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PubMed | Texas Commission on Environmental Quality TCEQ, Sielken & Associates Consulting Inc. and Texas A&M University
Type: Journal Article | Journal: Regulatory toxicology and pharmacology : RTP | Year: 2015

A unit risk factor (URF) was developed for isoprene based on evaluation of three animal studies with adequate data to perform dose-response modeling (NTP, 1994, 1999; Placke et al., 1996). Ultimately, the URF of 6.2E-08 per ppb (2.2E-08 per g/m(3)) was based on the 95% lower confidence limit on the effective concentration corresponding to 10% extra risk for liver carcinoma in male B6C3F1 mice after incorporating appropriate adjustment factors for species differences in target tissue metabolite concentrations and inhalation dosimetry. The corresponding lifetime air concentration at the 1 in 100,000 no significant excess risk level is 160 ppb (450 g/m(3)). This concentration is almost 4400 times lower than the lowest exposure level associated with statistically increased liver carcinoma in B6C3F1 mice in the key study (700 ppm in Placke et al., 1996) and is above typical isoprene breath concentrations reported in the scientific literature. Continuous lifetime environmental exposure to the 1 in 100,000 excess risk level of 160 ppb would be expected to raise the human blood isoprene area under the curve (AUC) less than one-third of the standard deviation of the endogenous mean blood AUC. The mean for ambient air monitoring sites in Texas (2005-2014) is approximately 0.13 ppb.

Howell N.L.,University of Houston | Lakshmanan D.,University of Houston | Rifai H.S.,University of Houston | Koenig L.,Texas Commission on Environmental Quality TCEQ
Science of the Total Environment | Year: 2011

All 209 PCB congeners are quantified in water in both dry and wet weather urban flows in Houston, Texas, USA. Total water PCBs ranged from 0.82 to 9.4. ng/L in wet weather and 0.46 to 9.0. ng/L in dry. Wet weather loads were 8.2 times higher (by median) than dry weather with some increases of over 100-fold. The majority of the PCB load was in the dissolved fraction in dry weather while it was in the suspended fraction in wet weather. Dissolved PCB loads were correlated with rain intensity and highly developed land area, and a multiple linear regression (MLR) equation was developed to quantify these correlations. PCA generated five PCB components with nearly all positive loadings. They were interpreted as DOC-associated A1248, wet weather primarily suspended fraction A1254/A1260 likely from building sealants, truly dissolved-associated wastewater dechlorination, watershed-sourced PCB 11, and monochlorinated PCBs (likely connected to a different state or source of dechlorination). The PCB 11 component was statistically higher in wet versus dry weather when no other component showed such clear distinctions. Hierarchical cluster analysis (HCA) did not always group dry and wet weather samples from the same location together illustrating the different congener composition that often exists between dry and wet conditions. Four wet weather samples from high percentage developed land (> 90%) watersheds had nearly the same fingerprint suggesting a generic "urban" signature in runoff, which in this case was caused by residual A1254/A1260 PCB stocks and currently produced PCB 11 in consumer goods. © 2011 Elsevier B.V.

Howell N.L.,University of Houston | Rifai H.S.,University of Houston | Koenig L.,Texas Commission on Environmental Quality TCEQ
Chemosphere | Year: 2011

PCDD/F and PCB field data (1041 samples) in five media (dissolved, suspended sediment, bed sediment, catfish, and blue crab) were studied to explore dual contaminant patterns in the Houston Ship Channel, Texas, USA. PCDD/Fs showed greater concentration than PCBs in suspended sediments while PCBs were higher in apparent dissolved (truly dissolved+DOC-associated), fish, and crab. PCDD/Fs at nearly all locations contributed more strongly to dioxin-like toxicity. The fraction of PCB TEQ was, however, enriched in biotic over abiotic media due in large part to the presence of PCB 126, which was mostly undetected in water and sediment and yet exhibited a BAF three times greater than 2,3,7,8-TCDD. Dissolved-suspended sediment and suspended-bed sediment relationships showed that (1) observed apparent dissolved concentration differences (as fraction of total water were mean 10% PCDD/Fs and 63% PCBs) can reasonably be explained by a four-phase partition model (truly dissolved, DOC-associated, suspended OC, and suspended BC) for PCBs but not for PCDD/Fs and (2) the contaminants behaved similarly in bed to suspended sediment concentration ratios (Cbed/Csusp) upstream of a major confluence but not downstream. PCA-cluster analysis pointed to the possibility that suspended sediment PCB contamination originates from resuspended bed sediment while PCDD/Fs in suspended sediment originates more probably from other sediment sources such as upstream wash load or air deposition. Finally, examinations of a congener marker ratio (PCB 209/206) seemed to indicate that a source of pure PCB 209 may exist in bed sediment near Patrick Bayou though the source was not completely localized. © 2011 Elsevier Ltd.

