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.     

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 propanil, tebufenozide and mefenacet on growth of four freshwater species of phytoplankton: a microplate bioassay

The Albufera Natural Park situated in Valencia (Spain), with a very rich flora and fauna is surrounded by rice fields in which pesticide spraying is a regular practice. With this in mind, the sensitivity of four algal species, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila to pesticides propanil, tebufenozide and mefenacet was studied using single species toxicity tests. Organisms were exposed to different concentrations of these herbicides and the algal growth was measured in a microplate reader at 410 nm, at 0, 24, 48 and 72 h. Tebufenozide appeared to be the most inhibitory to Scenedesmus and Chlorella species growth. 72 h EC50 of propanil, tebufenozide and mefenacet ranged from 0.29 to 5.98 mg/l, 0.12 to 0.15 mg/l and from 0.25 to 0.67 mg/l, respectively for the four algal species. The two species of Chlorella were more tolerant than the two species of Scenedesmus.     

Effects of bensulfuron-methyl and cinosulfuron on growth of four freshwater species of phytoplankton

The acute toxicity of sulfonylurea herbicides bensulfuron-methyl and cinosulfuron was tested on the five species of freshwater phytoplankton: Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 8 to 104 mg/l for cinosulfuron and from 0.015 to 6.2 mg/l for bensulfuron-methyl. The pesticides bensulfuron-methyl, atrazine and benthiocarb were more toxic than cinosulfuron, chlorsulfuron, molinate, fenitrothion and pyridaphenthion in a toxicity study with the same algal species. The transformation of effective concentrations of bensulfuron-methyl and cinosulfuron and other pesticides, obtained from toxicity measurements, into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The herbicides cinosulfuron, methyl-bensulfuron, atrazine and chlorsulfuron were more dangerous than the herbicides benthiocarb and molinate and than the insecticides fenitrothion and pyridaphenthion, in a study of hazard evaluation. The two species of Chlorella were more tolerant to both herbicides than the two species of Scenedesmus. A potential environmental hazard of sulfonylurea herbicides to aquatic systems has to be expected even at low environmental concentrations.     

用水生生物对重金属污染土壤进行生态毒理评价

应用斜生栅藻（Scenedesmus obliquus）和明亮发光杆菌T3（Photobacterium phosphoreum）急性毒性实验方法对重金属污染土壤的进行生态毒理评价，结果表明，斜生栅藻的生长繁殖率和发光菌的相对发光度与土壤中的重金属含量明显相关，并且随重金属投加量的增加，其生长繁殖率和发光度逐渐降低。对3种测试参数进行比较可知，斜生栅藻细胞数增长率是最敏感的土壤毒性检测指标。土壤的毒性在复合污染的条件下比在单一污染的条件下高很多。本研究的结果可以为污染土壤的优先修复提供理论依据。     

Comparison of different physiological parameter responses in Lemna minor and Scenedesmus obliquus exposed to herbicide flumioxazin

The sensitivity of different physiological parameters in Scenedesmus obliquus and Lemna minor exposed to herbicide (flumioxazin) was investigated to indicate the most convenient and sensitive parameter. To assess toxicity of flumioxazin, we used a panel of biomarkers: pigment contents, chlorophyll fluorescence parameters and antioxidative enzyme activities. Algae and duckweed were exposed to 48-h IC50 for growth rate. In L. minor, the sensitivity of the parameters was as follows: QN > Oxygen emmision > phiS(PSII) > QP > phi(PSII) > CAT, GR > Pigment> APO > Growth. For S. obliquus, this ranking was as follows: CAT > Oxygen emission > QP > APO > GR > Pigment > phiS(PSII) > Growth > phi(PSII) > QN (from the greatest to the least sensitive). The results demonstrated that the observed toxicity is related not only to interspecific variations but also to the selected parameter.     

家用洗衣粉中磷对斜生栅藻生长的影响

以洗衣粉中的有机磷为磷源,通过室内模拟的方法研究在不同磷浓度的水体条件下斜生栅藻的生长情况,以及磷对斜生栅藻的生长是否有毒害作用.通过显微计数测定藻细胞数目来探讨洗衣粉中磷对斜生栅藻生长的影响;同时分析了洗衣粉中磷对斜生栅藻96 h生长期中光合色素的影响.结果表明,洗衣粉中的磷除了促进藻生长外,其浓度过低或过高都会抑制藻的生长.由实验结果可得,磷对藻生长的富营养化作用和毒性作用取决于磷浓度的高低.     

