Influence of soil moisture on sorption and degradation of hexazinone and simazine in soil.

Sorption and degradation rates of hexazinone and simazine on soil were determined in a sandy loam soil incubated, during 44 days, at 25 degrees C with moisture contents ranging from 4% to 18%. Herbicide levels in soil solution were also measured, after extraction of this solution by a centrifugation method. All experiments were conducted with treated soil in plastic columns, and the results showed that this method is suitable for the simultaneous study of pesticide sorption and degradation in soil at different environmental conditions. In general, sorption of both herbicides was higher for aged herbicide residues compared to recently applied herbicides, and soil subjected to drying and rewetting cycles had the highest sorption values. K(f) values ranged from 0.5 to 1.2 for simazine and from 0.2 to 0.4 for hexazinone. Degradation rates increased with soil moisture content for both herbicides, and drying-rewetting of soil yielded degradation rates slower than that obtained at 10% soil moisture content. Hexazinone concentration in soil solution decreased with incubation time faster than simazine.     

Biochar concomitantly increases simazine sorption in sandy loam soil and lowers its dissipation

Biochar application has been receiving much attention as pesticide pollution mitigator because it reduces harmful chemicals. However, direct comparisons between the effect of biochar and straw on the simazine fate in soils remain poorly understood. We explored the impact of biochars and straw on the simazine behavior in a soil using a ¹⁴C labeling approach. Biochar was produced by the thermal treatment of wheat straw at four contrasting temperatures (250, 350, 450 and 550°C) and was incorporated into a sandy loam soil. The sorption of simazine in the biochar soil from 83.9% to 87.5% was significantly higher than 43.0% in the unamended soil and 35.7% in the soil amended with unprocessed straw, thus resulting in low samizine leaching from 21.8% to 42.6% in the biochar soil. However, biochar application suppressed the simazine decomposition, which is contrast in the straw soil. Furthermore, the biogeochemical behavior of simazine varied with the pyrolysis temperature. These results indicate biochar application can significantly increase simazine adsorption and reduce leaching, which is benefit to the environmental pollution. In conclusion, the simazine behaviors in the soil are strongly influenced by the biochar properties. In comparison to straw, biochar has potential to mitigate simazine pollution.     

Effects of solid olive-mill waste addition to soil on sorption, degradation and leaching of the herbicide simazine

Abstract. A laboratory study was conducted to investigate the effects of adding an intermediary byproduct of olive oil extraction ( alperujo or solid olive-mill waste, SOMW) on the sorption, degradation and leaching of the herbicide simazine in a sandy loam soil. The effect of SOMW addition on soil porosity was also assessed. The soil was amended in the laboratory with SOMW at two different rates (5% and 10% w/w). Simazine sorption isotherms showed a great increase in herbicide sorption after SOMW addition to soil; sorption increased with the amount of SOMW added. Incubation studies showed extended persistence by reduced biodegradation of simazine in the soil amended with SOMW compared with the unamended soil. Although the addition of SOMW to soil increased the total porosity, breakthrough curves of simazine in handpacked soil columns showed that SOMW addition retarded the vertical movement of the herbicide through the soil and reduced the total amount of herbicide leached. It appeared that the longer residence time of simazine in the amended soil columns (>20 days) compared with that in the unamended soil column (<20 days) allowed enhanced degradation and/or irreversible sorption under column leaching conditions. The results revealed important changes in herbicide behaviour upon SOMW addition, confirming the need to assess these changes in order to optimize the combined use of organic wastes and soil-applied pesticides.     

Changes in sorption/bioavailability of imidacloprid metabolites in soil with incubation time

