Gastro-Intestinal Absorption of Lead in Children and Adults: Overview of Biological and Biophysico-Chemical Aspects

Tracking Childhood Lead Exposure in Early Industrial Romanians

Childhood lead exposure has been linked to severe adverse health outcomes throughout life. Measurements of lead in teeth have established that individuals living in contaminated environments show higher levels compared to individuals living further away, although less is known about when individuals are most susceptible to these exposures. We examined lead (Pb208) concentrations (ppm) in teeth over the first 2.5 years of life in 16 children born in the late 19th to early 20th century throughout Romania. This period of intense industrialization was characterized by increases in mining, coal burning, and oil refining-activities that contaminate air, water, and food with Pb. We hypothesized the distance from an operational mine or oil refinery, or being born in a city, would be positively associated with cumulative dentine Pb exposure (CDPE). We also predicted that Pb exposures would peak in the first six months of life when gastrointestinal (GI) absorption of Pb is likely highest. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) of sectioned tooth dentine followed by Bayesian statistical analyses revealed that living 30 km or more from a mine or oil refinery did not explain CDPE. However, being born in a city explained 42% of CDPE. All individuals showed maximum Pb exposures after six months of age, likely due to contaminated solid food and/or non-milk liquids. This research demonstrates how tooth formation can be coupled with comprehensive elemental mapping to analyse the context and timing of early-life neurotoxicant exposures, which may be extended to well-preserved teeth from clinical and historic populations.

Maternal APOE ε2 as a possible risk factor for elevated prenatal Pb levels

Lead (Pb) is a global contaminant associated with multiple adverse health effects. Humans are especially vulnerable during critical developmental stages. During pregnancy, exposure to Pb can occur through diet and release from maternal bones. Apolipoprotein E gene (APOE) variants (ɛ2, ɛ3, ɛ4 alleles) may influence sex steroid hormones, bone metabolism, and Pb kinetics. We examined the interplay among maternal APOE (mAPOE) genotypes, fetal sex, parity, and Pb in maternal and cord blood (mB-Pb, CB-Pb) using linear regression models. Our study involved 817 pregnant women and 772 newborns with measured adequate levels of zinc and selenium. We compared carriers of the ε2 and ε4 alleles to those with the ε3/ε3 genotype. The geometric means (range) of mB-Pb and CB-Pb were 11.1 (3.58-87.6) and 9.31 (1.82-47.0) ng/g, respectively. In cases with female fetuses, the maternal mAPOE ε2 allele was associated with higher, while the mAPOE ε4 allele was associated with lower mB-Pb and CB-Pb levels. Nulliparity increased the strength of the observed associations. These findings highlight the significance of mAPOE genetics, fetal sex, and parity in prenatal Pb kinetics. Notably, the maternal ε2 allele may increase the risk of Pb exposure.

Lead exposure and its relationship with fecal cortisol levels in black howler monkeys (Alouatta pigra)

Efficiently detecting early environmental threats to wildlife is vital for conservation. Beyond obvious dangers like habitat loss or deforestation, our study focuses on one of the most hazardous toxic metals for wildlife: lead (Pb). Pb is a widespread, cumulative, and insidious environmental pollutant that can trigger a wide range of physiological, biochemical, and behavioral disorders. In fact, Pb can cause permanent dysfunction of the major stress system, the hypothalamic pituitary adrenal (HPA) axis. We analyzed Pb and cortisol concentrations in fecal samples from Alouatta pigra in southern Mexico. Fecal samples were collected across six sites categorized as free-ranging (n = 65; conserved and disturbed) and from captive animals (n = 58). Additionally, we collected soil samples (n = 35). We found that Pb was present in 28% of fecal samples and 83% of soil samples. There was a positive relation between fecal and soil Pb levels, and fecal Pb concentration was negatively associated with cortisol levels. However, the claim of Pb being a direct interference with HPA axis requires further investigation. Given our findings, assessing wildlife exposure can be a valuable tool for understanding potential Pb exposure levels in the environment and its possible implications for human health. It can also serve as an early warning system of these consequences.

Involvement of Nrf2 Signaling in Lead-induced Toxicity

Nuclear factor erythroid 2-related factor 2 (Nrf2) is used as one of the main protective factors against various pathological processes, as it regulates cells resistant to oxidation. Several studies have extensively explored the relationship between environmental exposure to heavy metals, particularly lead (Pb), and the development of various human diseases. These metals have been reported to be able to, directly and indirectly, induce the production of reactive oxygen species (ROS) and cause oxidative stress in various organs. Since Nrf2 signaling is important in maintaining redox status, it has a dual role depending on the specific biological context. On the one hand, Nrf2 provides a protective mechanism against metal-induced toxicity; on the other hand, it can induce metalinduced carcinogenesis upon prolonged exposure and activation. Therefore, the aim of this review was to summarize the latest knowledge on the functional interrelation between toxic metals, such as Pb and Nrf2 signaling.

Extending Regulatory Biokinetic Lead Models towards Food Safety: Evaluation of Consumer Baby Food Contribution to Infant Blood Lead Levels and Variability

The U.S. Food and Drug Administration released proposed lead (Pb) action levels for foods intended for babies and young children in January 2023 based on the agency's interim reference value of 2.2 µg/day for dietary Pb. Since the 1980s, biokinetic models have estimated blood lead levels (BLLs) associated with environmental contamination, but their use in food safety assessment has been limited. We compared three recent biokinetic models (IEUBK Model, ICRP Model Version 5, and AALM) to develop insights on contributors to variability in potential exposures to Pb in consumer baby food products. While modest variation was observed for babies, the predictions trended to convergence for children aged 3 and older, approaching the U.S. FDA dietary conversion factor of 0.16 µg Pb/dL blood per µg Pb intake/day. We applied the IEUBK model in a probabilistic exposure assessment framework characterizing the distribution of Pb in soil, dust, water, and food intake in the United States. Soil and dust were the primary contributors to variance in infant BLLs, while food and water contributed <15% combined. Thus, reductions in upper-bound soil and dust concentrations will be necessary before achieving appreciable reductions in the frequency of BLLs greater than the BLRV of 3.5 µg/dL.

