Relationship of bioaccessibility and fractionation of cadmium in long-term spiked soils for health risk assessment based on four in vitro gastrointestinal simulation models

Prediction of the bioaccessibility and accumulation of cadmium in the soil-rice-human system based on optimized DGT and BCR coupled models

Cadmium, as a typical heavy metal, has the potential to induce soil pollution and threaten human health through the soil-plant-human pathway. The conventional evaluation method based on the total content in soil cannot accurately represent the content migrated from the food chain to plants and the human body. Previous studies focused on the process of plant enrichment of heavy metals in soil, and very few studies directly predicted human exposure or risk through the labile state of Cd in soil. Hence, a relatively accurate and convenient prediction model of Cd release and translocation in the soil-rice-human system was developed. This model utilizes available Cd and soil parameters to predict the bioavailability of Cd in soil, as well as the in vitro bioaccessibility of Cd in cooked rice. The bioavailability of Cd was determined by the Diffusive Gradients in Thin-films technology and BCR sequential extraction procedure, offering in-situ quantification, which presents a significant advantage over traditional monitoring methods and aligns closely with the actual uptake of heavy metals by plants. The experimental results show that the prediction model based on the concentration of heavy metal forms measured by BCR sequential extraction procedure and diffusive gradients in thin-films technique can accurately predict the Cd uptake in rice grains, gastric and gastrointestinal phase (R2=0.712, 0.600 and 0.629). This model accurately predicts Cd bioavailability and bioaccessibility across the soil-rice-human pathway, informing actual human Cd intake, offering scientific support for developing more effective risk assessment methods.

How does the biochar-supported sulfidized nanoscale zero-valent iron affect the soil environment and microorganisms while remediating cadmium contaminated paddy soil?

In previous studies, iron-based nanomaterials, especially biochar (BC)-supported sulfidized nanoscale zero-valent iron (S-nZVI/BC), have been widely used for the remediation of soil contaminants. However, its potential risks to the soil ecological environment are still unknown. This study aims to explore the effects of 3% added S-nZVI/BC on soil environment and microorganisms during the remediation of Cd contaminated yellow-brown soil of paddy field. The results showed that after 49 d of incubation, S-nZVI/BC significantly reduced physiologically based extraction test (PBET) extractable Cd concentration (P < 0.05), and increased the immobilization efficiency of Cd by 16.51% and 17.43% compared with S-nZVI and nZVI/BC alone, respectively. Meanwhile, the application of S-nZVI/BC significantly increased soil urease and sucrase activities by 0.153 and 0.446 times, respectively (P < 0.05), improving the soil environmental quality and promoting the soil nitrogen cycle and carbon cycle. The results from the analysis of the 16S rRNA genes indicated that S-nZVI/BC treatment had a minimal effect on the bacterial community and did not appreciably alter the species of the original dominant bacterial phylum. Importantly, compared to other iron-based nanomaterials, incorporating S-nZVI/BC significantly increased the soil organic carbon (OC) content and decreased the excessive release of iron (P < 0.05). This study also found a significant negative correlation between OC content and Fe(II) content (P < 0.05). It might originate from the reducing effect of Fe-reducing bacteria, which consumed OC to promote the reduction of Fe(III). Accompanying this process, the redistribution of Cd and Fe mineral phases in the soil as well as the generation of secondary Fe(II) minerals facilitated Cd immobilization. Overall, S-nZVI/BC could effectively reduce the bioavailability of Cd, increase soil nutrients and enzyme activities, with less toxic impacts on the soil microorganisms.

Biofuel Ash Aging in Acidic Environment and Its Influence on Cd Immobilization

Biofuel ash (BFA), which is the ash generated by biomass combustion in a biomass power plant, can be prepared as a heavy metal immobilizer and have a good immobilization effect on Cd in the soil environment of southern China, but the long-term effects of BFA on Cd immobilization remained unclear. Therefore, research about BFA aging and its influence on Cd immobilization was conducted in the paper. BFA was naturally aged into BFA-Natural aging (BFA-N) in the soil environment of southern China, and to simulate BFA-N, BFA was also artificially acid aged into BFA-Acid aging (BFA-A). The result indicated that BFA-A could partially simulate BFA-N in physicochemical properties. The Cd adsorption capacity of BFA reduced after natural aging and the decrease was more obvious in BFA-A according to Qm in Langmuir equation and qe from the pseudo-second-order kinetic model. The adsorption processes of BFA before and after aging were mainly controlled by chemical action rather than physical transport. The immobilization of Cd included adsorption and precipitation, and adsorption was the dominant factor; the precipitation proportion was only 12.3%, 18.8%, and 1.7% of BFA, BFA-N, and BFA-A, respectively. Compared with BFA, both BFA-N and BFA-A showed Ca loss, and BFA-A was more obvious than BFA-N. Ca content level was consistent with Cd adsorption level among BFA, BFA-N, and BFA-A. It could be inferred that the main immobilization mechanism of Cd by BFA before and after aging was consistent and closely related to Ca. However, the adsorption mechanism of electrostatic interaction, ion exchange, and hydroxyl complexation changed to varying degrees in BFA-N and BFA-A.

