Mercury accumulation in grass and forb species as a function of atmospheric carbon dioxide concentrations and mercury exposures in air and soil

The goal of this study was to investigate the potential for atmospheric Hg degrees uptake by grassland species as a function of different air and soil Hg exposures, and to specifically test how increasing atmospheric CO(2) concentrations may influence foliar Hg concentrations. Four common tallgrass prairie species were germinated and grown for 7 months in environmentally controlled chambers using two different atmospheric elemental mercury (Hg major; 3.7+/-2.0 and 10.2+/-3.5 ng m(-3)), soil Hg (<0.01 and 0.15+/-0.08 micro g g(-1)), and atmospheric carbon dioxide (CO(2)) (390+/-18, 598+/-22 micro mol mol(-1)) exposures. Species used included two C4 grasses and two C3 forbs. Elevated CO(2) concentrations led to lower foliar Hg concentrations in plants exposed to low (i.e., ambient) air Hg degrees concentrations, but no CO(2) effect was apparent at higher air Hg degrees exposure. The observed CO(2) effect suggests that leaf Hg uptake might be controlled by leaf physiological processes such as stomatal conductance which is typically reduced under elevated CO(2). Foliar tissue exposed to elevated air Hg degrees concentrations had higher concentrations than those exposed to low air Hg degrees , but only when also exposed to elevated CO(2). The relationships for foliar Hg concentrations at different atmospheric CO(2) and Hg degrees exposures indicate that these species may have a limited capacity for Hg storage; at ambient CO(2) concentrations all Hg absorption sites in leaves may have been saturated while at elevated CO(2) when stomatal conductance was reduced saturation may have been reached only at higher concentrations of atmospheric Hg degrees . Foliar Hg concentrations were not correlated to soil Hg exposures, except for one of the four species (Rudbeckia hirta). Higher soil Hg concentrations resulted in high root Hg concentrations and considerably increased the percentage of total plant Hg allocated to roots. The large shifts in Hg allocation patterns-notably under soil conditions only slightly above natural background levels-indicate a potentially strong role of plants in belowground Hg transformation and cycling processes.     

The effect of winter stress on Ilex aquifolium L.previously fumigated with ozone

European Holly (Ilex aquifolium) received either charcoal-filtered air (CFA) or CFA with 70 nl l(-1) ozone added for 7 h day(-1) over a 28 day period. Plants were then transferred into cooling incubators for hardening (4 degrees C day/2 degrees C night; day length 12 h) for 7 days and then to the frosting stage (2 degrees C day and -5, -10 or -15 degrees C night) for 4 days. The plants were then placed in ambient conditions. Treatment produced significant differences in chlorophyll fluorescence data. Stomatal conductance was significantly higher for the ozone treatments though both showed a general decline over all temperature regimes. Ozone also significantly increased electrolyte leakage and reduced winter survival. These results show that ambient concentrations of ozone can reduce the tolerance of I. aquifolium to freezing stress, which may have serious implications for its establishment and survival.     

Gas-particle partitioning of PCDD/Fs in Nagoya urban air, Japan

Polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) in the atmosphere were sampled by a high-volume filter/sorbent air sampler at an urban (Nagoya, Japan) site from May 2000 to January 2001 under the average ambient temperatures ranging from 1 degrees C to 33 degrees C. The gas and particle phase concentrations of PCDD/Fs were measured and then the field gas-particle partitioning data were used to assess the Junge-Pankow adsorption model and the K(OA) absorption model. For both PCDDs and PCDFs, passable agreement was obtained between the measured and predicted particulate-band fraction (phi) values by the Junge-Pankow model, but the model tends to overpredict phi for all individual Cl4-8DD/F congeners, especially for the lower chlorinated congeners. On the other hand, good agreement was obtained between the measured and predicted log K(p) values by the K(OA) model for both PCDDs and PCDFs. However, the K(OA) absorption model did not fit the field data at low ambient temperature below 5 degrees C. The disagreement at low ambient temperatures was estimated to arise from the gas adsorption artifacts during the sampling. From the validation by the field measurement data in Nagoya urban air, it is found that the K(OA) absorption model is capable of predicting more accurately gas-particle partitioning of PCDD/Fs than the Junge-Pankow adsorption model.     

