The role of soil humic and fulvic acid in the sorption of endosulfan (alpha and beta)

The sorption behaviour of alpha- and beta-endosulfan in soil organic matter was investigated using standard soil humic acid (HA) and soil fulvic acid (FA) with a modified solubility enhancement method and a dialysis bag technique. For HA, all the experiments were conducted at an ionic strength of 0.001 mol/L, in both the presence and absence of calcium and at an ionic strength of 0.01 mol/L. For FA, the experiments were conducted at two ionic strengths: 0.001 mol/L (with calcium) and 0.01 mol/L. This study is the first to describe the striking differences in the sorption behaviours of the two stereoisomers of endosulfan in HA and in FA. The sorption coefficients of alpha-endosulfan in HA and FA were significantly higher than those of beta-endosulfan. Beta-endosulfan has comparable sorption coefficients (1.5–5.4 L/g) in HA and in FA. Ionic strength and the presence of calcium have no significant effect on the sorption of beta-endosulfan in HA. However, calcium can significantly (p=0.01) enhance the solubility of alpha-endosulfan in HA. Changes in ionic strength by one order of magnitude also affect the solubility of alpha-endosulfan in HA. The sorption coefficients of alpha-endosulfan in HA (10–36 L/g) were greater than those in FA (9–14 L/g). The chirality of the alpha-isomer was hypothesised to be the primary reason behind its higher sorption in soil organic matter relative to the beta-isomer. In the presence of dissolved HA and FA found in natural soil environments, solubility of endosulfan can be increased by five times than the aqueous solubility of endosulfan without HA and FA.     

Diazinon leaching through a sandy soil amended with different humic materials

The water leaching of diazinon (O,O‐diethyl‐O‐2‐isopropyl‐6‐methylpyrirnidin‐4‐yl phosphoroth‐ioate) through soil columns, was studied after column amendments with two well characterized humic acids (HA), in both liquid and solid state, and with the original raw organic materials, an oxidized coal and a leonardite, from which the HA were extracted. The percolation curves and the pesticide distribution over the soil columns showed that the addition of the raw organic materials and the solid HAs reduced significantly the mobility of the pesticide along the soil column. The oxidized coal was more effective than the leonardite original material; the different origin of the two carbon‐rich materials had an influence on the diazinon movement along the soil columns and such difference was enhanced with increasing addition rates. Moreover, incubation at field capacity for two months of the soil columns treated with raw oxidized coal and leonardite, largely enhanced the described effects on pesticide behaviour. A complete adsorption of diazinon on columns and a practical absence of leaching was observed when the HA from both materials were added in dissolved form. These results were explained with the swelling of the humic micelles in water and the enhanced availability of inner hydrophobic surfaces for the strong adsorption of diazinon. The water diffusion into the solid humic materials after two months incubation, also explains their high pesticide retention capacity. This work indicates the usefulness of either solid o dissolved humic substances, with the proper hydrophobic character, in preventing the vertical leaching of non‐polar organic pesticides in soils.     

The determination of fluoride in water in the presence of organic acids and iron using a fluoride-selective electrode

