Zinc toxicity on N2O reduction declines with time in laboratory spiked soils and is undetectable in field contaminated soils

Denitrification assays in soils spiked with zinc salt have shown inhibition of the N₂O reduction resulting in increased soil N₂O fluxes with increasing soil Zn concentration. It is unclear if the same is true for environmentally contaminated soils. Net production of N₂O and N₂ was monitored during anaerobic incubations (25 °C, He atmosphere) of soils freshly spiked with ZnCl₂ and of corresponding soils that were gradually enriched with metals (mainly Zn) in the field by previous sludge amendments or by corrosion of galvanized structures. Total denitrification activity (i.e. the sum of N₂O+N₂ production rate) was not inhibited by freshly added Zn salts up to 1600 mg Zn kg⁻¹, whereas N₂O reduction decreased by 50% (EC₅₀) at total Zn concentrations of 231 mg Zn kg⁻¹ (ZEV soil) and 368 mg Zn kg⁻¹ (TM soil). In contrast, N₂O reduction was not reduced by soil Zn in any of the field contaminated soils, even at total soil Zn or soil solution Zn concentrations exceeding more than 5 times corresponding EC₅₀'s of the freshly spiked soil. The absence of adverse effects in the field contaminated soils was unrelated to soil NO₃ or organic matter concentration. Ageing (2-8 weeks) and soil leaching after spiking reduced the toxicity of Zn on N₂O reduction, either expressed as total Zn or soil solution Zn, suggesting adaptation reactions. However, no full recovery after spiking was identified at the largest incubation period in one soil. In addition, the denitrification assay performed with sewage sludge showed elevated N₂O release in Zn contaminated sludges (>6000 mg Zn kg⁻¹ dry matter) whereas this was not observed in low Zn sludge (<1000 mg Zn kg⁻¹ dry matter) suggesting limits to adaptation reactions in the sludge particles. It is concluded that the use of soils spiked with Zn salts overestimates effects on N₂O reduction. Field data on N₂O fluxes in sludge amended soils are required to identify if metals indeed promote N₂O emissions in sludge amended soils.     

Effect of Field Aging on Nickel Concentration in Soil Solutions

Abstract

The effect of field aging on nickel (Ni) concentration in soil solutions was studied on three soils, with pH 4.5, 6.1, and 7.6, that were spiked with Ni and aged outdoors for 5, 10, and 15 months. Field aging resulted in a minor decrease in total Ni content and a dramatic decrease in Ni concentration in soil solution. Nickel release isotherms in field‐aged soils differ from those in freshly spiked ones. The decrease in soluble Ni in noncalcareous soils at Ni loadings from 25 to 4800 mg kg^?1 followed a first‐order kinetic equation. In calcareous soil the observed relationships imply that soluble Ni may be controlled by dissolution of a surface precipitate either on the surface of soil carbonates [NiCO₃ or NiCO₃ · 2Ni(OH)₂] or on the surface of clay minerals (Ni‐aluminum double‐layer hydroxide).     

Influence of microbial inoculation (Pseudomonas sp. strain ADP), the enzyme atrazine chlorohydrolase,and vegetation on the degradation of atrazine and metolachlor in soil

The concentrations of atrazine in the freshly added soils and the soils that had been incubated for 50 days significantly decreased 1 day after the addition of the enzyme atrazine chlorohydrolase or the soil bacterium Pseudomonas sp. strain ADP as compared with those in the uninoculated soils. Atrazine chlorohydrolase or ADP had no effect on the degradation of metolachlor. The half-lives of atrazine in the freshly added soils and in the aged soils after the treatment with atrazine chlorohydrolase or ADP markedly decreased as compared with those in the uninoculated soils. The half-lives of metolachlor in the aged soils were much longer than those of freshly added metolachlor. The percentage atrazine degraded in the freshly treated soils was much higher than that in the aged soils. This indicates that aging significantly decreased the bioavailability of atrazine. Vegetation significantly decreased the concentration of metolachlor. However, vegetation showed no effect on the degradation of atrazine.     

