The use of a physiologically-based extraction test to assess relationships between bioaccessible metals in urban soil and neurodevelopmental conditions in children

Assessment of heavy metal contamination in street dust: concentrations, bioaccessibility, and human health risks in coal mine and thermal power plant complex

Coal mining has also been associated with adverse environmental and health impacts including cancer and respiratory disorders, with the presence of thermal power plants exacerbating the problem of heavy metal pollution. Minimal studies have been conducted on the environmental impacts, health risks, and bioaccessibility of heavy metals in coal mine areas. Consequently, samples of street dust were collected from different locations in the Singrauli mine complex and analysed. Heavy metals (Cu, Ni, Zn, Cr, Co, As, and Mo) were found to be higher than the background concentration, with the maximum concentration was found in areas close to the Thermal Power Plants, like Near Vindyachal TPP, Near Shakti Nagar TPP, and Anpara. The highest geo-accumulation index value was found for Co, Mo, Zn, and As, indicating moderate to strong pollution levels. Health risk assessment (for both adults and children) revealed that Cr and Fe posed significantly higher Hazard Quotient and Hazard Index (HI) values, indicating significant non-carcinogenic threats. Moreover, Carcinogenic Risk (CR) values for Cd, Cr, and Ni indicated a risk of carcinogenicity to the public exposed to road dust. The study also examined the bioaccessibility of the metals, which showed that the gastric phase accumulated a higher percentage of Ni (42.52%), Pb (34.79%), Co (22.22%), As (20%) and Cu (15%) than the intestinal phase. Strong positive correlation was observed between metal concentration (Cu, Pb, Cr, Fe, Zn, and Mn), HI, and CR of adult and child, while bioaccessibility of intestinal phase was positively correlated with gastric phase of metals (Cu, Ni, Co, As, and Mn).

Disparities in Toxic Chemical Exposures and Associated Neurodevelopmental Outcomes: A Scoping Review and Systematic Evidence Map of the Epidemiological Literature

BACKGROUND

Children are routinely exposed to chemicals known or suspected of harming brain development. Targeting Environmental Neuro-Development Risks (Project TENDR), an alliance of > 50 leading scientists, health professionals, and advocates, is working to protect children from these toxic chemicals and pollutants, especially the disproportionate exposures experienced by children from families with low incomes and families of color.

OBJECTIVE

This scoping review was initiated to map existing literature on disparities in neurodevelopmental outcomes for U.S. children from population groups who have been historically economically/socially marginalized and exposed to seven exemplar neurotoxicants: combustion-related air pollution (AP), lead (Pb), mercury (Hg), organophosphate pesticides (OPs), phthalates (Phth), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs).

METHODS

Systematic literature searches for the seven exemplar chemicals, informed by the Population, Exposure, Comparator, Outcome (PECO) framework, were conducted through 18 November 2022, using PubMed, CINAHL Plus (EBSCO), GreenFILE (EBSCO), and Web of Science sources. We examined these studies regarding authors' conceptualization and operationalization of race, ethnicity, and other indicators of sociodemographic and socioeconomic disadvantage; whether studies presented data on exposure and outcome disparities and the patterns of those disparities; and the evidence of effect modification by or interaction with race and ethnicity.

RESULTS

Two hundred twelve individual studies met the search criteria and were reviewed, resulting in 218 studies or investigations being included in this review. AP and Pb were the most commonly studied exposures. The most frequently identified neurodevelopmental outcomes were cognitive and behavioral/psychological. Approximately a third (74 studies) reported investigations of interactions or effect modification with 69% (51 of 74 studies) reporting the presence of interactions or effect modification. However, less than half of the studies presented data on disparities in the outcome or the exposure, and fewer conducted formal tests of heterogeneity. Ninety-two percent of the 165 articles that examined race and ethnicity did not provide an explanation of their constructs for these variables, creating an incomplete picture.

DISCUSSION

As a whole, the studies we reviewed indicated a complex story about how racial and ethnic minority and low-income children may be disproportionately harmed by exposures to neurotoxicants, and this has implications for targeting interventions, policy change, and other necessary investments to eliminate these health disparities. We provide recommendations on improving environmental epidemiological studies on environmental health disparities. To achieve environmental justice and health equity, we recommend concomitant strategies to eradicate both neurotoxic chemical exposures and systems that perpetuate social inequities. https://doi.org/10.1289/EHP11750.

