Study On The Pollution Characteristic And Enzymatic Remediation Of POPs Analogues In Soil-Vegetables

The organic pollutants have the characteristics with the persistence in environment and serious harm to human health and ecological environment safety like persistent organic pollutants are defined as POPs analogues.Studying the pollution characteristics,health risks and green remediation technology of POPs analogues in farmland is of great practical significance for the protection of agricultural soil and the restoration of ecological functions.POPs analogues including paclobutrazol and uniconazole,novel brominated flame retardants?NBFRs?,dechlorane plus?DPs?and phthalate esters?PAEs?were selected in this work.The distribution characteristics of POPs analogues concentrations in agricultural soil and vegetable tissues were studied,and their potential human exposure risks and environmental ecological risks were evaluated.The effects of laccase concentration,temperature,pH,humidity,illumination,air velocity,sterility,metal ions(Fe²⁺and Cd²⁺)and mediators?ABTS and HBT?on the degradation of paclobutrazol and uniconazole were studied.The active site of?-H,halogen,C=C bond and-OH were used to speculate the degradation pathway of paclobutrazol and uniconazole.The main intermediate degradation products of paclobutrazol and uniconazole were preliminarily identified by UPLC-MS/MS.Molecular docking can was used to reveal the formation of combination between laccase molecule and pesticides and explain the degradation mechanism between biolaccase and compounds.The main results of this study are as follows:?1?The mean concentrations of triazole pesticides in soils and vegetables were7.1 ng·g^-1 and 57 ng·g^-1,respectively.The mean concentrations of NBFRs in soil and vegetables were 1.5 ng·g^-1 and 2.4 ng·g^-1,respectively.The mean concentrations of DPs in soil and vegetables were 0.72 ng·g^-1 and 0.73 ng·g^-1,respectively.The mean concentrations of PAEs in soil and vegetables were 15120 ng·g^-1 and 20036 ng·g^-1,respectively.The average daily intake of paclobutrazol and uniconazole,NBFRs,DPs and PAEs was 456 ng d^-1,279 ng·d^-1,59 ng·d^-1 and 1406 ng·d^-1,respectively.The environmental ecological risk index?RI?for paclobutrazol or/and uniconazole and PAEs was 1.4 and 6.6,respectively.?2?The degradation rates of paclobutrazol and uniconazole relied on laccase concentration,temperature,pH,humidity,illumination,air velocity,sterility,metal ions(Fe²⁺and Cd²⁺)and mediators?ABTS and HBT?were analyzed.The degradation ratios of paclobutrazol and uniconazole were 66%and 44%under the optimal conditions including laccase concentration?4U?,temperature?25??,pH?4.5?,humidity?15%?,light?16h?,sterile?bacterium?and HBT?2.7mM?mediator.The degradation rates of paclobutrazol and uniconazole reached to 71%and 73%in the oxygen-enriched soils,respectively.The maximum degradation ratios of paclobutrazol and uniconazole reached to 81%in the presence Fe²⁺with the concentration of 5.0 mg kg^-1.?3?The degradation pathway was identified by the analysis of intermediate products.Laccase catalyzes the oxidation of parent compounds to form small molecular compounds by breaking bonds at the active sites of?-H,halogen,C=C bond and-OH.The differences of paclobutrazol and uniconazole degradation pathway were attributed tothe presence of the C=C double bond in the molecular structure of uniconazole and the absence of the bond in the molecular structure of polyclobutrazol.?4?The results of molecular docking suggested that ortho-and para-NH of pesticides intergrated with-NH and-OH of laccase by hydrogen bonds.The energy consumed by the binding between paclobutrazole and laccase was 13.52 kcals·mol^-1,and the energy consumed by the binding between uniconazole and laccase was 7.213kcals·mol^-1,which proved that paclobutrazole was easier to degrade than uniconazole.