Validation of the stomatal flux approach for the assessment of ozone visible injury in young forest trees. Results from the TOP (transboundary ozone pollution) experiment at Curno, Italy

This paper summarises some of the main results of a two-year experiment carried out in an Open-Top Chambers facility in Northern Italy. Seedlings of Populus nigra, Fagus sylvatica, Quercus robur and Fraxinus excelsior have been subjected to different ozone treatments (charcoal-filtered and non-filtered air) and soil moisture regimes (irrigated and non-irrigated plots). Stomatal conductance models were applied and parameterised under South Alpine environmental conditions and stomatal ozone fluxes have been calculated.The flux-based approach provided a better performance than AOT40 in predicting the onset of foliar visible injuries. Critical flux levels, related to visible leaf injury, are proposed for P. nigra and F. sylvatica (ranging between 30 and 33 mmol O₃ m⁻²). Soil water stress delayed visible injury appearance and development by limiting ozone uptake. Data from charcoal-filtered treatments suggest the existence of an hourly flux threshold, below which may occur a complete ozone detoxification.     

Response of Brazilian native trees to acute ozone dose

Ozone (O₃) is a toxic secondary pollutant able to cause an intense oxidative stress that induces visual symptoms on sensitive plant species. Controlled fumigation experiment was conducted with the aim to verify the O₃ sensibility of three tropical species: Piptadenia gonoachanta (Mart.) Macbr. (Fabaceae), Astronium graveolens Jacq. (Anacardiaceae), and Croton floribundus Spreng. (Euphorbiaceae). The microscopical features involved in the oxidative stress were recognized based on specific histochemical analysis. The three species showed visual symptoms, characterized as necrosis and stippling between the veins, mostly visible on the adaxial leaf surface. All the studied species presented hypersensitive-like response (HR-like), and peroxide hydrogen accumulation (H₂O₂) followed by cell death and proanthocyanidin oxidation in P. gonoachanta and A. graveolens. In P. gonoachanta, a decrease in chlorophyll autofluorescence occurred on symptomatic tissues, and in A. graveolens and C. floribundus, a polyphenol compound accumulation occurred. The responses of Brazilian native species were similar to those described for sensitive species from temperate climate, and microscopical markers may be useful for the detection of ozone symptoms in future studies in the field.     

Photocatalytic removal of organic pollutants in aqueous solution by Bi(4)Nb(x)Ta((1-x))O(8)I

In this work, Bi₄Nb_xTa_(1−x)O₈I photocatalysts have been synthesized by solid state reaction method and characterized by powder X-ray diffraction, scanning electron microscope and UV-Vis near infrared diffuse reflectance spectroscopy. The photocatalytic activity of these photocatalysts was evaluated by the degradation of methyl orange (MO) in aqueous solutions under visible light, UV light and solar irradiation. The effects of catalyst dosage, initial pH and MO concentration on the removal efficiency were studied, and the photocatalytic reaction kinetics of MO degradation as well. The results indicated that Bi₄Nb_xTa_(1−x)O₈I exhibited high photocatalytic activity for the removal of MO in aqueous solutions. For example, the removal efficiency of MO by Bi₄Nb_0.1Ta_0.9O₈I was as high as 92% within 12 h visible light irradiation under the optimal conditions: initial MO concentration of 5-10 mg L⁻¹, catalyst dosage of 6 g L⁻¹ and natural pH (6-8), the MO molecules could be completely degradated by Bi₄Nb_0.1Ta_0.9O₈I within 40 min under UV light irradiation, and the photodegradation efficiency reaches to 60% after 7 h solar irradiation. Furthermore, the photocatalytic degradation of Bisphenol A (BPA) was also investigated under visible light irradiation. It is found that 99% BPA could be mineralized by Bi₄Nb_0.1Ta_0.9O₈I after 16 h visible light irradiation. Through HPLC/MS, BOD, TOC, UV-Vis measurements, we determined possible degradation products of MO and BPA. The results indicated that MO was degradated into products which are easier to be biodegradable and innocuous treated, and BPA could be mineralized completely. Furthermore, the possibility for the photosensitization effect in the degradation process of MO under visible light irradiation has been excluded.     

