Implications of chemical mixtures in public health practice

Evaluation of the cancer risk from PAHs by inhalation: Are current methods fit for purpose?

There is ample evidence from occupational studies that exposure to a mixture of Polycyclic Aromatic Hydrocarbons (PAHs) is causally associated with an increased incidence of lung cancers. In both occupational atmospheres and ambient air, PAHs are present as a mixture of many compounds, but the composition of the mixture in ambient air differs from that in the occupational atmosphere, and varies in time and space in ambient air. Estimates of cancer risk for PAH mixtures are based upon unit risks which derive from extrapolation of occupational exposure data or animal model data, and in the case of the WHO use one compound, benzo[a]pyrene as a marker for the entire mixture, irrespective of composition. The U.S. EPA has used an animal exposure study to derive a unit risk for inhalation exposure to benzo[a]pyrene alone, and there have been a number of rankings of relative carcinogenic potency for other PAHs which many studies have used to calculate a cancer risk from the PAHs mixture, frequently incorrectly by adding the estimated relative risks of individual compounds, and applying the total "B[a]P equivalent" to the WHO unit risk, which already applies to the entire mixture. Such studies are often based upon data solely for the historic US EPA group of 16 compounds which do not include many of the apparently more potent carcinogens. There are no data for human cancer risk of individual PAHs, and conflicting evidence of additivity of PAH carcinogenicity in mixtures. This paper finds large divergences between risk estimates deriving from the WHO and U.S. EPA methods, as well as considerable sensitivity to the mixture composition, and assumed PAH relative potencies. Of the two methods, the WHO approach appears more likely to provide reliable risk estimates, but recently proposed mixture-based approaches using in vitro toxicity data may offer some advantages.

Metallic nanoparticles affect uptake of polycyclic aromatic hydrocarbons and impacts in the Mediterranean mussels Mytilus galloprovincialis

The impact of metallic nanoparticles (NPs) on the uptake and toxicity of persistent organic pollutants by marine bivalves was assessed through a comparative laboratory study by exposing mussels to polycyclic aromatic hydrocarbon (PAHs), in the presence and absence of ZnO and TiO₂ NPs. PAHs and NPs concentration was analyzed after 14 days of exposure in mussels by GC/MS and ICP/AES. Furthermore, impact on the physiology and neurotoxicity of PAHs and NPs acting alone or in mixtures were also determined. Our results confirmed the bio-uptake of PAHs and NPs by mussels. In addition, the exposure NPs-PAHs resulted in different bio-uptake profile to that of PAHs alone. The NPs and accumulation of PAHs led to disturbance of essential metals concentration and to different impact profiles in the filtration and respiration capacities as well as in the acetylcholinesterase activity. Antagonist interactions between NPs and PAHs could occur after exposure.

The cadmium toxicity in gills of Mytilus coruscus was accentuated by benzo(a)pyrene of higher dose but not lower dose

In natural environment, the existence of interactions of toxic mixtures could induce diverse biochemical pathways and consequently exert different toxicological responses in aquatic organisms. However, little information is available on the effects of combined xenobiotics on lower aquatic invertebrates. Here, we assessed the effects of cadmium (Cd, 0.31 mg/L) as well as the mixture of Cd (0.31 mg/L) and benzo(a)pyrene (Bap, 5 or 50 μg/L) on bioaccumulation, antioxidant, lipid peroxidation (LPO) and metallothionein (MT) responses in gills of thick shell mussel Mytilus coruscus. Upon exposed to single Cd, the metal bioaccumulation, antioxidant enzymes activities, LPO and MT level significantly increased in the gills, suggesting an apparent toxicity to mussels. The interaction of Cd + 5 μg/L Bap did not significantly alter these endpoints compared to single Cd. However, once the dose of Bap elevated to 50 μg/L, the induction of bioaccumulation, antioxidant system and LPO was even more pronounced while the induction of MT was remarkably inhibited, implying an accentuated toxicity. Collectively, the current results demonstrated that 0.31 mg/L Cd exposure resulted in severe toxicity to mussels despite of the induction of MT system to alleviate the metal toxicity. Once the Cd exposure combined with Bap, the lower dose of Bap could not change the Cd toxicity while the higher dose of Bap accentuated the toxicity by inhibiting metallothionein synthesis. These findings might provide some useful clues for elucidation the mechanism of the interaction of combined xenobiotics in molluscs.

QSAR Models for Human Carcinogenicity: An Assessment Based on Oral and Inhalation Slope Factors

Carcinogenicity is a crucial endpoint for the safety assessment of chemicals and products. During the last few decades, the development of quantitative structure-activity relationship ((Q)SAR) models has gained importance for regulatory use, in combination with in vitro testing or expert-based reasoning. Several classification models can now predict both human and rat carcinogenicity, but there are few models to quantitatively assess carcinogenicity in humans. To our knowledge, slope factor (SF), a parameter describing carcinogenicity potential used especially for human risk assessment of contaminated sites, has never been modeled for both inhalation and oral exposures. In this study, we developed classification and regression models for inhalation and oral SFs using data from the Risk Assessment Information System (RAIS) and different machine learning approaches. The models performed well in classification, with accuracies for the external set of 0.76 and 0.74 for oral and inhalation exposure, respectively, and r2 values of 0.57 and 0.65 in the regression models for oral and inhalation SFs in external validation. These models might therefore support regulators in (de)prioritizing substances for regulatory action and in weighing evidence in the context of chemical safety assessments. Moreover, these models are implemented on the VEGA platform and are now freely downloadable online.

Fluoride and endosulfan together potentiate cytogenetic effects in Swiss albino mice bone marrow cells

In this study, the cytotoxic potential of fluoride and endosulfan in combination was investigated in Swiss albino mice bone marrow cells using the chromosomal aberration (CA) and micronucleus (MN) test systems. Fluoride (25.1 mg kg^-1 body weight [bw] in water) and endosulfan (1.8 mg kg^-1 bw by oral intubation) were administered orally alone and in combination (fluoride 25.1 mg kg^-1 bw + endosulfan 1.8 mg kg^-1 bw) to male Swiss albino mice daily for 30 days. A significant (p < 0.01) increase in micronuclei (MNs) induction and decreased ratio (p < 0.01) of polychromatic to normonochromatic erythrocytes (indicators of cytotoxicity) were observed compared with saline controls when animals were given the combination of fluoride and endosulfan. A significant (p < 0.01) increase in MNs induction and no change in the polychromatic erythrocytes to erythrocyte ratio were also observed when endosulfan was given alone. CAs such as gaps, breaks, fragments, rings, exchanges, and polyploidy were recorded in the bone marrow cells. The mean percent frequency of CAs was increased (p < 0.01) in all the treated groups compared with the control saline group. In the combination group (F + E), the percent frequencies of CAs were significantly higher (13.875%) compared with those in the individual treatment groups of fluoride (4.375%) and endosulfan (6.25%). The mitotic index was calculated as percentage of dividing cells. A significant (p < 0.01) decrease in mitotic index was observed in all treated groups compared with controls. In the combination group (F + E), mitotic index was significantly less than (p < 0.01; 4.1 ± 0.49) the saline control (10.8 ± 0.98). These results indicated that repeated intake of endosulfan through various sources in fluoride affected areas resulted in increased cytotoxic effects. The greater effect in the combination group indicated additive interaction of fluoride and endosulfan in inducing cytotoxicity in Swiss albino mice.

