Influence of toxicity and dissipation of racemic fenoxaprop and its R-enantiomer in Scenedesmus obliquus suspension by cyclodextrins

Cyclodextrins (CDs), a class of cyclic oligosaccharide molecules containing a variety of chiral centre, are capable of recognizing enantiomeric molecules through the formation of inclusion complexes. In this work, we selected three types of CDs, beta-CD and its two derivatives, randomly methylated beta-CD (RAMEB) and hydroxypropyl beta-CD (HP-beta-CD), to evaluate effects on toxicity of racemic fenoxaprop (rac-FA) and its R-enantiomer (R-FA) to freshwater alga Scenedesmus obliquus (S. obliquus) and their dissipation in S. obliquus suspension with and without CDs addition, respectively, in an attempt to get more detail about enantioselective behavior of fenoxaprop acid (FA) in the environment, using CDs as a remediation agent for FA and formulation additive for fenoxaprop-p-ethyl (FE). The significant difference between rac-FA and R-FA was not observed in their acute toxicity to S. obliquus and dissipation in S. obliquus suspension. RAMEB had no effect on either toxicity of FA to S. obliquus or dissipation of FA in S. obliquus suspension, and it also didn't change the extent of enantioselectivity in toxicity of FA to S. obliquus. But the addition of a certain amount of beta -CD and HP-beta -CD reduced the toxicity of FA to S. obliquus and increased dissipation of FA in S. obliquus suspension, as well as changed the enantioselectivity in toxicity of FA to S. obliquus. The results indicated beta-CD and HP-beta-CD could be used as a promising agent for remediation of aquatic contamination produced by FA, and RAMEB might be used as potential formulation additives for FE, the parent compound of FA, as RAMEB didn't decrease activity of R-FA and might be environmentally safer than the conventional additives.     

Effects of cyclodextrin on the stereoselectivity inhibition of acetylcholinesterase by isomalathion

ABSTRACT

In attempt to evaluate the effects of cyclodextrins (CDs) on enantioselectivity of chiral pesticides toxicity, this study investigated effects of three kinds of cyclodextrins including α-CD, β-CD and randomly methylated β-CD (RAMEB) on toxicity of four enantiomers of isomalathion including (1R, 3R)-isomalathion, (1S, 3S)-isomalathion, (1S, 3R)-isomalathion and (1R, 3S)-isomalathion. Generally, the addition of α-CD and RAMEB (1.5 g/L to 3.5 g/L concentration) could lead to reduction of isomalathion toxicity in most cases, while the presence of β-CD (0.3 g/L to 1.5 g/L concentration) enhanced the toxicity of isomalathion. It was speculated that higher electronic cloud density and lower water solubility of β-CD than α-CD and RAMEB might favor to combination between acetylcholinesterase (AChE) and isomalathion included by β-CD. With respect for α-CD and RAMEB, isomalathion included by them could be easily dissolved in water because of high water solubility of the two CDs. Therefore, α-CD and RAMEB can be used as remediation regent for the pollution of isomalathion, and β-CD can act as an additive in improving bioactivity of such pesticides. In addition, the presence of CDs can alter enantioselectivity of chiral pesticides. The differences on the extent of enantioselectivity variation of isomalathion induced by α-CD, RAMEB and β-CD might be ascribe to the different cavity, electron cloud density and solubility among the three CDs. In conclusion, the above results gave researchers a possibility to change enantioselectivity of chiral pesticides from undesirable outcomes to desirable ones.     

Enantioselectivity in toxicity and degradation of dichlorprop-methyl in algal cultures

