Variability in plant trace element uptake across different crops, soil contamination levels and soil properties in the Xinjiang Uygur Autonomous Region of northwest China.

This study investigated contamination status of eight trace elements (As, Cd, Cr, Hg, Pb, Cu, Zn and Ni) in farmland soils and crops at 535 sites across the Xinjiang Uygur Autonomous Region, Northwest China. Land use types of the sampling sites included vegetable patch, grain field and orchard. Our experimental results indicated all farmland soils were considered as trace element contamination based on the Nemerow comprehensive pollution index (NCPI > 1). However, 91.97% of the crop samples were uncontaminated according to the Chinese Risk Control Standard. Soils from the vegetable patch showed higher pollution level comparison with that from grain field and orchard. Health risks for both non-carcinogenic and carcinogenic risks were calculated through crop ingestion exposure pathway. Grain samples showed highest health risks, followed by melon and fruit, and vegetables. The health risks of crops were mainly driven by Cr and Cd. Crop consumption may pose risks for children but not adults. The source of trace element contamination in the different farmland soils varied and may be attributed to the different agricultural activities. Plant type had a greater influence on the trace element accumulation in crops compared with soil trace element contents and physicochemical properties.

Comparison of in vitro models in a mice model and investigation of the changes in Pb speciation during Pb bioavailability assessments.

In this study, the predominant Pb minerals prior to and after Pb relative bioavailability (Pb-RBA) and Pb bioaccessibility (Pb-BAc) tests were identified using SEM (scanning electron microscopy), XANES (X-ray absorption near edge structure) and XRD (X-ray diffraction). The correlations between in vitro Pb-BAc (using the UBM (Unified BARGE Method) and RBALP (Relative BioAccessibility Leaching Procedure) models) and in vivo Pb-RBA (using endpoints of kidney and liver in an mice model) were determined. The results demonstrated that both RBALP and UBM (gastric phase) reliably indicate Pb-RBA (Pb-RBA). However, raising the solid:liquid ratio of the gastric phase of UBM is necessary to determine Pb-BAc if the soils contain total Pb >10,000 mg/kg. The comparison of Pb minerals prior to and after in vitro extractions demonstrated that the relatively soluble forms of Pb (PbSO4, PbO2 and MgO Pb) start to dissolve than other forms of Pb minerals, suggesting there was no difference in Pb2+ release between chemical-based (RBALP) and physiologically-based (UBM) models. The identification of the Pb minerals of Pb5(PO4)3Cl and organically-complexed Pb in mice excreta demonstrated that a portion of Pb2+ combined with food and humic acid to generate organically-complexed Pb in mice excreta, and that Pb5(PO4)3Cl is not bioavailable.

Effects of the ephemeral stream on plant species diversity and distribution in an alluvial fan of arid desert region: An application of a low altitude UAV.

Biodiversity conservation, plant growth and spatial distribution of plant species are the central issues in contemporary community ecology. Ephemeral stream may influence soil properties, which in turn may determine biodiversity and function of an ecosystem in alluvial fan of arid desert region. Ephemeral stream is one of the most common natural disturbances, yet the effects of the ephemeral stream on plant communities in terms of species diversity and plant species distribution remain poorly studied. In this study, the information of species distribution, ephemeral stream beds ('washes'), and the characteristics of plant growth, i.e. height, crown area, were interpreted at different heights using the images of low altitude unmanned aerial vehicle (UAV). After that, soil properties such as soil texture (sand, silt and clay), soil water content, pH, soil organic matter, soil electric conductivity, soil bulk density and the percentage of gravel content, and their relationships with UAV data were assessed in order to explore the influences of ephemeral stream on species diversity, plant growth characteristics and species distribution in an alluvial fan of arid desert region. The results showed that deep-rooted plants were only distributed in washes whereas shallow-rooted plants were distributed in both washes and the outside of washes ('non-washes'). Species richness was significantly higher in washes than that in non-washes whereas the opposite pattern was true for abundance. Soil properties, plant height and crown area were higher in washes than that in non-washes. Plant height, crown area and the total number of individual plants increased with increasing wash width and per unit length of stream flow. This study highlights that the coupling factors of ephemeral stream, such as soil erosion, particle transport and sedimentation, can dramatically cause changes in soil properties and total number of individual plants, and hence, can influence species diversity, plant growth characteristics and spatial distribution of plant species in an alluvial fan of arid desert regions.

