Article pubs.acs.org/JAFC
Fate and Stereoselective Behavior of Benalaxyl in a Water−Sediment Microcosm Mingke Liu,† Donghui Liu,† Yangguang Xu,‡ Xu Jing,† Zhiqiang Zhou,† and Peng Wang*,† †
Department of Applied Chemistry, China Agricultural University, Beijing 100193, People’s Republic of China Chinese People’s Armed Police Force Academy, Langfang 065000, People’s Republic of China
‡
S Supporting Information *
ABSTRACT: The environmental behavior and stereoselectivity of the chiral fungicide benalaxyl and its chiral metabolite benalaxyl acid in water, sediment, and water−sediment microcosms were studied. The microcosms were incubated at 25 °C with light or under darkness. The influencing factors such as light and microorganism were investigated. The results showed that benalaxyl had half-lives of >21 days in the microcosm system and that the metabolite benalaxyl acid could exist in the microcosm for >70 days. Benalaxyl was mainly transformed through microbial degradation, and thus sediment microorganisms played a major role in the dissipation of benalaxyl in the aquatic microcosm. The stereoselective behavior of benalaxyl and benalaxyl acid was also investigated. (−)-Benalaxyl was preferentially degraded in the microcosm, resulting in an enrichment of the more toxic enantiomer (+)-benalaxyl, which may cause higher risk to the aquatic system. Moreover, (−)-benalaxyl acid was preferentially formed in the microcosm. The enantioselectivity of the enantiomers in the microcosm should be taken into consideration for an accurate risk assessment. KEYWORDS: benalaxyl, water−sediment microcosm, stereoselectivity, contamination
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plants such as cucumber and tomato.6,11 BX can enter the water system through rainfall, surface runoff, and leaching12−14 and then cause water pollution and affect aquatic organisms.15 Unfortunately, few studies have focused on the fate of BX in the aquatic system. Benalaxyl acid (BX acid) [(±)-N-(2,6-xylyl)-N(phenylacetyl)alanine] (Figure 1) is the primary metabolite, which is more water-soluble and persistent than BX in the environment and may be more harmful for aquatic organisms. It also possesses a chiral center to make a couple of enantiomers. There are no published reports for the degradation and stereoselective behavior of the metabolite BX acid. The impacts of pesticide and metabolite contamination for aquatic ecosystems are tremendous. As a research method for the environmental fate of pesticides, microcosms have been widely used with a series of advantages such as authenticity, flexibility, high performance−price ratio, and security.16−19 In an artificial microcosm, the incubation conditions can be controlled and the fate of the target compound can be understood clearly. In this study, the chiral analysis method for the enantiomers of BX and BX acid in water and sediment was set up. The fate and stereoselective behavior of BX and BX acid in water, sediment, and a water−sediment microcosm were studied to evaluate the environmental behavior of BX in the aquatic system. The effect of light and microorganism was also studied following the discussion of the degradation mechanism.