Surface waters in Scotland, notably from upland catchment areas, are commonly enriched in iron and organic acids. This study investigated the impact of these species on the direct potentiometric determination of fluoride using a fluoride-selective electrode. As the electrode technique is commonly used to monitor the fluoride content of potable waters, it is important that these effects are evaluated if such waters are to be fluoridated. The determination method used was that defined by Nicholson (1983) and Nicholson and Duff (1981) to minimise errors. This employs the TISAB III-TAC buffer system with the following composition (in 1L): 58.0 g sodium chloride, 57.0 mL glacial acetic acid, 4.0 g CDTA, 243.0 g tri-ammonium citrate adjusted to pH 5.4 with 10 M sodium hydroxide. Experimental solutions of fluoride with organic acid or iron were prepared, and the effect on fluoride concentration determined for each combination. Concentrations used: fluoride: 0.1, 1.0 mg L⁻¹; humic acid: 5, 10, 100, 1000, 10,000 mg L⁻¹; oxalic acid: 5, 10, 100, 1000, 10,000 mg L⁻¹; iron(III): 1, 10, 100, 500 mg L⁻¹; Humic acid (HA) concentrations had no impact on the determination of fluoride at the 1.0 mg L⁻¹ level. However, with 0.1 mg L⁻¹; F⁻, an increase in the apparent fluoride concentration was observed when HA > 1,000 mg L⁻¹; this increased with increasing HA content to a maximum of ∼600%. Oxalic acid (OA) generally had no impact on the fluoride determinations at the 1.0 mg L⁻¹; level, but at an OA concentration of 10,000 mg L⁻¹; fluoride concentrations were reduced by ∼50%. At 0.1 mg L⁻¹ F⁻, increasing OA concentrations produce a steady increase in the fluoride concentration of up to 200% with 1,000 mg L⁻¹; OA, greater OA contents produce a fall in the fluoride content. Iron had no effect on the fluoride determinations at both the 0.1 and 1.0 mg L⁻¹ levels. The causes of the apparent increases in fluoride concentration have not been determined, although fluoride contamination by the reagents has been ruled-out. However, the results demonstrate that the defined method and buffer system is suitable for the determination of fluoride in the presence of iron and organic acids at naturally occurring levels, and that fluoride will not be masked from detection.     

Distribution patterns of lead in urban soil and dust in Shenyang city, Northeast China

We investigated the spatial distribution of Pb in soil and dust samples collected from 54 sites in Shenyang city, Liaoning province, Northeast China. Soil background Pb concentration was 22 mg kg⁻¹ and control values from non-industrial areas were 33 mg kg⁻¹ for soil and 38 mg kg⁻¹ for dust. Soil Pb concentrations varied widely, ranging from 26 to 2911 mg kg⁻¹, with a mean concentration of 200 mg kg⁻¹, 9 times the background value and 6 times the control value. There was great variation in soil Pb, with a coefficient of variation (CV) of 1.06 and a standard deviation (SD) of 212 mg kg⁻¹. Dust Pb concentrations fluctuated from 20 to 2810 mg kg⁻¹, with a mean value of 220 mg kg⁻¹, almost 6 times the control value. No significant differences in distribution were observed between soil Pb and dust Pb. The highest Pb concentration was observed in Tiexi district in an industrial area. Soil Pb concentration decreased with depth and with distance from the pollution source. Lead concentrations initially changed little but then decreased with distance from the roadside, and were generally higher on the east side of roads than on the west. Lead contents in different categories of urban area differed substantially with dust and soil Pb concentrations decreasing in the sequence: industrial >business >mixed (residential, culture and education)> reference areas.     

Effect of low molecular weight organic acids on adsorption and desorption of fluoride on variable charge soils

The effect of four low molecular weight organic acids on F⁻ adsorption by two variable charge soils was investigated using a batch method. The organic acids reduced F⁻ adsorption through competition by the acids with F⁻ for sorption sites. Oxalic and malonic acids, both of which have simpler chemical structures, were more effective than citric or malic acid. The effect of organic acids on F⁻ adsorption was more prominent at higher pH values and with larger amounts of the organic acids. The desorption study showed that the organic acids enhanced the desorption of F⁻ adsorbed by the soils. In the control and malic acid systems, desorption increased sharply with decreasing pH, while in the oxalic acid system, desorption rose slightly with decreasing pH. Desorption also increased with increasing amount of organic acid added. There are two possible mechanisms for the effect of the organic acids on F⁻ adsorption and desorption: (1)␣competition of the organic acids with F⁻ for adsorption sites and (2) dissolution of the adsorbents, especially dissolution of soil Al.     

