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Protecting natural water resources is al the farefront af agroecosystem sustainability. The intensification of agricultural activity ineludes using pesticides for crop protection, but pesticides also have associated potential environmental risks. Pesticides can contaminate soils, and pesticide runoff and leaching can impact surface and groundwater quality. Terbuthylazine and 2-methyl-4-chlorophenoxyacetic acid (MCPA) are common herbicides used in olive agroecosystems in Southern Spain. Both terbuthylazine and MCPA are mobile and have a high risk as a water contaminate. Developing low-cost, effective adsorbents that sequester surp lus applied pesticides not utilized by the target may reduce the potential contamination risk. Biochars, carbon-rich materials created by heating biomass in a lowoxygen environment have been shown to have a high capacity to sorb organic compounds. In this work, the terbuthylazine and MCPA sorption properties of a biochar sourced from agricultural, garden, and sustainable forestry wastes are investigated. Sorption results and cost efficiency will be discussed. Biochar sourced from agricultural waste can be a low-cost sustainable strategy to reduce pesticide leaching and runoff, decreasing the risk of groundwater and surface water contamination.

Chirality has received progressive attention in the field of pesticides. Enantiomers of chiral pesticides have identical physicochemical properties but, commonly, they exhibit stereoselective response with chiral host systems and, therefore, enantioselectivity against the target pest. Despite this, approximately 30% of the pesticides in current use are formulated as mixtures of enantiomers or racemic mixtures. This has engendered new environmental problems, which demand exhaustive knowledge regarding the enantioselectivity of the processes that chiral pesticides may undergo in the soil environment. Changes in the enantiomer composition of chiral pesticides are caused mainly by biological interactions and, consequently, factors affecting the biodegradation of pesticides can also alter the enantioselectivity of the biotransformation of chiral pesticides in soils. Accordingly, soil parameters such as pH, redox conditions, texture, or agronomic practices have been reported to indirectly influence the final enantioselective behavior of these pesticides in soils, although there is limited knowledge in this regard. Hence, predicting the environmental behavior of chiral pesticides in soil turns challenging. This chapter summarizes the most recent enantioselective studies on chiral pesticide transfer and transformation processes in soils. Future research needs scientific foundations to establish under which agricultural and environmental conditions it is appropriate to replace racemic chiral pesticide mixtures with the biologically active purified enantiomers, the underlying mechanisms of enantioselective interactions, and the relationships between the soil microbial diversity and the biotransformation of chiral pesticides, which remain largely unknown. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.

An important issue regarding the presence of pesticides and other organic pollutants in agricultural soils relates to their mobility, which may imply surface and groundwater contamination risks. Soil application of sorbents that increase the retention capacity can be an excellent strategy to reduce the dispersion of organic contaminants in the environment. Biochar is a sustainable carbon-rich product prepared by pyrolysis of biomass that has been proposed as a soil amendment due to its great sorption capacity for organic compounds. Furthermore, biochar has been proven to enhance CO2 sequestration, increase water retention, and supply nutrients. However, once in the soil, biochar undergoes biogeochemical changes with residence time (aging) that may alter its physicochemical properties and modify its sorption capacity. Therefore, research on biochar aging in the field and its simulation in laboratory experiments is of great interest. In this work, the sorption of the pesticide ethofumesate (ETFM) and the antibiotic of veterinary use sulfamethoxazole (SFMX) in an agricultural soil with low retention capacity amended with a commercial wood-derived biochar was assessed. In addition, the possible change of biochar sorption capacity over time was studied, ssimulating aging in the field by incubating the unamended soil and the soil amended with biochar (5%) at 40 ºC and a soil water content of 30% for 48 days. At selected times, the incubated soils were sampled and the sorption of the two compounds was determined by the batch technique. To evaluate sorption over time, 24 hdistribution coefficients, Kd (l/kg), were determined at each sampling time from the expression Kd = Cs/Caq, where Cs (mg/kg) is the amount sorbed and Caq (mg/l) is the concentration remaining in the aqueous phase. The results showed that the addition of biochar to the soil markedly increased the sorption of both ETFM (Kd = 168 ± 40 l/kg) and SFMX (Kd = 3.89 ± 0.58 l/kg) in comparison with the unamended so