An Air Quality Data Analysis System for Interrelating Effects,Standards, and Needed Source Reductions: Part 3. Vegetation Injury

Acute leaf injury data are analyzed for 19 plant species exposed to ozone or sulfur dioxide. The data can be depicted by a new leaf injury mathematical model with two characteristics: (1) a constant percentage of leaf surface is injured by an air pollutant concentration that is inversely proportional to exposure duration raised to an exponent; (2) for a given exposure duration, the percent leaf injury as a function of pollutant concentration tends to fit a lognormal frequency distribution. Leaf injury as a function of laboratory exposure duration is modeled and compared with ambient air pollutant concentration measurements for various averaging times to determine which exposure durations are probably most important for setting ambient air quality standards to prevent or reduce visible leaf injury. The 8 hour average appears to be most important for most of the plants investigated for most sites, 1 hr concentrations are important for most plants at a few sites, and 3 hr S0₂ concentrations are important for some plants, especially those exposed to isolated point sources of the pollutant. The 1, 3, and 8 hr threshold injury concentrations are listed for each of the 19 plant species studied. To prevent or reduce acute leaf injury, fixed, nonoverlapping ambient air quality measurements and standards are recommended for averaging times of 1, 3, and 8hr.     

An analytical method to determine Henry's law constant for selected volatile organic compounds at concentrations and temperatures corresponding to tap water use

Henry's law constants (H) are needed to model human exposure to Volatile Organic Compounds (VOCs) in indoor air resulting from the use of tap water. This paper presents an experimental method to determine Hs for several common tap water pollutants at concentrations and temperatures used in household water. For 5 VOCs Henry's law constants were obtained simultaneously over the 25 degrees C to 45 degrees C temperature range, providing data on H beyond the currently available data (up to 35 degrees C). Henry's law constants were obtained as the ratio of equilibrium concentrations of VOCs in air and water, using simultaneous sampling from sealed bottles kept at constant temperatures. Air and water samples were concentrated by a purge-and-trap method, thermally desorbed from a Tenax trap, and analyzed with a gas chromatograph with an electron capture detector (GC-ECD). Experimental results agreed well with available literature data.     

PLATIN (plant-atmosphere interaction) II: Co-occurrence of high ambient ozone concentrations and factors limiting plant absorbed dose

There is an ongoing debate as to which components of the ambient ozone (O3) exposure dynamics best explain adverse crop yield responses. A key issue is regarding the importance of peak versus mid-range hourly ambient O3 concentrations. While in this paper the importance of peak atmospheric O3 concentrations is not discounted, if they occur at a time when plants are conducive for uptake, the corresponding importance of more frequently occurring mid-range O3 concentrations is described. The probability of co-occurrence of high O3 concentrations and O3 uptake limiting factors is provided using coherent data sets of O3 concentration, air temperature, air humidity, mean horizontal wind velocity and global radiation measured at representative US and German air quality monitoring sites. Using the PLant-ATmosphere INteraction (PLATIN) model, the significance of the aforementioned meteorological parameters on ozone uptake is examined. In addition, the limitations of describing the O3 exposure for plants under ambient, chamberless conditions by SUM06, AOT40 or W126 exposure indices are discussed.     

Accelerated dehardening in bilberry (Vaccinium myrtillus L.) induced by a small elevation in air temperature

The effect of climatic warming on the dehardening potential of bilberry (Vaccinium myrtillus L.) in a northern boreal environment (65 degrees N) was studied. Natural stands of bilberry were heated artificially in winter. No reference point for the heating was set, since the purpose was to follow the fluctuations in ambient air temperatures. These were 2-3 degrees C higher in the heated plots than in the control plots from October to May. Frost resistance (LT50) and the pH of cell effusate were monitored throughout. Bud phenology was assessed in May and related to various biochemical analyses, including glucose, fructose, sucrose, starch and total and reduced glutathione. Frost resistance started to decrease earlier in the heated plants, as did the pH of the cell effusate. Bud phenology was in accordance with the LT50 and pH results, since new growth had emerged in the heated plants by the beginning of May, when the controls still displayed dormancy. Concentrations of glucose, fructose and sucrose were significantly lower in the heated bilberries while concentrations of starch were higher. The heated plants also exhibited the lowest glutathione concentrations, but the difference was only marginal. The redox state of glutathione showed no difference between the treatments. The results suggest that a small elevation in air temperature can accelerate dehardening in the bilberry. It is thus concluded that climatic warming may entail a real risk of early dehardening and further frost damage for the bilberry.     