Cutleaf coneflower (Rudbeckia laciniata L.) response to ozone and ethylenediurea (EDU)

Cutleaf coneflower (Rudbeckia laciniata L.) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), non-filtered air (NF) or twice-ambient (2×) ozone (O₃). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O₃ (100%). Elevated O₃ resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDU × O₃ interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O₃ altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations.     

Enhanced nitrogen deposition exacerbates the negative effect of increasing background ozone in Dactylis glomerata, but not Ranunculus acris

The combined impacts of simulated increased nitrogen (N) deposition (75 kg N ha⁻¹ yr⁻¹) and increasing background ozone (O₃) were studied using two mesotrophic grassland species (Dactylis glomerata and Ranunculus acris) in solardomes, by means of eight O₃ treatments ranging from 15.5 ppb to 92.7 ppb (24 h average mean). A-C_i curves were constructed for each species to gauge effects on photosynthetic efficiency and capacity, and effects on biomass partitioning were determined after 14 weeks. Increasing the background concentration of O₃ reduced the healthy above ground and root biomass of both species, and increased senesced biomass. N fertilisation increased biomass production in D. glomerata, and a significantly greater than additive effect of O₃ and N on root biomass was evident. In contrast, R. acris biomass was not affected by high N. The study shows the combined effects of these pollutants have differential implications for carbon allocation patterns in common grassland species.     

Ecotoxicologial evaluation of wastewater ozonation based on detritus-detritivore interactions

Advanced oxidation technologies such as ozonation have been proposed to improve removal efficiency of micropollutants during wastewater treatment. In a meta-analysis of peer-reviewed literature, we found no ecotoxicological effects of wastewater ozonation on invertebrates (n = 82), but significant adverse effects on bacteria (n = 24) and fish (n = 5). As information on functional endpoints or trophic interactions is lacking, we applied a bioassay relating to leaf litter decomposition to fill this gap. Leaf discs exposed to ozone-treated wastewater with a high (1.04 mg O₃ (mg DOC)⁻¹, n = 49) ozone concentration were significantly preferred by an aquatic detritivore, Gammarus fossarum, over discs conditioned in wastewater not treated with ozone. This effect might have been mediated by reduced bacterial and elevated fungal biomass, and appears to be the first demonstration of wastewater ozonation impacts on invertebrates and an associated ecosystem process. In accordance with the food-choice trials, chemical analyses revealed significantly decreased concentrations of organic micropollutants in wastewater treated with ozone at high concentrations. Thus, food-choice trials as applied here hold promise to assess environmental effects of advanced oxidation technologies in wastewater treatment and appear to be a valuable complement to the ecotoxicological toolbox in general.     

Direct and indirect impact of sewage sludge compost spreading on Quercus coccifera monoterpene emissions in a Mediterranean shrubland

Monoterpene emissions of Quercus coccifera L. were repeatedly measured during the two years following the spreading of a sewage sludge compost at rates of 50 Mg ha⁻¹ and 100 Mg ha⁻¹, in a twelve-year-old post-fire Mediterranean shrubland. We also monitored the patterns of change in soil and leaf nutrient content, plant water potential, chlorophyll fluorescence, and plant growth. Compost spreading resulted in weak changes in leaf nutrient content and plant water status, and therefore no significant effect on monoterpene emissions at leaf scale, except during one summer sampling, probably related to advanced leaf maturity with the highest compost rate. However, compost increased plant growth, particularly the leaf biomass. The results suggest that compost spreading in Mediterranean shrublands has no strong short-term effect on Q. coccifera monoterpene emissions at leaf level, but may indirectly increase volatile organic compound fluxes at the stand scale, which may contribute to regional ozone pollution.     