Biochar is a nanoengineered sorbent proposed to control the contamination derived from the presence of residual concentrations of sulfonamides in soil. In this work, we evaluated the sorption of sulfanilamide (SFA) in commercial biochar (BC) produced at 500 °C from oak hardwood (Quercus ilex) and its analog activated with 2% (w/w) Fe (BC-Fe). Subsequently, the effect on dissipation and transport of SFA in untreated soil and soil treated with BC and BC-Fe was also assessed. Laboratory batch studies revealed that BC-Fe increased the sorption of SFA as compared to the pristine BC with Kd of 278 and 98 L/kg, respectively. The dissipation of SFA in either untreated soil or soil treated with BC or BC-Fe was similar, displaying half-lives ranging between 4 and 6.4 days. Conversely, the concurrent determination of sorption during the incubation experiment showed that lower amounts of SFA in solution at the beginning of the experiments were bioavailable in BC-Fe-treated soil when compared to the rest of the treatments shortly after application. Leaching column studies confirmed the amendment’s capability to bind the SFA compound. Therefore, the decrease in bioavailability and movement of SFA in treated soils suggest that biochar soil application can reduce SFA soil and water contamination. According to our results, BC surface modification after Fe activation may be more appropriate for water decontamination than for soil since there were no significant differences between the two types of biochar when added to the soil. Therefore, these outcomes should be considered to optimize the SFA mitigation potential of biochar.

BACKGROUND Allelochemicals can act as biopesticides or enhance the action of synthetic pesticides. In this work, we assessed the bioavailability of the allelochemical coumarin in soils amended with fresh or field-aged biochars (BCs). The fresh BC from oak wood (Fresh BC) was prepared at 550 degrees C and was buried for aging in two different places: in a sandy loam soil in Spain for 15 months (Aged BC_1) and a sandy loam soil in USA for six months (Aged BC_2). RESULTS Sorption experiments showed that all BCs were able to increase the affinity of soil towards coumarin, with the distribution coefficient following the order: unamended soil < Aged BC_2-amended soil < Aged BC_1-amended soil < Fresh BC-amended soil. All biochars ensure greater persistence of coumarin and the effect was more pronounced at high chemical dose (10 mg kg(-1)). Conversely, leaching studies in soil columns revealed that BCs were able to maintain coumarin within the first 5 cm of top-soil with total amount extracted ranging between 17% and 22% for BC-amended soil and <1% for unamended soil. Leaching was only observed when coumarin was added at the highest rate. Likewise, the bioefficacy of coumarin against lettuce was enhanced only at 10 kg ha(-1)with BC-amended soil. CONCLUSIONS Biochar application to agricultural soils is a promising tool for the management of natural compounds with potential use as biopesticides, such as coumarin, because it increases sorption, persistence and, in some cases, bioefficacy. The results reveal that this effect still persists with aging of BC in soils.

Biochar (BC) has been proposed as cost-effective and environmentally-friendly alternative to mitigate soil contamination produced by several veterinary antibiotics, such as sulfonamides. The intensification of agricultural and livestock activity has increased the environmental problems caused by their use. Although the sorptive behavior of biochars depends on the original feedstock and pyrolysis temperature, activation processes are being developed to increase the sorption by low-temperature biochars, which are the most suitable for soil fertility applications but have relatively low sorption capacities. In this study, we assessed the sorption, dissipation, and leaching of the antibiotic sulfanilamide in soil treated with low-temperature biochar and activated-biochar. The biochar used was a commercial wood biochar prepared at 500 ºC which was treated with KOH, NaOH, oxalic acid and FeNO3 at 10% (w/w) to improve its affinity towards the organic compound. The sorption capacities of the untreated and treated biochars were assessed in batch studies and revealed that only BC treated with FeNO3 (BC-Fe) noticeably increased sulfanilamide sorption. In the presence of soil, the dissipation of the antibiotic was similar in either untreated soil or soil treated with BC and BC-Fe added at 2 % (w/w). However, the simultaneous determination of sorption during the incubation experiment indicated that lower amount of sulfanilamide in the soil solution was bioavailable in soil treated with BC than in BC-Fe treated soil. The leaching column study indicated the ability of BC and BC-Fe to immobilize the compound in the first 5 cm of soil. Therefore, the decrease in bioavailability and movement of sulfanilamide in amended soils suggests that biochar can reduce contamination of water and soil due to this type of compounds. These results should be considered in order to optimize the performance of biochar-amended soils.

