Source and selectivity in the accumulation of mercury and other metals by the plants of Mt. Etna

The air Hg content at and near the summit of Mt. Etna is approximately 500- to 2000-fold lower than it is in the atmospheres around Antarctic, Hawaiian and Icelandic volcanoes. In contrast, the soils and plants on Mt. Etna show only 10- to 30-fold reductions in Hg content; in other words, there is at least a ten-fold enrichment relative to air. This disparity called into question the source of Hg in the vegetation and upper soil layers. Soils and a variety of plant species were analyzed for Hg, Fe, Cu, and Mn content at a number of stations on Mt. Etna including several also sampled for air Hg, and compared with the data for plants and soils from other volcanic and non-volcanic locations, especially Hawaii, Africa and Iceland. Etna vascular plants do not accumulate Hg, and lichens do so only to a moderate extent. Relative to their Fe content, however, all the Etna soils are enriched in Hg, but the reverse is true for Cu relative to Hg. The plants, on the other hand, when compared with their soils, are enriched in Hg relative to Cu. By comparing Fe/Hg atomic ratios for plants and soil, we calculated an Enrichment Factor (EF) for Hg. This value ranged from 19 to 102 for Etna, and 19 to 184 for all subtropical plants discussed here. The Hg EF for Icelandic samples was ca. 823, reflecting other environmental/geochemical determinants. No net surface deposition of Hg takes place on Etna from plant or atmospheric sources, and the relative Hg contents of soils and plants do not show a consistent relation to air Hg concenctration. Nevertheless, the plant/soil Cu and Hg ratios (CR) vary similarly as do the atomic ratio (AR) values for Fe and Hg. We conclude from these relationships that the atmosphere is not a major source of plant (or soil) Hg and that the likely alternatives are: release at some relatively remote point in time, but not to any significant degree since; release into the atmosphere as Hg = species other than Hg⁰; or movement from very deep subsurface compartments. These alternatives are not mutually exclusive. It is highly improbable that summit emissions constitute a significant source of Hg in the Mediterrean Basin.     

Equisetum and the cycling of mercury at Mount St. Helens: Plant-soil relations, 1980–1984

The Hg content ofEquisetum shoots at six stations near Mount St. Helens rose to a peak value in July 1982, 26 mo after the great eruption of May 1981. The July 1982 peak in plant Hg content was followed by a continual decline in plant tissue Hg at all six stations as measured in September 1982 and August 1984. During this 2 yr period, soil Hg levels declined at only three of the six stations, while remaining essentially unchanged at two stations and increasing nearly 20-fold at one station. Therefore, soil Hg behaved independently with respect to plant Hg at least at three of the six sites. This follow-up study at Mount St. Helens supports the notion of a major source of atmospheric mercury which is taken up directly by plants.     

Mercury pollution in the soil and mosses around a geothermal plant

Samples of soils and mosses were collected near a geothermal power plant, which is located in one of the most active geothermal fields of the world (Southern Tuscany). High concentrations of Hg (up to 1.8 μg g^?1 d.w.) occur in mosses as far as 0.6 km from the geothermal plant, and the Hg uptake of mosses is unrelated to the species except for Bryum torquescens. The Hg in the soil was lower than in mosses, and the greatest concentrations in soil were near the Travale-22 well, which feeds the most powerful geothermal plant (30 MW) in the area. In addition, the concentrations of Hg detected in soil cores and in old bottom leaves of several specimens of Hypnum cupressiforme show that this element has been emitted into the air also in the past probably since the discovery of T-22 well in 1972.     

Hg, Cu, Pb, Cd, and Zn Accumulation in Macrophytes Growing in Tropical Wetlands

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g^?1 Hg, 6.5?C250.3 mg g^?1 Cu, 0.059?C0.245 mg g^?1 Pb, 0.004?C0.066 mg g^?1 Cd, and 31.8?363.1 mg g^?1 Zn in roots and 0.033?C0.888 mg g^?1 Hg, 2.2?C70.7 mg g^?1 Cu, 0.005?C0.086 mg g^?1 Pb, 0.001?C0.03 mg g^?1 Cd, and 12.6?C140.4 mg g^?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.     

