Distribution and Mobility of Trace Elements in Soils and Vegetation Around the Mining and Smelting Areas of Tharsis, Ríotinto and Huelva, Iberian Pyrite Belt, SW Spain

Trace elements may present an environmental hazard in the vicinity of mining and smelting activities. However, the factors controlling their distribution and transfer within the soil and vegetation systems are not always well defined. Total concentrations of up to 15,195 mg . kg ^–1 As, 6,690 mg . kg^–1 Cu, 24,820 mg . kg^–1 Pb and 9,810 mg . kg^–1 Zn in soils, and 62 mg . kg^–1 As, 1,765 mg . kg^–1 Cu, 280 mg . kg^–1 Pb and 3,460 mg . kg ^–1 Zn in vegetation were measured. However, unusually for smelters and mines of a similar size, the elevated trace element concentrations in soils were found to be restricted to the immediate vicinity of the mines and smelters (maximum 2–3 km). Parent material, prevailing wind direction, and soil physical and chemical characteristics were found to correlate poorly with the restricted trace element distributions in soils. Hypotheses are given for this unusual distribution: (1) the contaminated soils were removed by erosion or (2) mines and smelters released large heavy particles that could not have been transported long distances. Analyses of the accumulation of trace elements in vegetation (median ratios: As 0.06, Cu 0.19, Pb 0.54 and Zn 1.07) and the percentage of total trace elements being DTPA extractable in soils (median percentages: As 0.06%, Cu 15%, Pb 7% and Zn 4%) indicated higher relative trace element mobility in soils with low total concentrations than in soils with elevated concentrations.     

土法炼锌区大气沉降Pb、Zn、Cd及其对土壤质量的影响

Dust emissions from smelters, as a major contributor to heavy metal contamination in soils, could severely influence soil quality. Downwind surface soils within 1.5 km of a zinc smelter, which was active for 10 years but ceased in 2000, in Magu Town, Guizhou Province, China were selected to examine Pb, Zn, and Cd concentrations and their fractionation along a distance gradient from a zinc smelter, and to study the possible effects of Pb, Zn, and Cd accumulation on soil microorganisms by comparing with a reference soil located at a downwind distance of 10 km from the zinc smelter. Soils within 1.5 km of the zinc smelter accumulated high levels of heavy metals Zn (508 mg kg-1), Pb (95.6 mg kg-1), and Cd (5.98 mg kg-1) with low ratios of Zn/Cd (59.1--115) and Pb/Cd (12.4--23.4). Composite pollution indices (CPIs) of surface soils (2.52--15.2) were 3 to 13 times higher than the reference soils. In metal accumulated soils, exchangeable plus carbonate-bound fractions accounted for more than 10% of the total Zn, Pb, and Cd. The saturation degree of metals (SDM) in soils within 1.5 km of the smelter (averaging 1.25) was six times higher than that of the reference soils (0.209). A smaller soil microbial biomass was found more frequently in metal accumulated soils (85.1--438 μg C g-1) than in reference soils (497 μg C g-1), and a negative correlation (P < 0.01) of soil microbial biomass carbon to organic carbon ratio (Cmic/Corg) with SDM was observed. Microbial consumption of carbon sources was more rapid in contaminated soils than in reference soils, and a shift in the substrate utilization pattern was apparent and was negatively correlated with SDM (R = -0.773, P < 0.01). Consequently, dust deposited Pb, Zn, and Cd in soils from zinc smelting were readily mobilized, and weredetrimental to soil quality mainly in respect of microbial biomass.     

Soil microbial community as bioindicator of the recovery of soil functioning derived from metal phytoextraction with sorghum