Fractionation analysis and risk assessment of potential toxic elements in reservoir sediments in central China

The pollution of potential toxic elements (PTEs) in the environment is a persistent issue and draws public attention constantly. However, there is no study comprehensively assessing the PTE pollution of water supply reservoirs in central China. This study determined the total contents and fractions of seven PTEs in 10 water supply reservoirs of central China, and evaluated PTE pollution risks by adopting various models. The results indicated that PTE pollution in water supply reservoirs was lower comparing that in estuary or river sediments, and Mn (manganese) was the predominant PTE in central China reservoirs. Fractionation analysis revealed that for B1 fraction (exchangeable/acid-soluble fraction) of Mn, Zn (zinc) and B2 fraction (reducible fraction) of Pb (lead) was high, while the effective state portion of Cr (chromium) was small. The monomial potential ecological risk indices and Igeo values were low among most samples, indicating overall modest PTE pollution. However, the results of the individual contamination factor (ICF) suggested that Pb might lead to potential health risks to human beings.

Metal(loid) concentrations, bioaccessibility and stable lead isotopes in soils and vegetables from urban community gardens

Community gardens are "green oases" of recent cities with many benefits for human society. From a human health perspective, these benefits can be damaged by chemical contamination of soil and cultivated vegetables. Using geochemical approaches, this study characterised (i) total metal(loid) concentrations in soils and two commonly grown vegetables in urban community gardens (Bratislava, Slovakia), (ii) gastrointestinal bioaccessibility using a modified physiologically based extraction test (PBET), and (iii) stable lead (Pb) isotopes in order to identify sources of metal(loid)s, solubilisation in the human body and migration of Pb from soil to vegetables. While some soils could be considered contaminated when compared to the Slovak legislation for agricultural soil, the bioaccessibility of metal(loid)s did not exceed 20% in the intestinal phase, with the exception of cadmium (Cd). Tomatoes and lettuce contained low total and bioaccessible concentrations of metal(loid)s, being safe for people who consume their own grown vegetables. There were differences in Pb isotope composition among bulk soils, vegetables and bioaccessible Pb, with less radiogenic Pb being preferentially mobilised. Statistical methods considering the compositional nature of the geochemical data and the enrichment factor (EF) distinguished well metal(loid)s of natural origin (As, Co, Cr, Fe, Mn, Ni, V) from those with anthropogenic contributions. This research has shown the usefulness of integrating different methodologies to better understand the geochemistry of metal(loid)s in urban soils with their highly diversified sources.

Characteristics and Assessment of Soil Heavy Metals Pollution in the Xiaohe River Irrigation Area of the Loess Plateau, China

Heavy metals in soil are a potential threat to ecosystems and human well−being. Understanding the characteristics of soil heavy metal pollution and the prediction of ecological risk are crucial for regional eco−environment and agricultural development, especially for irrigation areas. In this study, the Xiaohe River Irrigation Area in the Loess Plateau was taken as the study area, and the concentration, as well as their accumulation degree and ecological risk and distribution of soil heavy metals, were explored based on the geo−accumulation index (Igeo) and Hakanson potential ecological risk index methods. The results showed that the concentrations of soil heavy metals were all lower than the second grade Environmental Quality Standard for Soils of China. However, the average concentrations of Cu, Hg, Cd, Pb, Zn, Ni and As were higher than the above−mentioned standard. Compared with the soil background values of Shanxi Province, eight heavy metals of all samples presented different accumulation degrees, with the highest accumulation degree in Hg, followed by Cd, and the values were 11.3 and 4.0 times more than the background value, respectively. Spatially, the distribution of soil heavy metals in the Xiaohe River irrigation area was quite different, generating diverse pollution patterns with significant regional differences and complex transportation routes. The content of soil heavy metals in the Xiaohe River irrigation area was highly affected by land use types. The pollution degree varied with the distance to an urban area, declining from the urban area to suburban farmland, and the outer suburban farmland. Among these heavy metals, Hg and Cd were the principal contamination elements, and transportation, service industry and agricultural activities were the main potential contamination sources. The potential ecological risk of soil heavy metal positioned as follows: Hg > Cd > Pb > Zn > Cu > As > Ni > Cr. As indicated by the Hakanson potential ecological risk index strategies, except for the Wangwu examining site, the other six sampling sites experienced extremely strong risks, and as a whole, the entire study region was in a condition of incredibly impressive perils. Consequently, these results suggest that improving soil environmental investigation and assessment, setting up soil heavy metal contamination prevention and control innovation framework and reinforcing contamination source control are effective approaches for soil heavy metal contamination anticipation and control in irrigated areas of the Loess Plateau.

