Bioaccessibility Tests Research Articles

Enhanced phosphorus adsorption using modified drinking water treatment residues: A comparative analysis of powder and alginate bead forms

This study provides an analysis of the phosphorus adsorption efficacy of three modified drinking water treatment residues (MDWTRs): MDWTR-P (powdered form), MDWTR-D2, and MDWTR-D5 (alginate bead-entrapped forms with bead diameters of 2 mm and 5 mm, respectively). The preparation process involved washing and drying the drinking water treatment residue, followed by grinding and sieving to achieve particle sizes below 90 μm. The residue was then incinerated at 600 °C in oxygen-limited conditions. Subsequently, the MDWTR was formulated into alginate beads by mixing with sodium alginate and FeCl3 solutions, resulting in spherical particles of specified diameters. The evaluation of surface area, pore volume, pore size, and CHN concentration revealed that MDWTR-D5 possesses the largest surface area (284.7 m2 g−1) and highest micropore volume (0.04 cm3 g−1), indicating a greater capacity for adsorption. SEM-EDS analysis demonstrated significant compositional changes post-treatment, particularly elevated phosphorus levels, confirming effective adsorption. Metal content analysis indicated high aluminum levels in MDWTR-P and increased iron content in MDWTR-D5. Toxicity Characteristic Leaching Procedure (TCLP) and in vitro bioaccessibility (IVBA) tests confirmed the non-hazardous nature of all MDWTRs, ensuring their safety for environmental applications. Kinetic analyses using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models highlighted the superior performance of MDWTR-D5, with the highest equilibrium adsorption capacity and initial adsorption rate across all tested concentrations, suggesting both high efficiency and rapid adsorption potential. Further validation using Langmuir and Freundlich isotherms revealed MDWTR-D5's highest monolayer adsorption capacity (22.88 mg g−1) and Freundlich adsorption capacity parameter (6.97 mg g−1). Statistical analysis via one-way ANOVA confirmed significant differences in phosphorus concentrations among the MDWTRs samples (p-value <0.001), consistently underscoring MDWTR-D5's superior adsorption performance. These findings highlight MDWTR-D5's potential as an effective adsorbent for phosphorus removal in wastewater treatment, emphasizing its applicability in environmental remediation strategies.

Bioaccessibility of plastic-related compounds from polymeric particles in marine settings: Are microplastics the principal vector of phthalate ester congeners and bisphenol A towards marine vertebrates?

Marine vertebrates are known to ingest significant amounts of microplastics (MPs). Once ingested, MPs might cause gastrointestinal injuries and serve as a path of harmful plastic components, such as phthalate esters (PAEs) and bisphenol A (BPA) in the food chain. However, there is a lack of standardized in-vitro methods capable of simulating fish uptake of chemicals from MPs in the environment as potential vectors of such contaminants. In this work, leaching and in-vitro oral bioaccessibility testing of PAEs and BPA from MPs were conducted batchwise using artificial seawater and gut fluids mimicking gastric, intestinal, and gastrointestinal compartments of marine vertebrates at physiological temperature. The environmental and physiologically relevant extraction tests were applied to medium-density polyethylene (PE) and polyvinyl chloride (PVC) certified reference materials containing eight PAEs of varying hydrophobicity, namely, dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate, benzylbutyl phthalate, diethylhexyl phthalate, di-n-octyl phthalate, diisononyl phthalate and diisodecyl phthalate, and BPA (only in PE) as MP surrogates with realistic analyte concentrations of additives for primary MPs. The analysis of the leachates/gut fluid extracts was performed via dilute-and-shoot by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Only the most hydrophilic compounds, i.e. DMP, DEP and BPA, were found to get released significantly in saline waters, and exhibited the highest oral bioaccessibility rates (34–83 %). Based on our results, a dual-compartment physiologically relevant gastrointestinal test is recommended for appropriate estimation of fish bioaccessibility. The fish daily intakes of DMP, DEP and BPA from MPs, and seawater ingestion as well were estimated using several contamination scenarios (10th percentile as the low level, 50th percentile as the medium level and 90th percentile as the high level) based on probabilistic distributions and cumulative probability curves of measured environmental concentrations of (i) MPs in seawater throughout the world, (ii) DMP, DEP and BPA in beached MPs and those sampled in the open ocean (including both incurred and adsorbed contaminants), and (iii) DMP, DEP and BPA in seawater as reported in recent literature. Under a medium-level concentration scenario (50th percentile) in marine settings, and taking the gastrointestinal bioaccessibility factor into account, the daily intake of DMP, DEP and BPA from MPs accounted for a mere 0.02 % of the waterborne contribution. Hence, the ingestion of MPs should not be considered the primary route of fish exposure to BPA and the most polar PAEs in marine environments. However, more studies on the local and the global scales for mass concentrations of MPs and additives in marine settings are needed for further confirmation of our findings.

