suitable for the construction of hydraulic structures, including the internal coating of pipes and drinking water tanks. However, in addition to improving the characteristics of cement mixtures, additives can have a negative impact on the environment and human health by leaching out of cement into drinking water. The definition of only the main components specified in the “Universal sanitary-epidemiological and hygienic requirements for goods subject to sanitary-epidemiological supervision (control)” (hereinafter - the Universal Requirements) does not provide complete information about the chemical safety of cement materials during the hygienic assessment. Materials and methods. There were studied eleven samples of cement mixtures from various manufacturers repaired of reinforced concrete products and structures of general and special purpose, including those in contact with drinking water, and used for the sanitation of the internal surfaces of steel pipelines (including hot water supply systems) and repair and restoration work. The evaluation of samples was carried out taking into account Universal requirements, and indicators that are not mandatory for the evaluation of these materials were investigated. Results. Hygienic assessment of cement mixtures showed lithium to be detected in some extracts in concentrations from 20 mg/L to 0.18 mg/L, which is 666 times higher than its maximum permissible concentration - 0.03 mg/L. Also, two samples showed a slight excess of the permissible chromium concentration - 0.065 mg/L and 0.09 mg/L (MPC < 0.05). Iron and zinc in insignificant concentrations were found in aqueous extracts; in one of the samples a 2-fold excess of the manganese concentration was observed. One water extract contains silicates at a concentration of 34.24 mg/L, which exceeds their permissible levels in drinking water. The analysis also identified a number of organic compounds related to oxygen-containing compounds (alcohols, phenol derivatives, ketones, esters, phthalates), for most of which no MPC has been established. Limitations. The study was carried out on eleven samples of cement mixtures under standard conditions: infusion in model media for 30 days at room temperature in the ratio: 1 cm2 of the sample surface to 1 cm3 of water. Sampling was carried out on the Days 1, 3, 5, 10, 20 and 30 of research, without changing the test water. It is necessary to conduct similar studies under experimental conditions close to the operating conditions of these materials. Conclusion. Assessing the efficiency of migration from cement-bound materials, it is necessary to take into account their capillary-porous structure on the one hand and the ability to improve the coating properties over time by converting calcium hydroxide present in freshly applied cladding into denser calcium bicarbonate. The migration of chemicals from cement-bound material is to be evaluated by taking into account the specific conditions of their use in the practice of drinking water supply, and the assessment of the additives introduced should be carried out on test cement samples, since it is impossible to theoretically calculate the migration rate of the components from the finished material.