Estimating human exposure through multiple pathways from air, water, and soil

Relation between solid phase speciation and oral/lung bioaccessibility of metal(loid)s polluted soils in inhabited area: Contribution of synchrotron-based experiment

The presence of contaminated sites/soils in or near cities can pose significant risks to public health. The city of Viviez (France) was taken in reference site bears significant industrial responsibility, particularly in zinc metallurgy, with the presence of a now rehabilitated smelter. This has led to soil contamination by zinc (Zn), lead (Pb), arsenic (As), and cadmium (Cd), with concentrations reaching up to 4856 mg kg-1, 1739 mg kg-1, 195 mg kg-1, and 110 mg kg-1, respectively. The aim of this study is to comprehend the contamination patterns of the site post-rehabilitation, the geochemical behavior of each element, and their speciation (analyzed through BCR, XRD, and XANES) in relation to associated health risks due to metals accessibility for oral ingestion and inhalation by the local population. The findings revealed that elements inducing health risks were not necessarily those with the highest metal contents. All results are discussed in terms of the relationship between element speciation, stability of bearing phases, and their behavior in different media. XANES is an important tool to determine and estimate the Pb-bearing phases in garden soils, as well as the As speciation, which consist of Pb-goethite, anglesite, and Pb-humate, with variations in proportions (the main phases being 66 %, 12 % and 22 % for Pb-goethite, anglesite, and Pb-humate, respectively) whereas As-bearing phase are As(V)-rich ferrihydrite-like. A new aspect lies in the detailed characterization of solid phases before and after bioaccessibility tests, to qualify and quantify the bearing phases involved in the mobility of metallic elements to understand the bioaccessibility behavior. Ultimately, the health risk associated with exposure to inhabitants, in terms of particle ingestion and inhalation, was assessed. Only ingestion-related risk was deemed unacceptable due to the levels of As and Pb.

Impacts of Agricultural Pesticide Contamination: An Integrated Risk Assessment of Rural Communities of Eswatini

Marked reductions in mean annual rainfall associated with climate change in Eswatini in Southern Africa have encouraged the recycling of irrigation water and the increased use of pesticides in agricultural production, raising concerns about potential ecological and health risks due to long-term exposure to pesticide residues in soil and irrigation water. This probabilistic integrated risk assessment used liquid chromatography with tandem mass spectrometry to analyze the concentrations of four commonly used agricultural pesticides (ametryn, atrazine, pendimethalin, and 2,4-dichlorophenoxyacetic acid (2,4-D)) in irrigation water and topsoil samples from farmlands in Eswatini to assess potential ecological and health risks due to exposure. The concentrations of these pesticides ranged from undetectable to 0.104 µg/L in irrigation water and from undetectable to 2.70 µg/g in soil. The probabilistic multi-pathway and multi-route risk assessments conducted revealed hazard indices exceeding 1.0 for all age groups for ametryn and atrazine, suggesting that the daily consumption of recycled irrigation water and produce from the fields in this area may pose considerable health risks. The indices pertaining to ecological risks had values less than 0.1. Adaptation measures are recommended to efficiently manage pesticide use in agriculture, and further research will ensure that agriculture can adapt to climate change and that the general public and ecosystem are protected.

Insight into the Potential Mechanisms of Endocrine Disruption by Dietary Phytoestrogens in the Context of the Etiopathogenesis of Endometriosis

Phytoestrogens (PEs) are estrogen-like nonsteroidal compounds derived from plants (e.g., nuts, seeds, fruits, and vegetables) and fungi that are structurally similar to 17β-estradiol. PEs bind to all types of estrogen receptors, including ERα and ERβ receptors, nuclear receptors, and a membrane-bound estrogen receptor known as the G protein-coupled estrogen receptor (GPER). As endocrine-disrupting chemicals (EDCs) with pro- or antiestrogenic properties, PEs can potentially disrupt the hormonal regulation of homeostasis, resulting in developmental and reproductive abnormalities. However, a lack of PEs in the diet does not result in the development of deficiency symptoms. To properly assess the benefits and risks associated with the use of a PE-rich diet, it is necessary to distinguish between endocrine disruption (endocrine-mediated adverse effects) and nonspecific effects on the endocrine system. Endometriosis is an estrogen-dependent disease of unknown etiopathogenesis, in which tissue similar to the lining of the uterus (the endometrium) grows outside of the uterus with subsequent complications being manifested as a result of local inflammatory reactions. Endometriosis affects 10-15% of women of reproductive age and is associated with chronic pelvic pain, dysmenorrhea, dyspareunia, and infertility. In this review, the endocrine-disruptive actions of PEs are reviewed in the context of endometriosis to determine whether a PE-rich diet has a positive or negative effect on the risk and course of endometriosis.

