Assessment of in vitro lead bioaccessibility in house dust and its relationship to in vivo lead relative bioavailability

Magnetic response and bioaccessibility of toxic metal pollution in outdoor dustfall in Shanghai, China

Toxic metal content testing, environmental magnetic monitoring and in vitro bioaccessibility experiments each have their own advantages and are often used independently for environmental monitoring, but there are few studies that combine the three to evaluate the hazards of toxic metals to humans. This paper investigated the total content, magnetic properties and bioaccessibility of nine potentially toxic metal elements (Zn, Sn, Pb, Cu, Fe, Ni, Cr, Sr, Mn) in dustfall from different functional zones in Shanghai, China, and systematically compared the related results. The results show that these nine metal elements have different degrees of contamination and enrichment in outdoor dustfall, and their content distribution shows the following trend: Zn > Sn > Pb > Cu > Fe > Ni > Cr > Sr > Mn. Magnetic characteristics χlf and SIRM are mostly positively correlated with the metal elements, indicating that the higher the content of magnetic minerals in the sample, the higher the concentration of metal elements. It was also found that χlf, SIRM, and χARM can well reflect the characteristics of dustfall pollution. The magnetic minerals have a certain degree of enrichment, and the particle size of the magnetic minerals is relatively coarse, mainly in the form of coarse multi-domain and pseudo-single-domain particles, which are largely derived from anthropogenic pollution. The χlf and PM10 concentrations in the precipitation show relatively similar spatial trends, so χlf, SIRM, and χARM can be used as air pollution indices to facilitate the evaluation of metal elements pollution in dustfall. The overall trend in gastric bioaccessibility is Pb > Zn > Mn > Cu > Cr. Due to the increase in the pH of digestive fluid, the bioavailability of toxic metals decreases significantly from the gastric stage to the intestinal stage. χlf, SIRM, and χARM/SIRM are all related to the bioaccessibility of toxic metals in the intestinal stage, so they can be used as toxicity indicators to evaluate the bioaccessibility of toxic metals in dustfall.

Source and bioavailability of quaternary ammonium compounds (QACs) in dust: Implications for Nationwide Exposure in China

Quaternary ammonium compounds (QACs), widely used in various disinfectants products during the COVID-19 Pandemic, raised the concerns on their exposure and health effect. To date, the sources of QACs in indoor environments have been largely ignored. Additionally, there is no information on the nationwide human exposure assessment of QACs in China after the COVID-19. Herein, analysis of QACs in household products, including personal care (n = 27), cleaning (n = 6) and disinfection products (n = 11) from different manufacturing companies further confirmed there are extensive application of QACs in household products, raising their potential exposure to humans. QACs were frequently detected in indoor dust samples (n = 370) from 111 cities of 31 provinces/municipalities across China, with median concentration of 6778 ng/g. Benzalkyldimethylammonium compounds (BACs) and alkyltrimethylammonium compounds (ATMACs) were identified as the dominant QACs in dust samples, with the proportions of 44 % and 46 %, respectively. The in vivo bioavailability experiment (C57BL/6 male mice) showed that the relative bioavailability (RBA) of QACs through dust ingestion ranged from 5.08 % to 66.3 % and 60.3 % to 118 % in the low and high-dose group, respectively. Compared to the pre-adjustment scenario of RBA values, the exposure risk of QACs was overestimated by 2.23 - 5.14 times.

Bioaccessibility and bioavailability of Pb and Cd in rice is affected by propolis and its extracts and Fe intervention

Increasing the intake of dietary supplements containing antioxidant components can reduce the oral bioavailability of lead (Pb) and cadmium (Cd) and benefit human health. In this study, the effects of propolis and its extracts (kaempferol (KAE), quercetin (QR), and caffeic acid phenethyl ester (CAPE)) in conjunction with proanthocyanidins (PA) on Pb and Cd bioaccessibility (BAC) and the relative bioavailability (RBA) in brown and polished rice are investigated. The results of in vitro tests showed that propolis and its extracts were effective in reducing Pb BAC in both brown and polished rice. A medium dose of PA had a significant reduction effect on Cd BAC (76 %) and RBA in both brown and polished rice. Based on mouse bioassays, the supplementation of propolis and its extracts significantly (p < 0.05) reduced the Pb-RBA in brown rice, resulting in a decrease in Pb RBA from 25 % in the control group to 16.5-17.6 %. The results showed that the BAC and RBA of Pb in brown rice with dietary supplements decreased significantly, which may be related to the enhanced inhibitory effect of high Fe. It was also found that the Pb RBA was negatively correlated with the Fe content in mice kidneys. This result provided evidence that antioxidants better inhibit the bioavailability of heavy metals, highlighting that propolis and PA may be alternative dietary supplements for intervening in human Pb and Cd exposure.

Bioaccessibility and bioavailability of exogenous and endogenous toxic substances in traditional Chinese medicine and their significance in risk assessment

Scientific risk assessment of exogenous and endogenous toxic substances in traditional Chinese medicine (TCM) is of great significance. The present review comprises a comprehensive summary of progress in the health risk assessment of harmful exogenous substances in TCMs. Such substances include heavy metals, pesticide residues, biotoxins, and endogenous toxic components involving pyrrolizidine alkaloids. The review also discusses the strengths and weaknesses of various bioaccessibility and bioavailability models, and their applications in risk assessment. Future avenues of risk assessment research are highlighted, including further exploration of risk assessment parameters, innovation of bioaccessibility and bioavailability techniques, enhancement of probabilistic risk assessment combined with bioavailability, improvement of cumulative risk assessment strategies, and formulation of strategies for reducing relative bioavailability (RBA) values in TCMs. Such efforts represent an attempt to develop a risk assessment system that is capable of evaluating the exogenous and endogenous toxic substances in TCMs to ensure its safe use in clinics, and to promote the sustainable development of the TCM industry.

Carcinogenic metal(loid)s in house dust compared to soil: Concentrations and gastric bioaccessibility

As a sink and a source of chemicals, house dust represents a relevant medium to assess indoor exposure to metal(loid)s via incidental ingestion or inhalation. However, nationally representative indoor data are scarce. Results from the Canadian House Dust Study (CHDS, 2007-2010; n = 1025) provide nationally representative mean, median and 95th percentile concentrations for 38 elements in typical urban house dust, along with their gastric bioaccessibility. Total concentrations (median/95th percentile) of carcinogenic metal(loid)s in Canadian house dust (μg g-1) are as follows: As (9.0/40), Be (0.4/0.9), Cd (3.5/17), Co (5.6/19), Cr (99/214), Ni (62/322) and Pb (100/760). Total As and Pb concentrations in house dust exceed residential soil guidelines for the protection of human health in about one-third of Canadian homes. Percent bioaccessibilities (median) are: Cd (65%) > Pb (63%) > Be ∼ Ni (36%) > Co (35%) > As (20%) > Cr (15%). Lead, Cd and Co concentrations are significantly greater in older houses (< 1976). Data from two pilot studies (n = 66 + 51) further demonstrate the distinct geochemistry of house dust compared to soils, notably enrichment of carcinogenic metal(loid)s and their increased bioaccessibility. These results provide essential baseline values to refine risk assessment and inform on health risk at contaminated sites.

Considering the bioavailability and bioaccessibility of metal(loid)s for risk assessment of soils affected by different non-ferrous metal activities in Southwest China

Toxic metal(loid)s released into the soil by non-ferrous metal mining and smelting activities pose a serious threat to residents and the surrounding ecosystem. Considering only total metal(loid) concentrations likely overestimates routine (eco)toxicological risk assessment of soil. We hypothesize that considering metal(loid) bioavailability/accessibility will improve the accuracy of risk assessment. To test this hypothesis, four mining areas in Southwest China, including mining and surrounding sites, were studied. Bioavailability was determined considering metal(loid)s leached by a simulated strong acid rain (SSAR) treatment. In the four areas, the mining site showed higher cumulative releases of metal(loid)s under SSAR treatment than the agricultural field located in the surrounding sites. Thus, the bioavailable metal(loid)s contents were continuously being released during SSAR treatment and likely increased the environmental risk. Ecological and health risk assessment of soil, calculated using total metal(loid)s content, was corrected considering bioavailable/accessible metal(loid)s, which was determined by the heavy metal(loid)s forms and in vitro simulated intestinal stages. Although the corrected indices indicated that the risk of metal(loid)s-contaminated soil was reduced, unfavorable ecological and health risks remained in the four areas. Our study provides new perspectives to better predict the risk of bioavailable/accessible metal(loid)s in non-ferrous metal contaminated and surrounding soils.