Enantioselectivity in the toxicity and degradation of the herbicide dichlorprop-methyl (2,4-DCPPM) in algal cultures was studied. Enantioselectivity was clearly observed in the toxicity of racemic 2,4-DCPPM and its two enantiomers. R-2,4-DCPPM showed low toxicity to Chlorella pyrenoidosa and Chlorella vulgaris, but higher toxicity to Scenedesmus obliquus. The observed toxicity was ranked: R-2,4-DCPPM > S-2,4-DCPPM ? Rac-2,4-DCPPM; the toxicity of R-2,4-DCPPM was about 8-fold higher than that of Rac-2,4-DCPPM. Additionally, 2,4-DCPPM was quickly degraded, in the initial 12 h, and different algae cultures had different enantioselectivity for the 2,4-DCPPM enantiomers. There was no significant enantioselectivity for 2,4-DCPPM in Chlorella vulgaris in the initial 7 h. However, racemic 2,4-DCPPM was degraded by Scenedesmus obliquus quickly, in the initial 4 h, much quicker, in fact, than the S- or R-enantiomers (racemate > R- > S-), indicating that the herbicide 2,4-DCPPM was absorbed enantioselectively by Scenedesmus obliquus. The rapid formation of 2,4-DCPP suggested that 2,4-DCPPM adsorbed by algal cells was catalytically hydrolyzed to the free acid, a toxic metabolite. The production rates of 2,4-DCPP were as follows: Scenedesmus obliquus > Chlorella pyrenoidosa > Chlorella vulgaris, consistent with the degradability of 2,4-DCPPM. Scenedesmus obliquus had quick, but different, degradative and uptake abilities for R-, S-, and Rac-2,4-DCPPM. The R- and S- enantiomers were not hydrolyzed in the first 12 h, while both enantiomers were hydrolyzed slowly after that. These results indicate that some physical and chemical properties of compounds are of importance in determining their enantioselective toxicity and degradation. The ester and its metabolite likely played an important role in enantioselective toxicity to the three algae.     

Studies on the Coupling Product between Oxidation Products Derived from Pentachlorophenol and Cyclodextrins

The coupling products (CPs), which were formed via the peroxosulfate catalyzed oxidation of pentachlorophenol (PCP) with iron(III)-tetrakis(sulfonatophenyl)porphyrin (Fe(III)-TPPS) in the presence of hydroxypropyl-β -cyclodextrin (HP-β -CD) or HP-γ -CD, were separated by ultrafiltration from the reaction mixture. When the percentages of chlorine species in the reaction mixture were calculated from the concentrations of organic chlorine in the reaction mixture and CPs, 10–25% of chlorine species in the reaction mixture was organic chlorine that was incorporated into CDs. Analyses of the CPs by pyrolysis-GC/MS (Py-GC/MS) and ¹³C NMR showed that the PCP-derived products were covalently incorporated into the CDs. To evaluate the acute toxicity of the CPs, a Microtox® test was examined. Toxicities of the CPs were reduced slightly, compared to the controls (PCP alone and PCP + reaction blanks). In the reaction blanks, mesaconic acid (MA) moieties were detected as a result of the oxidation of CDs in the absence of PCP. Thus, factors in the toxicities, detected in the CPs, can be attributed to the oxidation products derived from CDs, such as MA, as well as the PCP-derived products incorporated into the CDs.     

Influence of selected cyclodextrins in sorption-desorption of chlorpyrifos,chlorothalonil, diazinon,and their main degradation products on different soils

Cyclodextrins (CDs) can improve the apparent solubility and bioavailability of a variety of organic compounds through the formation of inclusion complexes; accordingly, they are suitable for application in innovative remediation technologies of contaminated soils. However, the different interactions in the tertiary system CD/contaminant/soil matrix can affect the bioavailability of the inclusion complex through the possible sorption of CD and CD complex in the soil matrix, as well as with the potential of the sorbed CD to form the complex, concurrent with the desorption processes. This work focuses in changes produced by three different CDs in soil sorption-desorption processes of chlorpyrifos (CPF), diazinon (DZN), and chlorothalonil (CTL), and their major degradation products, 3,5,6-trichloro-2-pyridinol (TCP), 2-isopropyl-6-methyl-4-pyrimidinol, and hydroxy-chlorothalonil (OH-CTL). Cyclodextrins used were β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Mβ-CD), and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD). The studied soils belong to the orders Andisol, Ultisol, and Mollisol with different organic matter contents, mineral composition, and pH. The apparent sorption constants were significantly lower for the three pesticides in the presence of all CDs. The highest displacement of sorption equilibria was produced by the influence of Mβ-CD, with the most pronounced effect for CPF, a pesticide strongly sorbed on soils. The same was obtained for TCP and OH-CTL, highlighting the need to assess the risk of generating higher levels of groundwater contamination with polar metabolites if degradation rates are not controlled. The highest desorption efficiency was obtained for the systems CPF-β-CD, DZN-Mβ-CD, and CTL-Mβ-CD. Since the degree of adsorption of the complex is relevant to obtain an increase in the bioavailability of the contaminant, a distribution coefficient for the complexed pesticide in all CD–soil–pesticide system was estimated by using the apparent sorption coefficients, the stability constant for each CD–pesticide complex, and the distribution coefficients of free pesticide.     

