Freundlich Sorption Coefficient Research Articles

Raw feedstock vs. biochar from olive stone: Impact on the sorption–desorption of diclosulam and tropical soil improvement

The addition of carbon-rich materials, such as raw feedstocks (RAW) and biochars, to agricultural soils is on the rise. This activity has many advantages, such as improving fertility, increasing water retention, and sequestering carbon. However, they can also increase the sorption of residual herbicides in the soil, reducing the effectiveness of weed control. Thus, the objective of this study was to evaluate soil improvement and the sorption–desorption process of diclosulam in soil unamended and amended with RAW from olive stone and their biochars produced in two pyrolysis temperatures (300 and 500 °C). Oxisol was used in this study, unamended and amended with RAW and biochars (BC300 and BC500) in a rate of 10% (w w−1). The sorption–desorption process was assessed by batch-equilibrium experiments and the analysis was performed using high-performance liquid chromatography (HPLC). The addition of the three materials to the soil increased the contents of pH, organic carbon, P, K, Ca, Mg, Zn, Fe, Mn, Cu, B, cation exchange capacity, base saturation and decreased H + Al. The unamended soil had Kf (Freundlich sorption coefficient) values of diclosulam sorption and desorption of 1.56 and 12.93 mg(1 − 1/n) L1/n Kg−1, respectively. Unamended soil sorbed 30.60% and desorbed 13.40% of herbicide. Soil amended with RAW, BC300, and BC500 sorbed 31.92, 49.88, and 30.93% of diclosulam and desorbed 13.33, 11.67, and 11.16%, respectively. The addition of RAW and biochars from olive stone has the potential to change the soil fertility, but does not interfere with the bioavailability of diclosulam in weed control under field conditions, since the materials slightly influenced or did not alter the sorption–desorption of diclosulam.

Sorption, leaching, and degradation of dicamba in two Brazilian soils: A study into soil layers

Understanding the behavior in soil of soluble and mobile herbicides, such as dicamba, is essential for efficient weed management. Thus, the objective of the research was to understand the sorption, leaching and degradation processes of dicamba along the profile of two Brazilian soils (Oxisol and Ultisol). The Oxisol collected is a very deep soil, the A horizon was collected in a layer of 0.10 m deep, the B horizon 2.0 m and the C horizon ranging from 5.0 to 6.0 m. In contrast, the Ultisol presents a difference between the most superficial horizons, the A horizon was collected at a depth of 0.10 m, the B horizon at around 1.0 m depth and the C horizon at a depth of 2.0–3.0 m. A High-Performance Liquid Chromatography (HPLC) was used to determine the herbicide in the soil solution. The Freundlich sorption coefficient (Kf) values of dicamba ranged from 0.53 to 0.88 mg (1-1/n) L1/n kg−1 in Oxisol and 0.25–0.69 mg (1-1/n) L1/n kg−1 in Ultisol, indicating a low sorption capacity of the herbicide in all profiles. The dicamba mobility index was higher in the Ultisol, ranging from 4.22 to 65.8 compared to the Oxisol, which ranged from 0.46 to 8.10. The degradation half-life time (DT50) of dicamba was short (∼4 days) in the A horizon of both soils compared to the other horizons. Moreover, persistence in the B and C horizons was higher in Oxisol (182 and > 250 days) compared to Ultisol (85.6 and 52.1 days, respectively). The sorption and mobility index of dicamba showed a correlation with soil pH and DT50 values, depending on the organic matter (OM) content. The recommendation of use of dicamba should consider the physical and chemical attributes of the soil as an alternative to reduce the risk of environmental contamination.

