Sorption and desorption of diuron and norflurazon in Florida citrus soils

The potential for surface and groundwater contamination of soil applied herbicides is partly dependent on soil properties. Sorption and desorption of diuron and norflurazon were studied in seven soils representative of the southern citrus-belt of Florida using the batch-equilibrium technique. Sorption of herbicides was influenced by soil properties. Sorption coefficients (K _d) ranged from 0.84 to 3.26 mL g^?1 for diuron and 0.63 to 2.20 mL g^?1 for norflurazon indicating weak to moderate binding of herbicides to soil. For norflurazon, K _dwas significantly related to organic C content, soil pH, and cation exchange capacity. For diuron, absence of a significant relationship between K _dand selected soil properties suggests that the soil properties other than those studied may play a role in determining sorption on these soils. Desorption studies showed that higher amounts of diuron and norflurazon was desorbed by water than by 0.5 M CaCl₂. An inverse relationship was apparent between herbicides sorbed and that which was desorbed among the soils studied. The soil which exhibited higher sorption had lower desorption and the soil which exhibited lower sorption had higher desorption.     

Effects of equilibrating salt solutions on phosphate sorption by soils

Abstract

Several equilibrating salt solutions have been used in the studies of P sorption by soils and sediments. This study was conducted to evaluate the effects of 10 salt solutions on estimation of P sorption by soils. Results obtained showed that, when the equilibrating solution was made to contain 0.01M with respect to CaCl₂, Ca(NO₃)₂, CaSO₄, MgCl₂, KCl, LiCl, Nacl, or KHCO₃, the amount of P sorbed by soil always exceeded the amount sorbed from the soil‐water system. In comparison with the amount of P sorbed from water, 0.01M NaHCO₃ reduced P sorption by soils. Use of THAM buffer (0.05M pH 7.0) to control the pH increased P sorption by some soils and decreased P sorption by others, relative to that sorbed from the soil‐water system. The results indicated that inclusion of salts in the equilibrating solution for P‐sorption studies should be avoided, especially in studies related to water quality.     

Denitrification in soil: Effects of herbicides

The effects of 20 herbicides on denitrification of nitrate in three soils were studied by determining the effects of 10 and 50μgg^?1 soil of each herbicide on the amounts of nitrate lost and the amounts of nitrite, N₂O and N₂ produced when soil samples were incubated anaerobically after treatment with nitrate. The herbicides used were butylate, EPTC, chlorpropham, propham, diuron, linuron, monuron, siduron, alachlor, trifluralin, 2,4-D amine, 2,4-D ester, atrazine, cyanazine, metribuzin, simazine, dalapon, chloramben, dicamba and dinoseb.None of the herbicides studied significantly affected denitrification of nitrate when applied at the rate of 10 μg g^?1 soil, but dinoseb increased the ratio of N₂ to N₂O in the gaseous products of denitrification when applied at this rate. Butylate, EPTC, diuron, simazine and dalapon had no significant effect on denitrification when applied at the rate of 50μgg^?1 soil, whereas metribuzin and dinoseb enhanced denitrification when applied at this rate. The influence of the other herbicides on denitrification when applied at the rate of 50μgg^?1soil depended on the soil, but all enhanced or inhibited denitrification in at least one soil.     

Effect of liming on phosphate sorption by acid soils

The sorption of phosphate (P) by four strongly acid Fijian soils from 0.01 M CaCl₂ decreased with increasing pH up to pH 5.5–6.0 and then increased again. The initial decrease in P sorption with increasing pH appears to result from an interaction between added P, negative charge, and the electrostatic potential in the plane of sorption. The results of a sorption study, involving KCl or CaCl₂ of varying concentrations as the background electrolyte and using Nadroloulou soil incubated with KOH or Ca(OH)₂, suggested that the increase in P sorption at pH values > 6.0 was caused by the formation of insoluble Ca-P compounds. For some soils this is consistent with the results of an isotopic-exchange study in which incubation with lime caused marked reductions in the amounts of exchangeable P at high pH.     

