Removal of Pesticides using Bacteria and Hydrogel Silver Nanocomposite

Abstract

To combat crop loss due to pest infestation, pesticide application has become integral part of agriculture. Despite of benefits like improved crop yield and pest removal, frequent use and lack of timely degradation of pesticides has led to their persistence in the environment, worsening the soil quality, contaminating ground water, entering the food chain and affecting all living systems. The current study was aimed at screening of bacterial isolates capable of degrading butachlor and monocrotophos and synthesis of silver immobilized chitosan-PVA hydrogel nanocomposite (Ch/PVA-Ag) for their remediation under in-vitro conditions. Degradation of monocrotophos and butachlor was carried out using 15 bacterial isolates, where maximum monocrotophos degradation was carried out by Bacillus licheniformis BPRIST030 (NA14), whereas, isolate A16 identified as B. altitudinis A16 by 16S rRNA sequencing showed maximum butachlor degradation. Monocrotophos spiked in Bushnell Hass broth was solely used as nutrient source by NA14, with increase in viable cell count from 0.8 × 106 to 54 × 1012 cfu ml-1 in 120 h. Monocrotophos degradation took longer in comparison to butachlor degradation by bacteria, as about 70% monocrotophos was degraded in 5 days. GC-MS analysis showed generation of five major metabolites including, dimethyl phosphate, phosphoric acid, malonic acid, dihydrazide, N-3-dimethylbut-2-enamide and N-methyl acetoacetamide. Based on the produced metabolites, a metabolic pathway was proposed. Butachlor was utilised as a sole source of carbon by B. altitudinis A16 degrading 90% of 50 mg L-1 butachlor in 5 days at a rate constant and half-life (t1/2) of 0.02 h-1 and 34.65 h, respectively, following the first-order reaction kinetics. Five metabolites (N-(butoxymethyl)-N-(2-chloroethyl)-2,6-diethylaniline, (N-(butoxymethyl)-2-chloro-N-(2-ethylphenyl) acetamide, N-(butoxymethyl)-2,6-diethyl-N-propylaniline, 2-chloro-N-(2,6-diethylphenyl) acetamide and 2,6-diethylaniline) were produced during the breakdown of but