Dissipation of terbuthylazine,metolachlor, and mesotrione in soils with contrasting texture

ABSTRACT

This study evaluates the dissipation of terbuthylazine, metolachlor, and mesotrione at different depths in soils with contrasting texture. The field trial was conducted at the Padua University Experimental Farm, north-east Italy. The persistence of three herbicides was studied in three different soil textures (clay soil, sandy soil, and loamy soil) at two depths (0–5 and 5–15 cm). Soil organic carbon content was highest in the clay (1.10%) followed by loam (0.67%) and sandy soil (0.24%); the pH of soils was sub-alkaline. Terbuthylazine, metolachlor, and mesotrione were applied on maize as a formulated product (Lumax®) at a dose of 3.5 L ha^?1. Their dissipation in the treated plots was followed for 2 months after application. The concentrations of herbicides were analyzed by liquid chromatography-mass spectrometry. The dissipation of terbuthylazine, metolachlor, and mesotrione could be described by a pseudo first-order kinetics. Terbuthylazine showed the highest DT50, followed by metolachlor and mesotrione. Considering the tested soil, the highest DT50 value was found in clay soil for terbuthylazine and metolachlor, whereas for mesotrione there was no difference among soils. Significant differences were found between the two soil depths for terbuthylazine and metolachlor, whereas none were found for mesotrione. These results suggest that soil texture and depth have a strong influence on the dissipation of terbuthylazine and metolachlor, whereas no influence was observed on mesotrione because of its chemical and physical properties.     

Movement of metolachlor and terbuthylazine in core and packed soil columns

Movement of metolachlor and terbuthylazine including a bromide tracer was studied in core and packed soil columns in PVC pipes (80 mm diameter, 15 mm depth) with two German soil types viz: silt loam and loamy silt. The breakthrough curves (BTCs) for bromide indicated some preferential flow of water both under conventional tillage (CN) and no-till (NT) simulation with silt loam soil. The herbicides leached to a greater extent in NT columns than in CN columns. Leaching was higher in loamy silt soil than in silt loam soil under CN conditions. This result is in agreement with the higher sorption capacity of silt loam having higher organic carbon compared to loamy silt having low organic carbon. Adsorption strength of the herbicides did not affect their breakthrough time, but was reflected in the slope and maximum height of the BTCs. The BTCs showed the expected inverse relationship between leaching and adsorption with greater mobility of the weakly-sorbed metolachlor than the more strongly sorbed terbuthylazine. Maximum amounts of the applied herbicides were recovered from the top soil layer in intact columns. Metolachlor was more mobile in packed columns than in core columns.     

Sorption of metolachlor and atrazine in fly ash amended soils: comparison of optimized isotherm models

Adsorption of metolachlor and atrazine was studied in the fly ash (Inderprastha and Badarpur)- amended Inceptisol and Alfisol soils using batch method. Results indicated that sorption of both the herbicides in soil+fly ash mixtures was highly nonlinear and sorption decreased with a higher herbicide concentration in the solution. Also, nonlinearity increased with an increase in the level of fly ash amendment from 0-5%. Three two-parameter monolayer isotherms viz. Langmuir, Temkin, Jovanovic and one imperical Freundlich models were used to fit the experimental data. Data analysis and comparison revealed that the Temkin and the Freundlich isotherms were best-suited to explain the sorption results and the observed and the calculated adsorption coefficient values showed less variability. The study suggested that sorption mechanism of metolachlor and atrazine involved the physical association at the sorbate surface and the nonlinearity in the sorption at higher pesticide or fly ash concentration was due to a decrease in the heat of adsorption and higher binding energy.     

Sorption behavior of a new acidic herbicide in soils

The sorptive behavior of the experimental herbicide quinmerac (7-chloro-3-methyl-quinoline-8-carboxylic acid) was investigated in soils of different organic carbon content. Distribution coefficients are low (K_d = 0.03 - 12 mL g⁻¹) and are mainly determined by the soil organic carbon content. The adsorption mechanism operating in neutral to slightly acid agricultural soils is supposed to be cation bridging with the anionic form of quinmerac. Under acid conditions (pH 5.2) the predominating sorption mechanism is hydrophobic interaction. Therefore soil pH and cationic composition are also major factors determining the sorptive capacity of soils for quinmerac.