Do plant species with different growth strategies vary in their ability to compete with soil microbes for chemical forms of nitrogen?

We used dual labelled stable isotope (¹³C and ¹⁵N) techniques to examine how grassland plant species with different growth strategies vary in their ability to compete with soil microbes for different chemical forms of nitrogen (N), both inorganic and organic. We also tested whether some plant species might avoid competition by preferentially using different chemical forms of N than microbes. This was tested in a pot experiment where monocultures of five co-existing grassland species, namely the grasses Agrostis capillaris, Anthoxanthum odoratum, Nardus stricta, Deschampsia flexuosa and the herb Rumex acetosella, were grown in field soil from an acid semi-natural temperate grassland. Our data show that grassland plant species with different growth strategies are able to compete effectively with soil microbes for most N forms presented to them, including inorganic N and amino acids of varying complexity. Contrary to what has been found in strongly N limited ecosystems, we did not detect any differential uptake of N on the basis of chemical form, other than that shoot tissue of fast-growing plant species was more enriched in ¹⁵N from ammonium-nitrate and glycine, than from more complex amino acids. Shoot tissue of slow-growing species was equally enriched in ¹⁵N from all these N forms. However, all species tested, least preferred the most complex amino acid phenylalanine, which was preferentially used by soil microbes. We also found that while fast-growing plants took up more of the added N forms than slow-growing species, this variation was not related to differences in the ability of plants to compete with microbes for N forms, as hypothesised. On the contrary, we detected no difference in microbial biomass or microbial uptake of ¹⁵N between fast and slow-growing plant species, suggesting that plant traits that regulate nutrient capture, as opposed to plant species-specific interactions with soil microbes, are the main factor controlling variation in uptake of N by grassland plant species. Overall, our data provide insights into the interactions between plants and soil microbes that influence plant nitrogen use in grassland ecosystems.     

ALUMINIUM TOXICITY AND TOLERANCE IN THREE HEATHLAND SPECIES

Arnica montana and Cirsium dissectum are characteristic species of species-rich heathlands and adjacent grasslands, which declined during the last decades in the Netherlands. It has been shown in a recent field survey that the decline of A. montana and C. dissectum might be caused by soil acidification. Calluna vulgaris is not susceptible to soil acidification. It was hypothesized that increased aluminium concentrations in the soil as a result of acidifying atmospheric inputs caused the decline of A. montana and C. dissectum whereas C. vulgaris would not be sensitive to enhanced aluminium concentrations. We studied the effects of different Al:Ca-ratios and of Al concentrations on the development of A. montana, C. dissectum and C. vulgaris in nutrient solution experiments. All three species showed aluminium accumulation in the shoots related with increased aluminium concentrations in the nutrient solutions. This accumulation was correlated with a reduction in growth when plants were cultured at high Al concentrations (200–500 µmol l^-1), in both A. montana and C. dissectum. In addition, indications of Al toxicity were observed in these plant species, e.g. poor root development, yellowish leaves and reduced contents of Mg and P in the plants. C. vulgaris did not show reduced growth or poor plant development due to high Al concentrations. The negative effects of aluminium in A. montana and C. dissectum were partly counterbalanced when plants were grown on the same Al concentrations but with increased Ca concentrations, resulting in lower Al:Ca-ratios. No effects of enhanced calcium concentrations on C. vulgaris have been observed.     