Persistence of herbicide fenoxaprop ethyl and its acid metabolite in soil and wheat crop under Indian tropical conditions

The persistence of fenoxaprop ethyl {Ethyl (RS)-2-[4-(6-chloro-1,3-benzoxazol-2-yloxy) phenoxy] propionate} herbicide and its active metabolite fenoxaprop acid was investigated in soil and wheat crop. Fenoxaprop acid was prepared by alkaline hydrolysis of fenoxaprop ethyl. A HPLC method was developed in which fenoxaprop ethyl herbicide and its acid metabolite showed sharp single peak at 6.44 and 2.61 min respectively. The sensitivity of the method for ester and acid was 2 and 1 ng respectively with limit of detection of 0.1 and 0.05 μg mL^?1. The recovery of fenoxaprop ethyl and fenoxaprop acid from soil, wheat straw and grain ranged between 73.8–80.2%. In a field experiment fenoxaprop ethyl (Puma super® 10 EC) when applied to wheat crop at the rate of 120 g and 240 g a.i. ha^-1 as post emergence spray, fenoxaprop ethyl converted to fenoxaprop acid. Residues of fenoxaprop ethyl and acid dissipated in soil with a half-life of 0.5 and 7.3 days, respectively. At harvest no detectable residues of fenoxaprop ethyl or acid were observed in soil, wheat grain and straw samples.     

Biodegradation of cyclodextrins in soil

Cyclodextrins, especially random methylated betaCD (RAMEB) and hydroxypropyl betaCD (HPbetaCD), are becoming common enhancing additives in the bioremediation of soils formerly contaminated by hydrocarbons and/or other poorly bioavailable organic pollutants. Therefore, their degradation in the soil, particularly the most persistent RAMEB, has been of great concern. Like oil contaminants, these additives should be biodegradable via an environmentally safe technology. Hence, in this paper, the biodegradability of eight different cyclodextrins (CDs) in four different soils was examined under various treatment conditions in laboratory and pilot scale field experiments. This paper is the first report on the potential biological fate of CDs studied under a large variety of environmental conditions and in different soil ecosystems. Data on the potential relationship between CD biodegradation and the biological removal of hydrocarbons in the CD-amended contaminated soils are also given. All CDs were found to be more or less biodegradable; even the most persistent RAMEB was depleted from soils under favourable conditions. In the field experiments, the depletion of RAMEB to about 40% of its initial level was observed for a period of 2 years in hydrocarbon-contaminated soils of high organic matter and cell concentration.     

Phytoplankton toxicity of the antibiotic chlortetracycline and its UV light degradation products

Two common freshwater phytoplankton species Microcystis aeruginosa and Scenedesmus obliquus were employed as test organisms to investigate the toxic effects of chlortetracycline widely used in human medicine and veterinary as antibiotic. Toxicity assays were performed into two parts: antibiotic toxicity test and antibiotic degraded products toxicity test. In general, chlortetracycline had significantly toxic effect on population growth and chlorophyll-a accumulation of two phytoplankton. Although M. aeruginosa had ability to grow after exposed to chlortetracycline at 0.5 mg L⁻¹, its photosynthesis function was also disrupted. Compared with the data in two phytoplankton species, the chlorophyceae was more sensitive than the cyanophyceae. The adverse effect on S. obliquus was stronger than that on M. aeruginosa with increasing concentrations. In addition, for M. aeruginosa, regardless of the UV light degradation time, the treated chlortetracycline also had adverse effect on population growth and chlorophyll-a accumulated. The degraded chlortetracycline under any treatment time was more toxic for S. obliquus than chlortetracycline itself excluding under 24 h. However, the correlation between the toxicity and degradation time was not clear and toxicity enhanced in fact did not follow the increase or decrease in degradation time. Our study showed that the antibiotic chlortetracycline and its degraded products had adverse effect on freshwater phytoplankton, the former has not been reported before and the latter has been overlooked in other research in the past.     