The application of biochar as a soil amendment can increase concentrations of soil organic matter, especially water-extractable organic substances. Due to their mobility and reactivity, more studies are needed to address the potential impact of biochar water-extractable substances (BWES) on the sorption of herbicides in agricultural soils that are periodically flooded. Two paddy soils (100 and 700 years of paddy soil development), unamended or amended with raw (BC) or washed biochar (BCW), were used to test the influence of BWES on the sorption behavior of the herbicides azimsulfuron (AZ) and penoxsulam (PE). The adsorption of AZ to biochar was much stronger than that to the soils, and it was adsorbed to a much larger extent to BC than to BCW. The depletion of polar groups in the BWES from the washed biochar reduced AZ adsorption but had no effect on PE adsorption. The adsorption of AZ increased when the younger soil (P100) was amended with BC and decreased when it was amended with BCW. In P700, which has lower dissolved organic carbon (DOC) content than P100, the adsorption of AZ increased regardless of whether biochar was raw or washed. The adsorption of PE slightly decreased when P100 was amended with BC or BCW and slightly increased when P700 was amended with BC or BCW. In order to evaluate compositional differences in the biochar and BWES before and after the washing treatment, we performed solid-state 13C NMR spectroscopy of BC and BCW, and high resolution mass spectrometry of BWES. Our observations stress the importance of proper consideration of soil and biochar properties before their incorporation into paddy soils, since biochar may reduce or increase the mobility of AZ and PE depending on soil properties and time of application. © 2019

A local low value bentonite from Southern Spain (Raw Bentonite), previously decarbonated (Bent), was modified to improve its pesticide adsorption capacity with Fe 3+ , hexadecyltrimethylammonium (HDTMA) and the biopolymer chitosan (CH). Adsorption of pesticides on powdered samples showed that Fe 3+ and HDTMA were appropriate modifiers for this purpose. The modification was optimized by saturation with Fe 3+ (Bent-Fe) and hexadecyltrimethylammonium (Bent-HDTMA) and the obtained adsorbents were characterized by several physicochemical techniques (X-ray diffraction, thermogravimetric analysis, X-ray fluorescence, physisorption of N 2 ). Their adsorption capacity to remove three widely used pesticides in Andalusian crops (terbuthylazine, tebuconazole and MCPA) from water was assessed and compared with the commercial organoclay Cloisite® 10A (Clo10). The modified bentonites adsorbed the selected pesticides in a percentage ranging from 30 to 100%, whereas sorption on Clo10 ranged from 30 to 90%. For their possible use as filtering beds, Bent-HDTMA, Bent-Fe and Clo10 were granulated by using three different binders (colophony resin and carnauba and bee waxes) at three different mixing ratios and the water resistance and pesticide adsorption of the granules were measured. Results showed that the granulation process did not alter the pesticide adsorption capacity of the powdered modified bentonites, and both waxes granules (carnauba and bee wax) showed better behavior than resin granules. In this work, we succeeded in the preparation of granulated adsorbents derived from a low cost material with similar behavior against a high purity smectite (precursor of Cloisite® 10A). This raises an alternative for this waste material to be used in filter systems for removing pesticides from contaminated water. © 2019 Elsevier B.V.

Objectives • Preparation of two complexes of terbuthylazine (TA) based on biochar (BC) obtained from olive oil mill waste at two different pyrolysis temperatures (350 and 700ºC); • Assessment of persistence, leaching and bioefficacy of TA applied to soil as BC-TA complexes. Highlights • TA slowly releases from BC-TA formulations when applied to soil; • TA degrades equally in all treatments; • Leaching of TA is reduced and retarded when the herbicide is applied as BC-TA formulations as compared with the application of the herbicide in a readily available form; • Bioassays demonstrated similar phytotoxicity of the prepared formulations in controlling the growth of Lepidum sativum respect to the free-TA.

