Chemical Migration Research Articles

Chemical weathering intensity and geochemical characteristics of Cretaceous terrigenous clastic rock‐purple soil profiles in the Pushi area, Xichang

The Pushi area of South‐west China features a large area of purple soil that formed by the weathering of Cretaceous terrigenous clastic rocks. In this study, four vertical profiles of the purple soil (P1, P2, P3, and P4) derived from different pedogenic parent rocks were investigated. Specifically, the chemical weathering intensity and element migration, enrichment, and differentiation characteristics were analysed and the influencing factors of chemical weathering were explored. According to the discrimination map of major and trace elements and content characteristics of rare earth elements, the soil profiles are controlled by complex chemical weathering processes. Various geochemical parameters and indicators exhibited good correlation, and the chemical weathering intensity of the profiles followed the order P1 (mudstone) > P3 (silty mudstone) > P4 (argillaceous siltstone) > P2 (sandstone). The overall chemical weathering intensity of argillaceous rocks was slightly higher than that of sandstone, and the four profiles generally reflected medium to strong chemical weathering. The migration, enrichment, and differentiation characteristics of geochemical elements were found to be mainly affected by different chemical weathering intensities and stages, followed by leaching deposition. The chemical weathering characteristics varied for the four profiles with different pedogenic parent rocks, which could be mainly attributed to internal factors such as the lithology of the pedogenic parent rock and external topographic factors such as altitude.

Food and beverage can coatings: A review on chemical analysis, migration, and risk assessment.

The internal surface of food and beverage cans is generally covered with polymeric coatings to preserve food and protect metal substrate from corrosion. Coating materials are complex formulations that contain different starting substances (e.g., monomers, prepolymers, additives, etc.) and in addition during the manufacture of the material several compounds can be formed (e.g., reaction products, degradation products, etc.). These substances have the potential to migrate into the food. Many of them have not been identified and only some have been toxicologically evaluated. This article aims to provide a comprehensive review on the analytical methods used for the identification of potential migrants in can coatings. The migration and exposure to chemicals migrating from can coatings are also reviewed and discussed so far, which is essential for risk assessment. Moreover, a brief section on the current status of the legislation on varnishes and coatings for food contact in Europe is also presented. Liquid chromatography coupled to diode array and fluorescence detectors and particularly to mass spectrometry and gas chromatography-tandem mass spectrometry seem to be the techniques of choice for the identification of potential migrants in can coatings. Some studies have reported migration levels of BPA (bisphenol A) and BADGE (bisphenol A diglycidyl ether) and derivatives exceeding the specific migration limits set in the European legislation. On the whole, low dietary exposure to migrants from can coatings has been reported. However, it is interesting to highlight that in these studies the combined exposure to multiple chemicals has not been considered.

Experimental evidence of chemical osmosis-driven improved oil recovery in low-salinity water flooding: Generation of osmotic pressure via oil-saturated sandstone

Chemical osmosis caused by semipermeability and salinity gradient of reservoir rock has been considered to improve oil recovery obtained by low-salinity water flooding. However, the generation of osmotic pressure by rocks containing crude oil has not been reported. In this study, an oil-saturated sandstone generated osmotic pressures of up to 37 kPa at a salinity difference of 0.6–0.1 M NaCl and expelled crude oil from the surface facing low-salinity water (LSW). The results demonstrate that chemical osmosis can drive directional oil migration toward LSW on the scale of rock. The tested sandstone exhibited a clay content of 17 wt%; however, the oil-free core did not generate osmotic pressure. In contrast, the oil-saturated core generated osmotic pressures at the high-salinity water (HSW) facing its surface five days after being exposed to the salinity difference. The delayed pressure generation can be attributed both to the water intrusion into potential membranes (i.e., clay minerals, crude oil, and the interface between oil and minerals) and to the evolution of salinity gradient in the core. In the last experiment, on the same core using a salinity difference of 0.9–0.1 M NaCl, osmotic pressure developed immediately because both the active membranes and saline water already existed across the core. These results suggest that the potential semipermeability of reservoir rocks containing crude oil and saline water can promptly cause chemical osmosis upon exposure to the change in salinity difference. Although the cumulative flux driven by the osmotic pressure likely exceeded the volume of injected crude oil, chemical osmosis continued generating osmotic pressure until the end of the experiments. These contradictory results suggest that the chemical osmosis-driven directional oil migration toward the LSW occurs preferentially through conductive large-sized pores, and the residual oil in small-sized pores and clay minerals exert long-lasting semipermeability to cause chemical osmosis further toward the HSW.

