Influence of ageing on lead bioavailability in soils: a swine study

Importance of arsenic bioaccessibility in health risk assessment based on iron "Minette" rocks and related soils

Total element concentrations by themselves are not always good predictors of toxicity and are therefore not suitable for eco- and/or human toxicological risk determination. In addition, despite the growing call for harmonization, countries show significant variation in risk assessment tools, screening/background values, protocols and legal management of soils. By incorporating mobility and bioaccessibility/availability into soil risk assessments, location-specific physico-chemical and geological conditions can be considered in routinely applied general risk assessment methodologies. Minette soils and rocks are a great case in point since they often are associated with high geogenic As concentrations and consequently potential risks. Minette iron ores form the world largest Fe ore deposits since the "great oxidation". For the first time, oral bioaccessibility during direct ingestion was assessed on Minettes from Luxembourg by applying the in vitro Solubility/Bioavailability Research Consortium (SBRC) method. Out of > 180 samples, 25 representative samples were selected providing a unique dataset which showed an average gastric bioaccessibility of ∼10% (7.8 ± 4.0 mg/kg) of the total As-concentration, with a maximum of 45% (17.9 mg/kg). Of importance is that bioaccessibility of As in Minette rocks and soils are controlled by, and can be estimated from, lithology, mineralogy and total Ca content. Soils and ooid grainstones with an iron oxide or clayey matrix, are characterized by average gastric bioaccessible As concentrations < 6 mg/kg. Gastric As bioaccessibility is highest in Fe-bearing calcite-cemented bioclastic grainstones (∼12 mg/kg). Importantly, for all samples the maximal bioaccessible As concentrations remain below the threshold from which significant adverse non-carcinogenic and/or carcinogenic health effects are expected. These new results are in strong contrast with what total As concentrations might suggest. Considering bioaccessibilities, consequently, can help to avoid disproportionate, costly and environmentally impacting risk management strategies. Furthermore, this study illustrates the importance of cross-disciplinary collaboration between geo- and health scientists.

Can the mouse model successfully predict mixed metal(loid)s bioavailability in humans from contaminated soils?

Mouse models have been employed by many scientific research groups worldwide to predict the bioavailability of metal (loid)s and other chemicals in humans. Their suitability for predicting mixed metal (loid) bioavailability has been questioned and debated for decades by many research teams. In this study soils contaminated by lead (Pb) and arsenic (As), either in the field or by spiking in the laboratory, were used in bioavailability and bioaccessibility tests. The spiked soils were aged for more than a year prior to testing to achieve steady state and eliminate soil ageing effects, as reported in previous research. The bioavailability of, firstly, Pb in the presence of As and secondly, As in the presence of Pb was determined using mice. Furthermore, bioaccessibility was determined using a range of in vitro methods: relative bioaccessibility leaching procedure (RBALP), the Unified Bioaccessibility Research Group Europe (BARGE) method (UBM) gastric and intestinal phases, and the National Institute for Public Health and the Environment (RIVM) gastric and intestinal phases. The correlations between Pb and As bioavailability and their in vitro bioaccessibility when they were present in mixtures were analysed. The results indicated that the bioavailability of Pb in mice kidney tissues significantly correlated with bioaccessibility of Pb in RBALP (p < 0.01), UBM gastric (p < 0.01) and intestinal phases (p < 0.01) and RIVM gastric phases when Pb is present in metal (loid) mixtures. Results of the current study reveal that the RBALP, and UBM gastric and intestinal phase were by far the best methods for predicting the RB of Pb when it is present in metal (loid) mixtures. Consequently, the mouse model can successfully explain the in vivo in vitro correlation (IVIVC) of Pb when it is present in metal (loid) mixtures. However, we did find that a mouse model may not be the best one to explain the IVIVC of As when it is present in metal (loid) mixtures.

