Koc Values Research Articles

Field versus laboratory measurements of PFAS sorption by soils and sediments

Sorption by soils and sediments is an important process that influences the distribution, transport, and fate of per and polyfluoroalkyl substances (PFAS) in the environment. Many laboratory studies have been conducted to quantify magnitudes of PFAS sorption as a function of the properties of the PFAS, solutions, and porous media. A critical question is how representative are laboratory-measured sorption magnitudes for field applications. To address this question, log Koc data were compiled from the literature for a range of PFAS of different chain lengths and functional groups. The aggregated field-based data consisted of two types, in-situ measurements comprising paired soil/sediment and water samples and ex-situ measurements obtained from laboratory desorption experiments employing field-contaminated media. These two sets of field-based measurements were compared to a comprehensive data set of standard laboratory batch-type measurements. The compiled data sets represent an extremely wide range of soil and sediment properties. One important novel outcome is the observation that the enhanced sorption of short-chain PFAS observed in several prior laboratory studies is also observed for the field data. This differential enhanced sorption should be accounted for in site investigations and modeling studies. Another relevant outcome is the observation of consistency between measurements obtained with standard batch adsorption experiments and those from desorption studies employing either field-contaminated or artificially-contaminated media. The mean log Koc values determined for the in-situ measured field data were generally larger than the mean laboratory-determined values, particularly for the short-chain PFAS. Notably, however, values for subsets of the laboratory data representing measurements for lower aqueous concentrations or for soils with low organic-carbon contents (<1 %) compared well to the in-situ field data. Measurements compiled for anionic-polyfluoroalkyl, neutral, and cationic PFAS compared well to those for PFCAs and PFSAs. Overall, the results indicate that the laboratory measurements of PFAS sorption were generally representative of the field-derived magnitudes when compared on a consistent basis.

Comparing occurrence of per- and polyfluoroalkyl substances (PFAS) in municipal biosolids and industrial wastewater sludge: A City of Los Angeles study

Biosolids and sludge are what remain after the liquid fraction of wastewater is separated during wastewater treatment. These high organic content matrices are known to contain organic contaminants, a few of which are the hazardous and environmentally persistent per- and polyfluoroalkyl substances (PFAS). The current study investigates whether sludge from a treatment facility serving mostly industrial establishments and biosolids from a facility serving mostly domestic dwellings retain these ‘forever chemicals’ similarly. Using 31 markers covering different classes of PFAS, the sludge was found to contain higher levels of PFAS (869 ± 791 ng/g; 21 of 31) than biosolids (31 ± 7 ng/g, 11 of 31). The most abundant overall was perfluorooctane sulfonic acid (PFOS), mostly in sludge (range: 71–1300 ng/g versus 0–18 ng/g in biosolids). The large PFAS concentration variability in sludge was seasonal and sinusoidal. Sludge, additionally, contained all long chain PFAS, precursors (mostly surfactant ingredients and their transformation byproducts) and short chain PFAS (perhaps because of higher moisture content). By regression, the sludge is shown to consistently contain twice as much PFAS as biosolids when the same amounts are exposed to increasing levels of PFAS. Factors observed to cause differential PFAS retention between sludge and biosolids were moisture (98.6 % and 72.1 %, respectively), chain length, input quality (industrial versus residential) and functional group. Sulfonic acids for instance are one C atom shorter than carboxylates with similar occurrence in sludge and biosolids. More studies are needed to define the roles that organic carbon of sludge/biosolids, water chemistry, temperature and factors not considered here play in partitioning PFAS between the two matrices with respect to inputs. Existing Koc values could not help in explaining observed trends, but the ratio of biosolids-to-influent concentrations was found to correlate positively with PFAS size. Using influent in the ratio, and not effluent, is novel. SynopsisSludge and biosolids are soil amendments; they contain hazardous and persistent PFAS. Methods of decoupling PFAS from these matrices start with understanding matrix-driven PFAS partitioning as shown here.