A three-month microcosm study was carried out in order to evaluate: (i) the capacity of sorghum plants to phytoextract Cd (50 mg kg⁻¹) and Zn (1000 mg kg⁻¹) from artificially polluted soil and (ii) the possibility of biomonitoring the efficiency of phytoremediation using parameters related to the size, activity and functional diversity of the soil microbial community. Apart from plant and soil (total and bioavailable) metal concentrations, the following parameters were determined: soil physicochemical properties (pH, OM content, electrical conductivity, total N, and extractable P and K), dehydrogenase activity, basal- and substrate-induced respiration (with glucose and a model rhizodeposit solution, both adjusted to 800 mg C kg⁻¹ DW soil and 45.2 mg N kg⁻¹ DW soil), microbial respiration quotient, functional diversity through community level physiological profiles and, finally, seed germination toxicity tests with Lepidium sativum. Sorghum plants were highly tolerant to metal pollution and capable of reaching high biomass values in the presence of metals. In the first two harvests, values of shoot Cd concentrations were higher than 100 mg Cd kg⁻¹ DW, the threshold value for hyperaccumulators. Nonetheless, in the third harvest, the bioconcentration factor was 1.34 and 0.35 for Cd and Zn, respectively, well below the threshold value of 10 considered for a phytoextraction process to be feasible. In general, microbial parameters showed lower values in metal polluted than in control non-polluted soils, and higher values in planted than in control unplanted pots. As a result of the phytoextraction process, which includes both plant growth and metal phytoextraction, the functioning of the phytoremediated soil, as reflected by the values of the different microbial parameters here determined, was restored. Most importantly, although the phytoextracted soil recovered its function, it was still more phytotoxic than the control non-polluted soil.     

Geochemical assessment,distribution, and dynamics of trace elements in urban agricultural soils under long‐term wastewater irrigation in Kano,northern Nigeria

A study was conducted to evaluate the distribution and origin of trace elements (Ti, Fe, Nb, Pb, Rb, Sr, Y, and Zr) in five representative long‐term wastewater‐irrigated urban vegetable gardens of Kano, Nigeria. Surface‐soil concentrations (0–15 cm) of Ti (4600–14 300 mg kg^–1), Fe (4000–31 800 mg kg^–1), Pb (96–355 mg kg^–1), and Y (33–98 mg kg^–1) were high compared to mean concentrations in comparable soils elsewhere. However, soil‐pollution assessment yielded no evidence of anthropogenic input of the trace elements studied. Indices such as the enrichment factor, the contamination factor, and the geoaccumulation index (I_geo) revealed little to no contamination with trace elements. The I_geo calculated for these metals varied across locations between 0.00 and 0.12 with Nb having the highest I_geo value. Similarly, the contamination factor was low for all metals with the exception of Fe reaching a contamination factor of 4.2 at one location. Geochemical‐balance evaluations showed depletion of all trace elements except for Fe which was 176% higher than in a natural uncultivated and unirrigated reference soil. Correlation and factor analyses showed that all determined trace elements likely originated from the same natural sources, which probably are the soil parent material and atmospheric depositions.     

长江三角洲地区城市污泥中苯并[a]芘和菲的初步研究

To evaluate the contaminated conditions of benzo[a]pyrene (B[a]P) and phenanthrene (PA) in sludge and to ascertain whether B[a]P limit for land application of sludge exists, the contents of B[a]P and PA in 46 sludge samples from 15 cities in the Yangtze River Delta area of China were determined using high performance liquid chromatography (HPLC) coupled with a fluorescence detector after ultrasonic extraction and silica gel cleanup. B[a]P contents ranged from non-detectable to 1.693 mg kg^-1 dry weight (DW), averaged 0.402 mg kg^-1 DW, and were < 1.0 mg kg^-1 DW in most of the sludge samples. PA was found in all the sludge samples analyzed; its contents ranged between 0.028 and 1.355 mg kg^-1 DW, with an average value of 0.298 mg kg^-1 DW. Most of the sludge samples contained < 0.5 mg kg^-1 DW PA. All 46 municipal sludge samples analyzed in this study showed B[a]P contents < 3.0 mg kg^-1 DW, which is the limit value for sludge applied to agricultural lands in China. The contents and distributions of B[a]P and PA in municipal sludge were related to sludge types, sources and treatment technologies, along with the physical and chemical properties of these pollutants.     

Water extractable concentrations of Fe,Mn, Ni,Co, Mo,Pb and Cd under different land uses of Danube basin in Croatia

