M. Sartakov, V. Chumak V. A., I. Grekhova, and M. Efanov, “The study of the chemical composition of humic acids of initial and heat-treated sapropels of lakes of the Surgut district of the Khanty-Mansi autonomous Okrug – Yugra”, Amazonia Investiga, vol. 7, no. 17, pp. 72-78, Dec. 2018.