Reactivity, characterization of reaction products and immobilization of lead in water and sediments using quercetin pentaphosphate

Abstract

Lead is currently ranked the number one heavy metal pollutant with a maximum contaminant level (MCL) of 0.015 mg L⁻¹. The use of organic solvent-free methods to immobilize lead from the environment is attracting the attention of scientists and environmental engineers. This study reports the application of water soluble quercetin pentaphosphate (QPP), a derivative of quercetin, for the detection and immobilization of Pb²⁺ from water and soil samples. The techniques employed include UV-visible, fluorescence, atomic absorption; inductively coupled plasma optical emission and Fourier transform infrared (FTIR) techniques. Results indicated the formation of a QPP–Pb complex that inhibits the fluorescence intensity of the parent molecule. The fluorimetric limit of detection was found to be 3.46 × 10⁻⁴ M. The QPP–Pb complex exhibited a corresponding stoichiometry with the predominant complex PX₂. A Scatchard plot of y = −4 × 10⁶x + 2916.3 was observed with a negative slope giving an equilibrium constant of 4 × 10⁶ M⁻¹ and 5.4 × 10⁵ M⁻¹ in acidic and alkaline conditions respectively. Results show 90.4% and 91.5% lead(II) immobilization from BRS and BU soil samples respectively. On the other hand, 91% lead immobilization efficiency from a water sample was achieved at room temperature and is in compliance with the MCL level of 15 ppm at ∼3.82% error margin. This approach does not require the use of organic solvents or the disposal of large amounts of sludge. Once complexed with lead, QPP may not release phosphate to cause any secondary pollution.