Investigation of Complex Formation Process of Lead (II) with Fulvic Acids at pH = 7: An Ecosystem Approach

Lead is a highly toxic element, which has unfavorable outcomes on the biological, neurological, and cognitive functions of the body. Complexes of lead with macromolecular organic substances are characterized with less bioavailability and accordingly with less toxicity. Fulvic acids are macromolecular natural organic substances. Through the functional groups, they take part actively in complex formation and sorption processes that move along in natural waters, bottom sediments, and soils. Fulvic acids form stable complexes with heavy metals and radioactive elements, and stipulate their migration forms in natural objects.

Already existing data about stability constants of complex compounds of fulvic acids along with heavy metals are heterogeneous. Even for the same metals (among them lead), at the same value of pH, the values of stability constants of fulvate complexes differ in several lines from one another, which make it impossible to calculate the migration forms of metals in natural waters and to determine the toxicity and bioavailability through the obtained stability constants. Such a condition is largely designated by disregarding the dependence of the ionization degree of fulvic acids and average molecular weights of the associates of fulvic acids at the value of pH in the complex formation process, which ends up by getting the wrong results.

218In this work, the complex formation process of fulvate complexes of lead (II) was studied by the gel chromatographic method at pH = 7.0.

Pure samples of fulvic acids were isolated from natural waters. Their elemental compositions and dissociation constants were established. The average molecular weight of oligomer of fulvic acids (Mw = 1350) was utilized to observe the composition of lead fulvate complex (1:1) and stability constant β = 3.14 ×¹⁰⁴; lg β = 4.50. Through the obtained results, it will be possible to calculate the migration forms of lead in natural waters, determine the toxicity and bioavailability, and evaluate the ecological condition of water reservoirs.