High Lead Bioavailability of Indoor Dust Contaminated with Paint Lead Species

Efficient Pb(II) removal from contaminated soils by recyclable, robust lignosulfonate/polyacrylamide double-network hydrogels embedded with Fe2O3 via one-pot synthesis

Soil heavy metal removal strategies are increasingly valued for effectively reducing contamination and preventing secondary pollution. In this work, a double network hydrogel (Fe2O3@LH), consisting of lignosulfonate (LS) and polyacrylamide with embedded Fe2O3 nanoparticles, was synthesized successfully via a one-pot method and subsequently applied to adsorb lead (Pb) from contaminated soil. Incorporating Fe2O3 into the hydrogel enhances the adsorption capacity of Fe2O3@LH for Pb(II). The Fe2O3@LH hydrogel demonstrates a maximum Pb(II) adsorption capacity of 143.11 mg g-1, with Pb(II) removal mechanisms involving electrostatic adsorption, cation exchange, precipitation reactions, and the formation of coordination complexes, achieving a 22.3 % maximum removal efficiency in soil cultivation experiments. Additionally, the application of Fe2O3@LH markedly reduces the concentrations of cadmium (Cd) and arsenic (As) in the soil, meanwhile enhances the levels of total nitrogen (TN), soil organic matter (SOM), and cation exchange capacity (CEC) by 23.1 %, 10.6 %, and 16.9 %, respectively. Following 90 days of continuous application in the soil, the recovery rate of Fe2O3@LH remains above 75 %. The toxicity assay using zebrafish larvae indicates that Fe2O3@LH demonstrates good biosafety. This study demonstrates the considerable potential of Fe2O3@LH hydrogel for practical application in reducing Pb(II) levels in contaminated soil.

Gas and particle emissions from rifle and pistol firing

Emissions were sampled from firing an M4 carbine rifle and a M9 (military issue of Beretta 75 FS 9 mm pistol) to develop sampling methods and assess potential exposures and range contamination issues. Breech and muzzle emissions were sampled from the rifle when firing M855A1 ammunition (lead (Pb)-free slugs) in single- and triple-shot burst mode and from single pistol shots when firing 9 mm XM1152 ammunition (not Pb-free). Emissions were sampled for carbon monoxide (CO), carbon dioxide (CO2), methane, hydrogen cyanide, ammonia, particulate matter by size, polycylic aromatic hydrocarbons, and volatile organics. Analyses on the particles included elemental composition, size distribution, carbon composition (black, total, organic, and elemental carbon), and particle composition and morphology. Emission concentrations from both the rifle and pistol were characterized by CO/CO2 ratios between, approximately, 1/1 and 2/1, respectfully, indicating incomplete carbon oxidation. The initial particle size distribution was dominated in number by particles smaller than 40 nm but the high particle concentrations led to rapid agglomeration. The abundance of CO and metals of inhalable particle size are noteworthy and indicate that further assessment of exposure would determine potential inhalation health hazards, particularly in indoor firing ranges.

Impacts of phosphorus amendments on legacy soil contamination from lead-based paint on a California, USA university campus

Lead (Pb) is one of the most common heavy metal urban soil contaminants with well-known toxicity to humans. This incubation study (2-159 d) compared the ability of bone meal (BM), potassium hydrogen phosphate (KP), and triple superphosphate (TSP), at phosphorus:lead (P:Pb) molar ratios of 7.5:1, 15:1, and 22.5:1, to reduce bioaccessible Pb in soil contaminated by Pb-based paint relative to control soil to which no P amendment was added. Soil pH and Mehlich 3 bioaccessible Pb and P were measured as a function of incubation time and amount and type of P amendment. XAS assessed Pb speciation after 30 and 159 d of incubation. The greatest reductions in bioaccessible Pb at 159 d were measured for TSP at the 7.5:1 and 15:1 P:Pb molar ratios. The 7.5:1 KP treatment was the only other treatment with significant reductions in bioaccessible Pb compared to the control soil. It is unclear why greater reductions of bioaccessible Pb occurred with lower P additions, but it strongly suggests that the amount of P added was not a controlling factor in reducing bioaccessible Pb. This was further supported because Pb-phosphates were not detected in any samples using XAS. The most notable difference in the effect of TSP versus other amendments was the reduction in pH. However, the relationship between increasing TSP additions, resulting in decreasing pH and decreasing Pb bioaccessibility was not consistent. The 22.5:1 P:Pb TSP treatment had the lowest pH but did not significantly reduce bioaccessible Pb compared to the control soil. The 7.5:1 and 15:1 P:Pb TSP treatments significantly reduced bioaccessible Pb relative to the control and had significantly higher pH than the 22.5:1 P:Pb treatment. Clearly, impacts of P additions and soil pH on Pb bioaccessibility require further investigation to decipher mechanisms governing Pb speciation in Pb-based paint contaminated soils.