Occurrence and dietary exposure risks of phthalate esters in food in the typical valley city Xi'an, Northwest China

Diet is an important exposure pathway of phthalate esters (PAEs) for humans. A total of 174 food samples covering 11 food groups were collected from Xi'an, a typical valley city in Northwest China, and analyzed to assess the occurrence and exposure risks for PAEs in the food. Twenty-two PAEs were detected. The sum of the 22 PAEs (∑22PAEs) varied between 0.0340 and 56.8 µg/g, with a mean of 3.94 µg/g. The major PAEs were di-iso-butyl phthalate (DiBP), di-n-butyl phthalate (DnBP), bis(2-ethylhexyl) phthalate (DEHP), di-iso-nonyl phthalate (DiNP), and di-iso-decyl phthalate (DiDP), which were associated mainly with the usage of plasticizers. Bio-availability of the PAEs in the combined gastro-intestinal fluid simulant of digestion was higher than that in the single gastric or intestinal fluid simulant. Bis(2-methoxyethyl) phthalate exhibited the highest bio-availability in each of the three simulants. Bio-availability of the PAEs was negatively correlated with the molecular weight and octanol-water partition coefficient of the PAEs and positively correlated with the solubility and vapor pressure of the PAEs. The estimated daily intake (EDI) of PAEs based on national and municipal food consumption data was lower than the reference dose (RfD) of the United States Environmental Protection Agency and the tolerable dairy intake (TDI) of European Food Safety Authority (EFSA), except for the EDI of DnBP and DiBP being higher than the TDI of EFSA. Grains and vegetables were the major sources of human dietary exposure to PAEs. The hazardous quotient for human dietary exposure to PAEs was less than the critical value of 1 and the cancer risk of butyl benzyl phthalate and DEHP was in the range of 10^-11-10^-6, suggesting relatively low health risks. The results indicated that human exposure to DnBP, DiBP, DEHP, DiNP, and DiDP in food is considerable and a health concern.

The Aging Process of Cadmium in Paddy Soils under Intermittent Irrigation with Acid Water: A Short-Term Simulation Experiment

Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.

The mechanistic understanding of potential bioaccessibility of toxic heavy metals in the indigenous zinc smelting slags with multidisciplinary characterization

Smelting slags is a well-known industrial solid waste, while there were limited studies on the key factors controlling the potential health risks caused by these smelting slags. In this work, the metal bioaccessibility in the size fractionated-zinc smelting slags was examined using various In vitro assays, in combination with multidisciplinary methods. The results indicated that the bioaccessible fractions of heavy metals showed a significant difference, but no statistical difference among different particle sizes of the zinc smelting slags. The bioaccessible metal fractions in the gastric (GP) and gastrointestinal (GIP) phases were 0 (Cr) - 91.39% (Cd)) and 0 (Cr) - 47.80% (Ni). Among the studied metals, Cd, Cu, Mn, Pb and Zn were the most bioaccessible to human. The Pearson correlation analysis showed that the carbonate bound phases of heavy metals were responsible for their bioaccessibility in GP and GIP. Moreover, the combined results of multidisciplinary characterization also further implied that the solubility behaviors of toxic elements in the smelting slags were dominated by soluble metal bearing- mineral phases and absorbable Fe, Mn and Al-rich minerals and metal bearing-precipitates during SBRC extractions. Therefore, these study results provide a insight into the potential controls of metal bioaccessibility in the zinc smelting slags, which was of great significance from the aspects of their resource recycling and risk management.

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.