Lead Speciation, Bioaccessibility, and Sources for a Contaminated Subset of House Dust and Soils Collected from Similar United States Residences

Residential lead (Pb) exposure is of critical concern to families globally as Pb promotes severe neurological effects in children, especially those less than 5 years old, and no blood lead level is deemed safe by the US Center for Disease Control. House dust and soils are commonly thought to be important sources of Pb exposure. Probing the relationship between house dust and soil Pb is critical to understanding residential exposure, as Pb bioavailability is highly influenced by Pb sources and/or species. We investigated paired house dust and soil collected from homes built before 1978 to determine Pb speciation, source, and bioaccessibility with the primary goal of assessing chemical factors driving Pb exposure in residential media. House dust was predominately found to contain (hydro)cerussite (i.e., Pb (hydroxy)carbonate) phases commonly used in Pb-based paint that, in-turn, promoted elevated bioaccessibility (>60%). Pb X-ray absorption spectroscopy, μ-XRF mapping, and Pb isotope ratio analysis for house dust and soils support house dust Pb as chemically unique compared to exterior soils, although paint Pb is expected to be a major source for both. Soil pedogenesis and increased protection from environmental conditions (e.g., weathering) in households is expected to greatly impact Pb phase differences between house dust and soils, subsequently dictating differences in Pb exposure.

Assessment of the stabilization effect of ferrous sulfate for arsenic-contaminated soils based on chemical extraction methods and in vitro methods: Methodological differences and linkages

Stabilization of arsenic-contaminated soils with ferrous sulfate has been reported in many studies, but there are few stabilization effects assessments simultaneously combined chemical extraction methods and in vitro methods, and further explored the corresponding alternative relationships. In this study, ferrous sulfate was added at FeAs molar ratio of 0, 5, 10 and 20 to stabilize As in 10 As spiked soils. Stabilization effects were assessed by 6 chemical extraction methods (toxicity characteristic leaching procedures (TCLP), HCl, diethylenetriamine pentaacetic acid (DTPA), CaCl2, CH3COONH4, (NH4)2SO4), and 4 in vitro methods (physiologically based extraction test (PBET), in vitro gastrointestinal method (IVG), Solubility Bioaccessibility Research Consortium (SBRC) method, and the Unified Bioaccessibility Research Group of Europe method (UBM)). The results showed that the HCl method provides the most conservative assessment results in non-calcareous soils, and in alkaline calcareous soils, (NH4)2SO4 method provides a more conservative assessment. In vitro methods provided significantly higher As concentrations than chemical extraction methods. The components of the simulated digestion solution as well as the parameters may have contributed to this result. The small intestinal phase of PBET and SBRC method produced the highest and lowest ranges of As concentrations, and in the range of 127-462 mg/kg and 68-222 mg/kg when the FeAs molar ratio was 5. So the small intestinal phase of PBET method may provide the most conservative assessment results, while the same phase of SBRC may underestimate the human health risks of As in stabilized soil by 51 %(at a FeAs molar ratio of 5). Spearman correlation analysis indicated that the small intestinal phase of PBET method correlated best with HCl method (correlation coefficient: 0.71). This study provides ideas for the assessment of stabilization efforts to ensure that stabilization meets ecological needs while also being less harmful to humans.

Release mechanism and interactions of cadmium and arsenic co-contaminated ferrihydrite by simulated in-vitro digestion assays

Cadmium (Cd) and arsenic (As) co-contamination is widespread and threatens human health, therefore it is important to investigate the bioavailability of Cd and As co-exposure. Currently, the interactions of Cd and As by in vitro assays are unknown. In this work, we studied the concurrent Cd-As release behaviors and interactions with in vitro simulated gastric bio-fluid assays. The studies demonstrated that As bioaccessibility (2.04 to 0.18 ± 0.03%) decreased with Cd addition compared to the As(V) single system, while Cd bioaccessibility (11.02 to 39.08 ± 1.91%) increased with As addition compared to the Cd single system. Release of Cd and As is coupled to proton-promoted and reductive dissolution of ferrihydrite. The As(V) is released and reduced to As(Ⅲ) by pepsin. Pepsin formed soluble complexes with Cd and As. X-ray photoelectron spectroscopy showed that Cd and As formed Fe-As-Cd ternary complexes on ferrihydrite surfaces. The coordination intensity of As-O-Cd is lower than that of As-O-Fe, resulting in more Cd release from Fe-As-Cd ternary complexes. Our study deepens the understanding of health risks from Cd and As interactions during environmental co-exposure of multiple metal(loid)s.

Bioaccessibility of lead and cadmium in soils around typical lead-acid power plants and their effect on gut microorganisms

Potentially toxic elements (Pb and Cd) contamination of soil can adversely affect human health. Moreover, these metal ions interact with the gut microbiota after entering the human digestive system. Based on the physiologically based extraction test and the simulator of human intestinal microbial ecosystem, the bioaccessibility of Pb and Cd in soils contaminated with lead-acid power plants was assessed. The gastric stage exhibited the greatest average bioaccessibility of lead and cadmium (63.39% and 57.22%), followed by the small intestinal stage (6.86% and 36.29%); due to gut microorganisms, the bioaccessibility of lead and cadmium was further reduced in the colon stage (1.86% and 4.22%). Furthermore, to investigate soil contamination's effects on gut microbes, 16S rRNA high-throughput sequencing was used to identify the gut microbial species after the colon period. Due to Pb and Cd exposure, the relative abundance of Firmicutes and unidentified_Bacteria decreased, while the relative abundance of Proteobacteria, Synergistota, and Bacteroidota increased. The relationship between environmental factors and the number of microbial species in the gut was also examined using Spearman correlation analysis. Pb and Cd exposure has been found to affect the composition and structure of the gut microbiota.

Total contents, fractionation and bioaccessibility of nine heavy metals in household dust from 14 cities in China

The potential health risk caused by long-term exposure to heavy metals in household dust is not only depended on their total content, but also bioaccessibility. In this study, twenty-one dust samples were collected from residential buildings, schools, and laboratories in 14 provincial-capital/industrial cities of China, aiming to evaluate the total contents, fractionation, bioaccessibility and health risks of nine heavy metals (As, Cd, Cr, Ni, Pb, Mn, Zn, Fe, and Cu). Results showed that the highest levels of Cd, Cr, Ni and Zn were found in laboratory dust, As, Pb and Mn in school dust, and Fe and Cu in residential dust, indicating different source profiles of the heavy metals. The mean bioaccessibility of the heavy metals across all samples as evaluated using SBRC (Solubility Bioavailability Research Consortium), IVG (In Vitro Gastrointestinal), and PBET (Physiologically Based Extraction Test) assays was 58.4%, 32.4% and 17.2% in gastric phase (GP), and 24.9%, 21.9% and 9.39% in intestinal phase (IP), respectively. Cadmium had the highest content in the fractions of E1+C2 (43.7%), as determined by sequential extraction, and Pb, Mn, and Zn had a higher content in E1+C2+F3 (64.2%, 67.2%, 78.8%), resulting in a higher bioaccessibility of these heavy metals than others. Moreover, the bioaccessibility of most heavy metals was inversely related to dust pH (R = -0.18 in GP; -0.18 in IP; P < 0.01) and particle size, while a positive correlation was observed with total organic carbon (R = 0.40 in GP; 0.38 in IP; P < 0.01). The exposure risk calculated by the highest bioaccessibility was generally lower than that calculated by the total content. However, Pb in one school dust sample had an unacceptable carcinogenic risk (adult risk = 1.19 × 10-4; child risk = 1.08 × 10-4). This study suggests that bioaccessibility of heavy metals in household dust is likely related to geochemical fractions and physical/chemical properties. Further research is needed to explore the sources of bioaccessible heavy metals in household dust.

The spatial distribution, health risk, and cytotoxicity of metal(loid)s in contaminated field soils: The role of Cd in human gastric cells damage

The spatial distribution and pollution level of heavy metal(loid)s in soil (0-6 m) from a typical industrial region in Jiangmen City, Southeast China was investigated. Their bioaccessibility, health risk, and human gastric cytotoxicity in topsoil were also evaluated using an in vitro digestion/human cell model. The average concentrations of Cd (87.52 mg/kg), Co (106.9 mg/kg), and Ni (1007 mg/kg) exceeded the risk screening values. The distribution profiles of metal(loid)s showed a downward migration trend to reach a depth of 2 m. The highest contamination was found in topsoil (0-0.5 m), with the concentrations of As, Cd, Co, and Ni being 46.98, 348.28, 317.44, and 2395.60 mg/kg, respectively, while Cd showed the highest bioaccessibility in the gastric phase (72.80 %), followed by Co (21.08 %), Ni (18.27 %), and As (5.26 %) and unacceptable carcinogenic risk. Moreover, the gastric digesta of topsoil suppressed the cell viability and triggered cell apoptosis, evidenced by disruption of mitochondrial transmembrane potential and increase of Cytochrome c (Cyt c) and Caspases 3/9 mRNA expression. Bioaccessible Cd in topsoil was responsible for those adverse effects. Our data suggest the importance to reduce Cd in the soil to decrease its adverse impacts on the human stomach.