Geochemical composition and potential health risks of geophagic materials: an example from a rural area in the Limpopo Province of South Africa

Geophagy is a common practice among rural population of the Fetakgomo Tubatse Local Municipality area in the Limpopo Province of South Africa. Although, the practice might be beneficial to the health of the consumers, its negative effects could overshadow the positive effects and might lead to detrimental health issues. The present work sought to investigate the geochemical composition as well as pH and organic matter (OM) content of geophagic materials commonly consumed in the study area. Furthermore, assessment of the potential health risk of the materials on geophagic individuals was also considered. Twelve samples were collected in the study area and analysed by X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for major and trace elements composition. The results showed higher concentrations of non-essential elements (e.g., As, Cr, Pb) than the proposed recommended daily standards intake, suggesting a potential health risk. The alkaline nature (pH 6.80 to 9.22) of the studied samples might affect the bioacessibility of some essential elements. Furthermore, the OM content (> 0.7%) observed in some of the studied samples may retain pathogenic micro-organisms detrimental to health. Although As and Cr presented a low bioaccessible fraction (< 16.0%), health risk assessment revealed that their concentrations represented a hazard (HQ > 1) and might induce non-carcinogenic health threats to geophagic individuals. Based on the geochemical analysis, pH and OM content as well as health risk assessment findings, the studied geophagic materials are not considered suitable for human consumption. The practice should therefore be discouraged amongst the population in the study area to avoid possible detrimental health issues.

Health risk assessment of heavy metals in road dust from the fourth-tier industrial city in central China based on Monte Carlo simulation and bioaccessibility

Health risks caused by heavy metal (HM) exposure in road dust has attracted extensive attention, but few studies have focused on the health risks of residents living in small- and medium-sized cities with rapid industrialization and urbanization. Thus, 140 road dust samples were collected across Anyang, a typical fourth-tier industrial city in central China, which were analysed for 10 different HMs (Mn, Zn, Pb, V, Cr, As, Cd, Ni, Cu and Co). Monte Carlo simulation and bioaccessibility were used to quantify the health risks of heavy metals comprehensively in road dust. Results revealed a remarkable accumulation of Mn, Zn, Pb, Cd and Cu. According to the Geo-accumulation index and potential ecological risk index, Cd was priority control pollutant. Moreover, 55.0% of the road dust samples reached heavily polluted level, and 52.86% of the samples were at high ecological risk levels. These results illustrated that HM contamination was serious and universal in the road dust of Anyang. The occurrences of HMs were allocated to traffic emissions, natural sources, industrial activities and agricultural activities with contribution rates of 35.4%, 6.0%, 41.6% and 17.0%, respectively. Except for Zn in the gastric phase, all other HMs had relatively low bioaccessibilities in the gastrointestinal system, usually less than 20%. The bioaccessibilities of most HMs were higher in the gastric phase, except for Cr, Ni and Cu, which remained higher in the intestinal phase. The non-carcinogenic risk and carcinogenic risk were remarkably reduced when considering the HM bioaccessibilities in the gastrointestinal system, especially for adults. The outcomes of this paper are valuable for understanding HM contamination in road dust and highlight the importance of risk assessment for populations living in the fourth- and fifth-tier cities.

Heavy metal(loid)s in agricultural soil from main grain production regions of China: Bioaccessibility and health risks to humans

Unintentional ingestion of metal-contaminated soils may pose a great threat to human health. To accurately evaluate the health risks of heavy metal(loid)s in soils, their bioaccessibility has been widely determined by in vitro assays and increasingly employed to optimize the assessment parameters. Given that, using meta-analysis, we analyzed the literature on farmland heavy metal(loid)s (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in Chinese main grain production regions, and collected their total and bioaccessibility data to accurately assess their human health risks. Monte Carlo simulation was used to reduce the uncertainty in metal concentration, intake rate, toxicity coefficient, and body weight. We found that the mean concentration (0.47 mg/kg) and geological accumulation index (I_geo, 0-5.24) of Cd were the priority position of controlling metals. Moreover, children are more vulnerable to carcinogenic risks than adults. Soil mineralogy, physicochemical properties, Fe, and the types of in vitro assays are the influencing factors of bioaccessibility discrepancy. Furthermore, appropriate bioaccessibility determination methods can be adapted according to the differences in ecological receptors for the risk assessment, like developing a "personalized assessment" scheme for polluted farmland soil management. Collectively, bioaccessibility-based models may provide an accurate and effective approach to human health risk assessment.

