Mechanisms of attenuation of metal availability in in situ remediation treatments

One suite of in situ technologies for remediating metal contaminated soils involves the addition of reactive materials which lower metal availability. Until now it has been difficult to assess whether the amendment induced decrease in metal availability is due simply to increased sorption of the metal or whether it is the result of surface precipitation or other fixation mechanisms. This has made it difficult to predict the long-term stability of such remedial treatments. Using an isotopic dilution technique coupled with a stepwise acidification treatment, we examined changes in the labile pool of Cd and Zn in a polluted soil amended with either CaCO3, KH2PO4, red mud, or a kaolin byproduct. Fixation of both Cd and Zn was greatest in the KH2PO4 treated soil. The mode of fixation in this treatment was also found to be resistant to soil acidification. The results allowed a clear distinction between three classes of attenuation mechanisms which are hypothesized to increase in their resilience to environmental change as follows: reversible sorption < irreversible "fixation" at constant pH < irreversible "fixation" across a range of pH.     

Starch–metal complexes and metal compounds

Recently, metal derivatives of starch evoked considerable interest. Such metal derivatives can take a form of starch compounds bearing metal atoms and metal carrying moieties either covalently bound or complexed. Starch metal complexes may have a character of either Werner, inclusion, sorption or capillary complexes. In this publication, preparation, structure, properties and numerous current and potential applications of those compounds as well as benefits resulting from the application and formation of the complexes are presented. © 2017 Society of Chemical Industry     

No tillage affects the phosphorus status,isotopic composition and crop yield of Phaseolus vulgaris in a rain‐fed farming system

BACKGROUND: Conservation tillage promotes the accretion of soil organic matter and often leads to improved soil fertility and moisture availability. However, few studies have looked at the physiological response of crop plants to different tillage practices. It was therefore hypothesised that measuring the nutrient concentrations and stable isotope composition (δ¹³C, δ¹⁸O, δ¹⁵N) of shoots could help evaluate the physiological response of common bean (Phaseolus vulgaris L.) to different tillage treatments (no tillage (NT) and mouldboard ploughing (MP)) in a rain‐fed farming system in northern Mexico. RESULTS: NT significantly enhanced shoot phosphorus concentration in bean plants. Tillage exerted a negative effect on the extent of root colonisation (%) by arbuscular mycorrhizal fungi (AMF). Lower shoot δ¹⁸O but unchanged δ¹³C values in plants from the NT system suggest enhanced stomatal conductance but also enhanced photosynthetic rate, which overall resulted in unchanged water use efficiency. Bean plants in the NT system showed lower shoot δ¹⁵N values, which suggests that a larger proportion of total plant nitrogen was obtained through atmospheric nitrogen fixation in this treatment. CONCLUSION: Greater diversity of AMF soil communities and heavier colonisation of roots by AMF in the NT compared with the MP system appeared to contribute to improved crop nutrition, water relations and yield in this rain‐fed agroecosystem. Copyright © 2010 Society of Chemical Industry     

