Soil Sorption Research Articles

An integrated remediation approach using combinations of biochar, Rhizobium leguminosarum, and Vigna radiata for immobilizing and dissipating cadmium contaminants from the soil-mustard plant system.

Cadmium (Cd) contamination of soils is an environmental concern, as cadmium harms food crops and can therefore impact human health. The use of combinations of biochar (seeded with Rhizobium leguminosarum) and Vigna radiata (as an intercrop) has the potential to reduce the mobilization of Cd from soil via mustard plants (Brassica juncea). Mustard plants are grown as a food and oil production crop that is consumed worldwide. However, this plant has the property of hyperaccumulation; thus, it bioaccumulates Cd in its tissues, which in turn, if eaten, can become part of the human food chain. Hence, reducing Cd bioaccumulation in mustard plants is crucial to making these plants a reliable and safe source of food for consumption. To improve soil sorption capacity and immobilization efficiency, biochar (in the form of wheat husk) was mixed with R. leguminosarum and intercropped (using V. radiata) with mustard plants for further investigation. Sampling was performed at an early growth stage (i.e., at 30 days) and at maturity (i.e., at 60 days) to determine the impact of Cd on a plant's morphophysiological attributes. Data were analyzed in two ways: first by analysis of variance (ANOVA) and then by the post hoc Tukey's honestly significant difference (HSD) test. The statistical analysis concluded that combinations effectively improved plant traits by 65%-90% in the early growth stage and by 70%-90% in the maturity stage. The T6 treatment combination [i.e., biochar+R. leguminosarum+V. radiata (BC+RL+VR)] provided the most effective results in terms of growth, biomass, pod yield, and pigmentation content. In addition, this combination reduced the translocation of Cd in mustard plants by 70%-95%. The combination of BC+RL+VR effectively reduced Cd contamination of mustard tissue and provided a suitable growing environment for the plants. A post-harvesting soil analysis using X-ray diffraction (XRD) found that Cd was undetectable in soil. This provides clear confirmation that these approaches can lead to Cd soil remediation. Moreover, this study provided insight into the responses of different morphophysiological attributes of mustard plants to Cd stress and could aid in developing Cd stress tolerance in mustard plants.

Influence of contamination with diesel oil on water sorptivity and hydrophobicity of sandy loam soil

AbstractThis paper shows the changes in water sorptivity (Sw) and hydrophobicity following soil contamination with petroleum hydrocarbons (PHs) under different soil moistures. Laboratory experiments were carried out to verify that contamination with PHs reduces Sw, thus affecting the infiltrability, which in practice influences the field water capacity and the availability of water for plants. Soil water repellency (SWR) was estimated by the repellency index (R) and water drop penetration time (WDPT). The increase in PHs contamination contributed to SWR and caused a significant decrease in Sw. With the decrease in moisture, the water sorptivity of the soil increased, reaching its maximum at 0.12–0.15 cm3 cm−3, which was the threshold value in the case of the analysed soil, and then decreased drastically. The R index and the WDPT revealed a similar trend, inversely related to the level of soil contamination with PHs. The increase in SWR and the accompanying decrease in Sw made the soil less resistant to drought. The total amount of water available to plants in the control soil was 19.04%, whereas contamination with PHs equal to 100 g kg−1 caused a decrease to 6.36%. The almost threefold decrease in the total amount of water has a fundamental influence on increasing the risk of soil drought. The results obtained indicated that the interrelationship presented between the level of contamination with PHs, water sorptivity, SWR and soil moisture are the keys to predicting the environmental effects of contamination with PHs. The obtained results indicate that the undertaken remediation measures aimed at restoring the hydrological function of the soil system should be preceded by an assessment of soil hydrophobicity.