In this study, we assessed the sorption, dissipation, and leaching of the herbicide mesotrione in soil amended with fresh and field-aged biochars, when added to the soil. The aging process was performed by burying the fresh biochar at 10 cm depth in three soils located in different points across the USA [Wisconsin (ABC_WI), Idaho (ABC_ID), and South Carolina (ABC_SC)] for six months. ABC_ID and ABC_SC slightly increased the sorption of mesotrione in soils, whereas ABC_WI removed greater amounts of herbicide from the solution. This was attributed to differences in water-soluble components and metal content of this aged biochar. Consequently, the persistence of the herbicide in the amended soils with fresh biochar and ABC_ID and ABC_SC were similar to that in unamended soils, while ABC_WI slightly increased mesotrione half-life. Differences between treatments were detected in leaching studies although no direct relationship with the dissipation batch studies was observed. Mesotrione leaching could not be detected in soil columns amended with ABC_WI and was high for the rest of treatments. The outcomes from this work demonstrate that temporal variability of biochar sorption capacities due to soil exposure can occur altering mesotrione’s behavior in biochar-amended soils.

Activation treatments are often used as a means of increasing a biochar’s sorption capacity for agrochemical compounds but can also provide valuable insight into sorption mechanisms. This work investigates the effects of H2O2 activation on a low-temperature (350 °C) grape wood biochar, evaluates subsequent changes to the removal efficiency (RE) of cyhalofop and clomazone, and elucidates potential sorption mechanisms. Activation by H2O2 decreased the biochar pH, ash content, and C content. Additionally, the biochar O content and surface area increased following activation, and Fourier transform infrared spectroscopy (FTIR) data suggested a slight increase in surface O groups and a decrease in aliphatic C. Cyhalofop RE significantly increased following activation, while clomazone RE was unchanged. The increased sorption of cyhalofop was attributed to pH effects and charge-based interactions with biochar O moieties. Results from this study suggest that H2O2 activation treatments on low-temperature biochars may improve the removal of organic acid herbicides but are of little value in optimizing the removal of polar, non-ionizable herbicides.

Como una posible estrategia para reducir la cantidad del herbicida terbutilazina que puede ser liberado a las aguas cercanas a zonas olivareras, se han realizado varios experimentos para determinar la capacidad de algunas arcillas para actuar como soporte de dicho herbicida en formulaciones de liberación controlada (FLC), así como comparar su efecto respecto a las formulaciones comerciales (FC). Se han elegido diferentes arcillas para realizar dichos estudios : una arcilla modelo, natural y modificada (SWy y SWHDTMA), una arcilla blanca de un yacimiento andaluz (Bailén) de bajo valor económico (CTI) y tres organoarcillas comerciales (SD-1 , SD-3 y CI-30). Los experimentos realizados han Incluido isotermas de adsorción-desorción. estudio de lixiviación en columnas empaquetadas con un suelo dedicado a olivar y bioensayos para determinar la efectividad biocida de las FLC. Los valores de Kf obtenidos a partir de la isoterma de adsorción-desorción indícan una mayor adsorción de terbutilazina a SD-3 (1205). SD-1 (465) y CI-30 (476) frente a las arcillas SW (108), SWHOTMA (230) Y CTI (28), aunque los porcentajes de desorción de terbutilazina son mayores en las arcillas comerciales (37.5%) respecto a las arcillas modelo y CTI (29%). El experimento de lixiviación en columnas y los bioensayos se han realizado con diferentes FLC: mezcla física (MF), complejo débil (CD) y complejo fuerte (CF) con distintos porcentajes deterbutilazina (4% para SW, SWHOTMA y al 20% para SDO-1, SD-3, y CL-30). La lixiviación de terbutilazina en suelo se vio reducida tanto en las FLC al 4% (52%) como las FLC al 20% (28%) respecto a la FC (86%). La reducción de la liberación de terbutilazina en las FLC no afectó a la capacidad biocida de este compuesto al presentar una efectividad similar a la FC medida como biomasa de Chenopodium álbum (0.1-0.15 9 para FLC y 0.13 9 para FC), lo que implica que el uso de FLC de terbutilazina, incluso cuando se utilizan como soporte arcillas locales y de bajo valor c

Polycyclic aromatic hydrocarbons (PAH) have become a threat for the conservation of wetlands worldwide. The halophyte Spartina densiflora has shown to be potentially useful for soil phenanthrene phytoremediation, but no studies on bacteria-assisted hydrocarbon phytoremediation have been carried out with this halophyte. In this work, three phenanthrene-degrading endophytic bacteria were isolated from S. densiflora tissues and used for plant inoculation. Bacterial bioaugmentation treatments slightly improved S. densiflora growth, photosynthetic and fluorescence parameters. But endophyte-inoculated S. densiflora showed lower soil phenanthrene dissipation rates than non-inoculated S. densiflora (30% below) or even bulk soil (23% less). Our work demonstrates that endophytic inoculation on S. densiflora under greenhouse conditions with the selected PAH-degrading strains did not significantly increase inherent phenanthrene soil dissipation capacity of the halophyte. It would therefore be advisable to provide effective follow-up of bacterial colonization, survival and metabolic activity during phenanthrene soil phytoremediation. © 2019 Elsevier Inc.