Long-term dynamics of phosphorus forms and retention in manure-amended soils

Phosphorus (P) leaching from soils with elevated P levels due to manure applications is increasingly becoming a concern as a source of eutrophication of streams and lakes. This study investigates the relationship between organic and inorganic P in soil pools and equilibrium leachate along a chronosequence of poultry and dairy manure additions in New York state. Resin-extractable P (molybdate-reactive P, RP) and total soil P reached very high levels of 2330 and 7343 mg of P kg(-1), respectively, after more than 25 years of continuous manure applications. After long-term manuring, the ability of these soils to retain additional P was low (Langmuir maximum sorption potential of 51-59 g of P kg(-1)) and equilibrium leachate concentrations of total dissolved P (TDP) were high (5.5-7.6 mg L(-1); saturated conditions, 0.15-m lysimeters in closed loop). Total dissolved P concentrations in equilibrium leachate increased linearly (r= 0.737) to a total soil P of 4500 mg kg(-1) and increased to a greater extent above 4500-5500 g kg(-1) (change point equivalent to about 1500 mg kg(-1) Mehlich 3-extractable RP). The proportion of dissolved unreactive P (DUP) in equilibrium leachate decreased from 90% of TDP in fields with a short manure application history to 2% of TDP where mainly poultry manure had been applied for >25 years, while unreactive P (UP) in soil decreased from 44% to 6%. Dissolved RP (DRP) was less mobile than DUP in soils with short duration of manure applications (p < 0.05), while differences between DUP and DRP mobility disappeared with longer duration of manure application and greater total soil P. Organic P forms in NaOH/NaF extracts determined by 31P NMR did not change with manure history, but sequential fractionation showed that the relative distribution of RP pools in soils changed. Dilute acid Pi increased from 10% to 62% with longer poultry manure additions, suggesting the formation of calcium phosphates as the soil pH increased from 4.1 to 6.0-7.2. The precipitation of P as calcium phosphates appeared to influence leachable P upon high and long-term applications of manure dominated by poultry litter.     

Extractable phosphorus related to forms of phosphorus and other soil properties

The soil P extracted by Olsen's, Bray's P-1, Morgan's, North Carolina, 0.01M-CaCl₂, acidic N-ammonium acetate and isotopic-exchange methods of determining available P were related to the forms of soil P and to other soil properties. Correlations between soil tests were higher when both test values were well correlated with a common P form, thereby indicating their similarity in selective dissolution of specific forms. Linear regression equations derived by stepwise inclusion of significant independent variables in order of importance for explanation of variations in soil-test values, indicated that the greatest contribution to Olsen's or Bray's test values was aluminium-P, to the isotopic exchange P was iron-P and to North Carolina test values was calcium-P. Dithionite-extractable aluminium and iron, organic matter, soil texture, base saturation and soil reaction were included in regression equations to reflect their significant influence on the dissolution of specific P forms and secondary reactions occurring during the extraction process. Based on observations for 343 differing soils, regression equations to predict soil-test values from significant P forms and soil properties accounted for more than 50% of variations in P soil-test values for Olsen's, Bray's, North Carolina and 0.01 M-CaCl₂ extraction methods. No improvement was found when P forms were included regardless of significance and significant soil properties were added to the regression equations.     

High-resolution characterization of organic phosphorus in soil extracts using 2D 1H-31P NMR correlation spectroscopy

Organic phosphorus (P) compounds represent a major component of soil P in many soils and are key sources of P for microbes and plants. Solution NMR (nuclear magnetic resonance spectroscopy) is a powerful technique for characterizing organic P species. However, (31)P NMR spectra are often complicated by overlapping peaks, which hampers identification and quantification of the numerous P species present in soils. Overlap is often exacerbated by the presence of paramagnetic metal ions, even if they are in complexes with EDTA following NaOH/EDTA extraction. By removing paramagnetic impurities using a new precipitation protocol, we achieved a dramatic improvement in spectral resolution. Furthermore, the obtained reduction in line widths enabled the use of multidimensional NMR methods to resolve overlapping (31)P signals. Using the new protocol on samples from two boreal humus soils with different Fe contents, 2D (1)H-(31)P correlation spectra allowed unambiguous identification of a large number of P species based on their (31)P and (1)H chemical shifts and their characteristic coupling patterns, which would not have been possible using previous protocols. This approach can be used to identify organic P species in samples from both terrestrial and aquatic environments increasing our understanding of organic P biogeochemistry.     

