Shanshan Di

Stereoselective Bioaccumulation and Metabolite Formation of Triadimefon in Tubifex tubifex

Triadimefon, a chiral fungicide, could be metabolized to triadimenol which has two chiral centers. In this work, Tubifex tubifex was exposed to triadimefon through the aqueous and soil phase to explore the relative importance of the routes of uptake. Bioaccumulation of triadimefon in tubifex was detected in both treatments, and the kinetics of the accumulation processes were significantly different in these two experiments. In spiked water treatment, (S)-triadimefon was preferentially accumulated over the (R)-triadimefon, whereas the enantioselective bioaccumulation was not detected in the spiked soil microenvironment. Simultaneously, four stereoisomers of triadimenol were also found in the tubifex tissue. Although the amount of these stereoisomers were different from each other with relatively more accumulation of the most fungi-toxic stereoisomer (1S,2R), the abundance ratios in the two exposure treatments were similar at the same sampling, following the order (1S,2S) > (1R,2S) > (1R,2R) > (1S,2R). The bioaccumulation factor was calculated for parent compound triadimefon and metabolite enrichment factor for metabolite. The results showed that both uptake routes, epidermal contact in the aqueous phase and ingestion of solid particles in soil, were important to the bioaccumulation of the triadimefon and triadimenol in tubifex.

Distribution, Metabolism and Toxic Effects of Beta-Cypermethrin in Lizards (Eremias argus) Following Oral Administration.

Beta-cypermethrin (BCYP), a synthetic pyrethriod (PYR) pesticide which is a mixture of the alpha- and theta- cypermethrin, have been reported various toxicological profiles to non-target organisms. But little is known about assimilation, accumulation and toxic effects of BCYP in reptiles. The present study firstly elucidated absorption, tissue distribution, excretion of BCYP in Eremias argus . Treated group were administered orally with BCYP 20mg/kg body weight (bw) dissolved in corn oil. Neurotoxicity was observed at 24h after gavage, and the poisoning symptom ameliorated at 72h. The changes of BCYP concentration depended on degradation time and tissues. Lizards had a strong capacity to eliminate BCYP with different tissue distribution. The tissues concentration of BCYP from high to low were intestine, stomach, heart, kidney, blood, lung, liver and brain. Bimodal phenomena were observed in lung, liver and kidney. These results may be due to the activities of enzymes, circadian rhythm, and enterohepatic circulation in lizards. Based on the results of organ coefficient and histopathology analysis in liver, the liver was confirmed as the main target organ.

Bioaccumulation of isocarbophos enantiomers from laboratory-contaminated aquatic environment by tubificid worms.

The benthic fauna is of great importance to assess the environmental fate of contaminations in aquatic ecosystem. In this study, tubificids were exposed to both laboratory-contaminated aqueous phases and spiked sediment to study the bioaccumulation of isocarbophos (ICP). Two types of spiked sediments were used in the spiked sediment experiment. During the exposure period, an enantioselective bioaccumulation was found in spiked water treatment, with concentrations of the (-)-ICP higher than that of the (+)-ICP, but no enantioselectivity was detected in the spiked sediment treatments. However, different bioaccumulation patterns were observed in the two spiked sediment treatments. Results showed that for spiked forest field sediment (FF sediment) incubation, bioaccumulation was governed by the concentrations in soil. Whereas ICP was bioaccumulated dominantly from overlying water in spiked Chagan Lake sediment (CG sediment) test. The dissipation rates were proved different in the two sediments and ICP dissipated much faster in CG sediment than that in FF sediment. Significant difference in ICPs half-life was also observed between worm-present and worm-free treatments in FF sediment. The detections of concentrations in overlying water indicated that much more ICP diffused to aquatic phase with the present of tubificids.

