Lead Bioaccessibility Research Articles

Bioaccessibility and radioisotopes of lead in soils around a fertilizer industry in Lebanon.

The use of phosphate ore by fertilizer industries is considered a major source of soil contamination by trace metals and radionuclides. Despite its low mobility and bioavailability, lead (Pb) is among soil contaminants that pose a serious risk to human health. This study evaluates the potential impact of a fertilizer factory in North Lebanon on the total content of Pb and the activity concentration of its radioisotopes in residential, non-agricultural lands around the industry, as well as its mobility and bioaccessibility in soil samples collected at different depths. Chemical extractions by EDTA and in vitro physiologically based extraction test were used to estimate, respectively, the available and bioaccessible fractions of Pb in soils. Radioisotopes 214Pb, 212Pb and 210Pb have been analyzed by gamma spectrometry. Different physicochemical soil parameters, such as pH, carbonate content, electrical conductivity, cation exchange capacity, clay, total nitrogen and redox potential, were studied. The pseudo-total Pb varied between 12.8 and 68.5mgkg-1, while the extractable fractions were more variable, between 12 and 72% of total Pb concentration for the EDTA extracted fraction and up to 28.5% for the bioaccessible fractions. The processing of the data shows the decreases with depth in most sites of the total and available Pb and of the activity concentration of 210Pb and their positive correlations with total nitrogen. These variations and relationships with the location of studied sites show the influence of emissions from the factory or the transport of ore and by-products. The correlations between available and bioaccessible Pb on one hand, between available Pb and 210Pb on another hand, raise the question of health risk assessments taking into account the bioaccessibility of Pb and its radioisotopes.

Bioaccessibility of Arsenic and Lead in Polluted Soils Using Three In-vitro Gastrointestinal Simulation Models

In human health risk assessment (HHRA), oral ingestion of soil can be a major route of exposure to many immobile soil contaminants. Development and validation of in vitro assays is currently being undertaken to avoid overestimation of pollutants absorbed by the human body when calculating total pollutant concentrations in HHRA. In this study, arsenic (As) and lead (Pb) bioaccessibility in polluted Australian soils (n = 6) was assessed using three in vitro assays: a physiologically based extraction test (PBET), Solubility/Bioavailability Research Consortium Assay (SBRC) and Unified Bioaccessibility Research Group Of Europe Method (UBM). In vitro results were compared among these three assays and the possible causes of their differences were discussed. A bioaccessibility-corrected HHRA was then conducted. Bioaccessibility varied greatly among metal(loid)s and methods, and extending the three assays from the gastric to the intestinal phase generally resulted in decreased As and Pb bioaccessibility. Using these bioaccessibility values, both hazard index (HI) and carcinogenic risk (CR) were calculated, and were found to be higher than threshold values in most samples, indicating a potential health risk to local inhabitants.

In vitro ingestion and inhalation bioaccessibility of soilborne lead, cadmium, arsenic and chromium near a chemical industrial park for health risk assessment

ABSTRACTSurface soils were collected near a chemical industrial park in the present study and in vitro inhalation and ingestion bioaccessibility of soilborne lead, cadmium, arsenic and chromium was evaluated using various in vitro bioaccessibility procedures including simulated lung fluid (SLF), artificial lysosomal fluid (ALF), modified Gamble solution (MGS), Solubility/Bioaccessibility Research Consortium (SBRC) procedure, and in vitro gastrointestinal (IVG) procedure. The in vitro inhalation and ingestion bioaccessibility of toxic elements showed elemental dependence and differed greatly among SBRC, IVG, SLF, ALF and MGS. The non-carcinogenic and lifetime carcinogenic risks of soilborne toxic elements based on the bioaccessible contents via ingestion and inhalation exposure were within the acceptable level. The present study reveals that the in vitro bioaccessibility of toxic elements was influenced greatly by the current in vitro bioaccessibility procedures, which resulted in great differences on the risk-based assessment via inhalation and oral ingestion exposure.

