Soil Sorption Coefficients Research Articles

Aquatic environmental fate of nitroguanidine

AbstractThe environmental fate of nitroguanidine (NQ) in surface waters is dominated by photolysis with surface half‐lives at 40°N ranging from 0.6 d in summer to 2.3 d in winter. The environmental quantum yield is 0.01. The NQ is initially photolyzed to nitrite and hydroxyguanidine; nitrite is photochemically converted to nitrate and hydroxyguanidine undergoes sensitized photolysis to unknown products. The photooxidation of nitrite is assisted by organic material in a process not involving H2O2 or singlet oxygen. Nitroguanidine biotransforms cometabolically; in the absence of extra organic nutrients the second‐order rate constant was (3.8 ± 0.9) × 10−10 ml cell−1 h−1. Half‐life estimates for aerobic, aquatic biotransformation range from 1 to 100 d. Cyanamide appears to be an end product of NQ use and no intermediate biotransformation products were observed. Nitroguanidine is expected to move readily through soils (soil sorption coefficient Kp < 0.1); however, anaerobic biotransformation occurs readily in soil, with an estimated half‐life of 4 d.Other fate parameters measured at 25°C are a water solubility of 2,600 ± 100 ppm, octanol/water partition coefficient of 0.148 ± 0.001 (dimensionless), Henry's constant of < 7 × 10−6 (dimension‐less), base hydrolysis constant of (3 ± 1) × 10−4 M−1 S−1, neutral hydrolysis constant ≤ 2 × 10−8 s−1, and biouptake constants of 110 g dry cells/g water for Anabena flos‐aquae and 150 g dry cells/g water for Selenastrum capricornutum.

Detecting Organic Contaminants in the Unsaturated Zone Using Soil and Soil-Pore Water Samples

ABSTRACT A lysimeter study was conducted to compare the effectiveness of soil core and soil-pore water samples in detecting the movement of organic constituents from land-treated industrial wastes. Lysimeters collected from the Bastrop (Udic Paleustalf), Padina (Grossarenic Paleustalf), and Weswood (Fluventic Ustochrept) soils were amended with a refinery separator sludge, a wood-preserving bottom sediment sludge, or a nonhalogenated solvent recovery sludge at rates of 50, 15, and 50 g kg−1, respectively. Soil-pore water samples from porous ceramic cups and soil cores were collected monthly at three depths in the lysimeters to monitor n-alkanes and polynuclear aromatic hydrocarbons from the petroleum waste, phenols and cresols from the wood-preserving waste, and aromatic solvents from the solvent recovery waste. The organic carbon normalized soil sorption coefficient (Koc) may be useful for determining when soil-pore water or soil core samples will be most effective in detecting organic chemicals in the u...

Quantitative modeling of soil sorption for xenobiotic chemicals.

Experimentally determining soil sorption behavior of xenobiotic chemicals during the last 10 years has been costly, time-consuming, and very tedious. Since an estimated 100,000 chemicals are currently in common use and new chemicals are registered at a rate of 1000 per year, it is obvious that our human and material resources are insufficient to experimentally obtain their soil sorption data. Much work is being done to find alternative methods that will enable us to accurately and rapidly estimate the soil sorption coefficients of pesticides and other classes of organic pollutants. Empirical models, based on water solubility and n-octanol/water partition coefficients, have been proposed as alternative, accurate methods to estimate soil sorption coefficients. An analysis of the models has shown (a) low precision of water solubility and n-octanol/water partition data, (b) varieties of quantitative models describing the relationship between the soil sorption and above-mentioned properties, and (c) violations of some basic statistical laws when these quantitative models were developed. During the last 5 years considerable efforts were made to develop nonempirical models that are free of errors imminent to all models based on empirical variables. Thus far molecular topology has been shown to be the most successful structural property for describing and predicting soil sorption coefficients. The first-order molecular connectivity index was demonstrated to correlate extremely well with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and heterosubstituted PAHs, and halogenated phenols. The average difference between predicted and observed soil sorption coefficients is only 0.2 on the logarithmic scale (corresponding to a factor of 1.5). A comparison of the molecular connectivity model with the empirical models described earlier shows that the former is superior in accuracy, performance, and range of applicability. It is possible to extend this model, with the addition of a single, semiempirical variable, to take care of polar and ionic compounds and to accurately predict the soil sorption coefficients for almost 95% of all organic chemicals whose coefficients have been reported. No empirical or nonempirical models have ever predicted the soil sorption coefficients to such a high degree of accuracy on such a broad selection of structurally diverse compounds. An additional advantage of the molecular connectivity model is that it is sufficient to know the structural formulas to make predictions about soil sorption coefficients.(ABSTRACT TRUNCATED AT 400 WORDS)

Prediction of Soil Sorption Coefficients of Hydrophobic Organic Pollutants by Adsorbability Index

Abstract The adsorbability index proposed by Abe et al. to predict the activated carbon adsorption of organic compounds from aqueous solution was well correlated with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and substituted PAHs, and halogenated phenols. The adsorbability index was also found to be well correlated with the first-order molecular connectivity index and the total molecular surface areas of these compounds.

Use of molecular connectivity indices to estimate soil sorption coefficients for organic chemicals

A correlation model is presented which relates log K oc to molecular connectivity indices (MCI) for a variety of organic compounds. Linear relationships are greatly improved when MCI indices relating to non-dispersive intermolecular interactions are included in the regression model.

