Adsorption and desorption characteristics of monosulfuron in Chinese soils

Estimating the bioavailability of acetochlor to wheat using in situ pore water and passive sampling

The intensive use of acetochlor in China leads to its extensive existence in soil which may result in contamination of crops and commodities. Therefore, it is vital to assess the bioavailability and phytotoxicity of acetochlor to crops. In this study, four measurements involved in in situ pore water extraction (C_IPW), passive sampling extraction (C_free), ex situ pore water extraction (C_EPW), and organic solvent extraction (C_soil) were conducted to assess the bioavailability and phytotoxicity of acetochlor to wheat plant plants in five soils. The results showed that the acetochlor concentrations accumulated in wheat foliage and roots were in the range of 0.11-0.87 mg/kg and 0.09-2.02 mg/kg in the five tested soils, respectively, and had a significant correlation with the acetochlor values analyzed by C_IPW (R² = 0.83-0.90, p < 0.0001) or the C_free method (R² = 0.86-0.92, p < 0.0001). The acetochlor concentrations in the five soils measured by these two methods were also correlated with the IC₅₀ values of acetochlor in wheat foliage and roots (R² > 0.69, p ≤ 0.05). The results indicated that the C_IPW and C_free methods were effective in evaluating acetochlor toxicity to wheat and the acetochlor concentrations in wheat. The effects of soil physical and chemical properties including pH, organic matter content (OMC), clay content, and cation exchange capacity (CEC) on the acetochlor toxicity to wheat were analyzed, and soil OMC was found to be the dominant factor affecting the toxicity of acetochlor in the soil-wheat system.

Structural characteristics of sediment humins from South Korean lakes and their phenanthrene binding compared to other carbon sources

Sediment humins are extremely important for binding hydrophobic organic contaminants in rivers and lakes. Nonetheless, little is known about their structure and binding. We, therefore, examined the structure and phenanthrene sorption affinity of sediment humin samples upstream, midstream, and downstream from two artificial lakes in South Korea by using the elemental ¹³C-NMR analysis, Freundlich model, and Langmuir model. The characteristics and phenanthrene sorption affinity of sediment humins were also compared with those of sediment humic acids from similar origins as well as soil humins/humic acids in South Korea from previous studies by using principal component analysis. In both lakes, downstream sediment humins exhibited lower N/C, O/C, and (N + O)/C ratios, lower internal oxidation, and higher aliphaticity due to the presence of long-chain aliphatic compounds generated during anaerobic decomposition. The principal component analysis results also showed that C,H-alkyl, O-alkyl, and polar organic carbon contents were significantly different when comparing the up-mid stream and downstream sediment samples in Daecheong Lake. In addition, midstream sediment humin in Andong Lake presented higher C,H-alkyl and lower polar organic carbon contents compared to those of up-downstream samples. In both lakes, the sorption coefficient and adsorption isotherm linearity were positively correlated with the C,H-alkyl content and negatively correlated with the O-aryl content. Similar to C,H-alkyl and POC, C,H-alkyl, and (N + O)/C had an extremely high correlation coefficient when predicting the sorption coefficient (Freundlich model) and the maximum adsorption capacity (Langmuir model) of sediment humins. Sediment humins had higher C,H-alkyl contents and lower sorption coefficients than those of sediment humic acids and soil humins/humic acids. These findings provide key information for monitoring water quality and polycyclic aromatic hydrocarbon contamination in South Korean lake sediments.

Effect of acid treated HY zeolites in adsorption of mesosulfuron-methyl

PURPOSE

Pollution of surface water and groundwater by bulky molecules such as pesticides has been recognized as a major problem in many countries due to their persistence in aquatic environment and potential adverse health effects. The main purpose of this study is the development of a capable adsorbent to remove these bulky molecules from wastewater such as the pesticide Mesosulfuron-Methyl (MM) by reducing the diffusion path, to overcome the problems of diffusional limitations on microporous adsorbents.

METHODS

The adsorption of mesosulfuron-methyl (MM) from aqueous solution is curried out using treated acid HY zeolite. Batch sorption equilibrium and kinetic experiments are conducted to evaluate the efficiency of these materials. Parent zeolites and their derivatives have been characterized by nitrogen adsorption-desorption, pyridine chemisorption followed by infrared spectroscopy and X-ray fluorescence.