Assessing Chemical Migration from Plastic Food Packaging into Food Simulant by Gas and Liquid Chromatography with High-Resolution Mass Spectrometry.

Some components of plastic food packaging can migrate into food, and whereas migration studies of known components are required and relatively straightforward, identification of nonintentionally added substances (NIAS; unknowns) is challenging yet imperative to better characterizing food safety. To this aim, migration was investigated across 24 unique plastic food packaging products including plastic wrap, storage bags, vacuum bags, and meat trays. Gas and liquid chromatography separation systems coupled with Orbitrap mass analyzers were used for comprehensive nontargeted screening of migrants. Tentative identifications of features were assigned by searching commercial databases (e.g., NIST, MZCloud, ChemSpider, Extractables and Leachables) and filtering results based on mass accuracy, retention time indices, and mass spectral patterns. Several migrants showed elevated levels in specific food packaging types, particularly meat trays and plastic wrap, and varying degrees of migration over the 10 days. Eleven putative migrants are listed as substances of potential concern or priority hazardous substances. Additionally, migration amounts of an Irgafos 168 degradation product determined by semiquantitation exceeded proposed theoretical maximum migration values.

Non-target screening for the identification of migrating compounds from reusable plastic bottles into drinking water

Reusable plastic sports bottles are used extensively worldwide, and little is known about the migration of chemicals from the bottles into drinking water. In this study, we investigated the chemical migration into drinking water stored for 24 h in new bottles, used bottles and bottles washed in the dishwasher. Non-target screening (NTS) by liquid-chromatography – high-resolution mass spectrometry (LC-HRMS) was performed to identify these compounds. We detected > 3500 dishwasher related compounds, with 430 showing migration even after subsequent flushing of the bottles. In addition, more than 400 plastic related compounds were detected, with high peaks for oligomers suspected to originate from the biodegradable polyester polycaprolactone, and aromatic amines, which may have been introduced as slip agents or antioxidants. These compounds have never been reported before in bottled water. Most of the identified compounds migrating out of the used bottles were plasticizers, antioxidants or photoinitiators. The presence of photoinitiators are of particular concern, due to possible endocrine disrupting effects. Furthermore, diethyltoluamide (DEET) was detected, which may have been formed from the plasticizer laurolactam. Typically, the dishwashing process enhanced the leaching of plastic related compounds, and even after additional water flushing, the average peak intensity of these compounds was only reduced by half.

The Role of Experiments in Monarch Butterfly Conservation: A Review of Recent Studies and Approaches

Monarch butterflies (Danaus plexippus) (Lepidoptera Danaidae Danaus plexippus (Linnaeus)) are an iconic species of conservation concern due to declines in the overwintering colonies over the past twenty years. Because of this downward trend in overwintering numbers in both California and Mexico, monarchs are currently considered 'warranted-but-precluded' for listing under the Endangered Species Act. Monarchs have a fascinating life history and have become a model system in chemical ecology, migration biology, and host-parasite interactions, but many aspects of monarch biology important for informing conservation practices remain unresolved. In this review, we focus on recent advances using experimental and genetic approaches that inform monarch conservation. In particular, we emphasize three areas of broad importance, which could have an immediate impact on monarch conservation efforts: 1) breeding habitat and host plant use, 2) natural enemies and exotic caterpillar food plants, and 3) the utility of genetic and genomic approaches for understanding monarch biology and informing ongoing conservation efforts. We also suggest future studies in these areas that could improve our understanding of monarch behavior and conservation.