Influence of hydroxypropyl-β-cyclodextrin on the biodegradation of C-phenanthrene and C-hexadecane in soil

Soil was spiked with [9-¹⁴C]phenanthrene and [1-¹⁴C]hexadecane at 50 mg kg⁻¹ and aged for 1, 25, 50, 100 and 250 d. At each time point, the microcosms were amended with aqueous solutions of cyclodextrin (HP-β-CD) at a range of concentrations (0-40 mM). Mineralisation assays and aqueous HP-β-CD extractions were performed to assess the effect of the amendments on microbial degradation. The results showed that amendments had no significant impact on the microbial degradation of either of the ¹⁴C-contaminants. Further, HP-β-CD extractions were correlated with the mineralisation of the target chemicals in each of the soil conditions. It was found that the HP-β-CD extraction was able to predict mineralisation in soils which had not been amended with cyclodextrin; however, in the soils containing the HP-β-CD, there was no predictive relationship. Under the conditions of this study, the introduction of HP-β-CD into soils did not enhance the biodegradation of the organic contaminants.     

Studies on the coupling product between oxidation products derived from pentachlorophenol and cyclodextrins

The coupling products (CPs), which were formed via the peroxosulfate catalyzed oxidation of pentachlorophenol (PCP) with iron(III)-tetrakis(sulfonatophenyl)porphyrin (Fe(III)-TPPS) in the presence of hydroxypropyl-beta -cyclodextrin (HP-beta -CD) or HP-gamma -CD, were separated by ultrafiltration from the reaction mixture. When the percentages of chlorine species in the reaction mixture were calculated from the concentrations of organic chlorine in the reaction mixture and CPs, 10-25% of chlorine species in the reaction mixture was organic chlorine that was incorporated into CDs. Analyses of the CPs by pyrolysis-GC/MS (Py-GC/MS) and 13C NMR showed that the PCP-derived products were covalently incorporated into the CDs. To evaluate the acute toxicity of the CPs, a Microtox test was examined. Toxicities of the CPs were reduced slightly, compared to the controls (PCP alone and PCP + reaction blanks). In the reaction blanks, mesaconic acid (MA) moieties were detected as a result of the oxidation of CDs in the absence of PCP. Thus, factors in the toxicities, detected in the CPs, can be attributed to the oxidation products derived from CDs, such as MA, as well as the PCP-derived products incorporated into the CDs.     

Environmental Significance of the Diclofop-methyl and Cyclodextrin Inclusion Complexes

Cyclodextrins (CDs) possess a hydrophilic external surface and a hydrophobic cavity. They are thus highly soluble and, in the meantime, effectively form inclusion complexes with hydrophobic organic compounds to enhance their solubilities. In this study, the complexation between modified β-CDs and the herbicide diclofop-methyl (DM), (2-(4-(2,4-dichlorophenoxy)-phenoxy) propionate), was investigated. The complexation was confirmed by the shifts in the wavelengths of maximum ultra violet (UV) absorption and fluorescence excitation/emission. The deuterium isotope effects indicate that in the presence of β-CDs the solubility of DM was lower while that of diclofop was higher in D₂O than in H₂O, suggesting the primary role of hydrophobic interactions in complexation. The solubility of DM was enhanced in the presence of β-CDs, the extent of which depended on the modification of β-CDs. The complexation reduced the hydrolysis of DM and hence increased its stability. The small inconsistency in the power of β-CDs between hydrolysis retardation and solubilization suggests that hydrolysis was affected by the properties of β-CDs and the configuration of DM in the complexes. Use of β-CDs may thus result in the mobilization of soil DM. Properly modified β-CDs may be utilized as formulation additives for improved delivery of DM and for enhanced environmental remediation.     

