Carbon black nanoparticles promote the maturation and function of mouse bone marrow-derived dendritic cells

Particulate matter including carbon black (CB) nanoparticles can enhance antigen-related inflammation and immunoglobulin production in vivo. Dendritic cells (DC) as antigen-presenting cells (APC) are the most capable inducers of immune responses. The present study was designed to determine whether CB nanoparticles affect the maturation/activation and function of DC in vitro. DC were differentiated from bone marrow (BM) cells of BALB/c mice by culture with granulocyte macrophage colony stimulating factor (GM-CSF). At day 8 of culture, BM-derived DC (BMDC) were exposed to CB nanoparticles with a diameter of 14nm or 56nm for 24h. The expression of major histocompatibility complex (MHC) class II, DEC205, CD80, and CD86 (maturation/activation markers of BMDC) was measured by flow cytometry. BMDC function was evaluated by an allogeneic mixed lymphocyte reaction (MLR) assay. CB nanoparticles significantly increased the expression of DEC205 and CD86 in BMDC and tended to increase MHC class II and CD80 expression; however, a size-dependent effect was not observed. On the other hand, BMDC-mediated MLR was significantly enhanced by the CB nanoparticles and the enhancement was greater by 14nm CB nanoparticles than by 56nm CB nanoparticles. Taken together, CB nanoparticles can promote the maturation/activation and function of BMDC, which could be related to their effects on allergic diseases and/or responses. In addition, BMDC-mediated MLR might be useful assay for in vitro screening for adjuvant activity of environmental toxicants.     

Inhalation of two putative Gulf War toxins by mice

We employed our inhalation methodology to examine whether biomarkers of inflammation and oxidative stress would be produced in mice following inhalation of aerosols containing carbonaceous particles or the vapor of pesticides prevalent during the first Gulf War. Exposure to two putative Gulf War Illness toxins, fine airborne particles and the pesticide malathion, increased biomarkers of inflammation and oxidative stress in Friend virus B (FVB) female mice. Mice inhaling particles 24 h before had increased lung lavage and plasma Leukotriene B4 (LTB₄) (a biomarker of inflammation) and PGF_2α (a biomarker of oxidative stress) levels, lung lavage protein and lung lavage lactic dehydrogenase (LDH) levels. These changes were a function of particle density and exposure time. Compared to particle inhalation, mice inhaling malathion 24 h before had small increase in plasma LTB₄ and PGF_2α levels but no increase in lung lavage LTB₄, lung lavage protein, lung lavage LDH, and lung lavage alveolar macrophage (AM) levels compared to unexposed control mice. AM from particle-exposed mice contained phagocytosed particles, while AM from malathion-exposed mice showed no abnormalities. Our results indicate that inhaling particles or malathion can alter inflammatory and oxidative biomarkers in mice and raise the possibility that these toxins may have altered inflammation and oxidative stress biomarkers in Gulf War-exposed individuals.     

Redox activity of urban quasi-ultrafine particles from primary and secondary sources

To characterize the redox activity profiles of atmospheric aerosols from primary (traffic) and secondary photochemical sources, ambient quasi-ultrafine particles were collected near downtown Los Angeles in two different time periods – morning (6:00–9:00 PDT) and afternoon (11:00–14:00 PDT) in the summer of 2008. Detailed chemical analysis of the collected samples, including water-soluble elements, inorganic ions, organic species and water soluble organic carbon (WSOC) was conducted and redox activity of the samples was measured by two different assays: the dithiothreitol (DTT) and the macrophage reactive oxygen species (ROS) assays. Tracers of secondary photochemical reactions, such as sulfate and organic acids were higher (2.1 ± 0.6 times for sulfate, and up to 3 times for the organic acids) in the afternoon period. WSOC was also elevated by 2.5 ± 0.9 times in the afternoon period due to photo-oxidation of primary particles during atmospheric aging. Redox activity measured by the DTT assay was considerably higher for the samples collected during the afternoon; on the other hand, diurnal trends in the ROS-based activity were not consistent between the morning and afternoon periods. A linear regression between redox activity and various PM chemical constituents showed that the DTT assay was highly correlated with WSOC (R² = 0.80), while ROS activity was associated mostly with water soluble transition metals (Vanadium, Nickel and Cadmium; R² > 0.70). The DTT and ROS assays, which are based on the generation of different oxidizing species by chemical PM constituents, provide important information for elucidating the health risks related to PM exposure from different sources. Thus, both primary and secondary particles possess high redox activity; however, photochemical transformations of primary emissions with atmospheric aging enhance the toxicological potency of primary particles in terms of generating oxidative stress and leading to subsequent damage in cells.     