In situ evolution of functional groups in char during cellulose pyrolysis under the catalysis of KCl and CaCl2

A combination of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) and two-dimensional correlation spectroscopy (2D-COS) was used to reveal the catalytic mechanism of KCl and CaCl2 on cellulose char evolution during slow pyrolysis. Pretreatments of the one-dimensional spectra ensure the semi-quantitative analysis of the evolution of functional groups in pyrolysis char, which invoked principal component analysis followed by a Butterworth filter for denoising and extended multiplicative scatter correction. Through the differential processing of the absolute changes, the char evolution product was divided into ‘char rearrangement’ and ‘char devolatilization’ processes containing a high contribution from chemical reactions and physical migration, respectively. The ‘char rearrangement’ of cellulose pyrolysis consists of four stages, i.e. the budding, development, climax and decline stages, which were dominated by H-bond network reconfiguration, the consumption of C–O–C and OH, homogeneous devolatilization and aromatization, respectively. The uppermost influence of the two salts on the pyrolysis is the relationship alteration of C–O–C cleavage, dehydration reactions and ‘char devolatilization’. For neat, KCl-loaded and CaCl2-loaded cellulose, the unsaturated bonds were formed in the light reaction intermediate, heavy reaction intermediates and cellulose chain, respectively. Especially, the cleavage of most C–O–C following dehydration reactions conduced a shoulder peak in the differential thermogravimetry curve before the maximum weight loss rate of CaCl2-loaded sample. Due to the alteration, the pyrolysis was advanced but slowed down by the high content of unsaturated bonds in char. This study provides a powerful tool for the in situ semi-quantitative analysis of char evolution during the non-catalytic and catalytic thermo-chemical conversion of solid fuels and waste, and the results benefit to both biomass pyrolysis mechanism revelation and industrial production of biochar.

Effects of Heat Treatment on The Wettability and Color Properties of Betung Bamboo (Dendrocalamus Asper) Strand

Betung bamboo (Dendrocalamus Asper) has recently attracted interest as a sustainable reinforcement fiber in (polymer) composite materials. Utilization of bamboo has an advantages and disadvantages. It has a short growth cycle, lightweight, and good mechanical properties, but with poor wettability, dimensional instability, and low resistance againts biodeterioration agent. Some efforts have been devoted to alter and enhance its properties, especially wettability properties. Heat treatment under various temperature can enhance wettability properties due to chemical changes and migration of extractives, but also can induce color changes. Therefore, this study aims to investigate wettability properties and color changes of heat-treated Betung bamboo strand. The 1/3 middle of Betung bamboo was used as main material and converted into strand. Heat treatment temperatures applied were 140oC and 160oC for 3 hours. The wettability of Phenol Formaldehyde (PF) adhesive on heat treated Betung bamboo strand was measured using a sessile drop contact angle method. Constant contact angle and K-value were used as parameter of wettability. Color change of heat-treated Betung bamboo strand was measured by portable color difference meter model CDX 105 and characterized by CIE Lab. Results showed that the increasing temperature of heat treatment affected wettability and color properties. Contact angle tended to increase with an increase of temperature which is indicated an enhancement of wettability by making wood more hydrophobic. Increasing of temperature made Betung bamboo strand to be darker than that of control sample. Total color change (AE) values were 21.06 and 29.23 at 140 and 160 oC, respectively.

Research on the treatment of heavy metal pollution in urban soil based on biochar technology

Biochar is a material for remediating soil contaminated by heavy metals, and it is also a remediation material for soil improvement. The remediation effect of biochar and its mechanism have been widely concerned in the environmental field. The most important factor that determines the effect of biochar remediation is the diversity of its physical and chemical properties. Cities are extremely important places for human life and production. From a global perspective, the area of cities only occupies less than 2% of the surface area. Urban soil refers to the general term for the original characteristics of the soil in the city or in the suburbs of the city, which are affected to varying degrees by human activities. Therefore, it is very meaningful to study the ecological effects, the chemical migration characteristics of the earth and the sources of heavy metals in urban soils. Based on the current status of heavy metal pollution in urban soils, and at the same time, due to the application potential of biochar in remediation of heavy metal contaminated soil and soil improvement, it is studied to study the effect of 400 °C sludge biochar on heavy metals (Cr, Zn, Cu) The remediation effect of contaminated soil, and at the same time, the raw material sludge is directly used as the remediation material to compare the long-term effects of sludge biochar and sludge on the physical and chemical properties of the soil, the form of heavy metals and the bioavailability, and fully consider The effect of biochar’s aging effect on the repair effect.