Suppression of estrogenic activity of 17-beta-estradiol by beta-cyclodextrin

The suppressive effects of cyclodextrins (CDs) on the strong estrogenic activity of 17β-estradiol (E2) in water environments were investigated in this study. Cyclodextrins are doughnut-shaped molecules that possess a hydrophobic cavity and a hydrophilic exterior. The cavity can incorporate nonpolar molecules as guests to form inclusion complexes. β-CD and 2-hydroxypropyl-β-CD (HP-β-CD) were the most successful in forming a complex with E2 and improving its low aqueous solubility. The E2/CDs complexes bound to the estrogen receptor in a cell-free system as determined by ELISA and suppressed the hormone activities as measured by a yeast two-hybrid assay. These results indicate that hydrophobic E2 is easily transported through the lipid zone of the plasma membrane into the target cell and can bind to the nuclear receptor. However, the hydrophilic E2/β-CD and E2/HP-β-CD complexes do not penetrate the membrane. Therefore, these CDs are able to suppress the hormone activity of E2 through complex formation.     

Enantioselective toxic effects and biodegradation of benalaxyl in Scenedesmus obliquus

Enantioselectivity in ecotoxicity and biodegradation of chiral pesticide benalaxyl to freshwater algae Scenedesmus obliquus was studied. The 96 h-EC₅₀ values of rac-, R-(−)-, S-(+)-benalaxyl were 2.893, 3.867, and 8.441 mg L⁻¹, respectively. Therefore, the acute toxicities of benalaxyl enantiomers were enantioselective. In addition, the pigments chlorophyll a and chlorophyll b, antioxidant enzyme activities catalase (CAT) and superoxide dismutase (SOD) as well as lipid peroxide malondialdehyde (MDA) were determined to evaluate the different toxic effects. Chlorophyll a was induced by S-(+)-benalaxyl but inhibited by R-(−)-benalaxyl at 1 mg L⁻¹. Chlorophyll b were both induced at 1 mg L⁻¹, but S-(+)-form was fourfold higher than R-(−)-form. S-(+)-benalaxyl inhibited more CAT activities at 3 mg L⁻¹ and 5 mg L⁻¹, induced less SOD activity and MDA content at 5 mg L⁻¹ than R-(−)-benalaxyl. Based on these data, enantioselectivity occurred in anti-oxidative stress when S. obliquus response to benalaxyl. In the biodegradation experiment, the half-lives of S-(+)-benalaxyl and R-(−)-benalaxyl were 4.07 d and 5.04 d, respectively, resulting in relative enrichment of the R-(−)-form. These results showed that toxic effects and biodegradation of benalaxyl in S. obliquus were enantioselective, and such enantiomeric differences must be taken into consideration in pesticide risk.     

Bioactivity,toxicity and dissipation of hexaconazole enantiomers

In this study, the bioactivity, acute toxicity and dissipation in vegetables of the individual enantiomers of the fungicide hexaconazole had been investigated. The optical pure single enantiomers were prepared and the bioactivity of (+)-, (−)- and rac-hexaconazole was tested using four target fungi including Colletotrichum gloeosporioides Penz, Alternaria solani, Alternaria mali Roberts and Monilinia fructicola. The results showed (−)-hexaconazole was always more active than (+)-hexaconazole with the fungicidal activity 11–13-fold higher to A. solani, A. mali Roberts and Monilinia fructicola, and 1.26-fold higher to C. gloeosporioides Penz. (−)-Hexaconazole also showed 1.3-fold higher acute toxicity to aquatic species Daphnia magna based on the 48 h EC₅₀ values. There was obvious enantioselectivity in the dissipation in tomato with (−)-hexaconazole degraded faster resulting an enrichment of (+)-form, and the half-lives of (−)-hexaconazole and (+)-hexaconazole in tomato were 2.96 d and 3.38 d respectively, while it was not enantioselective in green pepper, in which the both enantiomers had the half-lives about 4.36 d. The findings are helpful for better environmental and ecological risk assessment of hexaconazole on an enantiomeric level.     