INTRODUCTION The enantiomers of a chiral compound have identical physical and chemical properties but possibly have different bioactivities, toxicities, metabolisms, and environmental behaviors.1 Chiral pesticides are widely used in agriculture, and the number is increasing with the development of complex pesticide molecules. It is a common situation that only one of the enantiomers performs the desired effect, whereas the other ineffective enantiomers may be even more toxic to other nontarget organisms or ecosystem and cause environmental problems. For example, of the eight enantiomers of the chiral insecticide deltamethrin, only the (αS,1R,3R)-enantiomer has the desired insecticidal activity, whereas the others are noneffective or less active.2 The toxicity of the racemate of the herbicide metolachlor to Daphnia magna is 100 times higher than that of S-metolachlor, and rac-metolachlor degraded more slowly than S-metolachlor in soil.3 Therefore, it is necessary to study the environmental behavior of chiral pesticides on an enantiomeric level to evaluate the risks more accurately. The chiral fungicide benalaxyl (BX) [(±)-methyl N-(phenylacetyl)-N-(2,6-methylphenyl) alaninate] (Figure 1) has been widely used on cucumber, tomato, tobacco, and many other vegetables and fruit crops to control downy mildew, early blight, late blight, and Peronospora tabacina for many years. As a kind of chiral pesticide, BX has two enantiomers, with R(−)-BX more active than S-(+)-BX. It has a series of advantages such as high efficiency, low toxicity, and long effective period. Because of its wide usage and relatively long half-life period,4 BX could be detected in the environment.5 A number of studies have been conducted to evaluate the enantioselective environmental behaviors on an enantiomeric level in soil,6,7 animals such as lizards, earthworms, rainbow trout, and rabbits,8−10 and © 2015 American Chemical Society
Received: Revised: Accepted: Published: 5205
March 21, 2015 May 12, 2015 May 15, 2015 May 26, 2015 DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
Article
Journal of Agricultural and Food Chemistry
Figure 1. Chemical structures of BX and BX acid.
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and S4, respectively; Table 1). The sediment was sterilized by two periods of autoclaving (2 h per period). The light was provided by fluorescent bulbs in an incubator, and the intensity of light was 2640 lx.
MATERIALS AND METHODS
Chemicals. BX (>99.0% purity) was obtained from the Institute for the Control of Agrochemicals, Ministry of Agriculture (Beijing, China). Metabolite BX acid (>99.0% purity) was synthesized by the Department of Applied Chemistry, China Agricultural University (Beijing, China). All of the reagents were of analytical grade and obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Mobile phase reagents were distilled and filtered through a 0.22 μm filter membrane before use. Instrumental Analysis. HPLC analysis in this study was performed by using an Agilent 1200 series HPLC (Agilent Technology) equipped with a G1322A degasser, a G1311A pump, a G1328A injector, a G1314B VWD, and an AT-930 column attemperator (Tianjin Automatic Science Instrument Co. Ltd., China). The signal was received and processed by Agilent Chemstation software. A Chiralcel OD chiral column (250 mm × 4.6 mm i.d., Daicel Chiral Technology Co., Ltd.) was used to separate the enantiomers of BX and BX acid. Mobile phase was n-hexane and 2-propanol (91:9, v/ v) with trifluoroacetic acid (1‰, v/v) at the flow rate of 0.8 mL/min. The injection volume was 20 μL, and the UV detection wavelength was 225 nm. The separation was conducted at 20 °C. The elution order of BX and BX acid enantiomers was determined by a polarimeter detector. The polarimeter detector wavelength was 426 nm. The elution order was as follows: (−)-BX (15.4 min), (+)-BX (18.8 min), (−)-BX acid (21.6 min), and (+)-BX acid (32.0 min). Assay Validation. The linearity of the instrument for BX (5−1500 mg/L) and BX acid (5−600 mg/L) was investigated by standard solution in 2-propanol (n = 3). The linearity of the method, recovery, limit of detection (LOD), and limit of quantification (LOQ) of the method were investigated. Linearity and recoveries were determined in blank samples (uncontaminated environmental matrix) that were fortified with BX and BX acid at different levels. The linearity of BX (0.2−20 mg/kg) and BX acid (0.2−5 mg/kg) in water samples and of BX (0.2−50 mg/kg) and BX acid (0.2−20 mg/kg) in sediment samples was checked (n = 3). The recoveries of BX enantiomers in water and in sediment (1, 5, and 10 mg/kg) and of BX acid enantiomers in water (0.5, 1, and 2 mg/kg) and in sediment (1, 5, and 10 mg/kg) were investigated (n = 3). The external calibration curves were generated by regression analysis of the peak area against concentrations. Blank sediment and water samples were also analyzed to check the interference from the matrix. LOD and LOQ were defined as concentrations that produced signal-to-noise (S/N) ratios of 3 and 10, respectively. Degradation in Sediment. The test sediment and water were sampled from Shangzhuang reservoir (Beijing, China) that had not been treated with BX. The sediment was air-dried at room temperature and sieved (2 mm). It took 7 days to activate microorganisms before incubation. Sediment (400 g, moisture content = 25%, m/m) was added in a 500 mL beaker, and BX was fortified at 20 mg/kg. Four variations of incubation were designed: (1) unsterilized, with light (12 h per day); (2) unsterilized, under darkness; (3) sterilized, with light (12 h per day); (4) sterilized, under darkness (experiments S1, S2, S3,
Table 1. Summary of Experiment Designs system
contamination way
sterilizationa
lighta
sediment
× × √ √
√ × √ ×
S1 S2 S3 S4
water
water
× × √ √
√ × √ ×
W1 W2 W3 W4
water−sediment
water
× × × ×
√ × √ ×
WS1 WS2 SW1 SW2
sediment a
experiment
sediment
“√” means “yes” and “×” means “no”.