The role of soil mineralogy on oral bioaccessibility of lead: Implications for land use and risk assessment

Understanding the oral bioaccessibility of lead (Pb) present in soils in urbanized areas is important for the human exposure risk assessment. In particular, the role of the soil-mineralogy in the oral bioaccessibility has not been extensively studied. To investigate bioaccessibility, five types of periurban soils were collected, samples were spiked with the same amount of lead-chromates from traffic paint, and subjected to the in vitro Physiological Based Extraction Test (PBET). Ten samples of urban topsoils were collected at elementary schools playgrounds, Pb-bioaccessibility was measured, and a prediction equation for bioaccessibility was constructed. Mineralogy, and metal content were identified with a combination of X-ray powder diffraction, scanning electron microscopy, and portable X-ray fluorescence techniques. Traffic paint sample is made of 15% quartz (SiO2), 13% crocoite (PbCrO4), 55% calcite (CaCO3), and 17% kaolinite (Al2Si2O5(OH)4) and it contains high metal content (Pb, Cr, Zn, and Ca). Studied soils are characterized by variable amounts of acid-neutralizing minerals (carbonates) and low metal content. Spiked soils contained almost equal concentration of Pb, Cr, and Zn, because the contribution of these metals is from the added paint. However, obtained Pb-bioaccessibility at gastric and intestinal conditions are variable (40 to 51% gastric, 24 to 70.5% intestinal). Carbonate content shows significant correlation (p < 0.05) with Cr, Ca, calcite, crocoite, and Pb-bioaccessible at gastric conditions. Correlation of Pb-bioaccessible at intestinal conditions is significant (p < 0.05) with kaolinite.Variability of Pb-bioaccesibility in urban environments is commonly associated to differences in Pb-sources, however, our results show that the bioaccessibility of the same pollutant behaves different for each soil type. This suggests that soil mineralogy may play a role in Pb-releasing at gastrointestinal conditions. Soil information about mineralogical characteristics from this study may help to reduce exposure to lead from urban sources if data are incorporated into urban planning.

Folk prescription for treating rhinitis as a rare cause of childhood lead poisoning: a case series

BackgroundFolk prescriptions continue to be important sources of childhood lead poisoning. Nasal spray folk prescriptions for treating rhinitis has only been reported once previously as a cause of lead poisoning.Case presentationWe identified three pediatric cases of severe lead poisoning caused by nasal spray folk medicines prescribed for treating rhinitis. The three patients had similar clinical manifestations including: severe abdominal pain, headache, pale appearance and fatigue. Liver function tests were abnormal. Blood lead levels (BLLs) of the three patients were 91 μg/dL, 91 μg/dL, and 105 μg/dL, respectively. After chelation BLLs decreased. The lead content of the three folk remedies as measured by inductively coupled plasma mass spectrometry (ICP-MS) were 14.8, 22.3, and 33.4%. All the symptoms resolved during a course of chelation therapy. There were no severe side effects of treatment.ConclusionsNasal spray folk prescriptions for treating rhinitis may contain extremely high bio-accessible lead content and are potential sources of lead poisoning. Clinicians should be alert to this possibility especially in those children presenting with multisystem symptoms.

Point of zero charge: Role in pyromorphite formation and bioaccessibility of lead and arsenic in phosphate amended soils.

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite by adding sources of phosphorus (P), but uncertainties still remain in natural systems. Knowledge of PZC is important to predict the ionization of functional groups and their interaction with metal species in solution. This study utilized the Pb- and As-contaminated soils to determine the combined effect of pH with respect to PZC and different rates of P-application on pyromorphite formation, and Pb and arsenic (As) bioaccessibility as impacted by speciation changes. Solution chemistry analysis along with synchrotron-based Pb- and As-speciation, and bioaccessibility treatment effect ratios (TERs) were conducted. Results indicated no significant effect of PZC on pyromorphite formation in P-amended soils; however, the TERPb appeared significantly lower at pH>pHPZC and higher at pH<pHPZC (α = 0.05). In contrast, the TERAs was significantly higher at pH>pHPZC, compared to the other two treatments, for the tested soils. The lack of conversion of soil Pb to pyromorphite may be attributed to presence of stable minerals limiting soluble-Pb availability and high organic matter content of the tested soils.