用水生生物对重金属污染土壤进行生态毒理评价

应用斜生栅藻(Scenedesmusobliquus)和明亮发光杆菌T3(Photobacteriumphosphoreum)急性毒性实验方法对重金属污染土壤的进行生态毒理评价,结果表明,斜生栅藻的生长繁殖率和发光菌的相对发光度与土壤中的重金属含量明显相关,并且随重金属投加量的增加,其生长繁殖率和发光度逐渐降低。对3种测试参数进行比较可知,斜生栅藻细胞数增长率是最敏感的土壤毒性检测指标。土壤的毒性在复合污染的条件下比在单一污染的条件下高很多。本研究的结果可以为污染土壤的优先修复提供理论依据。     

3种载体固定化菌藻共生系统脱氮除磷效果的对比

采用3种不同载体（海藻酸钠、聚乙烯醇、复合载体）,分别将小球藻和栅藻与活性污泥固定成菌藻共生系统,制成菌藻凝胶小球,单独菌、单独藻的凝胶小球,用于处理人工污水。结果表明,（1）复合载体固定的菌藻共生系统氮磷去除效果最好,PVA载体的脱氮除磷效果次于复合载体优于海藻酸钠;（2）固定化菌藻共生系统的脱氮除磷效果明显优于单独固定菌和单独固定藻,固定菌的效果较差;（3）3种载体包埋下的固定化小球藻的脱氮除磷效果均较相同载体固定化的栅藻效果好。     

Removal of triazine herbicides from freshwater systems using photosynthetic microorganisms

The uptake of the triazine herbicides, atrazine and terbutryn, was determined for two freshwater photosynthetic microorganisms, the green microalga Chlorella vulgaris and the cyanobacterium Synechococcus elongatus. An extremely rapid uptake of both pesticides was recorded, although uptake rate was lower for the cyanobacterium, mainly for atrazine. Other parameters related to the herbicide bioconcentration capacity of these microorganisms were also studied. Growth rate, biomass, and cell viability in cultures containing herbicide were clearly affected by herbicide uptake. Herbicide toxicity and microalgae sensitivity were used to determine the effectiveness of the bioconcentration process and the stability of herbicide removal. C. vulgaris showed higher bioconcentration capability for these two triazine herbicides than S. elongatus, especially with regard to terbutryn. This study supports the usefulness of such microorganisms, as a bioremediation technique in freshwater systems polluted with triazine herbicides.     

Cultivating Chlorella vulgaris and Scenedesmus quadricauda microalgae to degrade inorganic compounds and pesticides in water

Environmental Science and Pollution Research - This work evaluates the possibility of cultivating Scenedesmus quadricauda and Chlorella vulgaris microalgae in wastewater from the hydroponic...     

Performance of different microalgal species in removing nickel and zinc from industrial wastewater

A series of batch experiments was conducted to compare the ability of 11 microalgal species of the same cell density in removing nickel (Ni) and zinc (Zn) from synthetic wastewater. These included Chlorella vulgaris (commercially available), Chlorella sorokiniana and Scenedesmus quadricauda (isolates from polluted water of Wuhan, China), and eight different isolates from Hong Kong. The Wuhan isolate of Scenedesmus removed most Ni, probably due to its large biomass. Nickel concentration was reduced from an initial 30 to 0.9 mg/l after 5 min (97% Ni removal), and further declined to 0.4 mg/l after 90 min of treatment. In wastewater containing 30 mg/l Ni and 30 mg/l Zn, more than 98%, Ni and Zn were removed simultaneously at the end of 5 min treatment, indicating that the presence of Zn in wastewater did not affect Ni removal by this Scenedesmus isolate. The second most effective species for Ni removal was an isolate, tentatively identified as Chlorella miniata, Ni concentration was reduced to 10 mg/l after 90 min, and was only slightly interfered by the presence of Zn. In terms of metal removal per unit biomass or unit surface area of algal cells, C. miniata was the best species in removing Ni and Zn. At the other extreme, one Hong Kong isolate (Synechocystis sp.) did not remove any Ni and only achieved 40% Zn removal. Performance of the other isolates was comparable with the commercial C. vulgaris, less than 50% Ni was removed after 5 h of treatment and Ni removal was significantly reduced by the presence of Zn. All algae tested were found to be viable, showing these 11 species could tolerate a mixture of 30 mg/l Ni and 30 mg/l Zn in wastewater.     

