Plant Absorption And Metabolic Process Of Benzothiazole Pollutants

Benzothiazoles（BTs）are a group of heterocyclic aromatic compounds with a1,3-thiazole ring fused to a benzene ring.As high production volume chemicals,BTH derivatives have been used in a variety industrial and consumer products,including vulcanization accelerators in rubber production,corrosion inhibitors inhibitors in antifreeze formulations,herbicides,algaecides,fungicides in leather and paper production,and ultraviolet light stabilizers in textiles and plastics.The extensive application of BTs in industrial and consumer products has led it frequently been detected in various matrices,sach as water,soil,sediments,street runoff,air,food,and even in human blood,urine,and fat.Due to its extensive presence and its mutagenicity,carcinogenicity,and other toxicity,the fate of BTs in the environment has been focused.In this paper,Benzothiazole（BTH）and its five analogues are used as target compounds to study the absorption,transport,enrichment,and metabolic processes on carrot,lettuce,squash and carrot cells.（1）The plant cultivation experiment of carrot and lettuce showed that each target compound reached a relatively stable state in all parts of the plant within 2-3 d,and the content in carrot is from 1056.16 to 1168.76 ng.The content of target compound enriched in different parts of carrot is different,specifically embodied as:root（mean:685.36 ng）>leaf（mean:255.49 ng）>stem（mean:170.42 ng）.Although the more content of some target compounds were been detected in the root,it was less in the stem and leaf.Less enrichment of 2-Hydroxy-Benzothiazole（2-OH-BTH）,2-Amino-Benzothiazole（2-NH₂-BTH）,and 2-Mercaptobenzothiazole（2-SH-BTH）which are relatively hydrophilic in root lipids of plant,but are easily transported to the ground.From the perspective of the whole plant,lettuce is more enriched with BTs than carrots.When analyzing the structural differences of target compounds,2-Methylthio-Benzothiazole（2-Me-S-BTH）has more content than others.These phenomena may be related to the octanol water partition coefficient（Log Kow）,translocation flow,and the specificity of different plant varieties.（2）The split-root experiment of gourd seedlings showed that the target compounds which were added in the experiment were also been detected in the unspiked roots and culture medium.The percentage range of different target compounds detected by the whole non-spiked system is 7.30～12.27%.2-SH-BTH was been released the most,and the least was 2-Me-S-BTH.It was confirmed that these target compounds can not only be absorbed by the root and then be transported to the aerial parts of the plant,but also be transported from the stem to the root.BTs could easily pass through the Casparian strip and even cell membrane and released to the ambient environment.（3）A dual-system control experiment of carrot plants and carrot callus showed that the content of the target compound in the culture solution decreased rapidly at the initial stage and gradually stabilized after 72 h.At the same time,the content of BTs in cells and carrots was also gradually increased,reaching the maximum at 8 h and 24h,respectively.And then the content showed a downward trend until equilibrium.The half-life(t_1/2)of the target compound in the plant is 16-22 h which was longer than in the cell of 9-18.75 h.The half-life of the target compound is proportional to the Log Kow.It shows the specificity of different plant varieties and the selectivity of different target compounds.（4）The cell extracts were analyzed on an Ultraperformance Liquid Chromatography Time-of-Flight（UPLC-TOF/MS）and the the metabolic pathway were benn inferred.It was found that the target compounds with-NH₂,-SH and-OH directly undergo phase II conjugation reaction,conjugated with endogenous molecules in plants,and generated glucose conjugate and amino acid conjugate.2-Me-S-BTH undergoes a demethylation reaction in the cell and became 2-SH-BTH.2-NH₂-BTH,2-Me-BTH,and BTH will undergo hydroxylation in the phase I to form hydroxyl conjugates.In this study,a variety of typical crops and BTs are used as target plants and target pollutants,respectively.The UPLC-TOF/MS was been uesd to study the absorption,transport,enrichment,and transform of BTs at booth the plant and cell level.It was confirmed that the BTs which present in farmland soil would be bio-enriched by crops,and revealed the potential ecological health risks of BTs through the food chain.