Changes in sorption/bioavailability of two metabolites, imidacloprid-urea {1-[(6-chloro-3-pyridinyl)methyl]-2-imidazolidinone} and imidacloprid-guanidine {1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-1H-imidazol-2-amine} of the insecticide imidacloprid {1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine} with aging in different soils were determined. Soil moisture was adjusted to -33 kPa and ¹⁴C- and analytical-grade imidacloprid-urea and imidacloprid-guanidine were added to the soil at a rate of 1.0 mg kg^-1. Spiked soils were incubated at 25°C for 8 weeks. Replicate soil samples were periodically extracted successively with 0.01 N CaCl₂, acetonitrile, and 1 N HCl. Imidacloprid-urea sorption, as indicated by sorption coefficient values, was highest in the soil with highest organic C content, and increased by an average factor of 2.6 in three soils during the 8-week incubation period. Imidacloprid-guanidine sorption increased by a factor of 2.3 in the same soils. The increase in sorption was the result of a decrease in the metabolite extractable with CaCl₂ (solution phase); the amount of metabolite extractable with acetonitrile and HCl (sorbed phase) did not significantly change with incubation time. It appears the increase in sorption was because the rate of degradation in solution and on labile sites was faster than the rate of desorption from the soil particles. It may have also been due to metabolite diffusion to less accessible or stronger binding sites with time. Regardless of the mechanism, these results are further evidence that increases in sorption during pesticide aging should be taken into account during characterization of the sorption process for mathematical models of pesticide degradation and transport.     

Influence of soil type on the mobility and bioavailability of chelated zinc

The objective of this study was to compare the distribution, mobility, and relative effectiveness of Zn from Zn-amino acids (Zn-AA) and Zn-DTPA-HEDTA-EDTA (Zn-CH) (DTPA, diethylenetriaminepentaacetate; HEDTA, N-2-hydroxyethyl-ethylenedinitrilotriacetate; and EDTA, ethylenedinitrilotetraacetate) sources by applying different Zn levels to weakly acidic and neutral soils in laboratory (incubation and soil column studies) and greenhouse conditions. The experiments were carried out for 60 days in incubation and column experiments and for 45 days in a greenhouse experiment. The zinc soil behavior was evaluated by DTPA-TEA and Mehlich-3 extractions and sequential speciation. The incubation experiment showed that the highest concentrations of available Zn in weakly acidic soil occurred with Zn-AA treatments, whereas in the neutral soil Zn-CH treatments produced the highest quantities of available Zn. The column experiment showed that in neutral soil, with slow to moderate permeability in the Ap and Bt horizons, only Zn-CH significantly increased the mobility of Zn through the column with respect to the control and the Zn-AA source: 31% of the Zn applied as synthetic chelate was leached from the column. The greenhouse experiment showed that, at different rates of Zn application, the Zn carriers increased Zn uptake by maize (Zea mays L.). The use of applied Zn by maize, or Zn utilization, was greatest when the Zn treatments were Zn-CH (3.3%) at 20 mg kg-1 and Zn-CH (4.9%) at 10 mg kg-1, in weakly acidic and neutral soils, respectively.     

Influence of Cry1Ac toxin on mineralization and bioavailability of glyphosate in soil

The impact of transgenic plants containing Bacillus thuringiensis (Bt) toxin on soil processes has received recent attention. In these studies, we examined the influence of the lepidopterean Bt Cry1Ac toxin on mineralization and bioavailability of the herbicide glyphosate in two different soils. The addition of 0.25-1.0 microg g(-1) soil of purified Cry1Ac toxin did not significantly affect glyphosate mineralization and sorption in either a sandy loam or a sandy soil. In contrast, extractable glyphosate decreased over the 28 day incubation period in both soils. Our findings suggest that the reduction in the bioavailability of glyphosate was not influenced by the presence of Cry1Ac toxin but rather the results of aging or sorption processes. Results from this investigation suggest that the presence of moderate concentrations of Bt-derived Cry1Ac toxin would have no appreciable impact on processes controlling the fate of glyphosate in soils.     

Influence of electrolyte composition and pH on cadmium sorption by an acid sandy soil