Combination of fluoride and endosulfan induced teratogenicity and developmental toxicity in Swiss albino mice exposed during organogenesis

The present investigation was conducted to evaluate the teratogenic and developmental toxicity of fluoride and endosulfan alone and in combination in pregnant Swiss albino mice exposed during the organogenetic period (5-14 days) of gestation. Fluoride (25.1 mg/kg body weight in water) and endosulfan (1.8 mg/kg bw by oral intubation) when administered alone and in combination (fluoride 25.1 mg/kg bw + endosulfan 1.8 mg/kg bw) to pregnant mice caused significant teratogenic effects in developing fetuses. There was no maternal mortality but significant decreases in maternal weight gain and numbers of live fetuses and significant increases in numbers of fetal resorption were recorded in the treated groups. The fetal body weight and litter size also decreased significantly in all treated groups. No external malformations were observed in any of the fetuses. The percent of visceral and skeletal anomalies increased in the fetuses of all treated groups. The fetal malformations observed were internal hydrocephaly, microphthalmia, anophthalmia, pulmonary edema, subcutaneous edema, reduced ossification of skull bones, widened cranial sutures, rib anomalies (short, wavy, partially ossified, or absent ribs), and reduced ossification of phalanges. The occurrence of visceral and skeletal malformations was more severe in the combination group, suggesting additive interaction of fluoride and endosulfan in inducing developmental toxicity in Swiss albino mice.

Antagonistic Interactions between Benzo[a]pyrene and Fullerene (C60) in Toxicological Response of Marine Mussels

This study aimed to assess the ecotoxicological effects of the interaction of fullerene (C60) and benzo[a]pyrene (B[a]P) on the marine mussel, Mytilus galloprovincialis. The uptake of nC60, B[a]P and mixtures of nC60 and B[a]P into tissues was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Biomarkers of DNA damage as well as proteomics analysis were applied to unravel the interactive effect of B[a]P and C60. Antagonistic responses were observed at the genotoxic and proteomic level. Differentially expressed proteins (DEPs) were only identified in the B[a]P single exposure and the B[a]P mixture exposure groups containing 1 mg/L of C60, the majority of which were downregulated (~52%). No DEPs were identified at any of the concentrations of nC60 (p < 0.05, 1% FDR). Using DEPs identified at a threshold of (p < 0.05; B[a]P and B[a]P mixture with nC60), gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that these proteins were enriched with a broad spectrum of biological processes and pathways, including those broadly associated with protein processing, cellular processes and environmental information processing. Among those significantly enriched pathways, the ribosome was consistently the top enriched term irrespective of treatment or concentration and plays an important role as the site of biological protein synthesis and translation. Our results demonstrate the complex multi-modal response to environmental stressors in M. galloprovincialis.

Applications and factors influencing of the persulfate-based advanced oxidation processes for the remediation of groundwater and soil contaminated with organic compounds

Persulfate is the latest oxidant which is being used increasingly for the remediation of groundwater and soil contaminated with organic compounds. It is of great significant to offer readers a general summary about different methods of activating persulfate, mainly including heat-activated, metal ions-activated, UV-activated, and alkaline-activated. Meanwhile, in addition to persulfate concentration as an influencing factor for persulfate oxidation process, selected information like temperature, anions, cations, pH, and humic acid are presented and discussed. The last section focuses on the advantages of different activated persulfate processes, and the suggestions and research needs for persulfate-based advanced oxidation in the remediation of polluted groundwater and soil.

Exposure to chemical hazards in petrol pumps stations in Ahvaz City, Iran

The objective of this study was to assess the level of exposure to BTEX (benzene, toluene, ethylbenzene, xylenes) in petrol pump stations in Ahvaz City. Two of the biggest fuelling stations were selected randomly among total 12 fuel stations of Ahvaz City, Iran, during September 2013. Thirty air samples were taken from different positions in the fuelling stations and 15 samples were taken from the personal breathing zone of operators and of customers in fuelling stations. Measuring the ambient concentration of benzene, toluene, ethylbenzene, and xylenes was done according to the method advised by National Institute for Occupational Safety and Health (NIOSH) 1501. This study showed that the concentration of benzene was very high (compared with the Iranian occupational exposure limit [OEL] standard) in ambient air of petrol stations in Ahvaz, which is considered as a high risk to the health of workers. Controlling the level of benzene in petrol stations is necessary. A new designed petrol nozzle was proposed for this purpose.

Combined endosulfan and cypermethrin-induced toxicity to embryo-larval development of Rhinella arenarum

The combined effects of two widely used pesticides, endosulfan and cypermethrin, on survival of embryo-larval development of the South American toad (Rhinella arenarum) were examined. The toxicity bioassays were performed according to the AMPHITOX test. Embryos and larvae were exposed to mixtures of these pesticides at equitoxic ratios from acute or chronic exposure to evaluate interaction effects. The results were analyzed using both Marking's additive index and combination index (CI)-isobologram methods. Acute (96-h) and intermediate (168-h) toxicity of endosulfan-cypermethrin mixtures remained almost constant for larvae and embryos, but when exposure duration was increased, there was a significant elevation in toxicity, obtaining chronic (240-h) no-observed-effect concentrations (NOEC) values of 0.045 and 0.16 mg/L for embryos and larvae, respectively. These are environmentally relevant concentrations that reflect a realistic risk of this pesticide mixture to this native amphibian species. The toxicity increment with the exposure duration was coincident with the central nervous system development on embryos reaching the larval period, the main target organ of these pesticides. The interactions of the pesticide mixtures at acute and chronic exposure were antagonistic for embryo development (CI > 1), and additive (CI = 1) for larvae, while chronic exposure interactions were synergistic (CI < 1) for both developmental periods. Data indicated that endosulfan-cypermethrin mixtures resulted in different interaction types depending on duration and developmental stage exposed. As a general pattern and considering conditions of overall developmental period and chronic exposure, this pesticide mixture usually applied in Argentine crop fields is synergistic with respect to toxicity for this native amphibian species.

Interspecies uncertainty in molecular responses and toxicity of mixtures

Most of the experimental toxicity testing data for chemicals are generated through the use of laboratory animals, namely, rodents such as rats and mice or other species. Interspecies extrapolation is needed to nullify the differences between species so as to use such data for human health/risk assessment. Thus, understanding of interspecies differences is important in extrapolating the laboratory results to humans and conducting human risk assessments based on current credible scientific knowledge. Major causes of interspecies differences in anatomy and physiology, toxicokinetics, injury repair, molecular receptors, and signal transduction pathways responsible for variations in responses to toxic chemicals are outlined. In the risk assessment process, uncertainty associated with data gaps in our knowledge is reflected by application of uncertainty factors for interspecies differences. Refinement of the risk assessment methods is the ultimate goal as we strive to realistically evaluate the impact of toxic chemicals on human populations. Using specific examples from current risk assessment practice, this chapter illustrates the integration of interspecies differences in evaluation of individual chemicals and chemical mixtures.

Patterns of exposure to multiple metals and associations with neurodevelopment of preschool children from Montevideo, Uruguay

While it is known that toxic metals contribute individually to child cognitive and behavioral deficits, we still know little about the effects of exposure to multiple metals, particularly when exposures are low. We studied the association between children's blood lead and hair arsenic, cadmium, and manganese and their performance on the Bayley Scales of Infant Development III. Ninety-two preschool children (age 13–42 months) from Montevideo, Uruguay, provided a hair sample and 78 had a blood lead level (BLL) measurement. Using latent class analysis (LCA), we identified four groups of exposure based on metal concentrations: (1) low metals, (2) low-to-moderate metals, (3) high lead and cadmium, and (4) high metals. Using the four-group exposure variable as the main predictor, and fitting raw scores on the cognitive, receptive vocabulary, and expressive vocabulary scales as dependent variables, both complete-case and multiple imputation (MI) analyses were conducted. We found no association between multiple-metal exposures and neurodevelopment in covariate-adjusted models. This study demonstrates the use of LCA together with MI to determine patterns of exposure to multiple toxic metals and relate these to child neurodevelopment. However, because the overall study population was small, other studies with larger sample sizes are needed to investigate these associations.