Arsenic contamination in water,soil, sediment and rice of central India

Arsenic contamination in the environment (i.e. surface, well and tube-well water, soil, sediment and rice samples) of central India (i.e. Ambagarh Chauki, Chhattisgarh) is reported. The concentration of the total arsenic in the samples i.e. water (n=64), soil (n=30), sediment (n=27) and rice grain (n=10) were ranged from 15 to 825 μg L⁻¹, 9 to 390 mg kg⁻¹, 19 to 489 mg kg⁻¹ and 0.018 to 0.446 mg kg⁻¹, respectively. In all type of waters, the arsenic levels exceeded the permissible limit, 10 μg L⁻¹. The most toxic and mobile inorganic species i.e. As(III) and As(V) are predominantly present in water of this region. The soils have relatively higher contents of arsenic and other elements i.e. Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ga, Zr, Sn, Sb, Pb and U. The mean arsenic contents in soil of this region are much higher than in arsenic soil of West Bengal and Bangladesh. The lowest level of arsenic in the soil of this region is 3.7 mg kg⁻¹ with median value of 9.5 mg kg⁻¹. The arsenic contents in the sediments are at least 2-folds higher than in the soil. The sources of arsenic contamination in the soil of this region are expected from the rock weathering as well as the atmospheric deposition. The environmental samples i.e. water, soil dust, food, etc. are expected the major exposure for the arsenic contamination. The most of people living in this region are suffering with arsenic borne diseases (i.e. melanosis, keratosis, skin cancer, etc.).     

Uptake of zinc, cadmium and phosphorus by arbuscular mycorrhizal maize (Zea mays L.) from a low available phosphorus calcareous soil spiked with zinc and cadmium

In a multifactorial pot experiment, maize (Zea mays L.) with or without inoculation with the arbuscular mycorrhizal (AM) fungus Glomus mosseae BEG167 was grown in a sterilized soil spiked with three levels of zinc (0, 300 and 900 mg Zn kg⁻¹ soil) and three levels of cadmium (0, 25 and 100 mg Cd kg⁻¹ soil). At harvest after 8 weeks of growth, the proportion of root length of inoculated plants colonized decreased with increasing Zn or Cd additon, and was 56% in the absence of both metals and was reduced significantly to 27% in the presence of the higher levels of both metals. Mycorrhizal plants had higher biomass than non-mycorrhizal controls except at the highest soil level of Cd. Cadmium had more pronounced effects on plant biomass than did Zn at the levels studied and the two metals showed a significant interaction. The data suggest that mycorrhizal inoculation increased plant growth with enchancement of P nutrition, perhaps increasing plant tolerance to Zn and Cd by a dilution effect. AM inoculation also led to higher soil solution pH after harvest, possibly reducing the availability of the metals for plant uptake, and lowered the concentrations of soluble Zn and Cd in the soil solution, perhaps by adsorption onto the extrametrical mycelium.     

Effect of metallic cations on the sorption of pesticides on soil

We studied the adsorption and desorption of two pesticides, namely isoproturon and dimetomorph, onto a model soil sample. We first show that the adsorption of isoproturon depends on pH, from 1 mg g⁻¹ at pH 4 to 2 mg g⁻¹ at pH 10, contrary to the adsorption of dimetomorph (5.8 mg g⁻¹). We also studied the influence of metallic cations, copper(II), iron(III), manganese(II), and chromium(III), on the sorption of isoproturon and dimetomorph. We found that in the case of isoproturon, the presence of metallic cations does influence the retention capacity of the soil sample. The sorption becomes very weak in the presence of copper and chromium, whereas in the case of iron and manganese the sorption properties are slightly modified.     