土壤中水溶性铜对西红柿的毒害影响因素及预测模型

该文选取17种具有代表性的中国土壤,研究了土壤孔隙水以及0.01mol/LCaCl2浸提态Cu对西红柿生长的毒害,结果发现对于土壤孔隙水中Cu对西红柿生物量10%抑制的毒性阈值(EC10)和50%抑制的毒性阈值(EC50),在17个非淋洗土壤中变化范围分别为0.06～1.47和0.17～3.42mg/L,淋洗土壤变化范围分别为0.05～2.24和0.13～4.37mg/L,最大值与最小值相差为23～41倍;0.01mol/LCaCl2提取态Cu的EC10和EC50,在非淋洗土壤变化范围分别为0.18～2.64和0.57～6.14mg/kg,淋洗土壤变化范围分别为0.18～1.28和0.61～7.11mg/kg,相差从6.9～14.4倍,表明土壤溶液性质影响水溶性Cu对西红柿的毒性阈值。同时,发现土壤孔隙水中Ca2+、溶解性有机碳是影响孔隙水中Cu对西红柿生长毒性的主要因子。当进一步考虑土壤溶液的重要因子(溶解性有机碳、土壤溶液pH值、电导率、全硫含量、Ca2+、Mg2+、K+、Na+),发现基于水溶性Cu的毒性阈值和土壤溶液性质的多元回归系数变化范围为0.75～0.99,说明利用土壤溶液性质能较好的预测土壤中水溶性Cu对西红柿的毒性阈值。该研究可为土壤水溶性Cu的风险评估提供参考。     

Remediation of vanadium contaminated soil by nano-hydroxyapatite

Purpose

Vanadium (V) contamination in soil can cause diverse damage to soil ecosystem and has attracted research interests in exploring soil V stabilization methods, but only a few materials were proposed and studied. Here, a pot experiment was firstly conducted to estimate the efficiency of nano-hydroxyapatite (n-HAP) in stabilizing V in soil. To verify the impact of n-HAP on soil V bioavailability and phytotoxicity, cabbages (Brassica chinensis L.) were grown in V-spiked soils after n-HAP amendment.

Materials and methods

Soils were sampled from a farmland in China, and the n-HAP was prepared in the laboratory. In each pot of soil spiked with 0, 75, 150, 300, and 600 mg/kg V, 2% n-HAP was amended for 30 days, while soils without n-HAP amendment were set as controls. The stabilization effect of n-HAP on V in soil was estimated by the water-extractable and bioavailable V concentrations in soils. Cabbages were grown in pots subsequently. The V(V/IV) concentrations in cabbage leaves and roots, the organic bound V concentrations in cabbage roots, and the chlorophyll concentrations in leaves were determined. Bioconcentration factor and translocation factor were calculated. The composition of organic bound V in leaf was characterized by fluorescence excitation–emission matrix.

Results and discussion

In soils spiked with 150 mg/kg V, n-HAP amendment yielded the highest stabilization rates of 51.0% and 42.4% for water-extractable and bioavailable V, respectively. In 75, 150, and 300 mg/kg V-spiked soil, the plant weight, plant height, and root length of cabbage after 60-day growing decreased 54.6%/89.6%, 30.9%/45.5%, and 41.5%/51.4% in groups with/without n-HAP, respectively. Cabbage leaf chlorophyll concentrations descend firstly then ascend with rising soil V concentration. Leaf V speciation analysis revealed that less leaf V was reduced to V(IV) in groups amended with n-HAP than groups without n-HAP amendment. In 150 and 300 mg/kg V-spiked soil, n-HAP effectively reduced the V content and the V bioconcentration factor of cabbage root. Tyrosine-like and humic acid-like analogues composed the principal part of V complex.

Conclusions

In general, n-HAP amendments are potential to decrease the mobility of V in soils, as well as inhibit the bioavailability and phytotoxicity of V to cabbage. In V-spiked soils, n-HAP amendment can alleviate the toxicity of V to the cabbage. Overall, 2% n-HAP is efficient for the amendment of slight V-polluted (150–300 mg/kg) soils to alleviate the soil V stress to cabbage.

     

Effect of Anthracene and Pyrene on Dehydrogenases Activity in Soils Exposed and Unexposed to PAHs

The effect of anthracene and pyrene on dehydrogenases activitywas compared between freshly spiked soils and soils previouslyexposed to PAHs. Four different soils (two soils from anunpolluted rural area and two soils from highly pollutedindustrial areas) were spiked with anthracene and pyrene atthe levels of 1, 10, 100 and 400 mg Σ2PAH per kg of soil (laboratory experiments). The soil samples were moisted to60% of water holding capacity and incubated in the dark at 18-20 °C. Dehydrogenase activity was determined after 7 and30 days. The results indicate that long-term exposure of soilfrom an industrial area to high level of PAHs (Σ13PAH = 40 mg kg^-1) caused the acclimatisation of soilmicroorganisms and lowered their sensitivity to these compounds.After the longer incubation period (30 days vs. 7 days)the soil microorganisms in the uncontaminated rural samples showed an increase in their tolerance to the freshly introduced PAH compounds; in the industrial soils the effect was less pronounced. However, this apparent adaptation of soil microorganisms may be also partly explained by the dissipation and/or ageing processes of anthracene and pyrene during incubation.     