Difference in ozone uptake in grassland species between open-top chambers and ambient air

Exposure-response data from open-top chamber (OTC) experiments are often directly applied to ambient air (AA) conditions. Because microclimatic conditions are modified and pollutant uptake by plants may differ (i.e. 'chamber effect'), there is concern about the influence of OTCs on these relationships. In addition, AA concentrations are often measured at a height which differs from canopy height and correction for the concentration gradient (i.e. 'gradient effect') is necessary. To quantify the relative contribution of plant characteristics and microclimatic factors to these effects, ozone uptake by horizontal leaves at the top of the canopy was calculated for plants grown in OTCs or AA by using a resistance analogy model. Data from an OTC experiment in 1996/97 for six species typical of productive grasslands were used. Ozone concentration inside OTCs was set equal to the concentration measured at a height of 3 m above ground (C(z(ref))) or at canopy height (C(0)). The gradient effect resulted in a 16-27% lower average C(0) than C(z(ref)), depending on species. The main determinant of the chamber effect was a systematic difference in leaf-to-air vapour pressure deficit between OTCs and AA which affected stomatal resistance and ozone uptake. In case of monocultures both effects were species-specific. In species mixtures the gradient effect differed between mixing ratios, whereas the chamber effect was species-specific. Because of the inter-specific difference in the chamber effect on ozone uptake, it is concluded that ozone effects on species mixtures differ systematically between OTCs and AA. The data underline that extrapolation of ozone flux-response relationships from OTC experiments must be based on canopy-level ozone concentrations, and that these relationships should be applied only to single species under microclimatic conditions similar to those prevailing in the experiment.     

Chronic ozone exposure increases the susceptibility of hybrid Populus to disease caused by Septoria Musiva

Rooted cuttings of hybrid Populus (DN34, Populus deltoides X nigra) were grown outdoors in pots in open-top chambers at Ithaca, NY (74.5 degrees W, 42.5 degrees N), during 1988 and 1989 (Experiment 1) and during 1989 and 1990 (Experiment 2). Ambient air was passed through charcoal filters to produce a 0.5 times ambient ozone treatment, and ozone generated from oxygen was added to produce one and two times ambient ozone treatments. In Experiment 1, treatments were applied for 8-12 h each day for 112 days of the 1988 growing season; then the plants were grown outdoors with ambient ozone in 1989. In Experiment 2, treatments were applied for 9 h each day for 98 days of the 1989 growing season; then the plants were grown outdoors with ambient ozone in 1990. Shallow wounds were made into the bark tissue and inoculated with either an aqueous suspension of conidia of Mycosphaerella populorum or sterile water on 1 and 2 September 1988 (Experiment 1) or 16 and 17 August 1989 (Experiment 2). In Experiment 1, wounds were inoculated either 0, 7, or 14 days after wounding. In Experiment 2, wounds were inoculated either 0, 3, or 6 days after wounding. Canker development was measured after harvest on 16 and 17 July 1989 (Experiment 1) and 28 May 1990 (Experiment 2). In both experiments, chronic exposure to ozone significantly increased the incidence of canker formation in inoculated wounds, and no cankers formed in wounds that received only sterile water. In Experiment 1, cankers formed only on plants inoculated the same day as wounding. No cankers formed on plants inoculated either 7 or 14 days after wounding. In Experiment 2, cankers formed on plants inoculated on the same day as wounding, and on a few plants inoculated 3 days after wounding. No cankers formed on plants inoculated 6 days after wounding. Additionally, in Experiment 2, exposure to increased concentrations of ozone caused a significantly higher number of plants to die during the subsequent winter. Analysis of partial correlation coefficients among plant growth and plant disease variables suggested that the observed ozone-induced increase in the susceptibility of the plants to disease was not mediated by alterations in plant growth.     