RESULTS

The acid treatment leads to an increase in the specific surface from 691 to 853 m2 g- 1 for HY(30) and from 631 to 806 m2 g- 1 for the HY(16.6) zeolites. It also leads to a reduction in Lewis acidity from 74 to 25 µmol g- 1 and from 135 to 31 µmol g- 1 for HY(30) and HY(16.6) zeolites respectively, and increases the adsorbent-adsorbate interaction. The adsorption capacity increased from 83 to 99 % after acid treatment. The equilibrium adsorption time is decreased from 15 h to 10 min for the HY(30)_A and from 20 h to 20 min for the HY(16.6)_A for an initial concentration of 20 mg L- 1. The adsorption capacity depends on the pH solution, and the neutral form of the MM is more easily adsorbed into zeolite than the dissociated form via the framework bridged oxygen atoms. For all the samples, the pseudo-second-order kinetic model fits very well with the experimental data. In the case of the modified zeolites, the approaching equilibrium factor R w decreases from 0.08183 to 0.00008 when the Lewis acid sites decrease; indicating that the equilibrium is reached more quickly. S-shape adsorption isotherms indicates that cooperative adsorption phenomena. Nevertheless, the shape of acid treated zeolites evolves to an L type indicating a significant enhancement of the adsorbent - adsorbate interactions inducing better adsorption efficiency.

CONCLUSIONS

Mesosulfuron-methyl adsorption has been successfully enhanced after acid treatments of zeolites HY.

Adsorption-desorption and leaching behavior of diuron on selected Kenyan agricultural soils

In this work, the adsorption-desorption dynamics of diuron in three typical Kenyan agricultural soils, Nzoia (NZ), Thika (TH) and Machakos (MK) was investigated. The equilibrium adsorption data, tested against three classical nonlinear adsorption isotherms, was best described by the Freundlich model. The Freundlich adsorption constant, (KF), increased in the order MK > TH > NZ soil. Additionally, the negative Gibb's free energy values indicate the adsorption processes were thermodynamically spontaneous and physical. Multiple linear regression analysis indicated that the adsorption-desorption behavior was controlled by the clay and phosphorus contents of the soil. Phosphorus negatively affected the adsorption of diuron and promoted desorption. The groundwater ubiquity score (GUS) indicated that diuron movement rating in MK soil was 'moderate' while the movement in TH and NZ soils was 'high'.

Sorption and desorption of seven steroidal synthetic progestins in five agricultural soil-water systems

Manure fertilization and wastewater irrigation can introduce the biologically potent synthetic progestins into agricultural soils, causing endocrine disruption in organisms of nearby surface waters. Therefore, this study investigated the sorption and desorption potential of etonogestrel, medroxyprogesterone, gestodene, norgestrel, cyproterone acetate, levonorgestrel, and dienogest in five agricultural soil-water systems. Sorption data were well-described by the linear sorption model. In most batch systems, cyproterone acetate exhibited the highest affinities for soils, followed by etonogestrel, medroxyprogesterone, levonorgestrel, gestodene, norgestrel, and dienogest. The sorption magnitudes (logK_oc or logK_d) were significantly correlated with the progestin hydrophobicities (R² = 0.72-0.86, p < 0.05). The K_d values of the progestins were also significantly correlated with organic carbon content and pore volumes of the soils (R² = 0.68-0.98, p < 0.05). In addition, 0.5 M urea resulted in 3-19% decreases in K_d values of the progestins. Taken together, these data indicated that hydrophobic partitioning interaction, hydrogen bonding interaction, and pore filling were the sorption mechanisms for the progestins in soil-water systems. No significant desorption hysteresis was observed for the progestins, indicating that they can be readily desorbed under rainfall or irrigation events. Based on the sorption and desorption data, we estimated the dynamic transport of the progestins in conventional agricultural management systems, and predicted the concentrations of the progestins as a function of soil-sorbed concentration, water-soil ratio, and dilution factor of receiving waters. This study will improve the understanding of the risks posed by the progestins under field-scale hydrological conditions.

Sorption and leaching of flucetosulfuron in soil

The adsorption-desorption and leaching of flucetosulfuron, a sulfonylurea herbicide, was investigated in three Indian soils. Freundlich adsorption isotherm described the sorption mechanism of herbicide with adsorption coefficients (K_f) ranging from 17.13 to 27.99 and followed the order: Clayey loam > Loam > Sandy loam. The K_f showed positive correlation with organic carbon (OC) (r = 0.910) and clay content (r = 0.746); but, negative correlation with soil pH (r = -0.635). The adsorption isotherms were S-type suggesting that herbicide adsorption was concentration dependent and increased with increase in concentration. Desorption followed the sequence: sandy loam > clayey loam > loam . Hysteresis (H) was observed in all the three soils with H < 1. Leaching of flucetosulfuron correlated positively with the soil pH; but, negatively with the OC content. Sandy loam soil (OC- 0.40%, pH -7.25) registered lowest adsorption and highest leaching of flucetosulfuron while lowest leaching was found in the loam soil (pH - 7.89, OC - 0.65%). The leaching losses of herbicide increased with increase in the rainfall intensity. This study suggested that the soil OC content, pH and clay content played important roles in deciding the adsorption-desorption and leaching behavior of flucetosulfuron in soils.