Oxidative weathering decreases bioaccessibility of toxic metal(loid)s in PM10 emissions from sulfide mine tailings.

Environmental contamination from legacy mine waste deposits is a persistent problem due to the long history of hard‐rock mining. Sulfide ore deposits can contain elevated levels of toxic metal(loid)s that, when mobilized by weathering upon O2 and H2O infusion, can result in groundwater contamination. Dry climate and lack of vegetative cover result in near‐surface pedogenic processes that produce fine‐particulate secondary minerals that can be translocated as geodusts leading to ingestion or inhalation exposure in nearby communities. In this study, in vitro bioassays were combined with synchrotron‐based X‐ray spectroscopy and diffraction to determine the potential risk for toxic element release from dust (PM10) samples into biofluid simulants. PM10 were isolated from across the oxidative reaction front in the top meter of tailings subjected to 50 years of weathering under semiarid climate and introduced to synthetic gastric and alveolar fluids. Aqueous concentrations were measured as a function of reaction time to determine release kinetics. X‐ray diffraction and absorption spectroscopy analyses were performed to assess associated changes in mineralogy and elemental speciation. In vitro bioaccessibility of arsenic and lead was highest in less‐weathered tailings samples (80–110 cm) and lowest in samples from the suboxic transition zone (40–52 cm). Conversely, zinc release to biofluids was greatest in the highly weathered near‐surface tailings. Results indicate that bioaccessibility of As and Pb was controlled by (i) the solubility of Fe2+‐bearing solids, (ii) the prevalence of soluble SO4 2−, and (iii) the presence of poorly crystalline Fe(III) oxide sorbents, whereas Zn bioaccessibility was controlled by the pH‐dependent solubility of the stable solid phase.

Applicability of an in vitro gastrointestinal digestion method to evaluation of toxic elements bioaccessibility from algae for human consumption

ABSTRACTThis study aimed to investigate the bioaccessibility of toxic elements, including aluminum (Al), arsenic (As), nickel (Ni), cadmium (Cd), and lead (Pb) in five commercial algae consumed by humans in Italy. The degree of bioaccessibility of these elements may have important implications for human health. Simulation of gastrointestinal tract (GIT) digestion was divided into three stages through use of synthetic saliva, gastric, and bile–pancreas solutions. After pre-treatment with a saliva solution, seaweed samples underwent one of the following treatments: (1) simulated gastric digestion only or (2) simulated complete GIT digestion (gastric digestion followed by bile-pancreas digestion). The bioaccessibility of these toxic elements ranged from approximately 5% to 73% and from 4% to 77% in gastric and GIT digestion, respectively. The bioaccessibility of Al and Pb is poor (5–15%), As and Ni were fairly (40–55%), while Cd displayed a high bioaccessibility. No significant differences in toxic elements mobility was found between samples that only underwent gastric digestion compared to those that underwent a complete GIT digestion.

Bioaccessibility and human health risk assessment of lead in soil from Daye City

Lead (Pb) in soil from 4 sampling sites of Daye City was studied. Bioaccessibilities of Pb in soil were determined by the method of simplified bioaccessible extraction test (SBET). Since traditional health risk assessment was built on the basis of metal total content, the risk may be overestimated. Modified human health risk assessment model considering bioaccessibility was built in this study. Health risk of adults and children exposure to Pb based on total contents and bioaccessible contents were evaluated. The results showed that bioaccessible content of Pb in soil was much lower than its total content, and the average bioaccessible factor (BF) was only 25.37%. The hazard indexes (HIs) for adults and children calculated by two methods were all lower than 1. It indicated that there were no no-carcinogenic risks of Pb for human in Daye. By comparing with the results, the average bioaccessible HIs for adults and children were lower than the total one, which was due to the lower hazard quotient (HQ). Proportions of non-carcinogenic risk exposure to Pb via different pathways have also changed. Particularly, the most main risk exposure pathway for adults turned from the oral ingestion to the inhalation.