Phytoextraction of Cu, Cd, Zn and As in four shrubs and trees growing on soil contaminated with mining waste

Mining activity has degraded large extensions of soil and its waste is composed of metals, anthropogenic chemicals, and sterile rocks. The use of native species in the recovery of polluted soils improves the conditions for the emergence of other species, tending to a process of ecosystem restoration. The objective of this study was to evaluate the bioaccumulation of metal(loid)s in four species of native plants and the effect of their distribution and bioavailability in soil with waste from an abandoned gold mine. Soil samples were taken from two sites in La Planta, San Juan, Argentina: Site 1 and Site 2 (mining waste and reference soil, respectively). In Site 1, vegetative organ samples were taken from Larrea cuneifolia, Bulnesia retama, Plectrocarpa tetracantha, and Prosopis flexuosa. The concentration of metal(loid)s in soil from Site 1 were Zn > As > Cu > Cd, reaching values of 7123, 6516, 240 and 76 mg kg^-1, respectively. The contamination indices were among the highest categories of contamination for all four metal(loid)s. The spatial interpolation analysis showed the effect of the vegetation as the lowest concentration of metal(loid)s were found in rhizospheric soil. The maximum concentrations of As, Cu, Cd and Zn found in vegetative organs were 371, 461, 28, and 1331 mg kg^-1, respectively. L. cuneifolia and B. retama presented high concentrations of Cu and Zn. The most concentrated metal(loid)s in P. tetracantha and P. flexuosa were Zn, As and Cu. Cd was the least concentrated metal in all four species. The values of BAF and TF were greater than one for all four species. In conclusion, the different phytoextraction capacities and the adaptations to arid environments of these four species are an advantage for future phytoremediation strategies. Their application contributes to the ecological restoration and risk reduction, allowing the recovery of ecosystem services.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 μg g-1) were found in plant tissue compared to Pb (277.2 ± 18.0 μg g-1) and Cu (255.3 ± 25.6 μg g-1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

Impacts of sewage sludges deposition on agricultural soils: Effects upon model soil organisms

During years sewage sludges have been worldwide poured in agricultural soils to enhance vegetal production. The "Landfill 17" located in Gernika-Lumo town (43°19'28.9"N 2°40'30.9"W) received for decades sewage sludges from the local Waste Water Treatment Plant (WWTP) with agricultural purposes. To this WWTP, several pollutants as heavy metals (Cd, Cr, Ni, Pb), PAHs (benzo(a)pyrene among many others) and pesticides (i.e. dieldrin) could have arrived from local industry and be widespread all over the landfill. Soil invertebrates like earthworms and plants are of special interest due to their close contact with the polluted matrix and their potential effects by the presence of pollutants. In this context, the aim of the present work was to determine the health status of landfill soils by evaluating the effects on model soil organisms exerted by long-lasted pollutants after on site deposition of WWTP active sludges. With such a purpose, different standard toxicity tests and cellular level endpoints were performed on lettuce and earthworms. Indeed, germination (EPA 850.4100) and root elongation (EPA 850.4230) tests were carried out in Lactuca sativa, while OECD acute toxicity test (OECD-204), reproduction test (OECD-222) and Calcein-AM viability test with coelomocytes were applied in Eisenia fetida worms. For the exposure, soils collected in the landfield containing low, medium and high concentrations of pollutants were selected, and as reference LUFA 2.3 natural standard soil was chosen. While no differences were shown in the assays with L. sativa, significant differences between sludge exposed groups and control group were recorded with E. fetida, with lower coelomocyte number and viability and higher tissue metal accumulation after 28 days of exposure to polluted soils. These results confirmed the impact of contaminants to soil biota even after long periods of time.

