Biochemical and photochemical degradation of the herbicide lontrel

Degradation of Lontrel by activated sludge (AS) of purification works and UV irradiation was studied. 3,6-Dichloropicolinic acid (3,6-DCPA, the main active principle of Lontrel) was not degraded by the microbial association of the AS. AS treated with nitrosourea under various conditions did not oxidize Lontrel either. Hard UV radiation degraded 3,6-DCPA within 4-24 h at constant sparging (bubbling) of air, oxygen, or ozone. The rate of oxidation with oxygen or ozone bubbling was three to four times higher than with air bubbling. It was found that the products of photochemical degradation of Lontrel were also toxic; however, they were readily degraded by AS microorganisms without additional AS treatment.     

Killing bacteria present on surfaces in films or in droplets using microwave UV lamps

The killing of bacteria on surfaces by two types of UV sources generated by microwave radiation is described. In both cases, UV radiation is produced by gas-discharge electrodeless lamps (Ar/Hg) excited by microwaves generated by a power supply from a standard domestic microwave oven. For UV lamp excitation, one of these sources makes use of a coaxial line with a truncated outer electrode that allows the excitation of gases and gaseous mixtures over a wide range of pressures at a comparatively low microwave power. In the second source, UV lamps are placed inside a microwave oven. Ultraviolet generated by the two sources was used to destroy vegetative Escherichia coli bacteria dispersed in thin films and in droplets on surfaces. Two types of UV lamps were used in the study. The first was constructed of quartz that filtered UV below 200 nm preventing the dissociation of oxygen in air and, hence, ozone production. The second type of tube was transparent to UV below 200 nm facilitating ozone production in air surrounding it. It was shown that bacterial cells dispersed in films on surfaces are killed more rapidly than cells present in droplets when using the lamps producing ozone and UV radiation. The UV sources described can effect rapid killing and constitute a cost-effective treatment of food and other surfaces, and, the destruction of airborne viruses and bacteria. The lamps can also be utilised for the rapid eradication of microorganisms in liquids.     

Products of the photolysis of 3,6-dichloropicolinic acid (the herbicide lontrel) in aqueous solutions

We studied the composition of products of the photochemical degradation of 3,6-dichloropicolinic acid (DCPA), the active principle of Lontrel, a herbicide broadly used in agriculture. Ultraviolet irradiation (mimicking the natural sunlight action) did not degrade DCPA completely to environmentally safe products. The rate of DCPA degradation was notably lower when distilled water was replaced by river water and even lower in sea water. Chromatomass spectrometry revealed 9 compounds among the photolysis products, in addition to undegraded DCPA.     

Ozone-3,6-dihydroxynaphtha-2,7-disulphonate chemiluminescence system is used for online ozone detection

The chemiluminescence (CL) reaction between ozone and 3,6-dihydroxynaphtha-2,7-disulphonate (DNDS) was found under alkaline conditions. Therefore, a novel CL system for ozone detection was established. The CL signal of the CL system is weak, and the CL signal is enhanced by adding nonionic surfactants. It was found that adding 16.4 g/l Triton X-100 can enhance the CL signal. The CL reagent activated by ultraviolet (UV) light produced a CL signal was nearly 10 times stronger than the CL reagent not activated by UV light; the CL signal was enhanced by adding 8 g/l NaHCO₃ to the CL reagent irradiated by UV light. Through the optimization of these test conditions, a high-selectivity, high-sensitivity online detection method for ozone CL was established. The linear range was 0.5–150 ppbv, and the limit of detection (LOD) was 0.092 ppbv (S/N = 3).     

Products of the photolysis of 3,6-dichloropicolinic acid (the herbicide lontrel) in aqueous solutions

We studied the composition of products of the photochemical degradation of 3,6-dichloropicolinic acid (DCPA), the active principle of Lontrel, a herbicide broadly used in agriculture. Ultraviolet irradiation (mimicking the natural sunlight action) did not degrade DCPA completely to environmentally safe products. The rate of DCPA degradation was notably lower when distilled water was replaced by river water and even lower in sea water. Chromatomass spectrometry revealed 9 compounds among the photolysis products, in addition to undegraded DCPA.     