Assessment of exposure to airborne ultrafine particles in the urban environment of Lisbon, Portugal

The aim of this study was the assessment of exposure to ultrafine in the urban environment ofLisbon, Portugal, due to automobile traffic, and consisted of the determination of deposited alveolar surface area in an avenue leading to the town center during late spring. This study revealed differentiated patterns for weekdays and weekends, which could be related with the fluxes of automobile traffic. During a typical week, ultrafine particles alveolar deposited surface area varied between 35.0 and 89.2 microm2/cm3, which is comparable with levels reported for other towns such in Germany and the United States. These measurements were also complemented by measuring the electrical mobility diameter (varying from 18.3 to 128.3 nm) and number of particles that showed higher values than those previously reported for Madrid and Brisbane. Also, electron microscopy showed that the collected particles were composed of carbonaceous agglomerates, typical of particles emitted by the exhaustion of diesel vehicles.     

Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles

The absorption of pesticide endosulfan on the surface of gold nanoparticles results from the formation of micrometric structures (1–10 μm) with irregular shape because of the aggregation of individual particles. Such aggregation of gold nanoparticles after absorption of pesticide shows a surface-enhanced Raman scattering (SERS) spectrum, whose intensity depends on the concentration of endosulfan. In addition, the discoloration of the colloidal solution and a diminishing of the intensity of the surface plasmon resonance absorption from individual particles were observed by UV-visible spectroscopy. At the same time, a second band between 638 and 700 nm confirms the formation of aggregates of gold nanoparticles as the concentration of endosulfan increases. Finally, we used the SERS intensity of the S?O stretching vibration at 1239 cm^?1 from the SO₃ group as a measure of concentration of pesticide endosulfan. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form.     

Detection of combustion formed nanoparticles

UV–visible extinction and scattering and two extra situ sampling techniques: atomic force microscopy (AFM) and differential mobility analysis (DMA) are used to follow the evolution of the particles formed in flames. These particle sizing techniques were chosen because of their sensitivity to detect inception particles, which have diameters, d<5 nm, too small to be observed with typical particle measurement instrumentation. The size of the particles determined by AFM and DMA compares well with the size determined by in situ optical measurements, indicating that the interpretation of the UV–visible optical signal is quite good, and strongly showing the presence of d=2–4 nm particles. UV–visible extinction measurements are also used to determine the concentration of d=2–4 nm particles at the exhausts of practical combustion systems. A numerical model, able to reproduce the experimentally observed low coagulation rate of nanoparticles with respect to soot particles, is used to investigate the operating conditions in the combustion chamber and exhaust system for which 2–4 nm particles survive the exhaust or grow to larger sizes. Combustion generated nanoparticles are suspected to affect human and environmental health because of their affinity for water, small size, low rate of coagulation, and large surface area/weight ratio. The ability to isolate nanoparticles from soot particles in hydrosols collected from combustion may be useful for future analysis by a variety of techniques and toxicological assays.     

汽车尾气颗粒物对动物肺泡巨噬细胞的免疫毒性及比较

研究汽车尾气颗粒物气管染毒后对大鼠肺泡巨噬细胞免疫功能的影响，结果是动物肺泡巨噬细胞Ｆｃ受体表达、ＡＭ抗肿瘤细胞毒作用、抗体介导细胞毒作用受到抑制，具有明显的剂量效应关系；总体比较，汽油车尾气颗粒物对ＡＭ免疫功能影响较柴油车严重。     

Combined biocidal action of silver nanoparticles and ions against Chlorococcales (S<Emphasis Type="Italic">cenedesmus quadricauda</Emphasis>, <Emphasis Type="Italic">Chlorella vulgaris)</Emphasis> and filamentous algae (<Emphasis Type="Italic">Klebsormidium sp.</Emphasis>)