Psidium guajava 'Paluma' (the guava plant) as a new bio-indicator of ozone in the tropics

Psidium guajava 'Paluma' saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF), and ambient non-filtered air+40ppb ozone (NF+O(3)) 8h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12 895ppbh(-1), respectively for the three treatments. After 5 days of exposure (AOT40=1497ppbh(-1)), interveinal red stippling appeared in plants in the NF+O(3) chamber. In the NF chamber, symptoms were observed only after 40 days of exposure (AOT40=880ppbh(-1)). After 60 days, injured leaves per plant corresponded to 86% in NF+O(3) and 25% in the NF treatment, and the average leaf area injured was 45% in NF+O(3) and 5% in the NF treatment. The extent of leaf area injured (leaf injury index) was explained mainly by the accumulated exposure of ozone (r(2)=0.91; p<0.05).     

Tibouchina pulchra (Cham.) Cogn., a native Atlantic Forest species, as a bio-indicator of ozone: visible injury

Tibouchina pulchra saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF) and ambient non-filtered air+40 ppb ozone (NF+O3) 8 h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12,895 ppb h(-1), respectively, for the three treatments. After 25 days of exposure (AOT40=3871 ppb h(-1)), interveinal red stippling appeared in plants in the NF+O3 chamber. In the NF chamber, symptoms were observed only after 60 days of exposure (AOT40=910 ppb h(-1)). After 60 days, injured leaves per plant corresponded to 19% in NF+O3 and 1% in the NF treatment; and the average leaf area injured was 7% within the NF+O3 and 0.2% within the NF treatment. The extent of leaf area injured (leaf injury index) was mostly explained by the accumulated exposure of ozone (r2=0.89; p<0.05).     

Assessment by laboratory simulation of approaches to amelioration of peat acidification

This study was conducted to determine whether acidic cloudwater and ozone (O3) influence the growth of red spruce (Picea rubens L.) seedlings growing at a high elevation site in the southern Appalachian Mountains. A field exclusion chamber study was established at Whitetop Mountain, VA (elevation 1689 m) which included the following treatments: (1) clouds and O3 excluded (COE); (2) exposure to ambient O3 with clouds excluded (CE); (3) exposure to clouds and O3 (CC); and (4) ambient air plots (AA) that served as a control to evaluate possible chamber effects. After 2 years, seedlings exposed to ambient levels of O3 and cloudwater (AA and CC) did not differ in biomass accumulation, diameter growth, or epicuticular wax amounts from seedlings grown in chambers where pollution levels were reduced (CE and COE). Treatments receiving cloudwater (AA and CC) had statistically lower current-year needle concentrations of Ca and Mg, indicating that the cloudwater exposure dynamics occurring at this site elicited reductions in needle Ca and Mg. Ozone had negligible impact on all of the seedling parameters measured.     

From critical levels to critical loads for ozone: a discussion of a new experimental and modelling approach for establishing flux-response relationships for agricultural crops and native plant species

Present critical levels for ozone (O3) for protecting vegetation against adverse effects are based on exposure-response relationships mainly derived from open-top chamber experiments and are expressed as an Accumulated exposure Over a Threshold of 40 ppb (AOT40). In that context with a revision of the UN (United Nations)-ECE (Economic Commission for Europe) Gothenburg protocol, AOT40 values should be replaced by flux-oriented quantities, i.e. in the end by critical loads. At present, the database for the derivation of critical loads for O3 is extremely inadequate. Furthermore, the currently available flux-response relationships are also derived from open-top chamber experiments. The use of a relationship for spring wheat in a risk assessment for an agricultural site in Hesse, Germany, demonstrates in principle, the applicability of the critical load concept for O3. Comparisons of diurnal variation of stomatal uptake and AOT40 showed that a major part of toxicologically effective stomatal uptake occurred before noon whereas the AOT40 values were dominated by the O3 concentrations during afternoon. In other words, the AOT40 exposure index do not adequately address the O3 burden during hours when plants are sensitive to O3 uptake. However, due to the differences in radiation, air temperature and humidity between the chamber and the ambient microclimates, a derivation of flux-response relationships from chamber experiments is likely to be questionable, especially for species rich ecosystems: Here, without any changes in the pollution climate, significant modifications of species composition as well as an earlier beginning of the growing season has been previously observed. To overcome the problems associated with chamber-derived flux-response relationships, a new experimental and modelling concept, was developed. The approach, briefly described in this paper, combines methods in air pollution toxicology and micrometeorology. As an analogy to the free-air fumigation concept, O3 is released into the air by an injection system above the plant canopy. The assessment of dispersion and surface deposition of O3 released is based on Lagrangian trajectory modelling. Depending on wind direction and velocity, atmospheric stratification and surface roughness, without any disturbance of the microclimate and micrometeorology, several sub-areas can be identified around the source position with differing deposition rates above the ambient level. Taking into account the actual O3 background deposition, deposition rates and vegetation responses observed in these sub-areas can easily be used to derive flux-effect relationships under ambient conditions and more realistic limiting values to protect our environment.     