Gulf War illness: an overview of events, most prevalent health outcomes, exposures, and clues as to pathogenesis

INTRODUCTION

During or very soon after the 1990-1991 Persian Gulf War, veterans of the conflict began to report symptoms of illness. Common complaints included combinations of cognitive difficulties, fatigue, myalgia, rashes, dyspnea, insomnia, gastrointestinal symptoms and sensitivity to odors. Gradually in the USA, and later in the UK, France, Canada, Denmark and Australia, governments implemented medical assessment programs and epidemiologic studies to determine the scope of what was popularly referred to as "the Gulf War syndrome". Attention was drawn to numerous potentially toxic deployment-related exposures that appeared to vary by country of deployment, by location within the theater, by unit, and by personal job types. Identifying a single toxicant cause was considered unlikely and it was recognized that outcomes were influenced by genetic variability in xenobiotic metabolism.

METHODS

Derived from primary papers and key reports by the Research Advisory Committee on Gulf War Veterans' Illnesses and the Institute of Medicine, a brief overview is presented of war related events, symptoms and diagnostic criteria for Gulf War illness (GWV), some international differences, the various war-related exposures and key epidemiologic studies. Possible exposure interactions and pathophysiologic mechanisms are discussed.

RESULTS

Exposures to pyridostigmine bromide, pesticides, sarin and mustard gas or combinations thereof were most associated with GWI, especially in some genotype subgroups. The resultant oxidant stress and background exposome must be assumed to have played a role.

CONCLUSION

Gulf War (GW) exposures and their potential toxic effects should be considered in the context of the human genome, the human exposome and resultant oxidant stress to better characterize this unique environmentally-linked illness and, ultimately, provide a rationale for more effective interventions and future prevention efforts.

Mixture genotoxicity of 2,4-dichlorophenoxyacetic acid, acrylamide, and maleic hydrazide on human Caco-2 cells assessed with comet assay

Assessment of genotoxic properties of chemicals is mainly conducted only for single chemicals, without taking mixture genotoxic effects into consideration. The current study assessed mixture effects of the three known genotoxic chemicals, 2,4-dichlorophenoxyacetic acid (2,4-D), acrylamide (AA), and maleic hydrazide (MH), in an experiment with a fixed ratio design setup. The genotoxic effects were assessed with the single-cell gel electrophoresis assay (comet assay) for both single chemicals and the ternary mixture. The concentration ranges used were 0-1.4, 0-20, and 0-37.7 mM for 2,4-D, AA, and MH, respectively. Mixture toxicity was tested with a fixed ratio design at a 10:23:77% ratio for 2.4-D:AA:MH. Results indicated that the three chemicals yielded a synergistic mixture effect. It is not clear which mechanisms are responsible for this interaction. A few possible interactions are discussed, but further investigations including in vivo studies are needed to clarify how important these more-than-additive effects are for risk assessment.

Unknown risk: co-exposure to lead and other heavy metals among children living in small-scale mining communities in Zamfara State, Nigeria

The lead poisoning crisis in Zamfara State, Northern Nigeria has been called the worst such case in modern history and it presents unique challenges for risk assessment and management of co-exposure to multiple heavy metals. More than 400 children have died in Zamfara as a result of ongoing lead intoxication since early in 2010. A review of the common toxic endpoints of the major heavy metals advances analysis of co-exposures and their common pathologies. Environmental contamination in Bagega village, examined by X-ray fluorescence of soils, includes lead, mercury, cadmium, arsenic and manganese. Co-exposure risk is explored by scoring common toxic endpoints and hazard indices to calculate a common pathology hazard risk ranking of Pb > As > Hg >> Cd > Mn. Zamfara presents an extreme picture of both lead and multiple heavy metal mortality and morbidity, but similar situations have become increasingly prevalent worldwide.

Lipid adjustment for chemical exposures: accounting for concomitant variables

BACKGROUND

Some environmental chemical exposures are lipophilic and need to be adjusted by serum lipid levels before data analyses. There are currently various strategies that attempt to account for this problem, but all have their drawbacks. To address such concerns, we propose a new method that uses Box-Cox transformations and a simple Bayesian hierarchical model to adjust for lipophilic chemical exposures.

METHODS

We compared our Box-Cox method to existing methods. We ran simulation studies in which increasing levels of lipid-adjusted chemical exposure did and did not increase the odds of having a disease, and we looked at both single-exposure and multiple-exposure cases. We also analyzed an epidemiology dataset that examined the effects of various chemical exposure on the risk of birth defects.

RESULTS

Compared with existing methods, our Box-Cox method produced unbiased estimates, good coverage, similar power, and lower type I error rates. This was the case in both single- and multiple-exposure simulation studies. Results from analysis of the birth-defect data differed from results using existing methods.

CONCLUSION

Our Box-Cox method is a novel and intuitive way to account for the lipophilic nature of certain chemical exposures. It addresses some of the problems with existing methods, is easily extendable to multiple exposures, and can be used in any analysis that involves concomitant variables.

Impact of benzo(a)pyrene, Cu and their mixture on the proteomic response of Mytilus galloprovincialis

In natural waters, chemical interactions between mixtures of contaminants can result in potential synergistic and/or antagonic effects in aquatic animals. Benzo(a)pyrene (BaP) and copper (Cu) are two widespread environmental contaminants with known toxicity towards mussels Mytilus spp. The effects of the individual and the interaction of BaP and Cu exposures were assessed in mussels Mytilus galloprovincialis using proteomic analysis. Mussels were exposed to BaP [10 μg L(-1) (0.396 μM)], and Cu [10 μg L(-1) (0.16 μM)], as well as to their binary mixture (mixture) for a period of 7 days. Proteomic analysis showed different protein expression profiles associated to each selected contaminant condition. A non-additive combined effect was observed in mixture in terms of new and suppressed proteins. Proteins more drastically altered (new, suppressed and 2-fold differentially expressed) were excised and analyzed by mass spectrometry, and eighteen putatively identified. Protein identification demonstrated the different accumulation, metabolism and chemical interactions of BaP, Cu and their mixture, resulting in different modes of action. Proteins associated with adhesion and motility (catchin, twitchin and twitchin-like protein), cytoskeleton and cell structure (α-tubulin and actin), stress response (heat shock cognate 71, heat shock protein 70, putative C1q domain containing protein), transcription regulation (zinc-finger BED domain-containing and nuclear receptor subfamily 1G) and energy metabolism (ATP synthase F0 subunit 6 protein and mannose-6-phosphate isomerase) were assigned to all three conditions. Cu exposure alone altered proteins associated with oxidative stress (glutathione-S-transferase) and digestion, growth and remodelling processes (chitin synthase), while the mixture affected only one protein (major vault protein) possibly related to multi drug resistance. Overall, new candidate biomarkers, namely zinc-finger BED domain-containing protein, chitin synthase and major vault protein, were also identified for BaP, Cu and mixture, respectively.