Fate of diuron and terbuthylazine in soils amended with two-phase olive oil mill waste

The addition of organic amendments to soil increases soil organic matter content and stimulates soil microbial activity. Thus, processes affecting herbicide fate in the soil should be affected. The objective of this work was to investigate the effect of olive oil production industry organic waste (alperujo) on soil sorption-desorption, degradation, and leaching of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and terbuthylazine [N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine], two herbicides widely used in olive crops. The soils used in this study were a sandy soil and a silty clay soil from two different olive groves. The sandy soil was amended in the laboratory with fresh (uncomposted) alperujo at the rate of 10% w/w, and the silty clay soil was amended in the field with fresh alperujo at the rate of 256 kg per tree during 4 years and in the laboratory with fresh or composted alperujo. Sorption of both herbicides increased in laboratory-amended soils as compared to unamended or field-amended soils, and this process was less reversible in laboratory-amended soils, except for diuron in amended sandy soil. Addition of alperujo to soils increased half-lives of the herbicides in most of the soils. Diuron and terbuthylazine leached through unamended sandy soil, but no herbicide was detected in laboratory-amended soil. Diuron did not leach through amended or unamended silty clay soil, whereas small amounts of terbuthylazine were detected in leachates from unamended soil. Despite their higher sorption capacity, greater amounts of terbuthylazine were found in the leachates from amended silty clay soils. The amounts of dissolved organic matter from alperujo and the degree of humification can affect sorption, degradation, and leaching of these two classes of herbicides in soils. It appears that adding alperujo to soil would not have adverse impacts on the behavior of herbicides in olive production.     

不同金属盐强化乙醇/水预处理对蔗渣酶解效率的影响

预处理过程可以破坏木质纤维素生物质的致密结构、降低生物抗性,是木质纤维素生物质经酶解制备糖基平台化学的重要步骤。该研究以蔗渣为原料,在预处理温度为160 ℃、预处理时间为10 min时,选取0.025 mol/L 的不同金属盐FeCl₃、CrCl₃、AlCl₃、CuCl₂、FeCl₂、ZnCl₂、MnCl₂、MgCl₂、CaCl₂、NaCl、LiCl、Na₂CO₃对蔗渣进行乙醇/水预处理,并对预处理后样品进行酶解,探究不同金属盐强化乙醇/水预处理对蔗渣酶解效率的影响和规律,并进一步通过扫描电镜（scanning electron microscopy, SEM）、X射线衍射（X-ray diffraction, XRD）、傅里叶变换红外光谱（fourier transform infrared spectroscopy, FT-IR）和热重（thermogravimetric, TG）对蔗渣原料和预处理后的固体进行表征,探究金属盐强化乙醇/水预处理后蔗渣表面形貌与结构变化对酶解效率的影响,分析作用机理。结果表明:与原料甘蔗渣相比,不同金属盐强化乙醇/水预处理后样品中葡聚糖的质量分数从45.5%增加到77.2%,预处理后样品酶解48h后的葡萄糖得率也由51.14%增加到最高93.08%。其中,三价金属盐（FeCl₃、CrCl₃和AlCl₃）对蔗渣酶解效率的提升最为显著,这可归因于三价金属盐强化乙醇/水预处理可以更加有效的去除蔗渣中的半纤维素和木质素,增加酶对纤维素的可及性。后续表征分析也表明经过三价金属盐（FeCl₃、CrCl₃和AlCl₃）强化乙醇/水预处理后的样品比经过二价金属盐（CuCl₂、FeCl₂、ZnCl₂、MnCl₂、MgCl₂和CaCl₂）和一价金属盐（NaCl、LiCl和Na₂CO₃）强化乙醇/水预处理表面结构破坏更为彻底,结晶度相对增加最大,木素和半纤维素去除率最多,热稳定性也相对最高。该研究结果将为后续木质纤维素生物质的高效转化与利用提供参考。     

Effect of flow rate on the adsorption and desorption of glyphosate,simazine and atrazine in columns of sandy soils

Adsorption and desorption of the herbicides glyphosate [N-phosphonomethyl-aminoaceticacid], simazine [6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine] and atrazine [6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine] were studied in four sandy soils from Western Australia. Distribution coefficients (K_ds) were calculated from breakthrough curves (BTCs) resulting from leaching step changes in concentrations through small saturated columns of soil at flow rates ranging from 0.3 to 30 m day^–1. A comparison was made with K_ds obtained after batch equilibrating solutions of the herbicides with the same soils. The K_ds of herbicides in soils decreased with increasing flow rate and most strongly for glyphosate in soils rich in clay content. Resulting increases in mobility of about 40–50% were estimated for simazine and atrazine and > 50% for glyphosate at flow rates of 3 m day^–1. Adsorption and desorption rates were estimated by fitting numerically simulated BTCs to experimental BTCs. Best fits were obtained with a time-dependent Freundlich adsorption equation. The resulting coefficient for time dependency in the equation suggests that the rates of adsorption and desorption are controlled mainly by diffusion in an adsorbing layer on or in soil particles.     