United States house dust Pb concentrations are influenced by soil, paint, and house age: insights from a national survey

BACKGROUND

Lead (Pb) in house dust contributes significantly to blood lead levels (BLLs) in children which may result in dire health consequences. Assessment of house dust Pb in the United States, relationships with Pb in soil and paint, and residential factors influencing Pb concentrations are essential to probing drivers of house dust Pb exposure.

OBJECTIVE

Pb concentrations in vacuum-collected house dust are characterized across 346 homes participating in the American Health Homes Survey II (AHHS II), a US survey (2018-2019) evaluating residential Pb hazards. Connections between house dust Pb and soil Pb, paint Pb, and other residential factors are evaluated, and dust Pb concentration data are compared to paired loading data to understand Pb hazard standard implications.

RESULTS

Mean and median vacuum dust Pb concentrations were 124 µg Pb g-1 and 34 µg Pb g-1, respectively. Vacuum-collected dust concentrations and dust wipe Pb loading rates were significantly correlated within homes (α < 0.001; r ≥ 0.4). At least one wipe sample exceeded current house dust Pb loading hazard standards (10 µg ft-2 or 100 µg Pb ft-2 for floors and windowsills, respectively) in 75 of 346 homes (22%). House dust Pb concentrations were correlated with soil Pb (r = 0.64) and Pb paint (r = 0.57). Soil Pb and paint Pb were also correlated (r = 0.6).

IMPACT

The AHHS II provides a window into the current state of Pb in and around residences. We evaluated the relationship between house dust Pb concentrations and two common residential Pb sources: soil and Pb-based paint. Here, we identify relationships between Pb concentrations from vacuum-collected dust and paired Pb wipe loading data, enabling dust Pb concentrations to be evaluated in the context of hazard standards. This relationship, along with direct ties to Pb in soil and interior/exterior paint, provides a comprehensive assessment of dust Pb for US homes, crucial for formulating effective strategies to mitigate Pb exposure risks in households.

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.

Characterization and childhood exposure assessment of toxic heavy metals in household dust under true living conditions from 10 China cities

Health hazards caused by metal exposure in household dust are concerning environmental health problems. Exposure to toxic metals in household dust imposes unclear but solid health risks, especially for children. In this multicenter cross-sectional study, a total of 250 household dust samples were collected from ten stratified cities in China (Panjin, Shijiazhuang, Qingdao, Lanzhou, Luoyang, Ningbo, Xi'an, Wuxi, Mianyang, Shenzhen) between April 2018 and March 2019. Questionnaire was conducted to gather information on individuals' living environment and health status in real-life situations. Multivariate logistic regression and principal component analysis were conducted to identify risk factors and determine the sources of metals in household dust. The median concentration of five metals in household dust from 10 cities ranged from 0.03 to 73.18 μg/g. Among the five heavy metals, only chromium in household dust of Mianyang was observed significantly both higher in the cold season and from the downwind households. Mercury, cadmium, and chromium were higher in the third-tier cities, with levels of 0.08, 0.30 and 97.28 μg/g, respectively. There were two sources with a contribution rate of 38.3 % and 25.8 %, respectively. Potential risk factors for increased metal concentration include long residence time, close to the motorway, decoration within five years, and purchase of new furniture within one year. Under both moderate and high exposure scenarios, chromium showed the highest level of exposure with 6.77 × 10-4 and 2.28 × 10-3 mg·kg-1·d-1, and arsenic imposed the highest lifetime carcinogenic risk at 1.67 × 10-4 and 3.17 × 10-4, respectively. The finding highlighted the priority to minimize childhood exposure of arsenic from household dust.