Improving Equitability and Inclusion for Testing and Detection of Lead Poisoning in US Children

Policy Points Child lead poisoning is associated with socioeconomic inequity and perpetuates health inequality. Methods for testing and detection of child lead poisoning are ill suited to the current demographics and characteristics of the problem. A three-pronged revision of current testing approaches is suggested. Employing the suggested revisions can immediately increase our national capacity for equitable, inclusive testing and detection. ABSTRACT: Child lead poisoning, the longest-standing child public health epidemic in US history, is associated with socioeconomic inequity and perpetuates health inequality. Removing lead from children's environments ("primary prevention") is and must remain the definitive solution for ending child lead poisoning. Until that goal can be realized, protecting children's health necessarily depends on the adequacy of our methods for testing and detection. Current methods for testing and detection, however, are no longer suited to the demographics and magnitude of the problem. We discuss the potential deployment and feasibility of a three-pronged revision of current practices including: 1) acceptance of capillary samples for final determination of lead poisoning, with electronic documentation of "clean" collection methods submitted by workers who complete simple Centers for Disease Control and Prevention-endorsed online training and certification for capillary sample collection; 2) new guidance specifying the analysis of capillary samples by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectrometry with documented limit of detection ≤0.2 μg/dL; and 3) adaptive "census tract-specific" universal testing and monitoring guidance for children from birth to 10 years of age. These testing modifications can bring child blood lead level (BLL) testing into homes and communities, immediately increasing our national capacity for inclusive and equitable detection and monitoring of dangerous lower-range BLLs in US children.

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.

Melatonin alleviates lead-induced fatty liver in the common carps (Cyprinus carpio) via gut-liver axis

As a widespread aquatic environmental contaminant, Lead (Pb) can provoke hepatic injury in various animals. Melatonin (MT) plays a crucial role in the regulation of inflammatory response. Accumulating evidence elucidates exogenous toxins can elicit hepatic lipid metabolic disorders by influencing the gut microbiome. Nevertheless, the effects of Pb on gut microbiota and hepatic lipid metabolism of the common carps, and whether MT can prevent and cure Pb-induced toxicity via regulating microbiome remains unknown. Here, metagenomic and transcriptomic analysis were subsequently implemented to identify the Pb exposure-triggered prominent alternation of gut-liver signal. In the present study the severe intestinal injury and fatty liver formation caused by Pb in common carp were preliminarily determined. Metagenomic analysis confirmed that the gut microbiome dominant phyla, family and genus of the common carps were Fusobacteria, Fusobacteriaceae and Cetobacterium. Meanwhile, lipopolysaccharide (LPS) biosynthesis pathway was regarded as one of the main responsible for Pb exposure. Subsequently, LPS was demonstrated as the Pb-triggered microbial-derived signal of the common carps by ELISA analysis, and involves in the hepatic metabolic disorders via deteriorating the intestinal barrier. Additionally, it confirmed that hepatocytes ferroptosis associated with Pb-evoked fatty liver of the common carps, and the aggravation of lysosomal dyshomeostasis as well as inhibition of AMPK phosphorylation were referred to lipid metabolic disorders. The results of the present study demonstrated microbial-derived signal induced by aquatic Pb contaminant cause fatty liver formation in the common carps, and the protective effects of MT on Pb toxicity were performed by receding LPS over-synthesis, restraining microbiota-sourced LPS transport, along with attenuation of hepatocytes ferroptosis.

Impact of Heavy Metal Toxicity on the Gut Microbiota and Its Relationship with Metabolites and Future Probiotics Strategy: a Review

The gut microbiota has a vital role in the maintenance of intestinal homeostasis. Several studies have revealed that environmental exposure to pollutants such as heavy metals may contribute to the progression of extensive list of diseases which may further lead to perturbations in the gut leading to dysbiosis. This manuscript critically reviews the alterations in the gut microbiota composition and function upon exposure to various toxic heavy metals prevalent in the environment. The disturbance in gut microbial ecology also affects the microbial metabolic profile which may alter the speciation state and bioavailability heavy metals thus affecting metal uptake-absorption/detoxification mechanisms associated to heavy metal metabolism. The toxic effects of various heavy metals either in single or in multimetallic combination and the gut microbiota associated host health and disease condition need a comprehensive assessment with important consideration for therapeutic and protective strategies against the damage to gut microbiota.

Cereal and Juice, Lead and Arsenic, Our Children at Risk: A Call for the FDA to Re-Evaluate the Allowable Limits of Lead and Arsenic That Children May Ingest

Eliminating heavy metal contamination of foods is a goal yet to be achieved in the U.S. In recent months, efforts have been underway to have the Food and Drug Administration (FDA) re-evaluate the permissible limits of lead (Pb) and arsenic (As) allowable in cereals and juices aimed for consumption by children. This report discusses the recent scientific literature that support proposed revisions in these limits. It presents proactive suggestions for the FDA to consider in its response to concerns of ongoing Pb and As exposures in food and drinks. While more scientific studies are needed to better define ‘safe’ levels of Pb and As exposures and ingestion of these elements in general are neurotoxic, the higher sensitivity of children to these toxic elements makes it imperative that the FDA adjust standards to be most protective of infants, toddlers, and children.

Children's exposure to environmental lead: A review of potential sources, blood levels, and methods used to reduce exposure

Lead has been used for thousands of years in different anthropogenic activities thanks to its unique properties that allow for many applications such as the manufacturing of drinking water pipes and its use as additives to gasoline and paint. However, knowledge of the adverse impacts of lead on human health has led to its banning from several of its applications, with the main goal of reducing environmental pollution and protecting human health. Human exposure to lead has been linked to different sources of contamination, resulting in high blood lead levels (BLLs) and adverse health implications, primarily in exposed children. Here, we present a summary of a literature review on potential lead sources affecting blood levels and on the different approaches used to reduce human exposure. The findings show a combination of different research approaches, which include the use of inspectors to identify problematic areas in homes, collection and analysis of environmental samples, different lead detection methods (e.g. smart phone applications to identify the presence of lead and mass spectrometry techniques). Although not always the most effective way to predict BLLs in children, linear and non-linear regression models have been used to link BLLs and environmental lead. However, multiple regressions and complex modelling systems would be ideal, especially when seeking results in support of decision-making processes. Overall, lead remains a pollutant of concern and many children are still exposed to it through environmental and drinking water sources. To reduce exposure to lead through source apportionment methods, recent technological advances using high-precision lead stable isotope ratios measured on multi-collector induced coupled plasma mass spectrometry (MC-ICP-MS) instruments have created a new direction for identifying and then eliminating prevalent lead sources associated with high BLLs.