Estimating the proportion of bioaccessible lead (BaPb) in household dust wipe samples: a comparison of IVBA and PBET methods

Established methods for using standardized dust wipes to collect and measure total lead in household dust are readily available but the use of dust wipes to measure bioaccessible lead (BaPb) is less clear. This study compared two in vitro methods for estimating the proportion of BaPb in dust collected into dust wipes including the US-EPA's in-vitro bioaccessible assay (IVBA) method at two pH (1.5 and 2.5) values; and the physiologically based extraction test (PBET 2.5 pH). Two types of simulated household dust samples (Pb-soil contaminated and Pb-paint contaminated) each with three Pb concentrations were created. Equal amounts of simulated dust were applied to a smooth surface and collected following the standard EPA dust wipe protocol and were analyzed for BaPb and total Pb (ASTM-E1644-17, ICP-OES). Estimated BaPb levels differed significantly by the method of extraction. Mean percent BaPb were IVBA pH 1.5, > 90% (Pb-paint) and 59-63% (Pb-soil); IVBA pH 2.5 78-86% (Pb-paint) and 45-50% (Pb-soil); PBET pH 2.5 56 to 61% (Pb-paint) and 41-50% Pb-soil). Particularly for lead-paint contaminated dust, PBET showed significantly greater discrimination as suggested by the broader range of BaPb values and closer approximation to total lead concentrations in simulated household dust samples.

Variation of lead bioaccessibility in soil reference materials: Intra- and inter-laboratory assessments

Standard reference materials (SRMs) have been commonly used to perform quality assurance and quality control (QA/QC) in soil total metal concentration analyses or bioaccessibility assessment. In this study, 10 experimenters from 4 laboratories determined bioaccessibility of lead (Pb) in 4 widely-used SRMs (NIST 2710a, NIST 2587, BGS 102, and GBW 07405). Based on the gastric phase (GP) of the unified BARGE bioaccessibility method (UBM) and the Solubility Bioavailability Research Consortium procedure (SBRC), Pb bioaccessibility in SRMs was compared within and between laboratories to assess their intra-laboratory repeatability and inter-laboratory reproducibility. Lead bioaccessibility was 14.1 ± 2.44%-101 ± 2.48% in the 4 SRMs. The values were in vivo validated based on a mouse model in previous studies (R² = 0.97-0.98), suggesting the reliability of Pb bioaccessibility data. Strong correlations were observed for Pb bioaccessibility among 7 experimenters (R² = 0.94-0.99) at the Nanjing University (NJU) laboratory and similar strong correlations were also found between each two of the 4 laboratories (R² = 0.94-0.98), illustrating consistency in intra- and inter-laboratory performance. The intra-laboratory repeatability and inter-laboratory reproducibility were generally acceptable with relative standard deviations (RSDs) of Pb bioaccessibility being ≤10% within laboratory and ≤20% between laboratories, except in a soil with low bioaccessible Pb (BSG 102). Our study suggested that measurements of Pb bioaccessibility in SRMs based on the two in vivo validated methods were repeatable and reproducible within and between laboratories, further verified their reliability being used as QA/QC samples during Pb bioaccessibility assessment.

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.

Ca Minerals and Oral Bioavailability of Pb, Cd, and As from Indoor Dust in Mice: Mechanisms and Health Implications

BACKGROUND

Elevating dietary calcium (Ca) intake can reduce metal(loid)oral bioavailability. However, the ability of a range of Ca minerals to reduce oral bioavailability of lead (Pb), cadmium (Cd), and arsenic (As) from indoor dust remains unclear.

OBJECTIVES

This study evaluated the ability of Ca minerals to reduce Pb, Cd, and As oral bioavailability from indoor dust and associated mechanisms.

METHODS

A mouse bioassay was conducted to assess Pb, Cd, and As relative bioavailability (RBA) in three indoor dust samples, which were amended into mouse chow without and with addition of CaHPO 4 ,  CaCO 3 , Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate at 200 - 5,000 μ g / g   Ca . The mRNA expression of Ca and phosphate (P) transporters involved in transcellular Pb, Cd and As transport in the duodenum of mice was quantified using real-time polymerase chain reaction. Serum 1,25-Dihydroxyvitamin D3 [1,25 ( OH ) 2 D 3 ], parathyroid hormone (PTH), and renal CYP27B1 activity controlling 1,25 ( OH ) 2 D 3 synthesis were measured using ELISA kits. Metal(loid) speciation in the feces of mice was characterized using X-ray absorption near-edge structure (XANES) spectroscopy.

RESULTS

In general, mice exposed to each of the Ca minerals exhibited lower Pb-, Cd-, and As-RBA for three dusts. However, RBAs with the different Ca minerals varied. Among minerals, mice fed dietary CaHPO 4 did not exhibit lower duodenal mRNA expression of Ca transporters but did have the lowest Pb and Cd oral bioavailability at the highest Ca concentration (5,000 μ g / g   Ca ; 51%-95% and 52%-74% lower in comparison with the control). Lead phosphate precipitates (e.g., chloropyromorphite) were observed in feces of mice fed dietary CaHPO 4 . In comparison, mice fed organic Ca minerals (Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate) had lower duodenal mRNA expression of Ca transporters, but Pb and Cd oral bioavailability was higher than in mice fed CaHPO 4 . In terms of As, mice fed Ca aspartate exhibited the lowest As oral bioavailability at the highest Ca concentration (5,000 μ g / g   Ca ; 41%-72% lower) and the lowest duodenal expression of P transporter (88% lower). The presence of aspartate was not associated with higher As solubility in the intestine.

DISCUSSION

Our study used a mouse model of exposure to household dust with various concentrations and species of Ca to determine whether different Ca minerals can reduce bioavailability of Pb, Cd, and As in mice and elucidate the mechanism(s) involved. This study can contribute to the practical application of optimal Ca minerals to protect humans from Pb, Cd, and As coexposure in the environment. https://doi.org/10.1289/EHP11730.

Effects of various Fe compounds on the bioavailability of Pb contained in orally ingested soils in mice: Mechanistic insights and health implications

Reducing lead (Pb) exposure via oral ingestion of contaminated soils is highly relevant for child health. Elevating dietary micronutrient iron (Fe) intake can reduce Pb oral bioavailability while being beneficial for child nutritional health. However, the practical performance of various Fe compounds was not assessed. Here, based on mouse bioassays, ten Fe compounds applied to diets (100-800 mg Fe kg^-1) reduced Pb oral relative bioavailability (RBA) in two soils variedly depending on Fe forms. EDTA-FeNa was most efficient, which reduced Pb-RBA in a soil from 79.5 ± 14.7 % to 23.1 ± 2.72 % (71 % lower) at 100 mg Fe kg^-1 in diet, more effective than other 9 compounds at equivalent or higher doses (3.6-68 % lower). When EDTA-FeNa, ferrous gluconate, ferric citrate, and ferrous bisglycinate were supplemented, Fe-Pb co-precipitation was not observed in the intestinal tract. EDTA-FeNa, ferrous gluconate, ferric citrate, and ferrous sulfate suppressed duodenal divalent metal transporter 1 (DMT1)mRNA relative expression similarly (27-68 % lower). In comparison, among ten compounds, EDTA-FeNa elevated Fe concentrations in mouse liver, kidney, and blood (1.50-2.69-fold higher) most efficiently, suggesting the most efficient Fe absorption that competed with Pb. In addition, EDTA was unique from other organic ligands, ingestion of which caused 12.0-fold higher Pb urinary excretion, decreasing Pb concentrations in mouse liver, kidney, and blood by 68-88 %. The two processes (Fe-Pb absorption competition and Pb urinary excretion with EDTA) interacted synergistically, leading to the lowest Pb absorption with EDTA-FeNa. The results provide evidence of a better inhibition of Pb absorption by EDTA-FeNa, highlighting that EDTA-FeNa may be the most appropriate supplement for intervention on human Pb exposure. Future researches are needed to assess the effectiveness of EDTA-FeNa for intervention on human Pb exposure.

Impact of smelter re-development on spatial and temporal airborne Pb concentrations

Total suspended particulate (TSP) and PM₁₀ filters collected from two ambient air monitoring stations in Port Pirie were analysed to determine the impact of a lead (Pb) smelter redevelopment on air quality parameters including total elemental concentration, Pb isotopic ratio, Pb bioaccessibility and Pb speciation. Filters from 2009 to 2020 were analysed with a focus on samples from 2017 (immediately prior to smelter redevelopment) and 2020 (post-smelter redevelopment). Lead concentration in 2009-2020 TSP was variable ranging up to 6.94 μg m^-3 (mean = 0.57 μg m^-3), however, no significant decrease in Pb concentration was observed at either Port Pirie West (p = 0.56, n = 34) or Oliver Street (p = 0.32, n = 28) monitoring stations when 2017 and 2020 TSP values were compared. Similarly, no significant difference (p = 0.42) in PM₁₀ Pb concentration was observed in 2017 (mean = 0.80 μg m^-3) and 2020 (0.60 μg m^-3) Oliver Street filters. Although no change in percentage Pb bioaccessibility was observed when 2017 and 2020 Port Pirie West TSP samples were compared (mean of 88.7% versus 88.0%), Pb bioaccessibility was lower (p < 0.005) in both 2020 TSP (mean of 83.9% versus 62.9%) and PM₁₀ (mean of 70.8% versus 58.3%) Oliver Street filters compared to 2017. While scanning electron microscopy, energy dispersive x-ray spectroscopy identified a number of Pb phases within filters (galena, anglesite, cerussite, conglomerates), differences in Pb speciation between 2017 and 2020 filters could not be identified although it was presumed that this influenced Pb bioaccessibility outcomes at Oliver Street. Data from this study suggests that recent smelter redevelopments have not significantly decreased the concentrations of airborne Pb in Port Pirie although re-entrainment of soil-Pb from historical impact may also be a contributing Pb source.