The ability of biochars to sorb pesticides has been widely studied due to the potential effects on their fate in soil and interest in the adoption of biochar as a "low-cost" soil amendment. However the sorption capacity of biochars can be altered with time affecting pesticide behavior in soils. The purpose of this study was to assess the sorption degradation and leaching of the herbicide mesotrione in soil amended with fresh and aged biochar when added to the soil at a rate of 2% (w/w). The aging process was performed by burying the fresh biochar (BCf) at 10 cm in three soils located in different sites in USA [Wisconsin (BCW) Colorado (BCC) and South Caroline (BCSC)] for six months. Biochars slightly increased the sorption of mesotrione in soils. Only Wisconsin aged biochar removed greater amounts of herbicide from the solution which was attributed to water-soluble components of this biochar. As a consequence neither the fresh biochars nor Colorado and South Caroline aged BC had impact on mesotrione persistence while Wisconsin aged BC slightly increased mesotrione half life. Similar effect was observed in leaching experiments which was null for Wisconsin aged biochar and high for the rest of the treatments. The outcomes from this work demonstrate temporal variability of biochar sorption capacities due to soil exposure which can alter the behavior of mesotrione. These effects should be considered in order to optimize the performance of this herbicide in biochar-amended soils with time

Knowledge of long-term pesticide behavior in biochar (BC) amended soil is still contradictory. In this work, we compared the sorption of three highly persistent and ionizable pesticides [two anionic (imazamox and picloram) and one weak base (terbuthylazine)] on both fresh and field-aged BC as well as on a soil amended with these biochars. The aging process was performed by burying the biochar at 10 cm in a silt loam soil [Upper Midwest USA (Wisconsin)] for six months. Field aged BC removed the three pesticides from solution to a higher extent (>85%) than the fresh BC (<16%). This removal was attributed to water-soluble components on the biochar. Laboratory incubation experiments demonstrated that dissipation in soil and biochar mixtures were both a function of pesticide and biochar type. The amounts of soil extractable (i.e, bioavailable) pesticide were inversely related to the extent of sorption. Similar dissipation and sorption of imazamox was observed in unamended and BC-amended soils. Terbuthylazine dissipated similarly in all treatments, but sorption increased with incubation time in the aged BC-amended soil. Conversely, picloram dissipated to a higher extent in aged BC-amended soil when compared to unamended or fresh BC-amended soil. This work demonstrates temporal variability of biochar sorption capacities due to soil exposure, which alters the efficacy and bioavailability of soil applied pesticides

Background and aims: Myxodiaspores have been shown to enhance soil-seed contact and improve soil stability. We aim to demonstrate the effect of myxodiaspory on the stability of soil aggregates and gain insight on the nature of bonds. Methods: Mucilage extracted from chia (Salvia hispanica L.) fruits after hydration was mixed with three soils (sandy-loam, loam, clay loam), incubated and tested at different times up to 30 days. We measured aggerate stability by wet sieving and the dynamics of soil CO2 evolution. SEM imaging and 13CPMAS spectroscopy of mucilage were performed in order to infer mechanisms of soil stabilization. Results: The incorporation of mucilage resulted in a dose- and soil-dependent rise in aggregate stability. The dose of 2% mucilage overcame textural effects on soil aggregate stability by providing a 2.3-fold stability increase in the loam and clay-loam and a 4.9-fold increase in the sandy-loam compared to control. The effect persisted after 30 days in spite of C losses due to soil respiration. Mechanisms of soil bonding analogous to xanthan can be inferred from SEM imaging and 13C–CPMAS, since the mucilage was identified as a biopolymer containing 93.39% carbohydrates and 22.02% uronic acids. Conclusions: We demonstrate that mucilage extruded by hydrated diaspores strongly increases soil aggregate stability. This represents a potentially important ecosystem service provided by myxodiasporous crops during germination. Our findings confirm potential applications of mucilage from myxodiaspores as natural soil stabilizers.