Natural soils in OECD 222 testing — influence of soil water and soil properties on earthworm reproduction toxicity of carbendazim

Soil sorption properties can influence the bioavailability of substances and consequently the toxicity for soil organisms. Current standardised laboratory testing for the exposure assessment of pesticides to soil organisms uses OECD artificial soil that does not reflect the high variation in chemical-physical soil properties found in natural agroecosystems. According to guideline OECD 222, earthworm reproduction tests with Eisenia fetida and the pesticide carbendazim were performed in four natural soils and OECD artificial soil. By using pF 1.6, which ensures a uniformity in actual soil water availability, the control reproduction performance of E. fetida in all natural soils was at the same level as OECD artificial soil. In a principle component analysis, the variation in toxicity between the tested soils was attributable to a combination of two soil properties, namely total organic carbon content (TOC) and pH. The largest difference of 4.9-fold was found between the typical agricultural Luvisol with 1.03% TOC and pH 6.2 (EC10: 0.17 (0.12–0.21) mg a.i. kg−1 sdw, EC50: 0.36 (0.31–0.40) mg a.i. kg−1 sdw) and OECD artificial soil with 4.11% TOC and pH 5.6 (EC10: 0.84 (0.72–0.92) mg a.i. kg−1 sdw, EC50: 1.07 (0.99–1.15) mg a.i. kg−1 sdw). The use of typical agricultural soils in standardised laboratory earthworm testing was successfully established with using the measure pF for soil moisture adjustment. It provides a more application-oriented approach and could serve as a new tool to refine the environmental risk assessment at lower tier testing or in an intermediate tier based approach.

Source apportionment and suitability evaluation of seasonal VOCs contaminants in the soil around a typical refining-chemical integration park in China

Accurate source apportionment of volatile organic compounds (VOCs) in soil nearby petrochemical industries prevailing globally, is critical for preventing pollution. However, in the process, seasonal effect on contamination pathways and accumulation of soil VOCs is often neglected. Herein, Yanshan Refining-Chemical Integration Park, including a carpet, refining, synthetic rubber, and two synthetic resin zones, was selected for traceability. Season variations resulted in a gradual decrease of 31 VOCs in soil from winter to summer. A method of dry deposition resistance model coupling partitioning coefficient model was created, revealing that dry deposition by gas phase was the primary pathway for VOCs to enter soil in winter and spring, with 100 times higher flux than by particle phase. Source profiles for five zones were built by gas sampling with distinct substance indicators screened, which were used for positive matrix factorization factors determination. Contributions of the five zones were 14.9%, 20.8%, 13.6%, 22.1%, and 28.6% in winter and 33.4%, 12.5%, 10.7%, 24.9%, and 18.5% in spring, respectively. The variation in the soil sorption capacity of VOCs causes inter-seasonal differences in contribution. The better correlation between dry deposition capacity and soil storage of VOCs made root mean square and mean absolute errors decrease averagely by 8.8% and 5.5% in winter compared to spring. This study provides new perspectives and methods for the source apportionment of soil VOCs contamination in industrial sites.

Coapplication of water treatment residual and compost for increased phosphorus availability in arable sandy soils

AbstractIntroductionSoil degradation coupled with poor access to organic nutrient resources remains a major constraint in increased crop productivity in sub‐Saharan Africa, thus hindering the continent's efforts in achieving the United Nations' Sustainable Development Goals, particularly goals 1 (end poverty), 2 (zero hunger) and 3 (improve human health). Water treatment residual (WTR), a by‐product of clean water treatment, has been identified as an alternative organic nutrient resource for crop production. However, there are some inconsistences in soil phosphorus (P) dynamics following aluminium WTR (Al‐WTR) application.Materials & MethodsA laboratory experiment was conducted to evaluate the P sorption of a sandy soil amended with 10% Al‐WTR, 10% compost (C) as a quasi‐control, 10% C + 10% Al‐WTR (10% coamendment) and 5% C + 5% Al‐WTR (5% coamendment) under varying levels of pH, particle size and P concentration. We calculated crop P fertilizer requirements under different amendments.ResultsThe results demonstrated that all amendments exceeded the minimum of 0.2 mg P L−1 needed in soil solution at equilibrium to maintain plant growth. However, the maximum P sorption capacity was higher for 10% Al‐WTR single amendment, ranging from 770 to 1000 mg P Kg−1, and from 714 to 1000 mg P Kg−1 and 555 to 909 mg P Kg−1 for 10% and 5% coamendments, respectively, across a range of pH and soil particle size fractions. The coamendments showed a reduction in crop P fertilizer requirements by ranges of 30–60% and 60–70% for the 10% and 5% coamendment levels, respectively, across different pH and particle sizes, relative to 10% Al‐WTR.ConclusionResults show that the use of 5% coamendment in sandy soils increases P availability sufficiently to improve crop yields. The results provide scope for using Al‐WTR coamendments to rebuild soil health in sandy soils in urban agriculture and increase macronutrient provision in crops to support human health.