Spike/Leach Procedure to Prepare Soil Samples for Trace Metal Ecotoxicity Testing: Method Development Using Copper

Soil trace metal ecotoxicity testing requires a set of soil samples with increasing metal concentrations that are otherwise chemically similar. Leaching samples amended with soluble metal salts has been proposed as a means to reduce chemical artefacts of the spiking procedure (i.e., salt effect), thereby improving their environmental relevance. Demonstrating with copper (Cu), we proposed a spike/leach procedure whereby metal solutions were added to test soils over 5 days and subsequently leached with dilute nutrient solutions until the electrical conductivity in leachates stabilized. During the 5 days of Cu additions, pH in leachates from Cu-spiked samples decreased by up to 0.90 pH units and showed up to 30- and 25-fold increases in calcium (Ca) and magnesium (Mg) concentrations, indicative of the salt effect. Leaching removed the excess acidity and dissolved cations and minimized the differences in leachate pH, Ca, Mg, aluminum (Al), iron (Fe), manganese (Mn), and dissolved organic carbon (DOC) concentrations between control and Cu-spiked samples. Leaching also reduced dissolved Cu concentrations in spiked samples by up to an order of magnitude, resulting in more environmentally relevant concentrations than were achieved prior to leaching.     

Effect of pH on Potentially Toxic Trace Elements (Cd,Cu, Ni,and Zn) Solubility in Two Native and Spiked Calcareous Soils: Experimental and Modeling

The effect of soil pH on solubility of the potentially toxic trace elements (PTEs) [cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn)] was assessed using two native and spiked calcareous soils. Multiple PTEs solutions were added to soils and equilibrated (aged) for 40 days. Then, PTEs solubility was measured at different pH level (1–3 units below and above the pH of native soils). In native soils, all PTEs displayed a V-shaped pH-dependent solubility pattern with important releases at pH 4 and 10 (native soil 1) and 5 and 11 (native soil 2). In spiked soils, the general tendency for the pH where solubility started was in the order Cd > Ni > Zn > Cu. Solubility of added trace elements increased with a decrease in pH. Solubility of PTEs occurred at a lower pH in the soil with a higher carbonate content than the other soil (both native and spiked). In order to predict the effect of soil pH on solubility of PTEs, surface complexation and ions exchange models of PHREEQC program were used. The model simulated the PTEs solubility in soils very well. Comparison of experimental and simulated data indicated that ions exchange and surface complexation were the main mechanisms for predicting PTEs solubility in soils. Environmental implications concerning PTEs mobility might be derived from these findings.     

Radio-labile cadmium and zinc in soils as affected by pH and source of contamination

The determination of radio‐labile metals in soil has gained renewed interest for predicting metal availability. There is little information on to what extent the fraction of labile metal is affected by the soil properties and the source of metal contamination. The radio‐labile content (E value) of Cd and Zn was measured in field‐collected soils with Cd and Zn originating from different sources. The E values were erratic and sometimes even exceeded total metal content when the concentration in the soil extract was less than 8 μg Zn l^?1 or less than 3 μg Cd l^?1. Addition of EDTA (0.1 mm ) to the radio‐labelled soil suspension resulted in larger concentrations of Cd and Zn in solution and smaller E values for these soils. The E values were, however, unaffected by the presence of EDTA (0.1 mm ) in soils with larger concentrations of Cd and Zn in solution. The %E values (E value relative to metal soluble in aqua regia) ranged from 9% to 92% (mean 61%) for Cd and from 3% to 72% (mean 33%) for Zn. No correlation between soil properties and %E was observed for Cd, and the %E of Zn was negatively correlated with soil pH (r = ?0.65). There was a strong negative correlation between pH and %E in soils enriched with metals in soluble form (e.g. metal salts, corrosion of galvanized structures). In soils where Cd or Zn were added in a less soluble form, no such correlation was found, and %E values were generally less than in soils spiked with metal salts, suggesting that the source of the contamination controls mainly the labile fractions of Cd and Zn.     