Health Risk Assessment of Road-Dust-Bound Heavy Metals via Ingestion Exposure from One Typical Inland City of Northern China: Incorporation of Sources and Bioaccessibility

Heavy metals in road dust pose potential health risks to humans, while oral bioaccessibility and sources are all important factors influencing this health risk. However, few prior studies have combined them for health risk analysis. In this study, road dust samples were collected from different geographical locations of Jinan (west area, WA; central area, CA; and east area, EA) to analyze the source-specific and bioaccessibility-based health risks of heavy metals. The mean concentrations of heavy metals in the three areas were CA &gt; EA &gt; WA, with Cd, Cu, Mn, Pb, and Zn exceeding their corresponding background values. A source analysis using a Positive Matrix Factorization (PMF) model showed that traffic emissions were the main source of heavy metals in the WA and CA, while industrial activities were the main source in the EA. The mean bioaccessibility of heavy metals extracted using the Solubility Bioaccessibility Research Consortium (SBRC) method followed the order of Cd (75.5%) &gt; Zn (42.2%) &gt; Mn (42.1%) &gt; Pb (42.0%) &gt; Cu (32.9%) &gt; As (23.6%) &gt; Ni (20.1%) &gt; V (16.8%) &gt; Cr (13.3%). According to the combined source analysis, traffic was the primary risk factor in the WA (54.5 and 58.3% of NCR and CR, respectively) and CA (61.8 and 51.2%), with solid waste being the main risk factor in the EA (41.9 and 51.3%). In oral bioaccessibility testing, lower non-carcinogenic (&lt;1.0) and carcinogenic risks (&lt;1 × 10−6) of heavy metals were observed than those based on the total metal content. More importantly, As (43.4%) was replaced by V (29.7%) as the main contributor to NCR. Source-specific and bioaccessibility-based health risk assessments can accurately identify priority pollutants and heavy metals in urban road dust that need to be controlled. This provides more effective and accurate urban environmental risk management recommendations for sustainable urban development and population health.

Metal(loid) bioaccessibility and risk assessment of ashfall deposit from Popocatépetl volcano, Mexico

Ash emission from volcanic eruptions affects the environment, society, and human health. This study shows the total concentration and lung bioaccessible fraction of eight potential toxic metal(loid)s in five Popocatépetl ashfall samples. Mineralogical phases and particle size distribution of the ashfall were analyzed by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) techniques, respectively. The bioaccessibility test of Gamble solution (GS) and Artificial Lysosomal Fluid (ALF) were conducted to simulate extracellular (pH 7) and intracellular (pH 4.5) conditions, respectively. The studied metal(loid)s showed the following total concentration (mg kg−1): 1.98 (As), 0.17 (Cd), 134.09 (Cr), 8.66 (Cu), 697.33 (Mn), 55.35 (Ni), 8.77 (Pb), and 104.10 (Zn). Geochemical indices suggested that some metal(loid)s are slightly enriched compared to the local soil background concentrations. Several mineralogical phases were identified in the collected ashfall deposits, such as plagioclase, pyroxene, and Fe–Ti oxide, among others. According to the risk assessment results, the non-carcinogenic risk related to ashfall exposure returns an HQ > 1 for children. In contrast, the estimation of carcinogenic risk was found to be within the tolerable limit. Metal(loid)s showed low bioaccessibility (< 30%) in GS and ALF, with the highest values found in ALF solution for As (12.18%) and Cu (7.57%). Despite their metal-bioaccessibility, our findings also showed that dominant ash particle size ranged between fine (< 2.5 μm) and extremely fine (< 1 μm), considered highly inhalable fractions. The results obtained in this work indicate that volcanic ashes are bioinsoluble and biodurable, and exhibit low bioaccessibility when in contact with lung human fluids.