Sorption of representative organic contaminants on microplastics: Effects of chemical physicochemical properties, particle size, and biofilm presence

Microplastic pollution has attracted mounting concerns worldwide. Microplastics may concentrate organic and metallic contaminants; thus, affecting their transport, fate and organismal exposure. To better understand organic contaminant-microplastic interactions, our study explored the sorption of selected polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), α-hexabromocyclododecane (α-HBCDD), and organophosphate flame retardants (OPFRs) on high-density polyethylene (HDPE) and polyvinylchloride (PVC) microplastics under saline conditions. Sorption isotherms determined varied between chemicals and between HDPE and PVC microplastics. Log Freundlich sorption coefficients (Log KF) for the targeted chemicals ranged from 2.01 to 5.27 L kg-1 for HDPE, but were significantly lower for PVC, i.e., ranging from Log KF data (2.84 – 8.58 L kg-1). Significant correlations between chemicals’ Log KF and Log Kow (octanol-water partition coefficient) indicate that chemical-dependent sorption was largely influenced by their hydrophobicity. Sorption was evaluated using three size classes (< 53, 53 – 300, and 300 – 1000 µm) of lab-fragmented microplastics. Particle size did not significantly affect sorption isotherms, but influenced the time to reach equilibrium and the predicted maximum sorption, likely related to microplastic surface areas. The presence of biofilms on HDPE particles significantly enhanced contaminant sorption capacity, indicating more complex sorption dynamics in the chemical-biofilm-microplastic system. Our findings offer new insights into the chemical-microplastic interactions in marine environment.

Assessment of potential mobility of selected micropollutants in agricultural soils of the Czech Republic using their sorption predicted from soil properties

The sorption of organic contaminants in soils and sediment is a crucial factor affecting their mobility in the vadose zone environment. The Freundlich sorption isotherms were evaluated for eleven micropollutants and eight soils. The highest Freundlich sorption coefficients, KF, were obtained for triclosan (324 ± 153 cm3/nμg1–1/ng−1) followed by sertraline (120 ± 74), venlafaxine (74.3 ± 41.2), telmisartan (33.3 ± 13.6), atorvastatin (8.66 ± 4.78), bisphenol S (8.03 ± 4.87), lamotrigine (6.92 ± 3.02), 2-phenylbenzimidazole-5-sulfonic acid (3.77 ± 2.25), memantine (3.42 ± 1.64), 1-methyl-1H-benzotriazole (2.05 ± 0.99), and valsartan (0.88 ± 0.89). The KF values for the individual compounds were correlated with soil properties. Multiple linear regressions were used to derive equations for predicting the KF values using the soil properties. The first set of equations contained mainly properties with the strongest correlations with the KF values, e.g., a base cation saturation for positively charged compounds or a hydrolytic acidity for negatively charged compounds. The second set of equations contained properties included in the map of agricultural soils of the Czech Republic. These equations always indicated positive correlations with oxidizable organic carbon and clay content. They also included either a negative or positive correlation with pHKCl. A positive correlation with pHKCl was obtained for venlafaxine, memantine, and sertraline, which were mostly positively charged. A negative correlation with pHKCl was obtained for the remaining compounds. The second set of equations, the soil map, and the database of soil properties were used to predict the KF value distributions within the Czech agricultural soils. It resulted in similar KF distributions' patterns for valsartan, lamotrigine, atorvastatin, and telmisartan (with a positive correlation between KF and hydrolytic acidity), which considerably differed from the KF patterns for the other compounds. These maps were used to delineate areas with a leaching potential of the compounds toward groundwater that will serve as a tool for assessing a potential groundwater vulnerability.

Phosphorous Sorption Characteristics of Soils in Smallholding Land Use in Southern Ethiopia