Abstract

Water extraction of trace elements can simulate the concentration of elements in the soil solution from where the plant takes up the elements. The objective of this investigation was to determine the water extractable concentration of seven trace elements (Fe, Mn, Ni, Co, Mo, Pb and Cd) and to assess their relationship with soil properties of the Danube basin in Croatia. Soil samples from the surface layer (0–25 cm) of 74 sites, having different land uses (forest and agricultural land), were collected. Samples were analysed for total and water extractable trace elements as well as for pH, DOC, SOC and CEC. The concentrations of water extractable fraction of trace elements were on average: 20.14 mg kg^?1 for Fe, 3.61 mg kg^?1 for Mn, 0.07 mg kg^?1 for Ni, 0.016 mg kg^?1 for Co, 0.01 mg kg^?1 for Mo, 0.01 mg kg^?1 for Pb and 0.0009 mg kg^?1 for Cd. Soil properties were in the following range: pH 4.3–8 (Avg: 6.35), DOC 6.1–73 mg l^?1 (Avg: 26 mg l^?1), CEC 1.3–24 cmol kg^?1 (Avg: 9 cmol kg^?1) and SOC 0.5–5% (Avg: 1.7%). The concentration of water extractable fraction of trace elements was significantly correlated with pH (p <0.001), DOC (p <0.001 – p <0.05) and CEC (p <0.001) but their relationship with total content of trace element and SOC was rather weak, suggesting that total metal alone cannot be an indicator of toxicity or deficiency. Results show that pH, DOC and CEC are important soil quality parameters taking part in the solubility control of trace metals in the soil rather than their total concentration. The difference between land uses has been observed as well, suggesting that a change in land use can cause a change in trace element solubility.     

Erosion rates and nutrient losses affected by composted cattle manure application in vineyard soils of NE Spain

Land preparation for mechanisation in vineyards of the Anoia–Alt Penedès region, NE Spain, has required major soil movements, which has enormous environmental implications not only due to changes in the landscape morphology but also due to soil degradation. The resulting cultivated soils are very poor in organic matter and highly susceptible to erosion, which reduces the possibilities of water intake as most of the rain is lost as runoff. In order to improve soil conditions, the application of organic wastes has been generalised in the area, not only before plantation but also every 3–4 years at rates of 30–50 Mg ha^− 1 mixed in the upper 30 cm.These organic materials are important sources of nutrients (N and P) and other elements, which could reduce further fertilisation cost. However, due to the high susceptibility to sealing of these soils, erosion rates are relatively high, so a higher nutrient concentration on the soil surface increases non-point pollution sources due to runoff.The aim of this study is to analyse the influence of applied composted cattle manure on infiltration, runoff and soil losses and on nutrients transported by runoff in vineyards of the Alt Penedès–Anoia region, NE Spain. In the two plots selected for the analysis, composted cattle manure had been applied in alternate rows 1 year previous to the study. In each plot soil surface samples (0–25 cm) were taken and compared to those of plots without manure application. The study was carried out at laboratory scale using simulated rainfall. Infiltration rates were calculated from the difference between rainfall intensity and runoff rates, and the sediment and total nitrogen and phosphorus were measured for each simulation. In addition, the influence of compost was investigated in the field under natural rainfall conditions by analysing the nutrient concentration in runoff samples collected in the field (in the same plots) after seven rainfall events, which amount different total precipitation and had different erosive character.Compost application increases infiltration rates by up to 26% and also increases the time when runoff starts. Sediment concentration in runoff was lower in treated (13.4 on average mg L^− 1) than in untreated soils (ranging from 16.8 to 23.4 mg L^− 1). However, the higher nutrient concentration in soils produces a higher mobilisation of N (7–17 mg L^− 1 in untreated soils and 20–26 mg L^− 1 in treated soils) and P (6–7 mg L^− 1 in untreated soils and 13–19 mg L^− 1 in treated soils). A major part of the P mobilised was attached to soil particles (about 90% on average) and only 10% was dissolved. Under natural conditions, higher nutrient concentrations were always recorded in treated vs. untreated soils in both plots, and the total amount of N and P mobilised by runoff was higher in treated soils, although without significant differences. Nutrient concentrations in runoff depend on rainfall erosivity but the average value in treated soils was twice that in untreated soils for both plots.     