Adsorption of a dye on clay and sand. Use of cyclodextrins as solubility-enhancement agents

Laboratory-scale studies were aimed at elucidating the physico-chemical aspects on the removal process of crystal violet (CV) from waters and solid substrates. The laponite clay (RD) and sand were chosen for the double aim at investigating them as CV adsorbents for water treatment and as substrates which mime the soil components. Sand is very effective in removing CV from waters. The cyclodextrins (CDs) were exploited as solubility-enhancement agents to remove CV from the solid substrates. They are powerful solvent media because they extract the CV from sand forming water-soluble CV/CD inclusion complexes and do not show affinity for sand. Optimum performance was shown by the modified CDs (i.e. hydroxypropyl-β-cyclodextrin and methyl-β-cyclodextrin). A linear correlation between the logarithm of the equilibrium constant for the CV/CD inclusion complexes formation (K_cpx) and the maximum amount of CV extracted from sand in the columns experiments at a flow rate of 1.5 ml min⁻¹ was drawn. This relationship predicts that CDs with K_cpx < 180 M⁻¹ are not suitable for CV removal from sand. CDs failed to displace CV from RD because they generate the formation of RD clusters where CV remains entrapped.     

Simultaneous mobilization of heavy metals and polychlorinated biphenyl (PCB) compounds from soil with cyclodextrin and EDTA in admixture

This study evaluated the efficacy of a washing process with cyclodextrin in combination with ethylenediaminetetraacetate (EDTA) for the simultaneous mobilization of heavy metals and PCBs from a field contaminated soil. Ultrasonically aided mixing of the field contaminated soil with a combination of cyclodextrin solution (10%, w/v) and a sparing quantity (2 mmol) of EDTA, simultaneously mobilized appreciable quantities of PCBs and much of the analyte metal (Cd, Cr, Cu, Mn, Ni, Pb, Zn) burdens. Relative to the action of individual reagents, a combination of randomly methylated (RAMEB) or hydroxypropyl beta-cyclodextrin (HPCD) with EDTA did not alter the PCB extraction efficiency nor did the presence of cyclodextrin change the efficiency of mobilization of most heavy metals (Al, Cd, Cr, Fe, Mn, Ni, and Zn) but did increase the recovery of Cu and Pb modestly. Three sonication-washes with the same charge of reagents mobilized appreciable quantities of PCBs (40-76%) and quantitatively extracted the labile fraction of Cd, Cu, Mn, and Pb. RAMEB proved to be more efficient than HPCD for PCB extractions. Three successive extractions with a single charge of cyclodextrin mobilized almost as much PCB (RAMEB, 76%; HPCD, 40%) as did the companion extractions that used fresh reagents each time (RAMEB, 78%; HPCD, 42%). Collectively, these studies demonstrated that PCB compounds and selected heavy metals can be co-extracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and cyclodextrin.     

Metribuzin impairs the unicell-colony transformation in the green alga Scenedesmus obliquus

Active growth is a prerequisite for the formation of grazing-protective, mostly eight-celled colonies by the ubiquitous green alga Scenedesmus in response to chemical cues from zooplankton. Colonies can also be evoked by chemically quite similar manmade anionic surfactants, such as FFD-6. In this study, it was hypothesized that growth-inhibiting concentrations of the herbicide metribuzin impair the ability of Scenedesmus obliquus to form colonies in response to the surfactant morphogen FFD-6. The results confirmed that the formation of colonies in S. obliquus was hampered by metribuzin. EC₅₀ values of metribuzin for colony inhibition (approximately 11 μg L⁻¹) were similar to those for growth and photosynthesis inhibition (12-25 μg metribuzin L⁻¹). In the absence of the colony-inducing surfactant FFD-6, S. obliquus populations were comprised of 92% unicells, having on average 1.2 cells per colony at all tested metribuzin concentrations (0-100 μg L⁻¹). In contrast, in the presence of FFD-6 and at low metribuzin concentrations (0 and 5 μg L⁻¹), S. obliquus had more than five cells per colony with a high portion of eight-celled colonies. However, increasing concentrations of metribuzin decreased the number of colonies in the FFD-6-exposed populations and caused them to remain mostly unicellular at the highest concentrations (50 and 100 μg L⁻¹). This study revealed that metribuzin impeded growth and by doing so, also obstructed the possibility for unicellular Scenedesmus to form colonies. Consequently, an increase in mortality of Scenedesmus from grazing is expected.     