Identifying periods of heightened susceptibility to lead exposure in relation to behavioral problems

BACKGROUND

Lead exposure is associated with behavioral problems in children, but the age(s) of greatest susceptibility to low-level lead exposure is unknown.

OBJECTIVE

We evaluated the association of repeated blood lead concentrations with parent-reported behaviors to identify periods of heightened susceptibility during infancy and childhood (HOME Study; Cincinnati, OH; 2003-2006; n = 244).

METHODS

We quantified lead in whole blood samples (ages 1, 2, 3, 4, 5, and 8 years) and assessed behavior using the Behavioral Assessment System for Children-2 (BASC-2; ages 2, 3, 4, 5, and 8 years). We used multiple informant models and modified Poisson regression to estimate covariate-adjusted associations of ln-transformed blood lead concentrations with continuous BASC-2 T-scores and the relative risk of behavior scores classified as at-risk or clinically significant, respectively.

RESULTS

We observed trends indicating that higher blood lead concentrations at all ages were adversely associated with scores on behavioral scales. On the Externalizing Problems and Adaptive Skills scales, these associations were strongest for blood lead concentrations at age 8 years (β = 3.1-point; 95% CI = 0.7, 5.4 and β = -2.2-point; 95% CI = -4.9, 0.5, respectively) compared with other ages. Overall, higher blood lead concentrations were associated with elevated risk of behavior scores classified as at-risk or clinically significant on the Adaptive Skills, Behavioral Symptom Index, and Externalizing Problems scales.

SIGNIFICANCE

Contemporary levels of lead exposure during the first 8 years of life were associated with ADHD-related behaviors, specifically aggression, hyperactivity, and conduct problems.

IMPACT STATEMENT

Our results highlight the importance of primary lead prevention across childhood.

Meta-inhibition of ocular and gastrointestinal dysfunctions by phenolic-rich fraction of Croton zambsicus leaves in a rat model exposed to chronic mixed metals

PURPOSE

This study was aimed at investigating the protective effect of antioxidant-rich fraction of Croton zambsicus (C-ZAMB) leaves on ocular-gastrointestinal dysfunction in rats exposed to environmental mixed-metal (EOMABRSL).

MATERIALS AND METHODS

The rats were divided into five (n = 10) groups. Group I designates the control which received 0.5 mL of distilled water. Group II and III received 0.5 mL of EOMABRSL for 98 days (non-withdrawal) and 70 days (withdrawal for 28 days), respectively. Group IV received 0.5 mL EOMABRSL for 70 days and 400 mg/kg C-ZAMB fraction for 28 days. Group V received 400 mg/kg C-ZAMB only for 28 days via oral route.

RESULTS

Exposure of the animals to EOMARBSL for 98 days and 70 days significantly up-regulated the activities of ocular-gastrointestinal aldolase-reductase, α-amylase, α-glucosidase and eco-5¹-nucleotidase with corresponding depletion of lactate dehydrogenase activity. Furthermore, exposure to EOMABRSL significantly altered the antioxidant proteins with up-production of MDA content. Apparently, management with 400 mg/kg C-ZAMB fraction significantly inhibited the key markers linked with ocular-gastrointestinal disorders.

CONCLUSION

Hence, this study underscores the biochemical mechanisms for managing ocular-gastrointestinal lesions by 400 mg/kg C-ZAMB fraction on exposure to mixture of environmental metals.

Combining human and snail indicators for an integrative risk assessment of metal(loid)-contaminated soils

With the new soil uses such as land restoration and to protect wilderness, the human health risk assessment (HHRA) and environmental risk assessment (ERA) should be combined. Based on the relationships demonstrated between an indicator of soil quality, the land snail, and human exposure, the aim of this study is to examine the snail and human risk indicators for twenty-nine soils contaminated by metal(loid)s. HHRA was evaluated by both hazard quotient and carcinogenic risk. When the human health indicators were ranked as uncertain, they were weighted by bioaccessibility to refine the risk assessment. The ERA was performed with risk coefficient after ex situ snail exposure. The results showed strong and novel relationships between human health and environmental risk indicators that had never been found before. For 62% of the soils, both indicators revealed either a confirmed risk or an uncertain level of risk. Overall pollutants present greater risk for human than for environment, with 55 vs 28% of the studied soils classified in the proven risk, respectively. An original integrative risk assessment of polluted soils has been proposed, that shall help setting up relevant strategies to manage contaminated soils considering not only human but also environmental indicators of risk.

ICP-OES assisted determination of the metal content of some fruit juices from Yemen's market

The levels of Cd, Cr, Cu, Pb, Zn, Sn, and Fe of 37 samples of 6 types of fruit juices (orange, mango, guava, pineapple, peach, and mixed fruit) marketed by different brands and of easy access in Sana'a food stores, Yemen (2019) were evaluated using the inductively coupled plasma-optical emission spectrometry (ICP-OES) technique. Traces of chromium were detected in two fruit juices and cadmium in seven juices. One sample presented a highly elevated Pb-content. High level of tin, iron and zinc were detected in some fruit juices. Metal content in some fruit juices sold on the Yemeni market exceeded the permissible limits set by health organizations for drinking water. The origin of metal contamination could be likely linked to war condition even though it is difficult to be totally affirmative, so far. Fruit juices available on the Yemeni market are globally safe, nonetheless, further risk-based surveillance studies must be carried out to decrease child exposure to toxic metals from fruit juice sources.

Lead immobilization by phosphate in the presence of iron oxides: Adsorption versus precipitation

As a commonly used corrosion inhibitor, phosphate (PO₄) has a complicated effect on the fate and transport of lead (Pb) in drinking water systems. While the formation of pyromorphite has been recognized to be the major driving force of the Pb immobilization mechanism, the role of adsorption on iron oxides is still not clear. This study aims to clarify the contributions of adsorption and precipitation to Pb removal in a system containing both iron oxides and PO₄. A combination of batch experiments, X-ray absorption spectroscopy, infrared spectroscopy, and electron spectroscopy was employed to distinguish the adsorbed and precipitated Pb species. The results indicated that the adsorption of Pb on iron oxides still occurred even when the solution was supersaturated to pyromorphite (i.e., 5 mg/L P with 0.1-30 mg/L Pb in 0.01 M NaCl solution at neutral pH). In the tap water containing 0.92 mg/L P and 1 mg/L Pb, adsorption on iron oxides contributed more (62-67%) than precipitation (33-38%) in terms of Pb removal. Surprisingly, the pre-formed pyromorphite is transformed to adsorbed species after mixing with iron oxides in water for 24 h. The illustration of this transformation is important to understand the immobilization mechanisms and transport behaviors of Pb in drinking water systems after the utilization of PO₄.

