Karen D. Bradham

Development of an Environmental Relative Moldiness Index for Us Homes

Objective: The objective of this study was to establish a national relative moldiness index for homes in the United States. Methods: As part of the Housing and Urban Developments American Healthy Homes Survey, dust samples were collected by vacuuming 2 m2 in the bedrooms plus 2 m2 in the living rooms from a nationally representative 1096 homes in the United States using the Mitest sampler. Five milligrams of sieved (300 &mgr;m pore, nylon mesh) dust was analyzed by mold-specific quantitative polymerase chain reaction for the 36 indicator species in 1096 samples. Results: On the basis of this standardized national sampling and analysis, an “Environmental Relative Moldiness Index” was created with values ranging from about −10 to 20 or above (lowest to highest). Conclusions: The Environmental Relative Moldiness Index scale may be useful for home mold-burden estimates in epidemiological studies.

Arsenic metabolism by human gut microbiota upon in vitro digestion of contaminated soils.

Background Speciation analysis is essential when evaluating risks from arsenic (As) exposure. In an oral exposure scenario, the importance of presystemic metabolism by gut microorganisms has been evidenced with in vivo animal models and in vitro experiments with animal microbiota. However, it is unclear whether human microbiota display similar As metabolism, especially when present in a contaminated matrix. Objectives We evaluated the metabolic potency of in vitro cultured human colon microbiota toward inorganic As (iAs) and As-contaminated soils. Methods A colon microbial community was cultured in a dynamic model of the human gut. These colon microbiota were incubated with iAs and with As-contaminated urban soils. We determined As speciation analysis using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry. Results We found a high degree of methylation for colon digests both of iAs (10 μg methylarsenical/g biomass/hr) and of As-contaminated soils (up to 28 μg/g biomass/hr). Besides the formation of monomethylarsonic acid (MMAV), we detected the highly toxic monomethylarsonous acid (MMAIII). Moreover, this is the first description of microbial thiolation leading to monomethylmonothioarsonic acid (MMMTAV). MMMTAV, the toxicokinetic properties of which are not well known, was in many cases a major metabolite. Conclusions Presystemic As metabolism is a significant process in the human body. Toxicokinetic studies aiming to completely elucidate the As metabolic pathway would therefore benefit from incorporating the metabolic potency of human gut microbiota. This will result in more accurate risk characterization associated with As exposures.

Relative Bioavailability and Bioaccessibility and Speciation of Arsenic in Contaminated Soils

Background: Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability. Objectives: We evaluated inexpensive methods for assessing As bioavailability in soil as a means to improve human exposure estimates and potentially reduce remediation costs. Methods: Nine soils from residential sites affected by mining or smelting activity and two National Institute of Standards and Technology standard reference materials were evaluated for As bioavailability, bioaccessibility, and speciation. Arsenic bioavailability was determined using an in vivo mouse model, and As bioaccessibility was determined using the Solubility/Bioavailability Research Consortium in vitro assay. Arsenic speciation in soil and selected soil physicochemical properties were also evaluated to determine whether these parameters could be used as predictors of As bioavailability and bioaccessibility. Results: In the mouse assay, we compared bioavailabilities of As in soils with that for sodium arsenate. Relative bioavailabilities (RBAs) of soil As ranged from 11% to 53% (mean, 33%). In vitro soil As bioaccessibility values were strongly correlated with soil As RBAs (R2 = 0.92). Among physicochemical properties, combined concentrations of iron and aluminum accounted for 80% and 62% of the variability in estimates of RBA and bioaccessibility, respectively. Conclusion: The multifaceted approach described here yielded congruent estimates of As bioavailability and evidence of interrelations among physicochemical properties and bioavailability estimates.

Effect of soil properties on lead bioavailability and toxicity to earthworms.

Soil properties are important factors modifying metal bioavailability to ecological receptors. Twenty-one soils with a wide range of soil properties (USA; http://soils.usda.gov/technical/classification/taxonomy/) were amended with a single concentration of Pb (2,000 mg/kg) to determine the effects of soil properties on Pb bioavailability and toxicity to earthworms. Earthworm mortality ranged from 0 to 100% acute mortality following exposure to the same total concentration of Pb (2,000 mg/kg) in amended field soils. Internal Pb concentrations in earthworms ranged from 28.7 to 782 mg/kg, with a mean of 271 mg/kg. Path analysis was used to partition correlations in an attempt to discern the relative contribution of each soil property. Results of path analysis indicated that pH was the most important soil property affecting earthworm mortality (p < 0.01) and internal Pb (p < 0.05). Soil pH was related inversely to mortality and internal Pb, soil solution Pb, and Pb bioavailability. The most important soil property modifying reproduction was amorphous iron and aluminum oxides (FEAL). Because FEAL is rich in pH-dependent cation-exchange sites, several soil properties, including pH, FEAL, and cation-exchange capacity, have a causal effect on Pb adsorption and soluble Pb. Path analysis is useful for assessing contaminated soils with a wide range of soil properties and can assist in ecological risk assessment and remediation decisions for contaminated sites. Soil properties are important factors modifying metal bioavailability and toxicity and should be considered during the ecological risk assessment of metals in contaminated soils.