New evidence for deleterious effects of environmental contaminants on the male gamete

The decreasing trend in human and domestic animal fertility in recent decades has resulted in the question of whether reduced sperm quality is associated with changes in global climate and the environment. Proposed causes for reduced sperm quality include environmental contaminants, which enter into the body of animals through the food chain and are transported to the reproductive tract, where contaminating agents can have effects on fertilization capacities of gametes. In this review, there is a focus on various environmental contaminants and potential effects on male fertility. Human-derived contaminants, particularly endocrine-disrupting phthalates and the pesticide atrazine, are discussed. Naturally occurring toxins are also addressed, in particular mycotoxins such as aflatoxin which can be components in food consumed by humans and animals. Mechanisms by which environmental contaminants reduce male fertility are not clearly defined; however, are apparently multifactorial (i.e., direct and indirect effects) with there being diverse modes of action. Results from studies with humans, rodents and domestic animals indicate there are deleterious effects of contaminants on male gametes at various stages of spermatogenesis (i.e., in the testis) during passage through the epididymis, and in mature spermatozoa, after ejaculation and during capacitation. Considering there is never detection of a single contaminant, this review addresses synergistic or additive effects of combinations of contaminants. There is new evidence highlighted for the long-lasting effects of environmental contaminants on spermatozoa and developing embryos. Understanding the risk associated with environmental contaminants for animal reproduction may lead to new management strategies, thereby improving reproductive processes.

Sublimation and Diffusion Kinetics of 2,4,6-Trinitrotoluene (TNT) Single Crystals by Atomic Force Microscopy (AFM)

In this article, we report the in-situ nanoscale experimental measurement of sublimation rates, activation energy of sublimation, and diffusion coefficients of 2,4,6-trinitrotoluene (TNT) single crystals in air using atomic force microscopy (AFM). The crystals were prepared by slow evaporation at 5 °C using acetone-dissolved TNT. The mass loss was calculated by monitoring the shrinkage of the surface area of layered islands formed on the surface of the TNT crystals due to sublimation upon isothermal heating at temperatures below the melting point. The results suggest the sublimation process occurs via two-dimensional detachment of TNT molecules from the non-prominent facets on the crystal surface which imitates the nucleation and crystal growth process. Sublimation rates are one order of magnitude smaller than previously reported values. However, the calculated activation energy (112.15 ± 3.2 kJ/mol) and temperature-dependent sublimation rates agree well with the reported values for TNT thin films and microcrystals determined by UV-vis absorbance spectroscopy and quartz crystal microscopy (QCM) (90–141 kJ/mol). The average diffusion coefficient is (4.35 × 10^–6 m²/s) which is within the range of the reported theoretical values with an average of 5.59 × 10^–6 m²/s, and about 25% less than that determined using thermogravimetric analysis for powder TNT.

Drinking water improvements and rates of urinary and gastrointestinal infections in Galápagos, Ecuador: Assessing household and community factors

OBJECTIVES

The Galápagos provides an important setting to investigate the health impacts of a new drinking water treatment plant (DWTP) in a limited resource environment. We examine how household perceptions and practices affect the relationship between water quality and infections before and after DWTP.

METHODS

Ethnographic data and self-reported infections were collected from 121 mothers and 168 children ages 2 to 10 from Isla San Cristóbal. Household tap water samples were tested for levels of fecal contamination. Community level infection rates were estimated using discharge records from the Ministry of Public Health. The effects of the new DWTP and fecal contamination levels on infections were tested using logistic and Poisson models.

RESULTS

Perceptions of water quality and household practices influenced exposures to contaminated tap water. We found minimal change in drinking water sources with 85% of mothers sampled before the DWTP and 83% sampled after using bottled water, while >85% from the pooled sample used tap water for cooking and hygiene practices. The DWTP opening was associated with lower odds of fecal contamination in tap water, reported urinary infections, and community level rates of urinary and gastrointestinal infections. The household practice of recently washing the cistern contributed to higher contamination levels after the DWTP opened.

CONCLUSIONS

To ensure access to clean water, public health works need to consider how household perceptions and practices influence tap water use and quality, in addition to infrastructure improvements. Exposures to contaminated tap water contribute to the burden of infectious disease in environments with inadequate water infrastructure.

Risk-based exposure assessment for multiple toxic elements encountered by children in school playgrounds and parks in the southwest region of Saudi Arabia

Children are in direct contact with surface soil and may inadvertently ingest and inhale toxic contaminants while playing; hence, special attention should be given to playgrounds regarding toxic contaminants. The concentrations of ten toxic metals were determined in soil samples collected from school playgrounds and children's parks from the southwest region of Saudi Arabia. The soils were moderately alkaline (pH 7.6-8.8), the texture was dominated by sand particles (54-88%), and the organic matter was in the range of 2.06 to 4.82%. Analytical solutions were prepared by microwave-digestion using a HNO₃/H₂O₂ mixture, and the concentrations of toxic elements were measured by inductively coupled plasma mass spectrometry (ICP-MS). Metal concentrations were recorded in the range of 0.014-0.087, 1.14-3.54, 0.85-23.29, 0.77-36.32, 312.6-2065.7, 285.3-822.6, 75.4-240.8, 0.00-53.12, 0.52-6.80, and 1.25-92.12 mg/kg dry soil for Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn, respectively. The levels of heavy metals in the studied playgrounds were below the permissible limits, indicating insignificant influence of anthropogenic activities and can be considered as unpolluted soil. Values of the enrichment coefficient (EC) and contamination factor (CF) were found to be less than one, suggesting that the source of these elements is mainly the local soil, with the exception of Ni and Zn in certain playgrounds (CF > 1), which indicates a possible contamination from external sources. The non-carcinogenic hazard index calculated for all of the metals was below one, indicating that the exposure to heavy metal through playground soil is unlikely to produce any adverse health effect in children playing in the playgrounds.