Enrichment and exposure assessment of As,Cr and Pb of the soils in the vicinity of Stawell,Victoria, Australia

Stawell Gold Mine in NW Victoria, Australia, mines ores that contain large concentrations of As and significant quantities of the metals Pb and Cr. The aim of this research was to understand the dispersion, enrichment and probable exposure of these potentially hazardous elements around the mine site. Fifty-five surface soil samples were collected near the mine (<15 km) and analysed by ICP-MS/OES following bioavailable and four-acid extractions. Soils near the mine show greater concentrations of As, Cr and Pb than those near a regionally determined background. This is attributed to the combination of a natural geochemical halo around mineralization and anthropogenic dispersion due to mining and urbanization. Total As concentrations were between 16 and 946 mg kg⁻¹ near the mine in a regional background of 1–16 mg kg⁻¹. Total Cr concentrations were between 18 and 740 mg kg⁻¹ near the mine in a regional background of 26–143 mg kg⁻¹. Total Pb concentrations were between 12 and 430 mg kg⁻¹ near the mine in a regional background of 9–23 mg kg⁻¹. Dispersion of contaminant elements from the present ore processing is <500 m. The most enriched soils occur close to the town and are unrelated to present mining practices. The bioavailable As, Cr and Pb, soil ingestion rates and Risk Reference Doses were used to estimate health risks. An average toddler (12 kg) would need to consume at least 1.5 g, and most likely 12 g, of soil per day to show some symptoms of As toxicity. The maximum measured bioavailable As would pose a risk at average ingestion rates of 200 mg per day. Individuals with soil-eating disorders would exceed the safe daily consumption limits for As, and potentially Cr and Pb. Small children are not typically exposed to soil everyday, very few have soil eating disorders, and, therefore, the health risk from the soils around the mine is minimal.     

Effect of cadmium alone and in combination with butachlor on soil enzymes

The ecological toxicity of cadmium (Cd, 10 mg kg⁻¹ of dry weight soil) and butachlor (10, 50 and100 mg kg⁻¹ of dry weight soil) in both their single and combined effects on soil urease and phosphatase was studied after 1, 3, 7, 14, 21 and 28 days exposure under controlled conditions in paddy and phaeozem soils. The results showed that Cd reduced the activities of urease and phosphatase at early incubation time (1–7 days), while the reduction almost disappeared at the end of the incubation. The effect of Cd on phosphatase was more pronounced than that on urease. The activities of urease and phosphatase were reduced by butachlor, while urease activity was significantly (P < 0.05 or P < 0.01) improved when the concentrations of butachlor were 10 and 50 mg kg⁻¹ at the end of the incubation. When Cd (10 mg kg⁻¹) was combined with butachlor (50 and 100 mg kg⁻¹), the activities of urease and phosphatase became lower than without combination at early incubation time, which indicated that the toxicity of Cd significantly increased (P < 0.05 or P < 0.01). However, when Cd (10 mg kg⁻¹) was combined with butachlor (10 mg kg⁻¹), the activities of urease and phosphatase became higher than those without combination at the end of the incubation, which indicated that the toxicity of Cd decreased. It was indicated that the combined effects depended largely on the incubation time and the concentration ratio of Cd and butachlor. In addition, it was showed that the combined effects of butachlor and Cd appeared different in paddy from phaeozem, which may be related to the different properties of these soils.     

Abiotic association of phthalic acid esters with humic acid of a sludge landfill

The abiotic association between phthalic acid esters (PAEs) and humic substances (HS) in sludge landfill plays an important role in the fate and stability of PAEs. An equilibrium dialysis combined with ¹⁴C-labeling was used to study the abiotic association of two abundant PAEs (diethyl phthalate and di-n-butyl phthalate) with humic acid (HA) isolated from a sludge landfill with different stabilization times and different molecular weights. Elemental analysis and Fourier Transform Infrared Spectrophotometer (FTIR) suggested that high K _A value of HA was related to the high aromatic content and large molecular weight of HA. The results indicated that the association strength of PAEs with HA depended on both the properties of the PAEs and the characteristics of HA. The K _A values of the association were strongly dependent on solution pH, and decreased dramatically as the pH was increased from 3.0 to 9.0. The results suggested that nonspecific hydrophobic interaction between PAEs and HA was the main contributor to the association of the PAEs with HA. The interactive hydrogen-bonds between the HA and the PAEs molecules may also be involved in the association.     