Nickel oral bioavailability in contaminated soils using a mouse urinary excretion bioassay: Variation with bioaccessibility

To assess the health risk of nickel (Ni) in contaminated soils, studies rarely evaluated Ni bioavailability in the gastrointestinal (GI) tract, limiting the accurate regulation of contaminated sites. Here, for 15 soil samples contaminated by Ni-electroplating, Ni oral relative bioavailability (RBA, relative to NiSO₄) was measured using a mouse urinary excretion bioassay. Nickel-RBA varied from 7.89% to 33.8% at an average of 19.1 ± 18.6%. The variation was not explained well by variation in soil properties including Ni speciation and co-contamination of other metals, which showed weak correlation with Ni-BRA (R² < 0.36). In comparison, the Ni-RBA variation was explained well by the variation of soil-Ni solubility in simulated human gastric or gastrointestinal fluids, i.e., Ni bioaccessibility. Determined using the gastric (GP) and intestinal phases (IP) of solubility bioaccessibility research consortium (SBRC), physiologically based extraction test methods (PBET), and unified BARGE method (UBM), Ni bioaccessibility explained 54-71% variation of the Ni-RBA, suggesting that Ni oral bioavailability was predominantly controlled by Ni solubility in the GI tract. The results highlight the suitability of using simple, fast, and cost-effective bioaccessbility assays to predict site-specific Ni oral bioavailability.

Effect of Polishing on Lead and Cadmium Bioavailability in Rice and Its Health Implications

Rice polishing is an important approach to reducing the concentrations of heavy metals in rice, but knowledge of its effect on the Pb and Cd bioavailability in produced rice and the related health risk remains limited. In this study, the effects of rice polishing on the bioaccessibility (BAC) and bioavailability (RBA) of Pb and Cd in rice are assessed using an in vitro method and an in vivo mouse bioassay. The Pb removal rate in brown rice (40%), lightly processed brown rice (62%), germinated rice (74%), and polished rice (79%) gradually enhanced with an increase in the polishing degree, while Cd was difficult to remove by polishing. The Pb and Cd BAC in germinated rice was the highest, while that in brown rice was the lowest. The polished rice Pb and Cd RBA in the liver and kidneys were significantly higher than those in the brown rice group. The Pb RBA in the livers and kidneys in the polished rice group was 26.6% ± 1.68% and 65.3% ± 0.83%, respectively, which was 1.6- and 2.6-times higher than that in the brown rice group, respectively. The Cd RBA values in both the livers and kidneys of the polished rice group were 1.3-times higher than those in the brown rice group. Although polishing reduced the total Pb in the polished rice, it was not enough to offset the increase in bioavailability, and its consumption risk was not weakened. This study highlighted the value of the oral-bioavailability-corrected health risk assessment for assessing the influence of rice polishing on Pb and Cd exposure via rice consumption.

Inhalation Bioaccessibility and Risk Assessment of Metals in PM2.5 Based on a Multiple-Path Particle Dosimetry Model in the Smelting District of Northeast China

PM2.5 can deposit and partially dissolve in the pulmonary region. In order to be consistent with the reality of the pulmonary region and avoid overestimating the inhalation human health risk, the bioaccessibility of PM2.5 heavy metals and the deposition fraction (DF) urgently needs to be considered. This paper simulates the bioaccessibility of PM2.5 heavy metals in acidic intracellular and neutral extracellular deposition environments by simulating lung fluid. The multipath particle dosimetry model was used to simulate DF of PM2.5. According to the exposure assessment method of the U.S. Environmental Protection Agency, the inhalation exposure dose threshold was calculated, and the human health risk with different inhalation exposure doses was compared. The bioaccessibility of heavy metals is 12.1−36.2%. The total DF of PM2.5 in adults was higher than that in children, and children were higher than adults in the pulmonary region, and gradually decreased with age. The inhalation exposure dose threshold is 0.04−14.2 mg·kg−1·day−1 for the non-carcinogenic exposure dose and 0.007−0.043 mg·kg−1·day−1 for the carcinogenic exposure dose. Cd and Pb in PM2.5 in the study area have a non-carcinogenic risk to human health (hazard index < 1), and Cd has no or a potential carcinogenic risk to human health. A revised inhalation health risk assessment may avoid overestimation.

Bioaccessibility of Cd and its Correlation with Divalent Mineral Nutrients in Locally Grown Rice from Two Provinces in China

Rice and rice products are the main sources of Cd contamination in humans. The total and bioaccessible concentrations of Cd and three divalent nutrients, Mn, Cu, and Zn, in locally grown rice grains from Hunan and Guangdong Provinces in China were investigated. An in vitro physiologically based extraction test method was introduced to evaluate the bioaccessibility of the target metals in the rice grains. The mean concentrations of Cd in the rice grains were 0.245 mg/kg and 0.235 mg/kg from Hunan and Guangdong Provinces, respectively. Large variations were observed in the Cd concentrations, indicating a heterogeneous distribution of Cd contamination throughout the study areas. The bioaccessibility of Cd, Mn, and Zn in the gastrointestinal fractions was significantly lower than that in the gastric fractions. In contrast, the bioaccessibility of Cu at the intestinal phase was detected in the rice grains from both provinces. The correlation analysis showed significant relationships between total Cd concentrations and bioaccessible Cd fractions, indicating that higher total Cd in rice grains always resulted in higher bioaccessible Cd. Consistent correlations in the rice grains were observed between Zn and Mn. However, a lack of correlation was found between Cd and Zn in the current study. Risk assessment according to bioaccessible Cd would significantly reduce the exposure risk to Cd from rice consumption.

Environmental and human health risk assessment of sulfidic mine waste: Bioaccessibility, leaching and mineralogy

Sulfidic mine waste can pose environmental and human health risks, especially when it contains high levels of mobile metal(loid)s. To assess the environmental and health risks of mine waste originating from three historic and active sulfidic Pb-, Zn- and/or Cu-mines in Europe, mineralogical and chemical characterizations were conducted in combination with in vitro bioaccessibility tests, sequential extractions and leaching tests. Results indicated that most samples contained highly elevated levels of metal(loid)s and key minerals consisting of pyrite, sphalerite and cerussite. The orally bioaccessible fraction varied amongst samples: Cd (13-100%), Zn (9-69%), Pb (4-67%), Cu (8-41%) and As (1-11%). Given these bioaccessible levels, the human health risk assessment indicated carcinogenic and non-carcinogenic risks for most investigated samples in a worst-case exposure scenario. The leaching tests revealed a high mobility of metal(loid)s, especially Pb, posing potential environmental risks. The sequential extractions coupled with mineralogical analyses highlighted the highly mobile levels of Cd, Pb and Zn, posing environmental and health risks. Cerussite dissolved in the easily exchangeable fraction, releasing elevated levels of Pb, while pyrite never completely dissolved. In conclusion, the studied wastes pose environmental and health risks, but the high mobility of some elements also provides opportunities for the valorization of the waste.

Beryllium in contaminated soils: Implication of beryllium bioaccessibility by different exposure pathways

Inhalation exposure and beryllium (Be) toxicity are well-known, but research on bioaccessibility from soils via different exposure pathways is limited. This study examined soils from a legacy radioactive waste disposal site using in vitro ingestion (Solubility Bioaccessibility Research Consortium [SBRC], physiologically based extraction test [PBET], in vitro gastrointestinal [IVG]), inhalation (simulated epithelial lung fluid [SELF]) and dynamic two-stage bioaccessibility (TBAc) methods, as well as 0.43 M HNO₃ extraction. The results showed, 70 ± 4.8%, 56 ± 16.8% and 58 ± 5.7% of total Be were extracted (gastric phase [GP] + intestinal phase [IP]) in the SBRC, PBET, and IVG methods, respectively. Similar bioaccessibility of Be (~18%) in PBET-IP and SELF was due to chelating agents in the extractant. Moreover, TBAc-IP showed higher extraction (20.8 ± 2.0%) in comparison with the single-phase (SBRC-IP) result (4.8 ± 0.23%), suggesting increased Be bioaccessibility and toxicity in the gastrointestinal tract when the contamination derives from the inhalation route. The results suggested Be bioaccessibility depends on solution pH; time of extraction; soil reactive fractions (organic-inorganic); particle size, and the presence of chelating agents in the fluid. This study has significance for understanding Be bioaccessibility via different exposure routes and the application of risk-based management of Be-contaminated sites.