Study on desulfurization mechanism of ionic liquid extractant based on Gaussian quantitative calculation

In this paper, five kinds of ionic liquids (ILs) are selected as desulfurization extractants to study the desulfurization mechanism. Based on density functional theory (DFT), B3LYP functional and 6–31++G** basis set, Quantum chemistry calculations were carried out on each substance. And the interaction mechanism between the ionic liquid extractant, benzothiophene (BT), and N-octane (OC) was explored. Through quantitative calculation, the interaction energy between the three is obtained. Natural Bond Orbital theory (NBO) analysis, AIM analysis and RDG analysis are adopted to study the desulfurization mechanism from the second-order perturbation energy of chemical bond orbits, charge migration, hydrogen bonding, and other types of van der Waals forces, etc. The results show that in the interaction force between ILs and BT, electrostatic interaction is the main force, followed by hydrogen bonding, π-π interaction and other types of weak interactions such as van der Waals forces have a certain degree of desulfurization.

The hydrodynamic mechanism of rainfall runoff from loess slopes treated with incorporated straw

AbstractThe hydrodynamic parameters of rainfall runoff are important for those studying hillslope water flow, which in turn affects soil erosion, chemical pollutant migration, and diffusion. Straw incorporation into the cultivated soil layer may affect soil properties, resulting in different hydrodynamic behaviours of hillslope runoff. The objective of this study was to evaluate the influences of straw incorporation, rainfall intensity, and slope gradient on hydraulic parameters, such as the Reynolds number (Re), Froude number (Fr), Darcy‐Weisbach friction factor (f), and hydrodynamic dispersion coefficient (DH). Laboratory experiments were conducted under four straw incorporation rates (SRs: 0, 2, 4, and 8 t ha−1), three rainfall intensities (RIs: 80, 120, and 160 mm hr−1), and three slope gradients (SGs: 10, 15, and 20°) to examine the hydrodynamic characteristics. The results show that the increase in SR significantly reduces the DH. Compared with bare soil slope (0.020 m2 s−1), the mean DH decreased by half (0.011 m2 s−1) at an SR of 2 t ha−1 and approximately three‐quarters (0.005 m2 s−1) at an SR of 8 t ha−1. Both Re and Fr decreased with a rise in the SR; however, the slope roughness increased, which caused a significant increase in frictional force compared to results observed for the bare soil. A rise in RI and SG increased the driving force on the farmland slope. The Re and Fr decreased with RI and SR, while f increased with RI and SG. Therefore, this study elucidates that the incorporation of straw in the soil can alter the hydrodynamic parameters, thus influencing water flow velocity and soil erosion.

Development of an in vitro model to simulate migration of organic contaminants from pad products to human sweat and enhance dermal exposure risk assessment

Dermal sorption is an important route for human exposure to organic chemicals embedded in consumer products, but the related chemical migration from consumer products to sweats was often overlooked in assessing skin exposure risk. To address this issue, the present study selected polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), and benzothiazoles (BTs) as the target compounds and developed an in vitro simulation model with two artificial sweats (i.e., acidic and alkaline), a sorbent, and a PVC standard material. An appropriate biological inhibitor (ampicillin) and incubation time of 20 d for assessing the maximum migration efficiency of chemicals were selected. The mass balance of the target compounds during the in vitro incubation was verified. The established in vitro simulation model was used to determine the migration ratios of PAEs and BTs in three types of mouse pads. The maximum migration ratios of DBP, DIBP, DEHP, and BT from leather pad to both sweats were less than those for silicone and rubber pads. Key controlling parameters in migration ratios should be examined in subsequent investigations. Risk assessment showed that the daily exposure doses of PAEs and BTs in mouse pads were higher than the literature data. The hazard index of PAEs in leather pad exceed 1, indicating that PAEs could induce non-carcinogenic effects to human health through hand contact. Overall, the established in vitro simulation model provides a feasible alternative for assessing the potential risk for dermal exposure to consumer products.