Performance of metal–organic frameworks for the adsorptive removal of potentially toxic elements in a water system: a critical review

Elevated levels of potentially toxic elements (PTEs) in aqueous environments have drawn attention recently due to their presence and toxicity to living beings. There have been numerous attempts to remove PTEs from aqueous media. The potential of metal–organic frameworks (MOFs) in removing PTEs from aqueous media has been recognized due to their distinctive advantages (e.g., increased removal capability, large surface area, adjustable porosity, and recyclability). Because of the poor stability of MOFs in water, pre and post synthetic modification and functionalization of MOFs have also been developed for water treatment investigations. This review addresses the performance and mechanisms of PTE removal in various modified MOFs in detail. In order to compare the performance of MOFs, here we used partition coefficient (PC) instead of maximum adsorption capacity, which is sensitively influenced by initial loading concentrations. Therefore, the PC of each material was used to evaluate the adsorption performance of different MOFs and to compare with other sorbents. Furthermore, it discusses the scale-up issues and forthcoming pathway for the research and development needs of MOFs for effective PTE removal. This review further elucidates the main removal mechanisms of PTEs by MOFs. Commercial or domestic water treatment systems or water filters can utilize engineered MOFs to treat water by adsorptive removal. However, marketable products have yet to be investigated thoroughly due to limitations of the large-scale synthesis of MOFs.

This review examines the performance of metal–organic frameworks based on partition coefficient data over the classic maximum adsorption capacities.

Autoimmune potential of perchloroethylene: Role of lipid-derived aldehydes

Tetrachloroethene (perchloroethylene, PCE), an ubiquitous environmental contaminant, has been implicated in inducing autoimmunity/autoimmune diseases (ADs), including systemic lupus erythematosus (SLE) and scleroderma in humans. However, experimental evidence suggesting the potential of PCE in mediating autoimmunity is lacking. This study was, therefore, undertaken to explore PCE's potential in inducing/exacerbating an autoimmune response. Six-week old female MRL+/+ mice, in groups of 6 each, were treated with PCE (0.5mg/ml) via drinking water for 12, 18 and 24weeks and markers of autoimmunity and oxidative stress were evaluated. PCE exposure led to significant increases in serum anti-nuclear antibodies (ANA), anti-dsDNA and anti-scleroderma-70 (anti-Scl-70) antibodies at 18weeks and, to a greater extent at 24weeks, suggesting that PCE exposure exacerbated autoimmunity in our animal model. The increases in autoantibodies were associated with time-dependent increases in malondialdehyde (MDA)-protein adducts and their antibodies, as well as significantly decreased levels of antioxidants GSH and SOD. The splenocytes isolated from mice treated with PCE for 18 and 24weeks showed greater Th17 cell proliferation and increased release of IL-17 in culture supernatants following stimulation with MDA-mouse serum albumin adducts, suggesting that MDA-modified proteins may act as an immunologic trigger by activating Th17 cells and contribute to PCE-mediated autoimmunity. Our studies thus provide an experimental evidence that PCE induces/exacerbates an autoimmune response and lipid-derived aldehydes (such as MDA) contribute to this response.

Soil Contamination and Human Exposure: A Comprehensive Assessment Framework

Soil is the thin outer zone of the earth's crust that supports rooted plants and is the product of climate and living organisms acting on rock. Throughout the world, soils are contaminated to some extent by local, regional, and global pollution sources of both natural and human origin. Sources of soil contamination are identified and discussed. With the possible exception of agricultural applications of pesticides and fertilizers, most contaminant releases to soil are not easily quantified and, as a result, remain highly uncertain. In establishing a comprehensive framework for human exposure to soil contaminants, it is revealed that such exposure occurs through multiple transfer processes. The process for linking human exposure to soil contact is considered and it is found that the magnitude and persistence of exposure depend not only on the level of soil contamination but also on physical and chemical properties of soil, chemical properties of the contaminant, and the frequency and duration of human factors such as occupational and recreational activities or the consumption of home-grown food, which result in direct and indirect soil contact. All of these factors possess some degree of variance that leads to probability distributions for representing total exposure and risk.

Element profiles in hair and nails of children reflect the uptake from food and the environment

The present study evaluated if the element profiles in hair and nails of children from the Lake Victoria region in Kenya reflect uptake from food and the environment. To this purpose, the element concentrations in hair and nails were related to element concentrations measured in food items, water, and soil. The highest intake of most elements occurred via ingestion of the fish Rastrineobola argentea, which is consumed in higher quantities than other fish and food items. Element concentrations in hair and nails were correlated to food and soil in element-specific patterns. Multivariate analysis combining principal component analysis and multidimensional scaling enabled us to cluster individuals from specific sites and to relate differences between sites to food-consumption patterns and environmental exposures. Site-specific differences in macroelement concentrations among the children were attributed to patterns of food consumption, while those in microelement concentrations reflected differences in geochemical background. It is concluded that the simultaneous analysis of elements in human hair and nails allows separation of populations based on food consumption and geochemical background.