Effect of pH, surface charge and soil properties on the solid–solution partitioning of perfluoroalkyl substances (PFASs) in a wide range of temperate soils

The pH-dependent soil–water partitioning of six perfluoroalkyl substances (PFASs) of environmental concern (PFOA, PFDA, PFUnDA, PFHxS, PFOS and FOSA), was investigated for 11 temperate mineral soils and related to soil properties such as organic carbon content (0.2–3%), concentrations of Fe and Al (hydr)oxides, and texture. PFAS sorption was positively related to the perfluorocarbon chain length of the molecule, and inversely related to solution pH for all substances. The negative slope between log Kd and pH became steeper with increasing perfluorocarbon chain length of the PFAS (r2 = 0.75, p ≤ 0.05). Organic carbon (OC) alone was a poor predictor of the partitioning for all PFASs, except for FOSA (r2 = 0.71), and the OC-normalized PFAS partitioning, as derived from organic soil materials, underestimated PFAS sorption to the soils. Multiple linear regression suggested sorption contributions (p ≤ 0.05) from OC for perfluorooctane sulfonate (PFOS) and FOSA, and Fe/Al (hydr)oxides for PFOS, FOSA, and perfluorodecanoate (PFDA). FOSA was the only substance under study for which there was a statistically significant correlation between its binding and soil texture (silt + clay). To predict PFAS sorption, the surface net charge of the soil organic matter fraction of all soils was calculated using the Stockholm Humic Model. When calibrated against charge-dependent PFAS sorption to a peat (Oe) material, the derived model significantly underestimated the measured Kd values for 10 out of 11 soils. To conclude, additional sorbents, possibly including silicate minerals, contribute to the binding of PFASs in soil. More research is needed to develop geochemical models that can accurately predict PFAS sorption in soils.

Polyethylene and polypropylene microplastics reduce chemisorption of cadmium in paddy soil and increase its bioaccessibility and bioavailability

Microplastics (MPs) usually coexist with heavy metals (HMs) in soil. MPs can influence HMs mobility and bioavailability, but the underlying mechanisms remain largely unexplored. Here, polyethylene and polypropylene MPs were selected to investigate their effects and mechanisms of sorption-desorption, bioaccessibility and bioavailability of cadmium (Cd) in paddy soil. Batch experiments indicated that MPs significantly reduced the Cd sorption in soil (p < 0.05). Accordingly, soil with the MPs had lower boundary diffusion constant of Cd (C1= 0.847∼1.020) and the Freundlich sorption constant (KF = 0.444–0.616) than that without the MPs (C1 = 0.894∼1.035, KF = 0.500–0.655). X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses suggested that the MPs reduced Cd chemisorption, by covering the soil active sites and thus blocking complexation of Cd with active oxygen sites and interrupting the formation of CdCO3 and Cd3P2 precipitates. Such effects of MPs enhanced about 1.2–1.5 times of Cd bioaccessibility and bioavailability in soil. Almost the same effects but different mechanisms of polyethylene and polypropylene MPs on Cd sorption in the soil indicated the complexity and pervasiveness of their effects. The findings provide new insights into impacts of MPs on the fate and risk of HMs in agricultural soil.

Study of Potentially Toxic Metal Adsorption in a Polluted Acid and Alkaline Soil: Influence of Soil Properties and Levels of Metal Concentration

In the present study, the adsorption of zinc (Zn), lead (Pb), copper (Cu), and cadmium (Cd) was studied in two already polluted urban soil samples with different pH values, an acidic and an alkaline one. The Langmuir and Freundlich adsorption isotherm equations were used to thoroughly study the adsorption of the metallic elements on the solid surface of the soils. Langmuir equation described the adsorption of each metal satisfactorily, with a slight predominance over Freundlich, in both soils, as the R2 value approached almost unity. Even though Zn and Cu were adsorbed on the soil phase, their adsorption was minimal compared to the adsorption of more harmful metals such as Pb and Cd. Using the values of the coefficients obtained from the equations of the mathematical models, we concluded that in alkaline soils, the retention of metals was much greater than in acidic soils. The simultaneous presence of metals during the addition of the single-element solutions of the metals to the already metal-contaminated soils caused competitive adsorption increasing the retention of the more toxic metals on the solid surface of the alkaline soil. Factors affecting soil sorption (such as soil pH and CaCO3 content) were studied to provide theoretical support for understanding the laws and causes of metal sorption in the soils of the survey.