The Effect of Lignite and Comamonas testosteroni on Pentachlorophenol Biodegradation and Soil Ecotoxicity

Biodegradation of pentachlorophenol (PCP) in soil by autochthonous microflora and in soil bioaugmented by the bacterial strain Comamonas testosteroni CCM 7530 was studied. Subsequent addition of lignite, an abundant source of humic acids, has also been investigated as possible sorbent for PCP immobilization. Biodegradation of PCP and number of colony-forming units were determined in the three types of soil, haplic chernozem, haplic fluvisol, and haplic arenosol, freshly spiked with PCP and amended with tested sorbent. The enhancing effect of sorbent addition and bioaugmentation on PCP biodegradation depended mainly on the soil type and the initial PCP concentration. Microbial activity resulted in biotransformation of PCP into certain potentially toxic substances, probably lower chlorinated phenols that are more soluble than PCP, and therefore more toxic toward present biota. Therefore, it was necessary to monitor soil ecotoxicity during biodegradation. Addition of lignite resulted in a significant improvement of PCP biodegradation and led to a considerable decrease of soil toxicity especially in bioaugmented soils. The method could potentially serve as a promising technique in remediation technology for reducing high initial PCP content in contaminated soils.     

Differential tolerance of canola to arsenic when grown hydroponically or in soil 1

Separate studies found canola tolerant to arsenic (As) when grown in hydroponic solutions and generally sensitive to As when grown in soil. Fourteen‐day‐old canola was transferred to pots containing either soil or nutrient solution and then grown for an additional 14 days in a growth chamber at different times for the two different media. Plants were grown in 0.25‐strength Hoagland's solution containing either 0, 0.27, 6.67, or 13.3μM As or in three soils with As added at rates of 0,5, and 10 mg.kg^‐1. Soil‐solution As concentrations were determined via column displacement and were the same or less (0.147 to 4.27μM) than the hydroponic As concentrations. Soil‐solution phosphorus (P) concentrations were determined in the same manner and averaged 9.28μM P compared to 500μM P from the hydroponic solutions. Chlorosis, wilting, and stunted growth—symptoms of As toxicity—occurred in canola at the highest As rate in two of the three soils used. Dry‐matter yields from the third soil were low from all treatments and a lack of response to As additions was probably due to injury from other soil‐related factors. Shoot As concentrations were generally similar from both experiments. Canola did not suffer a yield loss or exhibit As toxicity symptoms when grown in the hydroponic solutions. Leaf P was 8,000 mg.kg^‐1 in the hydroponically‐grown canola and 100 mg.kg^‐1 for the soil‐grown canola. These values are greater than (hydroponic) and lower than (soil media) sufficiency levels for plants similar to canola. High solution P concentrations in the hydroponic solution may have detoxified As by competing with As for uptake in the solution and during metabolism. Phosphate should be added to hydroponic solutions in As studies at levels close to normal soil P levels and added daily to replenish plant uptake.     

An anion resin membrane technique to overcome detection limits of isotopically exchanged P in P-sorbing soils

Isotopically exchanged phosphorus is difficult to determine in soils that strongly sorb P (so that there is little P in solution) and in soils with large concentrations of colloidal P in soil suspensions. A method is proposed in which anion exchange membranes (AEM) are added to the soil suspension after an initial period of isotopic exchange with ³²P‐labelled phosphate ions. Isotopically exchanged P, termed E_AEM, is calculated from the ratio of labelled phosphate ions to the total phosphate ions on the membrane. The E_AEM was compared with the E value measured in an aqueous soil extract (E_{Water extract}) for 14 soils with different degrees of P sorption. The two methods gave similar results in soils with large P concentrations in an aqueous soil extract. However, E_{Water extract} values significantly exceeded the E_AEM values by up to 18‐fold when soluble P was near the determination limit (0.008 mg P l^?1). In a second experiment, two Ferralsols received further P from inorganic and plant sources and were incubated for 7 days. Treatment effects on labile P were erroneous as detected by the E_{Water extract} but were significant as detected with the AEM method. Third, E_AEM values were followed in a Lixisol and a Ferralsol which received labelled phosphate ions with carrier just before the beginning of a 23‐day incubation. The approximate recovery of added inorganic P in the E_AEM value suggested that this method adequately samples labile P in P‐sorbing soils. All these results showed that errors in the determination of E values for soils with very small concentrations of P in the soil solution are reduced using the proposed method.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

