Toward a more realistic estimate of exposure to chromium and nickel in soils of geogenic and/or anthropogenic origin: importance of oral bioaccessibility.

To enhance risk assessment for contaminated sites, incorporating bioavailability through bioaccessibility as a corrective factor to total concentration is essential to provide a more realistic estimate of exposure. While the main in vitro tests have been validated for As, Cd, and/or Pb, their potential for assessing the bioaccessibility of additional elements remains underexplored. In this study, the physicochemical parameters, pseudototal Cr and Ni concentrations, soil phase distribution, and oral bioaccessibility of twenty-seven soil samples were analysed using both the ISO 17924 standard and a simplified test based on hydrochloric acid. The results showed wide variability in terms of the concentrations (from 31 to 21,079 mg kg-1 for Cr, and from 26 to 11,663 mg kg-1 for Ni) and generally low bioaccessibility for Cr and Ni, with levels below 20% and 30%, respectively. Bioaccessibility variability was greater for anthropogenic soils, while geogenic enriched soils exhibited low bioaccessibility. The soil parameters had an influence on bioaccessibility, but the effects depended on the soils of interest. Sequential extractions provided the most comprehensive explanation for bioaccessibility. Cr and Ni were mostly associated with the residual fraction, indicating limited bioaccessibility. Ni was distributed in all phases, whereas Cr was absent from the most mobile phase, which may explain the lower bioaccessibility of Cr compared to that of Ni. The study showed promising results for the use of the simplified test to predict Cr and Ni bioaccessibility, and its importance for more accurate human exposure evaluation and effective soil management practices.

Oral bioaccessibility of PTEs in soils: A review of data, influencing factors and application in human health risk assessment.

Understanding the behavior of metal(loi)ds transported from soil to humans is critical for human health risk assessment (HHRA). In the last two decades, extensive studies have been conducted to better assess human exposure to potentially toxic elements (PTEs) by estimating their oral bioaccessibility (BAc) and quantifying the influence of different factors. This study reviews the common in vitro methods used to determine the BAc of PTEs (in particular As, Cd, Cr, Ni, Pb, and Sb) under specific conditions (particularly in terms of the particle size fraction and validation status against an in vivo model). The results were compiled from soils derived from various sources and allowed the identification of the most important influencing factors of BAc (using single and multiple regression analyses), including physicochemical soil properties and the speciation of the PTEs in question. This review presents current knowledge on integrating relative bioavailability (RBA) in calculating doses from soil ingestion in the HHRA process. Depending on the jurisdiction, validated or non-validated bioaccessibility methods were used, and risks assessors applied different approaches: (i) using default assumptions (i.e., RBA of 1); (ii) considering that bioaccessibility value (BAc) accurately represents RBA (i.e., RBA equal to BAc); (iii) using regression models to convert BAc of As and Pb into RBA as proposed by the USA with the US EPA Method 1340; or (iv) applying an adjustment factor as proposed by the Netherlands and France to use BAc from UBM (Unified Barge Method) protocol. The findings from this review should help inform risk stakeholders about the uncertainties surrounding using bioaccessibility data and provide recommendations for better interpreting the results and using bioaccessibility in risk studies.

Is the co-application of self-produced compost and natural zeolite interesting to reduce environmental and toxicological availability in metal-contaminated kitchen garden soils?

Composting can turn organic waste into a valuable soil amendment that can improve physical, chemical, and biological soil quality. Compost amendments can also contribute to the remediation of areas anthropogenically degraded by metals. However, it is well known that compost, particularly self-produced compost, can show enrichment in metals. An experimental study was conducted to examine the short- and long-term distribution and the mobility of metals in soils amended with a self-produced compost when it was added alone or in combination with different doses of a natural zeolite to soil. The aim was also to study the interest of managing moderately metal-contaminated kitchen garden soils by assessing the chemical extractability, phytoavailability, and oral bioaccessibility of metals. When zeolite was added to compost alone, it had the tendency to better reduce extractability of Cd and Zn at 25%, and those of Pb at 15%. When the self-produced compost alone or in co-application with zeolite at these doses was applied to soils, the results showed (1) a decrease of NH4NO3-extractable Zn; (2) a reduction of Pb environmental availability, but not Pb bioaccessibility, and (3) an increase of ryegrass biomass. Nevertheless, the risk posed by the self-produced compost was minimal when applied at the proper rate (0.6% w/w). In the selected experimental conditions, the study recommends that self-produced compost be mixed with 15% zeolite to maximize vegetal biomass and minimize environmental risk. The question of sustainability of the results with repeated compost addition is also raised.