Arsenic and Environmental Health: State of the Science and Future Research Opportunities

Background: Exposure to inorganic and organic arsenic compounds is a major public health problem that affects hundreds of millions of people worldwide. Exposure to arsenic is associated with cancer and noncancer effects in nearly every organ in the body, and evidence is mounting for health effects at lower levels of arsenic exposure than previously thought. Building from a tremendous knowledge base with > 1,000 scientific papers published annually with “arsenic” in the title, the question becomes, what questions would best drive future research directions? Objectives: The objective is to discuss emerging issues in arsenic research and identify data gaps across disciplines. Methods: The National Institutes of Health’s National Institute of Environmental Health Sciences Superfund Research Program convened a workshop to identify emerging issues and research needs to address the multi-faceted challenges related to arsenic and environmental health. This review summarizes information captured during the workshop. Discussion: More information about aggregate exposure to arsenic is needed, including the amount and forms of arsenic found in foods. New strategies for mitigating arsenic exposures and related health effects range from engineered filtering systems to phytogenetics and nutritional interventions. Furthermore, integration of omics data with mechanistic and epidemiological data is a key step toward the goal of linking biomarkers of exposure and susceptibility to disease mechanisms and outcomes. Conclusions: Promising research strategies and technologies for arsenic exposure and adverse health effect mitigation are being pursued, and future research is moving toward deeper collaborations and integration of information across disciplines to address data gaps. Citation: Carlin DJ, Naujokas MF, Bradham KD, Cowden J, Heacock M, Henry HF, Lee JS, Thomas DJ, Thompson C, Tokar EJ, Waalkes MP, Birnbaum LS, Suk WA. 2016. Arsenic and environmental health: state of the science and future research opportunities. Environ Health Perspect 124:890–899; http://dx.doi.org/10.1289/ehp.1510209

Changes in silver nanoparticles exposed to human synthetic stomach fluid: Effects of particle size and surface chemistry

The significant rise in consumer products and applications utilizing the antibacterial properties of silver nanoparticles (AgNPs) has increased the possibility of human exposure. The mobility and bioavailability of AgNPs through the ingestion pathway will depend, in part, on properties such as particle size and the surface chemistries that will influence their physical and chemical reactivities during transit through the gastrointestinal tract. This study investigates the interactions between synthetic stomach fluid and AgNPs of different sizes and with different capping agents. Changes in morphology, size and chemical composition were determined during a 30 min exposure to synthetic human stomach fluid (SSF) using Absorbance Spectroscopy, High Resolution Transmission Electron and Scanning Electron Microscopy (TEM/SEM), Dynamic Light Scattering (DLS), and Nanoparticle Tracking Analysis (NTA). AgNPs exposed to SSF were found to aggregate significantly and also released ionic silver which physically associated with the particle aggregates as silver chloride. Generally, the smaller sized AgNPs (<10nm) showed higher rates of aggregation and physical transformation than larger particles (75 nm). Polyvinylpyrrolidone (pvp)-stabilized AgNPs prepared in house behaved differently in SSF than particles obtained from a commercial source despite having similar surface coating and size distribution characteristics.

Alterations in physical state of silver nanoparticles exposed to synthetic human stomach fluid

The bioavailability of ingested silver nanoparticles (AgNPs) depends in large part on initial particle size, shape and surface coating, properties which will influence aggregation, solubility and chemical composition during transit of the gastrointestinal tract. Citrate-stabilized AgNPs were exposed to synthetic human stomach fluid (SSF) (pH 1.5) and changes in size, shape, zeta potential, hydrodynamic diameter and chemical composition were determined during a 1h exposure period using Surface Plasmon Resonance (SPR), High Resolution Transmission Electron Microscopy/Energy Dispersive X-ray Spectroscopy (TEM/EDS), Dynamic Light Scattering (DLS) and X-ray Powder Diffraction (XRD) combined with Rietveld analysis. Exposure of AgNPs to SSF produced a rapid decrease in the SPR peak at 414nm and the appearance of a broad absorbance peak in the near infrared (NIR) spectral region. During exposure to SSF, changes in zeta potential, aggregation and morphology of the particles were also observed as well as production of silver chloride which appeared physically associated with particle aggregates.

Evaluating the contribution of soil properties to modifying lead phytoavailability and phytotoxicity.