Long-term human exposure to lead from different media and intake pathways

Lead (Pb) is well known as an environmental pollutant: it can accumulate in various media, so actual lead exposure reflects both historical and present contaminations. Two main challenges then emerge: obtaining updated information to gain an overall picture of the sources of exposure, and predicting the resulting internal body exposure levels and effects that occur under long-term exposure conditions. In this paper, a modeling approach is used to meet these challenges with reference to Danish exposure conditions. Levels of lead content in various media have been coupled with data for lead intake and absorption in the human body, for both children and adults. An age-dependent biokinetic model allows then for determination of the blood lead levels resulting from chronic exposure. The study shows that the actual intake of lead is up to 27% of the Provisional Tolerable Daily Intake (PTDI) for children and around 8% for adults. It is confirmed that the critical route of exposure is via ingestion, accounting for 99% of total lead intake, while inhalation contributes only to 1% of total lead intake. The resulting lead levels in the blood after 2 years of exposure to actual contamination conditions have been estimated as up to 2.2μg/dl in children and almost 1μg/dl in adults. Impacts from lead can occur even at such levels. The role of historical and present sources to lead in the environment is discussed, and, for specific child and adult exposure scenarios, external-internal concentration relationships for the direct linkage between lead in environmental media and resulting concentrations of lead in blood are then presented.

Early lifestage exposure and potential developmental susceptibility to tetrachloroethylene

BACKGROUND

Tetrachloroethylene, also known as perchloroethylene or "perc", is a highly volatile and lipophilic solvent widely used in dry cleaning, textile processing, and metal-cleaning operations. The limited epidemiological and toxicological data available for exposure to perc during developmental lifestages, as well as the evidence for critical windows of exposure, highlight early life as a period of potential susceptibility.

METHODS

A literature search was performed to identify all peer-reviewed epidemiological and toxicologial studies examining outcomes from early lifestage exposure to perc, and reviewed by developmental stage for both exposure and outcome.

RESULTS

Exposure scenarios to perc unique to early lifestages include transplacental and breast milk intake, along with inhalation, ingestion, or dermal exposure. Toxicokinetics factors that may influence early lifestage susceptibility to perc, along with existing physiologically based pharmacokinetic (PBPK) models, are described. Adverse outcomes examined include: reproductive outcomes examined prior to conception including reduced fertility, adverse effects on sperm, or altered reproductive hormones; prenatal outcomes examined after exposure prior to conception or prenatally including fetal death, birth defects, and decreased birth weight; postnatal outcomes examined after exposure prior to conception, prenatally, or during childhood including neurotoxicity, immunotoxicity, cancer, hepatotoxicity, congential anomalies and mortality; and adult schizophrenia examined after exposure prior to conception.

CONCLUSIONS

The limited evidence on early lifestage exposure to perc does not provide sufficient evidence of this sensitive period as being more or less important than exposure at a later lifestage, such as during adulthood. However, there are a number of adverse health effects observed uniquely in early lifestages, and increased sensitivity to visual system deficits is suggested in children. Other outcomes observed in adults may not have been adequately assessed in children to directly compare sensitivity.

Induction of heme oxygenase 1 by arsenite inhibits cytokine-induced monocyte adhesion to human endothelial cells

Heme oxygenase-1 (HO-1) is an oxidative stress responsive gene upregulated by various physiological and exogenous stimuli. Arsenite, as an oxidative stressor, is a potent inducer of HO-1 in human and rodent cells. In this study, we investigated the mechanistic role of arsenite-induced HO-1 in modulating tumor necrosis factor alpha (TNF-alpha) induced monocyte adhesion to human umbilical vein endothelial cells (HUVEC). Arsenite pretreatment, which upregulated HO-1 in a time- and concentration-dependent manner, inhibited TNF-alpha-induced monocyte adhesion to HUVEC and intercellular adhesion molecule 1 protein expression by 50% and 40%, respectively. Importantly, knockdown of HO-1 by small interfering RNA abolished the arsenite-induced inhibitory effects. These results indicate that induction of HO-1 by arsenite inhibits the cytokine-induced monocyte adhesion to HUVEC by suppressing adhesion molecule expression. These findings established an important mechanistic link between the functional monocyte adhesion properties of HUVEC and the induction of HO-1 by arsenite.

Dual actions involved in arsenite-induced oxidative DNA damage

Arsenic is a recognized human carcinogen, but the mechanism of carcinogenesis is not well understood. Oxidative stress and inhibition of DNA damage repair have been postulated as potential carcinogenic actions of arsenic. The present study tests the hypothesis that arsenite not only induces oxidative stress but also inhibits the activity of the DNA base excision repair protein, poly(ADP-ribose) polymerase-1 (PARP-1), leading to exacerbation of the oxidative DNA damage induced by arsenic. HaCat cells were treated with arsenite for 24 h before measuring 8-hydroxyl-2'-deoxyguanosine (8-OHdG), PARP-1 activity, and reactive oxygen species (ROS). Zinc supplementation and PARP-1 siRNA were used to increase or decrease, respectively, the PARP-1 protein's physiological function. At high concentrations (10 microM or higher), arsenite greatly induced oxidative DNA damage, as indicated by 8-OHdG formation. At lower concentrations (1 microM), arsenite did not produce detectable 8-OHdG, but was still able to effectively inhibit PARP-1 activity. Zinc supplementation reduced the formation of 8-OHdG, restored the PARP-1 activity inhibited by arsenite, but did not decrease ROS production. SiRNA knockdown of PARP-1 did not affect the 8-OHdG level induced by arsenic, while it greatly increased the 8-OHdG level produced by hydrogen peroxide indicating that PARP-1 is a molecular target of arsenite. Our findings demonstrate that in addition to inducing oxidative stress at higher concentrations, arsenite can also inhibit the function of a key DNA repair protein, PARP-1, even at very low concentrations, thus exacerbating the overall oxidative DNA damage produced by arsenite, and potentially, by other oxidants as well.