Mechanistic insight into the effects of interaction between biochar and soil with different properties on phenanthrene sorption

Soil composition varies considerably in nature, so it is vital to investigate the mechanism of the effect of various soil parameters on biochar sorption capacity. In this study, two biochars (W4 and W7) were derived from wheat straw at temperatures of 400 and 700 °C and were incubated with three different soils. Changes in biochar surface features by aging in the soils and the consequent impact on phenanthrene sorption were examined. The results showed that the effect of adding biochar on phenanthrene sorption capacity (Koc) varied by soil. When biochar was freshly mixed with soil, the Koc value in soil with higher clay content was more dramatically altered by biochar, which is due to clay particles adhering to the biochar surface. Moreover, the Koc value was significantly decreased by the addition of W4 but increased by the addition of W7 in general. After aging, most of the Koc value decreased. The greatest decrease in Koc value was observed in biochar and soil composed with the highest clay content for W4 (24–63%), as well as soil composed with the highest organic matter content for W7 (46–64%). This is because the surface polarity and micropores of biochar dropped the most rapidly in these mixes, resulting in a significant decrease in hydrophobic and pore-filling properties. The results revealed that the impact of biochar-soil interactions on phenanthrene sorption is related to not only biochar properties but also soil clay particles, soil organic matter content and pH. The findings of the study can be utilized to assess the efficacy of biochar application in soil remediation for various features.

Batch equilibrium experiments and modeling reveal weak temperature dependence of cyclic volatile methylsiloxane sorption in soil/sediment organic carbon-water systems

The organic carbon normalized partition coefficient, KOC, describes the equilibrium distribution of a chemical between water and organic carbon in soil or sediment. It is a key parameter in evaluating chemical persistence, mass distribution, and transport using multimedia fate and transport models. Considerable uncertainty remains about the KOC values of cyclic volatile methylsiloxane (cVMS) compounds, and in particular the dependence of KOC on temperature. In this study, we used a batch equilibrium (BE) method to measure KOC values and their temperature dependence between ∼5 and 25 °C for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) with soil and sediments. Approximate log KOC values at 25 °C were 4.5–5.0 for D4 and 5.5–6.1 for D5 with different sorbents, and decreased by 0.3 log units or less at 4–5 °C. Enthalpies of sorption, ΔHOC, obtained for the different sorbents ranged from +7.2 to +16 kJ mol−1, with average values of +7.9 and +13 kJ mol−1 for D4 and D5, respectively. These values differ in magnitude and direction from those reported elsewhere based on KOC values determined by a novel dynamic purge-and-trap (PnT) method, but are consistent with predictions based on their solvation properties. A new fugacity-based multimedia model incorporating sorption/desorption kinetics was developed and used to predict concentrations in the phases of BE and PnT systems during desorption of cVMS under different experimental and ideal conditions. Model simulations suggested that KOC values for cVMS compounds derived from the PnT systems could be influenced by sorption disequilibrium between water and solids controlled by desorption rates from the particle phase to water, and subsequent losses due to volatilization and degradation. This has the potential to result in overestimation of KOC values when fitting the experimental data of cVMS mass remaining in a PnT system over time, which could explain the observed differences between the methods.

Bioretention Design Modifications Increase the Simulated Capture of Hydrophobic and Hydrophilic Trace Organic Compounds.

Stormwater rapidly moves trace organic contaminants (TrOCs) from the built environment to the aquatic environment. Bioretention cells reduce loadings of some TrOCs, but they struggle with hydrophilic compounds. Herein, we assessed the potential to enhance TrOC removal via changes in bioretention system design by simulating the fate of seven high-priority stormwater TrOCs (e.g., PFOA, 6PPD-quinone, PAHs) with log KOC values between -1.5 and 6.74 in a bioretention cell. We evaluated eight design and management interventions for three illustrative use cases representing a highway, a residential area, and an airport. We suggest two metrics of performance: mass advected to the sewer network, which poses an acute risk to aquatic ecosystems, and total mass advected from the system, which poses a longer-term risk for persistent compounds. The optimized designs for each use case reduced effluent loadings of all but the most polar compound (PFOA) to <5% of influent mass. Our results suggest that having the largest possible system area allowed bioretention systems to provide benefits during larger events, which improved performance for all compounds. To improve performance for the most hydrophilic TrOCs, an amendment like biochar was necessary; field-scale research is needed to confirm this result. Our results showed that changing the design of bioretention systems can allow them to effectively capture TrOCs with a wide range of physicochemical properties, protecting human health and aquatic species from chemical impacts.