Health risk and bioaccessibility assessment of lead in waste from the Malaysian Lynas rare earth processing plant using an &lt;i&gt;in vitro&lt;/i&gt; DIN gastrointestinal model

This study examines the bioaccessibility of lead from water leach purification (WLP) waste collected from the Malaysian Lynas rare earth processing plant using an in vitro DIN digestion model. A contamination factor (Cf) value of 2.7 was obtained from study results, which is considered to be a moderate level of Pb contamination in WLP waste. The bioaccessibility of Pb in digested WLP waste ranged between 0.064 ± 0.010 to 0.080 ± 0.010% and 0.018 ± 0.013 to 0.103 ± 0.046% in the gastric and gastrointestinal phases f, respectively, during the 5-hour study period. To evaluate the human health risks associated with Pb in WLP waste, the bioaccessible estimated daily intake (BEDI) and bioaccessible target hazard quotient (BTHQ) were calculated. The values obtained for children exceeded the recommended safe limit, in contrast to the values obtained for adults, indicating potential human health risks. The results of this study suggest that the WLP waste from Lynas waste disposal facility should be further evaluated and monitored to eliminate any adverse health effects associated with accidental human exposure to Pb.

Anomalous bioaccumulation of lead in the earthworm Eisenoides lonnbergi (Michaelsen).

Lead concentrations in soil organisms are usually well below those in the associated soil and tend to decrease with each higher trophic level in a food chain. Earthworms of the species Eisenoides lonnbergi provide an exception to this observation, accumulating very high concentrations of lead from acidic soils. Earthworms belonging to this species were collected from strongly to extremely acidic soils at 16 sites on a wildlife refuge in Maryland, USA. A lead concentration as high as 766 mg/kg, dry weight, was detected in depurated E. lonnbergi collected from soil containing only 17 mg/kg of lead. Concentration factors (ratio of lead concentration in earthworms to lead concentration in soil, dry wt) were highly variable at the sites, from 1.0 to 83. As suggested previously, lead absorption by earthworms is enhanced in low-calcium soils. The anomalously high concentrations of lead found in E. lonnbergi are more closely correlated with the uptake of calcium from acidic soils than with bioaccessibility of soil lead. Environ Toxicol Chem 2018;37:914-919. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture.

While the presence of legacy lead (Pb) in urban soil is well documented, less is known about the bioaccessibility, transport, and exposure pathways of urban soil Pb. We study Pb bioaccessibility in Roxbury and Dorchester, MA, urban gardens to assess exposure risk and identify remediation strategies, applicable locally and in urban gardens across the country. We work in partnership with The Food Project, which brings the goals and perspectives of local farmers to the center of the research process and enables efficient local application of results to reduce Pb exposure. We measure changes in Pb bioaccessibility as a function of growing material, grain size, and Pb source. In comparison to soils, compost has lower total Pb concentrations, has lower Pb solubility in gastric fluid, and limits fine particle resuspension. The mean bioaccessible Pb concentration of compost is 265 mg/kg, nearly an order of magnitude lower than that of soils, and compost contains 14% higher carbon content than soils, which may account for the observed 19% lower Pb bioaccessibility in compost. For all matrices (soil, raised bed fill, and compost) grain sizes <37 μm contain a disproportionate fraction of the total pool of bioaccessible Pb. Furthermore, the isotopic composition of Pb in the size fractions linked with resuspension and elevated blood lead levels is indicative of leaded gasoline and leaded paint even decades removed from the primary deposition of these sources.

Relationship Between Total and Bioaccessible Lead on Children's Blood Lead Levels in Urban Residential Philadelphia Soils.