Priming responses of leek (Allium porrum L.) seeds to different dissolved oxygen levels in the osmoticum

Leek seeds (Allium porrum L.) cv. Winterreuzen were treated for 5 days in stirred bioreactors containing a -1.0 MPa polyethylene glycol (PEG 6000) solution. The level of dissolved oxygen was controlled from zero to approximately two and a half times that of saturation with respect to atmospheric air by bubbling through 0₂/N₂ gas blends from 0% O₂ to 50% O₂. The treatment with 0% O₂ (i.e. bubbling with N₂) gave no reduction in germination time compared to untreated seeds after allowing for the time for water imbibition. As the proportion of oxygen was increased, a rapid reduction was observed until a concentration equivalent to air was used. Further increases to the maximum, produced only a marginal further improvement. The reduction in germination times for seeds that had been cabinet dried was longer for all treatments due to the time required for re-imbibition of water but the general response to priming was the same as with undried seeds. Only dried seeds treated with air or higher oxygen concentrations showed enhanced synchronicity of germination times. The percentage germination of seeds from all treatments was the same, including the treatment with nitrogen gas. These tests help to explain the recently reported advantages of using enriched air for seed priming and are one of the necessary protocols for ensuring satisfactory bulk priming.     

Radiation-induced fluctuation of the polysome content in adequately oxygenated tetrahymena pyriformis.

The polysome content of the ciliate protozoan Tetrahymena pyriformis is transiently reduced by gamma-irradiation. In order to test whether this is a result of a respiration-produced or radiation-produced hypoxia or some other mechanism, the oxygen content of the culture was determined during and after irradiation, and the polysome contents and rates of amino acid incorporation were measured with and without air bubbling. Irradiation (40 krad at approximately 3 krad/min) produced approximately a 25 per cent loss in dissolved O2 content in the medium. This decrease is not sufficient to affect the polysome level, since (a) the same radiation-induced loss of polysomes and inhibiition of amino acid incorporation was observed whether or not the culture was bubbled with air during the irradiation and (b) bubbling unirradiated cultures with gas mixtures containing as little as 17 per cent of the normal O2 content did not influence the polysome level. As long as the cells are irradiated as a shallow layer in open flasks, replacement of O2 from the gas phase appears adequate, and neither respiration-induced nor radiation-induced hypoxia masks the effects of the radiation.     

Apoplastic Ascorbate Does not Prevent the Oxidation of Fluorescent Amphiphilic Dyes by Ambient and Elevated Concentrations of Ozone in Leavesl

Cut leaves of spinach were infiltrated with solutions containingoxidation-sensitive fluorescent dyes. Excess solution was removedfrom the intercellular space by centrifugation. Fluorescenceof the dyes D494 and D283 started to decrease immediately afterthe onset of fumigation with ozone at concentrations similarto or not much higher than ambient concentrations in air onsunny days. Only part of ozone entering the leaves was interceptedby the dye. The major part was degraded by unspecified reactions.Photosynthesis was not inhibited while the introduced dye wasoxidized by ozone, showing that open stomata facilitated gasexchange after the introduction of dye into the leaf interior.Feeding of ascorbate to the leaves via the petiole failed toaffect the ozone-dependent decrease in fluorescence emissionfrom the dye. Likewise, infiltration of leaves by solutionscontaining dye and 10 mM ascorbate did not produce significantprotection of the dye against oxidation by ozone. However, suchprotection was observed in vitro, when solutions of dye andascorbate were bubbled with air containing ozone. Although thereis little doubt that apoplastic ascorbate occupies a centralposition in the antioxi-dative defense of leaf tissue, we aresurprised to find that it is much less effective than expectedto decrease the oxidation of fluorescent lipophilic probes whichhad been introduced into the leaf interior. The data suggestthat ascorbate is not a primary reductant of ozone in the apoplast.With a microscope-mounted CCD-camera connected to the gas exchangeequipment we obtained spatial information on the fluorescencesignal and present first results on an heterogeneous distributionof ozone action. (Received June 20, 1997; Accepted December 26, 1997)     

