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Investigating the Foliar Uptake and Within-Leaf Migration of Phenanthrene by Moss (Hypnum Cupressiforme) Using Two-Photon Excitation Microscopy with Autofluorescence IAN KEYTE, EDWARD WILD, JOHN DENT, AND KEVIN C. JONES* Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, U.K.
Received January 29, 2009. Revised manuscript received May 28, 2009. Accepted June 22, 2009.
Mosses have the potential to play a significant role in the global cycling and fate of semivolatile organic compounds (SVOCs), due to their extensive distribution at high latitudes and the long-range atmospheric transport of SVOCs. Unlike vascular plants mosses lack a substantial cuticle, vascular system, or root structure, taking up water, nutrients and SVOCs primarily from the atmosphere. Mosses have thus been effectively used as passive air samplers for many SVOCs in urban and rural locations. The potential differences in atmospheric uptake and within-leaf movement, storage and processing of SVOCs between vascular and nonvascular living plants were investigated here by comparing the uptake and behavior of phenanthrene in spinach (Spinacia oleracea) and moss (Hypnum cupressiforme), using two-photon excitation microscopy coupled with autofluorescence. Chemical uptake, movement, storage, and compartmentalization of phenanthrene was directly detected, visualized, and monitored over a 12 day period following exposure to gas phase phenanthrene. Species differences in the uptake of phenanthrene between moss and spinach leaves were observed, showing how morphological differences affect the foliar uptake of SVOCs. In spinach, phenanthrene accumulated within the cellular cytoplasm and vacuole.Inmoss,phenanthreneaccumulatedpredominantlywithin the cell walls, before later migrating across the cell membrane into adjacent cells and the cellular cytoplasm. The study represents a further demonstration of how different plant species can display different and complex transport and storage pathways for the same chemical, and highlights the importance of the cellular structure and plant morphological and physiological features in controlling this behavior.
Introduction Vegetation forms a relatively small but dynamic environmental compartment which can play a significant role in the cycling and fate of semivolatile organic compounds (SVOCs) (1, 2). For example, the forest canopy has been shown to be important in scavenging, storing and processing SVOCs in woodland ecosystems (3, 4). In addition, the uptake of SVOCs * Corresponding author e-mail:
[email protected]. 10.1021/es900305c CCC: $40.75
Published on Web 07/06/2009
2009 American Chemical Society
by vegetation can be a key pathway by which these chemicals enter terrestrial food chains leading to human exposure through the diet (5). SVOCs undergo long-range atmospheric transport (LRAT) to remote high latitude regions (6, 7) during which compounds can be subject to global fractionation (8, 9). The vegetation cover in high latitude regions is often dominated by mosses such as in peat lands, bogs, polar tundra ecosystems, and the understory of boreal forests (10, 11). This vegetation has the potential to play a significant role in the long term fate and cycling of SVOCs (1, 2). Leaves of vascular plants are coated by a thin (0.1-10 µm) hydrophobic lipid layer, the cuticle, which has the key function of protecting and waterproofing the plant surface and preventing water loss from the epidermal cells (12, 13). The cuticle also takes up SVOCs due to its lipophilic nature, and can act as a barrier to the internal penetration of xenobiotics, and thus plays an important role in SVOC/ vegetation interactions (13). The cuticle membrane is composed of the biopolymers cutin and cutan along with associated cuticular waxes (14). SVOCs have been shown to have a higher affinity for the cuticular waxes than other cuticular components (15). These chemicals are believed to reach the internal compartments of the leaf primarily via sorption to, and diffusion through, the cuticular waxes (16). Following atmospheric deposition and uptake to vegetation, the fate of a SVOC will be largely dependent on the location of the compound on or within the plant. For example, a compound that is retained in the cuticle may be more likely to undergo photodegradation or revolatilization to the atmosphere, whereas a compound which has migrated into the epidermal or mesophyll cells may be more susceptible to metabolism or storage (17, 18). Determining precisely within which cellular compartments (internal or external) a compound becomes stored is therefore pivotal in determining and modeling its potential environmental fate (19). Two-photon excitation microscopy (TPEM) coupled with plant and chemical autofluorescence provides a unique method for tracking and monitoring chemicals in living plant cells (20). It enables the simultaneous identification of the plant’s structural components (e.g., the cuticle, cell walls, and chloroplasts) and fluorescing compounds of interest in 3D within a living sample at the cellular and subcellular level. Detailed discussion of the practical considerations, applications, and advantages of TPEM is provided by Wild et al. (21) and Wild and Jones (22). TPEM has so far been used to