Toxicity of fipronil and its enantiomers to marine and freshwater non-targets

Fipronil is a phenylpyrazole insecticide used in agricultural and domestic settings for controlling various insect pests in crops, lawns, and residential structures. Fipronil is chiral; however, it is released into the environment as a racemic mixture of two enantiomers. In this study, the acute toxicity of the (S,+) and (R,-) enantiomers and the racemic mixture of fipronil were assessed using Simulium vittatum IS-7 (black fly), Xenopus laevis (African clawed frog), Procambarus clarkii (crayfish), Palaemonetes pugio (grass shrimp), Mercenaria mercenaria (hardshell clam), and Dunaliella tertiolecta (phytoplankton). Results showed that S. vittatum IS-7 was the most sensitive freshwater species to the racemic mixture of fipronil (LC50 = 0.65 microg/L) while P. pugio was the most sensitive marine species (LC50 = 0.32 microg/L). Procambarus clarkii were significantly more sensitive to the (S,+) enantiomer while larval P. pugio were significantly more sensitive to the (R,-) enantiomer. Enantioselective toxicity was not observed in the other organisms tested. Increased mortality and minimal recovery was observed in all species tested for recovery from fipronil exposure. These results indicate that the most toxic isomer of fipronil is organism-specific and that enantioselective toxicity may be more common in crustaceans than in other aquatic organisms.     

Study of the toxicity of diuron and its metabolites formed in aqueous medium during application of the electrochemical advanced oxidation process "electro-Fenton"

Diuron (N'-[3,4-dichlorophenyl]-N,N-dimethylurea) is a herbicide belonging to the phenylurea family, widely used to destroy weeds on uncultivated surfaces. Because of its toxicity for aquatic organisms and suspicion of being carcinogenic for humans, diuron is the object of growing environmental concern. Therefore, we have developed the electro-Fenton method, an electrochemical advanced oxidation process (EAOP), to degrade diuron in aqueous medium, and we have studied the evolution of the toxicity of treated solution during the process. Indeed, the EAOPs catalytically generate hydroxyl radicals that oxidize the persistent organic pollutants, and can ultimately destroy and mineralize them. But, sometimes, relatively toxic organic metabolites are formed during the oxidation reaction. In this work, the evolution of toxicity of diuron aqueous solutions was studied at different initial concentrations, during treatment by the electro-Fenton method. Samples were collected at various electrolysis times and mineralization degrees during the treatment. The toxicity of the samples was measured using the bacteria Vibrio fischeri (Microtox) and the green alga Scenedesmus obliquus. Our results demonstrated that the toxicity of diuron aqueous solutions (concentrations=3.0-27.6 mg L(-1)) varied considerably with time. The formation and disappearance of several metabolites, having toxicity often stronger than that of the initial herbicide, were observed. To improve the efficiency of water decontamination, the electro-Fenton method should be applied during a time long enough (several hours) and at relatively high electrolysis current (I=250 mA) to reach a nearly complete mineralization of the herbicide in the aqueous medium.     

Enantioselective effects of herbicide imazapyr on Arabidopsis thaliana

The enantioselective toxicity of chiral herbicides in the environment is of increasing concern. To investigate the enantioselective effects of the chiral herbicide imazapyr on target organisms, we exposed Arabidopsis thaliana to imazapyr enantiomers and racemate. The results show that imazapyr was enantioselectively toxic to A. thaliana. The total chlorophyll content in A. thaliana was affected more by (+)-imazapyr than (±)-imazapyr and (?)-imazapyr. Concentrations of proline and malondialdehyde reflected a toxic effect in the order of (+)-imazapyr > (±)-imazapyr > (?)-imazapyr at every concentration. Acetolactate synthase (ALS) activity was inhibited more by (+)-imazapyr than (±)-imazapyr or (?)-imazapyr. At 100 mg L^?1 of imazapyr, ALS activity was 78%, 43%, and 19% with (?)-, (±)-, and (+)-imazapyr, respectively. The results suggest the significant enantioselective toxicity of imazapyr in A. thaliana for greater toxicity with (+)-imazapyr than (±)-imazapyr and (?)-imazapyr, which suggests that (+)-imazapyr has more herbicidal effect.     