Revisiting of a Three-Parameter One-Dimensional Vertical Infiltration Equation

In the present study, the three-parameter one-dimensional vertical infiltration equation recently proposed by Poulovassilis and Argyrokastritis is examined. The equation includes the saturated hydraulic conductivity (Ks), soil sorptivity (S), and an additional parameter c; it is valid for all infiltration times. The c parameter is a fitting parameter that depends on the type of porous medium. The equation is characterized by the incorporation of the exact contribution of the pressure head gradient to flow during the vertical infiltration process. The application of the equation in eight porous media showed that it approaches to the known two-parameter Green–Ampt infiltration equation for parameter c = 0.300, while it approaches to the two-parameter infiltration equation of Talsma–Parlange for c = 0.750, which are the two extreme limits of the cumulative infiltration of soils. The c parameter value of 0.500 can be representative of the infiltration behavior of many soils for non-ponded conditions, and consequently, the equation can be converted into a two-parameter one. The determination of Ks, S, and c using one-dimensional vertical infiltration data from eight soils was also investigated with the help of the Excel Solver application. The results showed that when all three parameters are considered as adjustment parameters, accurate predictions of S and Ks are not achieved, while if the parameter c is fixed at 0.500, the prediction of S and Ks is very satisfactory. Specifically, in the first case, the maximum relative error values were 33.29% and 39.53% for S and Ks, respectively, while for the second case, the corresponding values were 13.25% and 17.42%.

The uptake of selenium by perennial ryegrass in soils of different organic matter contents receiving sheep excreta

Background and aimsThe intake of selenium, an essential element for animals and humans, in ruminants is largely determined by selenium concentration in ingested forages, which take up selenium mainly from soil. Ruminant excreta is a common source of organic fertilizer, which provides both nutrients and organic matter. This study aims to unentangle the unclear effect of applying different types of ruminant excreta in soils of different organic matter contents on selenium uptake by forage.MethodsPerennial ryegrass (Lolium perenne) was grown in soils of different organic matter contents. Urine and/or feces collected from sheep fed with organic or inorganic mineral supplements, including selenium, were applied to the soils. The selenium in the collected samples were analyzed using ICP-MS. The associated biogeochemical reactions were scrutinized by wet chemistry.ResultsThe application of urine and/or feces resulted in either the same or lower selenium concentrations in perennial ryegrass. The excreta type did not affect total selenium accumulation in grass grown in low organic matter soil, whereas in high organic matter soil, feces resulted in significantly lower total selenium accumulation than urine, which was attributed to a possible interaction of selenium sorption in soil and microbial reduction of Se.ConclusionThis one-time excreta application did not increase, but further decrease in some treatments, selenium concentration and accumulation in the perennial ryegrass. Consequently, to increase ruminant selenium intake, supplementing selenium directly to animals is more recommended than applying animal manure to soil, which might drive selenium reduction and decrease selenium uptake by grass.

Critical Level of Chromium for Rice in Different Soil Type

The increasing number of industries and poor treatment of waste will damage environmental health, including agricultural land. Agricultural products from contaminated soil may contain hazardous heavy metals such as chromium which can be harmful to human health if consumed. Examination and determination of chromium critical level in paddy soil are required to evaluate the threshold of heavy metals to disable to distribute into paddy plants. This study aims to obtain the critical level of chromium in light and heavy textured soils with paddy as a plant indicator. The pot experiment was carried out at the greenhouse using a completely randomized design with two factors are heavy metal concentration (Cr) and soil texture (A) and five times repeated. The chromium adsorption test uses the Langmuir approach method. Chromium sorption in heavy-textured soil is higher than in light-textured soil. The maximum sorption of chromium metal in light-textured soil is 87.719 mg kg-1, while in heavy-textured soil is 204.082 mg kg-1. Total chromium in the soil decreases after harvest and reduces rice yields. The critical level of light-textured soil chromium in rice was 0.861 mg kg-1, while the critical level for heavy-textured soil Chromium in rice was 1.012 mg kg-1.