Coupling in vitro assays with sequential extraction to investigate cadmium bioaccessibility in contaminated soils

To understand how Cd in different fractions contributes to Cd bioaccessibility by in vitro assays, Cd bioaccessibility in 12 contaminated soils was determined by four assays (UBM, SBRC, IVG, and PBET) and correlated with different Cd fractions based on a sequential extraction scheme. The Cd bioaccessibility in the gastric phase (GP) was high (35-107%, averaging at 77%), implicating high risk to human health, while it decreased to 19-88% averaging at 47% in the intestinal phased (IP). From the GP to IP, the reduction of extractable Cd (0.45-48 mg kg^-1) and Fe (118-3884 mg kg^-1) showed significant correlation (R = 0.54-0.74) via UBM, SBRC, and IVG, suggesting co-precipitation with Fe and/or sorption onto Fe oxides maybe responsible for decrease in Cd bioaccessibility. Although Cd bioaccessibility varied among assays, their results show some consistency based on their correlation in the GP (R = 0.56-0.90) and IP (0.34-0.73, excluding UBM-IP and PBET-IP). Sequential extraction data show that Cd was primarily associated with the exchangeable fraction (E1; 7.05-72.9%, averaging 39.4%). The carbonate (C2; 6.86-44.8%, 21.9%) and Fe/Mn oxides fraction (F3; 12.5-53.6%, 28.2%) were similar, while organic (O4; 0.62-25.0%, 7.91%) and residual fraction (R5; 0.22-8.54%, 2.62%) were the lowest. Significant correlation (R = 0.59-0.88) between the first two fractions (E1+C2) and bioaccessible Cd suggest they were the main sources of bioaccessible Cd in those contaminated soils.

Effect of a low-cost and highly efficient passivator synthesized by alkali-fused fly ash and swine manure on the leachability of heavy metals in a multi-metal contaminated soil

Soil pollution, caused by heavy metals, is an environmental problem that requires an urgent solution in China. Chemical passivation is a technology that uses various passivators to reduce the availability of heavy metals in soil and realize the remediation of contaminated soil. In this study, we examined the effects of fly ash (FA), alkali-fused fly ash (AFFA), swine manure biochar (SB), and modifying biochar (MB) on the leachability of Cu, Zn, Pb, and Cd via soil culture experiments. The results showed that the addition of AFFA, SB, and MB significantly reduced the extractable contents of Cu, Pb, and Cd in the soil. AFFA and MB had the best passivation effect, followed by SB and FA. The passivation effect on Pb was the best, followed by that on Cu and Cd. AFFA modification significantly improved the passivation effect of MB on Cu, Pb, and Cd in composite contaminated soil. With the addition of 3% MB, the Pb, Cu, and Cd extracted by TCLP decreased by 95.7, 74.1, and 59.1%, respectively. Correlation analysis, Fourier transform infrared spectrometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy showed that the passivation mechanism is mainly due to an increase in the soil pH, silicate content, and cohesiveness. The soil culture experiments in this study proved that MB is a low-cost and highly efficient organic-inorganic composite passivator for multi-metal contaminated soils.

Effects of aging on surface properties and endogenous copper and zinc leachability of swine manure biochar and its composite with alkali-fused fly ash

Biochar aging is a key factor leading to the decline of biochar stability and the release of endogenous pollutants. This study investigated the effects of five artificial and simulated aging processes on the surface properties and endogenous copper (Cu) and zinc (Zn) leachability of swine manure biochar and its composite with alkali-fused fly ash. Aging obviously reduced carbon (C) content on the surface of swine manure biochar and increased oxygen (O) content. Among all the aging treatments, high-temperature aging had the greatest effect on C content. Following the aging treatments, the C-C bond contents on the surfaces of swine manure biochar decreased significantly, whereas the C-O bonds increased significantly; however, there were less changes in the amounts of C-C and C-O bonds on the surfaces of modified biochar than on swine manure biochar. Aging significantly enhanced the leaching toxicity of Cu and Zn, and Zn availability and bioaccessibility in swine manure biochar and modified biochar. However, it minimized Cu availability and bioaccessibility, especially under high-temperature aging. Greater amounts of Zn than Cu were extracted from swine manure biochar and modified biochar. However, under all the aging treatments, the leaching toxicity, availability, and bioaccessibility of Cu and Zn in modified biochar were significantly lower than in swine manure biochar. This implies that modified biochar application poses lower environmental risks than swine manure biochar.