Degradation in Water. Water (400 g) was added in a 500 mL beaker, and BX was fortified at 20 mg/kg. Four variations of incubation were designed: (1) unsterilized, with light (12 h per day); (2) unsterilized, under darkness; (3) sterilized, with light; (4) sterilized, under darkness (experiments W1, W2, W3, and W4, respectively; Table 1). The water was sterilized by two periods of autoclaving (1 h per period). Degradation in Water−Sediment Microcosm. The water− sediment microcosm was made up of 35 g of sediment (moisture content = 25%, m/m) and 150 g of water in a 500 mL beaker. There were two methods of contamination: water contamination and sediment contamination. For water contamination, BX was fortified in water at 20 mg/kg under light (12 h per day) or darkness (experiments WS1 and WS2, respectively; Table 1). For sediment contamination, BX was fortified in sediment at 20 mg/kg under light or darkness (experiments SW1 and SW2, respectively; Table 1). All experiments were conducted in an incubator at 25 °C, and water was added every 3 days for supplement of evaporation. Sediment and water samples were collected for analysis at 0, 1, 5, 12, 21, 35, 50, 70, and 90 days. Each incubation was carried out in triplicate. The summary of experiment designs is shown in Table 1. Dissipation curves were defined as C = C0 e−kt or C = at2 + bt + C0, in which C means concentration, C0 means the highest concentration, k means elimination rate coefficient, and a and b are empirical constants. Half-life (t1/2, days) was obtained from the equation t1/2 = ln 2/k or 0 = at2 + bt + 1/2C0 (t1/2 = t). The enantiomer fraction (EF) was used to evaluate the enantioselective behavior of enantiomers, which was defined by the equation EF = peak areas of the (−)/[(−) + 5206
DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
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Journal of Agricultural and Food Chemistry
Figure 2. Representative HPLC chromatograms of extract from (a) water fortified with BX (5 mg/kg) and BX acid (5 mg/kg) and (b) incubated water sample of experiment WS1 (35 days) or (c) sediment fortified with BX (5 mg/kg) and BX acid (5 mg/kg) and (d) incubated sediment sample of experiment S3 (35 days).