investigate the interaction of SVOCs with vegetation, specifically their uptake, movement, storage, and photodegradation in plant leaves (18, 20) and their uptake, storage, and metabolism in plant roots (23). These studies have focused on the vascular plants spinach, maize, and wheat. However TPEM is yet to be extended to nonvascular plants such as mosses. Mosses make up a prominent proportion of vegetation in many ecosystems, from oceanic temperate forests and tropical cloud forests, to bogs, tundra, and polar regions. Unlike vascular plants, most moss species lack roots and a vascular system, taking up water, nutrients, and pollutants via the atmosphere (24). Mosses carry substantial external water, which aids the interception and absorption of solutes from rain, cloud, or mist, enabling them to survive in nutrient poor environments, while simultaneously making them vulnerable to atmospheric pollutantssan attribute that has facilitated their extensive use as environmental biomonitors for many compounds including SVOCs (25-27, 29-33). VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Multipanel TPEM image showing a moss leaf contaminated with phenanthrene after 24 h. Phenanthrene is shown in panel 1, the moss cellular structure in panel 2, and a combined color image in panel 3. Phenanthrene is shown in red, the cellular structure in green. Phenanthrene is observed to be within the cell walls of the moss leaf. Unlike vascular plants, most moss species lack a cuticular layer, but carry at least a thin layer of cuticular material, which combined with thicker cell walls helps maintain cell water turgor, while slowing the diffusion of gases for photosynthesis. Mosses function largely within the laminar boundary layer, with CO2 uptake occurring solely through diffusion. Their high surface area, and moist surface, makes them efficient at trapping atmospheric gases and vapor phase compounds while providing free access to cells through diffusion. These physiological characteristics, in addition to their relatively large surface area allow mosses to efficiently absorb and retain contaminants from the atmosphere. This means moss can be effectively used as a passive air sampler for SVOCs, and as a surrogate for larger scale direct sampling (1, 25, 27, 32, 33). The extensive distribution of moss at high latitudes suggests they will play an important role in the storage transfer and fate of SVOCs in these habitats. Determining the capacity of moss to scavenge and process these chemicals will therefore aid our understanding of their broad environmental fate, and their effective use as passive air samplers. It is therefore important to address the uncertainties associated with precisely how SVOCs interact 5756
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with moss species. This includes understanding their kinetics of uptake from the atmosphere, the internal compartments within which they become stored and their likely fate and residence within the plant cells (19). Here we extend the application of TPEM to monitor and track phenanthrene in moss leaves. We investigate potential differences in uptake, movement, and storage in vascular and nonvascular plants, to help further understand the role of the cuticle in the foliar uptake of organic pollutants and the potential role of mosses in the global cycling of SVOCs.
Materials and Methods Leaves of spinach (Spinacia oleracea) and moss (Hypnum cupressiforme) were exposed to vapor phase phenanthrene over a 12 day contamination period. TPEM was used to monitor the uptake, movement, and cellular storage locations of phenanthrene in both species. Compound and Plant Selection. Phenanthrene was selected as the target compound because it is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in
FIGURE 2. Multipanel TPEM image showing a moss leaf contaminated with phenanthrene after 288 h. Phenanthrene only is shown in panel 1, the cellular structure in panel 2, and a combined color image in panel 3. Phenanthrene is shown in red and the cellular structure of the plant is shown in green. Phenanthrene is shown migrating across the cell membrane and entering the cellular cytoplasm of the cell. the atmosphere (33, 34) and displays characteristic properties (e.g., hydrophobicity, lipophilicity, and semivolatility) of many other SVOCs. Phenanthrene also fluoresces at a suitable wavelength for TPEM visualization (18).
Spinach leaves provide a useful comparison because of their well formed cuticle layer, vascular system, and extensive uptake and compartmentalization studies with phenanthrene (18). The moss species Hypnum cupressiforme was chosen VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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(UV400 DCLP), and filter B (HQ515/30). Filter A transmitted between 300 and 390 nm, corresponding to the emission of phenanthrene using red as the pseudo color channel. Filter B transmitted between 500 and 530 nm, detecting all plant components, including cuticle, cell walls, and chloroplasts using green as the pseudo color channel. Images were collected and processed using Bio-Rad Laser 2000 imaging software and Confocal assistant 4.02. Both XY and XZ images were made, and 3D reconstructions of samples were produced using Amira 5.0 software from Visage Imaging.
