Inorganic Contaminants In Soils Research Articles

Mobilization, Speciation, and Transformation of Organic and Inorganic Contaminants in Soil–Groundwater Ecosystems

The delicate balance of our ecosystems is under threat from the unrelenting release of contaminants into the environment [...]

Impact of biochar, fertilizers and cultivation type on environmentally persistent free radicals in agricultural soil.

Environmentally persistent free radicals (EPFRs) have been considered as emerging contaminants due to their detrimental effects on human health. The adverse health impacts are attributed to oxidative stress induced by EPFRs through the formation of reactive oxygen species (ROS). In soils, it may also increase the degradation process of polymeric organic matter and/or undesired organic pollutants through hydroxyl radical activity. The biochar pyrolysis process entails the thermal decomposition of organic compounds in the biomass, with the carbonization conditions and feedstock type facilitating the formation of EPFRs. When biochar is used to amend soil, these radicals may promote the formation of ROS, and thus influence the transformation of organic and inorganic contaminants in soil and impact the rhizosphere. Agricultural soils are being amended with biochar to mainly increase carbon content and facilitate the plant growing conditions. Therefore, agricultural soils may become a source of EPFRs. However, the fate and transformations of EPFRs in soils after biochar amendment are not well understood or studied. This paper presents the first (to our knowledge) studies of EPFRs behaviour in agricultural soil with different input of biochar, cultivation types and residence time period. Different cultivation types, addition of fertilisers and variation in biochar input, on the one hand, and presence of metals in soil, biochar and fertilizers, on the other hand, provide different conditions for EPFRs formation, accumulation and fate in agricultural soils. Two significant factors have been found to determine the fate of EPFRs in soil: transition metal content (particularly those in reaction available form) and cultivation level of soil. Cultivation significantly decreased presence of EPFRs, both carbon-centered and oxygen-centered, in relatively short periods of time, while metal presence (and particularly through fertilizer supplementation) increases the half-life of radicals and transforms organic matter to more oxygen-centered EPFRs. The amount of biochar addition plays a secondary role as the EPFRs content in the soils is in a longer term primarily controlled by the other two factors.

Effective remediation of heavy metals in contaminated soil by electrokinetic technology incorporating reactive filter media

Soil contamination is increasingly a global problem with serious implications for human health. Among different soil decontamination approaches, electrokinetic (EK) remediation is a relatively new technology for treating organic and inorganic contaminants in soil. This research aims to develop an enhanced EK treatment method incorporating a compost-based reactive filter media (RFM) with the advantages of low-cost and strong affinity for heavy metals and test and improve the treatment efficiency for multiple heavy metals in natural soil. A series of EK operations were performed to investigate the performance of EK-RFM under different operating conditions such as the electric current and voltage, processing time, and the amount of RFM. The electric current and treatment time demonstrated a significant positive impact on removing Zn, Cd and Mn ions while changing the amount of RFM had an insignificant impact on the efficiency of heavy metals removal. Overall, 51.6%–72.1% removal of Zn, Cd, and Mn was achieved at 30.00 mA of electric current and 14 days of treatment duration. The energy consumption of the EK process was 0.17 kWh kg−1. The soil organic matter adversely affected the mobilization and migration of heavy metals such as Cu and Pb during EK treatment. The results are valuable in optimizing the design of the EK-RFM system, which will extend its application to field-scale soil decontamination practices.

ESTIMATION OF EMBALMING CONTAMINANTS IN SOIL AND GROUNDWATER SAMPLES FROM CEMETERY LEACHATES IN MBAIORBO, MBADIM-MBATIAV LEACHFIELD IN GBOKO, NIGERIA