Responses to solar ultraviolet-B radiation in a shrub-dominated natural ecosystem of Tierra del Fuego (southern Argentina)

A study was made of the effects of solar ultraviolet‐B radiation (UV‐B) on the growth of the dominant plant species of a shrub‐dominated ecosystem in Tierra del Fuego. This part of southern Argentina can be under the direct influence of the Antarctic ‘ozone hole’ during the austral spring and lingering ozone‐depleted air during the summer. The plant community is dominated by an evergreen shrub (Chiliotrichum diffusum) with an herbaceous layer of Gunnera magellanica and Blechnum penna‐marina in the interspaces between the shrubs. Inspections of ozone trends indicate that the springtime and summertime ozone column over Tierra del Fuego has decreased by 10–13% from 1978/9 to 1998/9. In a set of well‐replicated field plots, solar UV‐B was reduced to approximately 15–20% of the ambient UV‐B using plastic films. Polyester films were used to attenuate UV‐B radiation and UV‐transparent films (～90% UV‐B transmission) were used as control. Treatments were imposed during the growing season beginning in 1996 and continued for three complete growing seasons. Stem elongation of the shrub C. diffusum was not affected by UV‐B attenuation in any of the three seasons studied. However, frond length of B. penna‐marina under attenuated UV‐B was significantly greater than that under near‐ambient UV‐B in all three seasons. Attenuation of solar UV‐B also promoted the expansion of G. magellanica leaves in two of the growing seasons. Differences between treatments in leaf or frond length in B. penna‐marina and G. magellanica did not exceed 12%. Another significant effect of UV‐B attenuation was a promotion of insect herbivory in G. magellanica, with a 25–75% increase in the leaf area consumed. Changes in plant phenology or relative species cover were not detected within the time frame of this study. The results suggest that the increase in UV‐B radiation associated with the erosion of the ozone layer might be affecting the functioning of this ecosystem to some degree, particularly by inhibiting the growth of some plant species and by altering plant–insect interactions.     

Degradation of 1,3-dichloropropene by a soil bacterial consortium and Rhodococcus sp. AS2C isolated from the consortium

A bacterial consortium capable of degrading the fumigant 1,3-D ((Z)- and (E)-1,3-dichloropropene) was enriched from an enhanced soil. This mixedculture degraded (Z)- and (E)-1,3-D only in the presence of a suitable biodegradable organic substrate, such as tryptone, tryptophan, or alanine. After 8 months of subculturing at 2- to 3-week intervals, a strain of Rhodococcus sp. (AS2C) that was capable of degrading 1,3-D cometabolically in the presenceof a suitable second substrate was isolated. (Z)-3-chloroallyl alcohol (3-CAA) and (Z)-3-chloroacrylic acid (3-CAAC), and (E)-3-CAA and (E)-3-CAAC were the metabolites of (Z)- and (E)-1,3-D, respectively. (E)-1,3-D was degraded faster than (Z)-1,3-D by the strain AS2C and the consortium. AS2C also degraded (E)-3-CAA faster than (Z)-3-CAA. Isomerization of (E)-1,3-D to (Z)-1,3-D orthe (Z) form to the (E) form did not occur.     

Specificity of aFlavobacterium in the metabolism of substituted chlorobenzoates

Summary A strain ofFlavobacterium breve capable of utilizing 3,5-dichlorosalicylate as a sole source of carbon and energy was identified. Degradation of 3,5-dichlorosolicylate, was specific as this strain did not metabolize dicamba (3,6-dichloro-2-methoxybenzoic acid), 3,5-dicamba (3,5-dichloros2-methoxybenzoic acid), or 3,6-dichlorosalicylate. The organism was able to remove completely 3,5-dichlorosalicylate in the presence of three times as much 3,6-dichlorosalicylate being degraded. The organism was able to utilize 3,5-dichlorosalicylate at concentrations up to 1000g/ml. A mixture of 3,5 and 3,6-dichlorosalicylate isomers purified by biological destruction of the unwanted isomer (3,5-dichlorosalicylate) would be useful for producing isomerically pure dicamba, an important herbicide.     