In vitro bioaccessibility, phase partitioning, and health risk of potentially toxic elements in dust of an iron mining and industrial complex

Dust emitted from mining, ore processing, and tailing dumps have direct effects on miners who work close to these operations. The Gol-E-Gohar (GEG) mining and industrial company is one of the most important iron concentrate producers in the Middle East. The objective of the present study was to estimate the distribution, fractionation, and oral bioaccessibility of potentially toxic elements (PTEs) in dust generated by the GEG mining and industrial company. Total PTE content including Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, V, and Zn was quantified for suspended particulate matter (PM) in PM_2.5, PM₁₀, and total suspended particulate matter (TSP). As, Cd, Co, Cu, Fe, Ni, and Pb were quantified in fallout dust samples for oral bioaccessibility using in vitro Unified BARGE (UBM) Method and modified BCR fractionation analysis. Enrichment factors (EF) were calculated for the studied elements in PM; Cu, Fe, and As were found to be extremely enriched. Oral bioaccessibility of selected PTEs in fallout dust samples ranged from 0.35% to 41.55% and 0.06-37.58% in the gastric and intestinal phases, respectively. Regression modeling revealed that the bioaccessibilities of the PTEs could mostly be explained by total concentrations in dust particles. Average daily intake (ADI) calculations revealed that the intake of PTEs did not exceed the tolerable daily intake (TDI) values and as such was not considered a significant risk to workers. Additionally, the hazard quotients (HQ) and carcinogenic risk (CR) values were lower than the acceptable level. This study can provide further risk assessment and management of PTE pollution in occupational environments.

Geochemical phases of soil and the bioaccessibility of some elements in soils and vegetables from boron mines

The bioaccessibility of some elements (As, B, Cd, Cu, Fe, Mn, Ni and Zn) in soils and vegetables was determined using the physiologically based extraction test. An investigation of the geochemical phases of soils through sequential extraction methods followed by ICP-MS detection was also undertaken. Samples were collected from Iskele, Begendikler and Yolbasi villages in the Bigadic region and Yildiz village in the Susurluk region of Balikesir province, Turkey. All of these villages are close to boron mines. Principal component analysis and correlation analysis demonstrated the interrelationship between the bioaccessibility values of these elements in the gastric and intestinal extracts of soils as well as the plant samples grown in those soils and the elements' concentrations in the different soil fractions. From the bioaccessible concentrations of the elements in the intestinal phases, it was shown that the amounts of As, B, Cu, Mn and Ni in some plant samples were higher than the recommended and tolerable values for human consumption. The bioaccessibilty of these elements in the soils and plants were statistically related with the concentrations of these elements in the labile phases of the soil. The methodology adopted here would be applicable to determining interactions between elements and soil fractions and the interrelationships between bioaccessibility data and soil fractions for any soil samples.

Concentrations, Speciation, and Bioavailability of Heavy Metals in Street Dust as well as Relationships with Physiochemcal Properties: A Case Study of Jinan City in East China

A total of 77 street dust samples were collected from Jinan City in East China and were analyzed for the concentrations, speciation, bioavailability, and influencing factors of ten heavy metals. The results showed that the average concentrations of Ba, Co, Cr, Cu, Cd, Mn, Ni, Pb, Zn, and V in the street dust were 642.77, 8.24, 114.09, 87.71, 1.08, 517.04, 30.29, 80.32, 497.84, and 51.76 mg/kg, and the concentrations of Ba, Cr, Cu, Cd, Ni, Pb, and Zn exceeded the local soil element background values. In the street dust, Ba, Co, Cr, Mn, Ni, and V were mainly in the residual; Cu and Pb were controlled by the oxidizable; Cd mainly existed in the acid extractable; and Zn was dominated by the reducible. According to the ratios of the acid extractable to the sum of four forms, Cd (39.85%) presented a high environmental risk; Mn and Zn (24.29% and 27.78%) exhibited a medium risk; and V, Cu, Pb, Ba, Co, Ni, and Cr had no environmental risk. The order of mobility or potential risk of heavy metals was Cd ( 85.8%) > Zn (77.1%) > Cu (64.3%) > Pb (62.0%) > Mn (51.7%) > Ba ( 38.9%) > Co (31.2%) > Ni (30.1%) > V (25.8%) > Cr (23.1%), suggesting that Cd, Zn, Cu, Pb, and Mn presented relatively high movability and risk. The bioavailability order of heavy metals was Cd (82.7%) > Zn (63.6%) > Mn (40.4%) > Ni (20.4%) > Pb (11.7%) > Cu (11.1%) > V (7.8%) > Cr (3.7%) in the gastric phase and Cu (24.6%) > Cd (19.9%) > Mn (16.2%) > Ni (6.6%) > Pb (5.7%) > Zn (4.4%) > Cr (3.0%) > V (2.3%) in intestinal phase, implying that Cd, Zn, Mn, and Cu were highly bioavailable in the gastrointestinal environment, which coincided with the risk of speciation. The speciation of heavy metals in street dust had certain correlations with their bioavailability. The physiochemical properties of street dust had significant effects on the concentrations, speciation, and bioavailability of heavy metals in street dust. The simple, fast, and nondestructive magnetic measurements could be used as indicators of the concentrations, speciation, and bioavailability of heavy metals in street dust.