Evaluation and updates to the Leggett model for pharmacokinetic modeling of exposure to lead in the workplace - Part I adjustments to the adult systemic model

California's Division of Occupational Safety and Health has initiated a process to update its standards for exposure to lead in workplaces. In support of this effort, the state's Office of Environmental Health Hazard Assessment evaluated the age-specific, bio-kinetic model of lead metabolism in humans, originally published by R.W. Leggett in 1993. This model was ultimately chosen for its physiologic realism and practicality in characterizing the relationship between air lead concentrations and blood lead levels in chronically exposed worker and its practicality in making necessary adjustments. Leggett's original model systematically under-predicts bone and blood levels in workers such that several adjustments to the parameters are needed to improve predictions for occupational exposure scenarios. The aim of this work is to incorporate new information about the bio-kinetics of lead in workers and to adjust the Leggett model to improve its predictions.The Leggett model was evaluated by comparing its predictions with information on lead concentrations in bone, blood, and urine from workers and other chronically exposed adults. Key model parameters were identified based upon a review of the relevant exposure assessment and modeling literature. Adjustments to the model parameters were made based on empirical evidence. They included reducing the level of lead in blood (BLL) where the rate of decrease in red blood cell binding begins and ends, lead accumulation rate in cortical bone, the rate of lead elimination in trabecular bone, and rate of lead transferred from diffusible plasma to urine. Regression methods and visual inspection of plotted data were used to assess the effect of adjustments on model predictions. When compared with the original, the adjusted Leggett model more accurately predicted lead concentrations observed in active and retired workers. Also, the adjusted Leggett model required less lead uptake to reach the same BLLs for BLLs less than 25 µg/dL and more time for BLLs to decline than the original Leggett model. These findings are important for defining an adequately protective occupational standard for lead exposure.

In vivo oral bioavailability of Pb sequestered in metal rich granules in bivalves

The present study was designed to evaluate in vivo the oral bioavailability of lead (Pb) present in the marine bivalve Dosinia exoleta. This infaunal clam, despite inhabiting in clean areas, presents Pb concentrations that are over the 1.5 mg kg^-1 wet weight limit for human consumption set by the European Commission. However, Pb is accumulated in this clam in the form of metal rich granules, and it has been shown to be unavailable for trophic transfer to a marine decapod, so it was hypothesised that it might be unavailable for human consumers as well. Twelve Sprague Dawley rats were fed during 14 days with a diet including control mussels (Mytilus galloprovincialis), D. exoleta, or mussels enriched in Pb to the same levels as those found in D. exoleta. Pb accumulation in different rat tissues (blood, bone, kidneys and liver) was analysed. It was observed that Pb assimilation from D. exoleta was about half of Pb assimilation from M. galloprovincialis, and absolute bioavailabilities were around 2% for M. galloprovincialis and 1% for D. exoleta. These results suggest that it might be possible to increase the limit for human consumption for this bivalve to 3 mg kg^-1 wet weight without representing an increase in the risk for consumers.

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

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

Lead Pellet Ingestion in 3 Children: Another Source for Lead Toxicity

Acute ingestions of spherical lead ammunition foreign bodies such as bullets and lead shot can cause acute blood lead level elevations and clinical symptoms necessitating emergency department evaluations and sometimes treatment. This article presents 3 cases of children ingesting lead ammunition, all receiving gastrointestinal (GI) decontamination and chelation therapy for significantly elevated blood lead level. Case-specific exposures and treatments for the lead ammunitions are presented. Radiographs documented lead pellet ingestion in all 3 cases. Pediatric patients absorb lead from the GI tract more quickly than adults and may necessitate more urgent evaluation and treatment than adolescents/adults. More rapid GI absorption has the potential to result in possible irreversible neurotoxicity and neurocognitive deficits as well as behavioral changes. Failure of lead foreign bodies to pass from the GI tract may require more aggressive interventions for their removal to prevent ongoing absorption. Emergency health care providers should be aware of alternative lead sources besides the most common source of paint, as these lead foreign bodies also need urgent evaluation and possibly treatment.

Food contamination as a pathway for lead exposure in children during the 2010-2013 lead poisoning epidemic in Zamfara, Nigeria

In 2010, an estimated 400 to 500 children died of acute lead poisoning associated with artisanal gold mining in Zamfara, Nigeria. Processing of gold ores containing up to 10% lead within residential compounds put residents, especially children, at the highest risk. Principal routes of exposure were incidental ingestion and inhalation of contaminated soil and dusts. Several Nigerian and international health organizations collaborated to reduce lead exposures through environmental remediation and medical treatment. The contribution of contaminated food to total lead exposure was assessed during the environmental health response. Objectives of this investigation were to assess the influence of cultural/dietary habits on lead exposure pathways and estimate the contribution of contaminated food to children's blood lead levels (BLLs). A survey of village dietary practices and staple food lead content was conducted to determine dietary composition, caloric intakes, and lead intake. Potential blood lead increments were estimated using bio-kinetic modeling techniques. Most dietary lead exposure was associated with contamination of staple cereal grains and legumes during post-harvest processing and preparation in contaminated homes. Average post-harvest and processed cereal grain lead levels were 0.32mg/kg and 0.85mg/kg dry weight, respectively. Age-specific food lead intake ranged from 7 to 78μg/day. Lead ingestion and absorption were likely aggravated by the dusty environment, fasting between meals, and nutritional deficiencies. Contamination of staple cereal grains by highly bioavailable pulverized ores could account for as much as 11%-34% of children's BLLs during the epidemic, and were a continuing source after residential soil remediation until stored grain inventories were exhausted.

Sub-chronic inhalation of lead oxide nanoparticles revealed their broad distribution and tissue-specific subcellular localization in target organs

BACKGROUND

Lead is well known environmental pollutant, which can cause toxic effects in multiple organ systems. However, the influence of lead oxide nanoparticles, frequently emitted to the environment by high temperature technological processes, is still concealed. Therefore, we investigate lead oxide nanoparticle distribution through the body upon their entry into lungs and determine the microscopic and ultramicroscopic changes caused by the nanoparticles in primary and secondary target organs.