Lethal and sublethal effects of imidacloprid on two earthworm species (Aporrectodea nocturna and Allolobophora icterica)

The chemical imidacloprid is the major component of many widely used insecticides and is relatively persistent in soils. A set of experiments was carried out to estimate the lethal (mortality) and sublethal (weight loss) effects of one of these insecticides, Confidor, on two earthworm species commonly found in agricultural soils. A preliminary experiment in the absence of earthworms showed that imidacloprid was not rapidly degraded, with a decrease of less than 10% after 2 weeks, and that it was distributed in a reasonably homogeneous manner throughout the soil (less than 10% of variation between samples). The LC₅₀ of imidacloprid for the anecic species Aporrectodea nocturna and the endogeic species Allolobophora icterica was between 2 and 4 mg kg^–1 dry soil. This result is consistent with previous findings obtained with other earthworm species and natural soils. When sublethal effects were examined, significant decreases in weight were observed at concentrations of 0.5 and 1 mg kg^–1 dry soil for the two earthworm species whereas no effect was observed at a concentration of 0.1 mg kg^–1 dry soil (NOEC value). These concentrations are close to 0.33 mg kg^–1 which is the Predictive Environmental Concentration. Weight loss appears to be a valuable endpoint that can be used with worms freshly collected in the field as long as variability in the response of a control is taken into account.     

我国一些土壤中较难提取的固定态铵

Ninety-three soil samples and 19 sedimentary rock samples collected from 21 provinces of China were analyzed for their contents of fixed ammonium and total N by Kjeldahl-HF method. Results showed that amount of difficultly extractable fixed ammonium (the fixed ammonium that is not determinable by Kjeldahl procedures commonly used for soils) in soils ranged from 0 to 202 mg kg^-1. It was generally more than 50 mg kg^-1 in soils in Changji and Turpan districts, Xinjiang, accounting for 3.2%~36.8% with an average of 13.9% of the total N. For some Orthents derived from purple shale and purple sandstone in Sichuan and Hunan provinces and Chao soils derived from secondary loess in Henan Province and Ningxia Autonomous Region it was generally around 30 mg kg^-1, accounting for 4%~7% of the total soil N, and for most of the rest of soils studied, with the exception of some subsoils, no or trace difficultly extractable fixed ammonium could be detected. It was suggested that the difficultly extractable fixed ammonium was originated from parent rock, and for slightly weathered soils derived from parent materials rich in this form of N the Kjeldahl method might give underestimation of total soil N.     

Assessment of soil contamination by potentially toxic elements in the aljustrel mining area in order to implement soil reclamation strategies

Land pollution due to past mining activities is a major environmental issue in many European countries. The Aljustrel mine (SW Portugal), located in the western sector of the Iberian Pyrite Belt (IBP) presents a negative visual and environmental impact as a consequence of the mining activity that has developed since the Roman era. Its impacts are also a restraint on the life quality of the population. The exposure of pyrite and other sulphides to air are responsible for the pollution observed in soils, surface water and stream sediments. This paper investigates the pollution load of potential toxic elements in soil samples collected around the Aljustrel mining area. The aim is to assess the levels of soil contamination with respect to average concentrations of toxic elements in the region and to understand the partitioning and availability of pollutants in the area. The results showed severe soil contamination (mainly As, Cd, Cu, Pb and Zn). The concentrations of As (up to 3936 mg kg⁻¹) and certain heavy metals (up to 5414 mg kg⁻¹ Cu, 61·6 mg kg⁻¹ Cd, 20 000 mg kg⁻¹ Pb and 20 000 mg kg⁻¹ Zn) are two orders of magnitude above the regional South Portuguese Zone (SPZ) background values. The median concentrations of As, Cd, Cu, Pb and Zn exceed the values established for world soils, the European Union, Portugal and Andalusia. The results suggest that the distribution patterns of Co, Cr and Ni element concentrations in the Aljustrel area are primarily influenced by the lithology and geochemistry nature of bedrock. The soil background of this geological domain is characterized by relatively high heavy metal contents, essentially derived from the parent rocks. Copyright © 2010 John Wiley & Sons, Ltd.     

Soil organic carbon changes in particle-size fractions following cultivation of Black soils in China