Effect of 3 years' free-air exposure to elevated ozone on mature Norway spruce (Picea abies (L.) Karst.) needle epicuticular wax physicochemical characteristics

We examined the effect of ozone (O₃) on Norway spruce (Picea abies) needle epicuticular wax over three seasons at the Kranzberg Ozone Fumigation Experiment. Exposure to 2× ambient O₃ ranged from 64.5 to 74.2 μl O₃ l⁻¹ h AOT40, and 117.1 to 123.2 nl O₃ l⁻¹ 4th highest daily maximum 8-h average O₃ concentration. The proportion of current-year needle surface covered by wax tubes, tube aggregates, and plates decreased (P = 0.011) under 2× O₃. Epistomatal chambers had increased deposits of amorphous wax. Proportion of secondary alcohols varied due to year (P = 0.004) and O₃ treatment (P = 0.029). Secondary alcohols were reduced by 9.1% under 2× O₃. Exposure to 2× O₃ increased (P = 0.037) proportions of fatty acids by 29%. Opposing trends in secondary alcohols and fatty acids indicate a direct action of O₃ on wax biosynthesis. These results demonstrate O₃-induced changes in biologically important needle surface characteristics of 50-year-old field-grown trees.     

SMX degradation by ozonation and UV radiation: a kinetic study

The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV₂₅₄ radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV₂₅₄ radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8) × 10⁻³ and (1.7-18.9) × 10⁻³ s⁻¹, respectively. The second-order rate constants of SMX with ozone (k_O3), under varying operational parameters, were also determined and varied in the range of (0.60-3.38) ± 0.13 × 10⁵ M⁻¹ s⁻¹. In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX.     

Use of the antiozonant ethylenediurea (EDU) in Italy: verification of the effects of ambient ozone on crop plants and trees and investigation of EDU's mode of action

Twenty-four experiments where EDU was used to protect plants from ozone (O₃) in Italy are reviewed. Doses of 150 and 450 ppm EDU at 2-3 week intervals were successfully applied to alleviate O₃-caused visible injury and growth reductions in crop and forest species respectively. EDU was mainly applied as soil drench to crops and by stem injection or infusion into trees. Visible injury was delayed and reduced but not completely. In investigations on mode of action, EDU was quickly (<2 h) uptaken and translocated to the leaf apoplast where it persisted long (>8 days), as it cannot move via phloem. EDU did not enter cells, suggesting it does not directly affect cell metabolism. EDU delayed senescence, did not affect photosynthesis and foliar nitrogen content, and stimulated antioxidant responses to O₃ exposure. Preliminary results suggest developing an effective soil application method for forest trees is warranted.     

Short term recovery of periphyton photosynthesis after pulse exposition to the photosystem II inhibitors atrazine and isoproturon

Aquatic organisms are exposed to fluctuating concentrations of herbicides which contaminate rivers following their use for agricultural or domestic purposes. The development of sensitive bioanalytical tests enabling us not only to detect the effects of those pollutants but to take into account this pattern of exposure should improve the ecological relevance of river toxicity assessment. In this respect, the use of chlorophyll fluorescence measurements is a convenient way to probe the effect of photosystem II (PSII) inhibitors on primary producers. This study was devoted to validate the combined use of two fluorescence parameters, the effective and the optimal quantum yields of PSII photochemistry (Φ_PSII and F_v/F_m), as reliable biomarkers of initial isoproturon (IPU) or atrazine (ATZ) toxicity to natural periphyton in a pulse exposition scenario. Φ_PSII and F_v/F_m were regularly estimated during a 7 h-exposure to each pollutant (0-100 μM) and also later after being transferred in herbicide-free water (up to 36 h). Our results showed that IPU was more toxic than ATZ, but with effects reversible within 12 h. Moreover, these two similarly acting herbicides (i.e. same target site) presented contrasted short term recovery patterns, regarding the previous exposure duration.     

Using optical remote sensing techniques to track the development of ozone-induced stress

In this paper, a literature review about optical remote sensing (RS) of O₃ stress is presented. Studies on O₃-induced effects on vegetation reflectance have been conducted since late ‘70s based on the analysis of optical RS data. Literature review reveals that traditional RS techniques were able to detect changes in leaf and canopy reflectance related to O₃-induced stress when visible symptoms already occurred. Only recently, advanced RS techniques using hyperspectral sensors, demonstrated the feasibility of detecting the stress in its early phase by monitoring excess energy dissipation pathways such as chlorophyll fluorescence and non-photochemical quenching (NPQ). Steady-state fluorescence (Fs), measured by exploiting the Fraunhofer line depth principle and NPQ related xanthophyll-cycle, estimated through the photochemical reflectance index (PRI) responded to O₃ fumigation before visible symptoms occurred. This opens up new possibilities for the early detection of vegetation O₃ stress by means of hyperspectral RS.     