Results and Discussion
FIGURE 3. A 3D reconstruction of a moss leaf showing phenanthrene (red) within the cellular structure of a moss leaf (green) including the location of the chloroplasts (blue). The reconstruction is generated from 123 XY images made through the leaf. Image a. shows an XY view of the leaf, and image b. shows an XZ cross section. Phenanthrene can be visualized within the cell walls and encapsulating the cells of the leaf. because it has previously been shown to accumulate relatively high concentrations of PAHs from the atmosphere compared to other moss species and vegetation types (30). Preparation and Contamination of Plants. Individual plants of both species were exposed to phenanthrene in separate 200 mL glass chambers. Fluorescent grade phenanthrene (98%) was obtained from Aldrich Chemical Co., and for each chamber, approximately 5 mg was dissolved in 1 mL of acetone and then coated onto the inside of the chamber using a glass pipet. Spinach seeds were obtained from Unwins Seeds Ltd., Chester, U.K. and were grown in Levington Compost original compost mix, M3 under a 14 h photoperiod, and were illuminated by 400W sodium solar lamps, whereas moss plants were collected locally and cultured in the lab. The germinated plants were grown in nutrient solution and placed in individual glass vials, which in turn were placed inside the glass chambers. Soil was not used in order to avoid any uptake and loss of chemical to the soil. Vials were placed in the center of each chamber to ensure no direct transfer of phenanthrene occurred from the chamber walls. Air was circulated using a 12 V fan within the chambers to simulate ambient turbulent conditions and encourage gaseous exchange. The chambers were sealed and placed inside a separate 54 dm3 chamber maintained in an indoor ambient environment at 25 °C throughout the experiment under natural indoor lighting. Leaves were taken for TPEM analysis after 1, 3, 6, and 12 days. Plants were removed from the contamination chamber, placed on glass slides, and transferred immediately to the TPEM for analysis. Triplicate samples were analyzed for each species at each time period. Uncontaminated control plants of both species were also analyzed on each occasion. Instrumentation. A Bio-Rad Radiance 2000 MP scanning system with a Spectra Physics Tsunami/millennia tunable laser (690-1050 nm) was used with a Nikon eclipse TE300 inverted microscope fitted with a Nikon 60 × /1.20 Plan Apo DIC water immersion lens. The laser wavelength was set to 710 nm. The emission detection filters and dichroic mirrors used were as follows: emission filter A (UG11/IR), dichroic mirror 5758
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Analysis of Control Samples. Uncontaminated control leaves of both species were analyzed to identify background levels of phenanthrene. Observations using TPEM after 0 h contamination detected no phenanthrene in leaves of either species; background levels of phenanthrene in both moss and spinach was below TPEM detection limits. Uptake of Phenanthrene in Spinach Leaves. The uptake and within-leaf transport of phenanthrene in leaves of maize and spinach has previously been reported by Wild et al. (18). They reported that air to leaf transfer of phenanthrene can take place via both particulate and gaseous deposition; the two mechanisms resulting in different distributions of phenanthrene across the leaf surface. Evidence of both transfer mechanisms to spinach leaves was also obtained in this investigation. Particulate deposition, attributed to fine dust circulating within the chamber resulted in distinctive localized regions of phenanthrene, while gaseous deposition results in a more uniform “diffusive” coverage across the leaf surface, corresponding with previous findings. Particulate matter within the chamber was limited, and particulate deposition to leaves was significantly lower than within the ambient environment. Wild et al. (18) described the movement of phenanthrene through the cellular structure of spinach leaves following atmospheric deposition. They reported that phenanthrene initially sorbed to the waxy cuticle and was retained in the cuticular matrix for 24-48 h before migrating into the underlying epidermal cell walls, cytoplasm, and vacuoles after 48-96 h, reaching the epidermal/mesophyll interface after 144 h. In this investigation, phenanthrene was visualized in several different compartments on and within spinach leaves; on the surface of the cuticle, within the cuticle matrix, within the stomatal plugs, within