Mercury Uptake by Trees: An Observational Experiment

We conducted a simple observational experiment to test whether differences in Hg in tissue of red pine (Pinus resinosa Ait.) were related to soil or to atmospheric sources of Hg. We sampled two plantations in each of three areas, and within each plantation sampled two sites with different levels of soil Hg. Woody tissue Hg concentration differed by area, and differences in foliar concentrations, though not statistically significant, were ranked in the same order. Total mass of Hg in forest floor and mineral soil also differed by area, but with ranking opposite that of tissue. On an individual-tree basis, concentrations of Hg in 1994 needles (2-year old) were about twice those in 1995 needles (1-year old) (r = 0.77). Neither woody tissue Hg nor any measure of Hg in soil or forest floor were closely related to foliar levels and some relationships were inverse. We interpret the data to indicate that Hg in plant tissue is derived directly from the atmosphere, not the soil. Tissue concentration by area was closely related to the respective growing season length (1994 needles, r = 0.88; 1995 needles, r = 0.97; wood, r = 0.97), as was total mass of Hg in forest floor and surface mineral soil (r = – 0.80). Other climatic measures, such as growing degree days and actual evapotranspiration, had similar relationships. These relationships imply that both foliar uptake of Hg⁰ from the atmosphere and efflux of Hg from the soil system depend on biological activity.     

Mercury Mobilization in a Contaminated Industrial Soil for Phytoremediation

The aim of this work was to investigate the possibility of using plants for mercury (Hg) removal from a contaminated industrial soil, increasing the metal's bioaccessibility by using mobilizing agents: ammonium thiosulphate [(NH₄)₂S₂O₃] and potassium iodide (KI). The selected plant species were Brassica juncea and Poa annua. The addition of the mobilizing agents promoted Hg uptake by plants, with respect to controls. Treatments promoted Hg translocation to aerial parts. In the case of Poa annua, greater Hg uptake was found in plants after the 100 mM KI treatment, reaching values that were nearly 400 mg kg^?1 in the aerial part. In contrast, Brassica juncea plants accumulated in their aerial part the greatest Hg quantities, about 100 mg kg^?1, after treatment with 0.27 M (NH₄)₂S₂O₃. The ratio between the concentration of Hg in the shoots and the initial concentration in the soil support the potential for successfully applying Hg phytoextraction on this soil.     

汞在山东省三种森林土壤上的吸附解吸特征研究

As one of the most toxic heavy metals with persistence, bioaccumulation, and toxicity in environment, mercury and its envi- ronmental problems have caused a global concern. To fully understand the behavior and fate of mercury (Hg)(Ⅱ) in forest soils, a series of batch experiments were conducted to determine the adsorption and desorption characteristics of Hg(Ⅱ) by three dark brown forest soils from Mount Taishan, Laoshan Mountain, and Fanggan Village in Shandong Province, China. The adsorption solution was prepared using 0.1 mol L-1 NaNO3 as background electrolyte, with Hg(Ⅱ) at rising concentration gradients of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mg L-1 . Fourier transform infrared (FTIR) spectroscopy was adopted to characterize the soil samples and soil-Hg complexes. It was found that Hg(Ⅱ) adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. The soil from Mount Taishan had the largest potential Hg(Ⅱ) adsorption capacity, though with less adsorptive intensity. The percentages of Hg(Ⅱ) desorbed from all soil samples were less than 0.6%, which suggested that all the soils studied had a high binding strength for Hg(Ⅱ). The soil from Mount Taishan had a higher Hg(Ⅱ) desorption capacity than the other soils, which indicated that the Hg(Ⅱ) deposited on the topsoil of Mount Taishan from atmosphere may easily discharge to surface water through runoff. Results of the FTIR spectroscopy showed that the three soils contained the same functional groups. The relative absorbencies of soil-Hg complexes changed significantly compared with those of the soil samples and the adsorption of Hg(Ⅱ) mainly acted on the O-H, C-O, and C=O groups of the soils.     