Selected organic and inorganic contaminants in soil and water around burial sites in Mbaiorbo, Mbadim-Mbatiav, Gboko, Nigeria was studied using standard analytical methods. Results of analysis revealed variations in some physicochemical parameters, concentrations of heavy and organic pollutants. Five sampling locations were chosen for collection of soil and water samples and one sampling location, about 2 km away from the cemetery e4was chosen for control sample. The soil parameters for analytical and control samples estimated were, pH 4.80±0.06 (4.89±03), Electrical conductivity (μS/cm) 148.37±0.18 (79.00±0.02), Total organic carbon (%) 1.837±0.04 (1.585±0.05), Organic matter (%) 3.167±0.03 (2.732±0.04) and Bulk density (g/cm) 1.32±0.03 (1.44±0.02). The water parameters estimated were, Temperature (oC) 28.00±0.00 (28.00±0.00), pH 5.27±0.06 (6.00±0.00), Electrical conductivity (μS/cm) 114.35±0.23 (88.23±0.11), Chloride (mg/L) 2.08±.004 (0.95±0.02) and Nitrate (mg/L) 0.8899±0.05 (0.6116±0.00). The concentrations in ppm of heavy metals in the soil analytical and control samples estimated were, As (was not detected, ND, in both samples), Cd 0.167 (0.146), Cr 0.332 (0.032), Ni ND (ND), Pb 0.354 (0.592), Cu ND (ND) and the heavy metals pollutants in the water analytical and control samples estimated were, As ND (ND) Cd 0.008 (0.009), Cr 0.334 (0.349), Ni ND (ND), Pb 0.142 (0.141), Cu ND (0.049), The concentrations in ppm of organic pollutants estimated were, Formaldehyde 0.04213 (ND), Ethanol 0.02022 (0.24654), n-propane 0.04665 (ND) Iso-butanol 0.08366 (0.89675) and Methanol ND (ND). Contamination factor and geo-accumulation index models used to estimate the level of soil and water pollution by heavy metals and organic pollutants revealed that the soil and water samples were highly contaminated with Cr but the level of organic pollutants in water were low. Green burial practice and strict monitoring of water quality in dug wells and streams in the vicinity of the burial sites from the study area is recommended.

Use of the Dynamic Technique DGT to Determine the Labile Pool Size and Kinetic Resupply of Pesticides in Soils and Sediments.

The diffusive gradients in thin films (DGT) technique has been successfully and widely applied to investigate the labile fractions of inorganic contaminants in soils and sediments, but there have been almost no applications to organic contaminants. Here we developed and tested the approach for the pesticide Atrazine (ATR) in a controlled soil experiment and in situ in an intact lake sediment core. The soil study explored the relationships between soil solution, DGT measured labile ATR and solvent extractable ATR in dosed soils of different organic matter, pH status and incubation times. The results are further interpreted using the DIFS (DGT-induced fluxes in soils and sediments) model. Resupply of ATR to the soil solution was partially sustained by the solid phase in all the soils. This was due to small labile pool size and slow kinetics, with soil pH being an important controlling factor. The in situ sediment study successfully used a DGT probe to examine labile ATR distribution through the core on the subcm scale. It demonstrated-for the first time-an easy to use in situ technique to investigate the effects of redox on resupply kinetics and biogeochemical processes of trace organic contaminants in sediments.

In Situ Biostimulation of Cr(VI) Reduction in a Fast-Flowing Oxic Aquifer

Hexavalent chromium is among the most common and hazardous inorganic contaminants in soils and groundwater. A promising in situ bioremediation approach is the delivery of electron donors to stimulate microbially mediated Cr(VI) reduction, producing relatively insoluble Cr(III) precipitates. Even though this strategy has been implemented successfully in the past, it was primarily under favorable hydrological conditions, such as relatively slow groundwater flow velocities. To evaluate whether microbially mediated Cr(VI) reduction can be sustained at high groundwater flow velocities and under nearly oxygen-saturated conditions, we have conducted laboratory-scale column experiments and a field-scale pilot study using molasses as the electron donor. Despite the unfavorable conditions, both experiments provided clear evidence for microbially mediated Cr(VI) reduction. In particular, the well used for injection in the field experiment became anoxic after two months of injection and the Cr(VI) concentration decreased by a factor of six. After stopping the injection, these conditions prevailed for at least four months. In the column experiments, Cr(VI) reduction was accompanied by distinct Cr isotopic fractionation characterized by an enrichment factor of −1.25‰. In contrast, Cr isotope data collected from the field experiment were ambiguous, which was because of the complexation of Cr(III) with organic carbon and the heterogeneous distribution of molasses due to the presence of narrow preferential flow paths. A substantial injectivity decrease likely caused by the formation of biofilm and the precipitation of Fe sulfides formed an additional challenge during the field experiment. Our data, however, also suggest that most of the identified challenges could be addressed by limiting the targeted dissolved organic carbon concentrations to about 10 mg/L. In conclusion, the injection of molasses constitutes a promising bioremediation strategy for the long-term treatment of Cr(VI) contamination even at high flow rates and under oxic conditions.