METHODS

Adult female mice (ICR strain) were continuously exposed to lead oxide nanoparticles (PbO-NPs) with an average concentration approximately 106 particles/cm3 for 6 weeks (24 h/day, 7 days/week). At the end of the exposure period, lung, brain, liver, kidney, spleen, and blood were collected for chemical, histological, immunohistochemical and electron microscopic analyses.

RESULTS

Lead content was found to be the highest in the kidney and lungs, followed by the liver and spleen; the smallest content of lead was found in brain. Nanoparticles were located in all analysed tissues and their highest number was found in the lung and liver. Kidney, spleen and brain contained lower number of nanoparticles, being about the same in all three organs. Lungs of animals exposed to lead oxide nanoparticles exhibited hyperaemia, small areas of atelectasis, alveolar emphysema, focal acute catarrhal bronchiolitis and also haemostasis with presence of siderophages in some animals. Nanoparticles were located in phagosomes or formed clusters within cytoplasmic vesicles. In the liver, lead oxide nanoparticle exposure caused hepatic remodeling with enlargement and hydropic degeneration of hepatocytes, centrilobular hypertrophy of hepatocytes with karyomegaly, areas of hepatic necrosis, occasional periportal inflammation, and extensive accumulation of lipid droplets. Nanoparticles were accumulated within mitochondria and peroxisomes forming aggregates enveloped by an electron-dense mitochondrial matrix. Only in some kidney samples, we observed areas of inflammatory infiltrates around renal corpuscles, tubules or vessels in the cortex. Lead oxide nanoparticles were dispersed in the cytoplasm, but not within cell organelles. There were no significant morphological changes in the spleen as a secondary target organ. Thus, pathological changes correlated with the amount of nanoparticles found in cells rather than with the concentration of lead in a given organ.

CONCLUSIONS

Sub-chronic exposure to lead oxide nanoparticles has profound negative effects at both cellular and tissue levels. Notably, the fate and arrangement of lead oxide nanoparticles were dependent on the type of organs.

Measurement of soil lead bioavailability and influence of soil types and properties: A review

Lead (Pb) is a widespread heavy metal which is harmful to human health, especially to young children. To provide a human health risk assessment that is more relevant to real conditions, Pb bioavailability in soils is increasingly employed in the assessment procedure. Both in vivo and in vitro measurements for lead bioavailability are available. In vivo models are time- consuming and expensive, while in vitro models are rapid, economic, reproducible, and reliable while involving more uncertainties. Uncertainties in various measurements create difficulties in accurately predicting Pb bioavailability, resulting in the unnecessary remediation of sites. In this critical review, we utilised available data from in vivo and in vitro studies to identify the key parameters influencing the in vitro measurements, and presented uncertainties existing in Pb bioavailability measurements. Soil type, properties and metal content are reported to influence lead bioavailability; however, the differences in methods for assessing bioavailability and the differences in Pb source limit one's ability to conduct statistical analyses on influences of soil factors on Pb bioavailability. The information provided in the review is fundamentally useful for the measurement of bioavailability and risk assessment practices.

Evaluation of exposure to lead from drinking water in large buildings

Lead results from 78,971 water samples collected in four Canadian provinces from elementary schools, daycares, and other large buildings using regulatory and investigative sampling protocols were analyzed to provide lead concentration distributions. Maximum concentrations reached 13,200 and 3890 μg/L following long and short stagnation periods respectively. High lead levels were persistent in some large buildings, reflected by high median values considering all taps, or specific to a few taps in the building. Simulations using the Integrated Uptake Biokinetic (IEUBK) model and lead concentrations after 30 min of stagnation in the dataset showed that, for most buildings, exposure to lead at the tap does not increase children's blood lead levels (BLLs). However, buildings or taps with extreme concentrations represent a significant health risk to young children attending school or daycare, as the estimated BLL far exceeded the 5 μg/dL threshold. Ingestion of water from specific taps could lead to acute exposure. Finally, for a few taps, the total daily lead intake reached the former World Health Organization (WHO) tolerable level for adults, suggesting potential health risks.

Paediatric pharmacokinetics: key considerations

A number of anatomical and physiological factors determine the pharmacokinetic profile of a drug. Differences in physiology in paediatric populations compared with adults can influence the concentration of drug within the plasma or tissue. Healthcare professionals need to be aware of anatomical and physiological changes that affect pharmacokinetic profiles of drugs to understand consequences of dose adjustments in infants and children. Pharmacokinetic clinical trials in children are complicated owing to the limitations on blood sample volumes and perception of pain in children resulting from blood sampling. There are alternative sampling techniques that can minimize the invasive nature of such trials. Population based models can also limit the sampling required from each individual by increasing the overall sample size to generate robust pharmacokinetic data. This review details key considerations in the design and development of paediatric pharmacokinetic clinical trials.

Factors controlling the oral bioaccessibility of anthropogenic Pb in polluted soils

In human risk assessment, ingestion of soil is considered a major route of toxic Pb exposure. A large body of research has focussed on the measurement of the 'total' Pb contents in sediment, soil and dust as a measure for the exposure to lead. We report that Pb bioaccessibility (i.e. the maximum bioavailability), determined with an in vitro test, does not necessarily depend on the total Pb content. In contrast, the Pb bioaccessibility is initially controlled by the chemical form and particle size of the Pb source, which in turn determine its solubility. Furthermore, when anthropogenic Pb resides within the soil, it may form new, more stable, minerals and/or binds to organic matter, clay, reactive iron or other reactive phases, changing its bioaccessibility. The bioaccessible Pb fraction of 28 soils, polluted with various Pb sources (including residues of Pb bullets and pellets, car battery Pb, city waste and diffuse Pb), was determined with an in vitro-test and varied from 0.5% to 79.0% of total Pb. The highest Pb bioaccessibility (60.7% to 79.0%) was measured in soils polluted with residues of Pb bullets and pellets (shooting range), while the lowest Pb bioaccessibility (0.5%-8.3%) was measured in soils polluted with city waste (including remnants of Pb glazed potsherds and rooftiles, Pb based paint flakes, and Pb sheets). Bioaccessibility of Pb was correlated with pH, organic matter and reactive Fe. These results indicate that soil characteristics play an important role in the oral bioaccessibility of lead in polluted soils. Instead of basing human risk assessment solely on total Pb contents we propose to incorporate in vitro bioaccessibility tests, taking factors such as soil pH, organic matter content and reactive iron content into account. This approach will result in a better insight into the actual risks of Pb polluted soils to children.