Despite the extensive research, the mechanism of the antimicrobial and biocidal performance of silver nanoparticles has not been unequivocally elucidated yet. Our study was aimed at the investigation of the ability of silver nanoparticles to suppress the growth of three types of algae colonizing the wetted surfaces or submerged objects and the mechanism of their action. Silver nanoparticles exhibited a substantial toxicity towards Chlorococcales Scenedesmus quadricauda, Chlorella vulgaris, and filamentous algae Klebsormidium sp., which correlated with their particle size. The particles had very good stability against agglomeration even in the presence of multivalent cations. The concentration of silver ions in equilibrium with nanoparticles markedly depended on the particle size, achieving about 6 % and as low as about 0.1 % or even less for the particles 5 nm in size and for larger ones (40–70 nm), respectively. Even very limited proportion of small particles together with larger ones could substantially increase concentration of Ag ions in solution. The highest toxicity was found for the 5-nm-sized particles, being the smallest ones in this study. Their toxicity was even higher than that of silver ions at the same silver concentration. When compared as a function of the Ag⁺ concentration in equilibrium with 5-nm particles, the toxicity of ions was at least 17 times higher than that obtained by dissolving silver nitrite (if not taking into account the effect of nanoparticles themselves). The mechanism of the toxicity of silver nanoparticles was found complex with an important role played by the adsorption of silver nanoparticles and the ions released from the particles on the cell surface. This mechanism could be described as some sort of synergy between nanoparticles and ions. While our study clearly showed the presence of this synergy, its detailed explanation is experimentally highly demanding, requiring a close cooperation between materials scientists, physical chemists, and biologists.     

Toxicity,uptake, and accumulation of nano and bulk cerium oxide particles in <Emphasis Type="Italic">Artemia salina</Emphasis>

Although the toxicological impact of metal oxide nanoparticles has been studied for the last few decades on aquatic organisms, the exact mechanism of action is still unclear. The fate, behavior, and biological activity of nanoparticles are dependent on physicochemical factors like size, shape, surface area, and stability in the medium. This study deals with the effect of nano and bulk CeO₂ particles on marine microcrustacean, Artemia salina. The primary size was found to be 15 ± 3.5 and 582 ± 50 nm for nano and bulk CeO₂ (TEM), respectively. The colloidal stability and sedimentation assays showed rapid aggregation of bulk particles in seawater. Both the sizes of CeO₂ particles inhibited the hatching rate of brine shrimp cyst. Nano CeO₂ was found to be more toxic to A. salina (48 h LC₅₀ 38.0 mg/L) when compared to bulk CeO₂ (48 h LC₅₀ 92.2 mg/L). Nano CeO₂-treated A. salina showed higher oxidative stress (ROS) than those treated with the bulk form. The reduction in the antioxidant activity indicated an increase in oxidative stress in the cells. Higher acetylcholinesterase activity (AChE) was observed upon exposure to nano and bulk CeO₂ particles. The uptake and accumulation of CeO₂ particles were increased with respect to the concentration and particle size. Thus, the above results revealed that nano CeO₂ was more lethal to A. salina as compared to bulk particles.     

Assessment of transport of two polyelectrolyte-stabilized zero-valent iron nanoparticles in porous media

This study investigated the breakthrough patterns of carboxymethyl cellulose- and polyacrylic acid-stabilized zero-valent iron (Fe(0)) nanoparticles (NZVI) from packed sand columns under a range of pore water velocities of 0.02, 0.2 and 1 cm min(-1) and NZVI influent concentrations of 0.1, 0.5 and 3 g L(-1). The NZVI effluent relative concentrations of both types of particles decreased with slower flow velocities and increasing particle concentrations. PAA-NZVI exhibited slower elution from the columns than CMC-NZVI under identical experimental conditions, and this is attributed to more rapid aggregation kinetics of PAA-NZVI. The elution patterns of PAA-NZVI showed a stronger trend of gradually increasing effluent concentrations with flushing of additional pore volumes, especially at low flushing velocities and higher influent particle concentrations and this phenomenon too can be attributed to increasing aggregate sizes with time which caused decreases in the values of the single collector efficiency and thus the deposition rate constant. A 7 nm increase in CMC-NZVI aggregate size over 60 min was observed using nanoparticle tracking analysis. The reduction in colloidal stability due to aggregation of CMC- and PAA-NZVI was verified using sedimentation tests, and it was found that PAA-NZVI were less stable than CMC-NZVI. There were also notable inherent differences in the two NZVI particles. The CMC-NZVI were monodisperse with a mean diameter of 5.7 ± 0.9 nm, whereas PAA-NZVI had a bimodal particle size distribution with a small sub-population of particles with mean size of 30 ± 21 nm and a more abundant population of 4.6 ± 0.8 nm diameter particles. Furthermore, PAA-NZVI had a lower surface potential. These characteristics are also responsible for the different elution patterns CMC- and PAA-NZVI.     