Trace Metal(loid) Migration from Road Dust to Local Vegetables and Tree Tissues and the Bioaccessibility-Based Health Risk: Impacts of Vehicle Operation-Associated Emissions

Traffic activities release large amounts of trace metal(loid)s in urban environments. However, the impact of vehicle operation-associated emissions on trace metal(loid) enrichment in road dust and the potential migration of these trace metal(loid)s to the surrounding environment remain unclear. We evaluated the contamination, sequential fraction, and bioaccessibility of trace metal(loid)s in urban environments by assessing their presence in road dust, garden vegetables, and tree tissues, including bark and aerial roots, at a traffic-training venue impacted by vehicle operation emissions and, finally, calculated the bioaccessibility-based health risk. The results indicated a significant accumulation of trace metal(loid)s in road dust, with the highest lead (Pb), cadmium (Cd), and antimony (Sb) concentrations in the garage entrance area due to higher vehicle volumes, frequent vehicle starts and stops, and lower speeds. Aerial roots exposed to hill start conditions exhibited the highest Pb, Zn, and Sb levels, potentially caused by high road dust resuspension, confirming that this tree tissue is an appropriate bioindicator. Sequential extraction revealed high percentages of carbonate-, Fe/Mn oxide-, and organic/sulphide-associated fractions of Pb, copper (Cu), and zinc (Zn) in road dust, while most Cd, Cr, Ni, and Sb occurred as residual fractions. According to the potential mobilizable fractions in sequential extraction, the in vitro gastrointestinal method could be more suitable than the physiologically based extraction test to evaluate the bioaccessibility-related risk of traffic-impacted road dust. The bioaccessibility-based health risk assessment of the road dust or soil confirmed no concern about noncarcinogenic risk, while the major risk originated from Pb although leaded gasoline was prohibited before the venue establishment. Furthermore, the cancer risks (CRs) analysis showed the probable occurrence of carcinogenic health effects from Cd and Ni to adults and from Cd, Cr, and Ni to children. Furthermore, the Cd and Pb concentrations in the edible leaves of cabbage and radish growing in gardens were higher than the recommended maximum value. This study focused on the health risks of road dust directly impacted by vehicle emissions and provides accurate predictions of trace metal(loid) contamination sources in the urban environment.

Potential use of hydroxyapatite combined with hydrated lime or zeolite to promote growth and reduce cadmium transfer in the soil-celery-human system

Although hydroxyapatite (HAP) can prominently lower Cd uptake by celery from Cd-polluted soil, its high application rates in reality may lead to high cost and potential environmental risk. Therefore, we aimed to clarify whether combined amendments of HAP and another low-cost material (hydrated lime, corn straw-derived biochar, or zeolite) with reduced application rate of each single amendment could significantly decrease Cd transfer in soil-celery-human system without side effect on celery growth through a pot experiment. Results revealed that adding biochar, HAP, zeolite, or combined amendments had no obvious side effect on celery growth, while adding 0.3% hydrated lime significantly decreased fresh edible celery yield by 69.0%. Conversely, adding 0.5% HAP + 0.05% hydrated lime increased fresh edible celery yield by 39.8%. Additionally, adding HAP, zeolite, or hydrated lime rather than adding biochar effectively decreased total and bioaccessible Cd in edible celery. Similarly, HAP + hydrated lime and HAP + zeolite were much more efficient than HAP + biochar in lowering Cd transfer in soil-celery-human system. The total and bioaccessible Cd in edible celery were even reduced by over 50.0% after adding HAP + hydrated lime or HAP + zeolite at low rates. Considering the effects on celery growth and Cd transfer, HAP + hydrated lime and HAP + zeolite have the potential in remediating soil Cd contamination.

Geochemical Contamination, Speciation, and Bioaccessibility of Trace Metals in Road Dust of a Megacity (Guangzhou) in Southern China: Implications for Human Health