Relationships between total soil or bioaccessible lead (Pb), measured using an in vitro bioaccessibility assay, and children's blood lead levels (BLL) were investigated in an urban neighborhood in Philadelphia, PA, with a history of soil Pb contamination. Soil samples from 38 homes were analyzed to determine whether accounting for the bioaccessible Pb fraction improves statistical relationships with children's BLLs. Total soil Pb concentration ranged from 58 to 2821 mg/kg; the bioaccessible Pb concentration ranged from 47 to 2567 mg/kg. Children's BLLs ranged from 0.3 to 9.8 μg/dL. Hierarchical models were used to compare relationships between total or bioaccessible Pb in soil and children's BLLs. Total soil Pb concentration as the predictor accounted for 23% of the variability in child BLL; bioaccessible soil Pb concentration as the predictor accounted for 26% of BLL variability. A bootstrapping analysis confirmed a significant increase in R2 for the model using bioaccessible soil Pb concentration as the predictor with 99.0% of bootstraps showing a positive increase. Estimated increases of 1.3 μg/dL and 1.5 μg/dL in BLL per 1000 mg/kg Pb in soil were observed for this study area using total and bioaccessible Pb concentrations, respectively. Children's age did not contribute significantly to the prediction of BLLs.

Effect of lead speciation on its oral bioaccessibility in surface dust and soil of electronic-wastes recycling sites

We measured bioaccessible lead (Pb) in simulated gastrointestinal fluids containing Pb-contaminated soil or dust from electronic waste (e-waste) recycling sites to assess the risk of Pb ingestion. The physiologically based extraction test (PBET) was used as in vitro bioaccessibility assay. Pb speciation was determined using X-ray absorption spectroscopy. The total Pb concentrations in dusts (n=8) and soils (n=4) were in the range of 1630–131,000 and 239–7800mg/kg, respectively. Metallic Pb, a common component of e-waste, was ubiquitous in the samples. We also found Pb adsorbed onto goethite and as oxides and carbonate, implying soil mixing and weathering influences. Pb phosphate and organic species were only found in the soil samples, suggesting that formation was soil-specific. We identified other Pb compounds in several samples, including Pb silicate, Pb chromate, and Pb(II) hydrogen phosphate. A correlation analysis indicated that metallic Pb decreased bioaccessibility in the stomach, while a Pb speciation analysis revealed a low bioaccessibility for Pb phosphates and high bioaccessibility for organic Pb species. The health risk based on bioaccessible Pb was estimated to be much lower than that of total Pb due to the lower concentrations.

Effect of phosphate amendment on relative bioavailability and bioaccessibility of lead and arsenic in contaminated soils

Hand-to-mouth activity is an important pathway for children’s exposure to contaminated soils, which is often co-contaminated by Pb and As in mining and smelting sites. To reduce soil Pb risk to humans by oral exposure, phosphate amendments have been used to reduce Pb relative bioavailability (RBA), but its efficiency has not been investigated using validated in vitro assays nor its influence on As-RBA. Here, 5 contaminated soils (A-E) were amended with 0.5% phosphoric acid (PA) to study its effect on Pb- and As- RBA using a newly-developed mouse kidney model and bioaccessibility using 4 in vitro assays including UBM, SBRC, IVG, and PBET. Based on the mouse kidney model, Pb-RBA in PA-amended soils decreased from 14.2–62.5% to 10.1–29.8%. In contrast, As-RBA decreased from 26.5% to 15.9% in soil B but increased from 27.5 to 41.2% in soil D, with changes being insignificant in 3 other soils (35.8–58.8 to 28.1–61.1%). When assessing Pb bioaccessibility in PA-amended soils, decreased bioaccessibility were found using PBET and SBRC. For As, its bioaccessibility increased in PA-amended soils, inconsistent with in vivo data. Our results shed light on the importance of method selection to assess risk in Pb- and As-contaminated soils amended with phosphate.