the cytoplasm of the epidermal cells, and at the interface between the epidermal cells and the mesophyll layer. These observations are in broad correspondence with the findings in the previous study. Phenanthrene was visualized at the interface between the epidermal and mesophyll layers after 144 h suggesting that phenanthrene followed a near identical pathway within spinach leaves and on a similar time scale to that observed in the previous investigation. Uptake of Phenanthrene in Moss. As with the foliar uptake in spinach, transfer of vapor phase phenanthrene to the surface of moss leaves was observed to occur via both particulate and gaseous deposition. Analysis suggests that gaseous deposition resulted in more phenanthrene reaching the leaf surface than particulate deposition (18). Notable differences between uptake characteristics and internal migration pathways of phenanthrene in moss and spinach leaves were observed. Phenanthrene was observed within the cell walls of moss leaves after 24 h (Figure 1). No phenanthrene was observed within the cellular cytoplasm; the chemical appeared to reside exclusively within the cell wall matrix, appearing to surround the epidermal cells. Wild et al. (18) reported a similar transfer of phenanthrene to the cell walls of maize leaves, however this was not observed until 72-96 h. Analysis after 72 and 144 h also detected no phenanthrene within the cellular
FIGURE 4. Schematic diagrams showing the locations of phenanthrene visualized within leaves of spinach (upper) and moss (lower) at different stages throughout a 12 day exposure to an atmosphere containing elevated levels of gas phase phenanthrene. cytoplasm of the moss leaves, suggesting a period of retention and accumulation within the cell walls over this period. The cell walls of moss are thicker than those of vascular plants, having an important role in maintaining cell turgour and reducing water loss while simultaneously allowing the slow diffusion of gases (24). After 288 h phenanthrene was observed to migrate from the cell walls across the cell membrane into the cytoplasm of adjacent cells (Figure 2). Phenanthrene initially remained adhered to the internal surface of the cell wall (Figure 2) before slowly migrating into the cellular cytoplasm (Figure 2). These observations suggest phenanthrene displayed a higher affinity for the cell wall components of the moss leaf than the cellular cytoplasm, preferentially “filling up” this compartment of the leaf before moving into the cytoplasm of the cells. The cell walls may thus have a greater storage capacity and uptake potential of SVOCs than the cellular cytoplasm. The Role of the Cuticle in Foliar Uptake of SVOCs. It has been widely reported that the cuticle can act as a barrier in the foliar uptake of organic chemicals, sorbing and retaining them within the cuticular matrix (35-37). Principal, cuticular components in the uptake of organic chemicals are the cuticular waxes. The solid, semicrystalline nature of these waxes means that solubility and mobility of organic chemicals in the cuticular waxes will be relatively low (38). Indeed, the extraction of cuticular waxes can increase mobility of organics through the cuticle by several orders of magnitude (39). The differences in foliar uptake of phenanthrene between spinach and moss may be attributed to the presence or absence of a cuticular layer. In spinach leaves, movement of phenanthrene to the internal cellular compartments occurred relatively slowly (48-96 h), whereas transfer of phenanthrene to the cell walls of moss was rapid (24 h). It is therefore suggested that the slower transfer of phenanthrene to underlying epidermal cells in spinach occurred through the relatively slow diffusion of chemical through the cuticular waxes. In moss phenanthrene diffused directly from the gas phase to the cell walls. While previous investigations into the mobility of organic chemicals through cuticles have often relied on the enzymatic