Environmental contaminant exposures and preterm birth: a comprehensive review

Preterm birth is a significant public health concern, as it is associated with high risk of infant mortality, various morbidities in both the neonatal period and later in life, and a significant societal economic burden. As many cases are of unknown etiology, identification of the contribution of environmental contaminant exposures is a priority in the study of preterm birth. This is a comprehensive review of all known studies published from 1992 through August 2012 linking maternal exposure to environmental chemicals during pregnancy with preterm birth. Using PubMed searches, studies were identified that examined associations between preterm birth and exposure to five categories of environmental toxicants, including persistent organic pollutants, drinking-water contaminants, atmospheric pollutants, metals and metalloids, and other environmental contaminants. Individual studies were summarized and specific suggestions were made for future work in regard to exposure and outcome assessment methods as well as study design, with the recommendation of focusing on potential mediating toxicological mechanisms. In conclusion, no consistent evidence was found for positive associations between individual chemical exposures and preterm birth. By identifying limitations and addressing the gaps that may have impeded the ability to identify true associations thus far, this review can guide future epidemiologic studies of environmental exposures and preterm birth.

Hydroxyl radical yields from reactions of terpene mixtures with ozone

Chamber studies were conducted to quantify hydroxyl radical (OH·) yields and to determine whether water vapor affected OH· formation in the reactions of ozone (O(3)) with a single terpene, two-component terpene mixtures, and a commercial pine oil cleaning product (POC). Solid-phase microextraction fibers (SPME) were used for sampling the terpenes and the 2-butanone formation from the hydroxyl reaction with 2-butanol as a measure of OH· yields. Analyses were performed using gas chromatography with flame ionization detection. The individual terpenes' OH· yields from α-terpineol, limonene, and α-pinene were 64 ± 8%, 64 ± 6%, and 76 ± 6%, respectively. OH· yields were also measured from two-component mixtures of these terpenes. In each mixture that contained α-terpineol, the overall OH· yield was lower than the modeled OH· yields of the individual components that comprised the reaction mixture. Reactions of a commercial POC with O(3) were also studied to determine how the individual terpenes react in a complex mixture system, and an OH· formation yield of 51 ± 6% was measured. Relative humidity did not have a significant effect on the OH· formation in the mixtures studied here.

PRACTICAL IMPLICATIONS

The data presented here demonstrate that mixtures may react differently than the sum of their individual components. By investigating the chemistry of mixtures of chemicals in contrast to the chemistry of individual compounds, a better assessment can be made of the overall impact cleaning products have on indoor environments.

Simulating quantitative cellular responses using asynchronous threshold Boolean network ensembles

BACKGROUND

With increasing knowledge about the potential mechanisms underlying cellular functions, it is becoming feasible to predict the response of biological systems to genetic and environmental perturbations. Due to the lack of homogeneity in living tissues it is difficult to estimate the physiological effect of chemicals, including potential toxicity. Here we investigate a biologically motivated model for estimating tissue level responses by aggregating the behavior of a cell population. We assume that the molecular state of individual cells is independently governed by discrete non-deterministic signaling mechanisms. This results in noisy but highly reproducible aggregate level responses that are consistent with experimental data.

RESULTS

We developed an asynchronous threshold Boolean network simulation algorithm to model signal transduction in a single cell, and then used an ensemble of these models to estimate the aggregate response across a cell population. Using published data, we derived a putative crosstalk network involving growth factors and cytokines - i.e., Epidermal Growth Factor, Insulin, Insulin like Growth Factor Type 1, and Tumor Necrosis Factor α - to describe early signaling events in cell proliferation signal transduction. Reproducibility of the modeling technique across ensembles of Boolean networks representing cell populations is investigated. Furthermore, we compare our simulation results to experimental observations of hepatocytes reported in the literature.

CONCLUSION

A systematic analysis of the results following differential stimulation of this model by growth factors and cytokines suggests that: (a) using Boolean network ensembles with asynchronous updating provides biologically plausible noisy individual cellular responses with reproducible mean behavior for large cell populations, and (b) with sufficient data our model can estimate the response to different concentrations of extracellular ligands. Our results suggest that this approach is both quantitative, allowing statistical verification and calibration, and extensible, allowing modification and revision as guided by experimental evidence. The simulation methodology is part of the US EPA Virtual Liver, which is investigating the effects of everyday contaminants on living tissues. Future models will incorporate additional crosstalk surrounding proliferation as well as the putative effects of xenobiotics on these signaling cascades within hepatocytes.

Antioxidant and lipid peroxidation responses in Mytilus galloprovincialis exposed to mixtures of benzo(a)pyrene and copper

This study aimed to assess the antioxidant system potential and lipid peroxidative effects, in the gill and digestive gland of Mytilus galloprovincialis exposed to individual and binary mixtures of benzo(a)pyrene (BaP) and Cu for 7 days. Data demonstrated that in mussels exposed to BaP antioxidant enzymes (catalase--CAT, total glutathione peroxidase--tGPx, glutathione S-transferase--GST and glutathione reductase--GR) and lipid peroxidation (LPO) increased in the gill. On the contrary, in the digestive gland inhibitory antioxidant effects (superoxide dismutase-SOD, GR, metallothioneins-MT) and no changes in LPO levels were detected. Cu was also a potent oxidant agent since MT and LPO levels increased in mussel gill, despite no LPO effect in the digestive gland. For both single contaminants the organ specificity and distinct physiologic/metabolism roles were evident in terms of antioxidant capacity. Gill SOD inhibition, MT and GST unchanged was a result of "simple independent action" of exposure to BaP and Cu. "Interactions" in the binary mixtures, led to absence of changes in LPO effects. In the digestive gland, BaP and Cu interactions were also responsible for the GST and LPO enhancement (antagonistic effects). The current findings demonstrate the differences in antioxidant responses where the organ dependency highlights each contaminant particular mode of action. Generally, in the gill "non-interactive" effects occurred with the lowest Cu concentration while "interactions" exist for the mixture with the highest Cu concentrations. In the digestive gland, "interactions" and "no interaction" effects occurred in all the binary mixtures. Complex contaminant mixtures interact differently based on target tissue which may lead to an imbalance in the mussels health status.

Evaluating pharmacokinetic and pharmacodynamic interactions with computational models in supporting cumulative risk assessment

Simultaneous or sequential exposure to multiple chemicals may cause interactions in the pharmacokinetics (PK) and/or pharmacodynamics (PD) of the individual chemicals. Such interactions can cause modification of the internal or target dose/response of one chemical in the mixture by other chemical(s), resulting in a change in the toxicity from that predicted from the summation of the effects of the single chemicals using dose additivity. In such cases, conducting quantitative cumulative risk assessment for chemicals present as a mixture is difficult. The uncertainties that arise from PK interactions can be addressed by developing physiologically based pharmacokinetic (PBPK) models to describe the disposition of chemical mixtures. Further, PK models can be developed to describe mechanisms of action and tissue responses. In this article, PBPK/PD modeling efforts conducted to investigate chemical interactions at the PK and PD levels are reviewed to demonstrate the use of this predictive modeling framework in assessing health risks associated with exposures to complex chemical mixtures.

Perinatal exposure to environmental contaminants detected in Canadian Arctic human populations changes bone geometry and biomechanical properties in rat offspring

Arctic inhabitants consume large proportions of fish and marine mammals, and are therefore continuously exposed to levels of environmental toxicants, which may produce adverse health effects. Fetuses and newborns are the most vulnerable groups. The aim of this study was to evaluate changes in bone geometry, mineral density, and biomechanical properties during development following perinatal exposure to a mixture of environmental contaminants corresponding to maternal blood levels in Canadian Arctic human populations. Sprague-Dawley rat dams were dosed with a Northern Contaminant Mixture (NCM) from gestational day 1 to postnatal day (PND) 23. NCM contains 27 contaminants comprising polychlorinated biphenyls, organochlorine pesticides, and methylmercury. Femurs were collected on PND 35, 77 and 350, and diaphysis was analyzed by peripheral quantitative computed tomography and three-point bending test, while femoral neck was assessed in an axial loading experiment. Dose-response modeling was performed to establish the benchmark dose (BMD) for the analyzed bone parameters. Exposure to the high dose of NMC resulted in short and thin femur with reduced mechanical strength in offspring at PND35. BMD of femur length, cortical area, and stiffness were 3.2, 1.6, and 0.8 mg/kg bw/d, respectively. At PND77 femur was still thin, but at PND350 no treatment-related bone differences were detected. This study provides new insights on environmental contaminants present in the maternal blood of Canadian Arctic populations, showing that perinatal exposure induces bone alterations in the young offspring. These findings could be significant from a health risk assessment point of view.