Road dust has been severely contaminated by trace metals and has become a major health risk to urban residents. However, there is a lack of information on bioaccessible trace metals in road dust, which is necessary for an accurate health risk assessment. In this study, we collected road dust samples from industrial areas, traffic intersections, and agricultural fields from a megacity (Guangzhou), China, and conducted a geochemical enrichment, speciation, and bioaccessibility-based health risk assessment of trace metals. In comparison with local soil background values, the results revealed a significant accumulation of trace metals, including Zn, Cd, Cu, and Pb in the road dust, which is considered moderate to heavy pollution. Sequential extraction indicated that most trace metals in the road dust were primarily composed of a Fe/Mn oxide-bound fraction, carbonate-bound fraction, and residual fraction, while the dominant fraction was the organic matter-bound fraction of Cu, and the residual fractions of As, Cr, and Ni. The in vitro gastrointestinal (IVG) method revealed that high percentages of Zn, Cd, Cu, and As were bioaccessible, suggesting the possible dissolution of trace metals from adsorbed and carbonate-associated fractions in road dust exposed to the biological fluid matrix. The IVG bioaccessibility-based concentration largely decreased the noncarcinogenic health risk to a negligible level. Nevertheless, the entire population is still exposed to the cumulative probability of a carcinogenic risk, which is primarily contributed to by As, Cd, Cr, and Pb. Future identification of the exact sources of these toxic metals would be helpful for the appropriate management of urban road dust contamination.

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

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

Levels, oral bioaccessibility and health risk of sand-bound potentially harmful elements (PHEs) in public playgrounds: Exploring magnetic properties as a pollution proxy

Children in urban environments are exposed to potential harmful elements (PHEs) through variable exposure media. Playing activities in outdoor playgrounds have been considered of high concern due to children's exposure to sand-bound PHEs through unintentional or intentional sand ingestion. Furthermore, the affinity of magnetic particles with dust-bound PHEs in playgrounds has been reported. In this study, playground sands (PG sands) from public playgrounds in the city of Thessaloniki, N. Greece were sampled and the levels, the contamination degree, oral bioaccessibility and exposure assessment of PHEs were evaluated. In addition, low-cost and fast magnetic measurements (i.e. mass specific magnetic susceptibility, χ_lf) were explored as potential pollution and health risk proxies. Mineralogically, siliceous PG sands dominated, while morphologically angular magnetic particles and Fe-rich "spherules" of anthropogenic origin were revealed and verified by enhanced χ_lf values. The average total elemental contents exhibited a descending order of Mn > Ba > Cr > Zn > Ni > Pb > Cu > Co > As > Sn > Bi > Cd, however only Cd, Bi, Pb, Cr, As and Zn were presented anthropogenically enhanced. Notable increase on PHEs levels and finer sand fractions were observed with continuous sand use. Anthropogenically derived elements (i.e. Cd and Pb with high I_geo values) exhibited higher bioaccessible fractions in PG sands and considered easily soluble in gastric fluids through ingestion. However, increased risks were found for specific PHEs (especially Pb) only in a worst case exposure scenario of an intentional sand ingestion (pica disorder). Statistical analysis results revealed a linkage of anthropogenic components with sand-bound magnetic particles. Moreover, the recorded high affinity of Pb contents (in an enhanced magnetized sub-set of PG sands) and bioaccessible Cd fractions with χ_lf provide a preliminary indication on the successful applicability of low-cost and fast magnetic measurements in high impacted playground environments.

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

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

Health risk assessment of heavy metals in street dust around a zinc smelting plant in China based on bioavailability and bioaccessibility

In order to investigate pollution level, chemical speciation and health risk of exposure to heavy metals in street dust from smelting district, we carried the following studies: (a). the differences in the morphology of street dust in smelting and non-smelting districts using a scanning electron microscope; (b). the chemical speciation and bioavailability of heavy metals in <100 μm and <63 μm particles near a smelting district using a modified three-stage BCR sequential extraction procedure and in vitro digestion test, respectively; (c). the evaluation of the non-carcinogenic risk of children and adults exposure to dust based on bioaccessibility. The results showed that most of the dust particles near Huludao Zinc Plant (HZP) were relatively solid with less porosity, which might originate from incompletely burned mineral particles from the smelting process. The concentrations of Pb, Cd and Cu were much higher than the background levels: 1560, 178.5 and 917.9 mg kg^-1 in <100 μm dust samples, and 2099, 198.4, 1038 mg kg^-1 in <63 μm dust samples, respectively. Pb was mostly present in the reducible fraction and the acid exchangeable fraction, while Cd and Cu were the most common heavy metals in the acid exchangeable fraction and oxidizable fraction, respectively. The rank order of bioaccessibility for the gastric and intestinal phase was Cd (58.13%) > Pb (50.00%) > Cu (19.19%) and Cd (20.36%) > Cu (15.67%) > Pb (5.08%), respectively. Hand-to-mouth ingestion poses the greatest non-carcinogenic exposure risk compared with other exposure pathways. When bioavailability is taken into account, children experienced higher non-carcinogenic and carcinogenic risks of dust exposure compared with adults, and the <63 μm particles posed greater risks than <100 μm particles.