Biochar Increases Diuron Sorption and Reduces the Potential Contamination of Subsurface Water with Diuron in a Sandy Soil

The herbicide diuron is widely used in agricultural areas in Brazil, whereas it has high potential for subsurface water contamination due to its physicochemical characteristics. Recent studies have demonstrated the potential of biochar as a sorbent and possible pesticide leaching mitigation. The objective of this study was to investigate the long-term effect of biochar application on the kinetics of sorption and desorption of diuron in a Cerrado Haplic Plinthosol. Samples were collected in an experiment conducted in the field in a randomized block design consisting of the combination of two levels of fertilizer application (0 and 300 kg ha^-1 of 5-25-15 formula of NPK fertilizers) and three doses of biochar (0, 16, and 32 Mg ha^-1). The Freundlich isotherm accurately described the sorption of diuron in all treatments. Biochar application increased the sorption and reduced the desorption of diuron. This effect was attributed to the contribution of biochar to total organic carbon (C) and C in the humin fraction and to the increase in the reactivity of the humic acid and humin fractions, which was significantly highly correlated with the sorption coefficient (K_f). A positive correlation between the partition coefficient of organic C and K_f confirmed the importance of the soil organic compartment for the sorption of diuron. The higher diuron sorption and lower diuron desorption capacities of sandy soils after biochar application could reduce the potential risk of diuron leaching and contamination of subsurface water.     

Sorption of Phosphorus from Swine,Dairy, and Poultry Manures

In most phosphorus (P) sorption studies, P is added as an inorganic salt to a predefined background solution such as calcium chloride (CaCl₂) or potassium chloride (KCl); however, in many regions, the application of P to agricultural fields is in the form of animal manure. The purpose of this study, therefore, was to compare the sorption behavior of dissolved reactive P (DRP) in monopotassium phosphate (KH₂PO₄)–amended CaCl₂ and KCl solutions with sorption behavior of DRP in three different animal manure extracts. Phosphorus single‐point isotherms (PSI) were conducted on eight soils with the following solutions: KH₂PO₄‐amended 0.01 M CaCl₂ solution, KH₂PO₄‐amended 0.03 M KCl solution, water‐extracted dairy manure, water‐extracted poultry litter, and swine lagoon effluent. The PSI values for the dairy manure extract were significantly lower than the CaCl₂ solution for all eight soils and lower than the KCl solution for six soils. The PSI values were significantly higher, on the other hand, for poultry litter extract and swine effluent than the inorganic solutions in four and five of the soils, respectively. Our observations that the sorption of DRP in manure solutions differs significantly from that of KH₂PO₄‐amended CaCl₂ and KCl solutions indicates that manure application rates based on sorption data collected from inorganic P salt experiments may be inaccurate.     

Assessment of three vermicomposts as organic amendments used to enhance diuron sorption in soils with low organic carbon content

Vermicomposts from the wine and distillery industry containing spent grape marc (V1), biosolid vinasse (V2) and alperujo (V3) from the olive‐oil industry were investigated as organic amendments to a sandy and a clay soil with low organic carbon (OC) contents (≤1%). The sorption‐desorption process was studied in batch experiments using diuron as a non‐ionic herbicide model. The effect of soil and vermicompost characteristics, the solution's ionic strength and incubation time of amended soils on the sorption process was studied. The addition of vermicompost changed soil properties and enhanced sorption capacity by two‐ to four‐fold. The K_oc variability showed that exogenous OC composition influenced diuron sorption. Vermicompost V1, which had the largest OC and lignin content, recorded the largest sorption increment. Vermicompost V3, which had the greatest dissolved organic carbon content and a high degree of humification, made the smallest contribution to sorption. Sorption was also dependent on extraneous calcium in the solution. The incubation of amended soils reduced diuron sorption efficiency except with V3. Pyrolysis‐gas chromatography (Py‐GC) analysis was a useful tool to characterize the vermicomposts and to understand the variation of diuron sorption constants after vermicompost incubation. This research encourages the use of vermicompost from agro‐industrial wastes as a sustainable means to minimize the side effects of neutral herbicides.     