Extraction of soil with CaCl₂, has been recommended as a measure of bioavailability of heavy metals. Interpretation of soil extraction data in terms of plant uptake potential may improve when the chemical behaviour of heavy metals in these extracts is ascertained. The effect of pH, Cd complexation by Cl, and competition between Cd and Ca on Cd sorption was studied at an ionic strength of 0.03 m . Sorption of cadmium was measured in 0.01 m CaCl₂, in 0.01 m Ca(NO₃)₂, in a mixture of 0.02 m NaCl and 0.01 m NaNO₃, and in 0.03 m NaNO₃, at different values of pH ranging from 3.8 to 4.9. Adsorption isotherms were all linear, with a negative intercept on the y-axis. This intercept indicated (linear) desorption of only part of the initial soil Cd content. About 50% of the Cd in solution was complexed in the presence of 0.02 m Cl at ionic strength of 0.03. Due to competition between Cd and Ca, sorption of Cd was reduced by 80% in the Ca-electrolytes as compared with the Na-electrolytes. Sorption was highly sensitive to pH as each 0.5 unit increase in pH resulted in twice as much sorption of Cd. An empirical factor in the sorption equation that accounts for this effect of pH showed a similar response to changes in pH as a mechanistic factor. This mechanistic factor was developed by assuming that Cd and protons sorb onto the same sites and that a two-site Langmuir sorption isotherm for protons was able to describe the titration curve of the soil. This similarity may explain the successful application of the empirical factor in this and previous studies.     

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.     

Chemical extraction to assess the bioavailability of chlorobenzenes in soil with different aging periods

Purpose  

Bioavailability is mainly influenced by aging and desorption of contaminants in soil. The purpose of this study was to investigate the desorption kinetics of chlorobenzenes (CBs) in soil and to investigate whether chemical extractions are suitable for the bioavailability assessment of CBs in soil.     

Influence of molecular structure on sorption of phenoxyalkanoic herbicides on soil and its particle size fractions

The sorption and desorption behaviors of four phenoxyalkanoic acid herbicides and their metabolites on four agricultural soils and soil particle size fractions were examined. Generally, there was a trend of increasing adsorption and decreasing desorption in the order mecoprop < MCPA < dichlorprop < 2,4-D. The significant increase in adsorption of the phenolic metabolites can be explained by their lower polarity and enhanced partition in the organic soil matrix. Estimation of sorption distribution coefficients from particle size fraction adsorption data was possible for a sandy soil and a silty Cambisol soil only. It is suggested that increasing steric demand, for example, molecular volume, and slight changes in the polarity of the compounds affect their adsorption properties. Comparison of adsorption and desorption data of structurally similar compounds obtained from a variety of soils allows investigation of structure-induced differences in sorption strength.     

Effects of nitrapyrin,terrazole, and simazine on soil nitrogen transformation and corn growth

Abstract

Nitrapyrin, terrazole and simazine were evaluated as chemical inhibitors of biological nitrification and denitrification. Corn (Zea mays L. cv. Hybrid Pioneer 3343) was grown in 60‐liter pots filled with a 50/50 (V/V) sand/Cecil clay mixture. Chemical treatments consisted of weekly applications of 0.25 ppm nitrapyrin, terrazole and/or simazine concurrently with 20 ppm N as either (NH₄)₂SO₄ or Ca(NO₃)₂ for 9 weeks. Thereafter, only N (20 ppm per pot) was applied to the media every three days for 4 weeks. Nitrapyrin, terrazole and simazine reduced nitrification resulting in both higher total plant N and residual soil NH₄ content relative to the control plants and soil. Plant growth was reduced by the inhibitory effects of the chemicals on nitrification and subsequent NH₄ accumulation in the medium. All chemicals reduced denitrification with terrazole being more effective than nitrapyrin as reflected by higher N contents of plants and residual soil NO₃‐N. Nitrapyrin and/or terrazole applied with Ca(NO₃)₂ increased plant biomass, but simazine, by inducing higher N0₂ concentration in the plant tissues, sharply reduced plant growth relative to the other treatments. When simazine was part of the chemical treatment, its effects on plant growth and total N contents generally outweighed or masked those of nitrapyrin or terrazole.     