Biomarker measurements of concurrent exposure to multiple environmental chemicals and chemical classes in children

Concern is mounting that children from disadvantaged, low-income neighborhoods are likely to be both more exposed to chemical hazards and more susceptible to related adverse health effects. This article reports measurements of >75 individual biomarkers spanning 7 chemical/pollutant classes in blood and urine from more than 100 children living in a socioeconomically disadvantaged and ethnically diverse area of south Minneapolis, MN. Results indicate that a significant proportion of children in the study were at the high end of the exposure distribution compared to national reference ranges for a variety of environmental chemicals and/or their metabolites, including phthalates, organochlorine pesticides, organophosphate pesticides, metals, polychlorinated biphenyls, and volatile organic compounds. In addition, levels of cotinine in urine indicate that more than half the children were regularly exposed to environmental tobacco smoke, with the upper 10th percentile exposed to relatively high concentrations.

Environmental contaminants and human health in the Canadian Arctic

The third Canadian Arctic Human Health Assessment conducted under the Canadian Northern Contaminants Program (NCP), in association with the circumpolar Arctic Monitoring and Assessment Programme (AMAP), addresses concerns about possible adverse health effects in individuals exposed to environmental contaminants through a diet containing country foods. The objectives here are to: 1) provide data on changes in human contaminant concentrations and exposure among Canadian Arctic peoples; 2) identify new contaminants of concern; 3) discuss possible health effects; 4) outline risk communication about contaminants in country food; and 5) identify knowledge gaps for future contaminant research and monitoring. The nutritional and cultural benefits of country foods are substantial; however, some dietary studies suggest declines in the amount of country foods being consumed. Significant declines were found for most contaminants in maternal blood over the last 10 years within all three Arctic regions studied. Inuit continue to have the highest levels of almost all persistent organic pollutants (POPs) and metals among the ethnic groups studied. A greater proportion of people in the East exceed Health Canada's guidelines for PCBs and mercury, although the proportion of mothers exceeding these guidelines has decreased since the previous assessment. Further monitoring and research are required to assess trends and health effects of emerging contaminants. Infant development studies have shown possible subtle effects of prenatal exposure to heavy metals and some POPs on immune system function and neurodevelopment. New data suggest important beneficial effects on brain development for Inuit infants from some country food nutrients. The most successful risk communication processes balance the risks and benefits of a diet of country food through input from a variety of regional experts and the community, to incorporate the many socio-cultural and economic factors to arrive at a risk management decision that will be the most beneficial in Arctic communities.

Assessing environmental and occupational risk factors for lung cancer in Mexican-Americans

BACKGROUND

We investigated environmental and occupational exposures and smoking history (while controlling for demographics) in a population of Mexican-American lung cancer cases and controls from the Houston metropolitan area.

METHODS

Data were collected between 1991 and 2005 as part of an on-going multi-racial/ethnic, lung cancer case-control study. Cases included 212 Mexican-American lung cancer cases from UT MD Anderson Cancer Center. Controls (n = 328) were recruited from Houston's largest multispecialty group practice and frequency matched to the cases by age (± 5 years), sex, and ethnicity. Environmental and occupational factors were analyzed and odds ratios and 95% confidence intervals were calculated using logistic regression.

RESULTS

We detected elevated risks of lung cancer associated with pesticide exposure and found conventional and antimicrobial (e.g., sterilizers, disinfectants, antiseptics) pesticides were associated with an increased risk of lung cancer in Mexican-Americans (conventional pesticides and antimicrobial pesticides combined: OR = 1.80, 95% CI 1.13-2.86; conventional pesticides: OR = 2.05, 95% CI 1.23-2.39; antimicrobial pesticides: OR = 2.48, 95% CI 1.46-4.21).

CONCLUSIONS

Although we found over a two-fold increased risk of lung cancer among Mexican-Americans for pesticides, we could not identify individual pesticides. Our findings are an important preliminary step in identifying factors that are specifically associated with lung cancer risk among Mexican Americans.

Virtual tissues in toxicology

New approaches are vital for efficiently evaluating human health risk of thousands of chemicals in commerce. In vitro models offer a high-throughput approach for assaying chemical-induced molecular and cellular changes; however, bridging these perturbations to in vivo effects across chemicals, dose, time, and species remains challenging. Technological advances in multiresolution imaging and multiscale simulation are making it feasible to reconstruct tissues in silico. In toxicology, these "virtual" tissues (VT) aim to predict histopathological outcomes from alterations of cellular phenotypes that are controlled by chemical-induced perturbations in molecular pathways. The behaviors of thousands of heterogeneous cells in tissues are simulated discretely using agent-based modeling (ABM), in which computational "agents" mimic cell interactions and cellular responses to the microenvironment. The behavior of agents is constrained by physical laws and biological rules derived from experimental evidence. VT extend compartmental physiologic models to simulate both acute insults as well as the chronic effects of low-dose exposure. Furthermore, agent behavior can encode the logic of signaling and genetic regulatory networks to evaluate the role of different pathways in chemical-induced injury. To extrapolate toxicity across species, chemicals, and doses, VT require four main components: (a) organization of prior knowledge on physiologic events to define the mechanistic rules for agent behavior, (b) knowledge on key chemical-induced molecular effects, including activation of stress sensors and changes in molecular pathways that alter the cellular phenotype, (c) multiresolution quantitative and qualitative analysis of histologic data to characterize and measure chemical-, dose-, and time-dependent physiologic events, and (d) multiscale, spatiotemporal simulation frameworks to effectively calibrate and evaluate VT using experimental data. This investigation presents the motivation, implementation, and application of VT with examples from hepatotoxicity and carcinogenesis.

Natural mixtures of persistent organic pollutants (POP) increase weight gain, advance puberty, and induce changes in gene expression associated with steroid hormones and obesity in female zebrafish

In the present study, developmental and reproductive effects of lifelong exposure to environmental relevant concentrations of two natural mixtures of persistent organic pollutants (POP) were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot (Lota lota) liver originating from freshwater systems in Norway: one mixture with high levels and one mixture with background levels of polybrominated diphenyl ethers (PBDE), polychlorinated biphenyls (PCB), and dichlorodiphenyltrichloroethane metabolites (DDT). The concentration of POP measured in the zebrafish ranged from levels detected in wild fish from Lake Mjøsa to concentrations reported in human and wildlife populations, indicating that the experimental fish were exposed to concentrations comparable with wild fish. Phenotypic effects observed in both exposure groups included earlier onset of puberty, increased male/female sex ratio, and differences in body weight at 5 mo of age. Interestingly, genome-wide transcription profiling showed changes in regulation of genes involved in endocrine signaling and growth. The transcriptomics changes include key regulator genes for steroid hormone functions (ncoa3), and growth (c/ebp, ncoa3). The effects observed in the experimental zebrafish model raise the question whether chemical pollution represents a risk to reproductive health of wild fish inhabitating the freshwater system.