Natural soil colloids To retard simazine and 2,4-D leaching in soil

Natural or synthetic sorbents for pesticides can be used to reduce contamination of soils and natural waters. The sorption of simazine and 2,4-D on montmorillonite minerals has been studied and their potential use to retard pesticide leaching in soil evaluated. Simazine and 2,4-D did not sorb on high-layer charge montmorillonite, whereas sorption on the lower layer charge montmorillonite SWy varied depending on the saturating cation. Simazine sorption increased in the order Ca(2+)SWy < K(+)SWy < Fe(3+)SWy. Simazine molecules sorb on hydrophobic microsites of the montmorillonite. Once protonated, further sorption through cation exchange takes place in the interlamellar space of the montmorillonite, as corroborated by X-ray diffraction and FT-IR studies. 2,4-D does not sorb on K(+)SWy or Ca(2+)SWy, but does sorb on Fe(3+)SWy, because the acidic character of this sorbent allows the molecular form of 2, 4-D to sorb by hydrogen bonding and/or by hydrophobic interactions. Leaching experiments in hand-packed soil columns indicate that simazine and 2,4-D application as a complex with FeSWy renders later breakthrough and lower maximum concentration peaks, and the total herbicide leached is lower than when applied as the pure analytical grade compound. These results suggest the possible use of natural soil colloids as sorbents for herbicides such as simazine and 2,4-D to retard pesticide leaching in soil, thus reducing their ground water contamination potential.     

Potential contaminant release from agricultural soil and dredged sediment following managed realignment

Purpose

Laboratory experiments were conducted to examine the potential for metal (Cu, Ni and Zn) and herbicide (simazine, atrazine and diuron) release from agricultural soil and dredged sediment in managed realignment sites following tidal inundation.

Materials and methods

Column microcosm and batch sorption experiments were carried out at low (5?practical salinity units, psu) and high (20?psu) salinity to evaluate the changes in the partitioning of metals and herbicides between the soil/sediment and the aqueous phase, and the release of metals and herbicides from soil/sediment to the overlying water column.

Results and discussion

For both the metals and herbicides, the highest contaminant loads were released from the sediment within the first 24?h of inundation suggesting that any negative impacts to overlying water quality in a managed realignment scheme will be relatively short term following tidal inundation of soil and sediment. The release of metals was found to be dependent on a combination of salinity effects and the strength of binding of the metals to the soil and sediment. In the case of the herbicides, salinity impacted on their release. Particulate organic carbon was found to control the binding and release of the herbicides, highlighting the importance of assessing soil and sediment organic matter content when planning managed realignment sites.

Conclusions

Our research demonstrates that metals and herbicides may be released from contaminated sediments and agricultural soils during initial periods of flooding by seawater in managed realignment sites.     

Leaching of Terbuthylazine and Bromacil Through Field Soils

A field experiment was designed to provide data on the effect of soil heterogeneity on the distribution of herbicides following leaching by irrigation and rain water. Terbuthylazine and bromacil, two nonconservative herbicides, together with CaBr₂, a conservative chemical, were used in the reported experiment. The experimental field consisted of a noncultivated 175-m² plot in which 20 observation points were randomly selected. A hundred and ten centimeters of irrigation and rainwater were applied and the field was periodically sampled for chemical distributions. The spatial variability of the field was determined by measuring the K_s (saturated conductivity) and α (Gardner parameter). Auxiliary laboratory experiments were performed to define the adsorption-desorption of the chemicals studied in these field soils. Results on the adsorption-desorption of terbuthylazine and bromacil and on the redistribution of these chemicals in the field to a depth of 120 cm during leaching are shown. Bromacil leached to a greater extent than terbuthylazine. The differences among the concentrations of herbicides in the various cores studied may be explained in terms of properties of the chemicals and soil spatial variability. The residual concentrations of terbuthylazine and bromacil were also determined to a depth of 400 cm after the leaching of 110 cm of water. In some of the cores, two zones showing a relatively high concentration of terbuthylazine and bromacil were observed at depths of 40–60 and 200–300 cm, respectively. This redistribution pattern of the herbicides could be explained by the preferential flow of the solute in the cores studied.     