Interactions among heavy metal bioaccessibility, soil properties and microbial community in phyto-remediated soils nearby an abandoned realgar mine

Soil samples were collected from a representative arsenic (As) contaminated region under phytoremediation of hyperaccumulation plants. Relative abundance and diversity of microbial communities in the soil samples were characterized via 16S rRNA genes sequencing. At the phylum level, Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes and Firmicutes shows the highest abundance, accounting for more than 90 % of the classified sequences in the soil samples. Physicochemical parameters including pH, total organic carbon (TOC), cation exchange capacity (CEC), and electrical conductivity (EC), and heavy metal concentrations including total and bioaccessible contents in the soil samples were determined to investigate potential relationships between the microbial communities and the environmental factors. Principal component analysis (PCA) based on the operational taxonomic units (OTUs) matrix revealed distinct separation among the samples. The soil pH was confirmed as the dominant force to discriminate the soil samples with similar land use type and heavy metal contamination. There was little relevance between the total concentrations of heavy metals and the microbial communities. However, the bioaccessible concentrations of heavy metals were associated with the physicochemical parameters and relative abundances of bacterial genera according to correlation analyses. Although the soil samples were considerably contaminated by As, the abundances of bacterial phyla linked with As were lower than 1.0 % in most of the soil samples. The results indicated that the abundances of microbial communities in the soils were the consequence of concerted effects from all the environmental factors.

Characteristics, distribution, and children exposure assessment of 13 metals in household dust in China: A big data pilot study

To explore the pollution characteristics of metals in household dust in China and their exposure to children, this study searched peer-reviewed papers published during 1980-2020 and analyzed 30 eligible papers screened under the per-decided strategy. We evaluated the sample-weighted concentration (SWC) of each metal, explored the sources of metals, and presented the quantitative description of spatial-temporary characteristics and children exposure to 13 metals with multi-route under a general living scenario. The results showed the concentrations of 13 metals with a range of 0.89-29 090.19 mg/kg. The SWC of Cd in household dust from rural areas was 3.29 times of that from urban areas, while the SWC of Ni from urban areas was 3.71 times of that from rural areas. The results showed that four principal components were extracted, and the cumulative contribution rate reached 79.127%. The exposure dose of 13 metals to children aged 2-3 years was presented with the highest by ingestion. Metals such as Fe, Zn, and Mn posed inevitable health risk to children with high exposure. Countermeasures should be carried out to minimize the children exposure to metals in household dust urgently, such as the establishment of environmental health standard for household dust.

Geochemical fractionation, bioavailability, and potential risk of heavy metals in sediments of the largest influent river into Chaohu Lake, China

As the largest tributary flowing into Chaohu Lake, China, the Hangbu-Fengle River (HFR) has an important impact on the aquatic environment security of the lake. However, existing information on the potential risks of heavy metals (HMs) in HFR sediments was insufficient due to the lack of bioavailability data on HMs. Hence, geochemical fractionation, bioavailability, and potential risk of five HMs (Cr, Cu, Zn, Cd, and Pb) in HFR sediments were investigated by the combined use of the diffusive gradient in thin-films (DGT), sequential extraction (BCR), as well as the physiologically based extraction test (PBET). The average contents of Cd and Zn in the HFR Basin were more than the background values in the sediments of Chaohu Lake. A large percentage of BCR-extracted exchangeable fraction was found in Cd (8.69%), Zn (8.12%), and Cu (8.05%), suggesting higher bioavailability. The PBET-extracted fractions of five HMs were all almost closely positively correlated with their BCR-extracted forms. The pH was an important factor affecting the bioavailability of HMs. The average DGT-measured contents of Zn, Cd, Cr, Cu, and Pb were 28.07, 7.7, 3.69, 2.26, 0.5 μg/L, respectively. Only DGT-measured Cd significantly negatively correlated with Eh, indicating that Cd also had a high release risk under reducing conditions, similar to the risk assessment results. Our results could provide a reference for evaluating the potential bioavailabilities and ecological hazards of HMs in similar study areas.

Leaching and In Vivo Bioavailability of Antimony in PET Bottled Beverages

Antimony (Sb) may leach from polyethylene terephthalate (PET) materials into bottled water under improper storage conditions, particularly at high temperatures, leading to potential Sb chronic exposure and adverse health effects. However, Sb leaching may be promoted by various beverage constituents, which has received limited attention to date. In addition, few studies have considered Sb bioavailability in beverages and the influence of the beverage matrix on Sb bioavailability. In this study, PET-bottled beverages (n = 50) covering six categories (namely, carbonated, fruit juices, tea, sports, protein, and coffee beverages) were explored. Antimony leaching was assessed following the incubation of beverages at 60 °C for 7 days, which resulted in Sb concentrations 1.10-10.9 times greater than concentrations observed pre-incubation. Although regulatory standards vary internationally, a total of 21 beverages exceeded the Japanese Sb drinking water standard of 2 μg/L (up to 4.08 ± 0.11 μg/L) following incubation at 60 °C. pH significantly influenced Sb leaching (r = -0.38, p = 0.007) with beverages displaying lower pH (e.g., carbonated drinks) exhibiting higher Sb concentrations. An in vivo mouse model, using the liver as the biological endpoint, was adopted to assess Sb relative bioavailability (RBA) in bottled beverages. Sb RBA ranged from 1.97-58.7% with coffee beverages exhibiting the lowest Sb RBA (1.97-13.7%) and protein drinks the highest (41.1-58.7%). Linear regression revealed that Sb RBA in beverages was negatively influenced by Fe (r = -0.69, p = 0.02) and P (r = -0.73, p = 0.01) concentrations but positively correlated with tartaric acid (r = 0.59, p = 0.02). When an exposure assessment was undertaken using data generated in this study, carbonated and protein-rich beverages exhibited a higher exposure risk due to elevated Sb leaching and high Sb RBA compared to other beverage categories.

Improving the predictive value of bioaccessibility assays and their use to provide mechanistic insights into bioavailability for toxic metals/metalloids - A research prospectus

Widespread contamination of soil, dust, and food with toxic metal(loid)s pose a significant public health concern. Only a portion of orally ingested metal(loid) contaminants are bioavailable, which is defined as the fraction of ingested metal(loid)s absorbed across the gastrointestinal barrier and into systemic circulation. Bioaccessibility tools are a class of in vitro assays used as a surrogate to estimate risk of oral exposure and bioavailability. Although development and use of bioaccessibility tools have contributed to our understanding of the factors influencing oral bioavailability of metal(loid)s, some of these assays may lack data that support their use in decisions concerning adverse health risks and soil remediation. This review discusses the factors known to influence bioaccessibility of metal(loid) contaminants and evaluates experimental approaches and key findings of SW-846 Test Method 1340, Unified BARGE Method, Simulated Human Intestinal Microbial Ecosystem, Solubility Bioaccessibility Research Consortium assay, In Vitro Gastrointestinal model, TNO-Gastrointestinal Model, and Dutch National Institute for Public Health and the Environment bioaccessibility models which are used to assess oral absolute bioavailability and relative bioavailability in solid matrices. The aim of this review was to identify emerging knowledge gaps and research needs with an emphasis on research required to evaluate these models on (1) standardization of assay techniques and methodology, and (2) use of common criteria for assessing the performance of bioaccessibility models.

Oral and inhalation bioaccessibility of potentially toxic elements in household dust from former Hg mining district, Idrija, Slovenia

One of the main sources of potential chronic exposure to potentially toxic elements is household dust, especially in an environment with known point sources of PTE pollution. The literature review clearly shows that the total concentrations of an element in the environment do not provide information to predict its bioavailability. The aim of the present study was to evaluate the oral and inhalation bioaccessibility of PTE present in household dust in the small town of Idrija, the site of the former mercury mine. Unified bioaccessibility method was used to assess oral bioaccessibility of PTE in the stomach and intestine, while inhalation bioaccessibility was assessed by extraction of household dust samples with two synthetic extraction solutions-Gamble's solution (GS) and artificial lysosomal fluid (ALF). A low bioaccessibility of mercury was observed in all synthetic solutions (less than 3%). The highest bioaccessibility of PTE was observed in ALF solution, especially for Zn, Pb and Cd. Only a slightly lower bioaccessibility of these three elements was also observed in the stomach, while the bioaccessibility of other elements in the gastric phase was less than 40%. In general, the bioaccessibility of all elements decreased in the intestine. With the exception of Cr, the lowest bioaccessibility of the elements was observed in GS. Daily ingestion and inhalation doses of PTE from household dust were calculated and their values were below the available recommended or tolerable daily intakes of PTE from food according to the European Food Safety Authority.

Comparison of heavy metal bioaccessibility between street dust and beach sediment: Particle size effect and environmental magnetism response

Direct ingestion of urban sediment particles represents an important pathway of human exposure to heavy metals. The effect of particle sizes on metal bioaccessibilities in human digestive system has not been fully understood. In this study, an in-vitro simulation experiment (PBET), along with environmental magnetic measurements, is conducted on two urban sediments (street dusts and beach sediments) with different particle sizes (Φ31.1 ± 7.36 μm for street dusts and Φ134 ± 21.1 μm for beach sediments) for the purposes of assessing the particle size effect on metal bioaccessibilities in simulated gastric and intestinal tracts, and exploring the environmental magnetism response to different digestion processes. For street dusts, the bioaccessibilities of heavy metals decrease significantly from gastric (12.1 (Cu) ~ 39.9% (Pb)) to intestinal phase (0.41 (Pb) ~ 2.08% (Cd)) due to an increase in digestive juice pH. However, for beach sediments, the metal bioaccessibilities in the intestinal phase is similar to, or even higher than, those in the gastric phase. These demonstrate that clay minerals and Fe/Mn oxides concentrated in fine particles play an important role in adsorbing and fixating heavy metals in neutral intestinal tract. Compared with those of the original samples, the χ_fd% values of the PBET treated street dusts decrease significantly, and the decreasing extents (Δχ_fd%) are positively correlated with the concentrations of the PBET extracted Fe (p < 0.05). However, a reverse trend is observed for the beach sediment samples. These findings suggest that the magnetic minerals formed during the digestion process might affect the metal bioaccessibilities in gastrointestinal tract.