Merging models and biomonitoring data to characterize sources and pathways of human exposure to organophosphorus pesticides in the Salinas Valley of California

We characterize cumulative intakes of organophosphorus (OP) pesticides in an agricultural region of California by drawing on human biomonitoring data, California pesticide use reporting (PUR) data, and limited environmental samples together with outputs from the CalTOX multimedia, multipathway, source-to-dose model. The study population is the CHAMACOS cohort of almost 600 pregnant Latina women in the Salinas Valley region. We use model estimates of OP intake and urinary dialkylphosphate (DAP) metabolite excretion to develop premises about relative contributions from different exposure sources and pathways. We evaluate these premises by comparing the magnitude and variation of DAPs in the CHAMACOS cohort with those of the whole U.S. population using data from the National Health and Nutrition Examination Survey (NHANES). This comparison supports the premise that diet is the common and dominant exposure pathway in both populations. Biomarker comparisons and model results support the observation that, relative to NHANES, the CHAMACOS population has a statistically significant (p < 0.001) added intake of OP pesticides with low inter-individual variability. We attribute the magnitude and small variance of this intake to residential nondietary exposures from local agricultural OP uses. These results show that mass-balance models can estimate exposures for OP pesticides within the range measured by biological monitoring.

Metals in soils of children's urban environments in the small northern European city of Uppsala

Metals occur naturally in soil, but contents are generally increased in the urban environment due to anthropogenic activities. The presence of elevated metals in soils of the urban environment has been recognized as an important source of metal intake in children and is linked to elevated metal levels in children's blood. Several metals have undesirable health effects, especially on children due to their still developing nervous system and small body volumes. Playgrounds are where urban children spend most of their time outdoors and are also where children most frequently come in contact with soil. Elevated contents of metals in playgrounds are therefore of great concern for children's wellbeing. This study investigates the soil metal content of 25 playgrounds located in different land use areas in urban Uppsala, Sweden's fourth largest city. Uppsala covers an area of approximately 100 km2 and has a population of 136,000. The soil samples were analysed for 12 metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, W, Zn) using aqua regia. Median metal contents were found to be 1.8, 3.4, 0.21, 32, 25, 2.5, 0.14, 494, 19, 26, 0.35 and 84 mg kg(-1) soil for each of the above metals, respectively. The median clay content was around 20% while the organic matter content was measured by loss on ignition at a median of 8%. The land use areas included industrial land, the city center, road verges, natural land and former industrial land. The results showed that land use did not have the expected large influence on the total metal contents of the soils tested. The clay content together with the age of the site proved to be a more important factor. Sites with elevated clay contents had in general elevated metal contents, which were explained by the relatively high adsorption capacity of clay particles. The soils at sites where land use had not been altered since the 1800s had increased metal contents compared to playgrounds constructed in the late 1900s. The immobility of metals once they had entered the soil system was the reason for increased metal content in soils of old playgrounds. It was concluded that in cities with few internal pollution sources, the soil characteristics of the site and the time the soil has been on-site to accumulate metal residues become important factors in determining the soil metal content.

Recovery of peroxides in saliva during home bleaching - influence of smoking

The study aimed at determining hydrogen peroxide recovery in saliva during use of different home bleaching products by smokers and non-smokers. Peroxide recovery was evaluated with respect to the safe level reported in the literature. Determination of peroxide levels in saliva was performed with peroxidase, phenol and 4-aminoantipyrin in a photometric method. Four different bleaching regimens were used by 10 smokers and 10 non-smokers: Whitestrips, Vivastyle (tray-based) and two paint-on products (Crest Night Effects, Colgate Simply White). Whole saliva was collected and total amount of peroxide (mg) released during the 60 min bleaching period was determined: Colgate Simply White: 2.67 +/-0.88 (non-smokers); 2.66 +/- 1.17 (smokers); Crest Night Effects: 0.23 +/- 0.13 (non-smokers); 0.25 +/-0.16 (smokers); Vivastyle: 2.47 +/- 0.82 (non-smokers), 2.44 +/- 1.31 (smokers); Whitestrips: 1.39 +/- 0.62 (non-smokers), 2.02 +/- 1.86 (smokers). In terms of amount of peroxide kg(-1) body weight the bleaching systems led to a single exposure of 0.004-0.046 mg kg(-1), which is distinctly less than safe daily dose of 0.26 mg kg(-1) day(-1), if calculated for a small person (58 kg). The criterion smoker versus non-smokers had no influence on peroxide levels in the oral cavity.

CONCLUSION

Smoking did not appear to impact the anti-oxidant defence capacity of the oral cavity with respect to degrading peroxides released from bleaching products. Significantly lower amounts of peroxides were detected in saliva during application of the paint-on product Crest Nights Effects compared with the other bleaching systems.