In situ immobilization of Cu(II) in soils using a new class of iron phosphate nanoparticles

This study tested the feasibility of using a new class of iron phosphate (vivianite) nanoparticles synthesized using sodium carboxymethyl cellulose (NaCMC) as a stabilizer for in situ immobilization of Cu(II) in soils. Transmission electron microscopy measurements demonstrated that the particle size was about 8.4+/-2.9 nm. Batch tests showed that nano-sized vivianite particles can effectively reduce the leachability and in vitro bioaccessibility of Cu(II) in three representative soils (calcareous, neutral, and acidic) at the low doses of 0.61 and 3.01 mg PO(4) g(-1) soil. The Cu leachability was evaluated by the toxicity characteristic leaching procedure and in vitro bioaccessibility was evaluated by the physiological based extraction test. In the case of soil amendment with nanoparticles in 3.01 mg PO(4) g(-1) soil, Cu leachability reduced 63-87% and Cu concentrations in TCLP extract decreased from 1.74-13.33 mg l(-1) to 0.23-2.55 mg l(-1) after those soils were amended for 56 d. Meanwhile, the bioaccessibility of Cu was reduced by 54-69%. Sequential extraction procedures showed the significant decrease of water soluble/exchangeable Cu(II) and carbonate bound fractions and concomitant increase of Cu residual fraction after the soils were amended with the nanoparticles, suggesting that the formation of copper phosphate minerals through precipitation and adsorption was probably responsible for the decrease of Cu availability in soils. Visual MINTEQ modeling further revealed that Cu(3)(PO(4))(2) and Cu(5)(PO(4))(3)OH were formed in the vivianite-solid Cu(II) system, resulting in the decreased solubility of the Cu(II) in the acidic pH range.     

Shape-dependent bactericidal activity of TiO2 for the killing of Gram-negative bacteria Agrobacterium tumefaciens under UV torch irradiation

This paper demonstrated the relative bactericidal activity of photoirradiated (6W-UV Torch, λ?>?340 nm and intensity?=?0.64 mW/cm²) P25–TiO₂ nanoparticles, nanorods, and nanotubes for the killing of Gram-negative bacterium Agrobacterium tumefaciens LBA4404 for the first time. TiO₂ nanorod (anatase) with length of 70–100 nm and diameter of 10–12 nm, and TiO₂ nanotube with length of 90–110 nm and diameter of 9–11 nm were prepared from P-25 Degussa TiO₂ (size, 30–50 nm) by hydrothermal method and compared their biocidal activity both in aqueous slurry and thin films. The mode of bacterial cell decomposition was analyzed through transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR), and K⁺ ion leakage. The antimicrobial activity of photoirradiated TiO₂ of different shapes was found to be in the order P25–TiO₂?>?nanorod?>?nanotube which is reverse to their specific surface area as 54?<?79?<?176 m² g^?1, evidencing that the highest activity of P25–TiO₂ nanoparticles is not due to surface area as their crystal structure and surface morphology are entirely different. TiO₂ thin films always exhibited less photoactivity as compared to its aqueous suspension under similar conditions of cell viability test. The changes in the bacterial surface morphology by UV-irradiated P25–TiO₂ nanoparticles was examined by TEM, oxidative degradation of cell components such as proteins, carbohydrates, phospholipids, nucleic acids by FT-IR spectral analysis, and K⁺ ion leakage (2.5 ppm as compared to 0.4 ppm for control culture) as a measure of loss in cell membrane permeability.     

Removal of nanoparticles from CMP wastewater by magnetic seeding aggregation

CMP wastewaters have high solids content resulted from abrasive nanoparticles. Tremendous amount of ultrapure water consumption also makes the removal of nanoparticles from CMP wastewaters an important issue. Magnetic seeding aggregation of silica nanoparticles from the oxide CMP wastewater is studied in this work. Magnetite nanoparticles were synthesized and used as seeding particles. The turbidity of the CMP wastewater was reduced from 110 NTU to 7 NTU when solution pH was 6 and no addition of salt. This is because silica and magnetite nanoparticles were highly oppositely charged and the aggregation between silica and magnetite nanoparticles was achieved by electrostatic attractions. When the seeded wastewater was placed in a magnetic field strength higher than 800 G, the turbidity of the CMP wastewater was reduced to 1 NTU, which was clearer than the CMP wastewater treated by many other technologies.     