Daniel S.,Texas Commission on Environmental Quality TCEQ | Lou C.,Iowa State University | Jo Min K.,Iowa State University
Electric Power Systems Research | Year: 2013

In the Public Utilities Regulatory Policies Act (PURPA) in the USA, to promote cogeneration, there exists a key provision for qualifying facilities to sell the cogenerated electric power to host utilities at a pre-determined price. In this paper, we investigate the economic implications and consequences of this "right to sell" provision. First, under PURPA, we show how the interaction between a cogeneration facility and an electric utility can be modeled as a Stackelberg game, and derive the equilibrium generation quantities, prices, as well as the corresponding profits and total surplus. We next construct a benchmark model under a deregulated environment. By comparing and contrasting these two models, we obtain various results of managerial insights, economic implications, and policy ramifications. For example, under the right to sell provision, we identify the conditions for a qualifying facility's arbitrage to occur. Also, relative to the deregulated benchmark model, we show how the government's right to sell provision may lead to inferior economic performance. © 2013 Elsevier B.V. All rights reserved.

Haney J.T.,Texas Commission on Environmental Quality TCEQ | Erraguntla N.,Texas Commission on Environmental Quality TCEQ | Sielken R.L.,Sielken and Associates Consulting Inc. | Valdez-Flores C.,Sielken and Associates Consulting Inc.
Regulatory Toxicology and Pharmacology | Year: 2012

The carcinogenicity of hexavalent chromium(CrVI) is of significant interest to regulatory agencies for the protection of public health and to industry. Additionally, the mode of action (MOA) and conditions under which CrVI may induce carcinogenicity (e.g., reductive capacity considerations) have recently been the subject of significant scientific debate. Epidemiological data supported by data relevant to the carcinogenic MOA support considering nonlinear-threshold carcinogenic assessments for comparison to default linear low-dose extrapolation approaches. This study reviews epidemiological studies available in the scientific literature and conducts additional statistical dose-response analyses to identify potential carcinogenic thresholds and points of departure (PODs) in the context of supportive MOA information for a nonlinear-threshold inhalation carcinogenic assessment. Dosimetric adjustments and application of appropriate uncertainty factors (total UF of 30) to the selected cumulative exposure POD results in a cancer-based chronic inhalation reference value (ReV) of 0.24μgCrVI/m 3. This chronic ReV is 300 times higher than the 1 in 100,000 excess cancer risk air concentration of 8E-04μg/m 3 based on USEPA's unit risk factor. © 2012 Elsevier Inc.

Dose-dependent changes in target tissue absorption have important implications for determining the most defensible approach for developing a cancer-based oral toxicity factor for hexavalent chromium (CrVI). For example, mouse target tissue absorption per unit dose is an estimated 10-fold lower at the CrVI dose corresponding to the federal maximum contaminant level (MCL) than at the USEPA draft oral slope factor (SFo) point of departure dose. This decreasing target tissue absorption as doses decrease to lower, more environmentally-relevant doses is inconsistent with linear low-dose extrapolation. The shape of the dose-response curve accounting for this toxicokinetic phenomenon would clearly be non-linear. Furthermore, these dose-dependent differences in absorption indicate that the magnitude of risk overestimation by a linear low-dose extrapolation approach (e.g., SFo) increases and is likely to span one or perhaps more orders of magnitude as it is used to predict risk at progressively lower, more environmentally-relevant doses. An additional apparent implication is that no single SFo can reliably predict risk across potential environmental doses (e.g., doses corresponding to water concentrations. ≤. the federal MCL). A non-linear approach, consistent with available mode of action data, is most scientifically defensible for derivation of an oral toxicity factor for CrVI-induced carcinogenesis. © 2015 Elsevier Inc..

Haney J.T.,Texas Commission on Environmental Quality TCEQ
Human and Ecological Risk Assessment | Year: 2016

Historical concentrations of trichloroethylene (TCE) and other chemicals in drinking water at the U.S. Marine Corps Base at Camp Lejeune, NC, were sufficiently elevated to raise potential health concerns. The 1952–1984 mean TCE concentration (138 µg/L) exceeded the U.S. Environmental Protection Agency's (USEPA's) current maximum contaminant level (MCL) of TCE by 28-fold, with the corresponding dose (3.9E–03 mg/kg-day) exceeding all three candidate USEPA reference dose (RfD) values by 8- to 11-fold. Today, TCE hazard quotients (HQs) of 8–11 compel immediate action by USEPA. The mean dose also exceeds the supporting RfD values for toxic nephropathy and increased kidney weight, as well as the point of departure (POD) for toxic nephropathy. Furthermore, the estimated doses for 34% of the 9-month rolling averages exceed the POD for the highest RfD value for fetal heart defects. The incidences of nephropathy and fetal heart defects should be thoroughly evaluated among those who were exposed. Long-term follow-up will be required to assess potential health effects for the 500,000 to 1 million people who may have used the contaminated water at Camp Lejeune or were exposed in utero. This should serve as a cautionary tale for the thousands of Department of Defense sites across the USA (and other similarly contaminated sites elsewhere in the world) that are commonly contaminated with chemicals such as those at Camp Lejeune, where necessary sampling should be conducted to identify and mitigate any likely ongoing (or future) exposures of potential health concern. © 2016 Taylor & Francis Group, LLC