The parametric uncertainty estimation of water and nitrogen transport simulation in a paddy field experiment using HYDRUS‐1D

AbstractThe HYDRUS model is an efficient technical means to study the process of complex nitrogen (N) transport in farmland. Nonetheless, spatial variability in soil water and N parameters has been observed at the field scale, leading to uncertainties in the HYDRUS model. In this study, the HYDRUS‐1D model was corrected and verified by the measured data. Generalized likelihood uncertainty estimation (GLUE) was used to estimate the uncertainty and sensitivity of the model parameters. The differences in simulated and measured data were expressed in terms of root mean square error, normalized root mean square error and coefficient of determination, and the model calibration and verification indicated that the result was reliable. The soil saturated water content, dispersion and sorption coefficient were well identified, with values ranging from 0.42 to 0.45 cm3/cm3, 0.26 to 0.29 cm and 0.141 to 0.158 L/mg, respectively. The denitrification rate and saturated hydraulic conductivity greatly influenced the uncertainty in the model results. Considering the uncertainty of the parameters, the predicted leaching of N accumulation from 0 to 100 cm depth ranged from 9.5 to 12.7 kg/ha. The HYDRUS‐1D model can simulate water and N transport in paddy fields. The prediction interval can be narrowed by considering the uncertainty of the model parameters.

A sorption isotherm model for soil incorporating external and internal surface adsorption, and capillarity

Soil water sorption isotherm is governed by soil–water interactions of adsorption and capillarity, depending on particle surface properties and pore size distribution, respectively. Recent studies have separated soil particle surfaces into two categories in terms of distinct adsorption behaviors, i.e., external and internal surfaces, identifying three independent sorption processes with varying energy levels, namely external adsorption, internal adsorption, and capillarity. Here, an isotherm model is developed to describe water sorption on soils in the full relative humidity ( RH) range by incorporating the three physical processes. The internal and external adsorptions are represented by an augmented-Brunauer–Emmett–Teller (A-BET) equation, and capillarity is described by Kosugi’s model. Two scaling factors are introduced to expand A-BET equation’s application RH range from 0%−40% to 0%−100%—one for the reduction of available adsorption area in restricted pores and another for the disparity between heats of adsorption and liquefaction. Experimental validation demonstrates that the proposed model excellently matches the isotherm data for a wide array of soils in the full RH range. Further, the proposed model performs well in capturing soil water retention data in the full matric potential range, providing a seamless linkage between soil sorption isotherm and water retention behaviors.

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.

Comparing two methods to perform a beerkan infiltration run in a loam soil at different dates

Performing beerkan infiltration runs with different heights of water pouring could help to obtain saturated soil sorptivity, S, and hydraulic conductivity, Ks, data usable to explain and simulate hydrological processes. However, most of the available information on the L (low height of water pouring, nearly 3 cm) – H (high height, 1–2 m) methodology refers to runs making use of a relatively limited number of water volumes and there is some sign that a few water volumes could yield an incomplete description of soil alteration phenomena induced by wetting. For a loam soil, the objective of this investigation was to determine water pouring height effects on the S and Ks values obtained in different sampling dates with more than usual amounts of applied water. Soil alteration due to the mechanical impact of the applied water appeared almost completed by the end of the runs in all cases but in a more advanced stage when the soil was initially more sorptive and conductive. Overall, the H runs yielded 2.3–2.8 times smaller S values and 8.5–14.5 times smaller Ks values than the L runs but differences between the L and H methodologies varied during the sampling period. In particular, these differences were smallest when the soil was initially relatively wet and little sorptive and conductive (S and Ks values differing with the experiment by no more than two times) and largest in the opposite conditions (S and Ks values differing by 3 and 17–21 times, respectively). The L runs yielded coefficients of variations, CV, of 14–60 % for S and 45–171 % for Ks, depending on the sampling date, and a ratio between the highest and the lowest mean of 2.5 for S and 11.8 for Ks. With the H runs, the corresponding CV values were 14–38 % for S and 35–107 % for Ks and two means differed at the most by 1.3 times for S and 2.2 times for Ks. Therefore, the H runs described a soil that was less sorptive, less conductive, more spatially homogeneous and more temporally stable than the L runs. Less runs could be enough to parameterize the soil in a disturbed condition as compared with the undisturbed one. Further testing the L-H methodology in other environmental conditions is recommended in the perspective to develop simple field methods to determine the hydrodynamic properties of both a nearly undisturbed soil and an intensively disturbed soil.