In vitro modeling of the post-ingestion mobilization and bioaccessibility of pesticides sorbed to soil and house dust

Soils and dusts can act as sinks for semivolatile lipophilic organic compounds and children ingest relatively large amounts of both soils and dusts. Following intake, sorbed chemicals may desorb (mobilize) and become available for intestinal absorption (bioaccessible). When chemicals are not degraded in the digestive tract, mobilization can approximate bioaccessibility. Alternatively, when gastrointestinal degradation of mobilized chemicals does occur, it can be useful to separate mobilization from bioaccessibility. In this study we used synthetic digestive fluids in a sequential, three-compartment (saliva, gastric, and intestinal) in vitro assay to construct mobilization and bioaccessibility models for 16 pesticides (log Kow 2.5-6.8) sorbed to 32 characterized soils and house dusts. To address the potential loss of mobilized pesticides due to absorption, the assays were repeated using a solid phase sorbent (tenax) added to the digestive fluid immediately after addition of the intestinal fluid components. We found that pesticide mobilization was predicted by pesticide log Kow and the carbon content of the soils and dusts. Pesticide loss measurably reduced the bioaccessibility of most pesticides, and bioaccessibility was largely predicted by log Kow and pesticide loss rate constants. Introduction of the sink increased mobilization by x̄ = 4 ± 6% (soil) and x̄ = 9 ± 7% (dust) while bioaccessibility increases were x̄ = 41 ± 21% (soil) and x̄ = 24 ± 12% (dust). The physicochemical properties of the soils, dusts, and pesticides used in this study successfully predicted the in vitro mobilization and bioaccessibility of the pesticides. This suggests that modeling of pesticide mobilization and bioaccessibility could reduce uncertainty in exposure and risk assessments.

In vitro modeling of the post-ingestion bioaccessibility of per- and polyfluoroalkyl substances sorbed to soil and house dust

Per- and polyfluoroalkyl substances (PFAS) are regularly found in soils and dusts, both of which can be consumed by children at relatively high amounts. However, there is little data available to model the bioaccessibility of PFAS in soils and dusts when consumed or to describe how the physiochemical properties of PFAS and soils/dusts might affect bioaccessibility of these chemicals. Because bioaccessibility is an important consideration in estimating absorbed dose for exposure and risk assessments, in the current study, in vitro assays were used to determine bioaccessibility of 14 PFAS in 33 sets of soils and dusts. Bioaccessibility assays were conducted with and without a sink, which was used to account for the removal of PFAS due to their movement across the human intestine. Multiple linear regression with backward elimination showed that a segmented model using PFAS chain length, number of branches, and percent total organic carbon explained 78.0%-88.9% of the variability in PFAS bioaccessibility. In general, PFAS had significantly greater bioaccessibility in soils relative to dusts and the addition of a sink increased bioaccessibility in the test system by as much as 10.8% for soils and 20.3% for dusts. The results from this study indicate that PFAS bioaccessibility in soils and dusts can be predicted using a limited set of physical chemical characteristics and could be used to inform risk assessment models.

Potassium jarosite seeding of soils decreases lead and arsenic bioaccessibility: A path toward concomitant remediation

Soils are common sources of metal(loid) contaminant exposure globally. Lead (Pb) and arsenic (As) are of paramount concern due to detrimental neurological and carcinogenic health effects, respectively. Pb and/or As contaminated soils require remediation, typically leading to excavation, a costly and environmentally damaging practice of removing soil to a central location (e.g., hazardous landfill) that may not be a viable option in low-income countries. Chemical remediation techniques may allow for in situ conversion of soil contaminants to phases that are not easily mobilized upon ingestion; however, effective chemical remediation options are limited. Here, we have successfully tested a soil remediation technology using potted soils that relies on converting soil Pb and As into jarosite-group minerals, such as plumbojarosite (PLJ) and beudantite, possessing exceptionally low bioaccessibility [i.e., solubility at gastric pH conditions (pH 1.5 to 3)]. Across all experiments conducted, all new treatment methods successfully promoted PLJ and/or beudantite conversion, resulting in a proportional decrease in Pb and As bioaccessibility. Increasing temperature resulted in increased conversion to jarosite-group minerals, but addition of potassium (K) jarosite was most critical to Pb and As bioaccessibility decreases. Our methods of K-jarosite treatment yielded <10% Pb and As bioaccessibility compared to unamended soil values of approximately 70% and 60%, respectively. The proposed treatment is a rare dual remediation option that effectively treats soil Pb and As such that potential exposure is considerably reduced. Research presented here lays the foundation for ongoing field application.

