Fluorine Concentrations in the Lena R. Water from 1995 to 2021.

The method of direct potentiometry with a fluoride ion-selective electrode was used to determine the average concentrations—0.110 and 0.082 mg/L—of dissolved fluorine in the waters of the Lena River in 1995 and 2021 at the recession and peak of the spring-summer flood. Measurement results are compared with the data of studies in 1954–1980. [ABSTRACT FROM AUTHOR]