Health risk assessment and bioaccessibilities of heavy metals for children in soil and dust from urban parks and schools of Jiaozuo, China

Urban parks and schools sever as the mainly activity areas for children, but risk assessment posed by heavy metals (HMs) from soil and dust in these area has rarely been investigated. In this study, six urban parks and seven schools in Jiaozuo, China, were taken as research objects to understand the contamination level and bioaccessibility of HMs from soil and dust in urban parks and schools. The results indicated that Zn, Cu, Pb, Cd, As, Ni and Co from soil and dust were above the background values, especially Zn and Cd in dust, and As and Cd in soil. Serious Cd pollution was discovered, and respective Cd concentrations in soil and dust were 17.83 and 7.52 times the background value. Additionally, the average concentration and bioaccessibility of Zn, Mn, Pb, Cd, Cr, Ni and Co in dust were both higher than in soil. High concentration and high bioaccessibility of HMs in dust suggested that HMs contamination were serious and universal in Jiaozuo. The concentrations of most HMs were higher in the gastric phase, except for Cu and Cd which remained higher in the intestinal phase. Both in the gastric phase and intestinal phase, Mn, As and Cd in soil and dust both have high bioaccessibility which all exceed 10%. The carcinogenic and non-carcinogenic risks base on the total HMs for children (soil: 7.93, 1.96E-05; dust: 6.44, 3.58E-05) were greater than those for adults (soil: 6.35E-01, 1.32E-05; dust: 5.06E-01, 2.42E-05), and urban parks and schools posed high potential risk for children. Therefore, assessment the risk posed by HMs contamination of soil and dust in urban parks and schools is vital and urgent for children.

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

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

Meconium identifies high levels of metals in newborns from a mining community in the U.S

BACKGROUND

This pilot study was conducted to determine if we could identify intrauterine exposure to metals in meconium, as a measure of exposure for mother-child pairs living in proximity to a mining operation.

OBJECTIVES

We used meconium as a means to measure metal exposure in utero. We set out to quantify the exposure to selected metals that are currently being mined and also are found in the Superfund site in Butte, Montana, and to compare it to that of Columbia, South Carolina, US, where mining is not occurring.

METHODS

This cross-sectional study was conducted between May and November 2018. We received Institutional Review Board approval and we consented women following the birth of their newborns, and collected meconium within 24 h of birth, without any identifiers. Each laboratory used the same protocol for collection, transport, and storage; and the same laboratory protocol was used for the analysis of all samples. Samples were digested using standard acid/peroxide digestion methods and measured by inductively coupled plasma mass spectroscopy.

RESULTS

We collected meconium specimens from 17 infants in Columbia, South Carolina and 15 infants in Butte, Montana. The concentrations found in Columbia were in the low μg kg^-1 range (or less) and were similar to the low levels that have been identified in other studies of meconium. The magnitude of the differences in concentrations found in Butte compared to Columbia was 1792 times higher for Cu, 1650 times higher for Mn, and 1883 times higher for Zn.

CONCLUSION

Using meconium to measure exposure of newborns has implications for risk assessment in a mining-exposed population. This approach was inexpensive and thorough. The magnitude of the differences in the metal levels identified from the two study sites suggests there is an urgent need for further research to learn if there are health consequences to these highly exposed infants.

Metal (Cd, Cr, Ni, Pb) removal from environmentally relevant waters using polyvinylpyrrolidone-coated magnetite nanoparticles

Water pollution is a major global challenge given the increasing growth in industry and human population, and certain metals can be highly toxic and contribute to this significantly. In this study, polyvinylpyrrolidone-coated magnetic nanoparticles (PVP–Fe₃O₄ NPs) were used to remove metals (Cd, Cr, Ni, and Pb) from synthetic soft water and sea water in the presence and absence of fulvic acid. Nanoparticle (NP) suspensions were added to water media at a range of metal concentrations (0.1–100 mg L⁻¹). Removal at different time points (1.5, 3, 6, 12, 24 hours) was also evaluated. Results showed that 167 mg L⁻¹ PVP–Fe₃O₄ NPs could remove nearly 100% of four metals at 0.1 mg L⁻¹ and more than 80% at 1 mg L⁻¹. The removal decreased as the initial metal concentration increased, although essentially 100% of the Pb was removed under all conditions. The kinetic adsorption fitted well to the pseudo-second-order model and in general, the majority of metal adsorption occurred within the first 1.5 hours. These NPs are a reliable method to remove metals under a wide range of environmentally relevant conditions. Our previous research showed the NPs effectively removed oil from waters, so these NPs offer the possibility of combined in situ remediation of oil and metals.

