Optimization of the Use of His₆-OPH-Based Enzymatic Biocatalysts for the Destruction of Chlorpyrifos in Soil

Abstract

Applying enzymatic biocatalysts based on hexahistidine-containing organophosphorus hydrolase (His₆-OPH) is suggested for the decomposition of chlorpyrifos, which is actively used in agriculture in many countries. The application conditions were optimized and the following techniques was suggested to ensure the highest efficiency of the enzyme: first, the soil is alkalinized with hydrated calcitic lime Ca(OH)₂, then the enzyme is introduced into the soil at a concentration of 1000 U/kg soil. Non-equilibrium low temperature plasma (NELTP)-modified zeolite is used for immobilization of the relatively inexpensive polyelectrolyte complexes containing the enzyme His₆-OPH and a polyanionic polymer: poly-l-glutamic acid (PLE₅₀) or poly-l-aspartic acid (PLD₅₀). The soil's humidity is then increased up to 60-80%, the top layer (10-30 cm) of soil is thoroughly stirred, and then exposed for 48-72 h. The suggested approach ensures 100% destruction of the pesticide within 72 h in soils containing as much as 100 mg/kg of chlorpyrifos. It was concluded that using this type of His₆-OPH-based enzyme chemical can be the best approach for soils with relatively low humus concentrations, such as sandy and loam-sandy chestnut soils, as well as types of soil with increased alkalinity (pH 8.0-8.4). Such soils are often encountered in desert, desert-steppe, foothills, and subtropical regions where chlorpyrifos is actively used.

Keywords: Dursban; agricultural pesticides; chlorpyrifos biodegradation; hexahistidine-containing organophosphorus hydrolase; organophosphorus and organochlorine compounds; soil.

Figure 1

Destruction of 100 mg·kg⁻¹ soil of chlorpyrifos under the action of His₆-OPH/PLE₅₀ immobilized in the plasma-modified (for 1.5 min) natural zeolite in various types of soil (a) and residual bioluminescence of immobilized Photobacterium phosphoreum used for evaluating the residual toxicity of the treated soil samples (b).