Mechanism of site-specific DNA damage induced by ozone

Ozone has been shown to induce lung tumors in mice. The reactivity of ozone with DNA in an aqueous solution was investigated by a DNA sequencing technique using 32P-labeled DNA fragments. Ozone induced cleavages in the deoxyribose-phosphate backbone of double-stranded DNA, which were reduced by hydroxyl radical scavengers, suggesting the participation of hydroxyl radicals in the cleavages. The ozone-induced DNA cleavages were enhanced with piperidine treatment, which induces cleavages at sites of base modification, but the inhibitory effect of hydroxyl radical scavengers on the piperidine-induced cleavages was limited. Main piperidine-labile sites were guanine and thymine residues. Cleavages at some guanine and thymine residues after piperidine treatment became more predominant with denatured single-stranded DNA. Exposure of calf thymus DNA to ozone resulted in a dose-dependent increase of the 8-oxo-7,8-dihydro-2'-deoxyguanosine formation, which was partially inhibited by hydroxyl radical scavengers. ESR studies using 5,5-dimethylpyrroline-N-oxide (DMPO) showed that aqueous ozone produced the hydroxyl radical adduct of DMPO. In addition, the fluorescein-dependent chemiluminescence was detected during the decomposition of ozone in a buffer solution and the enhancing effect of D2O was observed, suggesting the formation of singlet oxygen. However, no or little enhancing effect of D2O on the ozone-induced DNA damage was observed. These results suggest that DNA backbone cleavages were caused by ozone via the production of hydroxyl radicals, while DNA base modifications were mainly caused by ozone itself and the participation of hydroxyl radicals and/or singlet oxygen in base modifications is small, if any. A possible link of ozone-induced DNA damage to inflammation-associated carcinogenesis as well as air pollution-related carcinogenesis is discussed.     

Repair and tolerance of oxidative DNA damage in plants

DNA damage caused by exposure to reactive oxygen species is one of the primary causes of DNA decay in most organisms. In plants, endogenous reactive oxygen species (ROS) are generated not only by respiration and photosynthesis, but also by active responses to certain environmental challenges, such as pathogen attack. Significant extracellular sources of activated oxygen include air pollutants such as ozone and oxidative effects of UV light and low-level ionizing radiation. Plants are well equipped to cope with oxidative damage to cellular macromolecules, including DNA. Oxidative attack on DNA generates both altered bases and damaged sugar residues that undergo fragmentation and lead to strand breaks. Recent advances in the study of DNA repair in higher plants show that they use mechanisms similar to those present in other eukaryotes to remove and/or tolerate oxidized bases and other oxidative DNA lesions. Therefore, plants represent a valuable model system for the study of DNA oxidative repair processes in eukaryotic cells.     

Growth and cell wall changes in rice coleoptiles growing under different conditions I. Changes in turgor pressure and cell wall polysaccharides during intact growth

The effect of the oxygen supply on growth, water absorptionof cells and cell wall changes was studied in coleoptiles ofrice seedlings growing under three different conditions: underwater, under water with constant air bubbling and in air. Coleoptilegrowth was larger when they were grown under water than in waterwith air bubbling and in air. Coleoptile growth under waterwas limited by the suction force of their cells rather thanby mechanical properties of the cell wall, while that of thecoleoptiles growing under the other two conditions was limitedby the cell wall rigidity. A decrease in the relative amountof noncellulosic glucose of the cell wall, and an increase inthe noncellulosic xylose during coleoptile growth were foundfor all three culture conditions. ¹ Present address: Departamento de Fisiologia Vegetal, Facultadde Ciencias, Universidad, Salamanca, Spain. (Received May 21, 1979; )     