Soil properties affect Pb bioavailability to human and ecological receptors and should be considered during ecological risk assessment of contaminated soil. We used path analysis (PA) to determine the relative contribution of soil properties (pH, organic C [OC], amorphous Fe and Al oxides [FEAL], and cation-exchange capacity [CEC]) in modifying Pb bioavailability. The response of biological endpoints (bioaccumulation and dry matter growth [DMG]) of lettuce (Lactuca sativa) grown on 21 Pb-spiked (2,000 mg/kg) soils were determined. Lettuce tissue Pb ranged from 3.22 to 233 mg/kg, and relative DMG ranged from 2.5 to 88.5% of their respective controls. Simple correlation showed strong relationships between CEC and OC (p < 0.01) and weaker relationships between pH and FEAL (p < 0.05) and Pb bioaccumulation. Results of PA suggest that soil pH increased the negative surface charge of organic matter and clay, thereby increasing CEC and decreasing Pb bioaccumulation. Also, the direct effect of OC on tissue Pb can be attributed to formation of surface Pb complexes by organic matter functional group ligands. Increased OC and/or CEC reduced Pb solubility and bioavailability in the 21 soils in the present study. The relative importance of soil properties likely will vary between studies employing different soils. Soil properties should be considered during the ecological risk assessment of metal in contaminated soils. Path analysis is useful for ecological studies involving soils with a wide range of physicochemical properties and can assist in site risk assessment of metals and remediation decisions on contaminated sites.

Variability Associated with As in Vivo–in Vitro Correlations When Using Different Bioaccessibility Methodologies

To evaluate the capabilities of in vitro assays to predict arsenic (As) relative bioavailability (RBA), we examined the relationship between As bioaccessibility, determined using a number of in vitro bioaccessibility (IVBA) methodologies (SBRC, IVG, PBET, DIN and UBM) and As RBA determined in a mouse assay for nine As-contaminated soils and 1 NIST reference material (2710a). Significant differences (P < 0.05) in As IVBA were observed within and between assays indicating that different IVBA methodologies may not produce congruent data, as a result of variability in the extracting medium constituents and/or differences in the pH of gastric and intestinal phases. When results of in vivo determinations of As RBA were compared with As IVBA results, there was no significant difference in slopes of the relationships (P = 0.49-0.88) when SBRC, IVG, PBET, DIN, and UBM gastric and intestinal phase data were used. A significantly (P < 0.05) smaller y-intercept was, however, determined for the in vivo-SBRC gastric phase correlation compared to SBRC, IVG, PBET, and DIN intestinal phase, a factor that may influence prediction of As RBA, especially for soils with low As RBA. When in vivo-in vitro relationships were compared to previously derived correlations from the literature, some differences were observed. These differences may be attributed to factors affecting both in vivo and in vitro data including physiological differences in animal models (e.g., mouse versus swine), which may influence As absorption, differences in the approach used to estimate As RBA, and variability arising from subtle interoperator differences in performance of in vitro assays.

MOUSE ASSAY FOR DETERMINATION OF ARSENIC BIOAVAILABILITY IN CONTAMINATED SOILS

A mouse assay for measuring the relative bioavailability (RBA) of arsenic (As) in soil was developed. In this study, results are presented of RBA assays of 16 soils, including multiple assays of the same soils, which provide a quantitative assessment of reproducibility of mouse assay results, as well as a comparison of results from the mouse assay with results from a swine and monkey assay applied to the same test soils. The mouse assay is highly reproducible; three repeated assays on the same soils yielded RBA estimates that ranged from 1 to 3% of the group mean. The mouse, monkey, and swine models yielded similar results for some, but not all, test materials. RBA estimates for identical soils (nine test soils and three standard reference materials [SRM]) assayed in mice and swine were significantly correlated (r = 0.70). Swine RBA estimates for 6 of the 12 test materials were higher than those from the mouse assay. RBA estimates for three standard reference materials (SRM) were not statistically different (mouse/swine ratio ranged from 0.86–1). When four test soils from the same orchard were assessed in the mouse, monkey, and swine assays, the mean soil As RBA were not statistically different. Mouse and swine models predicted similar steady state urinary excretion fractions (UEF) for As of 62 and 74%, respectively, during repeated ingestion doses of sodium arsenate, the water-soluble As form used as the reference in the calculation of RBA. In the mouse assay, the UEF for water soluble AsV (sodium arsenate) and AsIII (sodium [meta] arsenite) were 62% and 66%, respectively, suggesting similar absolute bioavailabilities for the two As species. The mouse assay can serve as a highly cost-effective alternative or supplement to monkey and swine assays for improving As risk assessments by providing site-specific assessments of RBA of As in soils.