Removal mechanism of Pb(II) by Penicillium polonicum: immobilization, adsorption, and bioaccumulation

Currently, lead (Pb) has become a severe environmental pollutant and fungi hold a promising potential for the remediation of Pb-containing wastewater. The present study showed that Penicillium polonicum was able to tolerate 4 mmol/L Pb(II), and remove 90.3% of them in 12 days through three mechanisms: extracellular immobilization, cell wall adsorption, and intracellular bioaccumulation. In this paper. the three mechanisms were studied by Raman, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results indicated that Pb(II) was immobilized as lead oxalate outside the fungal cell, bound with phosphate, nitro, halide, hydroxyl, amino, and carboxyl groups on the cell wall, precipitated as pyromorphite [Pb₅(PO₄)₃Cl] on the cell wall, and reduced to Pb(0) inside the cell. These combined results provide a basis for additionally understanding the mechanisms of Pb(II) removal by P. polonicum and developing remediation strategies using this fungus for lead-polluted water.

Toxic effects of lead in plants grown in brazilian soils

Lead (Pb) in soils can be transferred to plants, animals, and even humans. The toxicity of Pb is worrisome and therefore environmental quality criteria, established by laws to support the management of contaminated sites, have been developed to prevent its deleterious effects in a wide range of soils, uses, and occupations. In Brazil, the CONAMA Resolution 420/2009 established that Brazilian states may define their prevention values (PV) for metals in soils. However, the established values should be well studied, since a wide variation of sensitivity of species exposed to Pb is reported and several have a high tolerance. We aimed to evaluate Pb toxicity to validate the suitability of the current Brazilian Pb-prevention value. A trial was carried with two plant species (sorghum and soybean) grown in two tropical soils (Typic Hapludox and Rhodic Acrudox), following ISO 11.269-2 protocols (ISO 2012). The tested soils were contaminated with Pb-acetate at the following concentrations: 0, 200, 400, 800, 1200, 1600, 2200, 2800, and 3200 mg kg^-1 of dry soil. Differences regarding species sensitivity were observed and sorghum seemed to be less sensitive to Pb concentration in soils. Soil characteristics as higher clay and organic matter content were responsible for decreasing the overall availability of Pb for plants. Using data from this study and from the literature, we constructed a species sensitivity distribution curve and calculated the HC5 (hazardous concentration to 5% of variables evaluated). The HC5 was 132.5 mg kg^-1, which suggests that the PV currently used in Brazil (72 mg kg^-1) is sufficiently protective for Brazilian soils.

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.

Sorption and immobilization of Cu and Pb in a red soil (Ultisol) after different long-term fertilizations

The sorption and immobilization of Cu and Pb in a red soil (Ultisol) treated by no fertilizer (Ck), chemical fertilizer (NPK), a mixture of chemical fertilizer and straw (NPKS), and animal manure (AM) from a long-term fertilization experimental site were studied. Compared to the sorption on Ck soil, the maximum amount of Cu and Pb sorption increased by 16% and 31%, 19% and 42%, and 30% and 45% on NPK, NPKS, and AM soil, respectively. The removal of organic matter from soils decreased the sorption of Cu but increased the sorption of Pb. The sorption of Cu and Pb on the examined soils was reduced by the presence of Ca. However, the inhibition was smaller on the fertilized soils than on non-fertilized soil and was weaker for Pb than for Cu. After the aging of Cu and Pb in the examined soils for 2 months, the proportion of reducible Pb was much higher than that of reducible Cu, whereas that of acid-soluble Cu was much higher than that of acid-soluble Pb in the corresponding soils. The fertilization, especially AM treatment, decreased the percentage of the acid-soluble fraction of Cu and Pb but increased the proportion of the reducible fraction, suggesting that the immobilization of Cu and Pb in the Ultisol was strengthened by the fertilization, especially by the animal manure treatment. These findings could be useful in assessing and controlling heavy metal pollution in Ultisols.