Unravelling the Role of Rhizospheric Plant-Microbe Synergy in Phytoremediation: A Genomic Perspective

Background Accretion of organic and inorganic contaminants in soil interferes in the food chain, thereby posing a serious threat to the ecosystem and adversely affecting crop productivity and human life. Both endophytic and rhizospheric microbial communities are responsible for the biodegradation of toxic organic compounds and have the capability to enhance the uptake of heavy metals by plants via phytoremediation approaches. The diverse set of metabolic genes encoding for the production of biosurfactants and biofilms, specific enzymes for degrading plant polymers, modification of cell surface hydrophobicity and various detoxification pathways for the organic pollutants, plays a significant role in bacterial driven bioremediation. Various genetic engineering approaches have been demonstrated to modulate the activity of specific microbial species in order to enhance their detoxification potential. Certain rhizospheric bacterial communities are genetically modified to produce specific enzymes that play a role in degrading toxic pollutants. Few studies suggest that the overexpression of extracellular enzymes secreted by plant, fungi or rhizospheric microbes can improve the degradation of specific organic pollutants in the soil. Plants and microbes dwell synergistically, where microbes draw benefit by nutrient acquisition from root exudates whereas they assist in plant growth and survival by producing certain plant growth promoting metabolites, nitrogen fixation, phosphate solubilization, auxin production, siderophore production, and inhibition or suppression of plant pathogens. Thus, the plant-microbe interaction establishes the foundation of the soil nutrient cycle as well as decreases soil toxicity by the removal of harmful pollutants.Conclusion The perspective of integrating genetic approach with bioremediation is crucial to evaluate connexions among microbial communities, plant communities and ecosystem processes with a focus on improving phytoremediation of contaminated sites.

Remediation of inorganic contaminants in soil using electrokinetics, phytoremediation techniques

During the last decade, the expansion of urbanization and industrial activities caused serious environmental problems such as soil pollution. Currently, the vast majority of remediation projects involve disposing of contaminated soil in a landfill. With the introduction of this, cause increased landfill tax and becoming less desirable, and so robust. Novel technologies are required to remediate soil contamination with toxic contaminants, including heavy metals and organic pollutants. Electrokinetic (EK) and Phytoremediation are better techniques. Electrokinetic is an emerging remediation technology for mixed contaminants, especially in low hydraulic conductivity soils. During the electrokinetic remediation process, an electric field is applied to the specimen to remove the contaminants from soil by means of electro-osmotic (EO), electromigration (EM), and electrophoresis (EP) processes. This paper addresses the problem of contaminants in soil and has investigated the use of electrokinetic phenomena and phytoremediation as tools to bring about an increase in this factor, leading to improved degradation. Electrokinetic separation is an emerging technology that relies on the application of a low-density, the direct current through the soil to separate and extract the heavy metal. When comparing these two techniques a significant increase in the effectiveness of the remediation was noted with electrokinetics technique, with substantially faster degradation to occur.

Information depth of elements affects accuracy of parallel pXRF in situ measurements of soils.