Decreased sperm motility in rats orally exposed to single or mixed pesticides

The Brazilian Agency of Sanitary Vigilance (ANVISA) conducted a study that demonstrated the presence of residues of several pesticides in fresh fruits and vegetables that were available for purchase by the general populace. In order to evaluate potential adverse health effects of low-level exposure to agrochemicals, the reproductive toxicity of the pesticides dicofol, dichlorvos, permethrin, endosulfan, and dieldrin was evaluated in rats dosed with these chemicals individually or as mixtures. Sixty male Lewis rats (6 wk old, 200 x g) were randomly allocated to 8 groups: (1) control group, received basal diet; (2) 5 groups designated a to e received the diet containing each pesticide individually, at the respective effective doses: lowest-observed-adverse-effect level (LOAEL) for dieldrin and endosulfan, lowest-observed-effect level (LOEL) for dicofol, and lowest effect level (LEL) for dichlorvos and permethrin, respectively, depending on the published data; (3) effective dose group, which received a mixture of pesticides added to basal diet at the respective doses reported to produce adverse effects; and (4) low dose group, which received a pesticide mixture added to the basal diet, where each pesticide was at its no-observed-effect level (NOEL). After 8 wk of treatment, reproductive parameters were evaluated. Sperm morphology, daily sperm production (DSP), sperm transit time through the epididymis, hormonal levels, and histopathological evaluation of testis and epididymis did not differ significantly among the groups. However, sperm motility was significantly decreased in animals that received a mixture of dieldrin, endosulfan, dicofol, dichlorvos, and permethrin, as well as in the group receiving dicofol alone. Exposure to the individual pesticides endosulfan, dichlorvos, and permethrin did not markedly affect sperm motility. The impairment of sperm motility in the mixture of pesticides at the NOEL level indicates that reproductive effects not seen with individual pesticides may occur in presence of several pesticides due to an additive effect. However, the pesticide mixtures did not appear to affect DSP or spermatogenesis despite reduced sperm motility.

Binary weight-of-evidence evaluations of chemical interactions--15 years of experience

The paper reflects on the last 15years of experience in the field of mixtures risk assessment. It summarizes results found in various documents developed by the Agency for Toxic Substances and Disease Registry (ATSDR) of the weight-of-evidence (WOE) approach applied to 380 binary combinations of chemicals. Of these evaluations, 156 assessments indicated possible additivity of effects [=], 76 indicated synergism (greater-than-additive effects [>]), and 57 indicated antagonism (less-than-additive effects [<]). However, 91 combinations lacked the minimum information needed for making any assessments and, hence, were undetermined. The paper provides examples of the rationale behind some of the WOE decisions and discusses the importance of expert judgments in risk assessment evaluations. Examples are given regarding the importance of human variability in mixtures' ability to affect human health and regarding the dose versus effect relationships.

Evaluating the similarity of complex drinking-water disinfection by-product mixtures: overview of the issues

Humans are exposed daily to complex mixtures of environmental chemical contaminants, which arise as releases from sources such as engineering procedures, degradation processes, and emissions from mobile or stationary sources. When dose-response data are available for the actual environmental mixture to which individuals are exposed (i.e., the mixture of concern), these data provide the best information for dose-response assessment of the mixture. When suitable data on the mixture itself are not available, surrogate data might be used from a sufficiently similar mixture or a group of similar mixtures. Consequently, the determination of whether the mixture of concern is "sufficiently similar" to a tested mixture or a group of tested mixtures is central to the use of whole mixture methods. This article provides an overview for a series of companion articles whose purpose is to develop a set of biostatistical, chemical, and toxicological criteria and approaches for evaluating the similarity of drinking-water disinfection by-product (DBPs) complex mixtures. Together, the five articles in this series serve as a case study whose techniques will be relevant to assessing similarity for other classes of complex mixtures of environmental chemicals. Schenck et al. (2009) describe the chemistry and mutagenicity of a set of DBP mixtures concentrated from five different drinking-water treatment plants. Bull et al. (2009a, 2009b) describe how the variables that impact the formation of DBP affect the chemical composition and, subsequently, the expected toxicity of the mixture. Feder et al. (2009a, 2009b) evaluate the similarity of DBP mixture concentrates by applying two biostatistical approaches, principal components analysis, and a nonparametric "bootstrap" analysis. Important factors for determining sufficient similarity of DBP mixtures found in this research include disinfectant used; source water characteristics, including the concentrations of bromide and total organic carbon; concentrations and proportions of individual DBPs with known toxicity data on the same endpoint; magnitude of the unidentified fraction of total organic halides; similar toxicity outcomes for whole mixture testing (e.g., mutagenicity); and summary chemical measures such as total trihalomethanes, total haloacetic acids, total haloacetonitriles, and the levels of bromide incorporation in the DBP classes.

Integrating research and action: a systematic review of community-based participatory research to address health disparities in environmental and occupational health in the USA

INTRODUCTION

Integrating research and action represents a goal and key principles of community-based participatory research (CBPR), but there has been little effort to synthesise the literature to evaluate whether such integration is occurring.

OBJECTIVES

(1) To examine the extent to which CBPR integrates action to effect community-level change and (2) to ascertain factors that facilitate such integration.

METHODS

Original articles reporting on CBPR in environmental and occupational health in the USA were identified primarily through a MEDLINE search. Inceptions, processes, methods and outcomes of the projects were reviewed.

RESULTS

In 14 of the 20 studies reviewed, CBPR led to community-level action to improve the health and well-being of the community members. Observational studies that investigated problems posed by the affected community and that incorporated qualitative methods were more likely to lead to action. The collaboration among government scientists, university researchers and community partners emerged as a new model of CBPR partnerships that effectively integrates research and action.

CONCLUSIONS

To help CBPR better integrate research and action, a shift towards community-initiated and action-oriented observational studies might be needed.

Chemical exposures at hazardous waste sites: Experiences from the United States and Poland

The U.S. Agency for Toxic Substances and Disease Registry (ATSDR) and the Polish Nofer Institute of Occupational Health collaborate on issues related to hazardous chemical exposure at or near hazardous waste sites. This paper outlines the scope of hazardous chemical exposure in the United States and in Poland and identifies priority chemicals and chemical mixtures. Special attention is paid to exposures to metals and to evaluation of the health risks associated with those exposures. Studies in the United States indicate that exposure to hazardous waste site chemicals may be associated with an increased risk of adverse developmental - specifically cardiovascular and neurodevelopmental - effects.

Human exposure to endocrine disrupters and semen quality

Reproductive pathology in the male represents about 20% of infertility cases. Male infertility may be attributed to a number of causes, including genetic and congenital abnormalities, infection, multisystemic diseases, varicocele, and others; however, a significant number of cases are idiopathic. Global declines in semen quality were suggested to be associated with enhanced exposure to environmental chemicals that act as endocrine disrupters as a result of our increased use of pesticides, plastics, and other anthropogenic materials. A significant body of toxicology data based upon laboratory and wildlife animals studies suggests that exposure to certain endocrine disrupters is associated with reproductive toxicity, including (1) abnormalities of the male reproductive tract (cryptorchidism, hypospadias), (2) reduced semen quality, and (3) impaired fertility in the adult. There is, however, a relative paucity of studies designed to measure exposure to endocrine disrupters on semen quality parameters (sperm concentration, motility, morphology). An overview of the human semen quality literature is presented that examines the role of endocrine disrupters including organochlorines (OC), dioxins, phthalates, phytoestrogens, and chemical mixtures (pesticides and tobacco smoke).