Metal(loid)s in urban soil from historical municipal solid waste landfill: Geochemistry, source apportionment, bioaccessibility testing and human health risks

Landfills, especially those poorly managed, can negatively affect the environment and human beings through chemical contamination of soils and waters. This study investigates the soils of a historical municipal solid waste (MSW) landfill situated in the heart of a residential zone in the capital of Slovakia, Bratislava, with an emphasis on metal (loid) contamination and its consequences. Regardless of the depth, many of the soils exhibited high metal (loid) concentrations, mainly Cd, Cu, Pb, Sb, Sn and Zn (up to 24, 2620, 2420, 134, 811 and 6220 mg/kg, respectively), classifying them as extremely contaminated based on the geo-accumulation index (Igeo >5). The stable lead isotopic ratios of the landfill topsoil varied widely (1.1679–1.2074 for 206Pb/207Pb and 2.0573–2.1111 for 208Pb/206Pb) and indicated that Pb contained a natural component and an anthropogenic component, likely municipal solid waste incineration (MSWI) ash and construction waste. Oral bioaccessibility of metal (loid)s in the topsoil was variable with Cd (73.2–106%) and Fe (0.98–2.10%) being the most and least bioaccessible, respectively. The variation of metal (loid) bioaccessibility among the soils could be explained by differences in their geochemical fractionation as shown by positive correlations of bioaccessibility values with the first two fractions of BCR (Community Bureau of Reference) sequential extraction for As, Cd, Mn, Ni, Pb, Sn and Zn. The results of geochemical fractionation coupled with the mineralogical characterisation of topsoil showed that the reservoir of bioaccessible metal (loid)s was calcite and Fe (hydr)oxides. Based on aqua regia metal (loid) concentrations, a non-carcinogenic risk was demonstrated for children (HI = 1.59) but no risk taking into account their bioaccessible concentrations (HI = 0.65). This study emphasises the need for detailed research of the geochemistry of wastes deposited in urban soils to assess the potentially hazardous sources and determine the actual bioaccessibility and human health risks of the accumulated metal (loid)s.

Oral bioaccessibility of potentially toxic elements in various urban environmental media

An important aspect of geochemical studies is determining health hazard of potentially toxic elements (PTEs). Key information on PTEs behaviour in the human body in case of their ingestion is provided with the use of in vitro bioaccessibility tests. We analysed and compared oral bioaccessibility of a wide range of PTEs (As, Cd, Ce, Cr, Cu, Hg, La, Li, Ni, Pb, Sb, Sn, Zn), including some that are not often studied but might pose a human health hazard, in soil, attic dust, street dust, and household dust, using Unified BARGE Method (UBM). Additionally, feasibility of usage of scanning electron microscope techniques in analyses of solid residuals of UBM phases was tested. Results show that bioaccessible fractions (BAFs) of PTEs vary significantly between individual samples of the same medium, between different media and between the gastric and gastro-intestinal phases. In soil, attic dust and street dust, bioaccessibility of individual PTE is mostly higher in gastric than in gastro-intestinal phase. The opposite is true for PTEs in household dust. In all four media, with the exception of Pb in household dust, among the most bioaccessible PTEs in gastric phase are Cd, Cu, Pb, and Zn. During the transition from the stomach to small intestine, the mean BAFs of most elements in soil, attic dust, and street dust decreases. The most bioaccessible PTEs in gastro-intestinal phase are Cu, Cd, Ni, and As. Micromorphological and chemical characterisation at individual particle level before and after bioaccessibility test contribute significantly to the understanding of oral bioaccessibility.