Though not litigable in most European countries, portable X-ray fluorescence spectrometers (pXRF) provide cost- and time-effective as well as prompt information about hot spots of inorganic soil contaminants. The quality of aqua regia analysis of contaminants can be approximated by a thorough sample preparation, i.e., homogenization, grinding, and sieving of the examined soil before pXRF measurement is carried out. However, elaborate sample preparation causes a trade-off in terms of the desired straightforwardness of the pXRF method. For a first assessment of the in situ accuracy of pXRF measurements, two equal pXRF devices were used in parallel to determine the contents of As, Cu, Fe, Mn, Pb, Rb, Sr, Zn, and Zr of 9 identical points of a riparian soil profile. Maximum measurement values were not restricted to one pXRF device, but changed from element to element. Pearson correlation coefficients of the parallel measurements varied between 0.07 (Cu) and 0.80 (Zn), reflecting small-scale heterogeneity of the soil constituents as well as element-specific interferences. For each element, overall deviations between measurement parallels were expressed as the root-mean-square error (RMSE) and contrasted against the element-specific information depth in soil, i.e., the depth interval, from which the received spectral signals originate. From this, a gradual relation could be derived: The greater the information depth, the more stable the measured element value turns out. This context should be taken into account, when interpreting contents of elements with small atomic numbers.

Pilot-scale field investigation of ex situ solidification/stabilization of soils with inorganic contaminants using two novel binders

Recently, two novel binders, one by-product-based binder named as GM and one phosphate-based binder named as KMP, have emerged that can stabilize soils spiked with mixed lead and zinc contaminants. However, field evaluations of the stabilization of actual soils that contaminated with mixed zinc (Zn) and inorganic chloride (Cl−) using GM and KMP have not been performed yet. This study presents a pilot-scale field test to evaluate the performance of GM and KMP to stabilize these inorganic contaminants in soils at two locations in an abandoned industrial plating plant site. The field soils were stabilized and cured for 1, 3, 7, and 28 days and tested for dry density, dynamic cone penetration, soil pH, and leachability. Laboratory unconfined compression tests were performed, and the relationship between unconfined compressive strength and dynamic cone penetrometer index was assessed. The results showed that the strength of both the GM- and KMP-stabilized soils after 28-day curing improved significantly, and the leached Zn and Cl− concentrations were well below the corresponding remediation limits. In general, the KMP-stabilized soil demonstrated superior performance in terms of higher dry density, unconfined compressive strength, average dynamic cone penetration resistance, lower dynamic cone penetrometer index in the early curing stage (7 days), and lower leached Zn concentration under all curing times. In contrast, the GM exhibited superior immobilization of Cl− in the contaminated soil irrespective of the curing time. The results demonstrate that GM and KMP are promising binders for treating Zn- and Cl−-contaminated soils at plating and other industry sites with similar contaminants.

A critical review of mechanisms involved in the adsorption of organic and inorganic contaminants through biochar

Successful application of low-cost adsorbent like biochar has introduced multidisciplinary areas of science, particularly with respect to remediation of both organic and inorganic contaminants in soil and water. This review briefly consolidates the currently available literature to comprehend the overall adsorption mechanisms of organic and inorganic contaminants through biochar. Generally, biochar produced at low pyrolysis temperature is suitable for the adsorption of inorganic contaminants by following the adsorption mechanisms of electrostatic interaction, precipitation, and ion exchange. However, relatively high pyrolysis temperature favors the adsorption of organic contaminants by increasing the surface area and micropores of biochar along with pore filling and hydrophobic and electrostatic interaction as predominant adsorption mechanisms. This review also summarizes the critical factors (pyrolysis temperature, solution pH, dosage of biochar, contact time, co-existed ions, modification/activation, aging process, etc) affecting the overall adsorption efficiency of the biochar. Overall, further field studies and experimentation are required for the reduction of cost in biochar production and its reuse.