Cadmium and lead bioavailability to poultry fed with contaminated soil-spiked feed

Geophagy is common for free-range chickens, however, the relative bioavailability (RBA) of heavy metals in contaminated soils consumed by chickens has not fully investigated. In this work, chickens were fed diets increasingly spiked with a contaminated soil (Cd = 105, Pb = 4840 mg kg^-1; 3, 5, 10, 20 and 30 % of overall feed by weight), or Cd/Pb reagent spikes (from CdCl₂ or Pb(Ac)₂), for 23 d. After the study period, chicken liver, kidney, femur and gizzard samples were analyzed for Cd and Pb concentrations, and organ/tissue metal concentrations were used to calculate Cd and Pb RBA. Linear dose response curves (DRCs) were established for both Cd/Pb reagents-spiked and soil-spiked treatments. Femur Cd concentrations of soil-spiked treatments were two times of Cd-spiked treatments with similar feed Cd levels, while feed spiked with Cd or Pb also resulted in elevated Pb or Cd concentrations in some organ/tissues. Metal RBA was calculated using three different methods. Most Cd and Pb RBA values were in the range 50-70 %, with the chicken gizzard as a potential endpoint for bioaccessible Cd and Pb. Cadmium and Pb bioavailability values can help with more precise estimation of Cd and Pb accumulation in chicken following heavy metal-contaminated soil ingestion, with overall results helping to protect human health.

Domestic dogs as sentinels of children lead exposure: Multi-pathway identification and source apportionment based on isotope technique

Environmental lead exposure poses risks to children' health, thus exposure sources and pathways identification remain important concern and research scope. Due to sharing the same environment, domestic animals, especially dogs, have been used as useful sentinels to identify human lead exposure. However, more evidence is needed on whether domestic dogs could be used to identify the lead exposure pathways and sources of children. Thus, this study investigated the dietary habits, behaviors, and household environment of children and dogs in a typical coal-fired area in China. The lead levels and lead isotope ratios (Acronym: LIRs, expressed as ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb) in dogs' and children's blood, as well as in environmental media (food, PM_2.5, indoor/outdoor dust, drinking water and soil) were measured to explore the predominant lead pollution sources and exposure pathways of children. The results showed that the LIRs of children's blood (²⁰⁸Pb/²⁰⁶Pb = 2.0703 ± 0.0076, ²⁰⁷Pb/²⁰⁶Pb = 0.8501 ± 0.0052) were similar to those of dogs' blood (²⁰⁸Pb/²⁰⁶Pb = 2.0696 ± 0.0085, ²⁰⁷Pb/²⁰⁶Pb = 0.8499 ± 0.0052), as well as similar to the LIRs of environmental media, i.e. children's food (²⁰⁸Pb/²⁰⁶Pb = 2.0731 ± 0.0057, ²⁰⁷Pb/²⁰⁶Pb = 0.8491 ± 0.0036) and coal (²⁰⁸Pb/²⁰⁶Pb = 2.0683 ± 0.017, ²⁰⁷Pb/²⁰⁶Pb = 0.8515 ± 0.01). Children and dogs had similar lead exposure pathways, but the contributions of each exposure pathway were different, i.e., 83.1% vs. 76.9% for children and dogs via food ingestion, 1.4% vs. 5.6% via particulate matter exposure, and 15.5% vs. 17.5% via household dust exposure, respectively. The contribution of food via ingestion to lead exposure remains dominant, and coal combustion is a main lead exposure source for children and domestic dogs.