Adsorption kinetics, equilibrium adsorption and desorption isotherms were determined in batch experiments. Sorption kinetics were investigated at various times from 15 min to 96 hours. A two-step sorption behavior with time was found for the anionic form indicating two types of sorption mechanisms or sorption sites. Equilibrium for the first type was reached at a time-scale of minutes and for the second type after 24 hours. Adsorption isotherms were determined for two soil/solution ratios 1/5 and 1/3. Alteration of the adsorbent concentration exerted a strong influence on the adsorption isotherms. An increase of sorption was found with increasing adsorbent concentration. Under natural soil conditions sorption is therefore expected to be higher compared to the batch experiments. Desorption isotherms were obtained using the consecutive desorption method. Desorption hysteresis was not observed which indicates weak interactions. Implications of the results for the movement of quinmerac under field conditions and for models describing transport are discussed.     

Sorption of atrazine and metolachlor by burrow linings developed in soils with different crop residues at the surface

Atrazine and metolachlor sorption by earthworm (Lumbricus terrestris L.) burrows was measured by introducing herbicides into the burrows and collecting the effluent between 0 to 3, 3 to 6, and 6 to 9 min of simulated burrow flow. On average, sorption by burrow linings reduced the herbicide concentration to 78% (atrazine) and 74% (metolachlor) of the applied herbicide solution concentration. For both herbicides, the amount sorbed was dependent on the food source available to the earthworm, as well as the duration of burrow flow. On average, soybean-fed- and corn-fed-earthworm-burrows significantly retained more herbicides relative to the Control Treatment (unfed-earthworms). More herbicides were transported through the burrows with time because the lateral flow movement from the burrow wall into the soil matrix decreased. It is also likely that herbicides retained on burrow linings during the first 3 min of flow saturated the adsorption sites on the burrow wall, which decreased the subsequent retention potential of herbicides in flow between 3 to 9 min. Based on these results, we conclude that herbicide transport through earthworm burrows in the field will be related to crop and crop residue management practices.     

Sorption of atrazine and metolachlor by earthworm surface castings and soil

Abstract

Atrazine and metolachlor were more strongly retained on earthworm (Lumbricus terrestris L.) castings than on soil, suggesting that earthworm castings at the surface or at depth can reduce herbicide movement in soil. Herbicide sorption by castings was related to the food source available to the earthworms. Both atrazine and metolachlor sorption increased with increasing organic carbon (C) content in castings, and Freundlich constants (K_f values) generally decreased in the order: soybean‐fed > corn‐fed > not‐fed‐earthworm‐castings. The amount of atrazine or metolachlor sorbed per unit organic carbon (K_oc values) was significantly greater for corn‐castings compared with other castings, or soil, suggesting that the composition of organic matter in castings is also an important factor in determining the retention of herbicides in soils. Herbicide desorption was dependent on both the initial herbicide concentration, and the type of absorbent. At small equilibrium herbicide concentrations, atrazine desorption was significantly greater from soil than from any of the three casting treatments. At large equilibrium herbicide concentrations, however, the greater organic C content in castings had no significant effect on atrazine desorption, relative to soil. For metolachlor, regardless of the equilibrium herbicide concentration, desorption from soybean‐ and corn‐castings treatments was always less than desorption from soil and not‐fed earthworm castings treatments. The results of this study indicate that, under field conditions, the extent of herbicide retention on earthworm castings will tend to be related to crop and crop residue management practices.     

Sorption of atrazine and metolachlor by earthworm surface castings and soil

Atrazine and metolachlor were more strongly retained on earthworm (Lumbricus terrestris L.) castings than on soil, suggesting that earthworm castings at the surface or at depth can reduce herbicide movement in soil. Herbicide sorption by castings was related to the food source available to the earthworms. Both atrazine and metolachlor sorption increased with increasing organic carbon (C) content in castings, and Freundlich constants (Kf values) generally decreased in the order: soybean-fed > corn-fed > not-fed-earthworm-castings. The amount of atrazine or metolachlor sorbed per unit organic carbon (Koc values) was significantly greater for corn-castings compared with other castings, or soil, suggesting that the composition of organic matter in castings is also an important factor in determining the retention of herbicides in soils. Herbicide desorption was dependent on both the initial herbicide concentration, and the type of absorbent. At small equilibrium herbicide concentrations, atrazine desorption was significantly greater from soil than from any of the three casting treatments. At large equilibrium herbicide concentrations, however, the greater organic C content in castings had no significant effect on atrazine desorption, relative to soil. For metolachlor, regardless of the equilibrium herbicide concentration, desorption from soybean- and corn-castings treatments was always less than desorption from soil and not-fed earthworm castings treatments. The results of this study indicate that, under field conditions, the extent of herbicide retention on earthworm castings will tend to be related to crop and crop residue management practices.     