Lability of Cd,Cu, and Zn in polluted soils treated with lime,beringite, and red mud and identification of a non-labile colloidal fraction of metals using istopic techniques

The use of soil amendments has been proposed as a low input alternative for the remediation of metal polluted soils. However, little information is available concerning the stability, and therefore the longevity, of the remediation treatments when important soil parameters change. In this paper we investigate the effect of pH changes on the lability of heavy metals in soils treated with lime, beringite, and red mud using a modified isotopic dilution technique in combination with a stepwise acidification procedure. Significant amounts of nonlabile (fixed) Cu and Zn were found to be associated with colloids <0.2 microm in the solution phase. The results obtained indicated that the mobility of fixed colloidal metals is significant and increases with soil pH. This must be considered because most of the soil amendments are alkaline and increase soil pH. All the soil amendments significantly decreased the lability of Cd, Zn, and Cu in the soils as a whole. However, when the soils were re-acidified, the labile pool of metals increased sharply and in the case of lime and beringite, the lability of the metals was similar, at equal pH, to the untreated soil. In contrast the lability of metals in the red mud treated soils was always smaller than that in the untreated soils across the range of pH values tested. These results suggest that the mechanism of action of lime and beringite is similar and probably related to increased metal adsorption and precipitation of metal hydroxides and carbonates at high pH. In the case of red mud, a combination of pH dependent and independent mechanisms (possibly solid-phase diffusion or migration into micropores) may be responsible for the metal fixation observed.     

Indicator to predict the movement of phosphorus from soil to subsurface flow

The movement of phosphorus (P) in subsurface flow can contribute to losses from agricultural land. This study aims to identify a soil P threshold above which P loss is likely to accelerate as a function of soil and management type. Lysimeters (25 cm i.d. by 30 cm deep) were taken of four soils from agricultural watersheds in Pennsylvania and New York. The soils had a range of Mehlich-3 extractable P (7-517 mg of P kg(-1)) in surface soil (0-7.5 cm for grassland and 0-23 cm for cultivated/arable) and reactive P, filtered <0.45 microm (RP(<0.45 microm) in subsurface flow (0.007-1.53 mg of P L(-1)). The loss of P from lysimeters increased greatly when Mehlich-3 extractable P was in excess of a mean concentration of 280 mg kg(-1), the degree of saturation of P sorption sites exceeded 38%, and the corrected P sorption strength (corrected for desorption) derived from the monolayer Langmuir equation was less than 0.07 L of P mg(-1). Of these variables, P sorption strength was most consistently related to RP(<0.45 microm) in subsurface flow across a range of soil managements. Use of the corrected Langmuir sorption strength parameter to estimate subsurface flow RP(<0.45 microm) derived from four U.S. soils was tested on four soils of different physiochemical characteristics (one calcareous) from the U.K. The U.K. soils showed similar concentration trends to the U.S. soils, with elevated RP(<0.45 microm) below a sorption strength of 0.07 L of P mg(-1). We propose that the P sorption strength derived from the monolayer Langmuir equation may be used to estimate the potential for P loss in subsurface flow, when simpler environmental tests such as P saturation derived from acid ammonium oxalate extraction are unclear or unsuitable.     

Correction for seed-phosphorus effects in L-value determinations

Measurements of the specific activity of plants grown in ³²P-labelled soils have frequently been used to estimate soil labile phosphorus (L-values). It is usually assumed that the plant-P uptake is totally derived from soil-P. The contribution of seed-P to plant-P uptake and L-values is seldom considered. This paper describes results of an experiment which measured the effects of seed-P on L-values and how correction for seed-P effects may be made when only the tops of plants are analysed. L-values were obtained from three harvests of ryegrass grown in three soils of very low, low and medium P status (soils I, II and III), containing 4, 14 and 37 mg initial NaHCO₃-soluble P kg^?1 soil, and supplied with increasing amounts of added P. Ryegrass, supplied with increasing amounts of ³²P-labelled ³¹P, was simultaneously grown in P-free sand, under identical experimental conditions to the soil-grown plants. The seed-P in the tops of the sand-grown plants, at increasing dry matter yields, was calculated and used to make appropriate corrections for seed-P in the tops of soil-grown plants. After correction for seed-P effects, L-values were reduced at the first harvest by 69% in soil I, 18% in soil II and 10% in soil III, at the second harvest by 27, 11 and 5%, and at the third harvest by 18, 6 and 4%, respectively. Increasing the amount of added P to soil-grown plants also caused some reduction in L-values in soil I but the effect was much less in soils II and III. The reduction in L-values at higher rates of added P in soil I was probably a result of increased P uptake diluting the effects of seed-P. In the other two soils, plant-P uptake was much greater, at all rates of added P, and this effect was very small.     