Comparison of bioaccessibility methods in spiked and field Hg-contaminated soils

Estimating bioaccessible content of mercury in soils is essential in evaluating risks that contaminated soils pose. In this study, soil samples spiked with HgCl₂ through adsorption were used to test the effects of liming, soil organic matter, soil depth, and Hg concentration on the following bioaccessibility tests: dilute nitric acid at room temperature, dilute nitric acid at body temperature, Simplified Bioaccessibility Extraction Test (SBET) method, and gastric phase of the In vitro Gastrointestinal (IVG) protocol. Soil and sediment samples from Descoberto, Minas Gerais (Brazil), a city with a well-known record of Hg contamination from artisanal mining, were subjected to these bioaccessibility tests for the first time, and the different methods of estimating bioaccessible content were compared. Bioaccessible fractions in spiked samples ranged from 10% to 60%, and this high bioaccessibility was due to the highly soluble species of Hg and the short time under adsorption. In general, clay and organic matter decreased bioaccessible content. Although the soil in Descoberto is undoubtedly polluted, mercury bioaccessibility in that area is low. In general, dilute nitric acid estimated higher bioaccessible content in soil samples, whereas the SBET method estimated higher bioaccessible content in sediment samples. In multivariate analysis, two groups of bioaccessibility tests arise: one with the two nitric acid tests, and the other with SBET and the gastric phase of the IVG protocol. The addition of pepsin and glycine in the last two tests suggests a more reliable test for assessing mercury bioaccessibility.

Potentially toxic metals and the risk to children's health in a coal mining city: An investigation of soil and dust levels, bioaccessibility and blood lead levels

Coal is a primary energy source in the world. Potentially toxic metals (PTMs) emission from coal mining and combustion are posing a serious public health concern. In order to quantify and evaluate the effect of PTMs on children's health, the concentrations of 12 PTMs (As, Co, Cr, Cu, Mn, Ni, Pb, Sr, Zn, Ca, Fe, and Mg) bound in urban soil and street dust are determined and blood lead levels of these PTMs in 229 children (0-6 years old) are collected from the coal mining city of Yulin, China. In vitro pulmonary bioaccessibilities of PTMs are evaluated by artificial lysosomal fluid and Gamble's solution, and gastrointestinal bioaccessibilities by the unified BAGRE method (UBM); correlations between chemical speciation of PTMs and their bioaccessibility are examined, and children's (0-6 years old) health risks are systematically studied. Similar distribution levels of PTMs are found in soils and dusts, with the most polluted metals being Co, Sr, Ca and Pb. All PTMs (except Cr, Fe) are from the considerable artificial lysosomal fluid extraction both in soil and dust, while Ca and Co are favorably extracted in gastro and intestinal phases than others. Significant correlations are observed between the bioaccessibilities (lung and gastrointestinal) and Fe/Mn hydroxide-bound and carbonate-bound phases, which are key factors influencing and determining PTMs' bioaccessibility. Blood lead levels for children (0-6 years old) are 27.47 (21.65, 33.30) for 0-1 year olds, 32.29 (26.39, 38.19) for 1-2 year olds, 36.99 (28.16, 45.81) for 2-3 year olds, 30.79 (22.56, 39.01) for 3-4 year olds, 27.12 (17.31, 36.93) for 4-5 year olds, 34.59 (24.22, 44.97) for 5-6 year olds and 37.83 (24.15, 51.51) μg/L for 6-7 year olds, respectively, with 3.93%, 3.49%, 4.80%, 2.62%, 1.31%, 1.75% and 1.31% exceeding 50 μg/L, respectively. This indicates that the blood lead levels elevate for 1-2 year and 5-6 year old groups, which should be paid more attention. Although the non-carcinogenic and carcinogenic risks of most PTMs are under the acceptable level, the higher carcinogenic risk of Ni and non-carcinogenic risk of Pb should be monitored continuously. We suggest that further actions will be taken to reduce PTMs exposure for children through sustainable clean and ecological energy technology for coal mining, especially for those infants of 1-2 years old.