Estimating mouthing exposure to chemicals in children\u2019s products

BackgroundExisting models for estimating children’s exposure to chemicals through mouthing currently depends on the availability of chemical- and material-specific experimental migration rates, only covering a few dozen chemicals.ObjectiveThis study objective is hence to develop a mouthing exposure model to predict migration into saliva, mouthing exposure, and related health risk from a wide range of chemical-material combinations in children’s products.MethodsWe collected experimental data on chemical migration from different products into saliva for multiple substance groups and materials, identifying chemical concentration and diffusion coefficient as main properties of influence. To predict migration rates into saliva, we adapted a previously developed migration model for chemicals in food packaging materials. We also developed a regression model based on identified chemical and material properties.ResultsOur migration predictions correlate well with experimental data (R2 = 0.85) and vary widely from 8 × 10−7 to 32.7 µg/10 cm2/min, with plasticizers in PVC showing the highest values. Related mouthing exposure doses vary across chemicals and materials from a median of 0.005 to 253 µg/kgBW/d. Finally, we combined exposure estimates with toxicity information to yield hazard quotients and identify chemicals of concern for average and upper bound mouthing behavior scenarios.SignificanceThe proposed model can be applied for predicting migration rates for hundreds of chemical-material combinations to support high-throughput screening.

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern- and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration.

Tackling the toxics in plastics packaging.

The widespread use of plastic packaging for storing, transporting, and conveniently preparing or serving foodstuffs is significantly contributing to the global plastic pollution crisis. This has led to many efforts directed toward amending plastic packaging’s end of life, such as recycling, or alternative material approaches, like increasingly using paper for food packaging. But these approaches often neglect the critical issue of chemical migration: When contacting foodstuffs, chemicals that are present in packaging transfer into food and thus unwittingly become part of the human diet. Hazardous chemicals, such as endocrine disrupters, carcinogens, or substances that bioaccumulate, are collectively referred to as “chemicals of concern.” They can transfer from plastic packaging into food, together with other unknown or toxicologically uncharacterized chemicals. This chemical transfer is scientifically undisputed and makes plastic packaging a known, and avoidable, source of human exposure to synthetic, hazardous, and untested chemicals. Here, I discuss this issue and highlight aspects in need of improvement, namely the way that chemicals present in food packaging are assessed for toxicity. Further, I provide an outlook on how chemical contamination from food packaging could be addressed in the future. Robust innovations must attempt systemic change and tackle the issue of plastic pollution and chemical migration in a way that integrates all existing knowledge.

Interfacial structures between aluminum nitride and Cu–P–Sn–Ni brazing alloy with Ti film

Control of Ag electro chemical migration is crucial for long–term reliability of electrical components in high–voltage applications. In this work, Cu was bonded onto an AlN substrate at temperatures between 650 °C and 950 °C for 1 h using a Ag free Cu–P–Sn–Ni brazing filler metal with Ti as an active metal addition. The interfacial structure between the Cu and the AlN and the mechanical properties of the bond were both investigated. Three different phases which contain Ti and O were observed during the growth process of the Cu/AlN interfacial reaction layer: an amorphous P–Ti–O phase, an amorphous Ti–O phase and rutile, TiO2. The most stable Cu/AlN interfacial structure occurred when rutile was present, and where a particular orientation relationship with AlN was observed: TiO2 (101)//AlN (0001), TiO2 [010]//AlN [ $$11\overline{2}0$$ ]. The probability of Cu/AlN interfacial fracture decreased as the bonding temperature was increased. Cu/AlN interfacial fracture was completely suppressed above 850 °C where rutile was the dominant phase at the Cu/AlN interface.

Migration of polymer additives and radiolysis products from irradiated PET/PE films into a food simulant

The commercial application of food irradiation has raised increasing concern regarding the migration of chemical hazards from irradiated food packaging materials which may threaten food safety and human health. In this study, polymer additives and radiolysis products that migrated from irradiated PET/PE films into a fatty food simulant (95% ethanol) were identified using a UHPLC-QTOF/MS method. Based on the identification results, six additives were selected and their migration behaviors were evaluated under the effect of gamma and electron beam irradiation at a dose of 10 kGy. No significant change in migration levels was observed after irradiation treatment in additives with superior resistance to irradiation (e.g., fatty acid amides). Migration levels of additives vulnerable to irradiation (e.g., antioxidants and disubstituted glycerides) exhibited a decrease, which varied between the different types of irradiation treatments. Decrease in the concentration of phosphite antioxidant (Irgafos 168) was associated with increase in the concentration of its oxidized product (Irgafos 168-ox) that was induced by irradiation. In addition, migration levels of additives were affected by partitioning between the polymer and the food simulant. A high migration level was observed in antioxidants that were predominantly present in the food simulant (due to migration) rather than in the polymer before irradiation treatment. The findings of the present study provide insights into future studies on chemical migration from packaging materials into irradiated food.

