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Marwood C.,ChemRisk Canada | Marwood C.,NovaTox Inc. | McAtee B.,ChemRisk | Kreider M.,ChemRisk | And 5 more authors.
Ecotoxicology | Year: 2011

Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC 50 values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC 50 value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC 50 values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios. © 2011 Springer Science+Business Media, LLC.


Frasch H.F.,U.S. National Institute for Occupational Safety and Health | Dotson G.S.,U.S. National Institute for Occupational Safety and Health | Bunge A.L.,Colorado School of Mines | Chen C.-P.,China Medical University at Taichung | And 6 more authors.
Journal of Exposure Science and Environmental Epidemiology | Year: 2014

A common dermal exposure assessment strategy estimates the systemic uptake of chemical in contact with skin using the fixed fractional absorption approach: the dermal absorbed dose is estimated as the product of exposure and the fraction of applied chemical that is absorbed, assumed constant for a given chemical. Despite the prominence of this approach there is little guidance regarding the evaluation of experiments from which fractional absorption data are measured. An analysis of these experiments is presented herein, and limitations to the fixed fractional absorption approach are discussed. The analysis provides a set of simple algebraic expressions that may be used in the evaluation of finite dose dermal absorption experiments, affording a more data-driven approach to dermal exposure assessment. Case studies are presented that demonstrate the application of these tools to the assessment of dermal absorption data. © 2014 Nature America, Inc.


Scott L.L.F.,ChemRisk | Scott L.L.F.,University of Minnesota | Nguyen L.M.,ChemRisk
International Archives of Occupational and Environmental Health | Year: 2011

Purpose: This study investigated the association between geographic region and blood lead levels (BLLs) in US children, as well as trends in this relationship, using data from the National Health and Nutrition Examination Survey (NHANES). Methods: SAS® and SUDAAN® software programs were utilized to develop linear regression models adjusted for several factors associated with BLLs. Results: The largest decline in BLLs was observed in Northeastern children, while the percentage of children with elevated blood lead levels decreased the most for the West and Northeast. Lead levels of Northeastern children were still higher than those of children living in the West. However, levels were not different among children residing in the Northeast, Midwest, and South, and the blood lead concentrations were less than 5 μg/dL for all but one subgroup of children and less than 2 μg/dL for >70% of the subgroups. More importantly, the effects of different risk factors for higher blood lead levels varied by region even after adjusting for all other covariates. Conclusions: The results of this study not only provide relevant and current blood lead levels for US children that can be used as reference values to evaluate biomonitoring data, but can also be used to help direct prevention and surveillance strategies to reduce lead in the environment of at-risk children. © 2011 Springer-Verlag.


Fillos D.,ChemRisk | Scott L.L.F.,ChemRisk | Scott L.L.F.,University of Minnesota | De Sylor M.A.,ChemRisk | And 3 more authors.
Environmental Toxicology and Chemistry | Year: 2012

Currently, environmental studies describing levels of polychlorinated biphenyls (PCBs) in imported shrimp are limited, particularly studies of aquaculture shrimp. In the present study, we measured concentrations of the 209 PCB congeners in 84 uncooked, warm-water shrimp samples from the United States and 14 other countries in three continents. Total PCB and dioxin-like PCB (DL-PCB) levels were not significantly different between wild-caught and farm-raised shrimp, and the distribution of total PCB levels did not vary considerably by country of origin although significant differences were observed in some cases. Regional trends in both total PCB and DL-PCB concentrations were observed, with the highest concentrations measured in shrimp from North America followed by Asia and then South America. The lower chlorinated homologues (i.e., mono-, di-, and tri-PCBs) generally comprised a greater fraction of the total levels measured in farm-raised shrimp and shrimp from Asia and South America whereas higher chlorinated homologues (i.e., hepta-, octa-, nona-, and deca-PCBs) contributed more to levels in wild-caught shrimp and shrimp from North America. Estimated daily intake of PCBs associated with shrimp consumption ranged from 2pg/kg/d (shrimp from South America) to 15pg/kg/d (shrimp from North America). Results from the present study were comparable to other studies conducted recently and demonstrate that exposure to PCBs from consumption of farm-raised and wild-caught shrimp imported from different regions are not likely to pose any health risks. © 2012 SETAC.