Geospatial evaluation of lead bioaccessibility and distribution for site specific prediction of threshold limits

Recent work identified the need for site-specific Pb bioaccessibility evaluation and scaled contaminant modeling. Pb heterogeneity has made bioaccessibility characterization difficult, and complicated distribution models. Using field testing, bioaccessibility measurement, Integrated Exposure Uptake and Biokinetic (IEUBK) modeling, and geospatial techniques, we propose a framework for conducting applied risk-based, multiscale assessment. This framework was tested and implemented in Burlington, VT, an area of old housing stock and high Pb burden (up to 15 000 mg kg−1) derived primarily from paint. After analyzing local soil samples for total and bioaccessible Pb, it was determined that bioaccessible and total Pb were well correlated in this area, through which an average bioaccessibility parameter was derived approximating Pb bioaccessibility for this soil type and Pb impact. This parameter was used with the IEUBK to recommend the local limit for residential soil Pb be reduced from 400 to 360 mg kg−1, taking into consideration the lowering of the blood lead level threshold for Pb poisoning from 10 to 5 μg dL−1 by the Centers for Disease Control (CDC). Geospatial investigation incorporated samples collected during this investigation and samples from a high school summer science academy, and relied on three techniques, used at different scales: kriging of total and background Pb alone, kriging of total and background Pb with housing age as a well-sampled, well-correlated secondary variable (cokriging), and inverse distance weighting of total and bioaccessible Pb. Modeling at different scales allowed for characterization of Pb impact at single sites as well as citywide. Model maps show positive correlation between areas of older housing and areas of high Pb burden, as well as potential at different scales for reducing the effects of Pb heterogeneity.

Investigating the relationship between lead speciation and bioaccessibility of mining impacted soils and dusts.

Lead (Pb) bioaccessibility measurements have been the subject of much research in recent years, given the desire to develop a cost-effective and reliable alternative method to estimate its bioavailability from soils and dusts. This study investigates the relationship between Pb bioaccessibility estimated using the Relative Bioavailability Leaching Procedure (RBALP) and solid phase speciation of Pb using mining impacted soils and associated dusts. Solid phase speciation was conducted prior to and after RBALP extractions. The average Pb concentrations were 59, 67, and 385mg/kg for top soil, sub-soil, and house dust samples, respectively. Lead bioaccessibility in selected top soils and dusts ranged from 16.7 to 57.3% and 8.9 to 98.1%, respectively. Solid phase speciation of Pb in <250μm residues prior to and after RBALP extraction revealed 83% decrease in Pb bound to carbonate fraction after RBALP extraction. This accounts for 69% of RBALP-extractable Pb. Besides contribution from carbonate bound Pb, 76.6 and 53.2% of Pb bound to Mn oxyhydroxides and amorphous Fe and Al oxyhydroxides contributed to bioaccessible Pb, respectively. However, Pb bound to Mn oxyhydroxides and amorphous Fe and Al oxyhydroxides account for only 13.8 and 20.0% of total RBALP-extractable Pb, respectively. Both non-specifically bound and easily exchangeable fractions and strongly bound inner-sphere complexes were also part of bioaccessible Pb. The present study demonstrates that bioaccessible Pb is released from both soil solution phase Pb as well as that from all soil solid phase with the most contribution being from Pb bound to carbonate mineral phase.

Evaluation of relative bioaccessibility leaching procedure for an assessment of lead bioavailability in mixed metal contaminated soils