Assessing and managing risks arising from exposure to endocrine-active chemicals

Managing risks to human health and the environment produced by endocrine-active chemicals (EAC) is dependent on sound principles of risk assessment and risk management, which need to be adapted to address the uncertainties in the state of the science of EAC. Quantifying EAC hazard identification, mechanisms of action, and dose-response curves is complicated by a range of chemical structure/toxicology classes, receptors and receptor subtypes, and nonlinear dose-response curves with low-dose effects. Advances in risk science including toxicogenomics and quantitative structure-activity relationships (QSAR) along with a return to the biological process of hormesis are proposed to complement existing risk assessment strategies, including that of the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC 1998). EAC represents a policy issue that has captured the public's fears and concerns about environmental health. This overview describes the process of EAC risk assessment and risk management in the context of traditional risk management frameworks, with emphasis on the National Research Council Framework (1983), taking into consideration the strategies for EAC management in Canada, the United States, and the European Union.

Effects of organochlorines, individually and in mixtures, on B-cell proliferation in marine mammals and mice

Organochlorines (OC) are lipophilic and stable, and therefore accumulate in tissues of top predators, such as marine mammals. While the immunomodulatory effects of individual OC have been studied in lab animals, their effects in other species (such as marine mammals) and the possible interactions between chemicals in mixtures are not well understood. This study investigated the immunomodulatory effects of four polychlorinated biphenyls (PCB, IUPAC numbers 138, 153, 169, and 180), as well as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), individually and in mixtures, in marine mammals and mice. Mitogen-induced B lymphocyte proliferation was mostly modulated by non-coplanar PCBs, for which general mechanisms underlying toxicity are poorly understood. Simple additive effects of OC in mixtures were found only in mice, while both synergistic and antagonistic interactions between OC were found in marine mammals. The toxic equivalency (TEQ) approach, which is currently used to assess the dioxin-like toxicity of OC mixtures, failed to predict immunotoxicity in mice and marine mammals, likely due to the complexity of interactions between OC and effects via dioxin-independent pathways. The commonly used mouse model failed to predict the immunotoxicity due to OC in the marine mammals tested. In addition, clustering data suggested that phylogeny might not help predict the toxicity of OC. Lymphoproliferative response was modulated in most species tested suggesting the possibility of increased susceptibility to infectious diseases in these animals. These findings may be helpful in more accurately characterizing the immunotoxic potential of OC in different target species and help in more relevant risk assessment.

Effects of physiological concentrations of heavy metals both individually and in mixtures on the viability and function of peripheral blood human leukocytes in vitro

Among environmental contaminants recognized for their toxicity and global distribution, heavy metals are elements known to exert serious ecological consequences. Published experiments on the immunotoxic effects of metals such as methylmercury (MeHg), cadmium (Cd), and lead (Pb) were often conducted at concentrations higher than those present in the environment or those in human blood. In the present study the in vitro effects on human blood of environmentally relevant concentrations of MeHg (33-200 mug/L), Cd (3.1-16 mug/L), and Pb (75-207 mug/L) were assessed individually and in mixtures on the viability and immune competence of peripheral blood leukocytes (PBLs). At MeHg concentrations of 120 and 200 mug/L both lymphocyte proliferation, as measured by [(3)H]thymidine incorporation, and natural killer (NK) cytotoxity activity, as determined by dioctadecyloacarbocyanine, were suppressed. Our results showed an increase of intracellular thiols in lymphocytes and in monocytes at all the concentrations of metals tested. A decrease in the level of metallothionein (MT) was seen in monocytes in presence of Hg at concentration of 120 mug/L and higher. For lymphocytes, a significant increase of MT in groups containing the lower concentrations of Cd, and Hg was noted. In summary, it appears that Hg represents the most toxic metal at environmentally relevant concentrations on human peripheral mononuclear cells. The effects of Hg exposure were greater on lymphocytes and NK cells than on monocytes.

Research needs for environmental health risk assessment

Risk characterization comprises hazard characterization and exposure assessment. Hazard characterization may not be based on human data alone, as these data (1) are seldom available, (2) are quite insensitive in identifying the hazards, and (3) mostly lack reliable exposure-response information. Thus epidemiological information needs to be complemented with information from experimental animals and in vitro systems. These observations suffer from the necessity for species-to-species extrapolation, which is often based on weakly based generic default values. Default values may be replaced by chemical-specific uncertainty factors, but need to be applied cautiously and preferably in a predetermined framework with transparent guidance on what constitutes reliable evidence. Structure-activity relationships (SARs) are useful in setting priorities for hazard characterization and data generation, but seldom alone constitute a sufficient basis for quantitative hazard characterization. Little progress has been made in the assessment of the hazards from multiple simultaneous or successive exposures. Information on the exposure of the population whose risks are to be assessed relies predominantly on models of varying complexity. In the assessment of exposure to elements, speciation and bioavailability are important parameters for which the information often is limited.

A solvatochromatic approach to quantifying formulation effects on dermal permeability

Dermal risk assessments are most often concerned with the occupational and environmental exposure to a single chemical and then determining solute permeability through in vitro or in vivo experimentation with various animal models and/or computational approaches. Oftentimes, the skin is exposed to more than one chemical that could potentially modulate dermal permeability of the chemical that could cause adverse health effects. The focus of this article is to demonstrate that these formulation effects on dermal permeability can occur with simple solvent formulations or complex industrial formulations and that these effects can be modeled within the context of a linear solvation energy relationship (LSER). This research demonstrated that formulation-specific strength coefficients (r p a b v) predicted (r(2) = 0.75-0.83) changes in the dermal permeability of phenolic compounds when formulated with commercial metal-working fluid (MWF) formulations or 50% ethanol. Further experimentation demonstrated that chemical-induced changes in skin permeability with 50% ethanol are strongly correlated (r(2) = 0.91) to similar changes in an inert membrane-coated fiber (MCF) array system consisting of three chemically diverse membranes. Changes in specific strength coefficients pertaining to changes in hydrogen donating ability (Deltab) and hydrophobicity (Deltav) across membrane systems were identified as important quantitative interactions associated with ethanol mixtures. This solvatochromatic approach along with the use of a MCF array system holds promise for predicting dermal permeability of complex chemical formulations in occupational exposures where performance additives can potentially modulate permeability of potential toxicants.

Environmental metabolite, 1,2-diacetylbenzene, produces cytotoxicity through ROS generation in HUVEC cells

Organic solvents are ubiquitous in industrial and household surroundings, and thus individuals are easily exposed. 1,2-Diethylbenzene (DEB) is one of organic solvents contained in gasoline or jet fuels. DEB is absorbed by dermal or inhalation routes, metabolized by cytochrome P-450 in the liver, and ultimately affects mammalian functions. 1,2-Diacetylbenzene (1,2-DAB), which is a putative metabolite of 1,2-DEB, resulted in neuropathological effects on rodent central and peripheral nervous systems. To elucidate the possibility of 1,2-DAB effects on the vascular system, studies were undertaken to examine whether 1,2-DAB induces endothelial cytotoxicity through reactive oxygen species (ROS) generation. Incubation of human umbilical vein endothelial cells (HUVEC) with lower concentrations (4 or 8 microM) of 1,2-DAB induced inhibition of cellular growth and at higher amounts (16 or 32 microM) produced apoptosis. Endothelial cells cultured with 1,2-DAB also showed increased intracellular ROS production and morphological alterations indicative of senescence. Pretreatment with the well-known antioxidant glutathione or N-acetylcysteine (NAC) reduced cytotoxicity induced by 1,2-DAB. Taken together, the results provide evidence that cytotoxicity induced by 1,2-DAB in endothelial cells may be mediated by ROS generation.