Ponding time, hydraulic conductivity, and sorptivity – experimental and numerical determination

Abstract Determination of actual soil sorptivity becomes one of the research preferences in the field of soil management and flash-flood protection. This Note presents an innovative approach to soil sorptivity determination. A single ring infiltration method, along with a simulation of rainfall of constant intensity, was used to measure ponding time t p. Hydraulic conductivity K was approximated from the analysis of the time series of the process of vertical non-steady cumulative infiltration appearing after the ponding time. Based on Philip's infiltration theory, a simple equation was derived in order to calculate sorptivity S from ponding time, rainfall intensity, and saturated hydraulic conductivity. Numerically determined results of S show to closely correspond with theoretical values published in the literature. To the best of our knowledge, this process of numerical determination of K and S has not been published so far. Moreover, unlike the traditional methods, e.g. single or double-ring in filtration experiments, this method provides more precise and representative values of S, verified by ponding time, as the results refer to the original soil sorptivity, not the sorptivity determined after the ponding time (meaning sorptivity of the fully saturated environment) which tends to reach zero. Our assumption was definitely confirmed by field experimental determination of ponding time and selected soil hydrology characteristics.

Pesticide extraction from soil into runoff under a rainfall simulator

Context Runoff estimation is an important aspect of pesticide environmental behaviour and is the major loss pathway to the environment. Aims To improve understanding of pesticide runoff. Methods Data from three rainfall simulator studies was used. Twelve pesticides were studied ranged from tightly sorbed (DDE, soil sorption coefficient (KD) ~15 000 L kg−1) to weakly sorbed (dimethoate, KD &lt; 30). Key results Event runoff pesticide concentrations were closely related to soil concentrations (0–25 mm depth). The ratio of runoff to soil concentration (the runoff extraction ratio, ERO), was similar for pesticides with a wide range of sorption and across the three soils: runoff concentration (μg L−1) = 28 × soil concentration (mg kg−1). ERO decreased with time after spraying, presumably due to lower concentrations in the top few mm of soil. Conclusions This model provides improved or similar estimates of pesticide runoff than previous models. Similar ERO values between sites was probably due to similar hydrology (high rainfall intensity, surface sealing, moist subsoils) and erosion, and because the same masses of soil and water are involved in mixing. Reduction in runoff concentrations by leaching was not influential, because infiltration was small and soil sorption too high. Implications Conditions studied apply during summer storms on most cotton and grain land on clay soils in the northern grain and cotton lands in eastern Australia. The model should be applicable under these conditions.

Using a batch test to derive sorption data of fluoroquinolone antibiotics in humic acids

Fluoroquinolone antibiotics (FQs) are of concern due to their disrupting effects on environmental bacterial communities. Evaluating FQ sorption by soil components is important to understand their interaction with soils and to address their environmental (bio)availability. However, data in soil organic components, especially humic acids, are scarce. Batch experiments following OECD guidelines are suitable for testing the sorption of pollutants in solid matrices. Here, we applied this methodology, with specific changes in the experimental setup, to derive sorption data and to identify the factors affecting sorption of four common FQs in seven humic acids with contrasting properties. The effect of shaking time, pH, calcium concentration in solution and dissolved organic carbon (DOC) content on the quantification of the solid-liquid distribution coefficient (Kd) of norfloxacin in three reference humic acids was evaluated. Sorption reversibility and sorption analogy of four FQs were additionally assessed in these three reference materials, whereas the effect of initial norfloxacin concentration was evaluated in the overall set of seven humic acids. Sorption was fast, strong, non-linear, irreversible and affected by changes in the pH and calcium levels in solution. The bell-shaped sorption trend at varying pH values confirmed the key role of FQ speciation in sorption and the high Kd values indicated a positive effect of soil organic matter components on FQ sorption in bulk soils at environmentally relevant pH values.•Relevant factors affecting sorption of pollutants in environmental matrices must be considered to derive Kd values with low variability and high representativeness.•In this article we modify the experimental conditions of standard batch tests to identify the factors that affect the sorption of FQs in humic acids.•The methodological approach followed can be extrapolated to the evaluation of other combinations of pollutant and environmental matrix.