Panko J.M.,ChemRisk | Kreider M.L.,ChemRisk | McAtee B.L.,ChemRisk | Marwood C.,NovaTox Inc.
Ecotoxicology | Year: 2013

Tire and road wear particles (TRWP) consist of a complex mixture of rubber, and pavement released from tires during use on road surfaces. Subsequent transport of the TRWP into freshwater sediments has raised some concern about the potential adverse effects on aquatic organisms. Previous studies have shown some potential for toxicity for tread particles, however, toxicity studies of TRWP collected from a road simulator system revealed no acute toxicity to green algae, daphnids, or fathead minnows at concentrations up to 10,000 mg/kg under conditions representative of receiving water bodies. In this study, the chronic toxicity of TRWP was evaluated in four aquatic species. Test animals were exposed to whole sediment spiked with TRWP at concentrations up to 10,000 mg/kg sediment or elutriates from spiked sediment. Exposure to TRWP spiked sediment caused mild growth inhibition in Chironomus dilutus but had no adverse effect on growth or reproduction in Hyalella azteca. Exposure to TRWP elutriates resulted in slightly diminished survival in larval Pimephales promelas but had no adverse effect on growth or reproduction in Ceriodaphnia dubia. No other endpoints in these species were affected. These results, together with previous studies demonstrating no acute toxicity of TRWP, indicate that under typical exposure conditions TRWP in sediments pose a low risk of toxicity to aquatic organisms. © 2012 Springer Science+Business Media, LLC.


Keenan J.J.,ChemRisk | Gaffney S.,ChemRisk | Gross S.A.,ChemRisk | Ronk C.J.,ChemRisk | And 3 more authors.
Human and Experimental Toxicology | Year: 2013

The presence of benzene in motor gasoline has been a health concern for potential increased risk of acute myelogenous leukemia and perhaps other lymphatic/hematopoietic cancers for approximately 40 years. Because of the widespread and increasing use of gasoline by consumers and the high exposure potential of occupational cohorts, a thorough understanding of this issue is important. The current study utilizes an evidence-based approach to examine whether or not the available epidemiologic studies demonstrate a strong and consistent association between occupational exposure to gasoline and lymphatic/hematopoietic cancers. Among 67 epidemiologic studies initially identified, 54 were ranked according to specific criteria relating to the relevance and robustness of each study for answering the research question. The 30 highest-ranked studies were sorted into three tiers of evidence and were analyzed for strength, specificity, consistency, temporality, dose-response trends and coherence. Meta statistics were also calculated for each general and specific lymphatic/hematopoietic cancer category with adequate data. The evidence-based analysis did not confirm any strong and consistent association between occupational exposure to gasoline and lymphatic/hematopoietic cancers based on the epidemiologic studies available to date. These epidemiologic findings, combined with the evidence showing relatively low occupational benzene vapor exposures associated with gasoline formulations during the last three decades, suggest that current motor gasoline formulations are not associated with increased lymphatic/hematopoietic cancer risks related to benzene. © The Author(s) 2013.


Knutsen J.S.,ChemRisk | Kerger B.D.,ChemRisk | Finley B.,ChemRisk | Paustenbach D.J.,ChemRisk
Risk Analysis | Year: 2013

A physiologically-based pharmacokinetic (PBPK) model of benzene inhalation based on a recent mouse model was adapted to include bone marrow (target organ) and urinary bladder compartments. Empirical data on human liver microsomal protein levels and linked CYP2E1 activities were incorporated into the model, and metabolite-specific conversion rate parameters were estimated by fitting to human biomonitoring data and adjusting for background levels of urinary metabolites. Human studies of benzene levels in blood and breath, and phenol levels in urine were used to validate the rate of human conversion of benzene to benzene oxide, and urinary benzene metabolites from Chinese benzene worker populations provided model validation for rates of human conversion of benzene to muconic acid (MA) and phenylmercapturic acid (PMA), phenol (PH), catechol (CA), hydroquinone (HQ), and benzenetriol (BT). The calibrated human model reveals that while liver microsomal protein and CYP2E1 activities are lower on average in humans compared to mice, the mouse also shows far lower rates of benzene conversion to MA and PMA, and far higher conversion of benzene to BO/PH, and of BO/PH to CA, HQ, and BT. The model also differed substantially from existing human PBPK models with respect to several metabolic rate parameters of importance to interpreting benzene metabolism and health risks in human populations associated with bone marrow doses. The model provides a new methodological paradigm focused on integrating linked human liver metabolism data and calibration using biomonitoring data, thus allowing for model uncertainty analysis and more rigorous validation. © 2012 Society for Risk Analysis.