Effect of charcoal amendment on adsorption, leaching and degradation of isoproturon in soils

The effects of charcoal amendment on adsorption, leaching and degradation of the herbicide isoproturon in soils were studied under laboratory conditions. The adsorption data all fitted well with the Freundlich empirical equation. It was found that the adsorption of isoproturon in soils increased with the rate of charcoal amended (correlation coefficient r=0.957**, P<0.01). The amount of isoproturon in leachate decreased with the increase of the amount of charcoal addition to soil column, while the retention of isoproturon in soils increased with an increase in the charcoal content of soil samples. Biodegradation was still the most significant mechanism for isoproturon dissipation from soil. Charcoal amendment greatly reduced the biodegradation of isoproturon in soils. The half-lives of isoproturon degradation (DT(50)) in soils greatly extended when the rate of added charcoal increased from 0 to 50 g kg(-1) (for Paddy soil, DT(50) values increased from 54.6 to 71.4 days; for Alfisol, DT(50) from 16.0 to 136 days; and for Vertisol, DT(50) from 15.2 to 107 days). The degradation rate of isoproturon in soils was significantly negatively correlated with the amount of added charcoal. This research suggests that charcoal amendment may be an effective management practice for reducing pesticide leaching and enhancing its persistence in soils.     

Sorption behaviour of acetochlor,atrazine, carbendazim,diazinon, imidacloprid and isoproturon on Hungarian agricultural soil

Laboratory studies were conducted to determine the sorption behaviour of six commonly used pesticides (acetochlor, atrazine, carbendazim, diazinon, imidacloprid and isoproturon) on Hungarian brown forest soil with clay alluviation (Luvisol) using the batch equilibrium technique. The sorption isotherms could be described by the Freundlich equation in non-linear form (n < 1) for all compounds, however in case of diazinon using the extended Freundlich equation proved to be a better approach. The adsorption constant related soil organic carbon content (Koc) calculated from Freundlich equation were 314 for acetochlor, 133 for atrazine, 2805 for carbendazim, 1589 for diazinon, 210 for imidacloprid and 174 for isoproturon. The octanol-water partition coefficients (Pow), which can be a useful parameter to predict of adsorption behaviour of a chemical on soil, and dissociation coefficients of these pesticides were calculated based on the chemical structure of them using a computerized expert system. The octanol-water partition coefficients were determined experimentally from high performance liquid chromatographic parameters as well. Good agreement was observed between experimental and the computer expert system estimated data. Computer estimated log Pow values ranged 0.5 and 3.86 for the examined pesticides, with imidacloprid and diazinon being the least and most hydrophobic respectively. Experimentally determined logPow ranged between 0.92 and 3.81 with the same tendency. It can be concluded that the Freundlich adsorption constants (Kf) are slightly related to the octanol-water partition coefficients of investigated chemicals, nevertheless no close correlation could be established because of the influence of further characteristics of solutes and soil.     

Intrinsic and induced isoproturon catabolic activity in dissimilar soils and soils under dissimilar land use

The catabolic activity with respect to the systemic herbicide isoproturon was determined in soil samples by (14)C-radiorespirometry. The first experiment assessed levels of intrinsic catabolic activity in soil samples that represented three dissimilar soil series under arable cultivation. Results showed average extents of isoproturon mineralisation (after 240 h assay time) in the three soil series to be low. A second experiment assessed the impact of addition of isoproturon (0.05 microg kg(-1)) into these soils on the levels of catabolic activity following 28 days of incubation. Increased catabolic activity was observed in all three soils. A third experiment assessed levels of intrinsic catabolic activity in soil samples representing a single soil series managed under either conventional agricultural practice (including the use of isoproturon) or organic farming practice (with no use of isoproturon). Results showed higher (and more consistent) levels of isoproturon mineralisation in the soil samples collected from conventional land use. The final experiment assessed the impact of isoproturon addition on the levels of inducible catabolic activity in these soils. The results showed no significant difference in the case of the conventional farm soil samples while the induction of catabolic activity in the organic farm soil samples was significant.     

Analytical methods for the determination of alachlor, metolachlor, simazine and atrazine mobility in soils

A method for the determination of the mobility of the herbicides, alachlor, metolachlor, simazine and atrazine in soil is described. The method is based on the use of soil thin-layer chromatography (TLC) and does not require the use of radiolabelled compounds. Soil on the TLC plate after development was separated into various bands, the material in each band was extracted with solvents and analyzed by gas chromatography.     