Soil and Foliar Mercury Emission as a Function of Soil Concentration

The goal of this study was to investigate net mercury flux associated with seedlings of two species (Populus tremuloides and Pinus ponderosa) grown in three soil exposure concentrations (0.010 ± 0.001, 6.15 ± 0.86, and 25.56 ± 2.10 µg Hg g^-1) and to determine if mercury flux from vegetation was directly correlated with mercury concentration in the soil. Net mercury flux was measured using a gas exchange system. Mercury emission from foliage was not influenced by mercury concentration in the soil. Experiments were also done to assess the significance of mercury emission from vegetation relative to that occurring from associated soils. Mean soil mercury emissions were 1 to 3 orders of magnitude higher than that from plants grown in similar soil mercury concentrations. Light and the addition of water were found to significantly increase mercury emission from soils, and the magnitude of the flux response to watering was correlated with soil mercury concentration.     

A Laboratory Study on Revegetation and Metal Uptake in Native Plant Species from Neutral Mine Tailings

Lygeum spartum, Zygophyllum fabago and Piptatherum miliaceum are typical plant species that grow in mine tailings in semiarid Mediterranean areas. The aim of this work was to investigate metal uptake of these species growing on neutral mine tailings under controlled conditions and their response to fertilizer additions. A neutral mine tailing (pH of soil solution of 7.1–7.2) with high total metal concentrations (9,100 and 5,200 mg kg^?1 Zn and Pb, respectively) from Southern Spain was used. Soluble Zn and Pb were low (0.5 and <0.1 mg l^?1, respectively) but the major cations and anions reached relatively high levels (e.g. 2,600 and 1,400 mg l^?1 Cl and Na). Fertilization caused a significant increase of the plant weight for the three species and decreased metal accumulation with the exception of Cd. Roots accumulated much higher metal concentrations for the three plants than shoots, except Cd in L. spartum. Shoot concentrations for the three plants were 3–14 mg kg^?1 Cd, 150–300 mg kg^?1 Zn, 4–11 mg kg^?1 Cu, and 1–10 mg kg^?1 As, and 6–110 mg kg^?1 Pb. The results indicate that neutral pH mine tailings present a suitable substrate for establishment of these native plants species and fertilizer favors this establishment. Metal accumulation in plants is relatively low despite high total soil concentrations.     

粤西地区土壤-植物系统中稀土元素地球化学特征

在广东省西部不同地区采取土壤、植物样品，并对其中的稀土元素含量采用ICP-MS法测定，研究了稀土元素在土壤、植物叶中的地球化学特征。结果表明：土壤一植物系统的各环节间稀土元素的含量模式基本相似。不同母岩发育的土壤稀土分布有较大的差异，其中以花岗岩发育的土壤稀土含量最高。在土壤的各个剖面层中，心土层和底土层稀土含量高于表土层，轻重稀土发生分异，均有不同程度的Eu亏损，Ce表现为土壤各层位中的正异常。同一采样点的不同种属植物具有相似的稀土分配模式，在不同母岩发育土壤上生存的同一种属植物稀土分配模式不同，其稀土分布均受其所生存土壤的影响和制约，同时具有自身的生物地球化学特性。生物吸收系数表明植物对稀土元素的吸收能力的差异，稀土元素在由土壤向植物体运输迁移中发生了明显的分馏作用，重稀士相对贫乏。     

Mercury in soils and crops from fields receiving high cumulative sewage sludge applications: Validation of U. S. EPA's risk assessment for human ingestion