PubMed | ChemRisk
Type: Journal Article | Journal: International archives of occupational and environmental health | Year: 2011

This study investigated the association between geographic region and blood lead levels (BLLs) in US children, as well as trends in this relationship, using data from the National Health and Nutrition Examination Survey (NHANES).SAS and SUDAAN software programs were utilized to develop linear regression models adjusted for several factors associated with BLLs.The largest decline in BLLs was observed in Northeastern children, while the percentage of children with elevated blood lead levels decreased the most for the West and Northeast. Lead levels of Northeastern children were still higher than those of children living in the West. However, levels were not different among children residing in the Northeast, Midwest, and South, and the blood lead concentrations were less than 5 g/dL for all but one subgroup of children and less than 2 g/dL for >70% of the subgroups. More importantly, the effects of different risk factors for higher blood lead levels varied by region even after adjusting for all other covariates.The results of this study not only provide relevant and current blood lead levels for US children that can be used as reference values to evaluate biomonitoring data, but can also be used to help direct prevention and surveillance strategies to reduce lead in the environment of at-risk children.


PubMed | ChemRisk
Type: Journal Article | Journal: Environmental toxicology and chemistry | Year: 2012

Currently, environmental studies describing levels of polychlorinated biphenyls (PCBs) in imported shrimp are limited, particularly studies of aquaculture shrimp. In the present study, we measured concentrations of the 209 PCB congeners in 84 uncooked, warm-water shrimp samples from the United States and 14 other countries in three continents. Total PCB and dioxin-like PCB (DL-PCB) levels were not significantly different between wild-caught and farm-raised shrimp, and the distribution of total PCB levels did not vary considerably by country of origin although significant differences were observed in some cases. Regional trends in both total PCB and DL-PCB concentrations were observed, with the highest concentrations measured in shrimp from North America followed by Asia and then South America. The lower chlorinated homologues (i.e., mono-, di-, and tri-PCBs) generally comprised a greater fraction of the total levels measured in farm-raised shrimp and shrimp from Asia and South America whereas higher chlorinated homologues (i.e., hepta-, octa-, nona-, and deca-PCBs) contributed more to levels in wild-caught shrimp and shrimp from North America. Estimated daily intake of PCBs associated with shrimp consumption ranged from 2pg/kg/d (shrimp from South America) to 15pg/kg/d (shrimp from North America). Results from the present study were comparable to other studies conducted recently and demonstrate that exposure to PCBs from consumption of farm-raised and wild-caught shrimp imported from different regions are not likely to pose any health risks.


PubMed | ChemRisk
Type: Journal Article | Journal: Ecotoxicology (London, England) | Year: 2012

Tire and road wear particles (TRWP) consist of a complex mixture of rubber, and pavement released from tires during use on road surfaces. Subsequent transport of the TRWP into freshwater sediments has raised some concern about the potential adverse effects on aquatic organisms. Previous studies have shown some potential for toxicity for tread particles, however, toxicity studies of TRWP collected from a road simulator system revealed no acute toxicity to green algae, daphnids, or fathead minnows at concentrations up to 10,000mg/kg under conditions representative of receiving water bodies. In this study, the chronic toxicity of TRWP was evaluated in four aquatic species. Test animals were exposed to whole sediment spiked with TRWP at concentrations up to 10,000mg/kg sediment or elutriates from spiked sediment. Exposure to TRWP spiked sediment caused mild growth inhibition in Chironomus dilutus but had no adverse effect on growth or reproduction in Hyalella azteca. Exposure to TRWP elutriates resulted in slightly diminished survival in larval Pimephales promelas but had no adverse effect on growth or reproduction in Ceriodaphnia dubia. No other endpoints in these species were affected. These results, together with previous studies demonstrating no acute toxicity of TRWP, indicate that under typical exposure conditions TRWP in sediments pose a low risk of toxicity to aquatic organisms.

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