Haney J.,Texas Commission on Environmental Quality TCEQ
Regulatory Toxicology and Pharmacology | Year: 2015

The mouse dose at the lowest water concentration used in the National Toxicology Program hexavalent chromium (CrVI) drinking water study (NTP, 2008) is about 74,500 times higher than the approximate human dose corresponding to the 35-city geometric mean reported in EWG (2010) and over 1000 times higher than that based on the highest reported tap water concentration. With experimental and environmental doses differing greatly, it is a regulatory challenge to extrapolate high-dose results to environmental doses orders of magnitude lower in a meaningful and toxicologically predictive manner. This seems particularly true for the low-dose extrapolation of results for oral CrVI-induced carcinogenesis since dose-dependent differences in the dose fraction absorbed by mouse target tissues are apparent (Kirman et al., 2012). These data can be used for a straightforward adjustment of the USEPA (2010) draft oral slope factor (SFo) to be more predictive of risk at environmentally-relevant doses. More specifically, the evaluation of observed and modeled differences in the fraction of dose absorbed by target tissues at the point-of-departure for the draft SFo calculation versus lower doses suggests that the draft SFo be divided by a dose-specific adjustment factor of at least an order of magnitude to be less over-predictive of risk at more environmentally-relevant doses. © 2014 The Author.

PubMed | Texas Commission on Environmental Quality TCEQ
Type: Journal Article | Journal: Regulatory toxicology and pharmacology : RTP | Year: 2015

A non-linear approach, consistent with available mode of action (MOA) data, is most scientifically defensible for assessing the carcinogenicity of oral exposure to hexavalent chromium (CrVI). Accordingly, the current paper builds upon previous studies (Haney, 2015a, 2015b) to first develop a non-linear, non-threshold approach as well as a non-linear threshold approach for assessing the oral carcinogenicity of CrVI, and then utilizes available MOA analyses and information for selection of the most scientifically-supported approach. More specifically, a non-linear, non-threshold dose-response function was developed that adequately describes the non-linearity predicted for potential human excess risk versus oral dose due to the sub-linear relationship between oral dose and internal dose (added mg Cr/kg target tissue) across environmentally-relevant doses of regulatory interest. Additionally, benchmark dose modeling was used to derive a reference dose (RfD of 0.003 mg/kg-day) with cytotoxicity-induced regenerative hyperplasia as a key precursor event to carcinogenesis in the mouse small intestine. This RfD value shows remarkable agreement with that published previously (0.006 mg/kg-day) based on a more scientifically-sophisticated, physiologically-based pharmacokinetic modeling approach (Thompson et al., 2013b). The RfD approach is the most scientifically-defensible approach based on the weight-of-evidence of available MOA information and analyses conducted for the most scientifically-supported MOA.

PubMed | Texas Commission on Environmental Quality TCEQ
Type: | Journal: Regulatory toxicology and pharmacology : RTP | Year: 2016

An inhalation unit risk factor (URF) was developed for cadmium. The URF is based on excess lung cancer mortality in a key epidemiological study of cadmium smelter workers (Park etal., 2012). The Park etal. (2012) study is an update of the Thun etal. (1985) cohort that was previously used to derive a URF in USEPA (1985). Park etal. re-analyzed the cadmium smelter worker population (near Denver, CO) using more detailed work history information, a revised cadmium exposure matrix, a detailed retrospective exposure assessment for arsenic (potential confounder), and updated mortality data (through 2002). Grouped observed and expected number of lung cancer mortalities along with cumulative cadmium exposures were used in the current study to obtain the maximum likelihood estimate and asymptotic variance of the slope () for the linear multiplicative relative risk model using Poisson regression modeling. Life-table analyses were used to derive the final URF for cadmium of 4.9E-04 per g Cd/m(3). The corresponding lifetime air concentration at the 1 in 100,000 no significant excess risk level is 0.020g Cd/m(3), which can be used to protect the general public in Texas against the potential carcinogenic effects from chronic exposure to cadmium and cadmium compounds.

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