On airborne nano/micro-sized wear particles released from low-metallic automotive brakes

The paper addresses the wear particles released from commercially available “low-metallic” automotive brake pads subjected to brake dynamometer tests. Particle size distribution was measured in situ and the generated particles were collected. The collected fractions and the original bulk material were analyzed using several chemical and microscopic techniques. The experiments demonstrated that airborne wear particles with sizes between 10 nm and 20 μm were released into the air. The numbers of nanoparticles (<100 nm) were by three orders of magnitude larger when compared to the microparticles. A significant release of nanoparticles was measured when the average temperature of the rotor reached 300 °C, the combustion initiation temperature of organics present in brakes. In contrast to particle size distribution data, the microscopic analysis revealed the presence of nanoparticles, mostly in the form of agglomerates, in all captured fractions. The majority of elements present in the bulk material were also detected in the ultra-fine fraction of the wear particles.     

Sources and concentration of nanoparticles (<10 nm diameter) in the urban atmosphere

Whilst limited information on particle size distributions and number concentrations in cities is available, very few data on the very smallest of particles, nanoparticles, have been recorded. Measurements in this study show that road traffic and stationary combustion sources generate a significant number of nanoparticles of diameter <10 nm. Measurements at the roadside (4 m from the kerb) and downwind from the traffic (more than 25 m from the kerb) show that nanoparticles (<10 nm diameter) accounted for more than 36–44% of the total particle number concentrations. Measurements designed to sample the plume of individual vehicles showed that both a diesel- and a petrol-fuelled vehicle generated nanoparticles (<10 nm diameter). The fraction of nanoparticles was even greater in a plume 350 m downwind of a stationary combustion source. On a few occasions, a temporal association between nanoparticles in the size range 3–7 nm and solar radiation was observed in urban background air at times when no other local sources were influential, which suggests that homogeneous nucleation can also be an important source of particles in the urban atmosphere.     

Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO₂ particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range.TiO₂ particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO₂ particles between roughly 20 and 300 nm. Analytical electron microscopy revealed that TiO₂ particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO₂ particles in the runoff.     

On the efficiency of impingers with fritted nozzle tip for collection of ultrafine particles

The aim of this study was to determine the collection efficiency of ultrafine particles into an impinger fitted with a fritted nozzle tip as a means to increase contact surface area between the aerosol and the liquid. The influence of liquid sampling volume, frit porosity and the nature of the sampling liquid was explored and it was shown that all impact on the collection efficiency of particles smaller than 220 nm. Obtained values for overall collection efficiency were substantially higher (～30–95%) than have been previously reported, mainly due to the high deposition of particles in the fritted nozzle tip, especially in case of finer porosity frits and smaller particles. Values for the capture efficiency of the solvent alone ranged from 20 to 45%, depending on the type and the volume of solvent. Additionally, our results show that airstream dispersion into bubbles improves particle trapping by the liquid and that there is a difference in collection efficiencies based on the nature and volume of the solvent used.     

SARA Title III,Section 313 —Looking Ahead

This study performed a workplace evaluation of emission control using available air sampling filters and characterized the emitted particles captured in filters. Characterized particles were contained in the exhaust gas released from carbon nanotube (CNT) synthesis using chemical vapor deposition (CVD). Emitted nanoparticles were collected on grids to be analyzed using transmission electron microscopy (TEM). CNT clusters in the exhaust gas were collected on filters for investigation. Three types of filters, including Nalgene surfactant-free cellulose acetate (SFCA), Pall A/E glass fiber, and Whatman QMA quartz filters, were evaluated as emission control measures, and particles deposited in the filters were characterized using scanning transmission electron microscopy (STEM) to further understand the nature of particles emitted from this CNT production. STEM analysis for collected particles on filters found that particles deposited on filter fibers had a similar morphology on all three filters, that is, hydrophobic agglomerates forming circular beaded clusters on hydrophilic filter fibers on the collecting side of the filter. CNT agglomerates were found trapped underneath the filter surface. The particle agglomerates consisted mostly of elemental carbon regardless of the shapes. Most particles were trapped in filters and no particles were found in the exhaust downstream from A/E and quartz filters, while a few nanometer-sized and submicrometer-sized individual particles and filament agglomerates were found downstream from the SFCA filter. The number concentration of particles with diameters from 5 nm to 20 µm was measured while collecting particles on grids at the exhaust piping. Total number concentration was reduced from an average of 88,500 to 700 particle/cm³ for the lowest found for all filters used. Overall, the quartz filter showed the most consistent and highest particle reduction control, and exhaust particles containing nanotubes were successfully collected and trapped inside this filter.