Figure 3. Concentration−time curves of (a) BX in sediment, (b) BX in water, (c) BX acid in sediment, and (d) BX acid in water. (Values represent the mean ± SD.) S1, unsterilized, with light; S2, unsterilized, under darkness; S3, sterilized, with light; S4, sterilized, under darkness. (sediment) or 3 min (water), exposed to ultrasonic vibration for 15 min, and then centrifuged at 4000 rpm for 7 min (sediment) or 3 min (water). After removing 15 mL of ethyl acetate (extraction solvent), the procedure described above was repeated by adding another 15 mL of ethyl acetate. The combined extraction solvent (30 mL of ethyl acetate) was evaporated to near dryness on a vacuum rotary evaporator at 37 °C and blown to dryness by a gentle stream of
(+)], in which (−) and (+) indicate the peak areas of the (−)-enantiomer and (+)-enantiomer, respectively. EF values vary from 0 to 1, with EF = 0.5 indicating no enantioselectivity. Sample Preparation. A solvent extraction method was used for extraction in the experiment. Ethyl acetate (15 mL) and saturated salt water (3 mL) were added to a 50 mL polypropylene centrifuge tube containing 15 g of sediment sample/10 g of water sample (pH was adjusted to 2 by HCl). The centrifuge tube was vortex-mixed for 5 min 5207
DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
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Figure 4. Concentration−time curves of (a) WS1 (with light, water contamination), (b) WS2 (under darkness, water contamination), (c) SW1 (with light, sediment contamination), and (d) SW2 (under darkness, sediment contamination). (Values represent the mean ± SD.) nitrogen. Finally, the extract was reconstituted with 0.5 mL of 2propanol and filtered through a 0.22 μm filter membrane.
in the degradation of BX and that photolysis affected the degradation slightly. The trend of metabolite BX acid in sediment is shown in Figure 3c. BX acid in experiments S1 (unsterilized, with light) and S2 (unsterilized, under dark) reached the highest values of 11.3 and 12.9 mg/kg at the 35th day, but in S3 (sterilized, with light) and S4 (sterilized, under dark), very low levels of BX acid were detected, showing microbial degradation was the main factor affecting the formation of BX acid. Degradation of BX in Water. As shown in Figure 3b, in experiments W1 (unsterilized) and W3 (sterilized) under light, the half-lives of BX were 95.6 and 98.3 days and in experiments W2 (unsterilized) and W4 (sterilized) under darkness, the halflives were 132.0 and 137.2 days. Obviously, microbial degradation was not a major pathway because water contained fewer microorganisms. Light could accelerate the degradation of BX in water, with a similar result as in sediment, indicating that photolysis was also a pathway for the dissipation of BX. In experiment W4 (sterilized, under darkness), the fact that BX also degraded obviously in unsterilized water under darkness indicated that hydrolysis was the main pathway for the degradation of BX in water. As shown in Figure 3d, in experiments W1−4, low levels of BX acid (about 0.8 mg/kg) were found from 12 to 90 days in water due to the slow degradation of BX, and further degradation of BX was very slow. Fate of BX in Water−Sediment Microcosm. Figure 4 shows the concentration−time curves of BX and BX acid in the water and sediment of the microcosm. In experiment WS1 (with light, water contamination), when the water of the microcosm was contaminated (BX was fortified in water), the concentration of BX decreased in water with t1/2 = 39.6 days and increased first and then decreased in the sediment because of adsorption and degradation. In WS2 (under darkness, water
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RESULTS AND DISCUSSION Assay Validation. The enantiomers of BX and BX acid were baseline separated, and there were no interference peaks from the matrix around the peaks of the four enantiomers (Figure 2). Linearities of the instrument for BX and BX acid in 2-propanol were satisfactory ((−)-BX, Y = 71.3 + 55.68X, R = 0.9993; (+)-BX, Y = 62.7 + 90.25X, R = 0.9996; (−)-BX acid, Y = −66.1 + 35.9X, R = 0.9991; (+)-BX acid, Y = −79.3 + 61.25X, R = 0.9994). Good linearities of method and recoveries were obtained in water and sediment for BX and BX acid enantiomers (see the Supporting Information, Table S1). Correlation coefficients (R) of linear regression equations were 0.9993−0.9999. In water, the recoveries of BX and BX acid enantiomers were 92.33−118.86 and 91.29−115.96%, respectively; in sediment, the recoveries of BX and BX acid enantiomers were 91.49−113.10 and 79.36−92.48%, respectively. The RSDs were all below 10%. The limits of detection (LODs) for BX and BX acid were 0.013−0.015 mg/kg in water and 0.014−0.016 mg/kg in sediment; the limits of quantitation (LOQs) for BX and BX acid were 0.06−0.08 mg/kg in water and 0.08−0.10 mg/kg in sediment. Degradation of BX in Sediment. Dissipation equations and half-lives are in the Supporting Information (Table S2). As shown in Figure 3a, the degradation of BX in unsterilized sediment in experiments S1 (unsterilized, with light) and S2 (unsterilized, under darkness) was rapid with half-lives of 26.8 and 28.0 days, but very slow in sterilized sediment in experiments S3 (sterilized, with light) and S4 (sterilized, under darkness) with half-lives of 112.7 and 132.0 days, indicating that microbial degradation played an important role 5208
DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
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Figure 5. Material balance−time bar chart of (a) WS1 (with light, water contamination), (b) WS2 (under darkness, water contamination), (c) SW1 (with light, sediment contamination), and (d) SW2 (under darkness, sediment contamination). BX, total amount of BX (μmol) in microcosms; BX acid, total amount of BX acid (μmol) in microcosms; other, total amount of other metabolites and nonextractable part in microcosms.