isolation of cuticular membranes and/or the extraction of cuticular waxes using organic solvents (37, 40, 41), this study has directly visualized chemical uptake in unmodified living plants. Although two different plant species have been used and their precise uptake kinetics will obviously differ, the observations discussed above clearly highlight the potential role of the cuticle as a barrier in the foliar uptake of SVOCs in living plant systems. The Influence of Leaf Morphology and Physiology. Differences in uptake between moss and spinach leaves have so far been considered in terms of the presence or absence of a leaf cuticle. However, there are significant morphological and physiological properties of the plant that will influence the air-vegetation transfer of SVOCs. The transfer of compounds from air to vegetation can be considered in two steps: transfer from the bulk air to the leaf boundary layer, and diffusion across the boundary layer to the leaf surface (16). The supply of phenanthrene to the leaf surface will therefore be dependent on the thickness and conductivity of the leaf boundary layer, which itself will be determined by leaf topography and wind speed, and the specific properties of the leaf surface. Leaf morphology (size, shape, surface area of leaves) is important in the foliar uptake of SVOCs as this will influence the size and conductivity of the leaf boundary layer. For example, Wild et al. (18) demonstrated how spinach can take up higher levels of phenanthrene at the leaf edge, where the boundary layer is thinner, than at the center of the leaf. It is suggested that differences in leaf morphology between the two species resulted in different rates of supply of phenanthrene to the leaf surface with uptake to moss being slightly faster than to spinach. Within-Leaf Transport Pathways. Phenanthrene appeared to follow different transport pathways within the two plant species. In spinach, phenanthrene moved rapidly through the epidermal cell walls into the cellular cytoplasm, preferentially accumulating within the cellular vacuoles, following a symplastic pathway (42). In contrast, moss leaves displayed an initial retention, movement, and accumulation of phenanthrene within the cell walls, displaying apoplastic movement, before phenanthrene diffused slowly across the VOL. 43, NO. 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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cell membrane into the cytoplasm as the cell wall compartment filled up, (see Figures 2 and 3). It has previously been demonstrated that different plant species can display different internal transport pathways for the same SVOC (18). In spinach, phenanthrene moved mainly through the cellular cytoplasm, whereas in maize, phenanthrene moved predominantly within the cell wall matrix (18). The work presented here provides further evidence of differing within-leaf transport characteristics between plant species. These differences can possibly be attributed to differences in the affinity of phenanthrene for the cell wall matrix. Transport storage and processing of chemicals within the cellular structure of plants is likely to involve the cell walls (41, 42). The precise composition of the cell walls will vary between plant species, influencing the fate and behavior of organic chemicals within the cell wall, and broader plant cellular structure. These observations suggest phenanthrene had a high affinity for the cell wall in moss, preferentially filling this compartment before migrating into the cellular cytoplasm. In contrast, phenanthrene rapidly passed through the epidermal cell walls in spinach, preferentially accumulating within the cellular vacuoles. This study has highlighted the importance of understanding the differences in cellular composition between species in order to assess the effect of cellular structure on the nature and extent of the within-leaf transport, storage, and processing of SVOCs. This is clearly an area for future research. Mosses represent a large and diverse class of vegetation globally. Their extensive distribution at high latitudes suggests mosses may play an important role in the cycling and fate of SVOCs due to the LRAT and cold condensation potential of these chemicals. While this study has identified interesting aspects of the uptake and internal cellular migration of SVOCs in moss leaves, more work is clearly needed to fully understand the interaction of these chemicals with this type of vegetation. Furthering our understanding of the uptake kinetics including depuration studies and ultimate fate (metabolism, storage, revolatilization, photodegradation) of SVOCs in moss leaves is therefore essential. The use of TPEM to visualize and monitor chemicals in living plant cells is currently constrained by the depth of laser penetration (visualization limited to a depth of 200-400 µm) and the minimum concentrations that can be detected (within the femtogram to picogram range). Additionally, because it requires the contaminant to naturally fluoresce and at a different wavelength to the plant, not all compounds can be tracked in all plants.