Implications: As concern for the toxicity of engineered nanoparticles grows, there is a need to characterize emission from carbon nanotube synthesis processes and to investigate methods to prevent their environmental release. At this time, the particles emitted from synthesis were not well characterized when collected on filters, and limited information was available about filter performance to such emission. This field study used readily available sampling filters to collect nanoparticles from the exhaust gas of a carbon nanotube furnace. New agglomerates were found on filters from such emitted particles, and the performance of using the filters studied was encouraging in terms of capturing emissions from carbon nanotube synthesis.     

Phase separation and regrowth of aerosol matter collected after size fractionation in an impactor

Aerosol matter in the size range <2 μm was collected in a Berner impactor and subsequently analysed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. Owing to the low electron beam energy of 5 keV (occasionally 10 keV), analysis was restricted to elements with atomic numbers 20 (Ca). Sub-micrometer aerosol matter was found to contain mostly S, O, and C as well as some K and Ca. Nitrogen appeared to escape detection, probably due to bombardment-induced sublimation of NO₃ and NH₄. During sampling at low to moderate relative humidity (<60%) the sulphur-rich fraction of the aerosol matter (most likely sulphates) regrew in the form of microcrystals with sizes up to 10 times larger than the mean aerodynamic diameter of the respective impactor stage. By contrast, when sampling during periods in course of which the relative humidity exceeded 70%, the aerosol matter regrew in the form of extended amorphous agglomerates. The aerosol deposits also contained large numbers of carbon nanoparticles, well separated from the regrown sulphate-rich matter. The nanoparticles were similar in size (20–40 nm), much smaller than the equivalent aerodynamic diameter of the impacting particles (63 nm–2 μm). Presumably, the carbon nanoparticles constituted the core of larger air-borne particles covered with sulphates (as well as with nitrates and organic carbon). The regrown microcrystals disappeared rapidly under electron bombardment at high current density, an observation that indicates high volatility at elevated temperatures. Aerosol matter collected in the size range between 1 and 2 μm contained large fractions of particles made of O, Si, P, K, and Ca (oxides). These particles were highly resistant to electron bombardment (hard) and showed little or no evidence for agglomeration or regrowth. After removing the soluble (acidic) material from the collected aerosol matter, only carbon nanoparticles and hard coarse particles were left behind. The observation of agglomerated or crystallized “soft” aerosol matter in combination with phase separation of carbon nanoparticles lends further support to the assertion that it is not possible to collect useful quantities of fine and ultrafine aerosol particles with as-suspended morphology. Some implications for health-related research are discussed.     

Influence of early stages of arbuscular mycorrhiza on uptake of zinc and phosphorus by red clover from a low-phosphorus soil amended with zinc and phosphorus

In a pot experiment, red clover (Trifolium pratense) was grown in sterilized Zn-amended low available P soil (0, 50 or 400 mg Zn kg(-1)) with or without 100 mg kg(-1) added P and with or without inoculation with the arbuscular mycorrhizal (AM) fungus G. mosseae. When the plants were harvested after 40 days, AM colonization of the roots was still at an early stage, with only 14-38% of total root length colonized on average. AM colonization was highest in low-P soil, and was lowest in soil amended with 400 mg Zn kg(-1). Shoot yields were highest in AM plants with added P, but root yields were unaffected by AM inoculation. Shoot and root yields were higher with 100 mg added P kg(-1) soil, but lower with 400 mg Zn kg(-1) than 50 mg Zn kg(-1) or controls unamended with Zn. Shoot and root P concentrations were seldom higher in AM plants, but shoot P offtakes were higher in AM plants with added P. Concentrations of Zn and Cu were much higher in the roots than in the shoots. Shoot and root Zn and shoot Cu were lower, but root Cu was higher, in AM plants. Soil residual pH after plant growth was higher in AM treatments, and residual total Zn was also higher, indicating lower Zn uptake by AM plants. Soil solution pH was higher in AM treatments, and soil solution Zn was lower in the presence of mycorrhiza. The results are discussed in terms of AM protection of the plants against excessive shoot Zn uptake.