Bioavailability and risk estimation of heavy metal(loid)s in chromated copper arsenate treated timber after remediation for utilisation as garden materials.

There is increasing concern about the use of chromated copper arsenate (CCA) treated timber due to the possible leaching of toxic metals or metalloids. CCA-treated timber waste are currently stockpiled across Australia with limited information about their risks to the environment or human health. In this study, the treatment and utilisation of CCA-treated timber waste as garden mulch, garden retaining walls, and soil additive were investigated. Iron materials were used as immobilising agents. The bioavailability of Cr, Cu and As to Spinacia oleracea from CCA-treated timber, before and after treatment, was determined in the context of human health risk assessment. The results showed that the iron-based treatments resulted in significant decreases in the concentrations of Cu and As in spinach grown in CCA-treated timber in soil. Analyses of CCA derived Cu and As in spinach showed that they accumulated in the roots rather than in the leaves. The risks of toxicity to humans varied for different utilisation scenarios and the immobilisation amendments were shown to reduce carcinogenic and non-carcinogenic risks. The information obtained in this study can inform development of utilisation options for CCA-treated timber wastes.

The source of lead determines the relationship between soil properties and lead bioaccessibility.

Lead (Pb) contaminated soil is of particular concern for infants and children due to their susceptibility to exposure, fast metabolic rates and rapidly developing neuronal systems. Determining the bioaccessibility of Pb in soils is critical in human health risk assessments, which can vary due to different soil properties and sources of Pb contamination. In this study, the potential relationships between soil properties and Pb bioaccessibility from various Pb sources including Pb contamination from mining (specifically, Broken Hill), three shooting ranges, a smelter and two industry sites (pottery and battery), were investigated using the Relative Bioavailability Leaching Procedure (RBALP). We found the following: (1) CEC, TOC, sand and silt content, and total Pb were significantly different (p < 0.05) between the two particle size fractions of < 2 mm and < 250 µm; (2) EC, CEC and total Pb were significantly correlated to Pb bioaccessibility (p < 0.05); and (3) soil analyses based on source of Pb demonstrated a strongly significant relationship between Pb bioaccessibility and soil properties (CEC, EC, clay content and total Pb) for mining soils from Broken Hill (r2 = 0.86, p < 0.05, n = 18). These results demonstrated the influences of Pb contamination sources, soil properties and particle size fractions on Pb bioaccessibility as well as the prediction of Pb bioaccessibility using soil properties. The findings documented here will help in developing a predictive tool for human health risk assessment and the remediation of Pb contaminated soils.

A Pooled Data Analysis to Determine the Relationship between Selected Metals and Arsenic Bioavailability in Soil.

Chronic exposure to arsenic (As) is a global concern due to worldwide exposure and adverse effects, and the importance of incorporating bioavailability in the exposure assessment and risk assessment of As is increasing acknowledged. The bioavailability of As is impacted by a number of soil properties, such as pH, clay and metal concentrations. By retrieving 485 data from 32 publications, the aim of this study was to determine the relationship between selected metals (Fe and Al) and As bioavailability. In present study, the bioaccessibility (BAC) data measured by in vitro approaches were converted into bioavailability data based on the previously determined relationship between BAC and bioavailability. The As relative bioavailability (RBA) was summarized to be 24.36 ± 18.49%, which is in the range previously reported. A significant association between Fe concentration and the bioavailability of As was observed while this association varied for different types of RBA data. This disparity may suggest a non-reliable association between Fe and As bioavailability. The correlations between logarithmically transformed total content of Fe + Al and As bioavailability is then outlined: RBA = (−8.40 ± 1.02) × Ln(Fe + Al) + (58.25 ± 4.09), R² = 0.25, p < 0.001, n = 212. Jackknife resampling was also applied to validate the relation between total content of (Fe + Al) and As bioavailability, which suggested that the relation is robust. This is the first pooled study to address the relations between selected metal concentrations and As bioavailability, which may provide some implications to establish soil properties-based RBA prediction for As.