Associations between blood lead level and substance use and sexually transmitted infection risk among adults in the United States

The effects of low-level lead exposure on neuropsychological status in the United States (US) general adult population have been reported, and the relationship between neuropsychiatric dysfunction and health risk behaviors including substance use and sexual risk taking is well established. However, the potential influence of lead exposure on risk-taking behavior has received little attention. Using the National Health and Nutrition Examination Survey (NHANES) 2005-2010, we estimated multivariable logistic regression models to measure odds ratios (ORs) and 95% confidence intervals (CIs) for the cross-sectional associations between blood lead level and risk behaviors including binge drinking, drug use, and indicator of sexually transmitted infection (STI) risk. STI indicators included past 12 month sexual risk behaviors (age mixing with partners who were at least five years younger or older and multiple partnerships), self-reported STI, and biologically-confirmed herpes simplex virus type 2 (HSV-2) infection. Dose-response like relationships were observed between blood lead and substance use, age mixing with younger and older partners, self-reported STI, and HSV-2. In addition, participants with lead levels in highest quartile versus those with levels in the lowest quartile had over three times the odds of binge drinking and over twice the odds of injection drug or cocaine use in the past 12 months, while being in one of the top two quartiles was significantly associated with 30-70% increased odds of multiple partnerships, sex with older partners, and self-reported and biologically confirmed STI. Results from this study suggested that lead exposure may contribute to substance use, sexual risk-taking, and STI. However, given limitations inherent in the cross-sectional nature of the study, additional studies that use longitudinal data and measure detailed temporal information are warranted.

Paediatric oral biopharmaceutics: key considerations and current challenges

The complex process of oral drug absorption is influenced by a host of drug and formulation properties as well as their interaction with the gastrointestinal environment in terms of drug solubility, dissolution, permeability and pre-systemic metabolism. For adult dosage forms the use of biopharmaceutical tools to aid in the design and development of medicinal products is well documented. This review considers current literature evidence to guide development of bespoke paediatric biopharmaceutics tools and reviews current understanding surrounding extrapolation of adult methodology into a paediatric population. Clinical testing and the use of in silico models were also reviewed. The results demonstrate that further work is required to adequately characterise the paediatric gastrointestinal tract to ensure that biopharmaceutics tools are appropriate to predict performance within this population. The most vulnerable group was found to be neonates and infants up to 6 months where differences from adults were greatest.

Experimental determination of the oral bioavailability and bioaccessibility of lead particles

In vivo estimations of Pb particle bioavailability are costly and variable, because of the nature of animal assays. The most feasible alternative for increasing the number of investigations carried out on Pb particle bioavailability is in vitro testing. This testing method requires calibration using in vivo data on an adapted animal model, so that the results will be valid for childhood exposure assessment. Also, the test results must be reproducible within and between laboratories. The Relative Bioaccessibility Leaching Procedure, which is calibrated with in vivo data on soils, presents the highest degree of validation and simplicity. This method could be applied to Pb particles, including those in paint and dust, and those in drinking water systems, which although relevant, have been poorly investigated up to now for childhood exposure assessment.

Status of toxic metals in biological samples of diabetic mothers and their neonates

The mechanism of transport of trace elements from the mother to the newborn is still not well known. The aim of present study was to compare the status of trace toxic elements, arsenic (As), cadmium (Cd), and lead (Pb) in biological samples (whole blood, urine and scalp hair) of insulin-dependent diabetic mothers (age ranged 30-40) and their newly born infants (n = 76). An age and socioeconomics matched 68 nondiabetic mothers and their infants, residing in the same locality, who were selected as referents. The elemental concentrations in all three biological samples were determined by an electrothermal atomic absorption spectrometer, prior to microwave-assisted acid digestion. The mean values of As, Cd, and Pb in all biological samples of diabetic mothers and their infants were significantly higher as compared to the referent mother-infant pair samples (p < 0.01). The high levels of As, Cd, and Pb in biological samples of diabetic women may play a role in the pathogenesis of diabetes mellitus and impacts on their neonates.

Assessing Cd, Pb, Zn human bioaccessibility in smelter-contaminated agricultural topsoils (northern France)

The extractability of Cd, Pb, and Zn was investigated in contaminated agricultural topsoils located in an area highly affected by the past atmospheric emissions of two smelters in northern France in order to assess their mobility and human bioaccessibility. The determination of Cd, Pb, and Zn bioaccessibility (Unified Barge Method, in vitro test) was made to evaluate the absolute trace element (TE) bioavailability. The results highlighted differences in bioaccessibility between Cd, Pb, and Zn (Cd > Pb > Zn). The mean values of the bioaccessible fractions of Cd, Pb, and Zn during the gastric phase were 82, 55, and 33%, respectively, of the pseudototal concentrations, whereas during the gastrointestinal phase, the bioaccessible fractions of metals decreased to 45, 20, and 10%, respectively. Stepwise multiple regression analysis showed that human bioaccessibility was affected by various physicochemical parameters (i.e., sand, carbonates, organic matter, assimilated P, free Al oxides, and pseudototal Fe contents). Sequential extractions were performed as an indication of the TE availability in these soils. Cadmium occurred in the more available fractions, Pb was mostly present as bound by oxides, and a significant contribution to the pseudototal Zn concentration was defined as the unavailable residual form related to the crystalline structures of minerals. The concepts of bioavailability and bioaccessibility are important for quantifying the risks associated with exposure to environmental pollutants and providing more realistic information for human health.

