Experimental hygienic estimation of calcium and magnesium concentrations in drinking water, and its hardness

Introduction. The lack of hygienic norms for Mg²⁺ and Ca²⁺ in drinking water and the wide ranges of acceptable hygienic norms (AHN) of these cations in water packaged in containers determine the relevance of experimental studies on the substantiation of AHN of Mg²⁺, Ca²⁺ and the hardness of drinking water with a centralized water supply to the population.

Material and methods. Chronic experiments were performed on 5 groups of adult Wistar rats (n = 50): control animals received drinking water (Ca²⁺ 20.0; Mg²⁺ 6.0 mg/dm³, hardness 1.5-1.8 mEq/dm³); four other groups received model drinking water with different contents of Ca²⁺ (50, 80, 100 and 140 mg/dm³) and Mg²⁺ (20, 40, 55 and 85 mg/dm³) by adding CaCl₂ or MgSO₄ salts to the control water. The effect of these drinking water samples on kidney function, ion osmotic blood parameters, plasma metabolites of lipid and protein metabolism, as well as the concentration of thyroid hormones (T3 and T4) and cortisol were studied.

Results. Prolonged action of increased concentrations of Ca²⁺ and Mg²⁺ on the organism was established to cause alterations in fat metabolism, the adaptive activation of osmoregulatory and ion regulatory kidney functions, increasing the concentration of thyroid hormones and a decrease of cortisol titer in plasma. Magnesium led to more pronounced changes in water-salt metabolism, and at a concentration of 85.0 mg/dm³ (7.0 mg-Eq/dm³) – to depletion of secretion of the described hormones.

Conclusion. Based on the obtained results, individual ranges for AHN of calcium and magnesium concentrations in water were recommended. The upper limit of AHN of drinking water total hardness is of 7.0 mg-Eq/dm3 at the joint presence of Ca²⁺ and Mg²⁺. The rule of hygienic qualitative and quantitative estimation of calcium and magnesium types of drinking water hardness is formulated.