In vitro estimation of oral bioaccessibility of brominated flame retardants in indoor dust by fasted and fed physiologically extraction test

Aim: There is a dearth of information on in vitro oral bioaccessibility, challenging the evaluation of the health risks arising from indoor dust exposure to the brominated flame retardants, tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCDD). Here, we estimate the human oral bioaccessibility of TBBPA and HBCDD in indoor dust by applying the standardized bioaccessibility test under fasting (UBM-like test) and fed (FOREhST test) conditions. Methods: In vitro bioaccessibility of HBCDD and TBBPA of sixteen indoor dust samples was conducted under fasted and fed states. In the fed test, food components, including healthy and unhealthy food. The concentrations of HBCDD and TBBPA were analyzed using LC-MS/MS. Bioaccessibility was calculated from the ratio of the amount of HBCDD and TBBPA in a simulated gut solution to that in indoor dust. The average daily dose (EDDbioaccessibility) was calculated from the estimated daily intake and percentage of bioaccessibility. Results: The concentration of TBBPA and HBCDD in indoor dust ranged from 137 to 14,671 ng g-1 and &lt; 0.7 to 528 ng g-1, respectively. A higher bioaccessible concentration was observed in the small intestine than in the stomach and mouth. The condition of the fed state with food containing fat showed greater bioaccessibility of TBBPA and HBCDD at 74.0% ± 9.5% and 62.2% ± 10.1%, respectively. In contrast, the fed state with lower fat food containing fiber presented the lowest bioaccessibility with a mean of 54.7% ± 10.7% for TBBPA and 53.7% ± 10.8% for HBCDD. Moreover, children are more exposed than adults, especially those who ingest indoor dust with fatty food. Conclusion: The oral bioaccessibility of TBBPA and HBCDD in indoor dust was highest in the fed state with fatty food, followed by fasted and fed states with lower fat, higher fiber food. Similarly, the estimated daily dose (EDDbioaccessibility) for children exceeded that for adults. Therefore, this study indicated that food consumption is a factor influencing the bioaccessibility of TBBPA and HBCDD present in indoor dust.

Relation between solid phase speciation and oral/lung bioaccessibility of metal(loid)s polluted soils in inhabited area: Contribution of synchrotron-based experiment

The presence of contaminated sites/soils in or near cities can pose significant risks to public health. The city of Viviez (France) was taken in reference site bears significant industrial responsibility, particularly in zinc metallurgy, with the presence of a now rehabilitated smelter. This has led to soil contamination by zinc (Zn), lead (Pb), arsenic (As), and cadmium (Cd), with concentrations reaching up to 4856 mg kg−1, 1739 mg kg−1, 195 mg kg−1, and 110 mg kg−1, respectively. The aim of this study is to comprehend the contamination patterns of the site post-rehabilitation, the geochemical behavior of each element, and their speciation (analyzed through BCR, XRD, and XANES) in relation to associated health risks due to metals accessibility for oral ingestion and inhalation by the local population. The findings revealed that elements inducing health risks were not necessarily those with the highest metal contents. All results are discussed in terms of the relationship between element speciation, stability of bearing phases, and their behavior in different media. XANES is an important tool to determine and estimate the Pb-bearing phases in garden soils, as well as the As speciation, which consist of Pb-goethite, anglesite, and Pb-humate, with variations in proportions (the main phases being 66 %, 12 % and 22 % for Pb-goethite, anglesite, and Pb-humate, respectively) whereas As-bearing phase are As(V)-rich ferrihydrite-like. A new aspect lies in the detailed characterization of solid phases before and after bioaccessibility tests, to qualify and quantify the bearing phases involved in the mobility of metallic elements to understand the bioaccessibility behavior. Ultimately, the health risk associated with exposure to inhabitants, in terms of particle ingestion and inhalation, was assessed. Only ingestion-related risk was deemed unacceptable due to the levels of As and Pb.

Toxicity of REEs, Th, and U: A Biodisponibility, Cytotoxicity, and Bioaccumulation Assessment in Marine Sediment.