Potentials of Miscanthus x giganteus for phytostabilization of trace element-contaminated soils: Ex situ experiment.

Phytomanagement is proposed as a cost-effective and environmentally-friendly suggestion for sustainable use of large metal-contaminated areas. In the current work, the energy crop miscanthus (Miscanthus × giganteus) was grown in ex situ conditions on agricultural soils presenting a Cd, Pb and Zn contamination gradient. After 93 days of culture, shoot and root growth parameters were measured. Soils and plants were sampled as well to study the TE accumulation in miscanthus and the effects of this plant on TE mobility in soils. Results demonstrated that miscanthus growth depended more on the soils silt content rather than TE-contamination level. Moreover, soil organic carbon at T93 increased in the soils after miscanthus cultivation by 25.5-45.3%, whereas CaCl2-extractible TEs decreased due to complex rhizosphere processes driving plant mineral uptake, and organic carbon inputs into the rhizosphere. In the contaminated soils, miscanthus accumulated Cd, Pb and Zn mainly in roots (BCF in roots: Cd " Zn > Pb), while strongly reducing the transfer of these elements from soil to all organs and from roots to rhizomes, stems and leaves (average TFs: 0.01-0.06, 0.11-1.15 and 0.09-0.79 corresponding to Cd, Pb and Zn respectively). Therefore, miscanthus could be considered a TE-excluder, hence a potential candidate crop for coupling phytostabilization and biomass production on the studied Metaleurop TE-contaminated soils.

Toward setting public health guidelines for chemicals in indoor settled dust?

Indoor settled dust may result in substantial human exposure to chemicals, especially by ingestion following hand-to-mouth or hand-to-object-to-mouth contact. As with other environmental media related to exposure, dust may thus be subject to regulation. An international scientific workshop was convened in Paris in September 2019 firstly to assess the relevance for public health of setting guidelines for indoor settled dust, and secondly to discuss scientific and technical challenges related to such guidelines. The main discussions and conclusions, with consensus achieved, are reported herein. Discussions concerned general considerations, objectives and definitions, relevance for a health-based guideline, units of measure, and finally derivation of the guideline. These points should be addressed when considering an indoor settled dust guideline as part of a policy to reduce exposure indoors to a given chemical or group of chemicals.

Urban kitchen gardens: Effect of the soil contamination and parameters on the trace element accumulation in vegetables - A review.

Trace element contaminants in kitchen garden soils can contribute to human exposure through the consumption of homegrown vegetables. In urban areas, these soils can be contaminated to various degrees by trace element (TE). They are characterized by a great variability in their physicochemical parameters due to the high anthropization level, the wide variety and combination of disturbance sources, as well as the diversity of cultivation practices and the large range of contamination levels. Pollutants can be taken up by vegetables cultivated in these soils and be concentrated in their edible parts. In this review, the behavior of vegetables cultivated in contaminated kitchen gardens is assessed through six examples of the most widely cultivated vegetables (lettuce, tomato, bean, carrot, radish, potato). The role of soil parameters that could influence the uptake of As, Cd, Cr, Ni, Pb, and Zn by these vegetables is also discussed.

Evaluation of single-extraction methods to estimate the oral bioaccessibility of metal(loid)s in soils.

Incidental ingestion of polluted soil particles exposes the population to toxic metal(loid)s. To refine the methods of exposure and risk assessment, it is relevant to use bioaccessible concentrations of metal(loid)s determined via in vitro digestion methods. However, some validated methods are complex and costly, involving high technical skills and numerous reagents. The objective of the present study was to evaluate the suitability of four simple chemical extractions to mimic the bioaccessible fraction of As, Cd, and Pb in the gastric (G) and gastrointestinal (GI) phases obtained using the validated UBM (unified bioaccessibility method) test. Acetic acid (0.11 M), citric acid (0.11 M), EDTA (0.16 M), and hydrochloric acid (HCl, 0.65%) were separately tested in 201 soil samples with a wide range of physicochemical parameters and metal(loid)s concentrations. Significant linear relationships were observed with HCl, EDTA, and to a lesser extent with citric acid. For the cheaper HCl method, correlations with the UBM ranged from 0.91 to 0.99 for the G phase and from 0.72 to 0.97 for the GI phase. This test can be used at least as a first-tier screening to assess the oral bioaccessibility of As, Cd, and Pb.