Toxicity and bioaccumulation of copper in three green microalgal species

The effective concentrations of copper on the inhibition of the growth of Scenedesmus obliquus, Chlorella pyrenoidosa and Closterium lunula at 96 h (96 h EC50) were determined to be 50, 68 and 200 microg/l, respectively. The low initial bioaccumulation of Cu by C. lunula was found to be responsible for its tolerance to Cu. The amount of Cu accumulated by all three microalgae reached the maximum value and decreased quickly after the peak followed by a slow decrease over the next 6 d. Bioaccumulation of Cu by C. lunula was directly proportional to the initial Cu concentration. After reaching the first peak after 1 d, the bioconcentration factor of Cu by microalgae declined to its minimum value during the exponential growth phase but increased in the stationary growth phase again. This indicates that desorption of Cu from microalgae was higher during the exponential growth phase but lower in the stationary growth phase. Smaller microalgae with low 96 h EC50 values are more efficient in removing Cu from wastewater.     

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, β-CD and its two derivatives, randomly methylated β-CD (RAMEB) and hydroxypropyl β-CD (HP-β-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 β -CD and HP-β -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 β-CD and HP-β-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.     

Pyrene-induced changes of glutathione-S-transferase activities in different microalgal species

The glutathione-S-transferase (GST, EC 2.5.1.18) activities in different freshwater microalgal species, namely, Chlorella vulgaris, Scenedesmus quadricauda, Scenedesmus platydiscus and Selenastrum capricornutum under the control condition (without pyrene addition) and at different pyrene concentrations were compared. During 7-days incubation under the control condition (without pyrene addition), all microalgal species exhibited measurable GST activities but the activities varied significantly among species and the difference could be more than 100-fold. The addition of pyrene at concentrations ranged from 0.1 to 1.0 mg l(-1) to microalgal cultures led to changes in GST activities but the patterns of changes varied from species to species. Among the four species, remarkably decreases in GST activities were found in S. quadricauda, a species most sensitive to pyrene toxicity, at high pyrene concentrations. On the contrary, GST activities in S. platydiscus and Se. capricornutum increased significantly as pyrene concentrations increased. These two species were found to be more resistant to pyrene and had higher efficiencies in metabolising pyrene than other species. C. vulgaris did not show any significant change in their GST activities with the addition of pyrene, and pyrene was not metabolised by this species. These results suggest that pyrene-induced changes of GST activities in microalgae might be related to their resistance and their ability to metabolise pyrene. In general, the pyrene-induced changes of GST activities were higher at 4-days than at 1- and 7-days incubation in all microalgae.     

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.     

Biodegradation capacity of tributyltin by two Chlorella species

Two microalgal species, Chlorella vulgaris and Chlorella sp., which showed high tributyltin (TBT) tolerant ability were investigated for their capabilities in degrading TBT at sublethal concentration. The distribution of TBT and its degraded products dibutyltin (DBT) and monobutyltin (MBT) in the incubation medium, extracellular surface and intracellular fraction were monitored during an exposure period of 14 days. Results showed that biosorption of TBT by the algal cell wall was the major mechanism in reducing 40% of the initial TBT from the medium in the first 2 days. The half-life of TBT incubated with C. vulgaris was 60 h while that of Chlorella sp. was 80 h. The occurrence of DBT at Day 1 in the culture medium provided direct evidence to the biodegradation of TBT by both Chlorella species. At the end of the experimental period, 27 and 41% of the original TBT were recovered as DBT and MBT in cultures of C. vulgaris, respectively. In contrast, DBT appeared to be the only degradation product of Chlorella sp. and only 26% of the original TBT was transformed to DBT. Despite the same genus, TBT was debutylated to a greater extent to MBT by C. vulgaris, while DBT was the end degradation product by Chlorella sp. The capability of such debutylating process therefore accounted for the higher tolerant ability of C. vulgaris than Chlorella sp.