Advances in research on the use of biochar in soil for remediation: a review

Soil contamination mainly from human activities remains a major environmental problem in the contemporary world. Significant work has been undertaken to position biochar as a readily-available material useful for the management of contaminants in various environmental media notably soil. Here, we review the increasing research on the use of biochar in soil for the remediation of some organic and inorganic contaminants. Bibliometric analysis was carried out within the past 10 years to determine the increasing trend in research related to biochar in soil for contaminant remediation. Five exemplar contaminants were reviewed in both laboratory and field-based studies. These included two inorganic (i.e., As and Pb) and three organic classes (i.e., sulfamethoxazole, atrazine, and PAHs). The contaminants were selected based on bibliometric data and as representatives of their various contaminant classes. For example, As and Pb are potentially toxic elements (anionic and cationic, respectively), while sulfamethoxazole, atrazine, and PAHs represent antibiotics, herbicides, and hydrocarbons, respectively. The interaction between biochar and contaminants in soil is largely driven by biochar precursor material and pyrolysis temperature as well as some characteristics of the contaminants such as octanol-water partition coefficient (KOW) and polarity. The structural and chemical characteristics of biochar in turn determine the major sorption mechanisms and define biochar’s suitability for contaminant sorption. Based on the reviewed literature, a soil treatment plan is suggested to guide the application of biochar in various soil types (paddy soils, brownfield, and mine soils) at different pH levels (4–5.5) and contaminant concentrations ( 50 mg kg−1). Research on biochar has grown over the years with significant focus on its properties, and how these affect biochar’s ability to immobilize organic and inorganic contaminants in soil. Few of these studies have been field-based. More studies with greater focus on field-based soil remediation are therefore required to fully understand the behavior of biochar under natural circumstances. Other recommendations are made aimed at stimulating future research in areas where significant knowledge gaps exist.

Assessing bioavailability of complex chemical mixtures in contaminated soils: Progress made and research needs

Understanding the distribution, behaviour and interactions of complex chemical mixtures is key for providing the evidence necessary to make informed decisions and implement robust remediation strategies. Much of the current risk assessment frameworks applied to manage land contamination are based on total contaminant concentrations and the exposure assessments embedded within them do not explicitly address the partitioning and bioavailability of chemical mixtures. These oversights may contribute to an overestimation of both the eco-toxicological effects of the fractions and the mobility of contaminants. In turn, this may limit the efficacy of risk frameworks to inform targeted and proportionate remediation strategies. In this review we analyse the science surrounding bioavailability, its regulatory inclusion and the challenges of incorporating bioavailability in decision making process. While a number of physical and chemical techniques have proven to be valuable tools for estimating bioavailability of organic and inorganic contaminants in soils, doubts have been cast on its implementation into risk management soil frameworks mainly due to a general disagreement on the interchangeable use of bioavailability and bioaccessibility, and the associated methods which are still not standardised.This review focuses on the role of biotic and abiotic factors affecting bioavailability along with soil physicochemical properties and contaminant composition. We also included advantages and disadvantages of different extraction techniques and their implications for bioavailability quantitative estimation. In order to move forward the integration of bioavailability into site-specific risk assessments we should (1) account for soil and contaminant physicochemical characteristics and their effect on bioavailability; (2) evaluate receptor's potential exposure and uptake based on mild-extraction; (3) adopt a combined approach where chemical-techniques are used along with biological methods; (4) consider a simplified and cost-effective methodology to apply at regulatory and industry setting; (5) use single-contaminant exposure assessments to inform and predict complex chemical mixture behaviour and bioavailability.

Pyrogenic carbon and its role in contaminant immobilization in soils

ABSTRACTPyrogenic carbon (PyC), including soil native PyC and engineered PyC (biochars), is increasingly being recognized for its potential role as a low-cost immobilizer of contaminants in soils. Published reviews on the role of soil native PyC as a sorbent in soils have so far focused mainly on organic contaminants and paid little or no attention to inorganic contaminants. Further, a comprehensive review on the production of both natural PyC and engineered PyC (biochars), mechanisms involved, and factors influencing their role as soil contaminant immobilizer is so far not available. The objective of this review is thus to systematically summarize the sources, formation, and properties of PyC, including its quantification in soils, followed by their roles in the immobilization of both organic and inorganic contaminants in soils. Effectiveness of PyC on bioavailability, leaching, and degradation of soil contaminants was summarized. Notably, the mechanisms and factors (for the first time) influencing the immobilization processes for soil contaminants were also extensively elucidated. This review helps better understand and design PyC for soil contaminant immobilization.