Environmental availability and oral bioaccessibility of Cd and Pb in anthroposols from dredged river sediments.

Dredging and disposal of sediments onto land sites is a common practice in urban and industrial areas that can present environmental and health risks when the sediments contain metallic elements. The aim of this study was to characterise and study the environmental and toxicological availability of Cd and Pb in anthroposols from dredged river sediments. To do this, 67 surface samples spread over 12 sediment disposal sites in northern France were studied. The results showed substantial heterogeneity for this matrix in terms of physicochemical parameters and contamination degree; however, ascending hierarchical clustering made it possible to classify the samples into eight groups. For each group, the mobile fraction of Cd and Pb was studied using single EDTA extraction, solid-phase distribution was analysed with sequential extractions and toxicological availability was assessed with the oral bioaccessibility test. The results showed that (i) Cd had a higher environmental and toxicological availability than Pb; (ii) this availability depends on the physicochemical characteristics of the matrix; and (iii) it is necessary to take into account the environmental and toxicological availability of contaminants when requalifying these sites in order to propose appropriate management measures. In the first years after sediment disposal, it would appear that the environmental and toxicological availability of Cd and Pb increased (from 52.5 to 71.8% and from 28.9 to 48.9%, respectively, by using EDTA and from 50.2 to 68.5% for Cd with the bioaccessibility test). Further studies would therefore be required to confirm this trend and understand the mechanisms involved.

Ex situ evaluation of the effects of biochars on environmental and toxicological availabilities of metals and polycyclic aromatic hydrocarbons.

The present study experimented five biochars, one made from wood (400 °C, 12 h) and four made from miscanthus cultivated on contaminated soils (temperature 400/600 °C, duration 45/90 min). They were used as amendments at a 2% application rate on soil, cultivated or not cultivated with ryegrass, contaminated with (i) metals (Cd, Pb, and Zn), (ii) eight polycyclic aromatic hydrocarbons (PAHs), and (iii) a mix of metals and PAHs. The objectives were (i) to compare the effectiveness of the five biochars on soil parameters and pollutant availability and (ii) to determine the influence of soil multicontamination and ryegrass cultivation on biochar effectiveness. The results showed that biochar application did not necessarily lead to lower pollutant extractability and metal bioaccessibility. However, differences were highlighted between the biochars. The miscanthus biochars produced at 600 °C (BM600) showed higher effectiveness at decreasing metal extractability than the miscanthus biochars produced at 400 °C (BM400) due to its better sorption characteristics. In addition, ryegrass cultivation did not impact pollutant availability but modified metal bioaccessibility, especially for the soil amended with the BM600 and the woody biochar. Moreover, the presence of PAHs also negatively impacted the metal bioaccessibility in the soil amended with the BM600, and, on the contrary, positively impacted it in the soil amended with the BM400. Complementary studies are therefore necessary to understand the mechanisms involved, particularly in a context where soils requiring remediation operations are often multicontaminated and vegetated.

Influence of amendments on metal environmental and toxicological availability in highly contaminated brownfield and agricultural soils.