Mobilization of heavy metals from contaminated paddy soil by EDDS,EDTA, and elemental sulfur

For enhanced phytoextraction, mobilization of heavy metals (HMs) from the soil solid phase to soil pore water is an important process. A pot incubation experiment mimicking field conditions was conducted to investigate the performance of three soil additives in mobilizing HMs from contaminated paddy soil (Gleyi-Stagnic Anthrosol): the [S, S]-isomer of ethylenediamine disuccinate (EDDS) with application rates of 2.3, 4.3, and 11.8 mmol kg⁻¹ of soil, ethylenediamine tetraacetate (EDTA; 1.4, 3.8, and 7.5 mmol kg⁻¹), and elemental sulfur (100, 200, and 400 mmol kg⁻¹). Temporal changes in soil pore water HM and dissolved organic carbon concentrations and pH were monitored for a period of 119 days. EDDS was the most effective additive in mobilizing soil Cu. However, EDDS was only effective during the first 24 to 52 days, and was readily biodegraded with a half-life of 4.1 to 8.7 days. The effectiveness of EDDS decreased at the highest application rate, most probably as a result of depletion of the readily desorbable Cu pool in soil. EDTA increased the concentrations of Cu, Pb, Zn, and Cd in the soil pore water, and remained effective during the whole incubation period due to its persistence. The highest rate of sulfur application led to a decrease in pH to around 4. This increased the pore water HM concentrations, especially those of Zn and Cd. Concentrations of HMs in the soil pore water can be regulated to a large extent by choosing the proper application rate of EDDS, EDTA, or sulfur. Hence, a preliminary work such as our pot experiment in combination with further plant experiments (not included in this study) will provide a good tool to evaluate the applicability of different soil additives for enhanced phytoextraction of a specific soil.     

Variations between rice cultivars in root secretion of organic acids and the relationship with plant cadmium uptake

To attempt to understand certain mechanisms causing the variations between rice cultivars with regard to Cd uptake and accumulation, pot soil experiments were conducted with two rice cultivars at different levels of Cd, i.e., 0 (the control), 10, 50 mg Cd kg⁻¹ soil. The two rice cultivars differ significantly with regard to Cd uptake and accumulation. Root secretions of low-molecular-weight organic acids (LMWOA) for each treatment were measured with ion chromatography. The results showed that LMWOA concentrations in the soil planted with Shan you 63 (a high soil Cd accumulator) were all higher than those in the soil planted with Wu yun jing 7 (low soil Cd accumulator) at different soil Cd levels, although the magnitudes of the differences varied for individual LMWOA and depend on soil Cd concentrations. For all six LMWOA, there were significant differences at P < 0.05 or < 0.01 levels for soils treated with 10 and 50 mg kg⁻¹ Cd. The magnitude of the differences was greater under soil Cd treatments, especially at relatively low levels (for example, 10 mg Cd kg⁻¹ soil), than in the control. Acetic acid and formic acid constituted more than 96% of the total concentration of the six LMWOA, while citric acid constituted only about 0.1%. The rice cultivar with higher concentrations of LMWOA in soil accumulated more Cd in the plants. The results indicate that LMWOA secretion by rice root, especially in Cd-contaminated soils, is likely to be one of the mechanisms determining the plant Cd uptake properties of rice cultivars.     