Towards sustainable remediation of contaminated soil by using diasporic bauxite: Laboratory experiments on soil from the sulfide mining village of Stratoni, Greece

Various mineral-based amendments can be used in raw or modified form for inducing immobilization of inorganic contaminants in soil with different modes of molecular-scale sequestration. In this study, diasporic bauxite in raw form as well as after heat treatment at different temperatures (105°C, 350°C and 450o C) was tested for its effectiveness in reducing the mobility of potentially harmful elements (PHEs) in contaminated soil. A pot experiment was set up where raw and calcined bauxite was mixed at different proportions with contaminated soil from the sulfide ore mining village of Stratoni, north Greece. Total concentrations in soil have averages of 1000mg/kg Pb, 712mg/kg Zn, 6mg/kg Cd, 2900mg/kg Mn and 296mg/kg As. The effectiveness of bauxite amendment was evaluated by comparing leachable PHE concentrations of treated and untreated soil after a four week period of repeated cycles of wetting and mixing. Both raw and calcined bauxite in a mixing proportion of 7% reduced leachable concentrations of the elements in comparison to the original soil. Samples that were mixed with activated bauxite (105°C, 350°C) and raw bauxite showed similar results. The corresponding reduction of water leachable fraction of PHEs was determined as high as 75% for Zn, 66% for Mn, 55% for Cd, 51% for Pb, and 41% for As. Extractable concentrations by the Toxicity Characteristic Leaching Procedure (TCLP) remained relatively low for Pb (60% reduction), Zn (30% reduction) and As (28% reduction). The maximum efficiency was observed by using treated bauxite at the temperature of 450°C with negligible water leachable concentrations after treatment. This difference in retention efficiency of elements between the heat treated bauxite samples is attributed to phase transitions that occur in Al-oxyhydroxides and Fe-oxides/oxyhydroxides of bauxite when heated at higher temperatures.

Effect of pyrolysis temperature on potential toxicity of biochar if applied to the environment

Biochars have increasingly been used as adsorbents for organic and inorganic contaminants in soils. However, during the carbonization process of pyrolysis, contaminants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dioxins and furans (PCDD/DF) can be generated. In this study, biochars made from sawdust, were prepared at various temperatures ranging from 250 to 700 °C. The Microtox® and rat hepatoma cell line H4IIE-luc assays were used to characterize the general toxic and effects, mediated through the aryl hydrocarbon receptor (AhR), or dioxin-like potencies of organic extracts of biochars. The greatest total concentrations of PAHs (8.6 × 102 μg kg−1) and PCDD/DF (6.1 × 102 pg g−1) were found in biochar generated at 400 °C and 300 °C, respectively. Results of the H4IIE-luc assay, which gives total concentrations of 2,3,7,8-TCDD equivalents (TEQH4IIE-luc), indicated that total potencies of aryl hydrocarbon receptor (AhR) agonists were in decreasing order: 300 °C > 250 °C > 400 °C > 500 °C > 700 °C. The 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQchem) calculated as the sum of products of 16 PAHs and 17 PCDD/DF congers multiplied by their respective relative potencies (RePs) was less than that of TEQH4IIE-luc determined by use of the bioanalytical method, with the H4IIE-luc assay, which measures the total dioxin-like potency of a mixtures. The ratio of TEQchem/TEQH4IIE-luc was in the range of 0.7%–3.8%. Thus, a rather small proportion of the AhR-mediated potencies extracted from biochars were identified by instrumental analyses. Results of the Microtox test showed similar tendencies as those of the H4IIE-luc test, and a linear correlation between EC50 of Microtox test and EC20 of H4IIE-luc test was found. The results demonstrated that biochars produced at higher pyrolysis temperatures (>400 °C) were less toxic and had lower potencies of AhR-mediated effects, which may be more suitable for soil application.