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

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

Effects of soil particle size on metal bioaccessibility and health risk assessment

Oral ingestion is the main exposure pathway through which humans ingest trace metals in the soil, particularly for children. Metals in different soil particle size fractions may vary in terms of concentration and properties. Urban school/kindergarten soil samples were collected from three cities: Lanzhou in northwest China, Wuhan in central China, and Shenzhen in southeast China. Soil samples were classified according to particle size (<63 μm, 63-150 μm, 150-250 μm, and 250-2000 μm) to estimate the effects of soil particle size on the total content and bioaccessibility of metals (Cd, Cr, Cu, Ni, Pb, and Zn). Based on the results, we assessed whether the standard size <150 μm (containing < 63 μm and 63-150 μm), recommended by the Technical Review Workgroup (TRW) of the Environmental Protection Agency (EPA), and <250 μm (containing < 63 μm, 63-150 μm, and 150-250) recommended by the Bioaccessibility Research Group of Europe (BARGE), are suitable where the largest proportion adhering to hands is the finest soil (<63 μm). The results showed that different metals exhibited different relationships between soil particle size and content and between soil particle size and bioaccessibility. Pb and Zn generally exhibited the greatest bioaccessibility in the coarsest particle sizes (250-2000 μm); whereas the highest Ni bioaccessibility occurred in the finest sizes (<63 μm); the bioaccessibility of other metals did not exhibit any obvious relationships with particle size. When assessing health risks using bioaccessible metal content in the recommended soil particle size ranges (<150 μm and <250 μm) and in finer particles (<63 μm), the results for noncarcinogenic risks to children exhibited no obvious difference, while the actual carcinogenic risks may be underestimated with the use of soil particle size ranges < 150 μm and <250 μm. Therefore, when choosing an optimal particle size fraction to evaluate the health risk of oral soil ingestion, we recommend the use of the bioaccessible metal content in <63 μm soil fraction.

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.

Health risk apportionment of arsenic from multiple exposure pathways in Paracatu, a gold mining town in Brazil

This study assessed various exposure pathways of arsenic and their health risk apportionment to the residents of Paracatu, a gold mining town in Brazil. We measured arsenic concentrations in 50 groundwater and surface town water samples from nearby residences, 38 surface soil dust from residential/commercial dwellings and roadside of Paracatu, and 600 airborne dust samples including PM₁₀ and total suspended particulates (TSP), in additional to a previous reported food survey containing 90 samples from 15 major food categories. For the surface soil dust, bioaccessibility of arsenic as a surrogate of bioavailability was determined using an in vitro physiologically based extraction test (PBET). Rice and bean were found to contain the highest levels of arsenic in which the arsenic speciation was measured whereas the percentages of inorganic arsenic of other food items were taken from the literature for the risk apportionment calculation. The results show that the contribution of inhaled arsenic is ≤3% of the total daily intake, even assuming 100% BAC. The average bioaccessibility of arsenic in the surface soil dust was 3.4 ± 2.0% (n = 17) with a bioaccessible concentration of 4.1 ± 3.7 mg/kg. Food was the main contributor of the daily total intake of arsenic with rice and beans being the most significant ones. The total arsenic intake (ingestion + inhalation) is about 10% of the JECFA BMDL_0.5 of 3 μg/kg b.w. per day, and the combined risk based on the cancer slope calculation is similar to the arsenic intake from the consumption of 2 L of water containing 10 μg/L of arsenic, a maximum concentration recommended by WHO. The holistic approach by addressing multiple pathways of exposure is considered a useful tool for health risk assessment throughout the life of mine including mine closure, and can be applied at legacy sites.