The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) has owned and operated a 6320 ha Dedicated Beneficial Sludge Utilization Site in Fulton County, Illinois since 1971. The site consists of calcareous strip mine spoil intermingled with placed land. Sewage sludge from Chicago is barged to the site, located approximately 185 miles southwest of the city, and utilized to reclaim the strip mined soils and to fertilize the corn and wheat crops grown on them. Fields have received as much as 1317 dry Mg ha^?1 of sewage sludge since 1971. Sludge Hg concentrations have ranged from 1.1 to 8.5 mg Hg kg^?1 with mean concentration of 3.31 mg Hg kg^?1, and maximum cumulative Hg loading rates are approximately 4 kg ha^?1. Sludge applications have significantly increased extractable soil Hg concentrations, and regression analysis indicates that from 80 to 100% of the Hg applied to soils in sewage sludge since 1971 still resides in the top 15 cm of soil. Since 1985 the MWRDGC has been monitoring Hg concentration in corn leaf and grain, wheat grain and soils at the Fulton County site. Monitoring data indicate that 98.8% of the corn grain samples, 93.0% of the wheat samples and 50.7% of the corn leaf samples collected from 1985 through 1992 had Hg concentrations below detectable limits (<25μg kg^?1). Cumulative Hg loading rates are utilized along with crop tissue concentrations to compute crop uptake response slopes (UC) for Hg into plant tissues at the Fulton County site. The UC for corn and wheat grain was zero and for corn leaf was ?0.0014 (mg Hg/kg tissue)/(kg Hg/ha soil), which indicate that sewage sludge additions did not increase plant tissue Hg concentrations at the Fulton County site. The negative UC obtained for corn leaf may actually indicate that sewage sludge applications decreased Hg uptake from mined soils possibly due to organic carbon and sulfides in the anaerobically digested sludge binding native Hg. The United States Environmental Protection Agency (U. S. EPA) has recently promulgated their 40 CFR Part 503 regulation for sewage sludge use and disposal. The rule sets risk based limits on ten metals, including Hg, in sludges that are land applied. Exposure pathways involving plant uptake of Hg are briefly discussed and it is shown that the UC used in U. S. EPA's risk assessment models for these pathways overpredict uptake of Hg by crops when compared with the UC derived from the MWRDGC's monitoring data at Fulton County.     

Plant species influence microbial diversity and carbon allocation in the rhizosphere

Plant species effects on microbial communities are attributed to changes in microbial community composition and biomass, and may depend on plant species specific differences in the quality of resources (carbon) inputs. We examined the idea that plant-soil feedbacks can be explained by a chance effect, which is the probability of a highly productive or keystone plant species is present in the community and will influence the functions more than the number of species per se. A ¹³C pulse labelling technique was applied to three plant species and a species mixture in a greenhouse experiment to examine the carbon flow from plants to soil microbial communities. The ¹³C label was given as CO₂ to shoots of a legume (Lotus corniculatus), a forb (Plantago lanceolata), a grass (Holcus lanatus) and a mixture of the three species. Microbial phospholipid fatty acids (PLFA) was analysed in order to determine the biomass and composition of the soil microbial community. The incorporation of the stable isotope into soil microorganisms was determined through GC-IRMS analyses of the microbial PLFAs. Plant species identity did not influence the microbial biomass when determined as total carbon of microbial phospholipid fatty acids. However, the labelled carbon showed that the grass monoculture (H. lanatus) and the plant mixture allocated more ¹³C into bacteria and actinomycete biomass than the other plant species. H. lanatus monocultures had also the highest amounts of ¹³C allocated to AM-fungi and saprophytic fungi. The carbon allocation from plants to soil microorganisms in a plant species mixture can thus be explained by the presence of a highly productive species that influence soil functions.     

Phytosequestration of Metals in Selected Plants Growing on a Contaminated Okhla Industrial Areas, Okhla, New Delhi, India