A system coefficient approach for quantitative assessment of the solvent effects on membrane absorption from chemical mixtures

A system coefficient approach is proposed for quantitative assessment of the solvent effects on membrane absorption from chemical mixtures. The complicated molecular interactions are dissected into basic molecular interaction forces via Abraham's linear solvation energy relationship (LSER). The molecular interaction strengths of a chemical are represented by a set of solute descriptors, while those of a membrane/chemical mixture system are represented by a set of system coefficients. The system coefficients can be determined by using a set of probe compounds with known solute descriptors. Polydimethylsiloxane (PDMS) membrane-coated fibres and 32 probe compounds were used to demonstrate the proposed approach. When a solvent was added into the chemical mixture, the system coefficients were altered and detected by the system coefficient approach. The system coefficients of the PDMS/water system were (0.09, 0.49, -1.11, -2.36, -3.78, 3.50). When 25% ethanol was added into the PDMS/water system, the system coefficients were altered significantly (0.38, 0.41, -1.18, -2.07, -3.40, 2.81); and the solvent effect was quantitatively described by the changes in the system coefficients (0.29, -0.08, -0.07, 0.29, 0.38, -0.69). The LSER model adequately described the experimental data with a correlation coefficient (r(2)) of 0.995 and F-value of 1056 with p-value less than 0.0001.

An experimentally based approach for predicting skin permeability of chemicals and drugs using a membrane-coated fiber array

A membrane-coated fiber (MCF) array approach is proposed for predicting the percutaneous absorption of chemicals and drugs from chemical or biological mixtures. Multiple MCFs were used to determine the partition coefficients of compounds (logK(MCF)). We hypothesized that one MCF will characterize one pattern of molecular interactions and therefore the skin absorption process can be simulated by a multiple MCF array having diverse patterns of molecular interactions. Three MCFs, polydimethylsiloxane (PDMS), polyacrylate (PA) and CarboWax (Wax), were used to determine the logK(MCF) values for a set of calibration compounds. The skin permeability log(kp) of the compounds was measured by diffusion experiments using porcine skin. The feasibility of the MCF array approach for predicting skin permeability was demonstrated with the three MCFs. A mathematical model was established by multiple linear regression analysis of the log(kp) and logK(MCF) data set: log(kp)=-2.34-0.124 logK(pdms)+1.91 logK(pa)-1.17 logK(wax) (n=25, R(2)=0.93). The MCF array approach is an alternative animal model for skin permeability measurement. It is an experimentally based, high throughput approach that provides high prediction confidence and does not require literature data nor molecular structure information in contrast to the existing predictive models.

Unidentified inert ingredients in pesticides: implications for human and environmental health

BACKGROUND

By statute or regulation in the United States and elsewhere, pesticide ingredients are divided into two categories: active and inert (sometimes referred to as other ingredients, adjuvants, or coformulants). Despite their name, inert ingredients may be biologically or chemically active and are labeled inert only because of their function in the formulated product. Most of the tests required to register a pesticide are performed with the active ingredient alone, not the full pesticide formulation. Inert ingredients are generally not identified on product labels and are often claimed to be confidential business information.

OBJECTIVES

In this commentary, we describe the shortcomings of the current procedures for assessing the hazards of pesticide formulations and demonstrate that inert ingredients can increase the toxicity of and potential exposure to pesticide formulations.

DISCUSSION

Inert ingredients can increase the ability of pesticide formulations to affect significant toxicologic end points, including developmental neurotoxicity, genotoxicity, and disruption of hormone function. They can also increase exposure by increasing dermal absorption, decreasing the efficacy of protective clothing, and increasing environmental mobility and persistence. Inert ingredients can increase the phytotoxicity of pesticide formulations as well as the toxicity to fish, amphibians, and microorganisms.

CONCLUSIONS

Pesticide registration should require full assessment of formulations. Evaluations of pesticides under the National Environmental Policy Act, the Endangered Species Act, and similar statutes should include impact assessment of formulations. Environmental monitoring for pesticides should include inert ingredients. To enable independent research and risk assessment, inert ingredients should be identified on product labels.

Endocrine disruption induced by organochlorines (OCs): field studies and experimental models

Long-range transport of persistent organic compounds by air and ocean currents from industrialized areas resulted in high levels of these pollutants in food webs in the Svalbard area. With the aim to test if organochlorine (OC) exposure in free-living polar bears from Svalbard affected their plasma steroid hormone concentrations, it was found that polychlorinated biphenyls (PCBs) were associated with increased progesterone levels in females. The sum of pesticides (sigma pesticides) and sigma PCBs contributed significantly negative to the variation of the plasma testosterone in males, and the overall contribution of the OCs to the plasma cortisol variation was negative. A second objective was to study the effects of selected OCs (i.e., PCB 153 and PCB 126) on animal health as a consequence of effects on endocrine-regulated functions such as reproduction and immunity in a goat model focusing on long-term and low-level exposure during the periods of fetal development and in the neonatal period. Additionally, acute exposure was studied in adult mice. The results indicated that exposure to low doses of PCB 153 in utero and in the suckling period influenced reproductive functions and both PCB 153 and PCB 126 exerted immunomodulatory effects on the offspring, whereas acute exposure of adult mice had minor effects on male reproductive function.

Perinatal exposure to low doses of PCB 153 and PCB 126 affects maternal and neonatal immunity in goat kids

Pregnant does (10 goats/group) were dosed orally either with polychlorinated biphenyl (PCB) 153 (98 microg/kg body weight/d) or PCB 126 (ng/kg body weight/d) dissolved in corn oil or with corn oil only (control group) from gestation day (GD) 60 until delivery. An additional group (n = 5) of pregnant does received the synthetic estrogen diethylstilbestrol (DES; 0.4 microg/kg body weight/d) by intramuscular injection using the same treatment schedule as for the PCB groups. Blood samples for immune analysis were collected at wk 0, 1, 2, 4, 6, and 8 of age. The effects of perinatal PCB exposure on postnatal humoral immune responses were examined by assessing the levels of total immunoglobulin G (IgG) and immunoglobulins to specific microbes at wk 0, 1, 2, 4, 6, and 8 of age, and immune responses following immunization of kids at 2 wk of age. PCB 153 exposure suppressed maternal and neonatal immunity, as demonstrated by reduced transfer of maternal IgG and specific antibodies to the environmental microbes Arcanobacterium pyogenes, Mannheimia haemolytica, and reovirus (REO-1). Furthermore, PCB 153 reduced the level of maternal antibodies to Mycobacterium avium paratuberculosis and equine influenza virus (EIV-1) in the newborn kids. The antibody response against EIV-1 was significantly higher in PCB 153-exposed kids 2 wk following immunization. PCB 126 exposure reduced the levels of maternal antibodies to REO-1. In contrast, gestational exposure to PCB 126 increased the concentrations of maternal antibodies to tetanus toxoid. No differences from controls in plasma total IgG levels at birth or colostrum IgG concentrations were observed in the PCB 126-treated does. However, a significant reduction in IgG levels from GD 60 until delivery was found in this group. Gestational exposure to DES reduced the concentrations of maternal antibodies against A. pyogenes, M. haemolytica, M. avium Paratuberculosis, and REO-1. These results suggest that perinatal exposure to low doses of PCB 126 and PCB 153 affects the maternal immunity in kids. The difference in responses between PCB 126 and PCB 153 treatment groups may strengthen the hypothesis that PCBs mediate immunotoxic effects through both AhR-dependent and -independent mechanisms. The observation that the effects produced by PCB 153 resembled those produced by DES raises the question of whether this congener may modulate immunity by estrogenic mechanisms.