Biosorption of zinc and copper from aqueous solutions by two freshwater green microalgae Chlorella pyrenoidosa and Scenedesmus obliquus

Purpose

The objective of this study was to determine the removal of zinc and copper by two freshwater green microalgae Chlorella pyrenoidosa and Scenedesmus obliquus and to investigate changes of algal ultrastructure and photosynthetic pigment.

Methods

Algal cells were exposed for 8 days to different initial zinc or copper concentrations. Heavy metal concentrations were detected by an atomic absorption spectrophotometer. Algal growth, ultrastructure, and photosynthetic pigment were analyzed by a microplate reader, transmission electron microscope, and spectrophotometer, respectively.

Results

Low zinc and copper concentrations induced increase in algal growth, whereas application of high zinc and copper concentrations suppressed the growth of both algae. High metal concentrations also decreased the photosynthetic pigments and destroyed algal cell ultrastructure. The zinc removal efficiency by both algae increased rapidly during the first day and thereafter remained nearly constant throughout the experiment. The copper removal efficiency by both algae increased slowly during the whole experimental periods. In all cultures, the quantity of both metals removed intracellularly was much lower than the adsorbed quantity on the cell surface.

Conclusions

Both strains of the microalgae had proven effective in removing zinc and copper from aqueous solutions, with the highest removal efficiency being near 100%. In addition, C. pyrenoidosa appeared to be more efficient than S. obliquus for removing copper ions. On the contrary, S. obliquus appeared to be more efficient than C. pyrenoidosa for removing zinc ions.     

Salmonella Enterica Serovar Typhimurium HilA-LacZY Fusion Gene Response to Iron Chelation or Supplementation in Rich and Minimal Media

Abstract

Virulence expression of Salmonella enterica serovar Typhimurium under iron limited condition was measured by β-galactosidase (β-gal) assay using a hilA-lacZY fusion strain and calculated as Miller units. hilA-lacZY β-galactosidase assays were performed in brain heart infusion (BHI) and minimal media (M9), after iron chelation with 2, 2-dipridyl and iron-supplementation respectively. Before performing virulence assays, concentrations of iron in the media were estimated using ferrozine. Iron content was found to be more in BHI (42.6 µg dL^?1) as compared to M9 (10.03 µg dL^?1). β-gal activity of Salmonella Typhimurium in BHI was generally less than that observed in M9. After exposure to various combinations of iron chelator in BHI, hilA-lacZY activity only increased at the highest concentration of chelator (200 µM) but decreased in M9 media for all iron concentrations when compared to controls with no iron amendment. These results indicate that iron availability may influence S. Typhimurium hilA expression.     

Selective separation of deltamethrin by molecularly imprinted polymers using a β-cyclodextrin derivative as the functional monomer

A deltamethrin-imprinted polymer (MIP₁) was prepared using bis(-6-O-butanediacid monoester)-β-cyclodextrin (BBA-β-CD) as the functional monomer and toluene 2,4-diisocyanate (TDI) as the cross-linker. In comparison to the molecularly imprinted polymer where β-CD was applied as the functional monomer (MIP₂), MIP₁ showed a higher specific binding capacity (ΔC_P) and an improved imprinting factor (IF) for deltamethrin. The selective recognition experiments demonstrated that compared to MIP₂, MIP₁ could better recognize its template over other substrates that had similar chemical structures. The solid phase extraction (SPE) of deltamethrin using MIP₁ as the adsorbent was further investigated. The recoveries of the molecularly imprinted solid phase extraction (MISPE) column for deltamethrin were 83.2–93.4% with relative standard deviations (RSD) of 2.03–6.19%. The method has been successfully applied to the enrichment of trace deltamethrin from real water samples.