Effect of age-dependent exposure to lead on hepatotoxicity and nephrotoxicity in male rats

Lead is known to induce a broad range of physiological, biochemical, and behavioral dysfunctions in laboratory animals and humans. This includes age-specific variations in absorption, retention, and tissue distribution of lead. This study was carried out to investigate the effects of chronic exposure to lead (50 mg/L) on liver and kidneys of two different age groups of male rats treated with lead from delivery until puberty period (40 days) and postpuberty period (65 days). For this purpose, the concentrations of thiobarbituric acid reactive substance (TBARS), total thiol groups (SH), and superoxide dismutase (SOD) activity were measured in the liver and kidney of rats. Renal function was analyzed by determining creatinine, acid uric, and urea. Plasma activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and albumin were determined spectrophotometrically to evaluate hepatic function. These markers of damage were determined to assess the level of toxicity in these animals. Our results clearly show that the administration of lead produces oxidative damage in liver and kidney, as strongly suggested by the significant increase in TBARS, decrease in total SH, and the alteration of SOD activity. In young lead-exposed animals, lead-induced perturbations on the synthetic function of the liver and the kidney were more pronounced. However, nephropathy is evident for adult lead-exposed animals. It is concluded that lead induces severe hepatic and renal toxicity, which depends on the age of the animals and the target organ.

Pharmacokinetic predictions in children by using the physiologically based pharmacokinetic modelling

Nowadays, 50-90% of drugs used in children have never been actually studied in this population. Consequently, either our children are often exposed to the risk of adverse drug events or to lack of efficacy, or they are unable to benefit from a number of therapeutic advances offered to adults, as no clinical study has been properly performed in children. Actually the main methods used to calculate the dose for a child are based on allometric methods taking into account different categories of age, the body weight and/or the body surface area. Unfortunately, these calculation methods consider the children as small adults, which is not the case. Physiologically based pharmacokinetics is one way to integrate the physiological changes occurring in the childhood and to anticipate their impact on the pharmacokinetic processes: absorption, distribution, metabolism and excretion/elimination. From different examples, the application of this modelling approach is discussed as a possible and valuable method to minimize the ethical and technical difficulties of conducting research in children.

Pilot study of temporal variations in lead bioaccessibility and chemical fractionation in some Chinese soils

The effect of ageing, following the addition of approximately 400mgkg(-1) lead (Pb) as Pb(NO(3))(2), on Pb bioaccessibility was examined in five typical Chinese soils using a physiologically based extraction test. Sequential extraction was employed to identify the source fraction(s) of bioaccessible Pb in the soils. Pb bioaccessibility decreased exponentially to nearly steady levels in mildly acidic or alkali (pH 6.09-7.43) soils, for both gastric (69.91-71.75%) and small intestinal (7.53-9.63%) phases within the first 2-4 weeks and 1-2 months of incubation, respectively; however, it took only 1-2 weeks for strongly acidic ( approximately pH 4.5) soils to reach nearly steady levels of Pb bioaccessibility (73.01-74.46% and 10.30-10.98% in the gastric and small intestinal phases, respectively). In addition to the water-soluble and exchangeable fractions, the carbonate fraction of mildly acidic or alkali soils appeared to be a third main source of bioaccessible Pb in the small intestinal phase; however, bioaccessible Pb was likely to derive principally from Pb in the water-soluble and exchangeable fractions of strongly acidic soils. Bioaccessible Pb in the gastric phase appeared to derive from all the fractions in all five studied soils, even the residual fraction.

Reciprocal inhibition of Cd and Pb sulfocomplexes for uptake in Caco-2 cells

Cadmium-lead interactions for uptake were studied in the TC7 clone of human enterocytic-like Caco-2 cells as a function of inorganic metal speciation. We have previously shown that Cd uptake in these cells involves both the free cation Cd2+ and chlorocomplex (CdCln(2-n)) species. Here we show 1.9 times higher uptake levels for 109CdCln(2-n) compared to 210PbCln(2-n). Reciprocal inhibitions of chlorocomplexes were observed with a much higher inhibitory effect of Cd compared to Pb. Replacing Cl- by NO3- increased both the level of aquo ion 109Cd2+ and 109Cd accumulation. In contrast, higher levels of 210Pb2+ did not favor 210Pb uptake. For both metals, higher uptake data were recorded in the presence of SO4(2-), leading to sulfocomplex formation, compared with Cl-. Reciprocal inhibitions were minimal at high-cation levels but were significant and comparable in the presence of sulfo-complexes. We conclude that, in addition to Cd2+ (but not Pb2+), sulfocomplexes of both metals would preferentially be taken up compared to chlorocomplexes. NRAMP2 is not involved in Pb2+ uptake, and the NRAMP2-mediated Cd2+ uptake is insensitive to Pb. Uptake of Pb chlorocomplexes could involve specific mechanisms but of very low affinity, whereas uptake of Pb sulfocomplexes occurs with high affinity.

Assessment of the effectiveness of different phosphorus fertilizers to remediate Pb-contaminated soil using in vitro test

The addition of P-containing amendments was found to effectively reduce the bioaccessibility of Pb in soils to the human, using an in vitro test. For all treatments with P additions, the removal of soluble Pb in the small intestinal phase was observed. The effectiveness of various P treatments in the small intestinal phase generally followed this order at the equivalent P addition level: hydroxyapatite (HA)>phosphate rock (PR)>HA+single super-phosphate (SSP)>SSP. The relatively low effectiveness of P amendments at the gastric phase may be explained by the high solubility of pyromorphite at relatively low pH of 1.7, compared with that at the neutral small intestinal pH. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in the gastric phase, possibly due to its highest solubility at pH 1.7. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in gastric phase, possibly due its highest solubility at pH 1.7. However, in the small intestinal phase, SSP appears to be the least effective amendment, possibly due to its lowest Ca supply level to replace Pb form exchangeable sites, as reflected by its lowest molar Ca/P ratio of 1:2. The disagreement of the sequential extraction results with that of the in vitro test results indicated that the sequential extraction was not suitable for the assessment of the effect of P addition on minimizing the bioaccessibility of Pb to human due to the formation of pyromorphite during the extraction procedure. Results from this study also suggested that the time required for the in vitro test might be shortened for fast screening.

Role of biokinetics in risk assessment of drugs and chemicals in children

Whether children incur different risks from xenobiotics than adults will depend on the exposure, biokinetics, and dynamics of compound. In this paper, current knowledge on developmental physiology and possible effects on biokinetics are evaluated and the role of biokinetics in risk assessment both for drugs and chemicals is discussed. It is concluded that most dramatic age-related physiological changes that may affect biokinetics occur in the first 6-12 months of age. The difference in internal exposure between children and adults can generally be predicted from already known developmental physiological differences. However, for risk assessment it will also be necessary to determine whether internal exposure is within the drug's therapeutic window or if it will exceed the NOAEL of a chemical. Furthermore, the effects of internal exposure of potentially harmful compounds on developing organ systems is of utmost importance. However, knowledge on this aspect is very limited. Risk assessment in children could be improved by: (1) application of pediatric PBPK-models in order to gain insight into internal exposure in children, (2) studies in juvenile animals for studying effects on developing systems, and (3) extrapolation of knowledge on the relationship between internal exposure and dynamics for drugs to other chemicals.

