Remediation of a chlorinated aromatic hydrocarbon in water by photoelectrocatalysis

Photoelectrocatalysis driven by visible light offers a new and potentially powerful technology for the remediation of water contaminated by organo-xenobiotics. In this study, the performance of a visible light-driven photoelectrocatalytic (PEC) batch reactor, applying a tungsten trioxide (WO₃) photoelectrode, to degrade the model pollutant 2,4-dichlorophenol (2,4-DCP) was monitored both by toxicological assessment (biosensing) and chemical analysis. The bacterial biosensor used to assess the presence of toxicity of the parent molecule and its breakdown products was a multicopy plasmid lux-marked E. coli HB101 pUCD607. The bacterial biosensor traced the removal of 2,4-DCP, and in some case, its toxicity response suggests the identification of transient toxic intermediates. The loss of the parent molecule, 2,4-DCP determined by HPLC, corresponded to the recorded photocurrents. Photoelectrocatalysis offers considerable potential for the remediation of chlorinated hydrocarbons, and that the biosensor based toxicity results identified likely compatibility of this technology with conventional, biological wastewater treatment.     

2,4-D完全抗原的合成及其免疫性能评价

以2,4-D为半抗原,BSA为载体蛋白,通过EDC的偶联反应条件优化试验,合成了多种结合比的完全抗原,制备了小分子环境污染物的多克隆抗体.结果表明,偶联反应优化步骤是2,4-D、BSA和EDC同时反应,4°C条件下反应18h.偶联反应可以在2,4-D的浓度为10.0～12.0 mg/mL的0.05mol/L的磷酸盐缓冲溶液中进行,反应缓冲体系pH控制在5.4～6.1之间.EDC的加入量低于12 mg时,采用2,4-D和多聚赖氨酸的偶联物为包被抗原.通过balb/c小鼠免疫试验评价结合比分别为6、12、18和25的完全抗原的免疫性能,结果表明结合比为12和18的完全抗原具有很好的免疫原性.其中以结合比为18的完全抗原免疫小鼠获得的抗血清对包被抗原载体的非特异性吸附低于阴性血清,2,4-D特异性血清含量高,适于作为完全抗原免疫小鼠进一步制备单克隆抗体.     

Derivation of aquatic predicted no-effect concentration (PNEC) for 2,4-dichlorophenol: comparing native species data with non-native species data

2,4-Dichlorophenol (2,4-DCP) is known as an important chemical intermediate and an environmental endocrine disruptor. There is no paper dealing with the predicted no-effect concentration (PNEC) of 2,4-DCP, mainly due to shortage of chronic and site-specific toxicity data. In the present study, toxicity data was obtained from the tests using six Chinese native aquatic species. The HC₅ (hazardous concentration for 5% of species) was derived based on the constructed species sensitivity distribution (SSD), which was compared with that derived from literature toxicity data of non-native species. For invertebrates, the survival no-observed effect concentrations (NOECs) were 0.05 and 1.00 mg L⁻¹ for Macrobrachium superbum and Corbicula fluminea, respectively. NOECs based on fishes’ growth were 0.10, 0.20 and 0.40 mg L⁻¹ for Mylopharyngodon piceus, Plagiognathops microlepis and Erythroculter ilishaeformis, respectively. For aquatic plant Soirodela polyrhiza, NOEC based on concentration of chlorophyll was 1.00 mg L⁻¹. A final PNEC calculated using the SSD approach with a 50% certainty based on different taxa ranged between 0.008 and 0.045 mg L⁻¹. There is no significant difference between HC₅ derived from native and that from non-native taxa.     

Maize,switchgrass, and ponderosa pine biochar added to soil increased herbicide sorption and decreased herbicide efficacy

Biochar, a by-product of pyrolysis made from a wide array of plant biomass when producing biofuels, is a proposed soil amendment to improve soil health. This study measured herbicide sorption and efficacy when soils were treated with low (1% w/w) or high (10% w/w) amounts of biochar manufactured from different feedstocks [maize (Zea mays) stover, switchgrass (Panicum vigatum), and ponderosa pine (Pinus ponderosa)], and treated with different post-processing techniques. Twenty-four hour batch equilibration measured sorption of ¹⁴C-labelled atrazine or 2,4-D to two soil types with and without biochar amendments. Herbicide efficacy was measured with and without biochar using speed of seed germination tests of sensitive species. Biochar amended soils sorbed more herbicide than untreated soils, with major differences due to biochar application rate but minor differences due to biochar type or post-process handling technique. Biochar presence increased the speed of seed germination compared with herbicide alone addition. These data indicate that biochar addition to soil can increase herbicide sorption and reduce efficacy. Evaluation for site-specific biochar applications may be warranted to obtain maximal benefits without compromising other agronomic practices.     

Water quality parameters controlling the photodegradation of two herbicides in surface waters of the Columbia Basin,Washington

The water quality parameters nitrate-nitrogen, dissolved organic carbon, and suspended solids were correlated with photodegradation rates of the herbicides atrazine and 2,4-D in samples collected from four sites in the Columbia River Basin, Washington, USA. Surface water samples were collected in May, July, and October 2010 and analyzed for the water quality parameters. Photolysis rates for the two herbicides in the surface water samples were then evaluated under a xenon arc lamp. Photolysis rates of atrazine and 2,4-D were similar with rate constants averaging 0.025 h⁻¹ for atrazine and 0.039 h⁻¹ for 2,4-D. Based on multiple regression analysis, nitrate-nitrogen was the primary predictor of photolysis for both atrazine and 2,4-D, with dissolved organic carbon also a predictor for some sites. However, at sites where suspended solids concentrations were elevated, photolysis rates of the two herbicides were controlled by the suspended solids concentration. The results of this research provide a basis for evaluating and predicting herbicide photolysis rates in shallow surface waters.     