Figure 6. EF−time curves of (a) BX in sediment, (b) BX in water, (c) BX acid in sediment, and (d) BX acid in water. (Values represent the mean ± SD.) S1, unsterilized, with light; S2, unsterilized, under darkness; S3, sterilized, with light; S4, sterilized, under darkness. EF = peak areas of the (−)/[(−) + (+)].
(with light). Correspondingly, the decline of BX in water in WS2 (under darkness) was faster (t1/2 = 18.4 days) than that in WS1 (with light) (t1/2 = 39.6 days). BX acid appeared since the
contamination) BX was more easily transferred from water into the sediment with the highest concentration of 34.9 mg/kg at the 12th day (Figure 4b) compared with the result in WS1 5209
DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
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Journal of Agricultural and Food Chemistry
Figure 7. EF−time curves of (a) WS1 (with light, water contamination), (b) WS2 (under darkness, water contamination), (c) SW1 (with light, sediment contamination), and (d) SW2 (under darkness, sediment contamination). (Values represent the mean ± SD.) EF = peak areas of the (−)/[(−) + (+)].
obvious decline of BX in the first 12 days, showing BX was relatively persistent in the aquatic environment. Stereoselectivity. Stereoselectivity of BX Enantiomers. EF−time curves were plotted (Figure 6 and 7) to characterize enantioselectivity of the enantiomers of BX and BX acid. As shown in experiments S3 (sterilized, with light), S4 (sterilized, under darkness) (Figure 6a) and experiments W1−4 (Figure 6b), the EF values of BX were all approximately 0.5, indicating that both photolysis and hydrolysis did not cause stereoselective degradation. Compared with experiments S3 (sterilized, with light) and S4 (sterilized, under darkness), stereoselectivity of BX enantiomers was found in experiments S1 (unsterilized, with light) and S2 (unsterilized, under darkness) with EF < 0.5. In conclusion, (−)-BX was preferentially degraded in the sediment and microbial degradation played the key role for the stereoselectivity. No stereoselectivity was found in water that contained fewer microorganisms. (−)-BX was also found to be preferentially degraded in the water−sediment microcosm, especially in experiments SW1 (with light, sediment contamination) and SW2 (under darkness, sediment contamination) (Figure 7c,d), which was caused by the microorganisms in the sediment. Stereoselectivity of BX Acid Enantiomers. (−)-BX acid was preferentially formed in the sterilized sediment in experiments S3 (sterilized, with light) and S4 (sterilized, under darkness) (Figure 6c), and no stereoselectivity was found in the unsterilized sediment (experiments S1 and S2). In water, almost only (−)-BX acid was formed (experiments W1−4, Figure 6d). Figure 7 shows the EF values of BX acid in the water−sediment microcosm. (−)-BX was found to be preferentially degraded in the water−sediment microcosm, and (−)-BX acid was the main form of the primary metabolite. Therefore, it could be inferred that (−)-BX was preferentially transformed to (−)-BX acid.