Soil texture can be an important control on soil organic carbon (SOC) retention and dynamics. The (clay + silt)-sized SOC pool (SOC < 20 μm) in non-cultivated or grassland soils has been proposed to reach an equilibrium or maximum level named protective capacity. Proper knowledge of SOC in this size fraction in non-cultivated and cultivated Black soils is important to evaluate management-induced changes in SOC in NE China. Twenty-seven paired soil samples (non-cultivated vs. cultivated) were collected in the Black soil zone in Heilongjiang and Jilin provinces. Bulk soil was dispersed in water with an ultrasonic probe and then soil size fractions were collected using the pipette technique for SOC analyses. Soil organic carbon in bulk soil and size fractions was measured by dry combustion. Average content of SOC < 20 μm was 23.2 g C kg⁻¹ at the 0–30 cm depth for the non-cultivated soils, accounting for 75.1% of the total SOC at the same depth. There was significant positive relationship between soil clay plus silt content and SOC < 20 μm in non-cultivated soils. Accordingly, a model of the maximum SOC < 20 μm in 0–30 cm depth of non-cultivated Black soils was developed: y = 0.36x where y is the maximum SOC < 20 μm pool (g C kg⁻¹) and x is the percentage of clay + silt (<20 μm) content. The average content of SOC < 20 μm was 18.7 g C kg⁻¹ at 0–30 cm depth for cultivated soils, accounting for 81.5% of total SOC. This average value of SOC was 4.4 g C kg⁻¹ less than the maximum value (23.1 g C kg⁻¹) and accounted for 55.0% of the difference of SOC between non-cultivated and cultivated Black soils. Cultivation resulted in 45.0% loss of sand-sized (>20 μm) SOC concentration relative to SOC < 20 μm. This result indicates that SOC < 20 μm and sand-sized SOC both play important roles in SOC dynamics resulting from management practices. This model can be applied to calculate the actual potential to restore SOC for cultivated Black soils under conservation tillage in NE China.     

Metal uptake in maize, willows and poplars on impoldered and freshwater tidal marshes in the Scheldt estuary

Foliar Cd and Zn concentrations in Salix, Populus and Zea mays grown on freshwater tidal marshes were assessed. Soil metal concentrations were elevated, averaging 9.7 mg Cd kg^?1 dry soil, 1100 mg Zn kg^?1 dry soil and 152 mg Cr kg^?1 dry soil. Cd (1.1–13.7 mg kg^?1) and Zn (192–1140 mg kg^?1) concentrations in willows and poplars were markedly higher than in maize on impoldered tidal marshes (0.8–4.8 mg Cd kg^?1 and 155–255 mg Zn kg^?1). Foliar samples of maize were collected on 90 plots on alluvial and sediment‐derived soils with variable degree of soil pollution. For soil Cd concentrations exceeding 7 mg Cd kg^?1 dry soil, there was a 50% probability that maize leaf concentrations exceeded public health standards for animal fodder. It was shown that analysis of foliar samples of maize taken in August can be used to predict foliar metal concentrations at harvest. These findings can therefore contribute to anticipating potential hazards arising from maize cultivation on soils with elevated metal contents.     

The distribution of volatile isoprenoids in the soil horizons around Pinus halepensis trees

We measured the terpene concentration in pentane and water extracts from soil horizons (litter, organic, top and low mineral) and from roots growing in top and low mineral horizons on a distance gradient from Pinus halepensis L. trees growing alone on a grassland. Terpene concentrations in pentane were higher than in water extracts, although β-caryophyllene showed relatively high solubility in water. The litter and roots were important sources of terpenes in soil. Alpha-pinene dominated in roots growing in both “top” (A1) and “low” (B) mineral horizons (123 ± 36 μg g⁻¹ or 14 ± 5 mg m⁻²) and roots in low mineral horizon (270 ± 91 μg g⁻¹ or 7 ± 2 mg m⁻²). Beta-caryophyllene dominated in litter (1469 ± 331 μg g⁻¹ or 2004 ± 481 mg m⁻²). Terpene concentration in soil decreased with increasing distance to the trunk. This is likely to be related to changes in litter and roots type on the distance gradient from pine to grass and herbs. The relative contributions of all compounds, except α-pinene, were similar in the mineral soils and litter. This suggests that litter of P. halepensis is probably the main source of major terpene compounds. However, long-term emissions of α-pinene from P. halepensis roots might also contribute to α-pinene concentrations in rhizosphere soils.     