Adsorption-Desorption Behavior of Polar Imidazolinone Herbicides in Tropical Paddy Fields Soils

Analysis of herbicides sorption behavior in soil is critical in predicting their fate and possible harmful side effects in the environment. Application of polar imidazolinone herbicides is growing in tropical agricultural fields. Imidazolinones have high leaching potential and are persistent. In this study, adsorption-desorption of imazapic and imazapyr herbicides were evaluated in different types of Malaysian agricultural soils. Effects of soil parameters were also investigated on the soils' sorption capacities. The adsorption data fitted best to Freundlich isotherm (R² > 0.991). The herbicides adsorptions were physical and spontaneous processes as ΔG values were negative and below 40 kJ/mol. The adsorption correlated positively with clay content, total organic carbon (TOC) content, and cation exchange capacity (CEC). There were strong negative correlations between hysteresis index and these factors indicating their importance in imidazolinones immobilization and, thus, their pollution reduction in the environment.

National assessment of spatiotemporal loss in agricultural pesticides and related potential exposure risks to water quality in China

Pesticide loss during agricultural development has a serious effect on related water quality, and the critical concern is quantifying the potential exposure risks that pesticide loss pose to water quality at the national scale. In this study, an integrated assessment framework is proposed to scale emission factors from 232 monitoring plots to the national scale, while also considering the physicochemical properties of pesticides in dissolved or adsorbed forms. Based on the results of this study, the total pesticide emissions increased by 29.39% from 146.55 tons in 2004 to 189.62 tons in 2013 and the average loss intensities of insecticides, herbicides and fungicides were 35.25 g/km², 44.24 g/km² and 48.57 g/km², respectively. Central and Southeastern China are identified as hotspots for pesticide loss, while the proportions of high or extremely high-risk areas mainly comprise >50% of farmland. In addition, single-field crops and single-crop rice are the major cropping patterns for pesticide loss in Northern and Southern China. Our results identify key areas for the management of pesticides at the national scale and have direct implications for environmental policies on reducing the potential exposure risk of agricultural pesticides to water quality.

Desorption and mobilization of three strobilurin fungicides in three types of soil

Phenamacril (JS399-19 with independent intellectual property developed by China), azoxystrobin, and kresoxim-methyl are strobilurin fungicide. Due to their broad spectrum and good control of most of known fungi, strobilurin fungicide has been widely used in agriculture management. Thus, it is important to evaluate their environmental behaviors particularly in soils and underground water. In this study, the sorption/desorption and mobility of strobilurin fungicides in three Chinese soils (Jiangxi red soil, Taihu paddy soil, and Northeast China black soil) were conducted using comprehensively analytic approaches including batch experiment and soil thin-layer chromatography. The strobilurin fungicides were hard to be adsorbed in Jiangxi red soil but had medium adsorption capability in Tanhu paddy soil and Northeast China black soil, while the desorption of three strobilurin fungicides ranked in the order of Jiangxi red soil > Taihu paddy soil > Northeast China black soil. Soil properties including soil organic matter (SOM), pH, and cationic exchange capacity (CEC) affected the adsorption/desorption of the fungicides. Azoxystrobin and kresoxim-methyl had weak mobility in the soils. JS399-19 was moderately mobile in Jiangxi red soil but was not easily moved in Taihu paddy soil and Northeast China black soil. Due to their weak mobility in soils, these strobilurin fungicides tended to remain in the soil phase but not to shift downward to underground water. As azoxystrobin and JS399-19 had a long retention period in soil, there may become persistent residues in the soil environment.

Effects of exogenous rare earth elements on phosphorus adsorption and desorption in different types of soils

Phosphorus (P) is an important biogeochemical element and the environmental fate of P receives increasing attention. Through batch equilibration experiments, the adsorption and desorption of P in the absence and presence of exogeneous rare earth elements (REEs) were investigated in five types of agricultural soil samples collected from China. The results showed that the addition of different doses of REEs had influences on P adsorption processes in the soils, and there were differences in different soil types and different P concentrations of the P solutions. The amount of P adsorption tended to decline when the five types of soils were amended with low concentrations of REEs. The characteristics of P adsorption were more complicated when high concentrations of REEs were added to the different soils. Affected by the high concentrations of REEs, when the P concentration of the P solution added to soils was less than 20 mg L(-1), the rate of P adsorption tended to increase in all the five types of soils. However, when the P concentration of the P solution added to soil was greater than 30 mg L(-1), the rate of P adsorption tended to decrease. The Langmuir equation fitted P adsorption in all the five types of soils well. Compared with the control, when soil samples were amended with REEs, the P desorption rates of the five types of soils increased.