Purpose. This study evaluated the P sorption characteristics of soils under smallholding land use in Wolaita Zone, Southern Ethiopia. Methods. Soil samples (0–20 cm) were collected from each of the home garden, grazing land, cropland, and woodlot in three replications at two sites and analyzed for P sorption isotherm data and selected soil properties. Results. The P sorption data were generated by equilibration with P solutions and the data were fitted with the Freundlich model (r2 = 0.88–0.98, SE = 0.16–0.24) and Langmuir model (r2 = 0.81–0.98, SE = 0.45–1.71). The Langmuir P sorption maximum (Qmax) and Freundlich sorption coefficient (Kf) were the highest in the cropland soils while these parameters were the lowest in the home garden. Maximum buffering capacity (MBC) was in the order cropland &gt; woodlot &gt; home garden &gt; grazing land, but Freundlich P buffering capacity (PBC) followed the order cropland &gt; grazing land &gt; home garden &gt; woodlot. Langmuir bonding energy (bL) and Freundlich phosphate sorption affinity (1/n) were in the order of home garden &gt; woodlot &gt; grazing land &gt; cropland. The Qmax was positively correlated (p &lt; 0.05) with clay, Kf, PBC, the oxalate and dithionates extractable Al, Fe, and Mn, but it negatively correlated (p &lt; 0.05) with soil pH, SOC, AP and bL. Conclusion. Generally, the effect of P sorption of the smallholding home garden was slightly different from eucalyptus woodlot and grazing lands but considerably different from cropland. The high P sorption capacity in cropland was attributed to the high amorphous and crystalline Fe/Al oxides/hydroxides, low SOC, and low soil pH. Hence, combinations of P managements are required for increasing P availability in the smallholding land uses.

Assessment of Mobilization Potential of Per- and Polyfluoroalkyl Substances for Soil Remediation

This study investigated the mobilization of a wide range of per- and polyfluoroalkyl substances (PFASs) present in aqueous film-forming foams (AFFFs) in water-saturated soils through one-dimensional (1-D) column experiments with a view to assessing the feasibility of their remediation by soil desorption and washing. Results indicated that sorption/desorption of most of the shorter-carbon-chain PFASs (C ≤ 6) in soil reached greater than 99% rapidly─after approximately two pore volumes (PVs) and were well predicted by an equilibrium transport model, indicating that they will be readily removed by soil washing technologies. In contrast, the equilibrium model failed to predict the mobilization of longer-chain PFASs (C ≥ 7), indicating the presence of nonequilibrium sorption/desorption (confirmed by a flow interruption experiment). The actual time taken to attain 99% sorption/desorption was up to 5 times longer than predicted by the equilibrium model (e.g., ∼62 PVs versus ∼12 PVs predicted for perfluorooctane sulfonate (PFOS) in loamy sand). The increasing contribution of hydrophobic interactions over the electrostatic interactions is suggested as the main driving factor of the nonequilibrium processes. The inverse linear relationship (R2 = 0.6, p < 0.0001) between the nonequilibrium mass transfer rate coefficient and the Freundlich sorption coefficient could potentially be a useful means for preliminary evaluation of potential nonequilibrium sorption/desorption of PFASs in soils.

Adsorption and degradation behavior of six herbicides in different agricultural soils

This study focuses on the assessment of herbicide adsorption and degradation in three soils (Haplic Chernozem, Haplic Fluvisol, and Arenic Regozem) from different agricultural regions of the Czech Republic where sunflower is cultivated. Soil samples were used in laboratory batch adsorption and degradation experiments for six herbicides commonly used on sunflower crops. The findings are used to examine the effect of soil and herbicide properties on adsorption and degradation, as well as to determine the possible relationship between the two processes. The (Kf) sorption coefficient ranged from 1.07 to 135.37 cm3/nμg1−1/ng−1, and sorption increased in the following order: dimethenamid-p < pethoxamid < S-metolachlor < flurochloridone < aclonifen < pendimethalin. Adsorption of all six herbicides was positively correlated with soil organic matter content (p < 0.001), and cation exchange capacity (p < 0.001). pH was negatively correlated with the adsorption of all six compounds (p < 0.001). Degradation rates of herbicides ranged from 0. 012 to 0. 048 day−1, which corresponding to the half-lives (DT50) between 14 and 57 days, respectively. The highest half-life values were found in Haplic Fluvisol (a loam with higher organic matter content and lower pH). Results showed that both adsorption and degradation of herbicides are mainly controlled by soil organic matter. A negative relationship was found between the sorption coefficient and the rate of degradation. It can be concluded that the Freundlich sorption coefficient (Kf) can be a good predictor for the degradation of the studied herbicides.