Adsorption and partition of the antibiotic ciprofloxacin in poultry litter

AbstractBACKGROUNDThe use of antibiotics on a large scale is a common practice in poultry farming. This research investigated the adsorption of the antibiotic ciprofloxacin (CIP) in poultry litter samples to assess the potential risk to ecosystems as a result of the compound mobility. This residue is used directly dispersed in agricultural soils as a biofertilizer.RESULTSExperimental data were evaluated in terms of fits of isotherm models. The mobility of CIP was assessed by the distribution coefficient and the partition coefficient related to organic matter. The studied poultry litter presented a pH of 8.5 ± 0.1, moisture content of 20.3 ± 1.3% and total solids content of 79.8 ± 1.2%, with a high amount of both inorganic matter (57.1 ± 1.7%) and organic matter (42.9 ± 1.7%) content in its composition. The Redlich–Petersen isotherm model satisfactorily described the experimental data, with higher maximum adsorption capacities at more alkaline pHs (pH 8.0 = 3015.0 ± 118.0 μg g−1, pH 7 = 2916.6 ± 1152.9 μg g−1 and pH 6 = 410.0 ± 18.1 μg g−1). The log Kd (pH 6 = 0.9, pH 7 = 1.2, and pH 8 = 1.4) and log Koc (pH 6 = 1.3, pH 7 = 1.7 and pH 8 = 1.8) values obtained for the sorption of ciprofloxacin at different pHs in poultry litter were considered low (log Koc &lt; 3.5).CONCLUSIONSThe analyte does not tend to adsorb in the poultry litter and might leach to other environmental compartments. The information obtained in this study reinforces the ecotoxicological concern about antibiotic residues in the environment. © 2024 Society of Chemical Industry (SCI).

Contamination status, partitioning behavior, ecological risks assessment of legacy and emerging per- and polyfluoroalkyl substances in a typical heavily polluted semi-enclosed bay, China

The contaminant status, spatial distribution, partitioning behavior, and ecological risks of 26 legacy and emerging perfluoroalkyl and polyfluoroalkyl substances (PFASs) in Laizhou Bay, China were investigated. The concentrations of ∑PFASs in surface and bottom seawater ranged from 37.2 to 222 ng/L and from 34.2 to 305 ng/L with an average of 116 ± 62.7 and 138 ± 93.8 ng/L, respectively. There were no significant differences in the average concentrations between the surface and bottom seawater (P > 0.05). Perfluorooctanoic acid (PFOA) and short-chain PFASs dominated the composition of PFASs in seawater. The concentrations of ∑PFASs in sediments ranged from 0.997 to 7.21 ng/g dry weight (dw), dominated by perfluorobutane sulfonate (PFBS), perfluorobutanoic acid (PFBA), and long-chain PFASs. The emerging alternatives of perfluoro-1-butane-sulfonamide (FBSA) and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) were detected for the first time in Laizhou Bay. The ∑PFASs in seawater in the southwest of the bay were higher than those in the northeast of the bay. The ∑PFASs in sediments in the northeast sea area were higher than those in the inner area of the bay. Log Kd and log Koc values increased with increasing carbon chain length for PFASs compounds. Ecological risk assessments indicated a low ecological risk associated with HFPO-DA but a moderate risk associated with PFOA contamination in Laizhou Bay. Positive matrix factorization (PMF) analysis revealed that fluoropolymer manufacturing, metal plating plants, and textile treatments were identified as major sources contributing to PFASs contamination.