Rhizosphere soil microbial index of tree species in a coal mining ecosystem

Microbial characterization of the tree rhizosphere provides important information relating to the screening of tree species for re-vegetation of degraded land. Rhizosphere soil samples collected from a few predominant tree species growing in the coal mining ecosystem of Dhanbad, India, were analyzed for soil organic carbon (SOC), mineralizable N, microbial biomass carbon (MBC), active microbial biomass carbon (AMBC), basal soil respiration (BSR), and soil enzyme activities (dehydrogenase, urease, catalase, phenol oxidase, and peroxidase). Among the tree species studied, Aegle marmelos recorded the highest value for MBC (590 mg kg⁻¹), urease (190.5 μg NH₄⁺-N g⁻¹ h⁻¹), catalase (513 μg H₂O₂ g⁻¹ h⁻¹), dehydrogenase (92.3 μg TPF g⁻¹ h⁻¹), phenol oxidase (0.057 μM g⁻¹ h⁻¹) and BSR/AMBC (0.498 mg CO₂-C mg biomass⁻¹ day⁻¹); Tamarindus indica for mineralizable N (69.5 mg kg⁻¹); Morus alba for catalase (513 μg H₂O₂ g⁻¹ h⁻¹) and phenol oxidase (0.058 μM g⁻¹ h⁻¹); Tectona grandis for peroxidase (0.276 μM g⁻¹ h⁻¹), AMBC/MBC (99.4%), and BSR/MBC (0.108 mg CO₂-C mg biomass⁻¹ day⁻¹); Ficus religiosa for AMBC (128.4 mg kg⁻¹) and BSR (12.85 mg CO₂-C kg⁻¹ day⁻¹); Eugenia jambolana for MBC/SOC (8.03%); Butea monosoperma for AMBC/SOC (1.32%) and Azadirachta indica for BSR/AMBC (0.1134 mg CO₂-C mg biomass⁻¹ day⁻¹). Principal component analysis was employed to derive a rhizosphere soil microbial index (RSMI) and accordingly, dehydrogenase, BSR/MBC, MBC/SOC, EC, phenol oxidase and AMBC were found to be the most critical properties. The observed values for the above properties were converted into a unitless score (0–1.00) and the scores were integrated into RSMI. The tree species could be arranged in decreasing order of the RSMI as: A. marmelos (0.718), A. indica (0.715), Bauhinia bauhinia (0.693), B. monosperma (0.611), E. jambolana (0.601), Moringa oleifera (0.565), Dalbergia sissoo (0.498), T. indica (0.488), Morus alba (0.415), F. religiosa (0.291), Eucalyptus sp. (0.232) and T. grandis (0.181). It was concluded that tree species in coal mining areas had diverse effects on their respective rhizosphere microbial processes, which could directly or indirectly determine the survival and performance of the planted tree species in degraded coal mining areas. Tree species with higher RSMI values could be recommended for re-vegetation of degraded coal mining area.     

Effect of heavy metals contamination on root-derived and organic matter-derived CO2 efflux from soil planted with Zea mays

The CO₂ efflux from loamy Haplic Luvisol and heavy metal (HM) uptake by Zea mays L. were studied under increased HM contamination: Cd, Cu, and Ni up to 20, 1000, and 2500 mg kg⁻¹ soil, respectively. Split-root system with contrasting HM concentrations in both soil halves was used to investigate root-mediated HM translocation in uncontaminated soil zones. To separate root-derived and soil organic matter (SOM)-derived CO₂ efflux from soil, ¹⁴CO₂ pulse labeling of 15-, 25-, and 35-days-old plants was applied. The CO₂ evolution from the bare soil was 10.6 μg C–CO₂ d⁻¹ g⁻¹ (32 kg C–CO₂ d⁻¹ ha⁻¹) and was not affected by HM (except 2500 mg Ni kg⁻¹). The average CO₂ efflux from the soil with maize was about two times higher and amounted for about 22.0 μg C–CO₂ d⁻¹ g⁻¹. Portion of assimilates respired in the rhizosphere decreased with plant development from 6.0 to 7.0% of assimilated C for 25-days-old Zea mays to 0.4–2.0% for 45-days-old maize. The effect of the HM on root-derived ¹⁴CO₂ efflux increased with rising HM content in the following order: Cd < Cu < Ni. In Cu and Ni contaminated soils, shoot and root dry matter decreased to 70% and to 50% of the uncontaminated control, respectively. Plants contained much more HM in the roots than in the shoots. A split-root system with contrasting HM concentrations allowed to trace transport of mobile forms of HM by roots from contaminated soil half into the uncontaminated soil half. The portion of mobile HM forms in the soil (1 M NH₄NO₃ extract) increased with contamination and amounted to 9–16%, 2–6% and 1.5–3.5% for Cd, Cu, and Ni, respectively. Corresponding values for the easily available HM (1 M NH₄OAc extract) were 22–52%, 1–20% and 5–8.5%. Heavy metal availability for plants decreased in the following order: Cd > Cu ≥ Ni. No increase of HM availability in the soil was found after maize cultivation.     