21st day and remained at a relatively low level in both water and sediment. There was no significant difference for BX acid between WS1 (with light) and WS2 (under dark), and the concentrations of BX acid in both experiments WS1 and WS2 were about 0.8 mg/kg. The result of SW1 (with light, sediment contamination) is shown in Figure 4c. When the sediment of the microcosm was contaminated (BX was fortified in sediment), the concentration of BX in sediment decreased with time, increased to 3.27 mg/ kg in water at the 12th day and could not be detected at the 90th day. Compared with SW1 (with light), less BX transferred from sediment into water in SW2 (under darkness, sediment contamination). The concentration of BX in water in SW2 (under darkness) was lower than that in SW1 (with light) at the corresponding time points (Figure 4d). It was found that light could help the distribution of BX in water. There was no significant difference for the formation of BX acid between SW1 (with light) and SW2 (under darkness), and the highest concentrations of BX acid in both experiments SW1 and SW2 were about 2.0 mg/kg. The concentrations of BX acid were always higher in water than in sediment, perhaps because of the high water solubility; for example, in SW2 (under darkness) BX acid could be detected at the 21st day and reached the highest values of 2.16 and 0.85 mg/kg in water and sediment, respectively (Figure 4d). The material balance in the microcosm during the experiments was also roughly investigated on the basis of the amount of BX/BX acid distributed in water and sediment in the microcosm. The original doses of BX fortified in microcosms were 9.22 μmol (3 mg WS1, WS2, water contamination) and 2.15 μmol (0.7 mg, SW1, SW2, sediment contamination). Considering the nonextractable amount (about 10% of BX and 15% of BX acid) according to the average recoveries, the material balance is shown in Figure 5, from which there was no 5210
DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
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Journal of Agricultural and Food Chemistry
(6) Wang, X.; Jia, G.; Qiu, J.; Diao, J.; Zhu, W.; Lv, C.; Zhou, Z. Stereoselective degradation of fungicide benalaxyl in soils and cucumber plants. Chirality 2007, 19, 300−306. (7) Qin, F.; Gao, Y. X.; Guo, B. Y.; Xu, P.; Li, J. Z.; Wang, H. L. Environmental behavior of benalaxyl and furalaxyl enantiomers in agricultural soils. J. Environ. Sci. Health, Part B 2014, 49, 738−746. (8) Wang, Y.; Guo, B.; Gao, Y.; Xu, P.; Zhang, Y.; Li, J.; Wang, H. Stereoselective degradation and toxic effects of benalaxyl on blood and liver of the Chinese lizard Eremias argus. Pestic. Biochem. Physiol. 2014, 108, 34−41. (9) Xu, P.; Liu, D.; Diao, J.; Lu, D.; Zhou, Z. Enantioselective acute toxicity and bioaccumulation of benalaxyl in earthworm (Eisenia fedtia). J. Agric. Food Chem. 2009, 57, 8545−8549. (10) Qiu, J.; Wang, Q.; Zhu, W.; Jia, G.; Wang, X.; Zhou, Z. Stereoselective determination of benalaxyl in plasma by chiral highperformance liquid chromatography with diode array detector and application to pharmacokinetic study in rabbits. Chirality 2007, 19, 51−55. (11) Gu, X.; Wang, P.; Liu, D.; Lv, C.; Lu, Y.; Zhou, Z. Stereoselective degradation of benalaxyl in tomato, tobacco, sugar beet, capsicum, and soil. Chirality 2008, 20, 125−129. (12) Goncalves, C. M.; Esteves da Silva, J. C. G.; Alpendurada, M. F. Evaluation of the pesticide contamination of groundwater sampled over two years from a vulnerable zone in portugal. J. Agric. Food Chem. 2007, 55, 6227−6235. (13) Patakioutas, G. I.; Karras, G.; Hela, D.; Albanis, T. A. Pirimiphos-methyl and benalaxyl losses in surface runoff from plots cultivated with potatoes. Pest Manage. Sci. 2002, 58, 1194−1204. (14) Guan, Y. F.; Wang, J. Z.; Ni, H. G.; Zeng, E. Y. Organochlorine pesticides and polychlorinated biphenyls in riverine runoff of the Pearl River Delta, China: assessment of mass loading, input source and environmental fate. Environ. Pollut. 