Sources, pathways and concentrations of potentially toxic trace metals in home environments

Despite ongoing concerns about trace metal and metalloid (trace metals) exposure risks from indoor dust, there has been limited research examining their sources and relationship to outdoor soils. Here we determine the concentrations and sources for potentially toxic trace metals arsenic (As), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) and their pathways into homes in Sydney, Australia, using home-matched indoor dust (n = 166), garden soil (n = 166), and road dust samples (n = 51). All trace metals were more elevated indoors versus their matched garden soil counterparts. Indoor Cu and Zn dust concentrations were significantly more enriched than outdoor dusts and soils, indicating indoor sources were more relevant for these elements. By contrast, even though Pb was elevated in indoor dust, garden soil concentrations were correspondingly high, indicating that it remains an important source and pathway for indoor contamination. Elevated concentrations of As, Pb and Zn in garden soil and indoor dust were associated with home age (>50 years), construction materials, recent renovations and deteriorating interior paint. Significant correlations (p < 0.05) between road dust and garden soil Cu concentrations, and those of As and Zn in soil and indoor dust, and Pb across all three media suggest common sources. Scanning electron microscopy (SEM) analysis of indoor dust samples (n = 6) showed that 57% of particles were derived from outdoor sources. Lead isotopic compositions of soil (n = 21) and indoor dust (n = 21) were moderately correlated, confirming the relevance of outdoor contaminants to indoor environments. This study illustrates the source, relationship and fate of trace metals between outdoor and indoor environments. The findings provide insight into understanding and responding to potentially toxic trace metal exposures in the home environment.

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.

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.

Successful Conversion of Pb-Contaminated Soils to Low-Bioaccessibility Plumbojarosite Using Potassium-Jarosite at Ambient Temperature

Methods promoting lead (Pb) phase transformation in soils are essential for decreasing Pb bioaccessibility/bioavailability and may offer an in situ, cost-efficient process for mitigating contaminant exposure. Recent plumbojarosite (PLJ) conversion methods have shown the greatest potential to reduce soil Pb bioaccessibility, an in vitro bioaccessibility assay measurement of the proportion of Pb solubilized under gastric chemical conditions. Soils tested utilizing the recent PLJ method were found to have a Pb bioaccessibility of <1%, compared to original soils possessing bioaccessibility of >70%. However, this technique requires heat (95-100 °C) to promote mineral transformation. Jarosite-group minerals may incorporate multiple interlayer cations; therefore, we probed the potential for jarosite to remediate Pb via intercalation by reacting presynthesized potassium (K)-jarosite with aqueous Pb and/or Pb-contaminated soil at room temperature. Both K-jarosite and heated PLJ-treated samples were investigated by pairing bioaccessibility analyses with advanced bulk and spatially resolved X-ray absorption spectroscopy analyses. Samples treated with K-jarosite promoted Pb transformation to low-bioaccessibility (<10%) PLJ, with soil being converted to 100% PLJ using both heated and nonheated techniques. μ-X-ray fluorescence (μ-XRF) and μ-X-ray absorption near-edge structure (μ-XANES) showcase significant differences between elemental interactions for heated and nonheated PLJ-treated samples with anglesite impurities being found on the microscale. Although further development is necessary to accommodate for suitable field conditions, results indicate, for the first time, that K-jarosite may successfully convert soil Pb to PLJ without high-temperature conditions. The newfound utility of K-jarosite is expected to be key to future jarosite-based soil Pb remediation method development.

In vitro and in silico bioaccessibility of urban dusts contaminated by multiple legacy sources of lead (Pb)

Lead contamination from gasoline, paint, pesticides, and smelting have unique chemical structures. Recent investigations into Pb speciation in urban soils and dusts from multiple sources have revealed emerging forms which differ from the initial sources. This results from reactions with soil constituents leading to transformation to new forms for which the bioaccessibilities remain uninvestigated. We investigated the in vitro and in silico bioaccessibility of these emerging forms in three physiologically relevant milieux: artificial lysosomal fluid (ALF), simulated epithelial lung fluid (SELF), and simulated gastric fluid (SGF). Species were validated using extended X-ray absorption fine structure spectroscopy. Results highlight diverse bioaccessibilities which are form and compartmentally-dependent. In ALF the bioaccessibility trend was humate-bound Pb (86%) > hydrocerussite (79%) > Fe oxide-bound Pb (47%) > galena (10%) > pyromorphite (4%) > Mn oxide-bound Pb (2%). Humate-bound Pb, hydrocerussite, Fe and Mn oxide-bound Pb were 100% bioaccessible in SGF while pyromorphite and galena were 26%, and 8%, respectively. Bioaccessibility in SELF was very low (< 1%) and significantly lower than ALF and SGF (p < 0.001). In silico bioaccessibilities modeled using equilibrium solubilities in extraction solutions were in good agreement with empirical measurements. These emerging forms of Pb have a wide range of bioaccessibilities that can influence their toxicity and impact on human health.