Trace element fractionation in water-bearing silicic magmas

Crystallization of a hydrous andesite within a thermal boundary layer at 500 MPa pressure is simulated experimentally using the intrinsic thermal gradient of 10 mm length capsules in a horizontally arranged piston-cylinder apparatus. Magma solidification is programmed at two distinct cooling rates, slow (0.6 °C/h) and rapid (9.6 °C/h). Bulk laser ablation (LA-ICP-MS) analyses across the thermal gradient shed light about fractionation efficiency for trace elements at conditions of slow cooling in which, water-rich fluids favours element mobility. Compositional and textural features of our experiments provide new insights on the kinetics of trace element fractionation in water-bearing intermediate magmas. These features, together with the unrealistic diffusion values measured in the capsules (close to 10–6 cm2 s−1), indicate that incompatible elements co-migrate with a water-rich fluid phase, expelled from a crystal-rich network or mush, by gas-driven filter pressing. In the studied system, diffusive transport proceeded in the same direction of chemical elements migration by advection. It is proposed that liquid segregation is particularly effective at the thermal boundary layers created at the margins of ascent conduits and the walls of magma chambers. Fluxing of a trace element-rich fluid into the hotter, crystal-poor areas, at central and/or upper zones of magma chambers, gives rise to compositional zoning and, eventually, to the formation of silicic cupolas, which are preferential places for ore deposit generation.

Potential impacts of shale and tight gas developments on unconfined aquifers – a chemical screening framework

The Geological and Bioregional Assessment Program examines the potential impacts of shale, tight and deep coal gas development on water and the environment. A key part of the project was quantifying the potential for a decline in the water quality of unconfined aquifers due to unintentional chemical release at the soil surface. To assess this hazard, a quantitative analysis of chemical migration pathways was undertaken, which involved the estimation of contaminant attenuation by dilution and dispersion in soil and groundwater. This provided a conservative screening approach to identify areas for further analysis. Attenuation calculations involved one-dimensional advection-dispersion (AD) simulations through the unsaturated zone, and three-dimensional AD solute transport within the surficial aquifers. Dilution factor (DF) relationships for the combined effect of attenuation in the unsaturated and saturated zone were used to construct spatial maps of the potential for impact on aquifer properties after accidental chemical spills. A higher DF (therefore lower consequence of the surface contamination) was associated with deeper unsaturated zones characterized by heavier soils near the surface, and lower ground water velocities due to lower hydraulic conductivity and/or hydraulic gradient in the saturated zone. The framework was applied across the Cooper Basin and Beetaloo Sub-basin and resulted in two types of maps. The first identified areas being more susceptible to contamination if soil remediation does not occur within a 10-year period. The second map shows the spatially variable combined DFs for a ground water receptor, which may be used to develop site-specific management plans and mitigation measures.

Element Accumulation Patterns of Native Plant Species under the Natural Geochemical Stress.

A biogeochemical study of more than 20,000 soil and plant samples from the North Caucasus, Dzungarian Alatau, Kazakh Uplands, and Karatau Mountains revealed features of the chemical element uptake by the local flora. Adaptation of ore prospecting techniques alongside environmental approaches allowed the detection of geochemical changes in ecosystems, and the lessons learned can be embraced for soil phytoremediation. The data on the influence of phytogeochemical stress on the accumulation of more than 20 chemical elements by plants are considered in geochemical provinces, secondary fields of deposits, halos surrounding ore and nonmetallic deposits, zones of regional faults and schist formation, and over lithological contact lines of chemically contrasting rocks overlain by 5–20 m thick soils and unconsolidated cover. We have corroborated the postulate that the element accumulation patterns of native plants under the natural geochemical stress depend not only on the element content in soils and the characteristics of a particular species but also on the values of ionic radii and valences; with an increase in the energy coefficients of a chemical element, its plant accumulation decreases sharply. The contribution of internal factors to element uptake from solutions gives the way to soil phytoremediation over vast contaminated areas. The use of hyperaccumulating species for mining site soil treatment depends on several external factors that can strengthen or weaken the stressful situation, viz., the amount of bedrock exposure and thickness of unconsolidated rocks over ores, the chemical composition of ores and primary halos in ore-containing strata, the landscape and geochemical features of sites, and chemical element migration patterns in the supergene zone.