How microbial community composition, sorption and simultaneous application of six pharmaceuticals affect their dissipation in soils

Pharmaceuticals may enter soils due to the application of treated wastewater or biosolids. Their leakage from soils towards the groundwater, and their uptake by plants is largely controlled by sorption and degradation of those compounds in soils. Standard laboratory batch degradation and sorption experiments were performed using soil samples obtained from the top horizons of seven different soil types and 6 pharmaceuticals (carbamazepine, irbesartan, fexofenadine, clindamycin and sulfamethoxazole), which were applied either as single-solute solutions or as mixtures (not for sorption). The highest dissipation half-lives were observed for citalopram (average DT50,S for a single compound of 152 ± 53.5 days) followed by carbamazepine (106.0 ± 17.5 days), irbesartan (24.4 ± 3.5 days), fexofenadine (23.5 ± 20.9 days), clindamycin (10.8 ± 4.2 days) and sulfamethoxazole (9.6 ± 2.0 days). The simultaneous application of all compounds increased the half-lives (DT50,M) of all compounds (particularly carbamazepine, citalopram, fexofenadine and irbesartan), which is likely explained by the negative impact of antibiotics (sulfamethoxazole and clindamycin) on soil microbial community. However, this trend was not consistent in all soils. In several cases, the DT50,S values were even higher than the DT50,M values. Principal component analyses showed that while knowledge of basic soil properties determines grouping of soils according sorption behavior, knowledge of the microbial community structure could be used to group soils according to the dissipation behavior of tested compounds in these soils. The derived multiple linear regression models for estimating dissipation half-lives (DT50,S) for citalopram, clindamycin, fexofenadine, irbesartan and sulfamethoxazole always included at least one microbial factor (either amount of phosphorus in microbial biomass or microbial biomarkers derived from phospholipid fatty acids) that deceased half-lives (i.e., enhanced dissipations). Equations for citalopram, clindamycin, fexofenadine and sulfamethoxazole included the Freundlich sorption coefficient, which likely increased half-lives (i.e., prolonged dissipations).

Competitive and synergic sorption of carbamazepine, citalopram, clindamycin, fexofenadine, irbesartan and sulfamethoxazole in seven soils

Sorption of pharmaceuticals, which can occur in soils, may differ when present in a soil solution as a single compound or in a solution with other pharmaceuticals. Therefore, the sorption isotherms described by the Freundlich equations were evaluated for 6 compounds, which were applied in solutions of a single pharmaceutical, two pharmaceuticals or all pharmaceuticals to seven soils. Study mainly focused on a behavior of fexofenadine and irbesartan that occurred in soils in 3 forms (cationic, zwitter-ionic or neutral, anionic). Sorption of both compounds slightly increased (in some soils) when applied together, largely increased when applied with carbamazepine (neutral), and extremely increased when applied in solutions with citalopram (strongly sorbed cation), which could be explained by a cooperative multilayer sorption on soil constituents. On the other hand, sorption of both compounds moderately decreased when applied with clindamycin (cation and neutral) or sulfamethoxazole (neutral or anion). The magnitude of an increase or decrease in the Freundlich sorption coefficient (KF) for a particular compound depended on soil conditions, a form of compound's molecule and its interaction with molecules of other compounds. Despite sorption being influenced by other compound(s) in solution, the KF coefficients evaluated for a particular compound under the different conditions were mostly correlated with the same soil properties: KF,CAR with an organic carbon content, KF,CIT and KF,CLI with a base cation saturation, KF,SUL with hydrolytic acidity, and KF,FEX and KF,IRB with sorption complex saturation.