Chemical fractionation of heavy metals in fine particulate matter and their health risk assessment through inhalation exposure pathway

Samples of PM_2.5 were collected from an urban area close to a national highway in Agra, India and sequentially extracted into four different fractions: water soluble (F1), reducible (F2), oxidizable (F3) and residual fraction (F4) for chemical fractionation of arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), nickel (Ni) and lead (Pb). The metals were analyzed by inductively coupled plasma optical emission spectroscopy in each fraction. The average mass concentration of PM_2.5 was 93 ± 24 μg m^-3.The total concentrations of Cr, Pb, Ni, Co, As and Cd in fine particle were 192 ± 54, 128 ± 25, 108 ± 34, 36 ± 6, 35 ± 5 and 8 ± 2 ng m^-3, respectively. Results indicated that Cd and Co had the most bioavailability indexes. Risk Assessment Code and contamination factors were calculated to assess the environmental risk. The present study evaluated the potential Pb hazard to young children using the Integrated Exposure Uptake Biokinetic Model. From the model, the probability density of PbB (blood lead level) revealed that at the prevailing atmospheric concentration, 0.302 children are expected to have PbB concentrations exceeding 10 μg dL^-1 and an estimated IQ (intelligence quotient) loss of 1.8 points. The predicted blood Pb levels belong to Group 3 (PbB < 5 μg dL^-1). Based on the bioavailable fractions, carcinogenic and non-carcinogenic risks via inhalation exposure were assessed for infants, toddlers, children, males and females. The hazard index for potential toxic metals was 2.50, which was higher than the safe limit (1). However, the combined carcinogenic risk for infants, toddlers, children, males and females was marginally higher than the precautionary criterion (10^-6).

Bioaccessibility of Drug Residues on Common Police Station Work Surfaces

The fraction of any surface-adsorbed contaminant available for absorption is considered the bioaccessible fraction. Applied previously to contaminants such as pesticides and heavy metals on surfaces such as soil, food and cosmetics, the term may also be used to describe the fraction of drug residue bound to work surfaces which may be mobilized via contact transfer with human skin. Police station work surfaces have been shown to commonly contain low levels of drug residues as thin films; however, no information is available on how readily these residues may be transferred to human skin during direct or glancing contact. A bioaccessibility study was undertaken in which jojoba oil and artificial sebum were used to mimic human sebum to identify how readily a mix of six licit and illicit drugs were transferred from three commonly used police station work surfaces. Transfer from surfaces was slightly greater for jojoba oil than sebum when using a direct pressure contact or a wiping motion. Generally, less than 5% of applied residues were recovered via direct contact, and up to 10% when a wiping motion was used to simulate a glancing contact. While swabbing of work surfaces with methanol provides a suitable environmental audit of drug residues present, it does not represent the bioaccessible fraction of residues available for contact transfer, and hence, absorption via skin or unintentional ingestion. The current study indicates that the ability of sebum to mobilize drug residues from thin films on work surfaces via casual contact is limited, and sebum may potentially assist in the preservation of residues on pitted work surfaces and on skin.

Bioavailability/speciation of arsenic in atmospheric PM2.5 and their seasonal variation: A case study in Baoding city, China

Arsenic (As) can be easily enriched in atmospheric particulate matters (PMs), especially in fine particulate matters (PM_2.5). In this study, thirty two PM_2.5 samples were collected in four seasons in Baoding, China, where the haze pollution was very serious in recent years. The total contents, species and bioavailability of arsenic in PM_2.5 samples were investigated. Species of arsenic in the PM_2.5 samples were discriminated as five fractions using a sequential extraction method: non-specifically sorbed fraction (F1), specifically-sorbed fraction (F2), amorphous and poorly-crystalline hydrous oxides of Fe and Al fraction (F3), well-crystallized hydrous oxides of Fe and Al fraction (F4) and residual fraction (F5). Bioavailabilities of arsenic in the PM_2.5 samples were evaluated by in vitro tests using both solubility bioavailability research consortium (SBRC) and Gamble's solution extraction methods. The total volume concentrations of As in PM_2.5 were significantly higher in winter than the other seasons. However, the highest mass concentration of As was found in spring. Scanning electron microscopy (SEM) characterization indicated that the physical morphology of the particles varied in different seasons. Significant differences of fraction distribution and BFs were found between different seasons. Arsenic in PM_2.5 samples mainly presented in F1 with high bioavailability factor (BF), especially for the samples in summer. In vitro tests indicated that arsenic in PM_2.5 could be dissolved more easily in gastric phase rather than intestinal and lung phases. There was a significant correlation between species and in vitro tests. Interestingly, a synergy effect was found between F2 and F3. Health risk assessment indicated that arsenic in PM_2.5via inhalation exposure for both children and adults could cause adverse effects. Principal component analysis suggested that the arsenic in PM_2.5 was from the similar sources between summer and autumn, winter and spring, respectively.