[EN]: The main objective of the development of clay materials that immobilize soil applied pesticides is the minimization of leaching losses that could lead to episodes of argricultural contamination of water. In this study, the modification of a low-cost natural clay will be optimized in order to increase the adsorption capacity for pesticides and therefore their immobilization in the soil. For this, natural clay supplied by Centro Tecnológico Innovarcilla (CTI) was modified by saturation at different initial concentrations of Fe3+ (CTI-Fe) and hexadecyltrimethyllammonium (CTI-HDTMA). In addition, for comparative purposes we used commercial clay, Cloisite 10A® (CL). For the granulation, carnauba wax, bee wax and resin were used in different amounts as binders. The tests of water resistance on granules showed good behaviour. Pesticide adsorption experiments concluded that wax granulates (carnauba and bee wax) showed higher percentages of adsorption than granules made with resin. These results could work as a preliminary study for the possible use of the granules of these modified clays for soil decontamination, [ES]: El desarrollo de materiales de tipo arcillosos que inmovilicen los plaguicidas aplicados en el suelo, tiene como principal fin la minimización de pérdidas por lixiviación que podría desembocar en episodios de contaminación agrícola en el agua. En este trabajo se busca optimizar la modificación de una arcilla natural de bajo coste suministrada por el Centro Tecnológico Innovarcilla conocida como Arcilla Blanca de Bailén (CTI), con el fin de aumentar su capacidad de adsorción de plaguicidas y por tanto su inmovilización en el suelo. De este modo, la CTI fue modificada mediante la saturación a distintas concentraciones iniciales de Fe3+ (CTI-Fe) y de HDTMA (CTI-HDTMA). Además, con fines comparativos, se utilizó una arcilla comercial, Cloisite® 10A (CL). Para la granulación se usaron como aglomerantes cera carnauba, cera de abeja y resina en diferentes cantidades. Los ensayos de resistencia de los gránulos en agua mostraron buen comportamiento. Los resultados de los experimentos de adsorción de los plaguicidas en las arcillas sin granular y granuladas, concluyeron que ambas ceras mostraron porcentajes de adsorcion superiores a los alcanzados en los gránulos preparados con resina. Estos resultados pueden servir como estudio preliminar para el posible uso de los granulados de estas arcillas modificadas en la descontaminación de suelos

BACKGROUND Biochar, a carbon‐rich product of biomass pyrolysis, could limit glyphosate transport in soil and remediate contaminated water. The present study investigates the sorption/desorption behavior of glyphosate on biochars prepared from different hardwoods at temperatures ranging from 350 to 900 °C to elucidate fundamental mechanisms. RESULTS Glyphosate (1 mg L−1) sorption on biochars increased with pyrolysis temperature and was highest on 900 °C biochars; however, total sorption was low on a mass basis (<0.1 mg g−1). Sorption varied across feedstock materials, and isotherms indicated concentration dependence. Biochars with a greater fraction of micropores exhibited lower sorption capacities, and specific surface groups were also found to be influential. Prepyrolysis treatments with iron and copper, which complex glyphosate in soils, did not alter biochar sorption capacities. Glyphosate did not desorb from biochar with CaCl2 solution; however, up to 86% of the bound glyphosate was released with a K2HPO4 solution. CONCLUSION Results from this study suggest a combined impact of surface chemistry and physical constraints on glyphosate sorption/desorption on biochar. Based on the observed phosphate‐induced desorption of glyphosate, the addition of P‐fertilizer to biochar‐amended soils can remobilize the herbicide and damage non‐target plants; therefore, improved understanding of this risk is necessary