Occurrence and partitioning of p-phenylenediamine antioxidants and their quinone derivatives in water and sediment

p-Phenylenediamine antioxidants (PPDs) and PPDs-derived quinones (PPDQs) may pose a threat to the river ecosystem. However, the knowledge on the occurrence and environmental behaviors of PPDs and PPDQs in the natural river environment remains unknown. In this study, we collected paired water (n = 30) and sediment samples (n = 30) from Jiaojiang River, China and analyzed them for nine PPDs and seven PPDQs. Our results showed that target PPDs and PPDQs are frequently detected in water samples, with the dominance of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD; mean 12 ng/L, range 4.0–72 ng/L) and 6PPD-derived quinone (6PPDQ; 7.0 ng/L, <LOD–21 ng/L), respectively. In sediment samples, detected PPDs and PPDQs were also dominated by 6PPD (mean 31 ng/g, range 1.6–172 ng/g) and 6PPDQ (14 ng/g, <LOD–46 ng/g), respectively. This study first reports the field-based log-transformed sediment-water coefficients (log Koc) for PPDs and PPDQs. Among PPDs, N, N′-diphenyl-p-phenylenediamine (4.0 ± 0.55) had the highest mean log Koc value, followed by N-isopropyl-N′-phenyl-p-phenylenediamine (3.6 ± 0.26). The mean log Koc values of detected PPDQs ranged from 2.0 ± 0.49 to 3.3 ± 0.44. To our knowledge, this is the first study comprehensively investigating the occurrence of PPDs and PPDQs in paired freshwater and sediment. Results of this study provide new insights into their occurrence, spatial distribution, and behaviors in the freshwater environment.

Fate of Iprobenfos and Tricyclazole at Paddy Cultivation Environment

Objectives : This study aimed to identify the fate of iprobenfos and tricyclazole in the soil and paddy water during the rice cultivation process and to identify their exposure pathways into surface water.Methods : Both iprobenfos and tricyclazole were sprayed onto two sample sites following the pesticide safety usage guidelines. Residues in the samples. Soil, paddy water, and drainage water samples were collected for 28 days after post-application. Residues were subsequently analyzed using LC-MS/MS.Results and Discussion : The fate of the two pesticides, iprobenfos and tricyclazole, in the rice cultivation environment was influenced by factors such as soil half-life, Koc, water solubility, formulation, and precipitation patterns. Initial concentrations of iprobenfos and tricyclazole in the paddy field near the drainage were 5,774 μg/L and 307 μg/L, respectively, while concentrations in the drain water were 1,850 μg/L and 182 μg/L. Four days after application, the residual concentrations of iprobenfos and tricyclazole in both paddy and drain water ranged from N.D. (Not Detected) to 5.6 μg/L and N.D. to 56 μg/L, respectively, indicating a rapid decline. During the experimental period, the average concentration reduction ratios in drain water near the drainage compared to the drain water were higher for tricyclazole (90%) than for iprobenfos (52%).Conclusion : The soil and water half-life of tricyclazole exceeded that of iprobenfos, leading to a slower rate of concentration reduction. The lower Koc value for tricyclazole suggests enhanced soil desorption due to rainfall, increasing its concentration in paddy fields. The presence of iprobenfos and tricyclazole in surface water is likely due to dispersion during pesticide application. While concentrations diminish owing to the dilution effect when water moves from paddy fields to surface water, it's posited that runoff could affect nearby stream water within seven days post-application.

Differential Sorption of Short-Chain versus Long-Chain Anionic Per- and Poly-Fluoroalkyl Substances by Soils

The impact of chain length on the sorption of anionic PFAS by soils and sediments was investigated by aggregating and synthesizing data sets from the literature. Quantitative structure/property relationship (QSPR) analysis was applied to characterize the influence of molecular size and soil properties on sorption. The log of the organic carbon-normalized equilibrium sorption coefficient (Koc) exhibited a biphasic relationship with molar volume, wherein the log Koc values for the short-chain PFAS were generally greater than would be predicted using the QSPR correlation determined for the long-chain PFAS. This enhanced differential sorption is observed to different degrees for all studies, which are compiled and synthesized for the first time. The results reveal remarkable congruency across a wide array of soils comprising a large range of properties and indicate that the observed enhanced differential sorption of short-chain PFAS is a prevalent phenomenon. Aggregating the long-chain PFAS data for all soils and sediments with organic carbon contents &gt; 1% produced a strong correlation, indicating that the resultant QSPR model can produce representative log Koc values irrespective of the other properties of the medium. Silt+clay content was shown to be an important soil component for the short-chain PFAS for most soils, as well as the long-chain PFAS for soils with organic carbon contents &lt; 1%. The results indicate that while the simple Koc-foc approach may produce reasonable estimates of Kd values for long-chain anionic PFAS, particularly for soils and sediments with larger organic carbon contents, it is unlikely to do so for short-chain anionic PFAS.