Influence of inorganic and organic fertilization on soil microbial biomass, metabolic quotient and heavy metal bioavailability

 We studied the long-term effects (12 years) of municipal refuse compost addition on the total organic carbon (TOC), the amount and activity of the microbial biomass (soil microbial biomass C, B_C and metabolic quotient qCO₂) and heavy metal bioavaiability in soils as compared to manuring with mineral fertilizers (NPK) and farmyard manure (FYM). In addition, we studied the relationships between among the available fraction [Diethylenetriaminopentacetic acid (DTPA) extractable] of heavy metals and their total content, TOC and B_C. After 12 years of repeated treatments, the TOC and B_C of control and mineral fertilized plots did not differ. Soils treated with FYM and composts showed a significant increase in TOC and B_C in response to the increasing amounts of organic C added. Values of the B_C/TOC ratio ranged from 1.4 to 2, without any significative differences among soil treatments. The qCO₂ increased in the organic-amended soil and may have indicated microbial stress. The total amounts of metals in treated soils were lower than the levels permitted by the European Union in agricultural soils. DTPA-extractable metals increased in amended soils in response to organic C. A multiple regression analysis with stepwise selection of variables was carried out in order to discriminate between the influence exerted on DTPA-extractable metals by their total content, TOC and B_C. Results showed that each metal behaved quite differently, suggesting that different mechanisms might be involved in metal bioavailability Received: 31 October 1997     

Effect of soil components on the surfactant-enhanced soil sorption of PAHs

Purpose  

The use of cationic surfactants was proposed to enhance the soil retention of hydrophobic organic contaminants (HOCs). However, due to the complexity of soil composition, the effect of cationic surfactants on the soil sorption of HOCs was limited to a qualitative understanding. To gain further insight into the mechanism of the surfactant and predict its efficiency, a comparative study on the HOCs sorption capacities of the surfactants sorbed on pure typical soil components was investigated.     

The enhanced mineralization of simazine and bentazon in soil after plant uptake

[triazine-ring-¹⁴C] simazine and [benzene-ring-¹⁴C] bentazon were added to the epipedon of a Luvisol from loess with and without maize shoots or roots (2 g/100 g soil) and mineralization proceeded in accordance with the standardized BBA degradation method at 50% of the maximum water holding capacity of the soil and at 22°C. The same degradation study was conducted using maize shoots (simazine) and maize roots (bentazon) which had taken up either ¹⁴C-simazine or ¹⁴C-bentazon from soil application. After 93 days of incubation 6.6% (simazine) or 7.2% (bentazon) of this plant incorporated ¹⁴C was mineralized to ¹⁴CO₂. This was 4–10 times greater than the mineralization of active ingredients applied to the soil and 4–6 times higher when compared to variants which in addition received maize shoots (simazine) or roots (bentazon) as an additional energy source for microbial development. Apparently as a consequence of the more intensified degradation processes, the bound residue fractions were higher by a factor of 2 when the residual radiocarbon reached the soil already incorporated into plant material.     

Cadmium soil sorption at low concentrations: II. Reversibility,effect of changes in solute composition,and effect of soil aging

Water, Air, & Soil Pollution - Desorption of Cd from two Danish soils (loamy sand, sandy loam) previously exposed to low concentrations of Cd was examined in terms of reversibility, effect of...     

红壤基质组分对磷吸持指数的影响

在红壤旱地肥料长期定位试验(始于1988年)中,选取了无机肥试验区的NPK、NP、NK、PK,有机无机配施试验区的CK、CK+猪厩肥(BM)及CK+花生秸秆(SR)等7个施肥处理土壤,测定了土壤磷吸持指数(Phosphate sorption index,PSI),分析了PSI与红壤最大吸磷量(Xm)的相关关系,讨论了土壤pH、有机质、黏粒、铁铝氧化物及无机磷酸盐等基质组分对PSI的影响。结果表明:长期施磷或配施有机肥均可显著降低红壤PSI值,随着土壤pH的升高、有机质及铁结合态磷酸盐(Fe-P)含量的增加,红壤PSI显著降低;土壤游离铁铝氧化物及黏粒含量越高,PSI也越大。PSI与Xm呈显著线性相关关系(Xm=0.5PSI+412.8,n=15,r=0.967**,p<0.01),因此,可以用PSI替代Xm来表征土壤固磷能力,亦可由PSI的大小来推断土壤磷的供磷能力。     