Soil magnetic signature for identification of areas with different sorption potentials of imazaquin

It is imperative that the increase in world agricultural production be carried out in a sustainable way, minimizing negative environmental effects caused, among other reasons, by herbicide use. This study aimed to assess the potential of using soil magnetic signature to identify areas with different sorption capacities of the herbicide imazaquin. A total of 374 soil samples were collected at a depth of 0.0–0.25 m from a grid with sampling density of 1 point every 2.4 ha in an area of 908 ha for determining the organic matter, pH, dithionite and oxalate iron contents, clay content, Freundlich sorption coefficient of the herbicide imazaquin, and magnetic susceptibility (MS). The results were submitted to descriptive statistics and Pearson correlation analysis. Regression models were constructed to estimate the Freundlich sorption coefficient of the herbicide imazaquin from MS. The spatial dependence was assessed by geostatistical analysis and spatial pattern maps and cross-variograms were constructed. MS allows an indirect quantification of imazaquin sorption. Soils with higher magnetic expression have higher sorption potential of imazaquin. Soil magnetic signature can assist in mapping and identifying areas with different potentials of herbicide application.

Evaluation of Adsorptive Characteristics of Cow Dung and Rice Husk Ash for Removal of Aqueous Glyphosate and Aminomethylphoshonic Acid

Glyphosate (GLY) is a major herbicide used throughout the world, and its continuous application has become an environmental issue. Adsorption is an important mechanism for removing organic contaminant in water. The present study characterized cow dung (CD) and rice husk ash (RHA), and determined the adsorption-desorption of GLY and its metabolite, aminomethylphoshonic acid (AMPA), on to them. The results revealed that both CD and RHA were alkaline and had no or low content of arsenic, cadmium, chromium and lead. The CD had lower surface area (13.104 mg2g−1) than RHA (21.500 m2g−1). The CD contained amines, phenol, ethers and carboxylic functional groups, while in addition to carboxylic and ether, RHA contains siloxane. Both CD and RHA had high affinities for GLY and AMPA. The Freundlich sorption coefficient (Kf) on AMPA were 2.915 and 2.660 for CD and RHA, respectively, while the values on GLY were 1.168 and 1.166 (mg g−1) for CD and RHA, respectively. Desorption of GLY only occurred at lower concentrations, while no desorption of AMPA was recorded, indicating their strong adsorption on CD and RHA. Considering their availabilities and affordable prices, both CD and RHA can be recommended as economical adsorbent for the removal of GLY and AMPA.

Fiproles in urban surface runoff: Understanding sources and causes of contamination

Urban-use pesticides present a unique risk to non-target organisms in surface aquatic systems because impervious pavement facilitates runoff that may lead to serious contamination and ensuing aquatic toxicity. Fipronil is an insecticide used at high rates in urban environments, especially in regions such as California. This compound and its biologically active degradation products have been detected in urban runoff drainage and downstream surface water bodies at concentrations exceeding toxicity thresholds for sensitive aquatic invertebrates, necessitating a better understanding of the runoff sources and causes of this contamination at sites of application. In this study, we evaluated sorption of fipronil, fipronil desulfinyl, fipronil sulfide, and fipronil sulfone in urban dust, soil, and concrete, matrices commonly associated with the perimeter of a residential home. Samples were also collected from five single family homes treated with fipronil in Riverside, California, for five months to determine the occurrence of fipronil and its degradates in runoff water, urban dust, soil, and on concrete surfaces. Statistical analysis was performed to determine which urban matrices contributed more significantly to the contaminant levels in runoff water. Freundlich sorption coefficients for fipronil and its degradation products in dust were 3- to 9-fold greater than their values in soil. Fipronil and its degradates were detected in 100% of runoff samples and their presence was observed in dust, soil, and concrete wipe samples for 153 d after the treatment. Linear regression analysis showed that concrete surfaces were a primary source of all four compounds to runoff, and loose dust on concrete pavement also served as an important contributor. This study represents the first comprehensive investigation of the sources and causes for surface runoff contamination by fipronil and its degradation products. Findings highlight the importance to reduce fipronil residues on concrete surfaces through improved application methods and other mitigation practices.