Extractive biofilm membrane bioreactor with energy recovery from excess aeration and new membrane fouling control

Hybrid biofilm membrane bioreactor (BF-MBR) system featuring new mechanisms for recovering the excess energy from air bubbling flow in the biofilm reactor and for controlling membrane biofouling was preliminarily investigated in this study. Alternative design of the biofilm reactor was developed to utilize the bubbling flow from the lower aerobic chamber to generate a mechanical mixing in the upper anoxic chamber in the vertical biofilm reactor. Suspended solid (SS) concentration in the system was hydrodynamically controlled to be lower than 70 mg/L. The ultraviolet (UV) inactivation unit was integrated with the membrane filtration tank to limit biological activities for biofoulant productions and to decelerate the unwanted biofilm formation in the permeate tube. Membrane relaxations at various operating conditions were studied for optimum membrane fouling reductions under low SS environment. Combinations of membrane relaxation and the UV inactivation significantly prolonged sustainable operation periods of the membrane filtration in the BF-MBR process.     

Ozone tolerance in snap bean is associated with elevated ascorbic acid in the leaf apoplast

Ascorbic acid (AA) in the leaf apoplast has the potential to limit ozone injury by participating in reactions that detoxify ozone and reactive oxygen intermediates and thus prevent plasma membrane damage. Genotypes of snap bean ( Phaseolus vulgaris L) were compared in controlled environments and in open-top field chambers to assess the relationship between extracellular AA content and ozone tolerance. Vacuum infiltration methods were employed to separate leaf AA into extracellular and intracellular fractions. For plants grown in controlled environments at low ozone concentration (4 nmol mol⁻¹ ozone), leaf apoplast AA was significantly higher in tolerant genotypes (300–400 nmol g⁻¹ FW) compared with sensitive genotypes (approximately 50 nmol g⁻¹ FW), evidence that ozone tolerance is associated with elevated extracellular AA. For the open top chamber study, plants were grown in pots under charcoal-filtered air (CF) conditions and then either maintained under CF conditions (29 nmol mol⁻¹ ozone) or exposed to elevated ozone (67 nmol mol⁻¹ ozone). Following an 8-day treatment period, leaf apoplast AA was in the range of 100–190 nmol g⁻¹ FW for all genotypes, but no relationship was observed between apoplast AA content and ozone tolerance. The contrasting results in the two studies demonstrated a potential limitation in the interpretation of extracellular AA data. Apoplast AA levels presumably reflect the steady-state condition between supply from the cytoplasm and utilization within the cell wall. The capacity to detoxify ozone in the extracellular space may be underestimated under elevated ozone conditions where the dynamics of AA supply and utilization are not adequately represented by a steady-state measurement.     

Effect of oxygen, ozone and hydrogen peroxide bleaching stages on the contents and composition of extractives of Eucalyptus globulus kraft pulps

The effects of oxygen (O), ozone (Z) and hydrogen peroxide (P) bleaching stages on the composition and total amount of Eucalyptus globulus kraft pulp lipophilic extractives was studied. These bleaching stages led to the partial removal and to several oxidative transformations of fatty acids and sterols, the main lipophilic extractives found in the unbleached pulp. Unsaturated extractives were found to be partially degraded while saturated ones were, in general, stable. The oxygen and hydrogen peroxide bleaching stages were more effective than ozone in removing fatty acids from pulp, by dissolution in the liquid phase. On the other hand, the ozone stage was more effective in the oxidative degradation of sterols. Oxygen and hydrogen peroxide bleaching stages were also effective in sterols removal, but led to the formation of sterol oxidation derivatives, previously shown to be involved in the formation of pitch that accumulates in the bleaching filtrates.     