Analytical methods for the determination of alachlor,metolachlor, simazine and atrazine mobility in soils

Abstract

A method for the determination of the mobility of the herbicides, alachlor, metolachlor, simazine and atrazine in soil is described . The method is based on the use of soil thin‐layer chromatography (TLC) and does not require the use of radiolabelled compounds. Soil on the TLC plate after development was separated into various bands, the material in each band was extracted with solvents and analyzed by gas chromatography.     

Sorption and desorption of sulfentrazone in Brazilian soils

This study was undertaken to obtain information about the behavior of sulfentrazone in soil by evaluating the sorption and desorption of the herbicide in different Brazilian soils. Batch equilibrium method was used and the samples were analyzed by high performance liquid chromatography. Based on the results obtained from the values of Freundlich constants (Kf), we determined the order of sorption (Haplic Planosol < Red-Yellow Latosol < Red Argisol < Humic Cambisol < Regolitic Neosol) and desorption (Regolitic Neosol < Red Argisol < Humic Cambisol < Haplic Planosol < Red-Yellow Latosol) of sulfentrazone in the soils. The process of pesticide sorption in soils was dependent on the levels of organic matter and clay, while desorption was influenced by the organic matter content and soil pH. Thus, the use of sulfentrazone in soils with low clay content and organic matter (low sorption) increases the probability of contaminating future crops.     

Sorption of thiamethoxam in three Indian soils

The sorption behavior of the insecticide thiamethoxam [3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine] on three Indian soils with different physico-chemical properties was investigated. The soils represent the major grapevine growing areas of India, where the vineyards frequently receive thiamethoxam applications as foliar spray, soil drenching and through drip irrigation for the management of various insect pests. The rate constants for adsorption and desorption at two different temperatures were obtained from the Lindstrom model, which simultaneously evaluated adsorption and desorption kinetics. The data for rate constants, activation energies, enthalpy of activation, entropy of activation and free energy indicated physical adsorption of thiamethoxam on soil. The adsorptivity of different soils might be attributed to the organic matter and clay contents. A good fit to the linear and Freundlich isotherms was observed for both adsorption as well as desorption. Thiamethoxam could be categorized as a chemical with medium leaching potential.     

Effect of drying on the desorption of diuron and terbuthylazine from natural soils

This work was initiated to study the effects of climate induced soil water status variations which can reach extreme values under natural conditions on the sorption process of hydrophobic organic compounds. Based on the classical slurry batch methodology an approach is developed that allows the fast and careful complete drying of soil suspensions (microwave technique). Classical adsorption experiments were followed by three desorption steps with and without drying cycles. Drying and re-wetting enhanced the sorption-desorption hysteresis and Freundlich adsorption coefficients increased from 5.9 to 16 and 5.2 to 21 over three drying cycles for diuron and terbuthylazine respectively. Assuming the validity of a dual stage adsorption process, model evaluation suggests that drying is as a shrinking-like process leading to conformational changes of the dominant sorbent (soil organic matter) which restrict the intra-micro-particle diffusion. Rewetting only leads to a partial recovery of the diffusional pore space.     

Sorption and degradation of neonicotinoid insecticides in tropical soils

ABSTRACT

Neonicotinoids are the most widely applied class of insecticides in cocoa farming in Ghana. Despite the intensive application of these insecticides, knowledge of their fate in the Ghanaian and sub-Saharan African environment remains low. This study examined the behavior of neonicotinoids in soils from cocoa plantations in Ghana by estimating their sorption and degradation using established kinetic models and isotherms. Studies of sorption were conducted using the batch equilibrium method on imidacloprid, thiamethoxam, clothianidin, acetamiprid and thiacloprid, while degradation of imidacloprid, thiamethoxam and their respective deuterated counterparts was studied using models proposed by the European forum for coordination of pesticide fate and their use (FOCUS). Analytes were extracted using the quick, easy, cheap, effective, rugged and safe (QuEChERS) procedure and quantified by liquid chromatography-tandem mass spectrometry (LC–MS/MS). Average recoveries were high (≥ 85%) for all analytes. The findings from the study suggest that neonicotinoid insecticides may be persistent in the soils studied based on estimated half-lives > 150 days. The study also revealed generally low-sorption coefficients for neonicotinoids in soils, largely influenced by soil organic carbon.     