The immobilizing effects of wood biochar (BW2%) and iron grit (Z1%) applied alone or in combination (BW2% + Z1%) to agricultural (M750) and brownfield (MAZ) soils highly contaminated by metals were assessed in a greenhouse experiment. The results showed that Z1% and BW2% + Z1% were the most efficient amendments to reduce Cd, Cu, Pb, and Zn mobility, environmental availability, and phytoavailability in the M750 soil. The oxidation of Z1% allowed part of the Cu and Zn pools present in exchangeable or carbonate-bound forms (labile fraction) to complex in less mobile forms. In this soil, the metal chemical extractions (0.01 M CaCl2 and 0.05 M EDTA) and the DGT (diffusive gradient in thin films) devices to assess metal in soil solution and soil pore water (SPW) also highlighted the immobilizing characteristic of Z1%. In most cases, the addition of BW2% to Z1% (BW2% + Z1%) did not improve this effect, except for the dissolved Pb and Zn concentrations in the M750 soil solution. It was also observed that Cd, Pb, and Zn passed throughout DGT mimicking the biological cell membrane were reduced by all amendments of the M750 soil corroborating metal concentrations measured in rye grass shoots. In the MAZ soil, metals were less available as shown by their low extractability rate, low capacity of metal resupply from the solid phase to pore water, and low phytoavailability. The poor metal availability could be explained by the high levels of carbonate and organic matter contents in this soil. Nevertheless, a decrease of the Cu environmental availability and the Cu concentrations in rye grass shoots grown on the MAZ soil was also observed in the soil amended with Z1% alone or in combination with BW2%. From a health point of view, the most effective amendment to reduce human exposure through ingestion of soil particles for the M750 and MAZ soils was BW2% for Cd and BW2% + Z1% for Pb. However, the presence of rye grass minimized the amendments' beneficial effects.

Bioavailability of mercury in contaminated soils assessed by the diffusive gradient in thin film technique in relation to uptake by Miscanthus × giganteus.

We assessed the relationship between the diffusive gradient in thin film (DGT) technique using the new ion-exchange resin Ambersep GT74 and the uptake of mercury (Hg) by a model plant cultivated on metal-contaminated agricultural soils under greenhouse conditions. Based on the total Hg content, 0.37 to 1.17% of the Hg passed to the soil porewater from the solid phase, and 2.18 to 9.18% of the Hg is DGT-available. These results were confirmed by calculating the R value (the ratio of the concentrations of bioavailable Hg measured by DGT and soil solution), which illustrated the strong bonding of Hg to the solid phase of soil and its extremely low mobility. Only inorganic Hg2+ species were found in the metal-contaminated agricultural soils, as determined by a high-performance liquid chromatography-cold vapor atomic fluorescence spectrometry speciation analysis. The Hg was distributed in Miscanthus × giganteus organs in the following order for all sampling sites: roots (55-82%) >> leaves (8-27%) > stems (7-16%) > rhizomes (4-7%). Environ Toxicol Chem 2019;38:321-328. © 2018 SETAC.

From environmental data acquisition to assessment of gardeners' exposure: feedback in an urban context highly contaminated with metals.

Although growing vegetables in urban gardens has several benefits, some questions in relation with the safety of foods remain when the self-production is carried out on highly contaminated garden soils. To better assess the local population's exposure to Cd and Pb induced by the past activities of a lead smelter, a participatory program was initiated in 115 private kitchen gardens located in northern France to assist gardeners in understanding their soil environment. The challenge included contributing to the database of urban garden soils with the collection of a large number of samples: 1525 crops grouped into 12 types (leaf, fruiting, root, stem and bulbous vegetables, tubers, cabbages, leguminous plants, celeriac, fresh herbs, fruits, and berries), 708 topsoils, and 52 samples of self-produced compost. The main results were as follows: (i) topsoils were strongly contaminated by Cd and Pb compared to regional reference values; (ii) great variability in physicochemical parameters and metal concentrations in topsoils; (iii) the highest concentrations of Cd and Pb for celeriac and fresh herbs and the lowest for fruits and fruiting vegetables; (iv) a high percentage of vegetables that did not comply with the European foodstuff legislation; and (v) most self-produced compost samples were strongly contaminated. This study aimed to raise awareness and generate functional recommendations to reduce human exposure and to provide useful data that could be considered in other environmental contexts.

Do biochars influence the availability and human oral bioaccessibility of Cd, Pb, and Zn in a contaminated slightly alkaline soil?