PVP–Fe₃O₄ NPs synthesized with no organic solvents, low toxicity reactants and low temperature/energy requirements could remove Cd, Cr, Ni, Pb efficiently in the different synthetic water media under environmentally relevant conditions.

Environmental exposure to low-level lead (Pb) co-occurring with other neurotoxicants in early life and neurodevelopment of children

Lead (Pb) is a worldwide environmental contaminant that even at low levels influences brain development and affects neurobehavior later in life; nevertheless it is only a small fraction of the neurotoxicant (NT) exposome. Exposure to environmental Pb concurrent with other NT substances is often the norm, but their joint effects are challenging to study during early life. The aim of this review is to integrate studies of Pb-containing NT mixtures during the early life and neurodevelopment outcomes of children. The Pb-containing NT mixtures that have been most studied involve other metals (Mn, Al, Hg, Cd), metalloids (As), halogen (F), and organo-halogen pollutants. Co-occurring Pb-associated exposures during pregnancy and lactation depend on the environmental sources and the metabolism and half-life of the specific NT contaminant; but offspring neurobehavioral outcomes are also influenced by social stressors. Nevertheless, Pb-associated effects from prenatal exposure portend a continued burden on measurable neurodevelopment; they thus favor increased neurological health issues, decrements in neurobehavioral tests and reductions in the quality of life. Neurobehavioral test outcomes measured in the first 1000 days showed Pb-associated negative outcomes were frequently noticed in infants (<6 months). In older (preschool and school) children studies showed more variations in NT mixtures, children's age, and sensitivity and/or specificity of neurobehavioral tests; these variations and choice of statistical model (individual NT stressor or collective effect of mixture) may explain inconsistencies. Multiple exposures to NT mixtures in children diagnosed with 'autism spectrum disorders' (ASD) and 'attention deficit and hyperactivity disorders' (ADHD), strongly suggest a Pb-associated effect. Mixture potency (number or associated NT components and respective concentrations) and time (duration and developmental stage) of exposure often showed a measurable impact on neurodevelopment; however, net effects, reversibility and/or predictability of delays are insufficiently studied and need urgent attention. Nevertheless, neurodevelopment delays can be prevented and/or attenuated if public health policies are implemented to protect the unborn and the young child.

Fast Bootstrap Confidence Intervals for Continuous Threshold Linear Regression

Continuous threshold regression is a common type of nonlinear regression that is attractive to many practitioners for its easy interpretability. More widespread adoption of thresh-old regression faces two challenges: (i) the computational complexity of fitting threshold regression models and (ii) obtaining correct coverage of confidence intervals under model misspecification. Both challenges result from the non-smooth and non-convex nature of the threshold regression model likelihood function. In this paper we first show that these two issues together make the ideal approach for making model-robust inference in continuous threshold linear regression an impractical one. The need for a faster way of fitting continuous threshold linear models motivated us to develop a fast grid search method. The new method, based on the simple yet powerful dynamic programming principle, improves the performance by several orders of magnitude.

Differences in the risk assessment of soil heavy metals between newly built and original parks in Jiaozuo, Henan Province, China

Differences in the concentrations of heavy metals between newly built and original parks remain incompletely understood. In this work, two newly built and four original parks in Jiaozuo, China, were taken as research objects. Using the geo-accumulation index, ecological risk assessment index and human health risk model, differences in heavy metal pollution between the two types of parks were determined. In the surveyed region, five heavy metals, namely, Zn, Cu, As, Ni and Co, polluted the environment. Serious As pollution was discovered, and respective As concentrations in the soils of newly built and original parks were 5.9 and 3 times the background value. The concentrations of Zn, Mn, As, Pb, Cr and Ni in newly built parks were higher than those in the four original parks, although the concentrations of Cu and Co between the two types of parks were not significantly different. The carcinogenic and non-carcinogenic risks of these metals in newly built parks (adults: 4.27E-05, 1.08; children: 2.53E-04, 8.94) were greater than those in original parks (adults: 2.57E-05, 0.67; children: 1.52E-04, 5.39), and newly built parks posed higher potential risk than original parks. Therefore, the concentration of heavy metals in soil must be assessed before former industrial sites are transformed into parks.