Typically, biochar has been assumed to increase total water content of the soil system and thereby positively influence plant-soil moisture hydraulics. In this work, we focused on water's interaction with micro-pores (<2 nm) and its influence on water availability. In other words, the main question was if the driving force of water's behavior was the physics or chemistry of biochar pores. The temporal scale of liquid water entry into biochar's pore network is very complex, with observed bubbling occurring days, weeks, and even months after a piece of biochar is immersed under water at ambient conditions. Elevated temperature biochar typically has a positive heat of immersion measured calorimetrically, whereas the calculated BET energy of sorption from a water sorption isotherm typically decrease with production temperatures. To further complicate matters, different pieces of biochar interact differently with water even though the entire batch was created in the same reactor at the same time and after liquid water exposure the physical structure of biochar is irreversibly altered, sometimes negligible other times catastrophically. Nevertheless, based on the estimations of diffusion coefficients in biochar from drying curve analyses, pore surface moieties do reduce the effective diffusivity of water vapor in biochar. Contrary to the rule of thumb in soil physics, where higher gas filled porosity correlates with higher soil moisture holding capacities, our results indicate that biochar's water sorption rate and capacity is actually reduced at ambient conditions by an increase in microporous volume. Thereby, biochar's hydrophobic behavior is partly due to the entrapment of gas within the air-filled porosity which prevents liquid water's entry, even though these biochars possess elevated gas phase sorption capacities (e.g., BET N2/CO2 surface areas).

The ability of biochars to bind various organic compounds has been widely studied due to the potential effects on pesticide fate in soil and interest in the adoption of biochar as a “low-cost” filter material. However, the sorptive behaviors of biochars are extremely variable and much of the reported data is limited to specific biochar-chemical interactions. The lack of knowledge regarding biochar sorption mechanisms limits our current ability to predict and optimize biochar’s use. This work unveils mechanistic drivers of organic pesticide sorption on biochars through targeted alteration of biochar surface chemistry. Changes in the quantity and type of functional groups on biochars and other black carbon materials were achieved through treatments with H2O2, and CO2, and characterized using Fourier transform infrared spectroscopy and scanning electron microscope (SEM/EDX). The sorption capacities of these treated biochars were subsequently measured to evaluate the effects of different surface moieties on the binding of target herbicides cyhalofop acid ((R)-2-[4-(4-cyano-2-fluorophenoxy) phenoxy]propionic acid) and clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-1,2-oxazolidin-3-one). Sorption of both herbicides on the studied biochars increased following H2O2 activation; however, the influence of the H2O2 activation on sorption was more pronounced for cyhalofop acid (pKa = 3.9) than clomazone, which is non-ionizable. Increased cyhalofop acid sorption on H2O2 treated biochars can be attributed to the increase in oxygen containing functional groups as well as the decrease in biochar pH. In contrast, CO2 activation reduced the sorption of cyhalofop acid compared to untreated biochar. FTIR data suggest the reduced sorption on CO2 –treated biochar was due to the removal of surface carboxyl groups, further supporting the role of specific functionality in the sorption of ionizable herbicides. Results from this work offer insight into the mechanisms of sorption and provid

El biocarbón (BC) es un material rico en carbono obtenido a partir de biomasa mediante un proceso de pirólisis, que se ha demostrado puede ser buen adsorbente de Contaminantes orgánicos y metales pesados, capacidad que depende principalmente de las condiciones de preparación y materia prima inicial. Este estudio tiene como objetivo la evaluación de dos biocarbones, procedentes de dos materias primas residuales de la industria oleolícola olivarera, como adsorbentes de bajo coste para eliminar contaminantes en aguas. Se prepararon dos biocarbones a partir de dos residuos de almazara, alperujo (BCA) y orujo (BCO), mediante pirólisis a 550 Cº y atmósfera limitada de O2 y se seleccionaron contaminantes de origen diverso (agrícola e industrial) y diferentes características fisicoquímicas: a) cuatro contaminantes orgánicos, tres plaguicidas (MCPA, tebuconazol y terbutilazina) y una dioxina (dibenzofurano) y b) dos contaminantes inorgánicos los metales pesados Cu y Zn. La capacidad de adsorción de estos BCs se estudió mediante experimentos de adsorción a una sola concentración de contaminante, que se analizaron respectivamente por HPLC e ICP-MS. Los resultados demuestran que ambos biocarbones resultaron ser más eficientes para la eliminación de metales pesados y del contaminante altamente hidrófobo dibenzofurano, que para los contaminantes orgánicos polares (plaguicidas) y aunque mostraron poca diferencia en su capacidad de adsorción, siempre fue ligeramente superior la del BCA, a pesar de tener la menor superficie específica.