Different remediation techniques have been used to restore metal-contaminated sites, including stabilizing metals by adding amendments to the soils. This study experimented three biochars, made from wood and miscanthus, cultivated on contaminated and uncontaminated soils, used as amendments at a 2% application rate on a metal-contaminated soil for 9 months in laboratory-controlled conditions. The objective was to evaluate whether biochars were able to decrease the availability and human oral bioaccessibility of metals in an alkaline soil. To meet this goal, the modifications of the soil's physicochemical parameters, metal distribution in soil, and human bioaccessibility were evaluated at different sampling times. The results showed that biochar application to the alkaline soil did not always decrease the soil metal availability, which challenges the value of using biochars in already slightly alkaline soils at a low application rate. However, differences in efficiency between the three biochars tested were highlighted. The biochar produced with miscanthus cultivated on uncontaminated soil led to higher soil metal bioaccessibility. Moreover, because of the absence of any increase in soil metal availability with the biochar produced from biomass cultivated on contaminated soil, the use of such biochars can be recommended for the remediation of contaminated soil.

Assessment of oral and lung bioaccessibility of Cd and Pb from smelter-impacted dust.

Soil and dust contamination by metals engenders significant environmental and health problems in northern France where a lead smelter was in activity for more than a century. This study aims to examine the long-term effects of the smelter, 10 years after its closedown, on the presence of metal in sidewalk dust for a better assessment of the local population's exposure to Cd and Pb. The investigation included: (i) the metal distribution in different dust particle sizes and (ii) the assessment of metal bioaccessibility via ingestion and inhalation of dust. Seventy-two sidewalk dust samples were collected using a dust-sampling vacuum. The samples were sieved to collect different particle sizes from 0.3 to 1000 µm. The unified bioaccessibility method (UBM) was employed to evaluate the oral bioaccessibility of metals in the different particle sizes. The pulmonary bioaccessible fraction of Cd and Pb via the finest particles was extracted with lung-simulating solution (artificial lysosomal fluid). Ten years after the smelter closedown, (i) a strong relationship was observed between the concentrations of metals in dust and the distance to the former smelter, whatever the particle size; (ii) both total and oral bioaccessible concentrations of metals were high in the finest fraction (0.3-5 µm) and decreased when the particle size increased; (iii) a higher oral bioaccessibility of Cd and Pb was measured in the gastric phase (on average 43% for both metals for all particle sizes) and compared to the gastrointestinal phase (on average 16% for both metals for all particle sizes); and (iv) metal bioaccessibility via inhalation of dust was relatively high (on average 74 and 69%, for Cd and Pb, respectively). The results of the present study suggest that this environmental compartment may be a sensitive and effective indicator of anthropogenic metal contamination and the human exposure in urban areas.

Value of biochars from Miscanthus x giganteus cultivated on contaminated soils to decrease the availability of metals in multicontaminated aqueous solutions.

The objective of this study was to evaluate the sorption efficiency of eight biochars, made from Miscanthus x giganteus cultivated on contaminated agricultural soil, in aqueous solutions contaminated with metals alone or mixed with polycyclic aromatic hydrocarbons. These biochars were produced in different pyrolysis conditions (temperature, 400/600 °C; heating rate, 5/10 °C min-1; duration, 45/90 min) and compared with an uncontaminated commercialized biochar made of wood. The physicochemical characterization of the Miscanthus biochars confirmed the impact of the pyrolysis on the biochar parameters with substantial differences between the biochars in terms of pH, cation exchange capacity, and specific surface area. The sorption experiment showed higher sorption efficiency of Cd, Pb, and Zn for the Miscanthus biochars produced at 600 °C compared with the biochars produced at 400 °C when the aqueous solutions were mono- or multicontaminated. Furthermore, the desorption study showed that the sorption process was largely irreversible. Therefore, the high sorption capacity of Miscanthus biochars and the low sorption reversibility confirmed that these biochars are a suitable sorbent for metals.

In Vitro Investigations of Human Bioaccessibility from Reference Materials Using Simulated Lung Fluids.