Reconstructing population exposures from dose biomarkers: inhalation of trichloroethylene (TCE) as a case study

Physiologically based pharmacokinetic (PBPK) modeling is a well-established toxicological tool designed to relate exposure to a target tissue dose. The emergence of federal and state programs for environmental health tracking and the availability of exposure monitoring through biomarkers creates the opportunity to apply PBPK models to estimate exposures to environmental contaminants from urine, blood, and tissue samples. However, reconstructing exposures for large populations is complicated by often having too few biomarker samples, large uncertainties about exposures, and large interindividual variability. In this paper, we use an illustrative case study to identify some of these difficulties, and for a process for confronting them by reconstructing population-scale exposures using Bayesian inference. The application consists of interpreting biomarker data from eight adult males with controlled exposures to trichloroethylene (TCE) as if the biomarkers were random samples from a large population with unknown exposure conditions. The TCE concentrations in blood from the individuals fell into two distinctly different groups even though the individuals were simultaneously in a single exposure chamber. We successfully reconstructed the exposure scenarios for both subgroups - although the reconstruction of one subgroup is different than what is believed to be the true experimental conditions. We were however unable to predict with high certainty the concentration of TCE in air.

Contribution of locally grown foods in cumulative exposure assessments

Both laboratory and field studies confirm the importance of vegetation for scavenging semivolatile organic chemicals (SVOCs) from the atmosphere and a number of exposure studies have found that the dietary pathway is often a significant contributor to cumulative exposure for these chemicals. However, little information exists on the atmospheric source-to-dietary intake linkage for SVOCs. Because of higher SVOC emissions to urban regions, this linkage is particularly important for foods that are grown, distributed and consumed in or near urban regions. The food pathway can also contribute to dietary exposure for populations that are remote from a pollutant source if the pollutants can migrate to agricultural regions and subsequently to the agricultural commodities distributed to that population. We use available data, the characteristic travel distance, and the CalTOX multimedia model framework to assess the contribution of local sources of food to cumulative SVOC intake. Based on published concentration data for foods, our exposure calculations indicate that the potential intake through ingestion can be up to 1000 times that of inhalation for certain persistent SVOCs. We use the population-based intake fraction (iF) to determine how SVOC intake can vary among food commodities and exposure pathways, and to determine the contribution of airborne emitted SVOCs to the diet in the Northern Hemisphere. We focus on three representative multimedia SVOCs-benzo(a)pyrene, fluoranthene, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The approach presented here provides a useful framework and starting point for source-to-intake assessments for the ambient air-to-dietary exposure pathway.

Using stochastic risk assessment in setting information priorities for managing dioxin impact from a municipal waste incinerator

The objectives of this study were to assess site-specific carcinogenic risk of incinerator-emitted dioxins in a manner reflecting pollutant transfer across multimedia and multi-pathways. The study used site-specific environmental and exposure information and combined the Monte Carlo method with multimedia modeling to produce probability distributions of risk estimates. The risk estimates were further categorized by contaminated environmental media and exposure pathways that are experienced by human receptors in order to pinpoint significant sources of risk. Rank correlation coefficients were also calculated along with the Monte Carlo sampling to identify key factors that influenced estimation of risk. The results showed that ingestion accounted for more than 90% of the total risk and that risk control on ingestion of eggs, aboveground vegetables, and poultry should receive priority. It was also found that variation of parameters with variability accounted for around 35% of the total risk variance, while uncertainty contributed to the remaining 65%. Intake rates of aboveground vegetables, eggs, and poultry were the key parameters with the largest contribution to variance. In addition, sufficient sampling and analysis of dioxin contents in eggs, aboveground vegetables, poultry, soil, and fruit should be performed to improve risk estimation because the variation in concentrations in these media accounted for the largest overall risk variance. Finally, focus should be placed on reduction of uncertainty associated with the risk estimation through ingestion of aboveground vegetables, eggs, poultry, fruit, and soil because the risk estimates associated with these exposure pathways had the largest variance.

Health cancer risk assessment for arsenic exposure in potentially contaminated areas by fertilizer plants: a possible regulatory approach applied to a case study in Moscow region-Russia

At present, fertilizer industry plants are considered as a potential source of soil contamination in Russia. Therefore health risk assessment should be pursued in Russian fertilizer plant areas, but unfortunately risk assessment methodology for contaminated sites does not have yet a regulatory value in Russia. In this paper a possible and intentionally simple regulatory approach for health cancer risk assessment at phosphogypsum waste-storing potentially contaminated sites is presented. The proposed approach is applied to a potential contaminated area located in the Moscow river (Moscow Region) protective zone. At this case-study area, arsenic has been chosen as a contaminant indicator, according to the proposed selection procedure. For estimating the human exposure to arsenic through various pathways the original McKone & Daniels '91 model has been adapted. As a specific result of the risk assessment for the case-study area, it has been shown that arsenic exposure pathways (in risk-ranking order) "ingestion of agricultural products," "groundwater uptake," "dermal contact," and "soil ingestion" pose a significant health risk. From a general point of view, the proposed and applied health risk assessment approach could give some contribution (for comparison and discussion) for policies on contaminated soils to other countries. In this perspective, the paper expressly considers the current Italian regulative situation concerning restricted use of risk analysis and concerning soil quality for agricultural land use.