Retention of copper, cadmium and zinc in soil and its textural fractions influenced by long-term field management

The present study investigated the impact of long‐term soil management on the metal retention capacity of soil. We examined the sorption behaviour of Cu, Cd and Zn in soils and in the various particle‐size fractions of these soils, which had been amended with farmyard manure, mineral fertilizers or were fallow for 38 years in a long‐term field experiment. The soils investigated contained different amounts and origins of organic matter and differed in soil pH, but the mineral phase showed less response to the different soil managements. Batch adsorption and desorption experiments as well as a sequential fractionation schema, which defines seven geochemical fractions, were used to investigate the retention properties of soil. Sequential extraction was conducted with original as well as with metal‐spiked soils. Results showed that amounts of Cu, Cd and Zn retained differed by a factor of more than 3 among the treatments in the long‐term field experiment, when a massive concentration of metal was added to soil. An increased sorption on smaller particle size fractions occurred (clay ≫ silt > fine sand ≥ coarse sand) due to the larger surface area as well as the greater carbon content in the smaller fractions. Soil sorption behaviour in another long‐term field experiment was estimated based on the present particle‐sorption data. Differences in the sorption behaviour were related to differences in soil mineralogy and amounts of Fe‐ and Mn‐oxides. Fractionation of the original and the metal‐spiked soil underlined the contribution of organic matter to sorption capacity (sequence: Cu ≫ Cd > Zn). Different organic matter contents and a different soil pH considerably changed the amounts of metals in the defined geochemical fractions. Freshly added Cu, Cd and Zn ions were found mainly in more mobile fractions. In contrast, metals in non‐spiked soils appeared in less‐mobile fractions reflecting their long‐term sorption behaviour.     

Aluminium Toxicity Risk for Pinus pinaster in Acid Soils (Galicia,NW Spain)

The influence of bedrock on aluminium toxicity and aluminium speciation in the soil solution was studied in four Pinus pinaster plots. Growth and biomass parameters in the acidic soils were also evaluated in relation to different Al toxicity indices. The plots were developed over slate, biotitic schist, mica schist and granite. Samples of rhizospheric and non‐rhizospheric soil, 1‐year‐old needles and roots were collected in each study plot. Total Al, reactive Al, acid‐soluble Al, non‐labile and labile Al and Al species (Al³⁺, Al‐OH, Al‐F and Al‐SO₄) were determined in soil solution. Reactive Al dominated over the acid‐soluble Al, and the non‐labile Al predominated over the labile Al in all soils, but particularly over mica schist. In the biotitic schist soil, the Al forms and total Al were lower, whereas concentrations were always higher over mica schist. The Al forms considered most toxic were Al³⁺ and Al‐OH, and Al concentrations were highest over slate and mica schist. Al toxicity indices in soil, needle and roots showed a risk of toxicity in mica schist, slate and granite. The stand site indices over slate and mica schist were lower, consistent with the high labile Al and Al³⁺ + Al‐OH in soil solution. Despite the high stand site index over granite, the growth efficiency was low, in accordance with very low ratios of Ca/Al in needles or fine roots. This confirmed the adaptation of maritime pine to granitic substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

Labile lead in polluted soils measured by stable isotope dilution

It is well known that lead (Pb) is strongly immobilized in soil by adsorption or precipitation. However, the reversibility of these reactions is poorly documented. In this study, the isotopically exchangeable Pb concentration in soils (E‐value) was measured using a stable isotope (²⁰⁸Pb). Soils were collected at three industrialized sites where historical Pb emissions have resulted in elevated Pb concentrations in the surrounding soil. Lead concentrations ranged from background values, in the control soils collected far from the emission source, to highly elevated concentrations (5460–14440 mg Pb kg^?1). The control soil of each site was amended in the laboratory with Pb(NO₃)₂ to the same total Pb concentrations as the field‐contaminated soils. The %E values (E‐value relative to total Pb content) were greater than 84% in the laboratory‐amended soils, and ranged from 45% to 78% (mean 58%) in the field‐contaminated soils. The relatively large labile fractions of Pb in the field‐contaminated soils show that the majority of Pb is reversibly bound despite the fact that the binding strength is large. The Pb concentrations in soil solution were up to 3500‐fold larger for the laboratory‐amended soils than for field‐contaminated soils at corresponding total Pb concentrations. These differences cannot be explained by differences in labile fractions of Pb but are attributed to the decrease in soil solution pH upon addition of Pb²⁺‐salt.     