In this work, bioaccessibility tests for rare earth elements (REEs), Th, and U in marine sediment were carried out, in addition to complementary tests for cytotoxicity and bioaccumulation for the elements La, Ce, Eu, and Gd. The evaluation of human health risk through dermal absorption and oral ingestion was performed using the hazard quotient (HQ). According to the gastric digestion simulation (SBET), it was observed that the elements Ce and Nd exhibited higher absorption capacities in the human body (> 2µgg-1). La and Sc presented intermediate concentrations (close to 1µgg-1), while the remaining elements displayed concentrations below 0.5µgg-1. In the gastrointestinal digestion extraction stage (PBET), all the elements maintained a similar absorption capacity to that observed in SBET, except for the absorption of Y which increased. The results of the bioaccumulation test conducted with fibroblast cells (L929) indicated that La and Eu had a 25% probability of intracellular accumulation. The cell viability test, with exposure to a standard REEs, Th, and U solution in 2% v v-1 HNO3 medium (until 100μgmL-1) and an aqueous solution of La2O3, Gd(NO3)3, Ce(NO3)3, and Eu2O3 (until 1000μgmL-1), did not demonstrate cytotoxic effects on fibroblast cells. Considering the ingestion hazard quotient (HQing) and dermal hazard quotient (HQderm) obtained, it was suggested that there is no significant risk of non-carcinogenic effects (< 1). However, they had higher HQing values compared to HQderm, indicating that REEs pose more significant risk to human health through oral ingestion absorption than dermal absorption.

Bioaccessible metals in dust materials from non-sulfide Zn deposit and related hydrometallurgical operation

Mining and processing of ores in arid (desert) areas generates high amounts of dust, which might be enriched in potentially harmful elements. We studied dust fractions of ores, soils, and technological materials from mining and related hydrometallurgical operation at former Skorpion Zinc non-sulfide Zn deposit in southern Namibia (closed and placed under maintenance in 2020). Chemical and mineralogical investigation was combined with oral bioaccessibility testing of fine dust fractions (<48 μm and <10 μm) in simulated gastric fluid (SGF) to assess potential risk of intake of metallic contaminants (Cd, Cu, Pb, Zn) for staff operating in the area. The bulk metals concentrations were largely variable and ranked as follows: soils < tailings ≪ Skorpion ores < imported ores and dross used for feed ore blending. Maximum contaminant concentrations in the original granular materials were 927 mg Cd/kg, 9150 mg Cu/kg, 50 g Pb/kg and 706 g Zn/kg, respectively, and generally increased as a function of decreasing grain size. The highest bioaccessible concentrations of Cd and Pb yielded imported ores from Taiwan and Turkey and, together with the milled dross, these samples also exhibited the highest Zn bioaccessibilities. The exposure estimates calculated for a worker (weighing 70 kg) in this mining/ore processing operation at a dust ingestion rate of 100 mg/day indicated that most dust samples (soils, tailings, Skorpion ores) exhibited metals intake values far below tolerable daily intake limits. The overall health risk was limited in all mining and ore processing areas except for the ore blending area, where imported ores and recycled dross enriched in bioaccessible Cd, Pb and/or Zn were used for the ore blending. Safety measures required by the mine operator (wearing of masks by the operating staff) helped to prevent the staff's exposure to potentially contaminated dust even in this blending ore area.

Integrating multiple spheres to identify the provenance and risk of urban dust and potentially toxic elements: Case study from central Mexico

This study aims to improve the current method of studying potentially toxic elements (PTEs) in urban dust using direct chemical evidence (from dust, rock, and emission source samples) and robust geochemical methods. The provenance of urban dust was determined using rare earth elements (REEs) and geochemical diagrams (V–Ni–Th*10, TiO2 vs. Zr, and Zr/Ti vs. Nb/Y). The geogenic or anthropogenic source of PTEs was determined using the enrichment factor (EF) and compositional data analysis (CoDA), while a PTE's point emission source was identified using a 3.1*La–1.54*Ce–Zn diagram, mineralogy, and morphology analyses. The spatiotemporal distribution of PTEs was determined using a geographic information system, and their health risk (by inhalation) was estimated using a lung bioaccessibility test and particle size distribution. We collected urban dust (n = 38), rock (n = 4), and zinc concentrate (n = 2) samples and determined PTEs and REEs in a city of 1.25 million inhabitants in central Mexico. Results showed that urban dust derived from the San Miguelito Range. REEs, Sc, and Zr were geogenic, while Mn, Cu, Zn, As, and Pb were anthropogenic. Due to the presente of sphalerite particles, a zinc refinery was identified as the point emission source of Zn, As, and Pb. High concentrations of Zn (5000–20,008 mg/kg), As (120–284 mg/kg), and Pb (350–776 mg/kg) were found in urban dust near the zinc refinery. Additionally, particles of PM2.5 (66–84%), PM5.0 (13–27%), PM10 (3–8%), and PM20 (0–2%) and lung bioaccessibility of Sr (48.5–72.4%), Zn (9.6–28.4%), Cu (10.5–27.0%), Fe (4.5–8.6%), Mn (2.9–9.2%), Cr (38.3%) and Pb (30.6%) demonstrated a latent risk to human health. These approaches improve our understanding of the provenance of urban dust and its PTE emission sources in urban areas.