Enantioselective Determination of Triazole Fungicide Epoxiconazole Bioaccumulation in Tubifex Based on HPLC-MS/MS

In this study, the enantioselective bioaccumulation of epoxiconazole enantiomers in tubifex (Oligochaeta, Tubificida) was investigated in two uptake pathways. A sensitive and rapid chiral method was developed for the determination of epoxiconazole enantiomers in tubifex and soil based on high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry (HPLC-MS/MS). In the spiked-water or spiked-soil treatments, enantioselective bioaccumulation of epoxiconazole in tubifex was obersved. For spiked-water treatment, (-)-epoxiconazole accumulated in tubifex to a greater extent than (+)-epoxiconazole, leading to enrichments with a composition (-) > (+). However, for spiked-soil treatment, the enantioselectivity in tubifex was reversed with a preferential accumulation of (+)-epoxiconazole. Calculated accumulation factors (AFs) indicated that epoxiconazole in spiked-water treatment had higher bioaccumulation potential than that in spiked-soil treatment. The results from the spiked-soil treatment also revealed that the dissipation of epoxiconazole in soil was enantioselective, and tubifex has positive effects on epoxiconazole diffusion from soil to overlying water.

Enantioselective Bioaccumulation and Degradation of Sediment-Associated Metalaxyl Enantiomers in Tubifex tubifex

Knowledge about the enantioselective bioavailability of chiral pesticides in aquatic organisms facilitates more accurate interpretation of their environmental behaviors. In this study, the enantioselective bioaccumulation of metalaxyl enantiomers in Tubifex tubifex was detected in two uptake pathways. For the spike water treatment, a 16 day exposure experiment was employed and the enantiomer fractions (EFs) in tubifex tissue were maintained approximately at 0.47 during the experiment. For the spike sediment treatment, a 14 day bioaccumulation period indicated the concentrations of (-)-(R)-metalaxyl were higher than those of (+)-(S)-metalaxyl. Therefore, the bioaccumulation of metalaxyl in worms was enantioselective for these treatments. With the presence of tubifex, higher concentrations of metalaxyl in overlying water and lower concentrations in sediment were detected than in worm-free treatments. This means that tubifex has positive functions in metalaxyls diffusion from the sediment to overlying water and in the degradation of the sediment-associated metalaxyl.

Enantioselective Bioaccumulation and Dissipation of Soil‐Associated Metalaxyl Enantiomers in Tubifex

Many pesticides are chiral compounds and stereochemistry is an important factor for any reaction of chiral structures in biological systems. In this study, experiment about bioaccumulation of the two metalaxyl enantiomers in Tubifex (Oligochaeta, Tubificida) was conducted in laboratory aquatic ecosystems. Terrestrial soil spiked with two dose levels of metalaxyl was employed as the artificial bottom substrate. A method of determination of metalaxyl enantiomers in tubifex tissue, soil and overlying water were developed by HPLC. During a 14-day exposure, concentrations of metalaxyl in tubifex increased with the of soil concentration, however, the enantioselective bioaccumulation was only detected at high-dose exposure group, with the preferential accumulation of (-)-(R)-metalaxyl. The bioturbation activity of tubifex decreased water clarity and released soil-associated metalaxyl to overlying water. In those experiments where tubifex was exposed to metalaxyl from soil, pore water and overlying water, each route contributed to the total body burden, and our results indicated the pore water and soil are the primary exposure routes for high-dose exposure concentration treatment.

The chiral separation and enantioselective degradation of the chiral herbicide napropamide.

The chiral pesticide enantiomers often have different toxic effects and environmental behaviors, which suggests that the risk assessments should be on an enantiomeric level. In this work, the chiral separation of the napropamide enantiomers and the stereoselective degradation in tomato, cucumber, rape, cabbage, and soil were investigated. Napropamide enantiomers could be separated absolutely by high-performance liquid chromatography (HPLC) using a Chiralpak IC column with a resolution factor of 11.75 under the optimized condition. Solid phase extraction (SPE) was used for cleanup of the enantiomers in the vegetable samples. The residue analysis method was validated. Good linearities (R(2)  = 0.9997) and recoveries (71.43% -97.64%) were obtained. The limits of detection (LOD) were 0.05 mg/kg in soil and 0.20 mg/kg in vegetables. The results of degradation showed that napropamide dissipated rapidly in vegetables with half-lives of only 1.13-2.21 days, but much more slowly in soil, with a half-life of 11.95 d. Slight stereoselective degradation of the two enantiomers was only observed in cabbage, with enantiomeric fraction (EF) = 0.46, and there was no enantioselectivity in the other vegetables. The degradation of napropamide in the five matrixes was fast, and there was no enantioselectivity.