On the prediction of soil sorption coefficients of organic pollutants from molecular structure: application of molecular topology model

This study was undertaken to test the ability of the molecular connectivity model to predict the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and substituted PAHs, and halogenated phenols. Tests performed on 31 such compounds clearly demonstrate that this simple nonempirical model accurately predicts the soil sorption coefficients for the above classes of compounds. Moreover, the model out performs the traditional empirical models based on 1-octanol/water partition coefficients or water solubilities in accuracy, speed, and range of applicability. Additional tests on approximately 160 polar and ionic compounds show that the above topological model plus a single semiempirical variable is capable of accounting for the soil sorption properties of nearly 95% of all organic chemicals whose soil sorption coefficients have been measured. The results of these tests demonstrate that the molecular connectivity model is a very accurate predictive tool for the soil sorption coefficients of a wide range of organic chemicals and that it can be confidently used to rank potentially hazardous chemicals and thus to create a priority testing list. 55 references, 5 figures, 7 tables.

Adsorption and desorption of polydimethylsiloxane, PCBS, cadmium nitrate, copper sulfate, nickel sulfate and zinc nitrate by river surface sediments

An investigation into the adsorption and desorption of polydimethylsiloxane, PCBs, cadmium nitrate, copper sulfate, nickel nitrate and zinc nitrate by river sediments was carried out using either a flow-through system or a semi-static system. The material balance in the sediment compartment could be explained by the equation, d C s/d T = K 1 C w − K 2 C s. The adsorption rate constants ( K 1), desorption rate constants ( K 2) and concentration factors ( K 1/ K 2) were calculated. For hydrophobic chemicals, the K 1's were independent of water solubility, but the K 2's were relatively related to water solubility. For both hydrophobic chemicals and heavy metals, the concentration factors per fraction organic carbon were similar to the soil sorption coefficients ( K oc), expressed on a organic carbon basis.

Relationship between molecular connectivity indices and soil sorption coefficients of polycyclic aromatic hydrocarbons.

Relationship between molecular connectivity indices and soil sorption coefficients of polycyclic aromatic hydrocarbons.

Predicted bioconcentration factors and soil sorption coefficients of pesticides and other chemicals

Equations were used to calculate soil sorption coefficients ( K oc) and bioconcentration factors (BCF) for 358 compounds, mostly pesticides, from known water solubility values. Bioconcentration factor (BCF) values were also calculated from K oc values. Comparisons were made between calculated and actual values where possible. The highest experimental BCF values were associated with persistent chemicals having water solubilities below 0.1 ppm. With some exceptions, such as certain ionic compounds, the highest K oc values were also associated with low water solubility. Calculated values for BCF or K oc in excess of 1000 should be experimentally confirmed in order to be certain of their environmental significance. Of the values calculated from water solubility, 10% of the BCF values were over 1000 and 30% of the K oc values were over 1000. BCF and K oc values are simple to calculate from water solubility and are useful for estimation of partitioning in soil, and in animal tissues for contributing to early assessment of potential hazard. Low water solubility is not a good indicator for differentiating between insecticides, fungicides, and herbicides.

Soil Sorption-Desorption Characteristics of Imidacloprid in Croatian Coastal Regions

Sorption and desorption of insecticides are important processes that influence the amount of insecticide retained by the soil and that which is susceptible to runoff or movement in the soil profile. In this study, we examined the sorption and desorption characteristics of imidacloprid [1-(6-chloro-3pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] in ten coastal Croatian soils. In Croatia, imidacloprid is most commonly used in olive growing areas against olive fruit fly. Understanding variabilities in pesticide sorption than can occur among and within the regions can improve imidacloprid applicability. Therefore, the relationship between selected soil properties (particle size, organic carbon content, acidity), imidacloprid concentration and soil sorption coefficients (Kf and Kd) for soils among and within the regions, were analyzed. Additionally, applicability of the pseudo-first-order, pseudo-secondorder, Bangham and intraparticle diffusion kinetic models to predict imidacloprid kinetics of sorption and desorption processes was tested. Adsorption equilibrium data were analyzed by Langmuir, Freundlich and Temkin isotherm equation. The standard batch equilibrium method was used for quatifying imidacloprid in a soil + pesticide solution (1 + 5 by mass) for a wide range of initial concentrations and reaction times (48 h). After sorption of the imidacloprid, five consecutive desorption steps (5 day) were carried out. The aqueous phase was analyzed by HPLC using a UV/VIS detector (270 nm ). All analyses were performed on reverse phase C18 column (150 x 4.6 mm, 5 μm particle size). The mobile phase of acetonitrile + water (1 + 4 by volume) was used under isocratic conditions at a flow rate of 0.8 mLmin-1. Higher sorption was observed in soils with higher organic carbon and clay content. Kf and Kd correlated significantlly with the organic carbon (R2=0.994 ; P<0.01) and clay content (R2=0.987 ; P<0.01), but according to the multiple regression the organic carbon content predominantly influenced imidacloprid sorption. Kd statistically differed among and within the regions. In all soils, a greater sorption occurred at lower concentrations of imidacloprid. According to the calculated KOC value (250 Lkg-1), imidacloprid can be categorized as a medium mobility pesticide. Imidacloprid sorption data described well according to Freundlich (R2=0.96), Langmuir (R2=0.89) and Temkin (R2=0.90) isotherms. Imidacloprid sorption and desorption results were strongly kinetic for all soils. Pseudo-first order kinetic model found to best represent the data for imidacloprid sorption onto soil particle. After the five desorption steps, the percentage of desorbed amount of imidacloprid was decreased with the increase of the initial adsorbed concentration in all tested soils. Desorption data exibited hysteresis phenomena. These results emphasize the importance of sorption-desorption measurements for increasing the accuracy of models that attempt to predict the frequency of groundwater contamination by pesticides and expected pesticide concentrations in the subsurface. Understanding the variability of soil properties and processes as a function of soil profile is necessary for accurate prediction of pesticide dissipation.