| The neonicotinoid insecticide and pharmaceuticals and personal care products (PPCPs) have been increasingly of interest due to the close relationship with our daily life and health. The neonicoinoids are one of the most widely used pesticides worldwide, while PPCPs is class of contaminants of emerging concern, mainly oringinated from wastewater treatment plant (WWTPs). The biosolids from WWTPs are extensively used in agriculture as fertilizers while offering a practical solution for waste disposal. Biosolid amendment drastically changes a soil’s properties, which may alter the persistence of PPCPs and hence the risk for secondary contamination such as plant uptake. With the increase and worldwide use of neonicotinoids and PPCPs, the environmental problem induced by these pollutants are increasing concerned. The paichongding (IPP), 1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-8-nitro-5-propoxy-1,2,3,5,6, 7-hexahydro-imidazo [1,2-a] pyridine, is a novel insecticide with the property of high effective, low mammalian toxicity and broad spectrum. There are two chiral carbon atoms with four optical isomers in IPP. Triclosan and triclocarban are two representative PPCPs. They are frequently two of most frequently detected PPCPs in the environment, especially in the biosolids, thus have high environmental risk potential.The present thesis used representative PPCPs, i.e. triclosan and triclocarban, for the first time, systematically investigated the influence of biosolid application on their environmental fate in plant-soild system and elucidated the mechanism of the effects. To better solid the conclusion, this study collected the data reported in the literature, combined them with the data from the experiments in this study, and then analyzed the intergrated data to elucidate the impact of biosolid on the environmental behavior of triclosan and triclocarban. Passive sampler was used to investigate the influence of biosolido on the bioavailability of triclosan and triclocarban. Meanwhile, this study used patented pesticide IPP as model of chiral pesticide to study the enantioselective/diastereoselective distribution of mineralization, bound residue, and extractable residue, as well as metabolism of four stereoisomers of IPP in different soils under aerobic conditions. Combination use of radio labeling, moden instrument analysis, and biotechnology based on the OECD and EPA guideline were used to investigate the diastereoselective degradation, identified novel metabolites, and elucidated the transformation pathways. The conclusions are as followed:Biosolids consistently increased sorption of triclosan and triclocarban in soil. When a sandy loam soil was amended with biosolids at 2-10%, Kd of triclosan increased by 3.9-21 times. Concurrently, persistence of both compounds was prolonged, with t1/2 of triclosan increasing from 10 d in the unamended soil to 63 d after biosolid amendment at 10%. The relationship between t1/2 and Kd was further examined using data from this and all available literature and a significant linear relationship was observed for triclosan (r2=0.69, p<0.01) and triclocarban (r2= 0.38,p<0.05) in biosolid-amended soils. The potential of such secondary pollution depends closely on the persistence or half-life (t1/2) of PPCPs in soil, because a contaminant’s availability for plant uptake or offsite transport is directly proportional to its persistence.This study chosed two model root vegetables, i.e. carrot and radish, and further conducted the plant uptake and bioavailability of PPCPs in soils with and without biosolid amendment to better understand the effects of biosolids on environmental fate of PPCPs. Accumulation of triclosan and triclocarban was measured in roots of radish and carrot grown in soils with or without biosolids. Addition of biosolids significantly prolonged the persistence of triclosan in soil. When expressed in bioaccumulation factor (BCF), accumulation of triclosan drastically decreased in biosolid-amended soils, while the effect was limited for triclocarban. Compared to the unamended soil, amending biosolids at 2% decreased BCF of triclosan in the edible tissues of radish and carrot by 85.4 and 89.3%, respectively. Measurement using polymethylmethacrylate (PMMA) thin film provided direct evidence showing that chemical availability of triclosan drastically decreased in biosolid-amended soils. This finding highlights the importance to consider the effect of biosolids when evaluating the environmental risks of these and other biosolid-borne PPCPs.For the neonicotinoid insecticide, it was found that IPP exhibit diastereoselective but not enantioselective on mineralization, formation of bound residue and extractable residue (ER), as well as degradation. Through out the experiment, the cumulative mineralization was increasing but rather limited (<8% of applied radioactivity). The 14C-extractable residue, including parent and degradation products of IPP, decreased with the incubation time in the soilds. The extractable residue of each individual isomer of IPP is significantly different (p< 0.01) in three selected soils, following the order neutral soil> alkane soil> acidic soil. There were no significant differences (p> 0.1) on the ER of enantiomers (i.e. RR-IPP and SS-IPP, SR-IPP and RS-IPP) in neutral/alkane soils, but the differences were significant (p< 0.01) between diastereoisomers, i.e. RR and SR-IPP, RR and RS-IPP, SS and SR-IPP, SS and RS-IPP. In neutral and alkane soils, the pair of enantiomers RR and SS-IPP exhibited higher ER than that of the other pair of enantiomers SR and RS-IPP, but this differences disappeared in acidic soils. The bound residue of different stereoisomers of IPP in different soils gradually increased with the prolonged incubation time. TThis study further identified the metabolites and degradation pathway IPP in 3 different aerobic soils with C isotope tracer technique combined with HPLC-MS/MS. Finally,6 proposed metabolites were found as followed:1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-8-nitro-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridin-5-ol (Product 1, Ml);1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridin-8-ylamine (Product 2, M2); 1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine (Product 3, M3);1-(6-Chloro-pyridin-3-ylmethyl)-5-propoxy-hexahydro-imidazo[1,2-a]pyridin-8-one (Product 4, M4);1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-5-propoxy-hexahydro-imidazo[1,2-a]pyridin-8-one (Product 5, M5);1-(6-Chloro-pyridin-3-ylmethyl)-5-propoxy-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine (Product 6, M6). Depropylation, nitrosylation, denitration, demethylation, dehydroxylation, andketonization contributed to IPP transformation. According to the metabolites, the main degradation pathways of IPP in aerobic soils were further proposed accoridingly.The present study has high significance in this area by giving a better environmental risk assessment of PPCPs in biosolids, providing a better agricultural use of biosolids, and showing insights on the potential sencondary risk of PPCPs. Meanwhile, the results of this study afforded a more comprehensive understanding of the environment behavior of the novel chiral neonicotinoid IPP. On the one hand, this gives support and guide for developing "efficient and environment-friendly" pesticide with individual stereoisomer. On the other hand, the results also show scientific support for revising related policy and guideline on chiral pesticide. The methods used in this study is applicable for other novel chiral pesticides in the future. In summary, this study has high scientific significance on protecting environmental safety, agricultural products safety, and human health. |
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