Responses to ozone pollution of alfalfa exposed to increasing salinity levels

Stomatal closure and biosynthesis of antioxidant molecules are two fundamental components of the physiological machinery that lead to stress adaptation during plant's exposure to salinity. Since high stomatal resistance may also contribute in counteracting O₃ damages, we hypothesized that soil salinization may increase O₃ tolerance of crops. An experiment was performed with alfalfa grown in filtered (AOT40 = 0 in both years) and non-filtered (AOT40 = 9.7 in 2005 and 6.9 ppm h in 2006) open-top chambers. Alfalfa yield was reduced by O₃ (−33%) only in plants irrigated with salt-free water, while the increasing levels of soil salinity until 1.06 dS m⁻¹ reduced both stomatal conductance and plant O₃ uptake, thus linearly reducing O₃ effects on yield. Therefore a reliable flux-based model for assessing the effects of O₃ on crop yield should take into account soil salinity.     

Photocatalytic mineralization of hydroperfluorocarboxylic acids with heteropolyacid H₄SiW₁₂O₄₀ in water

The decomposition of hydroperfluorocarboxylic acids [H-PFCAs; HC_nF_2nCOOH (n = 4 and 6)] induced by heteropolyacid photocatalyst H₄SiW₁₂O₄₀ in water was investigated, and the results are compared with the results for the corresponding perfluorocarboxylic acids (PFCAs; C_nF_2n+1COOH). This is the first report on the photochemical decomposition of H-PFCAs, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative PFCAs. H-PFCAs were not decomposed by irradiation with UV-Visible light (>290 nm) in the absence of H₄SiW₁₂O₄₀. In contrast, UV-Visible light irradiation of H-PFCAs in the presence of H₄SiW₁₂O₄₀ efficiently decomposed H-PFCAs to F⁻ and CO₂. The decomposition reactions showed pseudo-first-order kinetics, and the decomposition rate constants were 1.8-2.5 times higher than those for the corresponding PFCAs. The reaction mechanism can be explained by elimination of H⁺ from the ω-H atom of the H-PFCAs by the excited catalyst, followed by formation of perfluorodicarboxylic acids.     

Responses of herbaceous plants to urban air pollution: Effects on growth, phenology and leaf surface characteristics

Vehicle exhaust emissions are a dominant feature of urban environments and are widely believed to have detrimental effects on plants. The effects of diesel exhaust emissions on 12 herbaceous species were studied with respect to growth, flower development, leaf senescence and leaf surface wax characteristics. A diesel generator was used to produce concentrations of nitrogen oxides (NO_x) representative of urban conditions, in solardome chambers. Annual mean NO_x concentrations ranged from 77 nl l^−l to 98 nl l⁻¹, with NO:NO₂ ratios of 1.4-2.2, providing a good experimental simulation of polluted roadside environments. Pollutant exposure resulted in species-specific changes in growth and phenology, with a consistent trend for accelerated senescence and delayed flowering. Leaf surface characteristics were also affected; contact angle measurements indicated changes in surface wax structure following pollutant exposure. The study demonstrated clearly the potential for realistic levels of vehicle exhaust pollution to have direct adverse effects on urban vegetation.     