Metal(loid) speciation in dermal bioaccessibility extracts from contaminated soils and permeation through synthetic skin

Dermal exposure to metal(loid)s from contaminated soils can contribute to health risk. Metal(loid) speciation will influence their bioaccessibility in sweat and subsequent permeation across the skin. Therefore, the speciation of the bioaccessible fraction of metal(loid)s in two synthetic sweat formulations (sweat A (pH 6.5) and B (pH 4.7)) was assessed using chemical equilibrium modelling (Visual MINTEQ). Permeation through synthetic skin and the influence of sebum in the permeation of As, Cr, Cu, Ni, Pb, and Zn were also investigated using Franz cells. Following dermal bioaccessibility tests for five Chromated Copper Arsenate (CCA)-contaminated soils and one certified soil (SQC001), mean metal(loid) bioaccessibility (%) was higher in sweat B (2.33–18.8) compared to sweat A (0.12–7.53). Arsenic was almost entirely found as As(V) in both sweats. In sweat A, comparable concentrations of Cr(III) and Cr(VI) were found whereas in sweat B, Cr was primarily present as Cr(III). Copper was primarily found as Cu2+. Bioaccessible Cr extracted from nearly all soils permeated through the Strat-M membrane when it was coated with sebum. The Cr permeation coefficient (Kp) ranged between 0.004 and 0.13 cm/h and the Kp for Cu was higher (0.024–0.52 cm/h). As, Ni, Pb, and Zn did not permeate the synthetic skin.

Assessment of lettuces grown in urban areas for human consumption and as bioindicators of atmospheric pollution

This study proposes using the network of urban gardens to grow vegetables and to monitor air quality, and it also evaluates whether food grown on a clean substrate in an urban environment is safe for consumption. For this purpose, lettuces were exposed to different degrees of air pollution in five locations in the city of Copenhagen, plus a reference site. Six specimens were placed at each site and, after the exposure period, half of each sample was washed. Subsamples were then digested by a total extraction method and a bioaccessible extraction method, and the concentration of 23 elements subsequently measured by ICP-MS. The results showed that exposed samples in areas of higher atmospheric pollution accumulated a larger amount of trace elements associated with typical urban sources. They also highlighted the importance of washing food to remove particles that adhere to their surface. However, bioaccessibility testing demonstrated the importance of including bioaccessibility in risk analyses and how this factor varies depending on the type of matrix. In this case, bioaccessibility was higher for plant tissue than for particulate matter. Lastly, metal concentrations in lettuce were compared with legal values and an analysis of daily intake showed that the levels in Copenhagen were within limits for the protection of human health.

The Bioaccessibility of Yak Bone Collagen Hydrolysates: Focus on Analyzing the Variation Regular of Peptides and Free Amino Acids

The lack of a bioaccessibility test for yak bone collagen hydrolysates (YBCH) limits their development as functional foods. In this study, simulated gastrointestinal digestion (SD) and absorption (SA) models were utilized to evaluate the bioaccessibility of YBCH for the first time. The variation in peptides and free amino acids was primarily characterized. There was no significant alteration in the concentration of peptides during the SD. The transport rate of peptides through the Caco-2 cell monolayers was 22.14 ± 1.58%. Finally, a total of 440 peptides were identified, more than 75% of them with lengths ranging from 7 to 15. The peptide identification indicated that about 77% of the peptides in the beginning sample still existed after the SD, and about 76% of the peptides in the digested YBCH could be observed after the SA. These results suggested that most peptides in the YBCH resist gastrointestinal digestion and absorption. After the in silico prediction, seven typical bioavailable bioactive peptides were screened out and they exhibited multi-type bioactivities in vitro. This is the first study to characterize the changes in peptides and amino acids in the YBCH during gastrointestinal digestion and absorption, and provides a foundation for analyzing the mechanism of YBCH's bioactivities.