Enantioselective Bioaccumulation, Tissue Distribution, and Toxic Effects of Myclobutanil Enantiomers in Pelophylax nigromaculatus Tadpole

Research on the enantioselective behavior of chiral pesticides on amphibians has received growing attention, because amphibians are experiencing a population decline and amphibian metamorphosis shares many similarities with human fetal development. In this study, the enantioselective behavior of myclobutanil on Pelophylax nigromaculatus tadpole was studied. The antioxidant enzyme (SOD, GST) activities and malondialdehyde (MDA) content were investigated to assess the different toxic effects when tadpoles were exposed to myclobutanil enantiomers for 96 h. In the chronic exposure experiment, the bioaccumulation concentration of (-)-myclobutanil in tadpoles is significantly higher than that of (+)-myclobutanil, and the concentration of myclobutanil in tadpole intestine and liver was higher compared with other tissues. During the elimination experiment, about 95% of myclobutanil in tadpoles was eliminated within only 24 h. On the basis of these data, the enantiomeric differences should be taken into consideration in the risk assessment of myclobutanil.

Toxicokinetics and oxidative stress in Tubifex tubifex exposed to hexachlorocyclohexane isomers

In this study, Tubifex tubifex (Oligochaeta, Tubificida) was exposed to hexachlorocyclohexane isomers (α-HCH, β-HCH and γ-HCH) in an aquatic environment to study the bioaccumulation and elimination of these chemicals in this organism. Rapid and linear accumulation processes with high accumulation factor values (AFs) were found during the 14 d water exposure, and there were no significant differences among the concentrations of HCH isomers. The unsteady state (linear shape) might be due to the change of feeding physiology of tubifex. The AFs of α-HCH were significantly different from those of β-HCH, which may be due to different physicochemical properties. Furthermore, no enantioselective bioaccumulation of α-HCH enantiomers was found in tubifex tissue. The data from elimination experiments fitted a typical first-order kinetics model. The elimination rates (ke) decreased with increasing hydrophobicity (Kow) for HCHs. If evaporation was not considered, the majority of HCHs were metabolized by tubifex. So the existence of worms and their biotransformation ability could change the distribution of HCHs in the aquatic environment and reduce the surrounding HCHs levels, which is significant in environmental pollution control. This study also assessed the responses of biochemical biomarkers. Increased superoxide dismutase (SOD) and malondialdehyde (MDA) levels demonstrated the presence of oxidative stress in worms. The different changes of catalase (CAT) activities depend on many factors, and there are other enzymes involved in H2O2 catabolism. Additionally a reduction of glutathione-S-transferase (GST) was observed indicating the toxic impacts of HCHs. Our results suggested that bioaccumulation of HCHs in T. tubifex can cause sublethal toxicity. T. tubifex could reflect the HCHs contaminant concentrations in the environment to some extent, and the worms may be proposed as biomarkers to characterize water contamination.

Determination of cyanamide residue in 21 plant-derived foods by liquid chromatography-tandem mass spectrometry

Cyanamide is widely used in agriculture, and has a modest toxicity in humans. In the present study, a simple, sensitive, and widely applicable method for detecting cyanamide in 21 plant-derived foods was developed. In the proposed method, after the samples were homogenized and extracted, the method employs clean-up with multi-walled carbon nanotubes (MWCNTs) and derivatization with dansyl chloride. The derivatized sample extracts were quantified with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The mean recoveries were in the range of 67.4%-107.1%, and the RSDs were between 1.0% and 17.8%. The quantification limit in shiitake‬, green tea and chinese pepper was 0.05mg/kg, and in others 18 plant-derived foods was 0.01mg/kg. Among the data of 5 different laboratories, the repeatability limits (r) ranged from 0.0010 to 0.0941, and the reproducibility limits (R) ranged from 0.0031 to 0.2667. Moreover, the repeatability among different testing personnels in the same laboratory also has been examined.