Effect of hexokinase activity on tomato root metabolism during prolonged hypoxia

Hypoxically induced tolerance to anoxia in roots of tomato (Solanum lycopersicum) was previously shown to depend on sucrose and the induction of sucrose synthase. In contrast to maize, root hexokinase (HXK) activities did not increase during hypoxia and glucose was unable to sustain glycolytic flux under anoxia. In this paper, we asked whether hypoxic metabolism in roots would be altered in transgenic tomato plants overexpressing either a plant (Arabidopsis) or a yeast (Saccharomyces cerevisiae) HXK and whether such modifications could be related to improved energy metabolism and consequently root tolerance under anoxia. Tomato plants grown hydroponically with shoots always maintained in air were submitted to a 7 d hypoxic treatment applied by stopping air bubbling. A combination of techniques including (1)H-nuclear magnetic resonance spectroscopy, RT-PCR and enzyme analyses was used to obtain a broad picture of hypoxic root metabolism. In normoxic conditions, HXK overexpression resulted in higher ADP and AMP levels only in roots of AtHXK1 transgenic plants. During hypoxic treatment, oxygen levels in the hydroponic tank decreased rapidly to 5 kPa within the first 2 d and then remained at 5 kPa throughout the 7 d experiment. Oxygen levels were similar at 5 and 20 cm below the water surface. A decline of the adenylate energy status was observed after 2 d of hypoxic treatment, with a further decrease by 7 d in roots of non-transgenic (WT) and ScHXK2, but not in AtHXK1 transgenic plants. Sucrose synthase activity increased to comparably higher levels at 7 d of hypoxic treatment in WT and ScHXK2 compared with AtHXK1 roots. Differences between WT and the transgenic plants are discussed with respect to the metabolic response to low (hypoxia) but not zero (anoxia) oxygen.     

Investigating deleterious effects of ultraviolet (UV) radiations on wheat by a quick method

Increasing air pollution has resulted in ozone depletion, which has led to an increase in the amount of ultraviolet (UV) radiation reaching the surface of earth posing hazardous effects on the plant yield. The chlorophyll a fluorescence transients were recorded in vivo using plant efficiency analyzer and analyzed according to JIP test, which can monitor photosystem II (PSII) behavior. This study aims to evaluate the sensitivity of different components of PSII to UV radiations and the extent of damage caused when wheat plants were exposed to UV radiations for 2 and 4 h. It was observed that functional disconnection of light harvesting complexes from PSII complex, accumulation of inactive reaction center, inactivation of oxygen evolving complex, and thus the linear electron transport process (ET₀/CS), were drastically affected by UV radiations. This study will contribute to understanding of the basic photosynthetic mechanisms affected in crop plants due to increased UV radiations. The knowledge obtained will be relevant for environmental and plant scientists to plan strategies to cope with stresses.     

Aerobic and two-stage anaerobic-aerobic sludge digestion with pure oxygen and air aeration

The degradability of excess activated sludge from a wastewater treatment plant was studied. The objective was establishing the degree of degradation using either air or pure oxygen at different temperatures. Sludge treated with pure oxygen was degraded at temperatures from 22 degrees C to 50 degrees C while samples treated with air were degraded between 32 degrees C and 65 degrees C. Using air, sludge is efficiently degraded at 37 degrees C and at 50-55 degrees C. With oxygen, sludge was most effectively degraded at 38 degrees C or at 25-30 degrees C. Two-stage anaerobic-aerobic processes were studied. The first anaerobic stage was always operated for 5 days HRT, and the second stage involved aeration with pure oxygen and an HRT between 5 and 10 days. Under these conditions, there is 53.5% VSS removal and 55.4% COD degradation at 15 days HRT - 5 days anaerobic, 10 days aerobic. Sludge digested with pure oxygen at 25 degrees C in a batch reactor converted 48% of sludge total Kjeldahl nitrogen to nitrate. Addition of an aerobic stage with pure oxygen aeration to the anaerobic digestion enhances ammonium nitrogen removal. In a two-stage anaerobic-aerobic sludge digestion process within 8 days HRT of the aerobic stage, the removal of ammonium nitrogen was 85%.