The suitability of different methods for assessing the phosphorus status of hill soils

The availability of P for pasture plants in a range of acid hill soils with organic matter content up to 80% was assessed by extraction, exchange, sorption, isotopic dilution and digestion methods and was verified by plant P uptake using ryegrass and white clover as test plants. Values obtained by the conventional extraction and equilibration methods were inversely but non-significantly related to P uptake expressed in mg kg^?1 units: the relationships were only marginally improved with the data in mg litre^?1 units. The size of labile pool (‘L’ value) and amounts of both total- and organic-P ranked the soils in the same order as P uptake, but only when the data were expressed in mg litre^?1 units were the relationships highly significant. Reasons are suggested for the unsuitability of conventional extraction methods for acid, organic hill soils. Organic-P (in mg litre^?1 units) may provide the best indication of soil P status, but the determination of total-P appears to be the most practical alternative.     

Terrestrial biotic ligand model. 2. Application to Ni and Cu toxicities to plants, invertebrates, and microbes in soil

The Terrestrial Biotic Ligand Model (TBLM) is applied to a number of noncalcareous soils of the European Union for Cu and Ni toxicities using organisms and endpoints representing three levels of terrestrial organisms: higher plants, invertebrates, and microbes. A comparison of the TBLM predictions to soil metal concentration or free metal ion activity in the soil solution shows that the TBLM is able to achieve a better normalization of the wide variation in toxicological endpoints among soils of disparate properties considered in this study. The TBLM predictions of the EC50s were generally within a factor of 2 of the observed values. To our knowledge, this is the first study that incorporates Cu and Ni toxicities to multiple endpoints associated with higher plants, invertebrates, and microbes for up to eleven noncalcareous soils of disparate properties, into a single theoretical framework. The results of this study clearly demonstrate that the TBLM can provide a general framework for modeling metals ecotoxicity in soils.     

Kinetics of Zn release in soils and prediction of Zn concentration in plants using diffusive gradients in thin films

Effective concentrations (CE) of Zn measured by the technique of DGT (diffusive gradients in thin films) were compared, along with total concentrations of Zn and the concentrations of Zn in soil solutions, to Zn concentrations in plants. Soils variously contaminated with Zn were collected in the vicinity of two galvanized electrical transmission towers (pylons) and two motorway crash barriers. Lepidium sativum was grown in each soil and in corresponding control soils amended with ZnCl2 to similar total Zn concentrations. CE, concentrations in soil solution, and total Zn were measured in all soils, and total Zn was measured in the plant shoots. The CE values, soil solution Zn, and shoot Zn concentrations were all larger in ZnCl2 amended soils than in field contaminated soils at corresponding total Zn. Correlations between the concentration of Zn in the plants and the measured soil parameter followed the order CE > soil solution > total Zn. The low scatter in the plot of log plant concentration versus log CE revealed a relationship with two distinct features. Plant Zn was between 100 and 300 mg/kg up to an effective Zn concentration of about 2 mg/L, above which plant Zn increased steadily with increasing CE. Use of a dynamic model to interpret the DGT measurement suggests that the intrinsic rate of release of Zn from solid phase to solution, expressed as a rate constant, is much higher for soils that receive fresh supplies of Zn. This finding provides a mechanistic basis for reconciling laboratory experiments, where metal is freshly amended, to data obtained in the field. The potential of DGT as a surrogate for metal availability to plants is further confirmed by this work.     