English

Herbicide mixture is a widely used weed control practice in many agricultural areas. However, interactions between the herbicide mixture and soil may alter the soil dynamics. This research evaluated the effect of the physicochemical properties of the soils in the application of diuron alone and in a mixture with hexazinone, by means of sorption-desorption Freundlich isotherms. 14C-diuron sorption (isolated and mixed) was evaluated by batch equilibration at five concentrations of diuron (0.14, 0.16, 0.19, 0.26 and 0.39 μg mL-1) and hexazinone (0.03, 0.06, 0.13, 0.19 and 0.26 μg mL-1), corresponding to the recommended field dose (D) of D/4, D/2, D, 2×D and 4×D, respectively, in five soils cultivated with sugarcane. The sorption of the diuron applied separately and in mixture presented Freundlich sorption coefficient (Kf) values in the range of 1.47 to 5.08 and 0.59 to 3.77 µmol(1-1/n) L1/n kg-1, respectively. The lowest desorption values were found for Clay-1 soil (72.5% clay), with 6.01 and 5.87% for diuron isolated and blended, respectively. Diuron sorption was slightly higher when applied alone rather than in the herbicide mixture, and this sorption correlated positively with the clay content of the soils, regardless of the application form. The disponibility of diuron improved in mixture of hexazinone in soil, which can increase its absorption and control efficiency; on the other hand, the transport of herbicide can rise. Future researches about the transport, runoff or leaching are required for complete information of the behavior of this mixture of herbicides in soil. Key words: Retention process, sorption kinetics, hysteresis, commercial mixture.

A Global Meta-Analysis to Predict Atrazine Sorption from Soil Properties.

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is one of the most widely used herbicides worldwide, and groundwater contamination is of concern, especially in heavily used regions and in edaphic conditions prone to leaching. Soil sorption plays an essential role in atrazine environmental fate, yet consistent atrazine risk prediction remains limited. A quantitative meta-analysis was conducted to characterize the effect of soil properties on atrazine sorption, using 378 previous observations in 48 publications from 1985 to 2015 globally, which included data on soil properties and sorption parameters. A supplemental regional study was conducted to test the derived meta-analysis models. The meta-analysis indicated that percentage organic C (OC) was the most important parameter for estimating atrazine sorption, followed by percentage silt, soil pH, and percentage clay. Meta-analysis and supplemental study models were developed for Freundlich sorption coefficients () and sorption distribution coefficients () as a function of OC. The global meta-analysis models generated positive linear trends for OC with and ( = 0.197 and 0.205, respectively). Organic C was highly correlated with and in supplemental experimental study models ( = 0.93 and 0.92, respectively), indicating accurate prediction of sorption within the evaluated region. Continental models were investigated, which improved the goodness of fit. Models developed via meta-analysis may be used to predict atrazine sorption over wide ranges of data, whereas more accurate and refined prediction can be achieved by specific regional models through experimental studies. However, such models could be improved if standardized agroclimatic conditions, soil classification, and other key variables were more widely reported.

Sorption behaviors of antimicrobial and antiparasitic veterinary drugs on subtropical soils