Occurrence, spatiotemporal distribution patterns,partitioning and risk assessments of multiple pesticide residues in typical estuarine water environments in eastern China

The low terrain and the prosperous agriculture in the east of China, have caused the accumulation of pesticide residues in the estuaries. Therefore, this study analyzed the spatiotemporal distribution and partition tendency of 106 pesticides based on their abundance, frequencies, and concentrations in the aquatic environment of 16 river estuaries in 7 major basins in the eastern China by using solid-phase extraction (SPE) with high-performance liquid chromatography tandem mass spectrometry (HPLC‒MS/MS) and gas chromatography tandem mass spectrometry (GC‒MS/MS). In addition, potential risk of multiple pesticides was also evaluated. The results showed that herbicides were the dominant pesticide type, while triazines were the predominate substance group of pesticide. In addition, triadimenol, vinclozolin, diethylatrazine, prometryn, thiamethoxam, atrazine, and metalachlor were the major pesticides in the water, while prometryn, metalachlor, and atrazine were the main pesticides in the sediment. The average total concentration of pesticide was 751.15 ng/L in the dry season, 651.17 ng/L in the wet season, and 617.37 ng/L in the normal season, respectively. The estuaries of the Huai River Basin, the Yangtze River Basin, the Hai River Basin, and the Yellow River Basin have been affected by the low pollution treatment efficiency, weak infrastructure, and agricultural/non-agricultural activities in eastern China, resulting in relatively serious pesticide pollution. The estuaries of Huaihe River, Yangtze River, Xiaoqing River, and Luanhe River had large pesticide abundance and comparatively severe pesticide pollution, while the estuaries of Tuhai River and Haihe River had heavy pesticide contamination in the sediment, which might be induced by historical sedimentary factors. The log KOC values showed that except for thioketone, other pesticides were relatively stable due to the adsorption by sediment. The ecological risk assessment results indicated that insecticides had a high risk. Teenagers were the most severely affected by the noncarcinogenic risk of pesticides, while adults were mostly affected by the carcinogenic risk of pesticides. Therefore, pesticide hazards in the water environment of estuaries in eastern China needs to be further close supervision.

Influence of SOM Composition, Clay Minerals, and pH on 2,4-D and MCPA Retention in Peri-Urban Soils

The use of ionic herbicides in urban and peri-urban areas has serious environmental and health consequences due to their common overapplication and mobility in the soil profile. The specific objective of this study was to evaluate the influence of soil organic matter (SOM) fractions and clay minerals on the retention of 2,4-D and MCPA on loamy sand and loam topsoil materials under the pH range of 3–7. The results obtained indicate their weak, unfavorable, and physical sorption, presumably governed by partitioning. 2,4-D exhibited high affinity for polar SOM fractions as well as to kaolinite and montmorillonite, both present in the studied peri-urban soils. MCPA sorption was mainly related to soil fulvic (FA) and humic acid (HA) content; however, the pesticide was sorbed to a lesser extent than 2,4-D due to its great water solubility. This was reflected in MCPA’s low Koc values (41.33 and 84.21), indicating its very high mobility and leachability in the studied soils. Meanwhile, 2,4-D was moderately mobile in sandy soil while classified as a non-leacher in the loam topsoil material. Both herbicides were preferably retained at a low soil pH (3–4), which, together with soil amendment with exogenous, well-humified organic matter, could minimize the potential health and environmental risks of their application.