Relationships between labile-P,NAHCO3-soluble P,and mobilisation of non-labile P in soils treated with inorganic phosphate fertilisers and organic manures

Weighted-mean L-values and uptakes of P by plants were determined using ryegrass grown in a controlled environment on soils obtained from long-term field experiments at Rothamsted (Batcombe and Winchester soil series), Woburn (Stackyard and Cottenham series) and Saxmundham (Beccles series) given different organic and inorganic manurial treatments. Linear regression analysis showed that, under the experimental conditions used, (small soil volume, weekly additions of all nutrients other than P) initial soil NaHCO₃-soluble P accounted for more than 95% of the variance of plant-P uptake and weighted-mean L-values. The relationships between NaHCO₃-soluble P, plant-P uptakes and weighted-mean L-values (labile P) were all independent of soil type and form of P fertiliser applied. In most soils, L-values increased with increasing cut number, and the rate of increase was linearly related to initial soil NaHCO₃-soluble P, suggesting that NaHCO₃-P measurements may provide useful information on the availability of initially non-isotopically exchangeable soil-P reserves. The plants removed about 68% more P from the soils than was measured as initially NaHCO₃-soluble and about one-half the labile soil-_P. Labile soil-P was 3.5 times greater than initial NaHCO₃-soluble P. The initial soil NaHCO₃-soluble P required to provide at least 95% of maximum yield increased with increasing cut number (from 37 mg P kg^?1 soil at cut 1 to 160 mg P kg^?1 soil at cut 4), probably because the NaHCO₃-P pool was replenished more slowly than P was removed by the plants.     

Speciation of Cu and Zn in drainage water from agricultural soils

Inputs of copper and zinc from agricultural soils into the aquatic system were investigated in this study, because of their heavy agricultural usage as feed additives and components of fertilizers and fungicides. As the mobility and bioavailability of these metals are affected by their speciation, the lipophilic, colloidal and organic fractions were determined in drainage water from a loamy and a humic soil treated with fungicides or manure. This study therefore investigates the impact of agricultural activity on a natural environment and furthers our understanding of the mobility of metals in agricultural soils and aquatic pollution in rural areas. Marked increases in the total dissolved metal concentrations were observed in the drainage water during rain events with up to 0.3 microM Cu and 0.26 microM Zn depending on the intensity of the rainfall and soil type. The mobile metal fractions were of a small molecular size (<10 kD) and mainly hydrophilic. Lipophilic complexes originating from a dithiocarbamate (DTC) fungicide could not be observed in the drainage water; however, small amounts of lipophilic metal complexes may be of natural origin. Cu was organically complexed to > 99.9% by abundant organic ligands (log K 10.5-11.0). About 50% of dissolved Zn were electrochemically labile, and the other 50% were complexed by strong organic ligands (log K 8.2-8.6). Therefore very little free metal species were found suggesting a low bioavailability of these metals in the drainage water even at elevated metal concentrations.     

Linking phosphorus sequestration to carbon humification in wetland soils by 31P and 13C NMR spectroscopy

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution (31)P and solid state (13)C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.     

Assessment of a sequential extraction procedure for perturbed lead-contaminated samples with and without phosphorus amendments

Sequential extraction procedures are used to determine the solid-phase association in which elements of interest exist in soil and sediment matrixes. Foundational work by Tessier et al. (Tessier, A.; Campbell, P. G. C.; Bisson, M. Anal. Chem. 1979, 51, 844-851) has found widespread acceptance and has been employed as an operational definition for metal speciation in solid matrixes. However, a major obstacle confronting sequential extraction procedures is species alteration of extracted metals before, during, and after separation of solids from solution. If this occurs, the results obtained from sequential extraction do not provide an accurate account of metal speciation within the matrix because the metal forms are altered from their field state. Many researchers dismiss this drawback since several sorption and precipitation processes are believed to occur at time scales much longer than any particular extraction step. This assumption may not be valid. The objectives of this study were to investigate the potential formation of pyromorphite (Pb5(PO4)3Cl) during the sequential extraction steps of Pb-spiked samples with and without calcium phosphate amendments and to examine the differences in the operationally defined distribution of Pb in samples with and without the presence of P. The systems that were examined in the absence of phosphate behaved, for the most part, adequately according to the operational definitions of the extraction procedure. However, when the samples were amended with phosphate, results were drastically changed with a significant shift of extractable Pb to the residual phase. This redistribution was due to pyromorphite formation during the extraction procedure as confirmed by X-ray diffraction and X-ray absorption (XAS) spectroscopies. These results indicate that sequential extraction methods may not be suitable for Pb speciation in perturbed environmental systems (i.e., fertilized agricultural soils or amended contaminated soils) and that rigorous interpretation should be avoided, if not supported by methods to definitively prove metal speciation (e.g., XAS).     