Ability of sorption–desorption experiments to predict potassium leaching from calcareous soils

When potassium (K⁺) fertilizers are applied to the soil, K⁺ is subject to displacement through the soil profile. Leaching can play an important role in agricultural K⁺ losses that can decrease groundwater quality. To avoid overfertilization, estimation of K⁺ leaching from soil is important. The ability of the soils to retain K⁺ against leaching varies according to the adsorption coefficient of the soils. The aim of this study was to relate the K⁺ leaching from a wide range of calcareous soils to the values obtained from a sorption–desorption experiment. The soil columns were leached with 10 mM CaCl₂ solution and the leachate was analyzed for K⁺. The breakthrough curves for K⁺ were different, and the amounts of K⁺ leached varied considerably between different soils. In these calcareous soils where crops are irrigated with water containing significant concentrations of Ca²⁺ and other cations, large amounts of K⁺ will be leached. Cumulative K⁺ leached after five pore volumes leaching with 10 mM CaCl₂ was significantly (r = 0.776, p < 0.01) related to the equilibrium K⁺ concentration. The results of this study enabled us in many cases to estimate the K⁺ leaching from soil without conducting column experiments, minimizing the laborotary work.     

Ionic interactions and salinity affect monoterpene and phenolic diterpene composition in rosemary (Rosmarinus officinalis)

In this study, we evaluated how increased cation supply can alleviate the toxic effects of NaCl on plants and how it affects essential oils (EOs) and phenolic diterpene composition in leaves of rosemary (Rosmarinus officinalis L.) plants grown in pots. Two concentrations of the chloride salts KCl, CaCl₂, MgCl₂, and FeCl₃ were used together with 100 mM NaCl to study the effects of these nutrients on plant mineral nutrition and leaf monoterpene, phenolic diterpene, and EO composition. The addition of 100 mM NaCl, which decreased K⁺, Ca²⁺, and Mg²⁺ concentrations with increasing Na⁺ in leaves, significantly altered secondary metabolite accumulation. Addition of MgCl₂ and FeCl₃ altered leaf EO composition in 100 mM NaCl–treated rosemary plants while KCl and CaCl₂ did not. Furthermore, addition of CaCl₂ promoted the accumulation of the major phenolic diterpene, carnosic acid, in the leaves. The carnosol concentration was reduced by the addition of KCl to salt‐stressed plants. It is concluded that different salt applications in combination with NaCl treatment may have a pronounced effect on phenolic diterpene and EO composition in rosemary leaves thus indicating that ionic interactions may be carefully considered in the cultivation of these species to achieve the desired concentrations of these secondary metabolites.     

可变电荷土壤黏粒表面带电点与离子相互作用的Wien效应表征

To investigate the interactions of oppositely charged sites on the surfaces of variable-charge soil particles with cations and anions, and to evaluate the mean Gibbs free binding and adsorption energies of various cations on particles of red soil and latosol, clay fractions smaller than 2 μm were separated from samples of the two variable-charge soils. Ferric oxides were removed from part of the clay fractions, which were then saturated with various chlorides (NaCl, KCl, CaCl2, CdCl2 or LaCl3). Electrical conductivities (EC) of dilute suspensions of the original and of the iron oxides-free clay fractions in deionized water were measured with the SHP-2 short high-voltage pulse apparatus, which enables measurement of the Wien effect at field strengths (E) from 14 to 250 kV cm-1. The Wien effect (EC-E) curves revealed EC increases of red soil suspensions between 14 to 200 kV cm-1, of 8.3, 8.4, 12.1, 5.9, and 1.2 μS cm-1 for NaCl, KCl, CaCl2, CdCl2, and LaCl3, respectively, reflecting the differing interactions with the various cations and chloride. The EC increments with the iron-free red soil suspensions were higher, being 29.7, 17.2, and 15.3 μS cm-1 for NaCl, CaCl2, and CdCl2, respectively. In the natural latosol suspensions the EC increments were practically zero, whereas in the iron-free fractions there were significant EC increments of 10.3, 5.7, 5.0, and 1.6 μS cm-1 for NaCl, CaCl2, CdCl2, and LaCl3, respectively.     