Transfer of dioxin risk between nine major municipal waste incinerators in Taiwan

The objective of this study was to assess site-specific carcinogenic risks of incinerator-emitted dioxins and risk transfers among the areas covered by nine municipal incinerators in Taiwan. We used actual emission data and the industrial source complex short-term model (ISCST3) to determine the dioxin impact areas within the 8 x 8-km simulation regions surrounding the incinerators. We then used multimedia model to estimate cancer risks in individual impact areas for two exposure scenarios, which were sufficient (SFP) and insufficient food production (IFP) for residents' consumption in each impact area. We also used information of food supply and consumption between impact areas to calculate risk transfers among these nine incinerators. We found that dioxins' carcinogenic risks ranged from 1.4 x 10(-8) (Incinerator F) to 7.1 x 10(-5) (Incinerator A) for the nine incinerators under the exposure scenario of SFP, and ranged from 8.7 x 10(-8) (Incinerator D) to 1.1 X 10(-6) (Incinerator E) under the exposure scenario of IFP. The food ingestion was the main exposure pathway, which accounted for 64-99% of total dioxin risks among nine impact areas. For the nine major food items consumed by residents in the impact areas, eggs (14-35%) and chicken (11-26%) were two main routes of dioxin exposure in the SFP scenario, while chicken (8-78%) and vegetables (0.2-81%) were two main routes of dioxin exposure in the IFP scenario. Significant risks of dioxins were transferred among incinerators, which accounted for up to 88% among the incinerators. Incinerator E was the major risk-exporting source to six Incinerators C, D, F, G, H, and I. For these six incinerators, Incinerator E accounted for their 51-88% imported risks. We concluded that risk transfers among incinerators through routes of food consumption should be considered in assessing health risks associated with incinerator-emitted dioxins in Taiwan. We should place high priority on implementing control measures to lower dioxin emissions in important food-exporting areas like Incinerator E. We should also emphasize analyzing dioxin contents in eggs, chicken, and vegetables in order to improve dioxin-related health risk assessments in the future.

Concordance across species in the reproductive and developmental toxicity of tetrachloroethylene

Reproductive and developmental toxicities resulting from exposure to tetrachloroethylene include delayed or impaired conception, sperm quality, death during development, developmental neurotoxicity, and growth retardation. In most cases there was concordance between rodents and humans. The risk assessments indicated that neurotoxicity was the most sensitive endpoint for inhalation, whereas growth retardation was the most sensitive endpoint when exposure was by the oral route. The reference concentration (RfC) of 0.01 ppm was based on neurotoxicity among human subjects. The reference dose (RfD) of 0.0006 mg/kg per day was based on small for gestation age infants. In both cases, studies in rodents supported the credibility of these assessments. For the RfD, similar findings for other trihalomethanes have been reported. The latter part of pregnancy and early life may constitute a susceptible period for alterations leading to behavioral deficits. During this period, the capacity to metabolize tetrachloroethylene is reduced and may further contribute to the sensitivity during this phase of development. Studies suggest that an effect on dopamine metabolism is a plausible mode of action for some types of neurotoxicity. In addition, it has been suggested that this alteration may affect reproductive integrity by influencing prolactin levels.

Parameter uncertainty and variability in evaluative fate and exposure models

The human toxicity potential, a weighting scheme used to evaluate toxic emissions for life cycle assessment and toxics release inventories, is based on potential dose calculations and toxicity factors. This paper evaluates the variance in potential dose calculations that can be attributed to the uncertainty in chemical-specific input parameters as well as the variability in exposure factors and landscape parameters. A knowledge of the uncertainty allows us to assess the robustness of a decision based on the toxicity potential; a knowledge of the sources of uncertainty allows us to focus our resources if we want to reduce the uncertainty. The potential dose of 236 chemicals was assessed. The chemicals were grouped by dominant exposure route, and a Monte Carlo analysis was conducted for one representative chemical in each group. The variance is typically one to two orders of magnitude. For comparison, the point estimates in potential dose for 236 chemicals span ten orders of magnitude. Most of the variance in the potential dose is due to chemical-specific input parameters, especially half-lives, although exposure factors such as fish intake and the source of drinking water can be important for chemicals whose dominant exposure is through indirect routes. Landscape characteristics are generally of minor importance.

Assessing environmental exposure to PCBs among Mohawks at Akwesasne through the use of geostatistical methods

The Mohawk Nation at Akwesasne is a Native American community located along the St. Lawrence River in New York State, Ontario, and Quebec. One component of a multiphase human health study was to assess the impact of different pathways of human exposure resulting from the off-site migration of polychlorinated biphenyl (PCB) contamination in this area. This paper illustrates how mapped residential information and environmental sampling data can be united to assist in exposure assessment for epidemiologic studies using geographic information system (GIS) technology and statistical methods. A proportional sampling scheme was developed to collect 119 surface soils. Using a method of cross validation, the average estimated error can be computed and the best estimator can be selected. Seven spatial methods were examined to estimate surface soil PCB concentrations; the lowest relative mean error was 0.42% for Inverse 3 nearest neighbor weighted according to the inverse distance, and the highest relative mean error was 4.4% for Voronoi polygons. Residual plots indicated that all methods performed well except near some of the sampling points that formed the outer boundaries of the sampling distribution.