Toxicity of nanoparticulate and bulk ZnO, Al2O3 and TiO2 to the nematode Caenorhabditis elegans

Limited information is available on the environmental behavior and associated potential risk of manufactured oxide nanoparticles (NPs). In this research, toxicity of nanoparticulate and bulk ZnO, Al₂O₃ and TiO₂ were examined to the nematode Caenorhabditis elegans with Escherichia coli as a food source. Parallel experiments with dissolved metal ions from NPs were also conducted. The 24-h median lethal concentration (LC₅₀) and sublethal endpoints were assessed. Both NPs and their bulk counterparts were toxic, inhibiting growth and especially the reproductive capability of the nematode. The 24-h LC₅₀ for ZnO NPs (2.3 mg L⁻¹) and bulk ZnO was not significantly different, but significantly different between Al₂O₃ NPs (82 mg L⁻¹) and bulk Al₂O₃ (153 mg L⁻¹), and between TiO₂ NPs (80 mg L⁻¹) and bulk TiO₂ (136 mg L⁻¹). Oxide solubility influenced the toxicity of ZnO and Al₂O₃ NPs, but nanoparticle-dependent toxicity was indeed observed for the investigated NPs.     

Polarity effect of pulsed corona discharge for the oxidation of gaseous elemental mercury

The effect of polarity on the oxidation of Hg⁰ was examined in the presence of O₂ via a pulsed corona discharge (PCD). The experimental result showed no difference in the energy yield of Hg⁰ oxidation at both positive and negative PCDs (∼8 μg Hg W h⁻¹ at following conditions: total flow rate = 2 L min⁻¹ (Hg⁰ = 50 μg N m⁻³, O₂ = 10%, and N₂ balance), temperature = 150 °C, and specific energy density = 5-15 W h N m⁻³). This suggests that the positive PCD process used to control gaseous air pollutants may play an essential key role in Hg⁰ oxidation because it consumes enough energy (∼15 W h N m⁻³) but an electrical precipitator could not because it consumes less energy (∼0.3 W h N m⁻³) to oxidize Hg⁰.     

Protection of palak (Beta vulgaris L. var Allgreen) plants from ozone injury by ethylenediurea (EDU): Roles of biochemical and physiological variations in alleviating the adverse impacts

Ameliorative effects of ethylenediurea (N-[2-(2-oxo-1-imidazolinidyl) ethyl]-N′ phenylurea, abbreviated as EDU) against ozone stress were studied on selected growth, biochemical, physiological and yield characteristics of palak (Beta vulgaris L. var Allgreen) plants grown in field at a suburban site of Varanasi, India. Mean eight hourly ozone concentration varied from 52 to 73 ppb which was found to produce adverse impacts on plant functioning and growth characteristics. The palak plants were treated with 300 ppm EDU at 10 days after germination at 10 days interval up to the plant maturity. Lipid peroxidation in EDU treated plants declined significantly as compared to non-EDU treated ones. Significant increment in F_v/F_m ratio in EDU treated plants as compared to non-EDU treated ones was recorded. EDU treated plants showed significant increment in ascorbic acid contents and reduction in peroxidase activity as compared to non-EDU treated ones. As a result of the protection provided by EDU against ozone induced stress on biochemical and physiological characteristics of palak, the morphological parameters also responded positively. Significant increments were recorded in shoot length, number of leaves plant⁻¹, leaf area and root and shoot biomass of EDU treated plants as compared to non-EDU treated ones. Contents of Na, K, Ca, Mg and Fe were higher in EDU treated plants as compared to non-EDU treated ones. The present investigation proves the usefulness of EDU in partially ameliorating ozone injury in ambient conditions.     

Effects of chronic elevated ozone exposure on gas exchange responses of adult beech trees (Fagus sylvatica) as related to the within-canopy light gradient

The effects of elevated O₃ on photosynthetic properties in adult beech trees (Fagus sylvatica) were investigated in relation to leaf mass per area as a measure of the gradually changing, within-canopy light availability. Leaves under elevated O₃ showed decreased stomatal conductance at unchanged carboxylation capacity of Rubisco, which was consistent with enhanced δ¹³C of leaf organic matter, regardless of the light environment during growth. In parallel, increased energy demand for O₃ detoxification and repair was suggested under elevated O₃ owing to enhanced dark respiration. Only in shade-grown leaves, light-limited photosynthesis was reduced under elevated O₃, this effect being accompanied by lowered F_v/F_m. These results suggest that chronic O₃ exposure primarily caused stomatal closure to adult beech trees in the field regardless of the within-canopy light gradient. However, light limitation apparently raised the O₃ sensitivity of photosynthesis and accelerated senescence in shade leaves.