Bioavailability Evaluation of Perchlorate in Different Foods In Vivo: Comparison with In Vitro Assays and Implications for Human Health Risk Assessment

Perchlorate in various foods continuously arouses public health concern. Bioavailability is a critical parameter to better estimate perchlorate exposure from diets. In this study, perchlorate bioavailability in five foods was determined in an in vivo mouse model and compared with in vitro bioaccessibility/bioavailability. The estimated in vivo perchlorate bioavailability for different foods ranged from 18.01 ± 4.53% to 45.60 ± 7.11%, with the order lettuce > pork > rice > milk powder > soybean. Moisture, fiber, and fat in foods were identified as critical factors affecting perchlorate bioavailability (correlation r = 0.71, 0.52, and -0.67, respectively). Linear regression analysis revealed that the in vitro perchlorate bioavailability determined using the Caco-2 cell model has the potential to estimate the in vivo perchlorate bioavailability in foods (R² = 0.67, slope = 1.33, and y intercept = 4.99). These findings provide insights into the effects of the food matrices on perchlorate bioavailability and could contribute to decrease the uncertainty regarding perchlorate dietary exposure risk assessment.

Assessment of human health risk due to lead in urban park soils using in vitro methods

Beijing parks always have a large flow of local residents and tourists, and the soil Pb could threaten human health by incidental ingestion. Soil samples from eleven parks in Beijing were collected to assess the human health risk associated with Pb. Lead bioaccessibility in these parks ranged from 3.2 ± 0.4% to 12.1 ± 0.5% in the physiologically based extraction test (PBET) gastric phase and increased when approaching the city center. The chemical forms and soil properties (Fe, organic matter, and grain size) were important factors affecting the soil Pb bioaccessibility. The geo-accumulation index of Beihai Park (BH, near the city center) reached 1.3 ± 0.1 indicating moderate contamination. Lead health risk to children in BH should be of concern though its hazard quotient was below one. Results obtained from the Diffusive Gradients in Thin-films (DGT)-induced fluxes in the soils (DIFS) model showed that Pb-release in some parks farther from the city center was a "partially sustained case" (R_diff < R < 0.95) indicating that soil particles could partially replenish effective Pb to the soil solution. A relatively higher desorption rate constant (k₁) and shorter characteristic response time (T_c) were also found in these parks, indicating non-negligible release risk. Soil Pb based on the PBET method and DIFS model could provide a reliable reference to park managers for the health risk management of Pb pollution.

Selenium bioaccessibility in native seleniferous soil and associated plants: Comparison between in vitro assays and chemical extraction methods

Selenium (Se) bioaccessibility in soil and crops from seleniferous areas is closely relevant to Se intake risks of local residents. The current in vitro digestion methods used for Se bioaccessibility evaluation are single and inconsistent, and most of them are only for food and neglect soil. In this study, 14 Se-contaminated soils and their corresponding crops in Naore Village (seleniferous area) were used as the research objects. Four in vitro digestion assays, including Solubility Bioaccessibility Research Consortium method (SBRC), physiologically-based extraction test (PBET), in vitro gastrointestinal method (IVG), and Unified Bioaccessibility Method (UBM) were used to determine the bioaccessible Se concentration in soil and edible parts of crops. Results showed that the Se in natural seleniferous soil mainly existed in relatively stable forms, i.e., residual and Fe-Mn oxide-bound Se (average of 80%). Only 10.6% of the total Se was distributed in water-soluble and exchangeable Se fractions. The Se content in crops was significantly positively correlated with the organic-bound and phosphate-extractable Se contents in the corresponding soil (p < 0.05). The organic-bound Se was clearly a potentially bioavailable Se source in soil. The Se bioaccessibility in soil and crops measured using the four in vitro methods in gastric/intestinal digestions were in the same order, which was PBET > UBM > SBRC > IVG. Similar to the absorption and utilization of soil Se fractions by crops, the water-soluble, organic-bound and exchangeable Se in soil were the main contributors of bioaccessible Se in the digestive juices in various in vitro methods. Furthermore, the bioaccessible Se in crops and soil measured via PBET method demonstrated the most significant correlation between the total Se in crops and the phosphate-extractable Se in soil. Therefore, the PBET method was the optimum in vitro method for the evaluation of Se bioaccessibility in crops and soil.

Temporal Potential of Phragmites australis as a Phytoremediator to Remove Ni and Pb from Water and Sediment in Lake Burullus, Egypt

In the current work, we investigated the concentration of Ni and Pb in different organs of Phragmites australis to evaluate its potential application as a phytoremediator to remove these two metals from contaminated water and sediment in Lake Burullus (a Ramsar site in Egypt). Above- and below-ground biomass of P. australis, water and sediment were sampled monthly for 1 year at six sites of Lake Burullus (three sites represent each of the northern and southern parts of the lake) using six randomly distributed quadrats (each of 0.5 × 0.5 m) at each sampling site. Significant variation was detected for Ni and Pb concentrations in the sediments and waters between the northern and southern sites of the lake. The biomass of P. australis in the southern sites was greater than that in the northern sites; in addition, the above-ground biomass was higher than the below-ground biomass. The above-ground organs accumulated higher concentrations of Ni and Pb than the below-ground organs. The Ni and Pb standing stocks data indicated that the organs of P. australis extracted higher amounts of Ni and Pb per its area from the southern rather than the northern sites. In the current study, the Ni and Pb above-ground standing stocks increased from the early growing season (February) and reached its peak during August and then decreased. The highest monthly Ni and Pb standing stock (18.2 and 18.4 g m^- 2, respectively) was recorded in the above-ground organs of plants in the southern sites in August. The bioaccumulation factor of Ni was 157.6 and 153.4 in the northern and southern sites, respectively, whereas that of Pb was 175.3 and 158.3. The translocation factor of Ni and Pb from the below- to above-ground organs was generally > 1. Thus, this reed species is a potential candidate for Ni and Pb phytoextraction. Based on our results, P. australis could be used for the extraction of Ni and Pb to reduce the pollution in Lake Burullus, if the above-ground biomass is harvested at its maximum value in August, as was the case regarding the maximum standing stock of Ni and Pb.

Heavy metals in indoor dust: Spatial distribution, influencing factors, and potential health risks

Given the large proportion of time that people spend indoors, the potential health risks posed by heavy metals in the indoor environment deserve greater attention. A global-scale assessment of heavy metal contamination in indoor dust was conducted in this study based on >127 articles published between 1985 and 2019. The pollution levels, spatio-temporal variations, sources, bioaccessibilities, influencing factors, and health risks of heavy metals associated with indoor dust were analyzed. Children's blood lead levels (BLLs) were also estimated using the integrated exposure uptake biokinetic model. The results indicated that the median concentrations of Cu and Zn in 71.9% and 71.0% of the study sites surpassed the corresponding permissible limits, 100 and 300 mg/kg, respectively; thus, their control should be given priority. Heavy metal concentrations in indoor dust from different areas of the world varied greatly, which was closely associated with the type of local human activities, such as mining, melting, e-waste recycling and Pb-related industries. The bioaccessibilities of some key elements, e.g., Pb, Cd, Cu, and Zn, in household dust were high. The levels of heavy metals in indoor dust were mainly affected by a combination of outdoor and indoor sources and related critical factors, and future studies should focus on quantifying the contributions of different sources. Based on the health risk assessment, dust Pb exposure is a major health concern in e-waste recycling areas, which warrants greater attention. 49.8%, 36.8% and 14.4% of study sites showed BLLs exceeding 35 μg/L (threshold limit in Germany), 50 μg/L (threshold limit in the USA), or 100 μg/L (threshold limit in China), respectively. Finally, Pb exposure from indoor dust represents a major contributor to children's blood Pb poisoning in many developing countries. This study details the overall heavy metal contamination status of indoor dust and provides insights for policymakers with respect to pollution prevention measures.

Risk Assessment for Oral Bioaccessibility of Lead and Cadmium in the Potato Growing in Smelter-Impacted Soil

Smelting activities are an important source of heavy metals in soil. More seriously, oral ingestion of crops growing in contaminated soil potentially cause harmful effects on human health. The main purpose of this study is to apply the in vitro model (PBET) and Monte Carlo Simulation (MSC) to the health risk assessment process in order to more accurately and realistically evaluate health risks of residents eating contaminated potato. Results indicated in the raw and cooked potato, the bioaccessibility of Pb was 65.9% and 74.5%, and that of Cd was 79.6% and 61.7%, respectively. Additionally, the bioaccessible hazard quotient (BHQ) was less than the permitted level except for the BHQ of Pb for children. This indicated there wasn't potential non-carcinogenic risk for most potato-consumers but the dietary exposure risk for local children cannot be neglected. Sensitivity analysis showed that the bioaccessibility and ingestion rate appeared decisive with respect to potentially deleterious health effects.