Uncertainty and variability in human exposures to soil contaminants through home-grown food: a Monte Carlo assessment

This paper presents a general model for exposure to homegrown foods that is used with a Monte Carlo analysis to determine the relative contributions of variability (Type A uncertainty) and true uncertainty (Type B uncertainty) to the overall variance in prediction of the dose-to-concentration ratio. Although classification of exposure inputs as uncertain or variable is somewhat subjective, food consumption rates and exposure duration are judged to have a predicted variance that is dominated by variability among individuals by age, income, culture, and geographical region. Whereas, biotransfer factors and partition factors are inputs that, to a large extent, involve uncertainty. Using ingestion of fruits, vegetables, grains, dairy products, and meat and soils assumed to be contaminated by hexachlorobenzene (HCB) and benzo(a)pyrene (BaP) as cases studies, a Monte Carlo analysis is used to explore the relative contribution of uncertainty and variability to overall variance in the estimated distribution of potential dose within the population that consumes home-grown foods. It is found that, when soil concentrations are specified, variances in ratios of dose-to-concentration for HCB are equally attributable to uncertainty and variability, whereas for BaP, variance in these ratios is dominated by true uncertainty.

Maternal toxicity and the identification of inorganic arsenic as a developmental toxicant

Assessment of the potential developmental toxicity of arsenic in humans must be based entirely on the extensive animal literature; no appropriate human data are available. Hazard identification of developmental toxicity of arsenic in animal studies is complicated by the co-occurrence of maternal and developmental toxicity when the pregnant dam is exposed to the toxicant. Current regulatory guidance requires that, when maternal and developmental toxicity occur at the same or similar doses, detailed consideration needs to be given to whether developmental toxicity is secondary to maternal toxicity or whether it represents a distinct hazard. In this review, these principles were applied to the relatively large database of animal studies available for hazard identification of inorganic arsenic as a developmental toxicant. It is concluded that maternal and developmental toxicity occur in the same dose range for this potent cytotoxicant, although differential no observed adverse effect levels can be identified depending on the endpoints used. Various evidence from the basic science literature indicates that developmental toxicity is not secondary to maternal toxicity. Current regulatory guidance falls short of defining effective approaches to resolving the difficulties posed by co-occurrence of maternal and developmental toxicity.

Assessing the relationship between environmental lead concentrations and adult blood lead levels

This paper presents a model for predicting blood lead levels in adults who are exposed to elevated environmental levels of lead. The model assumes a baseline blood lead level based on average blood lead levels for adults described in two recent U.S. studies. The baseline blood level in adults arises primarily from exposure to lead in diet. Media-specific ingestion and absorption parameters are assessed for the adult population, and a biokinetic slope factor that relates uptake of lead into the body to blood lead levels is estimated. These parameters are applied to predict blood lead levels for adults exposed to a hypothetical site with elevated lead levels in soil, dust and air. Blood lead levels ranging from approximately 3-57 micrograms/dl are predicted, depending on the exposure scenarios and assumptions.

Risk assessment of water pollutants

The sources of toxic xenobiotics and different factors such as ecological diversity, differences in comparative anatomy, physiology and biochemistry, food chain variation, interrelationship within species and life span, etc., are considered during risk assessment of pollutants, and their impact on aquatic ecotoxicology is identified. A fugacity and multimedia compartment model is suggested, based on toxicodynamic (toxicity of the chemical) and toxicokinetic (metabolism of the chemical) considerations to predict and screen the behaviour of pollutants quantitatively in the aquatic environment. The significance of the risk analysis approach in anticipatory actions and regulation of pollution levels is discussed.

A proposed approach to regulating contaminated soil: identify safe concentrations for seven of the most frequently encountered exposure scenarios

Since 1980, more than 10,000 sites in the United States have been shown to contain soil which has elevated concentrations of various xenobiotics. Since that time, guidelines for deciding whether the level of contamination is worthy of concern have been proposed or promulgated by dozens of local, state, and federal regulatory agencies. Unfortunately, there has been little consistency in the guidelines suggested for each soil contaminant. For example, (a) the basis or rationale for some of the cleanup levels is unclear, (b) approaches to setting cleanup levels vary between states and agencies, (c) cleanup objectives often vary among agencies within the same state, and (d) the cleanup levels are usually set in a scientifically haphazard manner. This paper proposes that the most cost-effective and efficient way to quickly regulate contaminated soil is to establish "safe" concentrations for each chemical for the seven most common exposure scenarios. These exposure scenarios include (1) residential, (2) industrial, (3) agricultural, (4) recreational, (5) groundwater, (6) wildlife and aquatic species, and (7) runoff/erosion of particulates to waterways. The scientific approach and rationale for calculating the cleanup criteria are illustrated by evaluating dioxin and benzene, toluene, and xylene (BTX). The methods suggested here indicate that levels of dioxin of 25 and 50 ppb in residential and industrial soils, respectively, should be acceptable. The predominant concern for the agricultural and recreational scenarios is the runoff of particulates to waterways. For BTX, benzene will dictate the degree of cleanup and the primary hazard at most residential sites will be the inhalation of vapors. Benzene concentrations of 2.5, 14, and 250 ppm should be acceptable for residential, industrial, and recreational soils, respectively. Depending on the depth to groundwater and aquifer use, protection of groundwater may be the driving concern for establishing BTX cleanup levels and must be determined using site-specific factors.