Incorporating oral, inhalation and dermal bioaccessibility into human health risk characterization following exposure to Chromated Copper Arsenate (CCA)-contaminated soils

Exposure to potentially toxic metal(loid)s (PTMs) in soil may happen via ingestion, inhalation, and dermal pathway. A more accurate risk characterization should consider PTM bioavailability. Using ten soil samples collected in the Montreal area (Canada) near CCA-treated utility poles, this study aims to characterize non-carcinogenic and carcinogenic human health risks associated with As, Cr, Cu, Pb, and Zn through a multi-pathway exposure approach. This innovative study incorporates, for the first time, the bioaccessible fraction of the metal(loid)s for three exposure routes and two different scenarios. For the residential and industrial scenarios, the oral and dermal pathways yielded a hazard index (HI) much higher than 1 with and without bioaccessibility considerations (range 1.7 – 349 without bioaccessibility and 0.8–134 with bioaccessibility), whereas the inhalation pathway caused a lower hazard (HI < 1). For the dermal pathway, the hazard quotient was higher when bioaccessibility of field-collected samples was considered due to inherent assumptions from the US EPA soil approach to calculate the dermal dose. For carcinogenic risk, As and Pb were the most significant contributors to risk for the oral pathway, followed by the same elements for the dermal pathway. The overall carcinogenic risk was higher than the acceptable risk ( > 10−4) with and without bioaccessibility considerations (range 1.9E-4 – 9.6E-3 without bioaccessibility and 6.8E-5 – 3.8E-3 with bioaccessibility). Bioaccessibility tests provide a more accurate assessment of exposure to PTMs compared to total concentrations in soils.

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.

Contaminant Binding and Bioaccessibility in the Dust From the Ni-Cu Mining/Smelting District of Selebi-Phikwe (Botswana).

We studied the dust fractions of the smelting slag, mine tailings, and soil from the former Ni-Cu mining and processing district in Selebi-Phikwe (eastern Botswana). Multi-method chemical and mineralogical investigations were combined with oral bioaccessibility testing of the fine dust fractions (<48 and <10μm) in a simulated gastric fluid to assess the potential risk of the intake of metal(loid)s contaminants. The total concentrations of the major contaminants varied significantly (Cu: 301-9,600mg/kg, Ni: 850-7,000mg/kg, Co: 48-791mg/kg) but were generally higher in the finer dust fractions. The highest bioaccessible concentrations of Co, Cu, and Ni were found in the slag and mine tailing dusts, where these metals were mostly bound in sulfides (pentlandite, pyrrhotite, chalcopyrite). On the contrary, the soil dusts exhibited substantially lower bioaccessible fractions of these metals due to their binding in less soluble spinel-group oxides. The results indicate that slag dusts are assumed to be risk materials, especially when children are considered as a target group. Still, this exposure scenario seems unrealistic due to (a) the fencing of the former mine area and its inaccessibility to the local community and (b) the low proportion of the fine particles in the granulated slag dump and improbability of their transport by wind. The human health risk related to the incidental ingestion of the soil dust, the most accessible to the local population, seems to be quite limited in the Selebi-Phikwe area, even when a higher dust ingestion rate (280mg/d) is considered.