Quantifying factors related to urban metal contamination in vegetable garden soils of the west and north of Melbourne, Australia

Vegetable gardens in cities provide communities with fresh vegetables but also may contribute towards public exposure to metals present in soil from historical pollution. Contamination of some Melbourne garden soils with Pb (range 12.9-773 mg kg^-1 in soil) was found with some soils exceeding the Australian human health screening criteria for residential land use of 300 mg kg^-1. Cadmium concentrations (0.12-1.04 mg kg^-1) were above the ambient background soil concentrations of <1 mg kg^-1. Nickel concentrations (7.6-40.5 mg kg^-1) and Cr (11.6-49.4 mg kg^-1) were within the range of expected ambient background concentrations. Distance from the nearest arterial road, house age and the likely use of lead-based paints were the main factors explaining approximately 75% of soil Pb variability in garden soils. Metal concentrations in garden soils of wooden houses were found to be significantly higher than the garden soil of brick and concrete houses (Pb (p < 0.0001)) and Cd (p < 0.001)). Significant correlations were found between backyard garden soil metal concentration and house age for Pb (R² = 0.83, p < 0.0001) and Cd (R² = 0.40, p < 0.0002) and the distance from arterial roads for Pb (R² = 0.38, p < 0.002), while Cr and Ni are related to soil characteristics cation exchange capacity, organic matter, and pH. Vegetable garden with elevated Pb and Cd had recognizable risk factors such as older, painted structures on adjacent houses and closer proximity to arterial roads with higher frequency traffic.

Lead and Arsenic in Shed Deciduous Teeth of Children Living Near a Lead-Acid Battery Smelter

Lead (Pb) is a potent neurotoxicant with no safe level of exposure. Elevated levels of Pb and arsenic (As) are found in the air and soil near facilities that recycle lead-acid batteries in the United States. In urban Los Angeles County, California, a facility processed ∼11 million batteries per year and operated for decades without proper environmental review. Measuring Pb and As in shed deciduous teeth is a promising technique to assess prenatal and early life exposure. In this pilot study coined the "Truth Fairy" Project, 50 shed deciduous teeth from 43 children living their entire lives within 2 miles of the smelter were analyzed to understand retrospective exposure to toxic metals using a community-driven research approach. Concentrations of Pb and As in teeth were assessed using laser-ablation-inductively coupled plasma-mass spectrometry. Soil Pb concentrations were determined using spatial kriging of surface soil measurements. The mean prenatal calcium normalized Pb levels in teeth samples (reported as a ratio 208Pb:43Ca) was 4.104 × 10-4 (SD 4.123 × 10-4), and the mean postnatal 208Pb:43Ca level was 4.109 × 10-4 (SD 3.369 × 10-4). Adjusted for maternal education and batch, we observe positive significant relationship between prenatal teeth Pb per 100 ppm increase in soil Pb (β = 3.48, 95% CI 1.11, 5.86). The Truth Fairy study suggests prenatal and early life exposure to toxic metals is associated with legacy soil contamination in an urban community near a smelter.

Alteration in cognitive behaviour, brain antioxidant enzyme activity and their gene expression in F1 generation mice, following Cd exposure during the late gestation period: modulation by quercetin

We investigated whether in-utero Cd(II) chloride exposure of the dams between 14th to 21st day of gestation affects memory and learning, oxidative stress, antioxidant enzyme activity and their gene expression in brain of the pups in their adulthood. In the Morris water maze, cadmium (Cd) exposure impaired spatial memory which was reversed following co-treatment with quercetin (100 mg/kg). In the passive avoidance paradigm, retention memory was adversely affected but was significantly reversed by co treatment with quercetin (25, 50, 100 mg/kg). The malondialdehyde and catalase (CAT) levels and glutathione-S-transferase (GST) activity were increased significantly in Cd-treated group, but were reversed by quercetin (all doses). The gene expression for CAT and GST in brain tissue of Cd treated animals also increased many folds as compared to the control, and this effect was decreased on co-treatment with quercetin (all doses), thus matching with the respective enzyme activities. Quercetin (25 mg/kg) when co-treated with Cd caused a decrease in GST activity compared to control, which points towards a complex interplay with oxidative free radicals and promoters and transcription factors. Thus, Cd exposure during late gestation causes impaired spatial and retention memory in the next generation which may be due to alteration of activity as well as gene expression of the antioxidant enzymes, CAT and GST. Quercetin may offer some protection of memory impairment probably by modulating these effects.