An investigation for assessing pulmonary bioaccessibility of metals from reference materials is presented using simulated lung fluids. The objective of this paper was to contribute to an enhanced understanding of airborne particulate matter and its toxic potential following inhalation. A large set of metallic elements (Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr, and Zn) was investigated using three lung fluids (phosphate-buffered saline, Gamble's solution and artificial lysosomal fluid) on three standard reference materials representing different types of particle sources. Composition of the leaching solution and four solid-to-liquid (S/L) ratios were tested. The results showed that bioaccessibility was speciation- (i.e., distribution) and element-dependent, with percentages varying from 0.04% for Pb to 86.0% for Cd. The higher extraction of metallic elements was obtained with the artificial lysosomal fluid, in which a relative stability of bioaccessibility was observed in a large range of S/L ratios from 1/1000 to 1/10,000. For further investigations, it is suggested that this method be used to assess lung bioaccessibility of metals from smelter-impacted dusts.

Determining the influence of the physicochemical parameters of urban soils on As availability using chemometric methods: A preliminary study.

An initial exploration was conducted using mathematical and statistical methods to obtain relevant information about the determination of the physicochemical parameters capable of controlling As uptake by ryegrass grown on contaminated topsoils. Concentrations of As in the soils were from 10 to 47mg/kg, mainly in the As(V) form (57%-73%). Concentrations of As in water extracts were very low (61-700µg/kg). It was suggested that As(III) was mainly in the uncharged species and As(V) in the charged species. Chemometric methods revealed that the values of the ratio As(III)/As(V) depended on the assimilated-phosphorus, the pseudo-total and water-extractable Fe contents and the soil pH. Arsenic concentrations measured in ryegrass shoots ranged from 119 to 1602µg/kg. Positive linear correlations were obtained between As in ryegrass shoots and water extractable-As. The transfer coefficient of As correlated well with the ratio assimilated-phosphorus/Fe-oxides. As(III) uptake by the shoot of ryegrass was controlled by the organic matter and Fe-oxide contents.

Metallothionein as a Scavenger of Free Radicals - New Cardioprotective Therapeutic Agent or Initiator of Tumor Chemoresistance?

Cardiotoxicity is a serious complication of anticancer therapy by anthracycline antibiotics. Except for intercalation into DNA/RNA structure, inhibition of DNA-topoisomerase and histone eviction from chromatin, the main mechanism of their action is iron-mediated formation of various forms of free radicals, which leads to irreversible damage to cancer cells. The most serious adverse effect of anthracyclines is, thus, cardiomyopathy leading to congestive heart failure, which is caused by the same mechanisms. Here, we briefly summarize the basic types of free radicals formed by anthracyclines and the main processes how to scavenge them. From these, the main attention is paid to metallothioneins. These low-molecular cysteine-rich proteins are introduced and their functions and properties are reviewed. Further, their role in detoxification of metals and drugs is discussed. Based on these beneficial roles, their use as a new therapeutic agent against oxidative stress and for cardioprotection is critically evaluated with respect to their ability to increase chemoresistance against some types of commonly used cytostatics.

Elaboration, characteristics and advantages of biochars for the management of contaminated soils with a specific overview on Miscanthus biochars.

Biochars are products that are rich in carbon obtained by pyrolysis processes that consist in introducing a biomass (such as wood or manure) in a closed container and heating it with little or no available air. This paper reports the impacts of pyrolysis parameters on biochar characteristics. A preliminary examination of the scientific literature revealed that the type of feedstock, the temperature, the heating rate and the gas flow were the major parameters influencing the biochar characteristics. This review highlights the multitude of biochars that can be made and shows the importance of characterizing them before their use in soils. Then we assess how the input of biochars in soils can affect soil parameters. A review of the literature showed modifications on: i) the physical properties of soils (i.e. the modification in soil structure and water retention), ii) the chemical properties of soils (i.e. the modification of pH, cation exchange capacity, nutrient availability, the organic matter content) and iii) the biological properties (i.e. the changes in microbial and faunal communities). All these modifications can lead to an increase in crop productivity, which confirms the value of biochars as a soil amendment. Moreover, biochars can also provide an advantage for soil remediation. Indeed, biochars efficiently reduce the bioavailability of organic and inorganic pollutants. In addition, this review focuses on a specific plant that can be used to produce biochars: Miscanthus, a non-wood rhizomatous C4 perennial grass. Miscanthus presents advantages for biochar production due to: i) its lignocellulosic content, ii) its silicon content, which can mitigate environmental stresses (notably for plants grown on contaminated sites) and iii) the greater surface area of the Miscanthus biochars compared to the biochars produced with other feedstock.