Abstract This study investigates the effect of contaminant zinc (Zn) on lead (Pb) bioavailability and bioaccessibility in six contrasting soils spiked with 1500 mg Pb/kg and aged 12 months under laboratory conditions. Zn was added to the soils (7500 mgZn/kg soil) and aged for a further two weeks. In vivo studies were conducted using juvenile swine as a surrogate model for young children. Two compartment pharmacokinetic models were used to analyze the biological response produced by Pb oral solution and spiked soils. Absolute and relative bioavailability of Pb in soils (oral dose of 100 μ g Pb/kg body weight/day) were estimated by comparing them with intravenously administered soluble Pb salt (25 μ g Pb/kg/day) and orally administered the same Pb salt [Pb acetate =(CH3COO)2Pb⋅3H2O] administered to 3 juvenile pigs per treatment. Lead bioaccessibility was calculated using the in vitro RBALP (i.e. relative bioaccessibility leaching procedure) method. The in vitro results of RBALP were compared to in vivo relative Pb bioavailability to ascertain whether the changes in bioaccessibility correlated with the in vivo data. Although the in vivo Pb relative bioavailability (RB) in all soils except in MLA (Mount Lofty Acidic) revealed an increase (18%–159%) in the presence of Zn, the in vitro RBALP bioaccessibility results indicated otherwise (1%–38% decrease). In vivo RB of Pb in MLA declined by 37% in the presence of Zn. However, the RBALP in vitro bioaccessible Pb did not correlate with the relative bioavailabilities of Pb in the juvenile swine dosing experiment. Caution is therefore needed when predicting Pb bioavailability/bioaccessibility in the presence of metal mixtures. The literature contains much information on the correlation of metal and metalloid bioaccessibility with their bioavailability. There is, however, a paucity of studies investigating the effects of other metals on Pb and their IVIVC (in vitro and in vivo correlations). The current study addresses this knowledge gap by assessing in vivoand in vitro bioavailability of Pb in the presence of Zn.

Biogeochemical characterization of municipal compost to support urban agriculture and limit childhood lead exposure from resuspended urban soils

Chronic low-level lead exposure among low-income minority children is an urgent environmental justice issue. Addressing this ubiquitous urban public health crisis requires a new transdisciplinary paradigm. The primary goals of this work are to inform best practices for urban gardeners working in lead contaminated soils and to reimagine urban organic waste management schemes to produce compost, which when covering or mixed with urban soil, could minimize lead exposure. We investigate bulk and bioaccessible lead from five types of compost used in urban gardens in Boston, MA. We categorized them by feedstock and measured bulk elemental concentrations and physical characteristics. Our results show that different feedstocks exhibit unique geochemical fingerprints. While bulk lead concentrations in compost are a fraction of what is typical for urban soils, the bioaccessible lead fraction in compost is greater than the default parameters for the Integrated Exposure Uptake Biokinetic (IEUBK) model. The lack of geochemical differences across feedstocks for lead sorption to carbon indicates a similar sorption mechanism for all compost. This suggests that municipal compost would be suitable for capping lead contaminated urban soils. Risk assessment models should consider lead bioaccessibility, to prevent the underprediction of exposure risk, and should include compost along with soils as urban matrices. Based on the observed bioaccessibility in our compost samples, 170 mg/kg total lead in compost will yield the same bioaccessible lead as the IEUBK model predicts for the 400 mg/kg EPA soil lead benchmark. Local logistical challenges remain for interdisciplinary teams of city planners, exposure scientists, and urban agricultural communities to design organic waste collection practices to produce compost that will support urban agriculture and primary lead exposure prevention.

Urban Lead: Modeling Its Distribution and Effects on Children

We model the transportation of lead from the atmosphere and from the surface of the soil simultaneously at the macroscale and mesoscale to study its health effects on children in Jersey City, NJ. We conceptualize Jersey City as an open system where lead is continuously emitted from a local smelting plant and a local power plant, deposited onto the surface soil of playgrounds, and ingested by children. The model is constructed using the diffusion-advection partial differential equation in three spatial dimensions and one temporal dimension with an initial condition and boundary conditions. The model is solved using the Crank-Nicolson numerical method at the macroscale to determine the deposition of lead from the smelting plant and the local power plant and at the mesoscale to refine the amount of lead deposition for the areas considered. We then determine the health consequences for the average child using the bioaccessibility of lead from soil to children, the bioavailability of ingested lead to the circulatory system, and the biological half-life of lead isotopes in the blood. The health effects on children from lead are directly proportional to the blood lead concentration.