Effect Factors and Model Prediction of Soil Heavy Metal Bioaccessibility

The soil environmental pollution situation has been severe in recent years, but studies on evaluating with bioavailability testing and prediction models are lacking, which makes it difficult to accurately assess the ecological risks of contaminated soil. As an important indicator of bioavailability, the bioaccessibility of cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), and lead (Pb) in the soil was analyzed in this study. The bioaccessibility content and their corresponding soil property data were screened and systematically analyzed to explore the relationship between bioaccessibility content and soil properties. Furthermore, some testing methods for bioaccessibility were summarized to analyze the relationship between bioaccessibility content, test methods, and bioavailability content. Additionally, the bioaccessibility content prediction models were established. The results showed that there was a strong correlation between the bioaccessibility content and the total content of heavy metals (P<0.01) and a significant (P<0.05) correlation with the soil pH. Different test methods had obvious effects on bioavailability. The proportion of bioaccessibility content determined via various test methods was as follows:in vitro gastrointestinal tract simulation>chemical reagent extraction. The proportions of bioaccessibility content of Cd and Pb in natural soil were relatively high, with mean values of 42.12% and 37.33%, respectively, indicating that Cd and Pb had higher risks of being absorbed by soil organisms. Moreover, 30 bioaccessibility prediction models for five heavy metals were constructed, which involved the soil properties and test methods. The results of this study can provide scientific information and bioaccessibility prediction models that can help in accurately assessing the ecological risks of contaminated soil.

Screening of low-Cd accumulating early rice cultivars coupled with phytoremediation and agro-production: Bioavailability and bioaccessibility tests

Previous studies have focused on total cadmium (Cd) accumulation in rice or its transformation in soil, but only a few have examined the entire soil-rice-human system. This study investigated the Cd bioaccessibility and bioavailability for humans from grains of early rice cultivars grown in a Cd-polluted field and further combined with multi-traits to discover and evaluate the optimum safe production and phytoremediation potential cultivars. The results revealed that Cd concentration in polished rice was <0.20 mg kg−1 in 79 % of early rice cultivars, implying that Cd levels in rice might be reduced by cultivar selection. Furthermore, the higher values of root to straw translocation factor indicates the maximal accumulation of Cd in straw and with highest soil to straw accumulation factor (>1.0) in 66.67 % of cultivars. However, bioaccessibility and bioavailability varied greatly among cultivars with corresponding values ranging from 5.68 to 7.67 % and 1.87 to 5.71 ng g−1, respectively. Despite the fact that polynomial fitting revealed a statistically significant relationship between Cd content in polished rice and bioavailable Cd in humans (R2 = 0.718, P = 0.025), poor goodness of fit for bioaccessibility, bioavailability, and toxicity varied even within low-Cd accumulating cultivars. As a result of multi trait analysis and bioavailability, Zhuliangyou4024 (ER-9), Lingliangyou211 (ER-3), and Yonxian15 (ER-28) were found to be the three best early rice cultivars with higher essential nutrients, less total and bioavailable Cd, and relative high phytoremediation potential and are suitable for healthy rice production and soil remediation.

Assessing bioaccessibility and bioavailability in vitro of phenolic compounds from freeze-dried apple pomace by LC-Q-TOF-MS

Apple pomace is one of the most abundant by-product in fruit processing industry. In this work, fresh and freeze-dried apple pomace variety ‘Red Delicious’ apples “I.G.P. Poma de Girona” was used to evaluate the potential amount of phenolic compounds available from the food matrix by in vitro bioaccessibility test. After the simulated digestion of freeze-dried apple pomace, an in vitro bioavailability test by using differentiated Caco-2 cells simulating the intestinal barried were assayed for 1 h, 2 h, 3 h and, 4 h. LC-Q-TOF-MS has permitted to perform a monitoring of phloridzin, chlorogenic and gallic acids in apple pomace in apical and basal compartments. Results obtained with LC-Q-TOF-MS demonstrated that chlorogenic acid had greater percentage of bioaccesibility (44%), than phloridzin (17%) and gallic acid (7%), with similar values for fresh and freeze-dried samples. Moreover, only chlorogenic acid reported higher bioavailability in basal compartments after 3 h and 4 h, in particular about 56% of chlorogenic acid passed the transepithelial barrier. This is the first work about the evaluation of bioavailability of polyphenols from digested freeze-dried apple pomace extract. Therefore, this interesting by-product rich in polyphenol, with a great bioavailability, should be a promising ingredient to develop new functional foods.