Chemical Structural Features Affecting the Soil Sorption of Sulfonylurea Herbicides

ABSTRACT The contamination of groundwater by herbicides depends on their mobility in soil, which is related to the organic carbon to water partition coefficient, KOC. Because the log KOC values of widely used sulfonylurea herbicides do not correlate with easily accessible log P estimations, multivariate image analysis (MIA) descriptors were employed to build structure-property models to classify these compounds according to their soil sorption capability. In addition, a deeper analysis based on MIA contour maps of PLS regression coefficients and variable importance in projection scores was performed to obtain insight into the chemical features responsible for the log KOC behavior. A multiple linear regression model obtained from selected descriptors demonstrated high predictability (r2 = 0.95, q2 = 0.84, and r2 pred = 0.71) and also provided chemical insight into the log KOC values. It has been found that triazine rather than pyrimidine derivatives are less prone to leach out, but substituents attached to the sulfonyl group play an important role in modulating the log KOC values. Consequently, useful guidance for environmental risk assessment is provided for the development of new sulfonylurea herbicides.

Do biotransformation data from laboratory experiments reflect micropollutant degradation in a large river basin?

Identifying a chemical's potential for biotransformation in the aquatic environment is crucial to predict its fate and manage its potential hazards. Due to the complexity of natural water bodies, especially river networks, biotransformation is often studied in laboratory experiments, assuming that study outcomes can be extrapolated to compound behavior in the field. Here, we investigated to what extent outcomes of laboratory simulation studies indeed reflect biotransformation kinetics observed in riverine systems. To determine in-field biotransformation, we measured loads of 27 wastewater treatment plant effluent-borne compounds along the Rhine and its major tributaries during two seasons. Up to 21 compounds were detected at each sampling location. Measured compound loads were used in an inverse model framework of the Rhine river basin to derive k’bio,field values – a compound-specific parameter describing the compounds’ average biotransformation potential during the field studies. To support model calibration, we performed phototransformation and sorption experiments with all the study compounds, identifying 5 compounds that are susceptible towards direct phototransformation and determining Koc values covering four orders of magnitude. On the laboratory side, we used a similar inverse model framework to derive k’bio,lab values from water-sediment experiments run according to a modified OECD 308-type protocol. The comparison of k’bio,lab and k’bio,field revealed that their absolute values differed, pointing towards faster transformation in the Rhine river basin. Yet, we could demonstrate that relative rankings of biotransformation potential and groups of compounds with low, moderate and high persistence agree reasonably well between laboratory and field outcomes. Overall, our results provide evidence that laboratory-based biotransformation studies using the modified OECD 308 protocol and k’bio values derived thereof bear considerable potential to reflect biotransformation of micropollutants in one of the largest European river basins.

Emerging poly- and perfluoroalkyl substances in water and sediment from Qiantang River-Hangzhou Bay

Many emerging poly- and perfluoroalkyl substances (PFASs) are being used in China, due to the gradual phase out of legacy PFASs. Occurrence and environmental behaviors of emerging PFASs in Chinese fresh water environment are still not well known. In this study, 31 PFASs, including 14 emerging PFASs, were measured in 29 pairs of water and sediment samples from Qiantang River-Hangzhou Bay, an important drinking water resource for cities in Yangtze River basin. Perfluorooctanoate was consistently the predominant legacy PFAS in water (8.8–130 ng/L) and sediment (3.7–49 ng/g dw). Twelve emerging PFASs were detected in water, with the dominance of 6:2 chlorinated polyfluoroalkyl ether sulfonates (6:2 Cl-PFAES; mean 11 ng/L, 0.79–57 ng/L) and 6:2 fluorotelomer sulfonate (6:2 FTS; 5.6 ng/L, < LOD–29 ng/L). Eleven emerging PFASs were found in sediment, and were also dominated by 6:2 Cl-PFAES (mean 4.3 ng/g dw, 0.19–16 ng/g dw) and 6:2 FTS (2.6 ng/g dw, < LOD–9.4 ng/g dw). Spatially, sampling sites closed to the surrounding cities had comparatively higher water concentrations of PFASs. Among emerging PFASs, 8:2 Cl-PFAES (3.0 ± 0.34) had the highest mean field-based log-transformed organic‑carbon normalized sediment-water partition coefficient (log Koc), followed by 6:2 Cl-PFAES (2.9 ± 0.35) and hexafluoropropylene oxide trimer acid (2.8 ± 0.32). p-perfluorous nonenoxybenzene sulfonate (2.3 ± 0.60) and 6:2 FTS (1.9 ± 0.54) had relatively lower mean log Koc values. To our knowledge, this is the most comprehensive study investigating the occurrence and partitioning behaviors of emerging PFASs in Qiantang River.