Measurement of soil lead bioavailability and influence of soil types and properties: A review.

Lead (Pb) is a widespread heavy metal which is harmful to human health, especially to young children. To provide a human health risk assessment that is more relevant to real conditions, Pb bioavailability in soils is increasingly employed in the assessment procedure. Both in vivo and in vitro measurements for lead bioavailability are available. In vivo models are time- consuming and expensive, while in vitro models are rapid, economic, reproducible, and reliable while involving more uncertainties. Uncertainties in various measurements create difficulties in accurately predicting Pb bioavailability, resulting in the unnecessary remediation of sites. In this critical review, we utilised available data from in vivo and in vitro studies to identify the key parameters influencing the in vitro measurements, and presented uncertainties existing in Pb bioavailability measurements. Soil type, properties and metal content are reported to influence lead bioavailability; however, the differences in methods for assessing bioavailability and the differences in Pb source limit one's ability to conduct statistical analyses on influences of soil factors on Pb bioavailability. The information provided in the review is fundamentally useful for the measurement of bioavailability and risk assessment practices.

Differences in the response of soil dehydrogenase activity to Cd contamination are determined by the different substrates used for its determination.

Dehydrogenase activity (DHA) is an important indicator of heavy metal toxicity in contaminated soils. Different instances of DHA were determined using various substrates and which could affect the description of heavy metal toxicity. Currently, too few investigations have been done on selecting appropriate substrates. This study employed indoor simulation to determine soil DHA and its response to external cadmium (Cd) using two substrates (TTC and INT). Hormesis for DHA obtained using the TTC method (DHA-TTC) in low Cd concentration was observed which was quickly inhibited in high Cd concentration. While DHA obtained using the INT method (DHA-INT) decreased slowly when Cd concentration increased. The DHA-TTC and DHA-INT in soils at Cd concentration of 500 mg kg-1 decreased 86% and 53%, respectively, compared to the control. The dose-response relationship of Cd to DHA can be well simulated using the logistic model (p < 0.01), which indicated DHA could be used to indicate soil Cd toxicity. Multiple stepwise regression analysis revealed that total organic matter (TOC) is the major factor influencing the toxicity of Cd to DHA-TTC, while TOC, pH and cation exchange capacity (CEC) are major factors influencing the toxicity of Cd to DHA-INT. The different responses of soil DHA-TTC and DHA-INT to Cd are due to the differences in electron transport chain characteristics between TTC and INT, as well as the influence of soil properties. Although both DHA-TTC and DHA-INT can monitor soil Cd contamination, DHA-INT is recommended as a superior bio-indicator to indicate and assess contamination of Cd in soil.

A meta-analysis to correlate lead bioavailability and bioaccessibility and predict lead bioavailability.

Defining the precise clean-up goals for lead (Pb) contaminated sites requires site-specific information on relative bioavailability data (RBA). While in vivo measurement is reliable but resource insensitive, in vitro approaches promise to provide high-throughput RBA predictions. One challenge on using in vitro bioaccessibility (BAc) to predict in vivo RBA is how to minimize the heterogeneities associated with in vivo-in vitro correlations (IVIVCs) stemming from various biomarkers (kidney, blood, liver, urinary and femur), in vitro approaches and studies. In this study, 252 paired RBA-BAc data were retrieved from 9 publications, and then a Bayesian hierarchical model was implemented to address these random effects. A generic linear model (RBA (%)=(0.87±0.16)×BAc+(4.70±2.47)) of the IVIVCs was identified. While the differences of the IVIVCs among the in vitro approaches were significant, the differences among biomarkers were relatively small. The established IVIVCs were then applied to predict Pb RBA of which an overall Pb RBA estimation was 0.49±0.25. In particular the RBA in the residential land was the highest (0.58±0.19), followed by house dust (0.46±0.20) and mining/smelting soils (0.45±0.31). This is a new attempt to: firstly, use a meta-analysis to correlate Pb RBA and BAc; and secondly, estimate Pb RBA in relation to soil types.