长期施肥与土壤性质对水稻土磷吸附的影响

基于长期定位试验(始于1981年),采用磷等温吸附试验方法,研究了不同施肥措施(包括无肥、单施化肥、稻草还田、沼肥)及相关土壤性质对耕层水稻土(0~15 cm)磷吸附特性的影响。结果表明,等温吸附试验中,不同施肥处理的水稻土,随着磷浓度的增加,磷的吸附量逐渐增大。对磷等温吸附曲线,用Langmuir方程拟合效果比Freundlich和Temkin方程好,各处理拟合优势度均在0.99以上。基于Langmuir方程计算,土壤磷最大吸附量(X_m)大小顺序为沼肥稻草单施化肥无肥,且沼肥处理显著高于其余3个处理(P0.05);同时,沼肥处理的磷吸附饱和度亦显著高于其它处理,但处理间土壤磷吸附常数与磷最大缓冲容量无显著差异。X_m值与土壤草酸浸提态磷(P-ox)、无定型铁(Fe-ox)、无定型铝、交换态钙、镁的含量有较高的相关性,其中与P-ox、Fe-ox的相关性最显著,相关系数分别为0.95(P0.01)、0.64(P0.05);主成分分析表明,无定型铁、铝与交换态钙、镁是引起不同施肥处理磷吸附差异的主要因素。与无肥及单施化肥相比,长期施用沼肥显著提高了土壤无定型铁、铝的含量(P0.05),从而增强了土壤磷吸附能力。     

施污泥土壤中铜的形态分布及其生物有效性

利用蔬菜盆栽试验研究了黄棕壤(pH 6.2)和红壤(pH 4.3)中施用污泥对土壤中Cu转化和蔬菜吸收的影响.施用污泥初期提高了土壤溶液的pH,但种植蔬菜后,降低了土壤溶液的pH,其中黄棕壤溶液pH的下降更大;施用污泥和种植蔬菜提高了土壤溶液的NO3--N含量,黄棕壤溶液中NO3--N含量的增幅高于红壤.施用污泥增加了土壤溶液中Cu的含量,特别是在酸性更强的红壤中影响更大;施用污泥的红壤中主要增加了冰醋酸溶解态Cu的比例,而黄棕壤中主要增加了铁锰氧化物结合态Cu的比例;施用污泥促进了蔬菜的生长,但对蔬菜植株中Cu含量的影响较小.土壤pH是影响污泥重金属在土壤中转化和植物吸收的主要因素,在酸性更强的红壤中施用污泥导致污泥中Cu更多地转化为植物有效性Cu,具有更高的环境风险.     

影响土壤中镉的植物有效性的因素及镉污染土壤的植物修复

阐述了镉的来源及其对人类的危害,并对影响土壤中镉的植物有效性的土壤因素中的pH、氧化还原电位(Eh)、有机物质、营养物质浓度对镉的植物有效性的作用作了详细的阐述。此外对其它如EDTA、淤泥等对土壤中镉的植物有效性的影响和镉污染土壤的植物修复等方面也进行了综述,并对镉污染土壤的修复治理与趋势进行了展望。     

Factors affecting the soil sorption of iodine

Iodine-129 is an important radionuclide released from nuclear facilities because of its long radioactive half-life and its environmental mobility. Its retention in surface soils has been linked to pH, organic matter, and Fe and Al oxides. Its inorganic solution chemistry indicates I will most likely exist as an anion. Three investigations were carried out to provide information on the role of the inorganic and organic chemistry during sorption of I by soil. Anion competition using Cl^? showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of Cl decreased the loss of I^? from solution by 30 and 50% for an organic and a carbonated sandy soil respectively. The I remaining in solution was associated primarily with dissolved organic carbon (DOC). The loss rate from solution appears to depend on two reactions of I with the soil solids (both mineral and organic) creating both a release to and a loss from solution, and the reaction of I with the DOC (from very low to high molecular weight). Composition analyses of the pore water and the geochemical modelling indicate that I sorption affects the double-charged anion species in solution the most, particularly SO₄ ^?. Iodide introduced to natural bog groundwater at three concentrations (10^?3, 10^?1 and 10 meq L^?1) remained as I^? and was not lost from solution quickly, indicating that the association of I with DOC is slow and does not depend on the DOC or I concentration. If sorption of I to soil solids or DOC is not sensitive to concentration, then stable I studies, which by necessity must be carried out at high environmental concentrations, can be linearly extrapolated to radioactive I at much lower molar concentrations.