Organic Amendments Addition on Altering the Sorption, Vertical Movement and Leaching Behavior of Herbicides in Soil

Herbicides are applied indiscriminately to achieve maximum weed control in agricultural production which might contaminate the food chain through the bio-augmentation of residue concentration in soil. One of the management suggested to overcome the herbicides contamination is treating with various organic amendments. Hence the laboratory column leaching and sorption experiments were conducted in Tamil Nadu Agricultural University (TNAU), Coimbatore to investigate the leaching behavior of herbicides viz., pendimethalin, atrazine and imazethapyr in soil as influenced by various organic amendments applied @ 5t/ha viz., FYM, vermicompost, composted coir pith, maize crop residue and biochar. Leaching experiment was conducted using PVC columns of 45 cm length and the sorption study was conducted using different concentrations of chosen herbicides as per OECD guidelines. Results showed that leaching and movement behavior of the studied herbicides in soil was modified by the applied organic amendments particularly the biochar and maize crop residue. Biochar treated soil retained 29.76, 40.20, and 38.07 percent of the applied pendimethalin, atrazine and imazethapyr respectively in surface 0-15 cm depth and reduced its movement to lower depths and to leachates. Herbicides adsorption was higher with biochar and is indicated by the Koc values of 225, 184 and 22 mg/L for pendimethalin, atrazine and imazethapyr respectively and was followed by the maize crop residue. It is concluded that the application of biochar @ 5t/ha as organic amendment is efficient in decreasing the herbicides movement viz., pendimethalin, atrazine and imazethapyr and modifying their sorption and leaching potential to groundwater.

Influence of grain size, organic carbon and organic matter residue content on the sorption of per- and polyfluoroalkyl substances in aqueous film forming foam contaminated soils - Implications for remediation using soil washing

A soil that was historically contaminated with Aqueous Film Forming Foam (AFFF) was dry sieved into size fractions representative of those produced during soil washing. Batch sorption tests were then conducted to investigate the effect of soil parameters on in situ per- and polyfluoroalkyl substances (PFAS) sorption of these different size fractions: < 0.063 mm, 0.063 to 0.5 mm, 0.5 to 2 mm, 2 to 4 mm, 4 to 8 mm, and soil organic matter residues (SOMR). PFOS (513 ng/g), 6:2 FTS (132 ng/g) and PFHxS (58 ng/g) were the most dominant PFAS in the AFFF contaminated soil. Non-spiked, in situ Kd values for 19 PFAS ranged from 0.2 to 138 L/Kg (log Kd −0.8 to 2.14) for the bulk soil and were dependant on the head group and perfluorinated chain length (spanning C4 to C13). The Kd values increased with decreasing grain size and increasing organic carbon content (OC), which were correlated to each other. For example, the PFOS Kd value for silt and clay (< 0.063 mm, 17.1 L/Kg, log Kd 1.23) were approximately 30 times higher compared to the gravel fraction (4 to 8 mm, 0.6 L/Kg, log Kd −0.25). The highest PFOS Kd value (116.6 L/Kg, log Kd 2.07) was found for the SOMR fraction, which had the highest OC content. Koc values for PFOS ranged from 6.9 L/Kg (log Koc 0.84) for the gravel fraction to 1906 L/Kg (log Koc 3.28) for the silt and clay, indicating that the mineral composition of the different size fractions also influenced sorption. The results here emphasize the need to separate coarse-grained fractions and fine-grained fractions, and in particular the SOMR, to optimize the soil washing process. Higher Kd values for the smaller size fractions indicate that coarser soils are better suited for soil washing.