Crop demand of manganese

The peri-urban soils of Huelva, one of the first industrial cities in Spain, are subject to severe pollution problems primarily due to past poor management of industrial wastes and effluents. In this study, soil cores were collected in seven sites potentially contaminated with toxic chemicals arising from multiple anthropogenic sources, in order to identify trace elements of concern and to assess human health risks associated with them. In most soil core samples, total concentrations of As (up to 4,390 mg kg⁻¹), Cd (up to 12.9 mg kg⁻¹), Cu (up to 3,162 mg kg⁻¹), Pb (up to 6,385 mg kg⁻¹), Sb (up to 589 mg kg⁻¹) and Zn (up to 4,874 mg kg⁻¹) were by more than one order of magnitude greater than the site-specific reference levels calculated on the basis of regional soil geochemical baselines. These chemicals are transferred from the hazardous wastes, mainly crude pyrite and roasted pyrite cinders, to the surrounding soils by acid drainage and atmospheric deposition of wind-blown dust. Locally, elevated concentrations of U (up to 96.3 mg kg⁻¹) were detected in soils affected by releases of radionuclides from phosphogypsum wastes. The results of the human health risk-based assessment for the hypothetical exposure of an industrial worker to the surface soils indicate that, in four of the seven sites monitored, cancer risk due to As (up to 4.4 × 10⁻⁵) is slightly above the target health risk limit adopted by the Spanish legislation (1 × 10⁻⁵). The cumulative non-carcinogenic hazard index ranged from 2.0 to 12.2 indicating that there is also a concern for chronic toxic effects from dermal contact with soil.     

Fluoride distribution in the environment along the gradient of a phosphate-fertilizer production emission (southern Brazil)

Airborne fluoride was determined in the rainwater, surface soil and groundwater along a gradient of emission of a phosphate fertilizer factory in Rio Grande, southern Brazil. Concentrations of fluoride in rainwater and groundwater achieved 3 mg l⁻¹ and 5 mg l⁻¹, respectively, and were dependent on pH. The fluoride deposited from emissions accumulated in a superficial horizon of soil in quantities comparable to those in the manufactured end-products—up to 23,000 mg kg⁻¹. Fluoride distribution in the environment is controlled by physical–chemical parameters of emission, rain intensity and soil properties. The highest fluoride concentrations were registered at a close distance of up to 2 km from the factory. The distribution of fluoride in groundwater resembled the same distribution in rainwater due to the high permeability of the local soils. Fluoride penetration to the groundwater also depended on the type of vegetation cover. The groundwater in woodland areas was less affected by contamination of fluoride than in the grassland areas, most probably because of the influence of eucalyptus throughfall, which increases the pH of wet precipitates.     

Strong adsorption of DNA molecules on humic acids

Analysing soil microbial communities is often hampered by DNA adsorption on soil organic compounds such as humic acids. However the role of humic acids in DNA adsorption and stability in soils remains controversial. To characterize DNA–humic acid interactions, we studied DNA adsorption on two commercially available humic acids and a soil humic acid extracted from an Andosol. Desorption of the adsorbed DNA using 4 different solutions—distilled water, 0.1 M NaCl, 0.1 M sodium phosphate buffer (pH 6.0), and 1% sodium dodecyl sulfate solution—was also studied to understand the mechanism of DNA adsorption on humic acids. Here, we show that humic acids play an important role in DNA adsorption to soils. DNA molecules were adsorbed on the humic acids, with adsorption increasing proportionally with the DNA concentrations in the solution. The adsorption on all humic acid samples was fitted with Freundlich equation, and the parameters obtained from the equation indicated a high affinity between the humic acids and DNA molecules. The total amount of DNA desorbed by the 4 solutions was less than 2% of the total DNA adsorbed on all the humic acids. The results demonstrate that DNA molecules are able to bind strongly to humic acids by ligand binding, hydrophobic interaction, aggregation, or precipitation.     

Uranium Accumulation of Crop Plants Enhanced by Citric Acid

Citric acid was applied to soil to enhance U accumulation in four crop plants. While the highest enhanced U accumulation of aboveground tissues (a.c. 2000 mg kg⁻¹ dry weight) occurred in the leaves of Indian mustard (Brassica juncea), the highest enhanced U accumulation of roots (a.c. 3500 mg kg⁻¹ dry weight) occurred in canola (Brassica napus var. napus). Uranium translocation among tissues of test plants is in the relation of roots>shoots ≅ leaves. The flowers of sunflower (Helianthus annuus) contained similar or higher U concentrations than those found in shoots, but concentrations in seeds are close to zero. In conclusion, Indian mustard is recommended as a potential species for phytoextraction for U-contaminated soil due to its high U accumulation of aboveground biomass (a.c. 2200 μg per plant). There is no evidence that two types of soils cause a significant difference of the enhanced U accumulation (p<0.05). Results, however, indicate that additional citric acid may result in downward U migration that may contaminate groundwater. Speciation of U that is taken up by plants is also discussed in the end.     