Contamination of metal ions in soil and water represents more pressing threats to resources as well as human health. The present research was carried out to screen the phytosequester plants growing in industrial waste- and wastewater-affected industrial areas of Okhla, New Delhi, India. Accumulation trend of metal Fe, Zn, Cu, Cr, Pb, Cd, Hg, and As from soil and wastewater by plants were collected for study. Among aquatic plants Hydrilla verticillata, Marsilea quadrifolia, and Ipomea aquatica were found to be highest metals accumulator, Eclipta alba and Sesbania cannabina among terrestrial plant were highest accumulator of metals. Among the algal spp. Spirulina platensis and Phormidium papyraceum were the most efficient in accumulating Cd and Hg. The maximum bioconcentration factor (BCF) was recorded in Hygroryza aristata for the metals (Hg, Cd) in M. quadrifolia (Cd, Cr), in E. alba (Cr, Cu), and in S. platensis (Hg, Pb). However, the translocation factor (TF) of metals was found more in M. quadrifolia followed by I. aquatica than other plants. Among all the plants, H. verticillata showed high TF and low BCF values for toxic metals (Pb, Cr) and was suitable for phytostabilization of these metals. Our study showed that native plant species growing on contaminated sites may have a potential of phytosequestration of these metals.     

Pioneer Mediterranean Shrub Species Revegetating Soils Developed on Mining Soils/Spoils

Spontaneous and autochthonous species of plants growing on degraded and contaminated soils/spoils that survive in such environments show, in general, no symptoms of toxicity. This study compares concentrations of chemical elements in different leaves maturation and in different seasons of several native species in a massive sulphide in an abandoned mine area. The objective is to evaluate if these species can play an important role on the stabilization of degraded soils and mine spoils. Total concentrations of chemical elements were great in soils. However, in general, only <1% of the total concentration was extracted by DTPA or ammonium acetate solutions. Total and available fraction of the chemical elements has similar behaviour between soil sites. Mature leaves have higher concentrations of As, Cu, Fe, Mn, Pb and Zn than younger ones. An opposite behaviour occurs with S. Winter and spring variations in most chemical elements concentrations in the plant leaves are not significantly different, except for As. Elemental concentrations of plant leaves are independent of the same elements concentrations (total and available fraction) in soils where plants have grown. The concentrations of As, Cu and Pb in plant leaves were below the level of risk to be ingested by grazing animals, although soils are above the reported thresholds. Therefore, all studied plant species can be considered for phytostabilization programmes, but the use of the land for pasture may not be a solution considering that animals ingest soil along with herbage. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of Mercury on Soybean Plants (Glycine max L.) at Low pH

The influence of Hg on soybean plants under different pH conditions and Hg concentrations was studied. Growth inhibition by Hg was higher in roots than the upper part of the plant, but was highly dependant on pH condition. Growth inhibition of roots was observed when Hg concentration was higher than 1 mg Hg L^?1 for pH 4.0 and 5 mg Hg L^?1 for pH 6.0. Using ²⁰³Hg as a radioactive tracer, the amount of Hg (1 mg Hg L^?1) uptake in root was found to be about 1.5 times higher at pH 4.0 than that at pH 6.0; suggesting that Hg when highly accumulated at the lower pH induced inhibition of root growth. Decreased amounts of Hg due to evaporation during the plant growth were very low, but were higher at pH 6.0 than that at pH 4.0. There was hardly any translocation of Hg from roots to the upper parts through the stem within 24 h.     

Do interactions with soil organisms mediate grass responses to defoliation?