Literature Cited (1) Simonich, S. L.; Hites, R. A. Organic pollutant accumulation in vegetation. Environ. Sci. Technol. 1995, 29, 2905–2914. (2) Simonich, S. L.; Hites, R. A. Vegetation-atmosphere partitioning of polycyclic aromatic hydocarbons. Environ. Sci. Technol. 1994, 28, 939–943. (3) McLachlan, M. S.; Horstmann, M. Forests as filters of airbourne organic pollutants: A model. Environ. Sci. Technol. 1998, 32, 413–419. (4) Howsam, M.; Jones, K. C.; Ineson, P. Dynamics of PAH deposition, cycling and storage in a mixed- deciduous (QuercusFraxinus) woodland ecosystem. Environ. Pollut. 2000, 113, 163– 176. (5) Thomas, G. O.; Sweetman, A. J.; Lohmann, R.; Jones, K. C. Derivation and field testing of air-milk and feed-milk factors for PCBs. Environ. Sci. Technol. 1998, 32, 3522–3528. (6) Halsall, C. J.; Barrie, L. A.; Fellin, P.; Muir, D. C. G.; Billeck, B. N.; Lockhart, L.; Ya Rovinsky, F.; Ya Kononov, E.; Pastukhov, B. Spatial and temporal variation of polycyclic aromatic hydrocarbons in the arctic atmosphere. Environ. Sci. Technol. 1997, 31, 3593–3599. (7) Hung, H.; Blanchard, P.; Halsall, C. J.; Bidleman, T. F.; Stern, G. A.; Fellin, P.; Muir, D. C. G.; Barrie, L. A.; Jantunen, L. M.; 5760
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 15, 2009
(8)
(9) (10) (11)
(12)
(13)
(14) (15)
(16)
(17)
(18)
(19)
(20)
(21)
(22) (23) (24) (25)
(26)
(27)
(28)
(29)
(30)
Helm, P. A.; Ma, J.; Konoplev, A. Temporal and spatial variabilities of atmospheric polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and polycyclic aromatic hydrocarbons (PAHs) in the Canadian Arctic: Results from a decade of monitoring. Sci. Total Environ. 2005, 342, 119–144. Meijer, S. N.; Steinnes, E.; Ockenden, W. A.; Jones, K. C. The influence of environmental variables on the spatial distribution of PCBs in Norwegian and UK soils: Implications for global cycling. Environ. Sci. Technol. 2002, 36, 2146–2153. Wania, F.; MacKay, D. Tracking the distribution of persistent organic pollutants. Environ. Sci. Technol. 1996, 30, 390A–396A. Carleton, T. J.; Dunham, K. M. M. Distillation in a boreal mossy forest floor. Can. J. For. Res. 2003, 33, 663–671. Longton, R. E.; Greene, S. W. Experimental studies of growth and reproduction in the moss Pleurozium schreberi (Brid.) Mitt. J. Bryo. 1979, 10, 321–338. Jeffree, C. E. Structure and ontogeny of plant cuticles. In Kerstiens, G. Plant Cuticle: An Integrated Functional Approach; BIOS Scientific Publishers Limited: Oxford, 1996; pp 33-82. Kirkwood, R. C. Recent developments in our understanding of the plant cuticle as a barrier to the foliar uptake of pesticides. Pestic. Sci. 1999, 55, 69–77. Schreiber, L. Polar paths of diffusion across plant cuticles: New evidence for an old hypothesis. Ann. Bot. 2005, 95, 1069–1073. Moeckel, C.; Thomas, G. O.; Barber, J. L.; Jones, K. C. Uptake and storage of PCBs by plant cuticles. Environ. Sci. Technol. 2008, 42, 100–105. Barber, J. L.; Thomas, G. O.; Kerstiens, G.; Jones, K. C. Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs. Environ. Pollut. 2004, 128, 99–138. Wild, E.; Dent, J.; Thomas, G. O.; Jones, K. C. Real-time visualisation and quantification of PAH photodegradation on and within plant leaves. Environ. Sci. Technol. 2005, 39, 268– 273. Wild, E.; Dent, J.; Thomas, G. O.; Jones, K. C. Visualising the air-to-leaf movement and distribution of phenanthrene: Further studies utilizing Two-photon excitation microscopy. Environ. Sci. Technol. 2006, 40, 907–916. Reiderer, M. Estimating partitioning and transport of organic chemicals in the foliage/atmosphere system: Discussion of fugacity based model. Environ. Sci. Technol. 1990, 24, 829– 837. Wild, E.; Dent, J.; Barber, J. L.; Thomas, G. O.; Jones, K. C. A Novel analytical approach for visualising and tracking organic chemicals in plants. Environ. Sci. Technol. 2004, 38, 4195– 4199. Wild, E.; Dent, J.; Thomas, G. O.; Jones, K. C. Use of two-photon excitation microscopy and autofluorescence for visualising the fate and behaviour of semivolitile organic chemicals within living vegetation. Environ. Toxicol. Chem. 2007, 26, 2486–2493. Wild, E.; Jones, K. C. Seeing chemicals in environmental samples. Environ. Sci. Technol. 