Soil hydrophobicity: a contribution of diuron sorption experiments

Retention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long‐term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient k_f decreased as pH increased and that the K_oc coefficient, k_f/TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO₃. In this case, the structure in micro‐aggregates was assumed to limit the accessibility of adsorption sites. The CaCO₃ and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 μm:C ratio differed. The higher retention of diuron in the CaCO₃ plot is attributed to the higher hydrophobicity of the < 2 μm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular.     

Spectral Reflectance Characteristics of Laboratory-Grown Salt Crusts on Silty Clay and Sandy Soils

Salinization of soils has led to the loss of cropland and represents a major threat to food production. Hyperspectral imaging may prove to be useful for characterizing the spectral behavior of salt-affected soils but the methodology needs to be better evaluated. In this study, we characterized the spectral behaviors of four types of chloride salt crusts [calcium chloride dehydrate, magnesium chloride dehydrate, potassium chloride, and sodium chloride (CaCl₂·2H₂O, KCl, and NaCl)] formed in the laboratory. We found that (1) as salt concentration increased, the reflectance intensity decreased for both soil types, and the decreases were especially pronounced for the soils leached with the CaCl₂·2H₂O and MgCl₂·2H₂O solutions; (2) soil texture had little if any effect on reflectance; and (3) reflectance intensity decreased in the order CaCl₂·2H₂O < MgCl₂·2H₂O < KCl < NaCl. By clarifying the spectral behavior of chloride salt crusts on soils, our work demonstrates hyperspectral imaging may differentiate some types of salts and determine relative salt concentrations.     

Influence of Increasing Soil Copper Concentration on the Susceptibility of Phosphomonoesterase and Urease to Heat Disturbance

The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species [Cr(III) and Cr(VI)] was examined using batch sorption, and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH, CEC, organic matter (OM), clay, water-extractable SO₄ ^2– and PO₄ ^3–, surface charge, and different iron (Fe) fractions of 12 different Australian representative soils on the sorption, and mobility of Cr(III) and Cr(VI) were examined. The amount of sorption as shown by K _f was higher for Cr(III) than Cr(VI) in all tested soils. Further, the amount of Cr(III) sorbed increased with an increase in pH, CEC, clay, and OM of soils. Conversely, the chemical properties of soil such as positive charge and Fe (crystalline) had a noticeable influence on the sorption of Cr(VI). Desorption of Cr(VI) occurred rapidly and was greater than desorption of Cr(III) in soils. The mobility of Cr species as estimated by the retardation factor was higher for Cr(VI) than for Cr(III) in all tested soils. These results concurred with the results from leaching experiments which showed higher leaching of Cr(VI) than Cr(III) in both acidic and alkaline soils indicating the higher mobility of Cr(VI) in a wide range of soils. This study demonstrated that Cr(VI) is more mobile and will be bioavailable in soils regardless of soil properties and if not remediated may eventually pose a severe threat to biota.     

Comparative sorption and leaching study of the herbicides fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) in a soil amended with biochars and other sorbents

Biochar, the solid residual remaining after the thermochemical transformation of biomass for carbon sequestration, has been proposed to be used as a soil amendment, because of its agronomic benefits. The effect of amending soil with six biochars made from different feedstocks on the sorption and leaching of fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) was compared to the effect of other sorbents: an activated carbon, a Ca-rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SA-HDTMA), and an agricultural organic residue from olive oil production (OOW). Soil was amended at 2% (w/w), and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, but decreased in soil amended with a biochar produced from macadamia nut shells made with fast pyrolysis. Lower leaching of the herbicides was observed in the soils amended with the biochars with higher surface areas BC5 and BC6 and the organoclay (OCl). Despite the increase in herbicide sorption in soils amended with two hardwood biochars (BC1 and BC3) and OOW, leaching of fluometuron and MCPA was enhanced with the addition of these amendments as compared to the unamended soil. The increased leaching is due to some amendments' soluble organic compounds, which compete or associate with herbicide molecules, enhancing their soil mobility. Thus, the results indicate that not all biochar amendments will increase sorption and decrease leaching of fluometuron and MCPA. Furthermore, the amount and composition of the organic carbon (OC) content of the amendment, especially the soluble part (DOC), can play an important role in the sorption and leaching of these herbicides.