Modeling fate and transport of pesticides from dryland agriculture using SWAT model

The aim of this study was to understand pesticide fate and transport from dryland agriculture in a major drinking water basin using SWAT and to identify critical source areas in the basin. Hydrological calibration results indicated satisfactory simulation of hydrologic processes within the catchment. Long term average observed sediment values (0.16 ton/ha) were compared with the annual average simulated SWAT outputs (0.22 ton/ha). Generally, the simulated concentrations were higher than the observed values, but the distribution pattern and trends were similar among the months. Average concentrations in water were 0.036 μg/L and 0.006 μg/L for fenpropimorph and chlorpyrifos, respectively. Transfer rates of pesticides from landscape to rivers showed that 0.36% of fenpropimorph and 0.19% of the applied amount of chlorpyrifos were exported to the river. Higher amount of fenpropimorph transport from land to the reach was attributed to its lower Koc (soil adsorption coefficient) value compared to chlorpyrifos. Higher amounts from HRUs were observed in the application month (April) and following month (May) for fenpropimorph, while the months after September showed higher amounts for chlorpyrifos. The specific HRUs (Hydrological Response Units) located in sub-basins 3, 5, 9 and 11 presented highest dissolved pesticide amounts, while HRUs in sub-basins 4 and 11 exhibited highest concentrations for adsorbed pesticides. Best management practices (BMPs) were recommended in critical subbasins to protect the watershed. Despite the limitations, the results demonstrate the potential contributions of modeling in terms of assessing pesticide loadings, critical zones and application timing.

Impact of biochar coexistence with polar/nonpolar microplastics on phenanthrene sorption in soil

Microplastics and biochar normally coexist in soil. In this study, two microplastics of different polarities (nonpolar polyethylene (PE) and polar polybutylene adipate-co-terephthalate (PBAT)) and two wheat straw biochars produced at 400 (W4) and 700 °C (W7) were selected to investigate the sorption behaviors of phenanthrene in soil where microplastics and biochar coexisted. The results showed that the presence of PE more significantly weakened the adhesion of soil particles onto biochar than the presence of PBAT. Meanwhile, the presence of biochar enhanced the soil particle attachment on the microplastic surface. As a result, the sorption behavior of phenanthrene was significantly different in soil where biochar coexisted with microplastics of different polarities. The Koc values of PE-biochar-soil mixtures at Ce= 0.005 Cs were up to 42 % lower than those of PBAT-biochar-soil mixtures, which is related to lower micropore area of particles isolated from the former. However, at Ce = 0.05 Cs and 0.5 Cs, the Koc values of PE-biochar-soil mixtures were up to 1.4 times higher than those of PBAT-biochar-soil mixtures because of a more significant reduction in biochar surface polarity when it coexisted with nonpolar PE.

Experimental Data and Modeling for the Adsorption/Desorption of Tetracycline and Diclofenac on the Agricultural Soils

The adsorption-desorption characteristics of tetracycline and diclofenac onto two different agricultural soils (S1 and S2) were investigated using the batch equilibrium method. The adsorption experiments were used to optimize the two variable parameters (contact time (5-120 min), initial pollutant concentration (5-300 mg/L)) on the adsorption of tetracycline and diclofenac. The adsorption kinetics for tetracycline and diclofenac onto soil are well described by a bi-exponential adsorption model characterized by fast and slow adsorption rates. Non-linear adsorption curves fitted well to the Langmuir, Freundlich and Temkin equations. The maximum adsorption capacity (qm) of tetracycline and diclofenac onto the soils S1 and S2 were calculated to be 55.90 mg/g, 41.92 mg/g, 26 mg/g and 6.42 mg/g, respectively. Kd, Koc, foc and qa values were calculated. The adsorption efficiency of tetracycline and diclofenac by the soils S1 and S2 was over 97%. The Kd parameters for the adsorption of tetracycline and diclofenac onto the soils S1 and S2 were found to be 3537 L/kg, 654 L/kg, 1669 L/kg and 3105 L/kg, respectively. The reversibility of the adsorption process was evaluated by desorption experiments using different concentrations of HDTMA and Triton-x surfactants. The desorption rates were higher for diclofenac than for tetracycline.