Brazil is one of the world's largest producers of animal protein, requiring the large-scale use of veterinary drugs. The administration of antimicrobials and antiparasitics is a common practice. However, there is a lack of information on how these drugs impact the environment. Antimicrobials are capable of altering the soil microbial population and are responsible for the development of multidrug-resistant microbial strains. Therefore, it is important to evaluate the fate and transport of these compounds in the environment, and one parameter used for this purpose is the soil-water partition coefficient. In this work, an assessment was made of the soil sorption behaviors of 18 drugs from seven different families, including antimicrobials (sulfonamides, fluoroquinolones, amphenicols, and macrolides) and antiparasitic drugs (milbemycin, avermectins, and benzimidazoles). Seven subtropical soils of different textural classes were tested. The Freundlich sorption coefficients, expressed as μg1−1/n (cm3)1/n g−1, were in the following ranges: 0.45 to 19 (sulfonamides), 72 to 2410 (fluoroquinolones), 9 to 58 (thiabendazole), 0.03 to 0.48 (florfenicol), 105 to 424 (moxidectin), 14 to 184 (avermectins), and 1.5 to 74 (macrolides). The results showed that the drugs belonging to the same family, with chemical structures in common, presented similar behaviors regarding sorption and desorption, for the different soils tested and are generally in agreement with soils from temperate regions. The data set obtained in this work give an overview of the fate of the veterinary drugs in Brazilian subtropical soils with different textures and composition and can be very helpful for exposure risk assessments.

Glyphosate sorption to soils of Argentina. Estimation of affinity coefficient by pedotransfer function

Argentine agricultural production is fundamentally based on a technological package that combines direct seeding and glyphosate with transgenic crops (soybean, maize and cotton), which makes glyphosate the most widely employed herbicide in the country. Glyphosate is strongly sorbed to soil in a reversible process that regulates the half-life and mobility of the herbicide, with the resulting risk of contaminating surface and groundwater courses. However, this behavior may vary depending on the characteristics of the soil on which it is applied. Sorption coefficients are thus the most sensitive parameters in models used for environmental risk assessment. The aim of this work was to study the affinity of glyphosate to 12 different soils of Argentina and create a model to estimate the glyphosate Freundlich sorption coefficient (Kf) from easily measurable soil properties. Batch equilibration adsorption data are shown by Freundlich adsorption isotherms. Principal component analysis and multiple linear regressions were used to correlate the effects of soil properties on glyphosate adsorption coefficients. Results indicate that pH and clay contents were the major soil parameters governing glyphosate adsorption in soils. The Freundlich (Kf) pedotransfer function obtained by stepwise regression analysis has 97.9% of the variation in glyphosate sorption coefficients that could be attributed to the variation of the soil clay contents, pH, PBray and Alin.

Phosphate and glyphosate sorption in soils following long-term phosphate applications

Phosphate and glyphosate molecules compete for sorption sites in soil. The objective of this study was to quantify the impact of Olsen P concentrations in two contrasting soils on phosphate and glyphosate sorption. Soils were a sandy clay loam soil rich in iron oxides (SCL-Fe2O3) and a clay loam soil rich in calcium carbonates (CL-CaCO3). The phosphate Freundlich sorption coefficient (Kf) ranged from 3 to 68L1/nmg1–1/nkg−1 in the SCL-Fe2O3 and from 21 to 76L1/nmg1–1/nkg−1 in the CL-CaCO3. Glyphosate sorption coefficient (Kd) ranged from 293 to 1173Lkg−1 in the SCL-Fe2O3 but only 99 to 141Lkg−1 in the CL-CaCO3. Glyphosate Kd and phosphate Kf values decreased significantly with increasing Olsen P concentrations in both soils. Glyphosate Kd values were further significantly reduced when phosphate was added to the slurry solutions, but phosphate Kf values were not impacted by the presence of glyphosate in solutions. We conclude that annual phosphate fertilizer applications leave phosphate concentrations in Prairie soils to the extent that soils have a lesser capacity to retain glyphosate and phosphate that are subsequently applied, but glyphosate residues will not influence phosphate sorption.