Potential ecological and health risks of heavy metals for indoor and corresponding outdoor dust in Hefei, Central China

The harm caused by indoor dust has received increasing attention in recent years. However, current studies have ignored comparisons with the corresponding outdoor dust. This study aimed to investigate the distribution of heavy metals in indoor and corresponding outdoor dust and the ecological and health risks they pose in Hefei, Central China. We analyzed O/I (outdoor/indoor concentration ratios) values, background comparison, and correlation analysis (heavy metal concentrations vs. particle size) and found that Cu, Zn, and Cd mainly existed in indoor sources, while V, Co, and As mainly existed in outdoor sources, and both family sizes and floor number influenced the variation of O/I. Through a new potential ecological risk assessment method, we determined that Cd risk levels in indoor and outdoor dust were extreme and high to extreme, respectively. Additionally, the carcinogenic risks of Ni, As, and Cr were not negligible. The risk of indoor dust was higher than that of outdoor dust for the heavy metals studied, implying a poor indoor environment. Notably, indoor dust from families with smaller sizes, lower floors, and smokers had higher ecological and carcinogenic risks.

Molecular Dynamics Beyond the Monolayer Adsorption as Derived from Langmuir Curve Fitting

Langmuir adsorption model is a classic physical-chemical adsorption model and is widely used to describe the monolayer adsorption behavior at the material interface in environmental chemistry. Traditional adsorption dynamic modeling solely considered the surface physiochemical interaction between the adsorbent and adsorbate. The surface reaction dynamics resulting from the heterogeneous surface and intrinsic electronic structure of absorbents were rarely considered within the reported adsorption experiments. Herein, by employing the chlorine hybrid graphene oxide (GO-Cl) to adsorb Ag⁺ in an aqueous solution, complicated molecular dynamics significantly deviated from the monolayer adsorption mechanism, as suggested by Langmuir adsorption curve fitting, has been elucidated down to atomic scale. In the time-dependent Ag adsorption experiments, both Ag single atoms and Ag/AgCl nanoparticle heterostructures are observed to be formed sequentially on GO-Cl. These observations indicate that for the surface adsorption dynamics, not only the surface chemical adsorption process involved but also photoreduction and the C-Cl bond cleavage reaction has been heavily engaged within the GO-Cl interface, suggesting a much more complicated vision rather than the monolayered adsorption algorithm as derived from curve fitting. This study uses GO-Cl as a simple example to disclose the complicated adsorption dynamic process underneath Langmuir adsorption curve fitting. It advocates the necessity of imaging the interfacial atomic-scale dynamic structure with high-resolution microscopy techniques in modern adsorption studies, rather than simply explaining the adsorption dynamics relying on the curve fitting results due to the complicated physiochemical reactivity of the adsorbents.

International Analysis of Sources and Human Health Risk Associated with Trace Metal Contaminants in Residential Indoor Dust

People spend increasing amounts of time at home, yet the indoor home environment remains understudied in terms of potential exposure to toxic trace metals. We evaluated trace metal (and metalloid) concentrations (As, Cu, Cr, Mn, Ni, Pb, and Zn) and health risks in indoor dust from homes from 35 countries, along with a suite of potentially contributory residential characteristics. The objective was to determine trace metal source inputs and home environment conditions associated with increasing exposure risk across a range of international communities. For all countries, enrichments compared to global crustal values were Zn > Pb > Cu > As > Cr > Ni; with the greatest health risk from Cr, followed by As > Pb > Mn > Cu > Ni > Zn. Three main indoor dust sources were identified, with a Pb-Zn-As factor related to legacy Pb sources, a Zn-Cu factor reflecting building materials, and a Mn factor indicative of natural soil sources. Increasing home age was associated with greater Pb and As concentrations (5.0 and 0.48 mg/kg per year of home age, respectively), as were peeling paint and garden access. Therefore, these factors form important considerations for the development of evidence-based management strategies to reduce potential risks posed by indoor house dust. Recent findings indicate neurocognitive effects from low concentrations of metal exposures; hence, an understanding of the home exposome is vital.