Biochar (BC), solid biomass subjected to pyrolysis, can alter the fate of pesticides in soil. We investigated the effect of soil amendment with several biochars on the efficacy of two herbicides, clomazone (CMZ) and bispyribac sodium (BYP). To this aim, we evaluated CMZ and BYP sorption, persistence, and leaching in biochar-amended soil. Sorption of CMZ and BYP was greater in soil amended with BC produced at high temperature (700 °C). Significant sorption of the neutral CMZ herbicide also occurred in amended soil with BC prepared at low temperature (350 and 500 °C). For both herbicides, desorption possessed higher hysteretic behavior in soil amended with BC made at 700 °C (pyrolysis temperature). Dissipation of CMZ was enhanced after addition of BCs to soil, but no correlation between persistence and sorption was observed. Persistence of BYP was up to 3 times greater when BC made at 700 °C was added to soil. All BCs suppressed the leaching of CMZ and BYP as compared to the unamended soil. Amendment with 700 °C BC inhibited the action of CMZ against weeds, but 350 and 500 °C BCs had no such effect when added to soil. BYP activity was similar to that exhibited by unamended soil after the addition of 700 °C BC. From these results, biochar amendments can be a successful strategy to reduce the environmental impact of CMZ and BYP in soil. However, the phytotoxicity of soil-applied herbicides will depend on BC sorption characteristics and the pesticide's chemical properties, as well as the pesticide application timing (e.g., pre- or postemergence). According to our results, proper biochar screening with intended pesticides in light of the application mode (pre- or postemergence) is required prior to use to ensure adequate efficacy.

The potential use of allelopathic and signaling compounds as environmentally friendly agrochemicals is a subject of increasing interest, but the fate of these compounds once they reach the soil environment is poorly understood. This work studied how the sorption, persistence, and leaching of the two enantiomers of the phytohormone abscisic acid (ABA) in agricultural soil was affected by the amendments of two organoclays (SA-HDTMA and Cloi10) and a biochar derived from apple wood (BC). In conventional 24-h batch sorption experiments, higher affinity toward ABA enantiomers was displayed by SA-HDTMA followed by Cloi10 and then BC. Desorption could be ascertained only in BC, where ABA enantiomers presented difficulties to be desorbed. Dissipation of ABA in the soil was enantioselective with S-ABA being degraded more quickly than R-ABA, and followed the order unamended > Cloi10-amended > BC-amended > SA-HDTMA-amended soil for both enantiomers. Sorption determined during the incubation experiment indicated some loss of sorption capacity with time in organoclay-amended soil and increasing sorption in BC-amended soil, suggesting surface sorption mechanisms for organoclays and slow (potentially pore filling) kinetics in BC-amended soil. The leaching of ABA enantiomers was delayed after amendment of soil to an extent that depended on the amendment sorption capacity, and it was almost completely suppressed by addition of BC due to its irreversible sorption. Organoclays and BC affected differently the final behavior and enantioselectivity of ABA in soil as a consequence of dissimilar sorption capacities and alterations in sorption with time, which will affect the plant and microbial availability of endogenous and exogenous ABA in the rhizosphere.

Azimsulfuron is an acidic herbicide with a high water solubility which makes risk of groundwater contamination a concern. Various wood based biochars produced at different pyrolysis temperatures were characterized along with their sorption capacity for the herbicide azimsulfuron. In addition, we compared sorption on biochars with sorption on mineral sorbents such as clay minerals and iron oxides. In biochar formed at high temperatures (500 °C and 700 °C), FT-IR studies confirmed the increase in aromaticity. Scanning electron microscope (SEM) images of the biochars showed differences in the macroporous structure and lower size pores at higher temperatures. SSA (Specific Surface Area) of the biochars increased with pyrolysis temperature and, for all different biochars, this resulted in higher sorption of azimsulfuron. In the case of mineral sorbents, sorption is not related to SSA. Higher sorption is observed in a montmorillonite, of lower SSA, than in mixture of clay minerals with 30% smectite (w/w). On the contrary as with the clays, sorption on the two iron oxyhydroxides increased with SSA. Desorption studies showed hysteresis. Leaching studies showed no effect on azimsulfuron retention on soil column amended with apple wood biochar, while a reduction of azimsulfuron in leachates in soil columns amended with the modified montmorillonite and alder wood biochar (500 °C). Total retention was shown for alder wood biochar.