Sorption and predicted mobility of herbicides in Baltic soils

This study was undertaken to determine sorption coefficients of eight herbicides (alachlor, amitrole, atrazine, simazine, dicamba, imazamox, imazethapyr, and pendimethalin) to seven agricultural soils from sites throughout Lithuania. The measured sorption coefficients were used to predict the susceptibility of these herbicides to leach to groundwater. Soil-water partitioning coefficients were measured in batch equilibrium studies using radiolabeled herbicides. In most soils, sorption followed the general trend pendimethalin > alachlor > atrazine approximately amitrole approximately simazine > imazethapyr > imazamox > dicamba, consistent with the trends in hydrophobicity (log K(ow)) except in the case of amitrole. For several herbicides, sorption coefficients and calculated retardation factors were lowest (predicted to be most susceptible to leaching) in a soil of intermediate organic carbon content and sand content. Calculated herbicide retardation factors were high for soils with high organic carbon contents. Estimated leaching times under saturated conditions, assuming no herbicide degradation and no preferential water flow, were more strongly affected by soil textural effects on predicted water flow than by herbicide sorption effects. All herbicides were predicted to be slowest to leach in soils with high clay and low sand contents, and fastest to leach in soils with high sand content and low organic matter content. Herbicide management is important to the continued increase in agricultural production and profitability in the Baltic region, and these results will be useful in identifying critical areas requiring improved management practices to reduce water contamination by pesticides.     

Sorption of sulfadiazine on Brazilian soils

Antimicrobials, among them sulfonamides are widely used in veterinary medicine and can contaminate the environment. The degree to which antimicrobials adsorb onto soil particles varies widely, as does the mobility of these drugs. Sulfadiazine (SDZ) was used to study the adsorption–desorption in Brazilian soil–water systems, using batch equilibrium experiments. Sorption of SDZ was carried out using four types of soils. Adsorption and desorption data were well fitted with Freundlich isotherms in log form (r > 0.999) and (0.984 < r < 0.999), respectively. An adsorption–desorption hysteresis phenomenon was apparent in all soils ranging from 0.517 to 0.827. The experimental results indicate that the Freundlich sorption coefficient (K_F) values for SDZ ranged from 0.45 to 2.6 μg^1?1/n (cm³)^1/n g^?1.     

Sorption and predicted mobility of herbicides in Baltic soils

This study was undertaken to determine sorption coefficients of eight herbicides (alachlor, amitrole, atrazine, simazine, dicamba, imazamox, imazethapyr, and pendimethalin) to seven agricultural soils from sites throughout Lithuania. The measured sorption coefficients were used to predict the susceptibility of these herbicides to leach to groundwater. Soil-water partitioning coefficients were measured in batch equilibrium studies using radiolabeled herbicides. In most soils, sorption followed the general trend pendimethalin > alachlor > atrazine～ amitrole～ simazine > imazethapyr > imazamox > dicamba, consistent with the trends in hydrophobicity (log K_ow) except in the case of amitrole. For several herbicides, sorption coefficients and calculated retardation factors were lowest (predicted to be most susceptible to leaching) in a soil of intermediate organic carbon content and sand content. Calculated herbicide retardation factors were high for soils with high organic carbon contents. Estimated leaching times under saturated conditions, assuming no herbicide degradation and no preferential water flow, were more strongly affected by soil textural effects on predicted water flow than by herbicide sorption effects. All herbicides were predicted to be slowest to leach in soils with high clay and low sand contents, and fastest to leach in soils with high sand content and low organic matter content. Herbicide management is important to the continued increase in agricultural production and profitability in the Baltic region, and these results will be useful in identifying critical areas requiring improved management practices to reduce water contamination by pesticides.     

Sorption and desorption of three endocrine disrupters in soils

Sorption of the estrogens estrone (E1), 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) on four soils was examined using batch equilibrium experiments with initial estrogen concentrations ranging from 10 to 1000 ng mL-1. At all concentrations, >85% of the three estrogens sorbed rapidly to a sandy soil. E1 sorbed more strongly to soil than E2 or EE2. Partial oxidation of E2 to E1 was observed in the presence of soils. Autoclaving was more effective at reducing this conversion than inhibition with sodium azide or mercuric chloride, and had little effect on sorption, relative to the chemical microbial inhibitors. Sorption of EE2 was greater for fine-textured than coarse-textured soils, but greater than 90% of EE2 sorbed onto all four soils. The greatest degree of desorption of estrogens from the sandy soil occurred with the lowest initial concentration of 10 ng mL-1 and reached levels >or=80% for E1 and E2. Desorption of EE2 was greater in coarser textured soils than finer-textured soils. Again, relative desorption from all soils was greatest with low initial concentrations. Therefore, at environmentally relevant concentrations, estrogens quickly sorb to soils, and soils have a large capacity to bind estrogens, but these endocrine-disrupting compounds can become easily desorbed and released into the aqueous phase.