High Lead Bioavailability of Indoor Dust Contaminated with Paint Lead Species

House dust and soils can be major sources of lead (Pb) exposure for children. The American Healthy Homes Survey (AHHS) was developed to estimate Pb exposure from house dust and soil, in addition to other potential household contaminants and allergens. We have combined X-ray absorption spectroscopic (XAS) fingerprinting and in vivo mouse relative bioavailability (RBA) measurements for a subset of house dust and residential soils collected in the AHHS, with the primary objective of gaining a better understanding of determinants of house dust Pb bioavailability. Lead speciation was well related to variations in RBA results and revealed that highly bioavailable Pb (hydroxy)carbonate (indicative of Pb-based paint) was the major Pb species present in house dusts. Measured Pb RBA was up to 100% and is likely driven by paint Pb. To our knowledge, this is the first report of in vivo Pb RBA for U.S. house dust contaminated in situ with paint Pb and corroborates results from a previous study that demonstrated high RBA of paint Pb added to soil. We also report a relatively low RBA (23%) in a residential soil where the major Pb species was found to be plumbojarosite, consistent with a previous report that plumbojarosite lowers Pb RBA in soils.

Provenance and bioaccessibility of rare earth elements in atmospheric particles in areas impacted by the optoelectronic industry

Rare earth elements (REEs) are widely used in optoelectronic industries, and they can be emitted into the environment and may induce biological effects. In this study, we investigated the provenance and bioaccessibility of REEs in atmospheric particles (APs) collected from areas impacted by the optoelectronic industry. The geoaccumulation index (I_geo) values showed that Y, Eu, and Tb were much more enriched in the APs from the optoelectronic recycling sites than in those from the optoelectronic producing sites and were not enriched in the APs from the optoelectronic administrative sites and background sites. The characteristic parameters and the distribution patterns of REEs demonstrated that the AP samples from the recycling sites and producing sites showed remarkably positive Eu and Tb anomalies. According to the positive matrix factorization (PMF) model, the optoelectronic industry was quantitatively determined to contribute 82.8% of Y, 86.5% of Eu, and 83.4% of Tb. Furthermore, an in vitro physiologically based extraction test (PBET) was performed to assess the bioaccessibility of REEs in the APs. The results showed that the bioaccessibility of all the REEs in the APs was below 50.0% in the human gastrointestinal tract, with higher values in the gastric phases than in the intestinal phases. In particular, extremely low gastric bioaccessibilities of Tb and Ce and relatively high gastric bioaccessibilities of Y and Eu were observed in the APs from the recycling sites and producing sites, which may due to the chemical composition of the compounds containing REEs that are used in the optoelectronic industry. In conclusion, our results provide additional information about the contribution and influence of the optoelectronic industry on the provenance and bioaccessibility of REEs in APs.

Influence of household smoking habits on inhalation bioaccessibility of trace elements and light rare earth elements in Canadian house dust

In this study, total concentration and inhalation bioaccessibility (dissolution in simulated biological solution) of trace elements (TE) and rare earth elements (REE) were assessed in PM₁₀ from Canadian house dust samples with smoking (n = 25) and non-smoking (n = 25) status. Compared to the natural background concentrations in Canadian soils, median Zn, Pb, Cd and Cu concentrations in PM₁₀ were 10-23 fold higher, while median La, Ce and Pr concentrations were 1.6-2.4 fold higher. Mann-Whitney tests (α = 0.05) indicated no difference between the median TE concentrations based on the smoking status of the household; however, median REE concentrations were significantly higher in the PM₁₀ of smoking households. Additionally, Cd and Ni were positively correlated (Spearman r, p < 0.05) to La, Ce and Nd in smoking households, suggesting that tobacco combustion may have contributed REE in the PM₁₀ of these households. Median inhalation-ingestion bioaccessibility assay outcomes of arsenic (As) and lead (Pb) was higher in the non-smoking households when compared to smoking households (Mann Whitney test, α = 0.05), suggesting that tobacco combustion products may be associated with less soluble species of As and Pb. Although REE bioaccessibility was negligible in simulated lung epithelial fluid regardless of the smoking status of the household, bioaccessibility in the lung-gastric phase was 23.6-27.6% in the smoking household and 34.7-36.7% in the non-smoking households, indicating a significantly lower REE dissolution in PM₁₀ of smoking households. In contrast, between 17 and 21.9% bioaccessibility of REE was observed when artificial lysosomal fluid was used, where the outcome was not significantly affected by the smoking status. This study indicates that despite a higher median REE concentration in the PM₁₀ of smoking households, inhalation bioaccessibility may be significantly influenced by the mineralogy.

Linking elevated blood lead level in urban school-aged children with bioaccessible lead in neighborhood soil

Lead (Pb) exposure is known to affect the health of children while soil Pb is an important contributor to human Pb exposure. To analyze the effects of both environmental and other factors, especially total and bioaccessible Pb in neighborhood soil, on school-aged urban children's blood lead level (BLL), 75 children (6-11 years old) were recruited from an industry city in eastern China for BLL measurement and questionnaire survey. Soil samples were collected from their living neighborhoods and measured for total and bioaccessible Pb. The mean BLL was 4.82 μg dL^-1, with 42 out of 75 children having BLL exceeding the international guideline of 5 μg dL^-1. Low Pb contamination was observed in soil with total Pb ranging from 12.5 to 271 mg kg^-1 (mean 34.3 mg kg^-1). Based on the in vitro Solubility Bioaccessibility Research Consortium (SBRC) gastric fluid extraction, bioaccessible Pb in soil ranged from 0.40 to 79.1 mg kg^-1 (mean 7.58 mg kg^-1) with Pb bioaccessibility ranging from 1.74 to 68.1 (mean 19.9%). When BLL was correlated with total Pb in soil, insignificant linear relationship was observed (P > 0.05, correlation coefficient 95%CI = -0.047-0.40, R² = 0.07). However, when BLL was correlated with soil bioaccessible Pb or Pb bioaccessibility, much stronger linear relationships were observed (P < 0.01, correlation coefficient 95%CI = 0.28-0.64, R² = 0.16-0.20), suggesting that bioaccessible Pb was a much stronger predictor of BLL. In addition, strong associations were also observed between BLL and social factors such as house decoration, residence time, and personal habits, suggesting that both soil Pb contamination and social factors play important roles in elevating BLL for city children.

Uptake of vegetable and soft drink affected transformation and bioaccessibility of lead in gastrointestinal track exposed to lead-contaminated soil particles

Accidental ingestion of Pb-contaminated soil particles by direct hand-to-mouth activity or by swallowing airborne dust particles is important pathway of human exposure to Pb. Appropriate evaluation of Pb risk to human is important in determining whether the soil needs remediation or not, however, there is paucity of data about the dietary influences on Pb bioaccessibility (Pb-BA) and transformation in humans. This study chose two typical foods, spinach and cola, representing vegetable and soft drink, respectively, and investigated their effects on Pb species in gastrointestinal tract using the physiologically based extraction test. Results showed that ingestion of spinach and cola decreased the Pb-BA by 52%-94% in the gastric phase and by 38%-95% in the intestinal phase, respectively. The reduction of Pb-BA by spinach was attributed to the precipitation of Pb with phosphorus in spinach and the sorption of Pb by the generated hydrolysate and un-hydrolysate from spinach in gastrointestinal tract. Cola decreased Pb-BA mainly via formation of insoluble Pb phosphates precipitates. Analysis of X-ray diffraction and MINTEQ modeling demonstrated that the dissolved Pb was transformed to precipitated or sorbed Pb with intake of cola or spinach. Our findings suggest that dietary habit greatly influence the speciation and subsequent Pb-BA in the gastrointestinal tract, which should be incorporated into human health risk assessment of Pb-contaminated soil.

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

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

Seasonal disparities in airborne lead (Pb) and associated foliar uptake by ryegrass (Lolium perenne L.): A Pb isotopic approach

Foliar uptake of airborne lead (Pb) may be particularly important for Pb accumulation in plant organs. However, the aerosol bioconcentration factor (BCF) in different seasons has seldom been reported. In the present study, we collected ryegrass (Lolium perenne L.) and size-segregated aerosols (SSA) during the corresponding growing seasons, and analyzed these for both Pb concentrations and isotopic ratios. Airborne Pb showed a seasonally varying concentration that was approximately 20% higher in winter than in spring. The bioavailability index, however, was higher in spring. Coupling the stable isotope technique with the bioavailable Pb of aerosol was more reliable in identifying airborne Pb accumulation in leaves than the total determination, suggesting that the hydrophilic absorption pathway was probably dominant for the foliar uptake of Pb in ryegrass. Contributions of airborne Pb accumulation were 88%-92% for washed ryegrass growing outdoors, indicating that the foliar uptake of Pb in the field was mainly from atmospheric deposition. The aerosol BCF of Pb for ryegrass was 6.4-11.4 m³/g in winter and 22.9-31.5 m³/g in spring. The increased aerosol BCF in spring was due to the suitable temperature, abundant rainfall, and increased Pb solubility of the aerosol. Therefore, our results indicate that, for the foliar uptake of Pb, both the aerosol Pb concentration, composition, and seasonal influence should be considered.