2009, 157, 618−624. (15) Huang, L.; Lu, D.; Diao, J.; Zhou, Z. Enantioselective toxic effects and biodegradation of benalaxyl in Scenedesmus obliquus. Chemosphere 2012, 87, 7−11. (16) Laabs, V.; Wehrhan, A.; Pinto, A.; Dores, E.; Amelung, W. Pesticide fate in tropical wetlands of Brazil: an aquatic microcosm study under semi-field conditions. Chemosphere 2007, 67, 975−989. (17) Cuppen, J. G. M.; Crum, S. J. H.; Van den Heuvel, H. H.; Smidt, R. A.; Van den Brink, P. J. Effects of a mixture of two insecticides in freshwater microcosms: I. Fate of chlorpyrifos and lindane and responses of macroinvertebrates. Ecotoxicology 2002, 11, 165−180. (18) Van den Brink, P. J.; Crum, S. J.; Gylstra, R.; Bransen, F.; Cuppen, J. G.; Brock, T. C. Effects of a herbicide-insecticide mixture in freshwater microcosms: risk assessment and ecological effect chain. Environ. Pollut. 2009, 157, 237−249. (19) Colombo, V.; Mohr, S.; Berghahn, R.; Pettigrove, V. J. Structural changes in a macrozoobenthos assemblage after imidacloprid pulses in aquatic field-based microcosms. Arch. Environ. Contam. Toxicol. 2013, 65, 683−692.
In this study, the fate and stereoselective behavior of BX and BX acid in a water−sediment microcosm were studied. BX and the metabolite BX acid had long half-lives in the water− sediment microcosm, and it was found that sediment in the microcosm played the most important role in the remediation of BX pollution in the aquatic environment and that microorganism biodegradation and hydrolysis were the major pathways. Significant enantioselective environmental behavior of BX (EF = 0.2−0.4 in microcosm) and the formation of BX acid (EF = 0.7−0.95 in microcosm) were found. It was reported that the toxicity of (+)-benalaxyl for some aquatic organisms was higher than that of rac-benalaxyl,4 so the evaluation of the enantioselective environmental behavior of BX is of significance. Furthermore, there were no published reports on the toxicology information on BX acid, which might be a potential concern to the aquatic environment. The evaluation of the metabolite BX acid should be taken into consideration for an accurate risk assessment, especially on an enantiomeric level.
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ASSOCIATED CONTENT
S Supporting Information *
Full validation results of BX and BX acid enantiomers in water and sediment samples for the HPLC-UV assay (Table S1); full dissipation results of BX enantiomers in all experiments (Table S2). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.5b01448.
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AUTHOR INFORMATION
Corresponding Author
*(P.W.) Mail: Department of Applied Chemistry, China Agricultural University, No. 2 Yuanmingyuan West Road, Beijing 100193, China. Phone: +8610-62731294. Fax: +861062731294. E-mail:
[email protected]. Funding
This work was supported by the National Natural Science Foundation of China (Contract Grants 21337005, 21277171), supported by the Program for Changjiang Scholars and Innovative Research Team in University, supported by the New-Star of Science and Technology and by Beijing Metropolis Beijing Nova program. Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/acs.jafc.5b01448 J. Agric. Food Chem. 2015, 63, 5205−5211