溶解性有机碳的主要组成对青鳉鱼铜急性毒性的影响

为揭示溶解性有机碳(DOC)的组成对生物配体模型(BLM)预测铜的生物毒性准确性的影响,研究了不同浓度黄腐酸(FA)、腐殖酸(HA)和两者不同浓度比例混合物影响铜对青鳉急性毒性。结果表明:在相同水质条件下,黄腐酸或腐殖酸浓度增加时,铜对青鳉的LC50均增加;两者共存时,当腐殖酸质量百分比从10%增至90%时,铜对青鳉的LC50也增加。当天然水中DOC的组成不确定时,可假设HA和FA的组成比例为1∶1,此时BLM预测铜对青鳉的LC50的偏差最小。     

Aluminium in tea plantations: mobility in soils and plants, and the influence of nitrogen fertilization

The levels of extractable aluminum (Al) in soils of tea plantations, Al concentrations in tea leaves and the impact of nitrogen fertilization on these two parameters were investigated. In addition, the properties of soils from tea plantations were compared to those from soils of adjacent non-tea fields to evaluate the effect of land use conversion (from non-tea soils to tea soils). Exchangeable Al (extracted in 1 mol l⁻¹ KCl) ranged from 0.03 to 7.32 cmol_c kg⁻¹ in 94 tea fields and decreased rapidly with increasing soil pH. In comparison with non-tea soils, tea soils had a significantly lower pH and exchangeable Mg²⁺ concentration but higher organic matter contents and exchangeable K⁺ concentration. Contents of extractable Al were not different (P > 0.05) between these two soils. The concentrations of Al in mature tea leaves correlated significantly with exchangeable Al in soil samples taken at a depth of 20–40 cm and with exchangeable Al saturations in soil sampled at␣depths of 0–20 and 20–40 cm. In the pot experiment, nitrogen fertilization significantly increased extractable Al levels but decreased soil pH and the levels of exchangeable base cations. Nevertheless, the levels of Al in mature leaves and young shoots were significantly reduced by the application of large amounts of N fertilizer.     

Spatial distribution of PAHs in a contaminated valley in Southeast China

A survey was conducted on the accumulation and spatial distribution of PAHs in surface soils under different land use patterns in a valley in the Yangtze Delta region with an area of 10 km² containing 15 small copper- and zinc-smelting furnaces. Sixty-five topsoil (0–20 cm) samples were collected and 16 PAHs were determined. The average amount of all the 16 PAHs ranged from 0 to 530 μg kg⁻¹ (oven dry basis), with a mean concentration of 33.2 μg kg⁻¹. Benzo[a]pyrene and indeno[1, 2, 3, -cd]pyrene were the two main PAHs present at high concentrations, while pyrene and fluorene had very low concentrations. PAH concentrations were higher in uncultivated than in cultivated soils, and areas of woods and shrubbery had the␣lowest soil PAH contents. The average PAH-homologue concentrations ranked as follows: 5-rings >> 3-rings, 4-rings > 6-rings >2-rings. Much higher concentrations of PAHs were found in the southern part of the sampling area, perhaps due to deposition of airborne particles by the southeasterly winds in winter and spring. We conclude that the small smelting furnaces were the dominant source of PAHs that accumulated in the soils and the southeasterly winds led to the spatial distribution of PAHs in the topsoils. Land vegetation cover and soil utilization patterns also affected the accumulation and distribution of soil PAHs.