Adsorption and biodegradation of antidiabetic pharmaceuticals in soils

Pharmaceuticals are emerging contaminants in the natural environment. Most studies of the environmental fate of these chemicals focus on their behavior in wastewater treatment processes and in sewage sludge. Little is known about their behavior in soils. In this study adsorption and biodegradation of four antidiabetic pharmaceuticals - glimepiride, glibenclamide, gliclazide and metformin - were examined in three natural soils. The sorption of sulfonylurea derivatives was high (higher than sulfonylurea herbicides for example), whereas metformin showed high mobility. Desorption rates were highest for metformin. Sorption isotherms in two of three soils fitted best to the Freundlich model. Despite their high affinity to for soil surfaces, biodegradation studies revealed that transformation of the drugs occurred. Biodegradation results were described by pseudo-first order kinetics with half-life values from 5 to over 120 d (under aerobic conditions) and indicate that none of the tested drugs can be classified as quickly biodegradable. Biodegradation under anoxic conditions was much slower; often degrading by less than 50% during time of the experiment.

Adsorption and desorption of herbicide monosulfuron-ester in Chinese soils

Monosulfuron-ester is a new, low rate, sulfonylurea herbicide that is being promoted for annual broadleaf and gramineal weed control; however, there is a lack of published information on its behavior in soils. The adsorption and desorption of monosulfuron-ester by seven type soils were measured using a batch equilibrium technique. The results showed that the Freundlich equation fitted its adsorption and desorption well, and the Freundlich constant values (K(f-ads)) ranged from 0.88 to 5.66. Adsorption isotherms were nonlinear with 1/n(f-ads) values < 1. Soil pH, organic matter (OM), and clay content were the main factors influencing its adsorption and desorption. Adsorption and desorption were negatively correlated with pH 4.0-8.0 while positively correlated with OM and clay content. The adsorption of monosulfuron-ester was mainly a physical process, because its free energy (deltaG) in seven soils was less than 40 kJ/mol. Monosulfuron-ester adsorption by three soils increased with increasing CaCl2 concentration using CaCl2 as a background electrolyte. Monosulfuron-ester desorption was hysteretic in all tested soils.

Phenanthrene sorption to humic acids, humin, and black carbon in sediments from typical water systems in China

Humic acid (HA) and humin (HM) were extracted with 0.1 M NaOH and black carbon (BC) was isolated using a combustion method at 375 degrees C from six sediments in different areas in China and their sorption isotherms for phenanthrene (Phen) were determined. All sorption isotherms were nonlinear and fitted well with the Freundlich model. Among the SOM, HM and BC with more aromatic carbon controlled the sorption nonlinearity and capacity. Compared to HM, higher K (oc) values were observed for BC due to the combustion of organic matter and native sorbates in HM. For HAs isotherms, a positive relation was observed between the K (oc) values and aliphaticity or H/C ratios, but a negative relation was shown between the n values and polarity of HAs. HA, HM, and BC were responsible for 0.4-9.3%, 46-97%, and 65-96% of the total sorption, respectively, indicating the dominance of HM and BC fractions in overall sorption of Phen by the sediments.

Adsorption and desorption behavior of herbicide diuron on various Chinese cultivated soils

The adsorption-desorption behaviors of diuron were investigated in six cultivated soils of China. The effect of system pH and temperature were also studied. The data fitted the Freundlich equation very well. The adsorption K(F) values indicated the adsorption of diuron in the six soils was in the sequence of black soil (D)>yellow earth (F)>paddy soil (B)>yellow-brown soil (C)>yellow-cinnamon soil (A)>lateritic red earth (E). The adsorption K(F) and Freundlich exponents n were decreased when temperature was increased from 298 K to 318 K. However, the Gibb's free energy values were found less negative with the increasing temperature. Meanwhile, the extent of diuron adsorption on soil was at rather high level under low pH value conditions and decreased with increasing pH value. In addition, the desorption behavior of diuron in the six soils was in the sequence of lateritic red earth (E)>yellow-cinnamon soil (A)>paddy soil (B)>yellow earth (F)>yellow-brown soil (C)>black soil (D). At the same time, desorption hysteresis of diuron were observed in all of the tested soils. And the soil organic matter content may play an important role in the adsorption-desorption behavior.