The consumption of clean water is the most relevant today, but natural water is delivered to our homes through plastic, iron and galvanized pipes. Metal ions, which are part of the pipe material, can get into drinking water and affect the human body, in particular the thymus. That is why the aim of the work was to determine the density of large, medium and small lymphocytes in the cortex and medulla of the thymus lobules of outbred white male rats of reproductive age when consuming small doses of heavy metal salts with water for three months. The study was conducted on 40 outbred white male rats of reproductive age, which were divided into 4 groups: 1 group – control animals that consumed distilled water; 2 group of animals that consumed aqueous solutions – CuSO4·5H2O at a dose of 0.247 mg/dm3; 3 group – aqueous solution of ZnSO4·7H2O at a dose of 1.505 mg/dm3; group 4 – aqueous solution of FeSO4·7H2O at a dose of 0.5 mg/dm3. Histological, electron microscopic and morphometric research methods were used to study the density of large, medium and small lymphocytes in different zones of the thymus lobules. It was found that in the control group of rats, the density of large lymphocytes is the highest in the subcapsular zone, and the lowest in the medulla. The density of medium lymphocytes is the lowest in the subcapsular zone. The density of small lymphocytes is the lowest in the medulla, and the highest in the cortico-medullary zone. When using CuSO4·5H2O salts with drinking water for three months, there were no significant changes in the density of lymphocytes compared to the control group, except for a slight decrease in the density of large lymphocytes in the cortex of the thymus lobules. The density of lymphocytes in the third group of animals that consumed zinc salts (ZnSO4·7H2O) with drinking water changes significantly: the density of large lymphocytes in the subcapsular zone decreases by 2.3 times, in the cortico-medullary zone it increases by 4.7 times, and in the medulla it increases by 2.7 times; the density of medium lymphocytes decreases in the subcapsular zone by 2 times; the density of small lymphocytes decreases by 1.5 times in the subcapsular zone, in the cortex and cortico-medullary zone – decreases by 1.2 times, and in the medulla by 1.1 times. When using FeSO4·7H2O salts with drinking water for three months, no special changes in the density of lymphocytes were noted: a decrease in the density of large lymphocytes in the subcapsular zone by 1.5 times and by 1.3 times in the cortex was observed; the density of medium lymphocytes decreases by 1.2 times in the cortex, and the density of small lymphocytes decreases by 1.2 times in the subcapsular zone and cortex, and increases by 1.2 times in the medulla, compared to the control group of animals. Ultrastructural changes in the structure of lymphocytes and reticuloepithelial cells were not detected when heavy metal salts were consumed with water. Thus, the study showed that the most toxic for the body are zinc salts (ZnSO4·7H2O), the consumption of which with drinking water in small doses for three months led to significant changes in the density of lymphocytes, compared to the control group experimental animals.