Influence of soil fractions on microbial degradation behavior of mineral hydrocarbons

Various interactions occurring between organic chemicals and soil constituents participate in the determination of the fate of these pollutants, including their biodegradability. These relations need to be characterized in order to design and successfully implement a bioremediation application. In the present study, biodegradation of spiked and aged crude oil contamination in two dissimilar soils was related to their composition. GC-FID analysis of bulk soil samples as well as sand- and <63 μm fractions showed considerable differences in contaminant distribution and degradation behavior within these fractions. Whereas a freshly spiked silty soil showed reasonable degradation (51%), degradation was not significant after ageing. By contrast, a sandy soil was degraded by 25% (recently contaminated) and 19% (aged). Biodegradation occurred in the fine fraction only, with a comparably high content of organic carbon whereas hydrocarbon concentration remained constant in the sand fraction. This was correlated with sorption to the fine fraction where hydrocarbon concentrations were higher by over an order of magnitude compared to the sand fraction. Soil composition, biology and chemistry exert a pronounced influence on microbial degradation in respect to (i) contaminant availability and (ii) the structure and density of the microbial community.     

Extractability and plant uptake of heavy metals in alum shale soils

Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH₄NO₃) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH₄NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg^‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘¹ d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH₄NO₃. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.     

Remobilization of sterically stabilized silver nanoparticles from farmland soils determined by column leaching

The increasing application of silver (Ag)‐engineered nanoparticles (ENP) will enhance their release to the aquatic and terrestrial environments. Hence, the retention potential of the sterically stabilized Ag ENP (AgNM‐300k, Organisation for Economic Cooperation and Development (OECD)) standard material was tested in a sandy Cambisol and in a clay‐ and silt‐rich Luvisol. In addition, the remobilization potential of the same soils spiked with AgNM‐300k was investigated in columns after 3 and 92 days of incubation. The AgNM‐300k dispersion and the soil solutions were examined with dynamic light scattering (DLS). Inductively coupled plasma optical emission spectroscopy (ICP‐OES) and inductively coupled plasma mass spectrometry (ICP‐MS) were used to analyse soils and soil solutions subjected to different digestion and extraction techniques (aqua regia, nitric acid (HNO₃) and EDTA (ethylenediamninetetraacetate)). The 24‐hour batch test showed a 10‐fold greater retention coefficient for AgNM‐300k in the silt‐ and clay‐rich Luvisol than in the sandy Cambisol. In addition, all applied extraction techniques indicate a greater potential for mobility of Ag ENP for the sandy Cambisol. However, a small release from the column of Ag_HNO3 (measured Ag content in the fraction < 0.45 µm after HNO₃ digestion) was observed after 3 as well as after 92 days of incubation for both soils. The largest amount of Ag was released from the Cambisol during the first percolation step (water:soil ratio = 1 l kg^?1) after the soil was incubated for 3 days. This Ag_HNO3 release corresponded to approximately 1% of the total amount of Ag in the soil column. The correlation obtained between released Ag_HNO3 and Al_HNO3 suggests that even the Ag released at small concentrations is associated with soil colloids. Thus, hetero‐aggregation is a potentially important process controlling retention.     

Methods of assessing boron availability to kiwifruit plants growing on high boron soils

Abstract

Five soil boron (B) extraction methods were evaluated for their ability to predict available B to kiwifruit plants in soils with high B concentration. The methods were hot water soluble (Hws‐B), 0.05M mannitol in 0.01M calcium chloride (CaCl₂ extractable (Man‐B), 0.05M hydrochloride acid (HCl) soluble (HC1‐B), resin extractable (Resin‐B), and saturation extract (Sat‐B). The amounts of B recovered by the first four methods investigated were strongly correlated with each other, the highest correlation obtained being between Hws‐B and HC1‐B. Plant B was highly correlated to the B recovered by the first four extractants and poorly correlated to the B determined by the saturation method. Soil B concentrations corresponding with B toxicity in kiwifruit are 0.51, 0.80, 0.18, and 2.0 μg‐g^‐1 soil for Hws‐B, Man‐B, HC1‐B, and Res‐B, respectively. The coefficients of determination in some cases were improved when in the regression equations, soil pH and clay content were included.