Defoliation-induced changes in grass growth and C allocation are known to affect soil organisms, but how much these effects in turn mediate grass responses to defoliation is not fully understood. Here, we present results from a microcosm study that assessed the role of arbuscular mycorrhizal (AM) fungi and soil decomposers in the response of a common forage grass, Phleum pratense L., to defoliation at two nutrient availabilities (added inorganic nutrients or no added nutrients). We measured the growth and C and N allocations of P. pratense plants as well as the abundance of soil organisms in the plant rhizosphere 5 and 19 d after defoliation. To examine whether defoliation affected the availability of organic N to plants, we added ¹⁵N-labelled root litter to the soil and tracked the movement of mineralized ¹⁵N from the litter to the plant shoots.When inorganic nutrients were not added, defoliation reduced P. pratense growth and root C allocation, but increased the shoot N concentration, shoot N yield (amount of N in clipped plus harvested shoot mass) and relative shoot N allocation. Defoliation also reduced N uptake from the litter but did not affect total plant N uptake. Among soil organisms, defoliation reduced the root colonization rates of AM fungi but did not affect soil microbial respiration or the abundance of microbe-grazing nematodes. These results indicate that interactions with soil organisms were not responsible for the increased shoot N concentration and shoot N yield of defoliated P. pratense plants. Instead, these effects apparently reflect a higher efficiency in N uptake per unit plant mass and increased relative allocation of N to shoots in defoliated plants. The role of soil organisms did not change when additional nutrients were available at the moment of defoliation, but the effects of defoliation on shoot N concentration and yield became negative, apparently due to the reduced ability of defoliated plants to compete for the pulse of inorganic nutrients added at the moment of defoliation.Our results show that the typical grass responses to defoliation—increased shoot N concentration and shoot N yield—are not necessarily mediated by soil organisms. We also found that these responses followed defoliation even when the ability of plants to utilize N from organic sources, such as plant litter, was diminished, because defoliated plants showed higher N-uptake efficiency per unit plant mass and allocated relatively more N to shoots than non-defoliated plants.     

Railway transportation as a serious source of organic and inorganic pollution

Polycyclic aromatic hydrocarbons and heavy metal (Pb, Cd, Cu, Zn, Hg, Fe, Co, Cr, Mo) contents were established in soil and plant samples collected in different areas of the railway junction I?awa G?ówna, Poland. Soil and plant samples were collected in four functional parts of the junction, i.e. the loading ramp, main track within platform area, rolling stock cleaning bay and the railway siding. It was found that all the investigated areas were strongly contaminated with polycyclic aromatic hydrocarbons (PAHs). The PAH contamination of the soil was the highest in the railway siding and in the platform area (59,508 and 49,670?μg?kg(-1), respectively). In the loading ramp and cleaning bay, the PAH concentration in soil was lower but still relatively very high (17,948 and 15,376?μg?kg(-1), respectively). The contamination in the railway siding exceeded the average control level up to about 80 times. In the soil of all the investigated areas, four- and five-ring PAHs prevailed. The concentrations of PAHs were determined in four dominating species of plants found at the junction. The highest concentration was found in the aerial parts of Taraxacum officinale (22,492?μg?kg(-1)) growing in the cleaning bay. The comparison of the soil contamination with PAHs in the investigated railway junction showed a very significant increase of the PAHs level since 1995. It was found that the heavy metal contamination was also very high. Pb, Zn, Hg and Cd were established at the highest levels in the railway siding area, whereas Fe concentration was the highest in the platform area. A significant increase in mercury content was observed in the cleaning bay area. The investigations proved very significant increase of contamination with PAHs and similar heavy metals contamination in comparison with the concentration determined in the same areas 13?years ago.     

小浪底低山丘陵区植物N素吸收特征及其与土壤因子的关系

 为探寻温带地区山地植物N素保存策略,找出影响植物N素回收率的环境因子,以便了解植物保持所吸收养分的机制,以小浪底库区山地为例,研究该区域3种生活型21种典型植物成熟绿叶中的N素含量、枯叶中N素含量以及N素回收效率（NRE）。结果表明:植物成熟绿叶中的N素含量和枯叶中N素含量有显著的正相关关系;所测定的21种植物NRE在17.4%～50.1%之间,平均值为28.8%,多数种的回收效率低于40%。测定的21种植物都属于N素回收不完全植物。不同生活型的植物其回收效率有显著的差异,一般表现为草本>灌木>乔木。植物叶片N素含量与土壤有机质、土壤N素含量和土壤含水量呈显著正相关;而NRE与土壤有机质、土壤N素含量和土壤含水量呈显著负相关关系。说明在研究区不利的土壤条件,可以导致植物NRE的提高,植物在不利的环境条件下,可以通过提高NRE等途径来应对环境的胁迫。