Lead bioaccessibility in farming and mining soils: The influence of soil properties, types and human gut microbiota

To better understand the risk assessment of Lead (Pb) in contaminated soils, 78 soil samples were collected from different locations in China and Pb bioaccessibility was assessed using the PBET (The Physiologically Based Extraction Test) method combined with SHIME (The Simulator of the Human Intestinal Microbial Ecosystem), and Pb bioaccessibility data from the PBET method on 88 soil samples that found in the literature were also used for the assessment. For all the soils, the mean Pb bioaccessibility was as follows: the gastric phase (31.25%) > colon phase (17.78%) > small intestinal phase (10.13%). The values of Pb bioaccessibility in most soils were lower than 60%, which is the typical default assumption for Pb (RBA, relatively bioavailability) by the US EPA. Mean Pb bioaccessibility (41.10% and 14.00% for gastric and small intestinal phases, respectively) in the present study was slightly higher than the values from the literature (24.80% and 8.68% for gastric and small intestinal phases, respectively) in the gastrointestinal tract. Mean Pb bioaccessibility was lower in acidic soil during the small intestinal phase, while the values for the alkaline soil were higher in the small intestinal and colon phases. In the gastric and small intestinal phases, mean Pb bioaccessibility in farming soils was slightly lower than it was in mining soils. However, the mean Pb bioaccessibility from farming soils was increased compared with mining soils in the colon phase given the action of human gut microbiota. Soil pH and type are important factors for predicting soil Pb bioaccessibility and health risk.

Size-fractionated particle-bound heavy metals and perfluoroalkyl substances in dust from different indoor air

The indoor air quality issue and its potential health problems are attracting increasingly attentions. In this study, micro-orifice uniform deposit impactor (MOUDI) was used to sample suspended particles from four typical indoor environments, including residence, office, cyber classroom, and chemical analysis room. Size-dependent concentrations of perfluoroalkyl substances (PFASs) and heavy metals in suspended particles were analyzed. Then, the International Commission on Radiological Protection deposition model was employed to estimate deposition efficiencies and fluxes of size-fractioned PFASs and heavy metals in the human respiratory tract. Most of the contaminants deposited in head airways, where coarse particles (aerodynamic diameter or Dp > 1.8 μm) contributed the most. By contrast, in the alveolar region fine particles (Dp < 1.8 μm) were dominant. The chronic daily intake through inhalation of PFASs and heavy metals via airborne particles were 10.3-37.5 pg kg^-1days^-1 and 3.1-25.9 mg kg^-1days^-1, respectively. The estimated total hazardous quotient of PFASs and heavy metals were 4.4 × 10^-5-1.7 × 10^-3 and 9.9 × 10^-3-1.05 × 10^-1, which is far lower than the acceptable threshold of 1. However, the incremental lifetime cancer risk induced by As, Cd, Co, Cr, and Ni were estimated to be 1.11 × 10^-5-1.41 × 10^-4 in total, which exceeded the acceptable threshold of 10^-6. These findings implicate that there were health risks, especially cancer risks caused by heavy metals associated with airborne particles in urban indoor environments.

Bioaccessibility of lead in Dittrichia viscosa plants and risk assessment of human exposure around a fertilizer industry in Lebanon

Total and bioaccessible lead (Pb) concentrations in Dittrichia viscosa and soil samples were considered for estimating the potential health risk, related to both plant intake and accidental soil ingestion by adult and child consumers, near a Lebanese fertilizer plant. A total of 27 plant samples, from 9 uncultivated sites situated around the plant, were analyzed in order to assess the total and bioaccessible Pb content. Physiologically based extraction test (PBET) was used to estimate oral bioaccessibility of Pb in edible plant parts. Washed and unwashed leaves were compared in order to show the importance of good consumer practice on Pb intake. Extracted Pb in the intestinal medium accounted for 24 up to 87% of Pb extracted in the gastric medium. The total hazard quotient (HQ_tot) and the total bioaccessible hazard quotient (BHQ), related to both plants' intake and soil ingestion, for two maximalist child and adult scenarios, were calculated in order to estimate human health risk assessment. HQ_tot estimations considering the total concentration of Pb in soil and plant suggest that this metal is a contributor in elevating health risks problems on local plants' consumers, especially children inhabitants. However, the integration of bioaccessible concentrations of Pb in risk estimations reduces remarkably the potential risk.

Oral Bioavailability of As, Pb, and Cd in Contaminated Soils, Dust, and Foods based on Animal Bioassays: A Review

Metal contamination in soil, dust, and food matrices impacts the health of millions of people worldwide. During the past decades, various animal bioassays have been developed to determine the relative bioavailability (RBA) of As, Pb, and Cd in contaminated soils, dust, and foods, which vary in operational approaches. This review discusses the strengths and weaknesses of different animal models (swine and mice), dosing schemes (single gavage dose, repeated gavage dose, daily repeated feeding, and free access to diet), and end points (blood, urine, and tissue) in metal-RBA measurement; compares metal-RBA obtained using mouse and swine bioassays, different dosing schemes, and different end points; and summarizes key findings on As-, Pb-, and Cd-RBA values in contaminated soils, dust, and foods. Future directions related to metal-RBA research are highlighted, including (1) comparison of metal-RBA determinations between different bioassays and different laboratories to ensure robust bioavailability data, (2) enhancing the metal-RBA database for contaminated dust and foods, (3) identification of physiological and physicochemical mechanisms responsible for variability in metal-RBA values, (4) formulation of strategies to decrease metal-RBA values in contaminated soils, dust, and foods, and (5) assessing the impacts of cocontaminants on metal-RBA measurement.

Speciation and bioaccessibility of heavy metals in PM2.5 in Baoding city, China

The health risks and toxicity of heavy metals (HMs) in PM_2.5 are not only associated with their total amounts, but also with their species and bioaccessibility. In this study, the speciation (fractions) and bioaccessibility of HMs (Pb, Cd, Cr, Cu and Zn) as well as their correlations in fine particulate matter (PM_2.5) samples from four seasons were studied. A sequential extraction procedure was applied to divide the studied HMs into four fractions: acid-soluble fraction (F1), reducible fraction (F2), oxidative fraction (F3) and residual fraction (F4). The simulated body fluids (gastrointestinal and lung phases) were used for in vitro tests in order to evaluate the bioaccessibility of HMs. The distribution of HMs in PM_2.5 was season and element dependent. It was found that Zn was the most abundant element among the five measured metals and followed by Pb, Cu, Cr and Cd. The total contents of each HM in different seasons were in the following order: winter > autumn > spring > summer. The studied HMs were mainly concentrated in acid-soluble fraction (F1) with high bioaccessibility (p < 0.05) except for Cr. Zn, Pb and Cu possessed the highest bioaccessibility in summer while Cd and Cr were the highest in winter. In vitro tests indicated that HMs in PM_2.5 were much more accessible to gastrointestinal fluids rather than lung phase (Gamble's solution). A significant correlation was found between the results from the optimized BCR sequential extraction and solubility bioaccessibility research consortium (SBRC). The fractions extracted by SBRC were consistent with the first two fractions extracted by the sequential extraction method.

Investigating Lead Species and Bioavailability in Contaminated Soils: Coupling DGT Technique with Artificial Gastrointestinal Extraction and in Vivo Bioassay

Although strong in vivo-in vitro correlations (IVIVCs) between relative bioavailability (RBA) and bioaccessibility of soil Pb were well reported, knowledge on the fractions of bioaccessible Pb in simulated gastrointestinal (GI) fluids that are available for absorption into the systemic circulation is limited. Here, Pb-RBA in 14 Pb-contaminated soils were assessed using an in vivo mouse bioassay and compared to Pb bioaccessibility by the gastrointestinal phase of the UBM (Unified Bioaccessibility research group of Europe (BARGE) Method) in vitro assay with and without 0.45 μm filtration of GI fluid. Results showed good IVIVC between Pb-RBA and Pb bioaccessibility without filtration ( r ² = 0.62), while Pb bioaccessibility with filtration provided a poor correlation with Pb-RBA ( r ² = 0.16). This suggested that besides dissolved Pb ions, Pb-complexes formed in the UBM gastrointestinal fluid might also contribute to bioavailable Pb. To ascertain this, DGT (diffusive gradients in thin-films) devices which can measure both Pb²⁺ ions and labile inorganic and organic Pb-complexes were introduced to the UBM fluids to measure Pb DGT-bioaccessibility, which showed strong correlation to Pb-RBA ( r ² = 0.71). With increasing diffusive gel thickness which could enhance release of Pb ions from Pb-complexes, Pb DGT-bioaccessibility increased by 3.4-5.7 times, while inclusion of dialysis membrane within DGT devices significantly decreased Pb DGT-bioaccessibility by inhibiting diffusion of Pb complexes to binding gel. These results confirmed the contribution of Pb-complexes to Pb bioavailability, providing new insights to Pb bioavailability.