Phosphorus sorption characteristics in the Sahel: Estimates from soils in Mali

&lt;abstract&gt; &lt;p&gt;Crop yield in sub-Saharan Africa is often limited by low phosphorus fertility. Farmers in the region can apply phosphate rock, which should increase the plant-available phosphorus level, but this may be prone to sorption in acid soils of the Sahel. The objective of this study was to determine phosphorus (P) sorption characteristics of four representative soil series in Sahelian Mali namely, Longorola (Gleysol), Danga (Fluvisol), Niessoumana (Arenosol) and Konobougou (Acrisol) under Tilemsi Phosphate Rock (TPR) treatment. Data for phosphorus sorption was obtained by equilibrating 5 g of soils for 7 days at room temperature in 50 ml of 0.01M CaCl&lt;sub&gt;2&lt;/sub&gt; containing six (6) rates of phosphate as TPR (0, 10, 20, 40, 80,160 mg/L). The linear form of the Langmuir equation was used to calculate sorption parameters of the soils. The Gleysol with the greatest clay content had the highest phosphorus sorption maximum which was over three times greater than that of the Acrisol with the least clay content. The sorption maxima in the range of 59–200 mg/kg were well estimated with Langmuir sorption isotherm (R&lt;sup&gt;2&lt;/sup&gt; ≥ 0.78). Soil organic matter and clay contents influenced phosphorus sorption from the TPR. The degree of phosphorus saturation ranged from 2.39 to 6.47 %, being greater in the Arenosol. In a two-season field experiment on the Haplic Acrisol, we tested on maize, the TPR in two forms (powder and pellet) in addition to water-soluble diammonium phosphate at different rates (0, 11 and 16 kg P /ha). The water-soluble DAP and TPR (powder) had similar effects (p &amp;lt; 0.05) on soil P availability but with DAP producing greater grain yields. This shows that application of TPR in powder form can improve phosphorus availability as water-soluble DAP with positive impact on grain yield. The study provides useful information on P sorption characteristics of TPR amendment in the Sahel.&lt;/p&gt; &lt;/abstract&gt;

Including the bioconcentration of pesticide metabolites in plant uptake modeling.

Although several models of pesticide uptake into plants are available, there are few modeling studies on the bioconcentration of metabolites in plants. Ignoring metabolites in plant uptake models can result in an underestimation of the parent compound's overall impacts on human health associated with pesticide residues in harvested food crops. To address this limitation, we offer a metabolite-based plant uptake model to predict the bioconcentration of the parent compound and its metabolites in plants. We used the uptake of glyphosate and its major metabolite (aminomethylphosphonic acid, AMPA) into potato as an example. The analysis of variability revealed that soil properties (affecting the soil sorption coefficient), dissipation half-life in soil, and metabolic half-life in the potato had a significant impact on the simulated AMPA concentration in the potato, indicating that regional variability could be generated in the plant bioconcentration process of metabolites. The proposed model was further compared using the non-metabolite model. The findings of the comparison suggested that the non-metabolite model, which is integrated with the AMPA bioconcentration process, can predict the AMPA concentration in the potato similarly to the proposed model. In conclusion, we provide insight into the bioconcentration process of metabolites in tuber plants from a modeling viewpoint, with some crucial model inputs, such as biotransformation and metabolic rate constants, requiring confirmation in future studies. The modeling demonstration emphasizes that it is relevant to consider bioaccumulation of metabolites, which can propagate further into increased overall residues of harmful compounds, especially in cases where metabolites have higher toxicity effect potency than their respective parent compounds.