Use of Routine Soil Tests to Estimate Pb Bioaccessibility

Soil lead (Pb) hazard level is contingent on bioavailability, but existing assays that estimate Pb bioavailability for human health risks are too expensive or otherwise inaccessible to many people that are impacted by Pb-contaminated soil. This study investigated the use of routine soil nutrient tests to estimate soil-Pb bioaccessibility as a surrogate measure of Pb bioavailability. A silt loam soil was spiked to a target concentration of 2000 mg Pb kg^-1 with Pb(NO₃)₂ and amended with H₃PO₄ (varying P-to-Pb molar ratios) and KCl (Cl-to-P molar ratio of 2:5) to generate soils with similar total Pb concentrations but a range of Pb bioavailability (and bioaccessibility). Soils were extracted using Mehlich 3, Mehlich 1, Bray P1, Olsen, and  micronutrient (DTPA) methods, and the results were compared to U.S. Environmental Protection Agency method 1340 data as well as to extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mehlich 3 and method 1340 treatment effect ratios were well-correlated ( r² = 0.88, p ≤ 0.05), whereas Bray P1, DTPA, and Olsen results were more reflective of EXAFS data. Preliminary animal-feeding trials suggest that the Mehlich 3 is as effective as method 1340 at predicting the impact of P treatment on Pb relative bioavailability; however, both methods over-estimated the Pb hazard to mice in P-amended soil. Other routine soil tests that have heightened sensitivity to P amendment (e.g., Bray P1) may be promising candidates for Pb bioaccessibility assessment.

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.

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.

Predicting plant uptake of cadmium: validated with long-term contaminated soils

Cadmium accumulates in plant tissues at low soil loadings and is a concern for human health. Yet at higher levels it is also of concern for ecological receptors. We determined Cd partitioning constants for 41 soils to examine the role of soil properties controlling Cd partitioning and plant uptake. From a series of sorption and dose response studies, transfer functions were developed for predicting Cd uptake in Cucumis sativa L. (cucumber). The parameter log K_f was predicted with soil pH_ca, logCEC and log OC. Transfer of soil pore-water Cd²⁺ to shoots was described with a power function (R ² = 0.73). The dataset was validated with 13 long-term contaminated soils (plus 2 control soils) ranging in Cd concentration from 0.2 to 300 mg kg^-1. The series of equations predicting Cd_shoot from pore-water Cd²⁺ were able to predict the measured data in the independent dataset (root mean square error = 2.2). The good relationship indicated that Cd uptake to cucumber shoots could be predicted with Cd_pore and Cd²⁺ without other pore-water parameters such as pH or Ca²⁺. The approach may be adapted to a range of plant species.

Feasibility of using humic substances from compost to remove heavy metals (Cd, Cu, Ni, Pb, Zn) from contaminated soil aged for different periods of time

There is a need for inexpensive, readily-available and environmentally-friendly soil washing agents to remediate polluted soils. Thus, batch washing experiments were performed to evaluate the feasibility of using a solution of humic substances (HS) extracted from compost as a washing agent for simultaneous removal of Cu, Cd, Zn, Pb and Ni from artificially contaminated soils aged for 1 month, 12 months and 24 months. The efficiency of metal removal in single and multiple washings and kinetic constants (equilibrium metal concentration qe and rate constant k from the second-order kinetic equation) were determined. On average, triple washing removed twice as much metal as that removed with a single washing. At pH 7 and a HS concentration of 2.2 g C L(-1), metal removal from all soils decreased in this order: Cd (79.1-82.6%) > Cu (51.5-71.8%) > Pb (44.8-47.6%) > Ni (35.4-46.1%) > Zn (27.9-35.8%). However, based on qe (mg kg(-1)), metal removal was in this order: Pb > Zn ≈ Cu > Ni > Cd. This difference was due to different concentrations of metals, which is typical for multi-metal contaminated soils. Regardless of washing mode, removal of Cd and Pb was not affected by soil age, whereas removal of Cu, Ni and Zn was higher in soils that had been aged for a shorter time. These results indicate that HS are suitable for remediating soil contaminated with multiple heavy metals in extremely high concentrations.