Influence of the atmospheric conductivity on the ozone exposure of plants under ambient conditions: Considerations for establishing ozone standards to protect vegetation

This paper provides results of ozone flux density measurements above a permanent grassland ecosystem as they relate to an establishment of air quality guidelines or standards. Using a resistance analogue, the product of zone concentration measured at a standard measurement height and the conductivity of the atmosphere reflect the maximum possible ozone flux density towards the envelope of the plants. In other words, this product can be regarded as the ozone exposure potential of the atmosphere for plants. It could be shown that ozone concentrations between 100 and 180 microg m(-3) are likely to have a great phytotoxic potential and are more important than concentrations greater than 180 microg m(-3). From the results presented one can deduce that the application of dose-response relationships based on chamber experiments to ambient conditions results in an overestimation of, for example, yield loses. Any guideline or standard has to take into account the influence of the atmospheric conductivity on the absorbed dose of ozone.     

Measurements of ultrafine particles and other vehicular pollutants inside a mobile exposure system on Los Angeles freeways

A mobile exposure and air pollution measurement system was developed and used for on-freeway ultrafine particle health effects studies. A nine-passenger van was modified with a high-efficiency particulate air (HEPA) filtration system that can deliver filtered or unfiltered air to an exposure chamber inside the van. State-of-the-art instruments were used to measure concentration and size distribution of fine and ultrafine particles and the concentration of carbon monoxide (CO), black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (PAHs), fine particulate matter (PM2.5) mass, and oxides of nitrogen (NOx) inside the exposure chamber. This paper presents the construction and technical details of the van and air pollutant concentrations collected in 32 2-hr runs on two major Los Angeles freeways, Interstate 405 (1-405; mostly gasoline traffic) and Interstate 710 (1-710; large proportion of heavy-duty diesel traffic). More than 97% of particles were removed when the flow through the filter box was switched from bypass mode to filter mode while the vehicle was driving on both freeways. The filtration system thus provides a great particulate matter exposure contrast while keeping gas-phase pollutant concentrations the same. Under bypass mode, average total particle number concentration observed inside the exposure chamber was around 8.4 x 10(4) and 1.3 x 10(5) particles cm(-3) on the I-405 and the I-710 freeways, respectively. Bimodal size distributions were consistent and similar for both freeways with the first mode around 16-20 nm and the second mode around 50-55 nm. BC and particle-bound PAH concentrations were more than two times greater on the I-710 than on the I-405 freeway. Very weak correlations were observed between total particle number concentrations and other vehicular pollutants on the freeways.     

Effect of SO2 on the reproduction of pea aphids, Acyrthosiphon pisum, and the impact of SO2 and aphids on the growth and yield of peas

Pea aphids feeding from birth to maturity on pea plants (Pisum sativum) exposed to SO(2) concentrations of 50 nl litre(-1) or 80 nl litre(-1) showed a significant 19% increase in the rate of nymph production during the reproductive period, compared to control aphids feeding on plants in charcoal-filtered air. The higher nymph production resulted in a mean 4.6% increase in the intrinsic rate of population increase (rm). In longer term glasshouse fumigation experiments pea aphid populations were, on average, 1.8 times greater on pea plants in ambient air plus 45 nl litre(-1) SO(2) than in ambient air alone. Aphid infestation in ambient air caused a 42% reduction in pea yield and affected most plant parameters adversely. Ambient air plus SO(2) had no direct effect on yield, but, in combination with aphid infestation, a further 10% reduction in yield was recorded.     