2007, 41, 5934–5938. Wild, E.; Dent, J.; Thomas, G. O.; Jones, K. C. Direct observation of organic contaminant uptake, storage and metabolism within plant roots. Environ. Sci. Technol. 2005, 39, 3695–3702. Shaw, A. J.; Goffinet, B. Bryophyte Biology; Cambridge University Press: Cambridge, 2000. Lim, T. B.; Xu, R.; Tan, B.; Obbard, J. P. Persistent organic pollutants in moss as bioindicators of atmosphere pollution in Singapore. Chemosphere. 2006, 64, 596–602. Wegener, J. W. M.; Van Schaik, M. J. M.; Aiking, H. Active biomonitoring of polycyclic aromatic hydrocarbons by means of mosses. Environ. Pollut. 1992, 76, 15–18. Holoubek, I.; Koøı´nek, P.; Sˇeda, Z.; Schneiderova´, E.; Holoubkova´, ` a´slavsky´, J. The use of mosses I.; Pacl, A.; Tøı´ska, J.; Cudlı´n, P.; E and pine needles to detect persistent organic pollutants at local and regional scales. Environ. Pollut. 2000, 109, 283–292. Viskari, E.-L.; Rekila, R.; Roy, S.; Lehto, O.; Ruuskanen, J.; Karenlampi, L. Airborne pollutants along a roadside: assessment using snow analyses and moss bags. Environ. Pollut. 1997, 97, 153–160. Liu, X.; Zhang, G.; Jones, K. C.; Li, X.; Peng, X.; Qi, S. Compositional fractionation of polyaromatic aromatic hydrocarbons (PAHs) in mosses (Hypnum plumaeformae WILS.) from the northern slope of Nanling Mountains, South China. Atmos. Environ. 2005, 39, 5490–5499. ¨ tvo¨s, E.; Koza´k, I. O.; Fekete, J.; Sharma, V. K.; Tuba, Z. O Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) in mosses (Hypnum cupressiforme) in Hungary. Sci. Total Environ. 2004, 330, 89–99.
(31) Lead, A. L.; Steinnes, E.; Jones, K. C. Atmospheric deposition of PCBs to moss (Hylocomium splendens) in Norway between 1977 and 1990. Environ. Sci. Technol. 1996, 30, 524–530. (32) Orlinski, R. Multipoint moss passive samplers assessment of urban airborne polycyclic aromatic hydrocarbons: Concentrations profile and distribution along Warsaw main streets. Chemosphere 2002, 48, 181–186. (33) Knulst, C. J.; Westling, H. O.; Brorstrom-Lunden, E. Airborne organic micropollutant concentrations in mosses and humus as indicators for local versus long range sources. Environ Model Assess. 1995, 36, 75–91. (34) Halsall, C.; Coleman, P. J.; Davis, B.; Burnett, V.; Waterhouse, K. S.; Harding-Jones, P.; Jones, K. C. Polycyclic aromatic hydrocarbons in UK air. Environ. Sci. Technol. 1994, 28, 2380–2386. (35) Prevedouros, K.; Brorstro¨m-Lunde´n, E.; Halsall, C. J.; Jones, K. C.; Lee, R. G. M.; Sweetman, A. J. Seasonal and long-term trends in atmospheric PAH concentrations: Evidence and implications. Environ. Pollut. 2004, 128, 17–27. (36) Schreiber, L. Review of sorption and diffusion of lipophilic molecules in cuticular waxes and the effects of accelerators on solute mobilities. J. Exp. Bot. 2006, 57, 2515–2523.
(37) Schreiber, L.; Scho¨nherr, J. Uptake of organic chemicals in conifer needles: surface adsorption and permeability of cuticles. Environ. Sci. Technol. 1992, 26, 153–159. (38) Santier, S.; Charnel, A. Reassessment of the role of cuticular waxes in the transfer of organic molecules through plant cuticles. Plant Physiol. Biochem. 1998, 36, 225–231. (39) Schreiber, L.; Scho¨nherr, J. Mobilities of organic compounds in reconstituted cuticular wax of barley leaves: determination of coefficients. Pestic. Sci. 1993, 38, 353–361. (40) Reiderer, M.; Scho¨nherr, J. Accumulation and transport of (2,4dichlorophenoxy) acetic acid in plant cuticles. II. Permeability of the cuticular membrane. Ecotox. Enviorn. Saf. 1985, 9, 196–208. (41) Baur, P.; Marzouk, H.; Scho¨nherr, J.; Bauer, H. Mobilities of organic compounds in the plant cuticles as affected by structures and molar volumes of chemicals and plants species. Planta. 1996, 199, 404–412. (42) Brett, C. T.; Waldron, K. W. Physiology and Biochemistry of Plant Cell Walls; Chapman and Hall Publishing: London, UK, 1996.
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