Health risks of heavy metals in sewage‐irrigated soils and edible seeds in Langfang of Hebei province,China

BACKGROUND: Human exposure to heavy metals is attributed to consumption of food crops grown in polluted soil environment. The objective of our study was to assess the health risks of heavy metals in edible seeds of crops grown in sewage‐irrigated soils located in the Langfang of Hebei province, China. Here, heavy metal contents in soils and plants were determined using an internal standard and high‐resolution inductively coupled plasma mass spectrometry. RESULTS: There was a relative buildup of heavy metals in sewage‐irrigated soils in the study area; in particular, all Cr and partial Zn and Cu showed higher concentrations than the limits proposed by the World Health Organization, European Union (EU) and UK. Heavy metal concentrations in edible seeds of plants grown in sewage‐irrigated soils partly exceeded the permissible limits set by the EU, UK and the State Environmental Protection Administration in China. With the exception of Cu, health risk index values of each heavy metal investigated by intake of the edible seeds were less than 1. Here, a health risk index of < 1 is considered safe for human consumption. CONCLUSION: The study indicated that there was a relative absence of health risks associated with the ingestion of sewage‐irrigated edible seeds. Copyright © 2009 Society of Chemical Industry     

Bioavailable phosphorus in animal waste amended soils: using actual crop uptake and p mass balance approach

Animal manure amended soils often contain large amounts of bioavailable phosphorus (P) and constitute high risk for the deterioration of surface water quality through eutrophication. Current standards set for the safe disposal of animal manure through soil application are based on the assumption that phosphorus in all P sources would behave similarly. The primary objective of this study was to understand the influence of P from several manure and mineral fertilizer sources applied at 0, 50, and 150 mg P kg(-1) on two measures of bioavailable P to six soils of different initial soil test P levels using corn (Zea mays L.) P uptake and an iron oxide strip method for soil analysis (FeO-P). Total net bioavailable P (TNBP) was calculated by subtracting total P uptake by corn after seven consecutive harvests in control treatments that did not receive P from the P uptake from P-amended treatments. Net biovavailable P after the first harvest (NBP1) was calculated in a similar fashion but only using data from the first harvest. Significant differences in TNBP and NBP1 were found when comparing P sources. The hog (Sus scrofa) manure had the greatest P bioavailability while turkey (Meleagris gallopava) litter had the lowest among the animal P sources across all soils and levels of P application. Significant differences were also found between soils with the highest amounts of TNBP and NBP1 found in the Woodson soil and lowest detected in the Crete soil for most P sources. The FeO-P method was useful in predicting TNBP from most P sources.     

Determination of phosphorus status of wheat and barley crops using a rapid root bioassay

A root bioassay of soil P availability, based on the amount of ³²P-labelled phosphorus taken up in 15 min from a solution in the laboratory, has been tested on seedlings of winter wheat (Triticum aestivum L) and spring barley (Hordeum vulgare L). The seedlings were taken in spring from six different fertiliser plots, selected to give an extreme range of P availability, from the Broadbalk and Hoosfield experiments at Rothamsted. The results showed a negative relationship between the rate of phosphorus uptake and (a) the phosphorus contents of plants, and (b) Olsen's bicarbonate extractable phosphorus of the soils. This pattern is consistent with the results previously obtained when determining the phosphorus status of trees and grasses. This rapid bioassay procedure may therefore be applicable to agricultural crops.