Accumulation And Metabolism Mechanism Of Butyl-And Phenyltins In Carp And Cera Tophyll Um Demersum L

From the1940s, organotin compounds (OTCs) have been extensively utilized as PVC stabilizers, catalyst, wood preservatives, pesticides, fungicides, mildew preventive, commodity coating, effective antifouling biocides of vessels and fishing gear, which have, undoubtedly, brought us a lot of convenience, beneficial and economic efficiency. However, until the early1980s, the serious pollution of OTCs has aroused more and more concerns, especially with persistent environmental pollution problems of tributyltin (TBT) and triphenyltin (TPT). TBT and TPT were considered to be the most toxic substance ever deliberately introduced into aquatic systems by human being. In addition, they also showed strong ability of bioaccumulation and biomagnification. In general, OTCs bring a threat to human health and life. So far, most researches were only limited to investigate the level of organotin pollution in organisms of actual environment. But no systematic study has been done about the accumulation and metabolism of OTCs in aquatic organisms, which has hindered an accurate evaluation of its ecological risks.In this work, the sorption of OTCs on dry powder samples of both carp and C demersum from water via the batch equilibrium technique as well as uptake and metabolism of them on live biota of both carp and C. demersum were determined, respectively, all of which allowed to gain an improved understanding of OTCs accumulation and degradation mechanisms in biota. The main research contents and results are as follows:1. A simple and efficient method for the determination of OTCs in biota by GC-MS coupling with NaBEt4derivatization was established. The results showed that recoveries for each OTCs spiked in blank freeze-dried biological samples (0.1g) following extraction (15ml0.035mol/L methanolic HC1solution for1h) and derivatization (2ml contained internal standard n-hexane and0.5ml of2%(m/v) NaBEt4solution for30min) were found above80%. The method is fast and easy to operate for determining OTCs in complex biological samples. The minimum limit of detection was about5ng Sn/g, and measured standard deviation values are within10%for six parallel samples.2. Sorption of TBT and TPT on freeze-dried carp powder as well as their uptake on carp from water at a static and a dynamic kinetics tests were measured, respectively. The results showed that the apparent uptake values were significantly higher than that of estimated by a simple sorption model, indicating the uptake of TBT and TPT did not only depend on lipids but also oxygen ligands or macromolecules such as amino acids and proteins of the living organism; The order of OTCs content was viscera> gill> muscle; No steady state in fish was observed during the dynamic experiment, and TBT or TPT almost linear increase with exposure time increase; Compared with static experiment, the fitting parameters obtained form dynamic experiment were more reliable, calculated BCF values of TBT and TPT in carp were44000and3333, respectively, the higher BCF values of TBT may be due to its higher hydrophobic.3. Sorption of TBT and TPT on freeze-dried C. demersum L. powder as well as their uptake on C. demersum L. from water at a static and a dynamic kinetics tests were measured, respectively. The results showed that little relation was observed between TBT and TPT concentrations and lipid contents in C. demersum L., suggesting the large surface area and kinds of chelating groups of C. demersum L. may be responsible for the uptake of TBT and TPT; Both TBT and TPT could be rapidly accumulated and then metabolized to less toxic organotin by C. demersum L., and their main degradation products were MBT and MPT, respectively; The estimated BCF value of TPT (1364) was much higher than that of TBT (331) although they had similar uptake rate, which was due to the rapider release and metabolic rate of TBT.4. The uptake of TBT in Plant of C. demersum L. at pH5.0and8.9were determined, respectively. The results showed that pH played an important role for both plant growth and TBT species existed in water, which in turn influenced the uptake and metabolism of TBT in plant; Although pH5.0was somewhat not suitable for C. demersum L. growth, they could uptake and metabolize more TBT than that of pH8.9, which may due to the fact that cationic speciation TBT+(at pH5.0) was metabolized more easily than the neutral hydroxide speciation TBTOH (at pH8.9). 5. Individual elimination kinetic experiments of TBT, DBT, MBT, TPT, DPT and MPT with carp and C. demersun L. were systematically studied, respectively. The results showed that the elimination rate of OTCs in carp was significantly slower than that of in C. demersun L., and the elimination mechanism of OTCs in carp were mainly via release, the release rate of each OTCs was as follow:MBT> DPT> MPT> DBT> TBT> TPT, whereas for C. demersun L., metabolism was the main power and the metabolic rate decreased with OTCs substituted decrease, and mono-substituted OTCs and inorganic tin compounds were the primary degradation products. OTCs could be rapidly metabolized to no-toxic inorganic tin by carp and C. demersum L. through a stepwise debutylation or dephenylation, namely:R3SnXâ†'R2SnX2â†'RSnX3â†'SnX4.6. The degradation mechanisms of TBT and TPT in crude enzyme extracted from C. demersum L. were determined. The results indicated that45%and37%of the original spiked TBT (400ng) and TPT (400ng) were metabolized after exposure for24h, respectively, and mono-substituted OTCs were the primary degradation products. Hence, the CYP450system enzymes was main responsible for the successive dealkylation or dephenylation reactions of OTCs in C. demersum L.Above all, both carp and C. demersum L. could not only accumulate strong toxic TBT and TPT, but also degradate them into low or non-toxic compounds, especially for C. demersum L.. However, the enrichment mechanisms of OTCs in biological body were not only partitioning effect on fat as other nonionic organic compounds with strong hydrophobicity, the complexation with other functional groups or macromolecules also played a key role. While concerning with OTCs degradation pathway, it is a successive debutylation or dephenylation process and could be converted into non-toxic inorganic compounds eventually. And the CYP450system enzymes in biological body may be main responsible for the successive dealkylation or dephenylation reactions. Moreover, low pH was better for TBT uptake and metabolism in C. demersum L., the reason was probably that the ionic form (TBT+) was easier to be accumulated and degradated than that of the neutral state (TBTOH).