Plumbojarosite Remediation of Soil Affects Lead Speciation and Elemental Interactions in Soil and in Mice Tissues

Lead (Pb) contamination of soils is of global concern due to the devastating impacts of Pb exposure in children. Because early-life exposure to Pb has long-lasting health effects, reducing exposure in children is a critical public health goal that has intensified research on the conversion of soil Pb to low bioavailability phases. Recently, plumbojarosite (PLJ) conversion of highly available soil Pb was found to decrease Pb relative bioavailability (RBA <10%). However, there is sparse information concerning interactions between Pb and other elements when contaminated soil, pre- and post-remediation, is ingested and moves through the gastrointestinal tract (GIT). Addressing this may inform drivers of effective chemical remediation strategies. Here, we utilize bulk and micro-focused Pb X-ray absorption spectroscopy to probe elemental interactions and Pb speciation in mouse diet, cecum, and feces samples following ingestion of contaminated soils pre- and post-PLJ treatment. RBA of treated soils was less than 1% with PLJ phases transiting the GIT with little absorption. In contrast, Pb associated with organics was predominantly found in the cecum. These results are consistent with transit of insoluble PLJ to feces following ingestion. The expanded understanding of Pb interactions during GIT transit complements our knowledge of elemental interactions with Pb that occur at higher levels of biological organization.

An interlaboratory evaluation of the variability in arsenic and lead relative bioavailability when assessed using a mouse bioassay

Animal bioassays have been developed to estimate oral relative bioavailability (RBA) of metals in soil, dust, or food for accurate health risk assessment. However, the comparability in RBA estimates from different labs remains largely unclear. Using 12 soil and soil-like standard reference materials (SRMs), this study investigated variability in lead (Pb) and arsenic (As) RBA estimates employing a mouse bioassay in 3 labs at Nanjing University, University of Jinan, and Shandong Normal University. Two performances of the bioassay at Nanjing University in 2019 and 2020 showed reproducible Pb and As RBA estimates, but increasing the number of mouse replicates in 2020 produced more precise RBA measurements. Although there were inter-lab variations in diet consumption rate and metal accumulation in mouse liver and kidneys following SRM ingestion due to differences in diet composition, bioassays at 3 labs in 2019 yielded overall similar Pb and As RBA estimates for the 12 SRMs with strong linear correlations between each 2 of the 3 labs for Pb (R² = 0.95-0.98 and slope = 0.85-1.02) and As RBA outcomes (R² = 0.46-0.86 and slope = 0.56-0.79). The consistency in RBA estimates was attributed to the relative nature of the final bioavailability outcome, which might overcome the inter-lab variation in diet consumption and metal uptake in mice. These results increased the confidence of use of mouse bioassays in bioavailability studies.

Urban-Soil Pedogenesis Drives Contrasting Legacies of Lead from Paint and Gasoline in City Soil

This study analyzed the impact of urban-soil pedogenesis on soil lead (Pb) contamination from paint and gasoline in the historic core of Durham, North Carolina. Total soil Pb in 1000 samples from streetsides, residential properties, and residual upland and floodplains ranged from 6 to 8825 mg/kg (mean = 211 mg/kg), with 50% of samples between 50 and 200 mg/kg soil Pb. The highest Pb concentrations were within 1 m of pre-1978 residential foundations, with concentrations inversely correlated with house age. Streetside soil Pb concentrations were elevated over the geologic background of <30 mg/kg and correlated with traffic flow. Streetside soil Pb concentrations were lower than Durham streetside soils collected in the 1970s, which was attributed to urban pedogenesis, the complex of natural and human processes that change soils over time. Accelerated erosion redistributes legacy Pb and floodplain sampling indicates sedimentation rates of up to 4 mm/year. Mixing and burial of soil with elevated Pb are also lowering soil Pb concentrations over time. These mechanisms are likely of greater significance on streetsides than near foundation soils. The development of an urban-pedogenesis framework can help guide public health approaches to Pb exposure by incorporating pedogenic processes that reduce and dissipate soil Pb contamination.