Weathering of sulphide minerals and trace element speciation in tailings of various ages in the Guanajuato mining district, Mexico

We studied the behavior of the trace elements (TE) As, Cu, Pb and Zn associated with sulphide minerals in tailings of different age at the Guanajuato mining district, Mexico. The objective was to determine the dominant fractions into which the TE move as tailings age and to identify how much time is needed until the dominant metal fractions approach equilibrium. We collected 21 samples from the surface of mine waste deposits of different ages (0, 2 , 4, 16, 70, 75, and 100 years), and measured their aqua regia extractable contents of As, Cu, Pb and Zn. We also applied a sequential extraction procedure to quantify water soluble TE as well as TE associated with carbonates, iron oxides, sulphides and the residual fraction. The mineralogy was analysed by X-ray diffraction, and selected samples were studied on polished specimens through a stereoscopic microscope. The TE in samples extracted with aqua regia ranged between 10 and 168 mg kg^− 1 for As, 12 to 194 mg kg^− 1 for Cu, 31 to 308 mg kg^− 1 for Pb, and 122 to 1129 mg kg^− 1 for Zn, and varied in a wide range within each age group of tailings. Water soluble Cu, Pb and Zn contents were below detection limits in almost all samples, which was attributed to the alkaline pH (7.17 to 8.61) in the tailings. Water extractable As was detected only in tailings older than 16 years, and concentrations ranged between 0.06 and 7.58 mg kg^− 1. The proportion of TE associated with sulphides decreased in the tailings as they age, while the proportion of TE associated with iron oxides increased with time of exposure to the atmosphere, approximating equilibrium after 60 years for As, Cu and Zn, and after 40 years for Pb. Observations of polished specimens suggests that oxidation proceeds until coatings of secondary minerals cover and protect sulphide mineral grains from further weathering. First order rate equations were adjusted to the proportions of TE associated with either sulphides or iron oxides. Assuming that the TE in sulphide fractions correspond to arsenopyrite (FeAsS), chalcopyrite (CuFeS₂), galena (PbS) and sphalerite (ZnS), the relative oxidation rate of sulphides followed the order: PbS > ZnS > FeAsS ≈ CuFeS₂, while the relative affinity of the elements with iron oxides followed the sequence Cu ≈ Zn > As > Pb.     

Effect of di-(2-ethylhexyl) phthalate (DEHP) on microbial biomass C and enzymatic activities in soil

The effects of di-(2-ethylhexyl) phthalate (DEHP) at five different doses from 10 to 1000 mg kg⁻¹ soil on biological properties were investigated over a period of 56 days. Meanwhile, the dissipation of DEHP was also monitored. The results indicated that the microbial biomass C (C_mic) fluctuated at around 70 mg kg⁻¹ soil for the control, whereas the C_mic varied significantly for the soil samples contaminated by DEHP. The catalase activities in all five treatments were stimulated at most time, and the activities of phosphatase in the soils treated by DEHP with 500 mg kg⁻¹ or 1000 mg kg⁻¹ were significantly higher than the other treatments from the 20th day. Urease was more sensitive and inhibited significantly during the initial period of incubation. Additionally, the dose–response relationship of invertase was presented in the later phase of incubation. The activities of urease and invertase might indicate soil perturbations caused by the introduction of DEHP. The dissipation of DEHP was found to follow the pseudo first-order kinetics behavior.     

湿地土壤质量退化的模糊综合评价

Due to frequent soil Cd contamination and wide use of butachlor in China,there is a need to assess their combined toxicity to soil microorganisms.The combined effects of cadmium (Cd,10 mg kg^-1 soil) and herbicide butachlor (10,50,and 100 mg kg^-1 soil) on enzyme activities and microbial community structure in a paddy soil were assessed using the traditional enzyme assays and random amplified polymorphic DNA (RAPD) analysis.The results showed that urease and phosphatase activities were significantly reduced by high butachlor concentration (100 mg kg^-1 soil).When the concentrations of Cd and butachlor added were at a ratio of 1:10,urease and phosphatase activities were significantly decreased whereas enzyme activities were greatly improved at the ratio of 1:5,which indicated that the combined effects of Cd and butachlor on soil urease and phosphatase activities depended largely on their addition concentration ratios.Random amplified polymorphic DNA (RAPD) analysis showed loss of original bands and appearance of new bands when compared with the control soil.Random amplified polymorphic DNA fingerprints suggested substantial differences between the control and treated soil samples,with apparent changes in the number and size of amplified DNA fragments.The addition of high concentration butachlor and the combined impacts of Cd and butachlor significantly affected the diversity of the microbial community.RAPD analysis in conjunction with other biomarkers such as soil enzyme parameters would prove a powerful ecotoxicological tool.Further investigations should be carried out to understand the clear link between RAPD patterns and enzyme activity.     