Heavy metal bioaccessibility and health risks in the contaminated soil of an abandoned, small-scale lead and zinc mine

The lack of management in small-scale mining operations has the potential for negative repercussions, e.g., mine collapses, compared with well-regulated large-scale mines. Here, we used an in vitro model to investigate heavy metal soil pollution characteristics and their attendant health risks in an abandoned, small-scale lead (Pb) and zinc (Zn) mine located in southwestern China that had suffered from collapse. Our results showed the following: (1) Even the mine had been closed for many years, the soil was still heavily polluted by Pb, cadmium (Cd), and Zn, and there is a risk of secondary pollution. Pb, Zn, and Cd concentrations in the mining areas were all approximately 22-42 times higher than the background soil levels of Guangxi Province. (2) Cd had the largest bioaccessibility, and mining areas tend to have soils containing more bioaccessible metals (78 ± 14%, 27 ± 4%, and 38 ± 12% for Cd, Pb, and Zn in gastric phase and 40 ± 12%, 10 ± 5%, and 19 ± 8% in intestinal phase correspondingly). (3) Results of a stepwise, multiple regression analysis revealed that the total soil content of the three metals (Pb, Zn, and Cd), TOC (total organic carbon), soil composition, and Mn content were the main impact factors for the Pb, Cd, and Zn soil bioaccessibility in study area (R² = 0.37~0.93). (4) A health risk assessment based on Pb, Cd, and Zn bioaccessibility indicated that the health risk for people in mine area is not high (HI is 1.07 at most and CR 2.40E-6 at most for children).

Bioaccessibilities and health implications of heavy metals in exposed-lawn soils from 28 urban parks in the megacity Guangzhou inferred from an in vitro physiologically-based extraction test

This study focused on characterizing the oral bioaccessibilities and human health risks of eight heavy metals (Cd, Pb, Cr, Ni, Cu, Zn, Fe, and Mn) in surface-exposed lawn soils from 28 urban parks in Guangzhou. The physiologically-based extraction test (PBET) method was used to assess bioavailability (in gastric and intestinal phases) and human health risk was assessed via statistical modelling (carcinogenic risk assessment, hazard quotients and hazard indices). Mean bioaccessibilities of Cd, Pb, Cr, Ni, Cu, Zn, Fe, and Mn from all soil samples were 50.90 ± 17.67%, 5.81 ± 1.67%, 7.12 ± 3.24%, 17.91 ± 18.34%, 11.93 ± 2.88%, 34.33 ± 10.02%, 1.68 ± 0.48%, 26.71 ± 5.06%, respectively. The concentrations of most heavy metals were higher in the gastric phase, except for Cr and Ni which remained higher in the intestinal phase. Principal component analysis revealed that the bioaccessibilities of the heavy metals could be split into three groupings, based on the urban park of soil origin. The carcinogenic risk probabilities for Pb and Cr were under the acceptable level (< 1 × 10^-4) for both adults and children. The hazard quotient and hazard index values indicated no significant risk of non-carcinogenic effects to children or adults exposed to Guangzhou urban park soils. This research will help inform further risk assessment and management of heavy metal contaminants in urban environments.

N-acetylcysteine alleviates cadmium-induced placental endoplasmic reticulum stress and fetal growth restriction in mice

Cadmium (Cd) is a developmental toxicant that induces fetal growth restriction (FGR). Placental endoplasmic reticulum (ER) stress is associated with FGR. This study investigated the effects of N-acetylcysteine (NAC) on Cd-induced placental ER stress and FGR. Pregnant mice were intraperitoneally injected with CdCl₂ daily from gestational day (GD)13 to GD17. As expected, Cd reduced fetal weight and crown-rump length. Cd decreased the internal space of blood vessels in the placental labyrinth layer and inhibited placental cell proliferation. Several genes of growth factors, such as Vegf-a, placental growth factor, Igf1 and Igf1r, and several genes of nutrient transport pumps, such as Glut1, Fatp1 and Snat2, were down-regulated in placenta of Cd-treated mice. Moreover, Cd evoked placental ER stress. Of interest, NAC alleviated Cd-induced FGR. Additional experiment showed that NAC inhibited Cd-induced impairment of placental development and placental ER stress. Therefore, NAC may be exploited for prevention of Cd-induced placental insufficiency and FGR.