Kinetic of carbonaceous substrate in an upflow anaerobic sludge sludge blanket (UASB) reactor treating 2,4 dichlorophenol (2,4 DCP)

The performance of an upflow anaerobic sludge blanket (UASB) reactor treating 2,4 dichlorophenol (2,4 DCP) was evaluated at different hydraulic retention times (HRTs) using synthetic wastewater in order to obtain the growth substrate (glucose-COD) and 2,4 DCP removal kinetics. Treatment efficiencies of the UASB reactor were investigated at different hydraulic retention times (2-20 h) corresponding to a food to mass (F/M) ratio of 1.2-1.92 g-COD g(-1) VSS day(-1). A total of 65-83% COD removal efficiencies were obtained at HRTs of 2-20 h. In all, 83% and 99% 2,4 DCP removals were achieved at the same HRTs in the UASB reactor. Conventional Monod, Grau Second-order and Modified Stover-Kincannon models were applied to determine the substrate removal kinetics of the UASB reactor. The experimental data obtained from the kinetic models showed that the Monod kinetic model is more appropriate for correlating the substrate removals compared to the other models for the UASB reactor. The maximum specific substrate utilization rate (k) (mg-COD mg(-1) SS day(-1)), half-velocity concentration (K(s)) (mg COD l(-1)), growth yield coefficient (Y) (mg mg(-1)) and bacterial decay coefficient (b) (day(-1)) were 0.954 mg-COD mg(-1) SS day(-1), 560.29 mg-COD l(-1), 0.78 mg-SS g(-1)-COD, 0.093 day(-1) in the Conventional Monod kinetic model. The second-order kinetic coefficient (k(2)) was calculated as 0.26 day(-1) in the Grau reaction kinetic model. The maximum COD removal rate constant (U(max)) and saturation value (K(B)) were calculated as 7.502 mg CODl(-1)day(-1) and 34.56 mg l(-1)day(-1) in the Modified Stover-Kincannon Model. The (k)(mg-2,4 DCP mg(-1) SS day(-1)), (K(s)) (mg 2,4 DCPl(-1)), (Y) (mg SS mg(-1) 2,4 DCP) and (k(d)) (day(-1)) were 0.0041 mg-2,4 DCP mg(-1) SS day(-1), 2.06 mg-COD l(-1), 0.0017 mg-SS mg(-1) 2,4 DCP and 3.1 x 10(-5) day(-1) in the Conventional Monod kinetic model for 2,4 DCP degradation. The second-order kinetic coefficient (k(2)) was calculated as 0.30 day(-1) in the Grau reaction kinetic model. The maximum 2,4 DCP removal rate constant (U(max)) and saturation value (K(B)) were calculated as 0.01 mg COD l(-1) day(-1) and 9.8 x 10(-3) mg l(-1) day(-1) in the Modified Stover-Kincannon model.     

水中本底成分对O3/H2O2氧化降解2,4-D的影响

重点考察了水中本底成分对O3/H2O2高级氧化工艺去除水中微量农药2,4-D的影响规律.实验结果表明,自来水本底比蒸馏水本底更有利于水中2,4-D的去除;自由基捕获剂叔丁醇对于2,4-D的催化臭氧化反应具有比较明显的抑制作用,但是HCO3-却对水中2,4-D的氧化降解有一定的促进作用;一定浓度的腐殖酸对于2,4-D的催化臭氧化反应具有比较明显的促进作用,较高浓度的腐殖酸对于2,4-D的催化臭氧化反应具有明显的抑制作用;水中的Na 、K 、Mg2 、Ca2 、Cu2 、Zn2 在较低浓度时对2,4-D的降解没有明显影响,在高浓度时有一定的抑制作用;Co2 、Ni2 、Ca2 、Cr3 在较低浓度时对2,4-D的氧化降解有促进作用,高浓度时候有一定的抑制作用.     

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.     

Detectability of phenoxy herbicides by chlorophyll fluorescence

Abstract

Trace amounts of 2,4‐D ‐ which does not cause visible damage in plant ‐ are detectable in plant leaves by chlorophyll fluorescence regeneration in two ways. (I) In illuminated leaves the level of first and second fluorescence peak differ in treated and untreated leaves. (2) By taking buffer solution (pH=8.6) in dark‐adapted leaves under vacuum, the first, second and the other fluorescence decrease levels differ in untreated and 2,4‐D or MCPA treated leaves.     

Procedure for the determination of 2,4‐D and dicamba in inhalation,dermal, hand‐wash,and urine samples from spray applicators

Abstract

Analytical procedures for the simultaneous determination of residues of 2,4‐D and dicamba from polyurethane foam plug air samplers, ethylene glycol impregnated glass‐fiber filter paper dermal samplers, 1% sodium bicarbonate hand wash solution, and urine are presented. Residues were derivatized with diazomethane and quantitated using electron capture gas chromatography. Recoveries were greater than 80% at the limit of detection in all substrates. The limits of detection for both herbicides were 0.1 μg/foam plug and 0.5 μg/filter paper, and in the urine, 1.7 μg/100 mL and 5.0 μg/100 mL for dicamba and 2,4‐D, respectively.