Derivation of Soil-Screening Thresholds to Protect the Chisel-Toothed Kangaroo Rat from Uranium Mine Waste in Northern Arizona

Chemical data from soil and weathered waste material samples collected from five uranium mines north of the Grand Canyon (three reclaimed, one mined but not reclaimed, and one never mined) were used in a screening-level risk analysis for the Arizona chisel-toothed kangaroo rat (Dipodomys microps leucotis); risks from radiation exposure were not evaluated. Dietary toxicity reference values were used to estimate soil-screening thresholds presenting risk to kangaroo rats. Sensitivity analyses indicated that body weight critically affected outcomes of exposed-dose calculations; juvenile kangaroo rats were more sensitive to the inorganic constituent toxicities than adult kangaroo rats. Species-specific soil-screening thresholds were derived for arsenic (137 mg/kg), cadmium (16 mg/kg), copper (1,461 mg/kg), lead (1,143 mg/kg), nickel (771 mg/kg), thallium (1.3 mg/kg), uranium (1,513 mg/kg), and zinc (731 mg/kg) using toxicity reference values that incorporate expected chronic field exposures. Inorganic contaminants in soils within and near the mine areas generally posed minimal risk to kangaroo rats. Most exceedances of soil thresholds were for arsenic and thallium and were associated with weathered mine wastes.

Selective Soil Particle Adherence to Hands: Implications for Understanding Oral Exposure to Soil Contaminants

Over the last 30 years, there has been extensive research designed to quantify the extent of oral bioavailability and bioaccessibility of organic and inorganic contaminants in soil. One aspect of this research is the soil particle size selected to represent environmental exposures, which may affect study results and comparability across studies. Different research groups have studied soil particle sizes ranging from <45 μm to <2000 μm. This article reviews the historical and technical considerations that pertain to the selection of an appropriate particle size fraction for evaluating the relative oral bioavailability of chemicals from soil, which include (1) how the resultant data will be used in human health risk assessment, (2) soil fractions historically used in oral bioavailability studies, (3) studies of soil adherence to human hands, (4) the distribution of contaminants in soils as a function of particle size, and (5) the effect of differential bioavailability as a function of soil particle size and geochemical matrix. These factors are first discussed from a general perspective, applicable to all contaminants in soil, and then more specifically for polycyclic aromatic hydrocarbons (PAHs) in soil. Based on this review, a specific soil particle size of <150 μm is recommended for future studies on the oral bioavailability and bioaccessibility of PAHs in soil.

Kinetics of radionuclides and heavy metals behaviour in soils: Implications for plant growth

The extent of metal and radionuclide contamination in the world is immense. In soils, metals and radionuclide can be dissolved in solution, or ion exchanged in reaction, complexed with soil organics or precipitate as pure or mixed solids. Soluble contaminants are subject to migration with soil water, uptake by plants or aquatic organisms or loss due to volatilization. Lead, chromium, zinc, arsenic and cadmium are the most frequently identified inorganic contaminants in soil and ground water. Unlike degradable organic contaminants and ever short-lived radionuclides that can become less toxic over time, metals can be considered conservative. However, many metals, especially radio-sensitive elements such as arsenic and chromium can undergo transformation or sorption reaction that alter both mobility and relative toxicity. This paper therefore, makes a review of these behaviours of radionuclides and heavy metals in soils, in connection to soil contamination and their effects on plant growth.

Influence of soil properties on heavy metal sequestration by biochar amendment: 1. Copper sorption isotherms and the release of cations

The amendment of carbonaceous materials such as biochars and activated carbons is a promising in situ remediation strategy for both organic and inorganic contaminants in soils and sediments. Mechanistic understandings in sorption of heavy metals on amended soil are necessary for appropriate selection and application of carbonaceous materials for heavy metal sequestration in specific soil types. In this study, copper sorption isotherms were obtained for soils having distinct characteristics: clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. The amendment of acidic pecan shell-derived activated carbon and basic broiler litter biochar lead to a greater enhancement of copper sorption in Norfolk soil than in San Joaquin soil. In Norfolk soil, the amendment of acidic activated carbon enhanced copper sorption primarily via cation exchange mechanism, i.e., release of proton, calcium, and aluminum, while acid dissolution of aluminum cannot be ruled out. For San Joaquin soil, enhanced copper retention by biochar amendment likely resulted from the following additional mechanisms: electrostatic interactions between copper and negatively charged soil and biochar surfaces, sorption on mineral (ash) components, complexation of copper by surface functional groups and delocalized π electrons of carbonaceous materials, and precipitation. Influence of biochar on the release of additional elements (e.g., Al, Ca) must be carefully considered when used as a soil amendment to sequester heavy metals.