Seasonal variations of nitrous oxide emission in relation to nitrogen fertilization and energy crop types in sandy soil

Nitrous oxide (N₂O) is a greenhouse gas and agricultural soils are major sources of atmospheric N₂O. Its emissions from soils make up the largest part in the global N₂O budget. Research was carried out at the experimental fields of the Leibniz-Institute of Agricultural Engineering Potsdam-Bornim (ATB). Different types (mineral and wood ash) and levels (0, 75 and 150 kg N ha⁻¹) of fertilization were applied to annual (rape, rye, triticale and hemp) and perennial (poplar and willow) plants every year. N₂O flux measurements were performed 4 times a week by means of gas flux chambers and an automated gas chromatograph between 2003 and 2005. Soil samples were also taken close to the corresponding measuring rings. Soil nitrate and ammonium were measured in soil extracts.N₂O emissions had a peak after N fertilization in spring, after plant harvest in summer and during the freezing–thawing periods in winter. Both fertilization and plant types significantly altered N₂O emission. The maximum N₂O emission rate detected was 1081 μg N₂O m⁻² h⁻¹ in 2004. The mean annual N₂O emissions from the annual plants were more than twofold greater than those of perennial plants (4.3 kg ha⁻¹ vs. 1.9 kg ha⁻¹). During January, N₂O fluxes considerably increased in all treatments due to freezing–thawing cycles. Fertilization together with annual cropping doubled the N₂O emissions compared to perennial crops indicating that N use efficiency was greater for perennial plants. Fertilizer-derived N₂O fluxes constituted about 32% (willow) to 67% (rape/rye) of total soil N₂O flux. Concurrent measurements of soil water content, NO₃ and NH₄ support the conclusion that nitrification is main source of N₂O loss from the study soils. The mean soil NO₃-N values of soils during the study for fertilized soils were 1.6 and 0.9 mg NO₃-N kg⁻¹ for 150 and 75 kg N ha⁻¹ fertilization, respectively. This value reduced to 0.5 mg NO₃-N kg⁻¹ for non-fertilized soils.     

Comparing concurrent in situ and batch‐extracted trace element concentrations

Different procedures to investigate dissolved trace element concentration at the transition from unsaturated to saturated zone in soils were compared by concurrent sampling of soil solution and solid soil material in this zone. The in situ sampled soil solution from the percolated water was used to measure in situ concentrations, while solid soil material was used to measure concentrations at two liquid–solid ratios using batch experiments on 250 sample pairs. The liquid–solid ratios were 2 L kg^–1 and 5 L kg^–1. At 5 L kg^–1, the ionic strength was adjusted with Ca(NO₃)₂ to a sample‐specific value similar to in situ, while at 2 L kg^–1, the ionic strength was not adjusted. The extracted concentrations of most trace elements exhibited a statistically significant but weak correlation (p value < 0.01) to the corresponding in situ concentrations. In the liquid–solid ratio of 2 L kg^–1 extracts, Pb and Cr showed very poor comparability with the in situ equivalent. A likely cause was the enhanced dissolved‐organic‐C release in the extract due to the lower ionic strength compared to in situ conditions in combination with effects from drying and moistening soil samples. For the other elements, correlation increased in the order As < Cu, Zn, Sb, Mo, V < Cd, Ni, Co where adjustment of the ionic strength led to slightly better results. In addition to the element‐specific shortcomings, it appeared that low concentration levels of in situ concentrations were generally underestimated by batch extraction methods. The liquid–solid ratio of 2 L kg^–1 extracts could only be used as a method to predict exceedance of thresholds if a safety margin of approximately one order of magnitude higher than the thresholds was adopted. The ability of the batch‐extraction methods to estimate in situ concentrations was equally limited.