Ozone exposure of field-grown winter wheat affects soil mesofauna in the rhizosphere

A 2-year open-top chamber experiment with field-grown winter wheat (Triticum aestivum L. cv. Astron) was conducted to examine the effects of ozone on plant growth and selected groups of soil mesofauna in the rhizosphere. From May through June in each year, plants were exposed to two levels of O₃: non-filtered (NF) ambient air or NF+ 40 ppb O₃ (NF+). During O₃ exposure, soil sampling was performed at two dates according to different plant growth stages. O₃ exposure reduced above- and below-ground plant biomass in the first year, but had little effect in the second year. The individual density of enchytraeids, collembolans and soil mites decreased significantly in the rhizosphere of plants exposed to NF+ in both years. Differences were highest around anthesis, i.e. when plants are physiologically most active. The results suggest that elevated O₃ concentrations may influence the dynamic of decomposition processes and the turnover of nutrients.     

Establishing the redox potential of Tibouchina pulchra (Cham.) Cogn., a native tree species from the Atlantic Rain Forest,in the vicinity of an oil refinery in SE Brazil

The present study aimed to establish the seasonal variations in the redox potential ranges of young Tibouchina pulchra plants growing in the Cubatão region (SE Brazil) under varying levels of oxidative stress caused by air pollutants. The plants were exposed to filtered air (FA) and non-filtered air (NFA) in open-top chambers installed next to an oil refinery in Cubatão during six exposure periods of 90 days each, which included the winter and summer seasons. After exposure, several analyses were performed, including the foliar concentrations of ascorbic acid and glutathione in its reduced (AsA and GSH), total (totAA and totG) and oxidized forms (DHA and GSSG); their ratios (AsA/totAA and GSH/totG); the enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR); and the content of malondialdehyde (MDA). The range of antioxidant responses in T. pulchra plants varied seasonally and was stimulated by high or low air pollutant concentrations and/or air temperatures. Glutathione and APX were primarily responsible for increasing plant tolerance to oxidative stress originating from air pollution in the region. The high or low air temperatures mainly affected enzymatic activity. The content of MDA increased in response to increasing ozone concentration, thus indicating that the pro-oxidant/antioxidant balance may not have been reached.     

Flow visualisation studies of aerodynamic characteristics of an open-top chamber

Studies to determine potential locations of ingress of ambient air into an open-top chamber, using flow visualisation, are described. Rates of chamber ventilation necessary to avoid ambient air entrainment have been estimated from wind tunnel experiments. The dependence of the exit velocity of air from the chamber on the ambient air velocity was non-linear, so that for low wind speeds other mechanisms are more important than for high ambient air flows. Wind speeds ranged from 0.5m s(-1)相似文献   

Simulation of effects of atmospheric ethylene on tree leaf shedding

This study made a preliminary assessment of the possibility that ethylene contained in polluted atmospheres affects leaf shedding of trees. The effect of ethylene dosage (ppb x h) on leaf shedding at various temperatures was approximated by using a polynomial regression. The effect of ethylene dosage on shedding of tree leaves with various sensitivities to this hydrocarbon was simulated in connection with the relationship between ethylene concentrations (10-100 ppb), dosage periods (0-50 days) and temperature (10-30 degrees C). The simulated results indicated the possibility that, for the tree group having high sensitivity, the rate of leaf shedding due to a dosage of ethylene with a concentration as low as 20 ppb, which is commonly observed in urban atmospheres, increased with temperature. On the other hand, the same concentration scarcely influenced leaf shedding in the low sensitivity group even at a temperature as high as 30 degrees C. The results for the real atmosphere determined at the Tokyo metropolitan center indicated the possibility that, for trees having high sensitivity, the rate of leaf shedding increased with rises in both monthly ethylene concentrations and air temperatures and reached a maximum of 90% in July. But in December when the concentration again reached the same value as in July while the mean monthly air temperature was 9.3 degrees C, the rate was only 10%.