Toxicity of environmental lead and the influence of intestinal absorption in children

Exposure to metals, particularly lead, remains a widespread issue that is associated with historical and current industrial practices. Whereas the toxic properties of metals are well described, exposure to metals per se is only one of many factors contributing to elevated blood metal concentrations and their consequent health effects in humans. The absorbed dose of metal is affected by geochemical, biochemical, and physiological parameters that influence the rate and extent of absorption. In children, the interplay among these factors can be of critical importance, especially when biochemical and physiological processes might not have matured to their normal adult status. Such immaturity represents an elevated risk to metal-exposed children because they might be more susceptible to enhanced absorption, especially via the oral route. This review brings together the more recent findings on the physiological mechanisms of metal absorption, especially lead, and examines several models that can be useful in assessing the potential for metal uptake in children.

Assessing remedial effectiveness through the blood lead:soil/dust lead relationship at the Bunker Hill Superfund Site in the Silver Valley of Idaho

The 21 square mile Bunker Hill Superfund Site in northern Idaho includes several thousand acres of contaminated hillsides and floodplain, a 365-acre abandoned lead/zinc smelter and is home to more than 7000 people in 5 residential communities. Childhood lead poisoning was epidemic in the 1970s with >75% of children exceeding 40 microg/dl blood lead. Health response activities have been ongoing for three decades. In 1991, a blood lead goal of 95% of children with levels less than 10 microg/dl was adopted. The cleanup strategy, based on biokinetic pathways models, was to reduce house dust lead exposure through elimination of soil-borne sources. An interim health intervention program, that included monitoring blood lead and exposures levels, was instituted to reduce exposures through parental education during the cleanup. In 1989 and 2001, 56% and 3% of children, respectively, exceeded the blood lead criteria. More than 4000 paired blood lead/environmental exposure observations were collected during this period. Several analyses of these data were accomplished. Slope factors derived for the relationship between blood lead, soil and dust concentrations are age-dependent and similar to literature reported values. Repeat measures analysis assessing year to year changes found that the remediation effort (without intervention) had approximately a 7.5 microg/dl effect in reducing a 2-year-old child's mean blood lead level over the course of the last ten years. Those receiving intervention had an additional 2-15 microg/dl decrease. Structural equations models indicate that from 40 to 50% of the blood lead absorbed from soils and dusts is through house dust with approximately 30% directly from community-wide soils and 30% from the home yard and immediate neighborhood. Both mean blood lead levels and percent of children to exceed 10 microg/dl have paralleled soil/dust lead intake rates estimated from the pathways model. Application of the IEUBK model for lead indicates that recommended USEPA default parameters overestimate mean blood lead levels, although the magnitude of over-prediction is diminished in recent years. Application of the site-specific model, using the soil and dust partitions suggested in the pathways model and an effective bioavailability of 18%, accurately predicts mean blood lead levels and percent of children to exceed 10 microg/dl throughout the 11-year cleanup period. This reduced response rate application of the IEUBK is consistent with the analysis used to originally develop the cleanup criteria and indicates the blood lead goal will be achieved.

The estimation of the bioaccessibility of heavy metals in soils using artificial biofluids by two novel methods: mass-balance and soil recapture

The possible human health effects resulting from the ingestion of soil bound heavy metals can be poorly estimated if concentration of total metals in soil, rather than bioavailable fraction of metals, are incorporated into dose calculations. Information regarding bioavailability often is obtained from animal studies, which are not easily conducted and still may not represent human conditions. A rapid simulation of the bioaccessible fraction of contaminant in a soil, in which that fraction is mass soluble in gastrointestinal tract fluids, has been employed in an in vitro sequential extraction technique. Using a mass-balance analytical approach to measure bioaccessibility in four soils, the results indicated that each metal had a bioaccessible fraction less than its total metal content. Lead (Pb) in Standard Reference Material, Montana SRM 2710, was found to be 62 +/- 1% bioaccessible; Pb in contaminated soil collected from Bunker Hill, ID, USA was 70 +/- 11%. Lead in Jersey City, NJ, USA slag material was only 39 +/- 14% bioaccessible while Pb in a residential soil was 69%. Arsenic (As) and chromium (Cr) data from select soils also have bioaccessibility less than the corresponding total metal in soil, with 41 +/- 2% As in a residential soil, 66 +/- 8% As in SRM 2710, and 34 +/- 14% Cr in Jersey City slag material. Recovering the soil at the end of the in vitro extraction allowed for the determination of the insoluble fraction of total metal in soil. This recaptured soil metal mass was a valuable measurement since it greatly reduced analysis and therefore labor and time, yet also provided a reasonable estimate of bioaccessibility. It also allowed for calculation of a bioaccessibility value in a soil containing very low metal mass, which would otherwise have resulted in a non-detectable concentration at the dilutions required in the synthetic human biofluid system.

Uses and limits of empirical data in measuring and modeling human lead exposure

This paper examines the uses and limits of empirical data in evaluating measurement and modeling approaches to human lead exposure. Empirical data from experiment or observation or both have been used in studies of lead exposure. For example, experimental studies have elucidated and quantified physiologic or biokinetic parameters of lead exposure under controlled conditions. Observation, i.e., epidemiology, has been widely applied to study population exposures to lead. There is growing interest in the use of lead exposure prediction models and their evaluation before use in risk assessment. Empirical studies of lead exposure must be fully understood, especially their limits, before they are applied as "standards" or reference information for evaluation of exposure models, especially the U.S. Environmental Protection Agency's lead biokinetic model that is a focus of this article. Empirical and modeled datasets for lead exposure may not agree due to a) problems with the observational data or b) problems with the model; caution should be exercised before either a model or observational data are rejected. There are at least three sources of discordance in cases where there is lack of agreement: a) empirical data are accurate but the model is flawed; b) the model is valid but reference empirical data are inaccurate; or c) neither empirical data nor model is accurate, and each is inaccurate in different ways. This paper evaluates some of the critical empirical input to biokinetic models, especially lead bioavailability.