Modeling Subsurface Fate of S‐Metolachlor and Metolachlor Ethane Sulfonic Acid in the Westliches Leibnitzer Feld Aquifer

Core Ideas Lysimeter experiments allow site‐specific knowledge about the fate of pesticides. Lysimeter‐based model calibration provides integrated parameter sets. Lysimeter scale‐based models were compiled to represent aquifer scale. Lysimeter scale‐based models were coupled with a groundwater transport model. The groundwater model reproduced observed metabolite groundwater concentrations. Pesticides and their metabolites have been increasingly detected in groundwater bodies in southeastern Austria in recent years. The main objective of this study was to model the fate of the herbicide S‐metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐[(1S)‐2‐methoxy‐1‐methylethyl]acetamide; SMET) and the main metabolite metolachlor ethane sulfonic acid (MESA) at the Westliches Leibnitzer Feld (WLF) aquifer. For this purpose, a modeling approach based on coupling the one‐dimensional vadose zone model PEARL and the two‐dimensional groundwater flow and solute transport model FEFLOW was developed. To calibrate the one‐dimensional pesticide fate model, we used leachate concentrations of SMET and MESA from lysimeter experiments. Additionally, samples of representative soil types in the WLF aquifer were analyzed to infer SMET‐ and MESA‐specific fate parameters (e.g., half‐life DT50, Freundlich sorption coefficient Kfoc), which were used for the PEARL model. The results show that using SMET fate parameters derived from the lysimeter data considerably improved the fit of the simulation results with the field observations compared with the application of standard laboratory‐derived fate parameters accounting for soil type differences. Although locally an overestimation of the monitoring data prevailed, the description of the subsurface fate of pesticides will improve the interpretation of concentration data and the design of mitigation measures.

Azithromycin sorption and biodegradation in a simulated California river system

Azithromycin (AZ) is a widely-used macrolide antibiotic that is continually deposited into natural waterways by sewage effluent. Though recognized as an emerging contaminant of concern, little is known about its fate and transport in aquatic systems. American River soils and water were used to determine degradation of AZ in microcosms simulating flooded (anaerobic) and non-flooded (aerobic) California watershed conditions. Under aerobic conditions the degradation rate constant (k=0.0084 ± 0.0039 day−1) and DT50 (82.52 ± 56.54 days) were calculated, as AZ disappearance indicated potential degradation. However, based on concurrent product appearance, less than one percent of the parent degraded over 150 days. Throughout the experiment microbial growth was observed by culturing in tryptic soy broth despite antibiotic addition and soil being autoclaved. Sorption likely contributes to AZ recalcitrance, thus the soil-water partition coefficient (log Kd = 2.18 Lkg−1), Freundlich sorption and desorption coefficients (log Kf = 1.90 ± 0.14 and log Kfd = 2.51 ± 0.30, respectively), and organic-carbon-normalized distribution coefficient (log Koc = 4.25 Lkg−1) were also calculated. Based on these results, AZ degradation in aquatic systems will likely be very limited and transport will fluctuate based on the extent of soil-water saturation or bulk movement of sediment.

Low-molecular-weight organic acids correlate with cultivar variation in ciprofloxacin accumulation in Brassica parachinensis L.

To understand the mechanism controlling cultivar differences in the accumulation of ciprofloxacin (CIP) in Chinese flowering cabbage (Brassica parachinensis L.), low-molecular-weight organic acids (LMWOAs) secreted from the roots of high- and low-CIP cultivars (Sijiu and Cutai, respectively) and their effects on the bioavailability of CIP in soil were investigated. Significant differences in the content of LMWOAs (especially maleic acid) between the two cultivars played a key role in the variation in CIP accumulation. Based on the Freundlich sorption coefficient (Kf) and distribution coefficient (Kd), the presence of LMWOAs reduced the CIP sorption onto soil particles, and higher concentrations of LMWOAs led to less CIP sorption onto soil. On the other hand, LMWOAs enhanced CIP desorption by lowering the solution pH, which changed the surface charge of soil particles and the degree of CIP ionization. LMWOAs promoted CIP desorption from soil by breaking cation bridges and dissolving metal cations, particularly Cu2+. These results implied that the LMWOAs (mainly maleic acid) secreted from Sijiu inhibited CIP sorption onto soil and improved CIP desorption from soil to a greater extent than those secreted from Cutai, resulting in higher bioavailability of CIP and more uptake and accumulation of CIP in the former.