Using publicly available data, a physiologically-based pharmacokinetic model and Bayesian simulation to improve arsenic non-cancer dose-response.

Publicly available data can potentially examine the relationship between environmental exposure and public health, however, it has not yet been widely applied. Arsenic is of environmental concern, and previous studies mathematically parameterized exposure duration to create a link between duration of exposure and increase in risk. However, since the dose metric emerging from exposure duration is not a linear or explicit variable, it is difficult to address the effects of exposure duration simply by using mathematical functions. To relate cumulative dose metric to public health requires a lifetime physiologically-based pharmacokinetic (PBPK) model, yet this model is not available at a population level. In this study, the data from the U.S. total diet study (TDS, 2006-2011) was employed to assess exposure: daily dietary intakes for total arsenic (tAs) and inorganic arsenic (iAs) were estimated to be 0.15 and 0.028µg/kg/day, respectively. Meanwhile, using National Health and Nutrition Examination Survey (NHANES, 2011-2012) data, the fraction of urinary As(III) levels (geometric mean: 0.31µg/L) in tAs (geometric mean: 7.75µg/L) was firstly reported to be approximately 4%. Together with Bayesian technique, the assessed exposure and urinary As(III) concentration were input to successfully optimize a lifetime population PBPK model. Finally, this optimized PBPK model was used to derive an oral reference dose (Rfd) of 0.8µg/kg/day for iAs exposure. Our study also suggests the previous approach (by using mathematical functions to account for exposure duration) may result in a conservative Rfd estimation.

Quantifying statistical relationships between commonly used in vitro models for estimating lead bioaccessibility.

Bioaccessibility to assess potential risks resulting from exposure to Pb-contaminated soils is commonly estimated using various in vitro methods. However, existing in vitro methods yield different results depending on the composition of the extractant as well as the contaminated soils. For this reason, the relationships between the five commonly used in vitro methods, the Relative Bioavailability Leaching Procedure (RBALP), the unified BioAccessibility Research Group Europe (BARGE) method (UBM), the Solubility Bioaccessibility Research Consortium assay (SBRC), a Physiologically Based Extraction Test (PBET), and the in vitro Digestion Model (RIVM) were quantified statistically using 10 soils from long-term Pb-contaminated mining and smelter sites located in Western Australia and South Australia. For all 10 soils, the measured Pb bioaccessibility regarding all in vitro methods varied from 1.9 to 106% for gastric phase, which is higher than that for intestinal phase: 0.2 ∼ 78.6%. The variations in Pb bioaccessibility depend on the in vitro models being used, suggesting that the method chosen for bioaccessibility assessment must be validated against in vivo studies prior to use for predicting risk. Regression studies between RBALP and SRBC, RBALP and RIVM (0.06) (0.06 g of soil in each tube, S:L ratios for gastric phase and intestinal phase are 1:375 and 1:958, respectively) showed that Pb bioaccessibility based on the three methods were comparable. Meanwhile, the slopes between RBALP and UBM, RBALP and RIVM (0.6) (0.6 g soil in each tube, S:L ratios for gastric phase and intestinal phase are 1:37.5 and 1:96, respectively) were 1.21 and 1.02, respectively. The findings presented in this study could help standardize in vitro bioaccessibility measurements and provide a scientific basis for further relating Pb bioavailability and soil properties.