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Regulatory Limit (regulatory + limit)

Distribution by Scientific Domains

Mathematics and Statistics	37%
Earth and Environmental Science	25%

Selected Abstracts

A Note on Comparing Exposure Data to a Regulatory Limit in the Presence of Unexposed and a Limit of Detection

BIOMETRICAL JOURNAL, Issue 6 2005
Haitao Chu
Abstract In some occupational health studies, observations occur in both exposed and unexposed individuals. If the levels of all exposed individuals have been detected, a two-part zero-inflated log-normal model is usually recommended, which assumes that the data has a probability mass at zero for unexposed individuals and a continuous response for values greater than zero for exposed individuals. However, many quantitative exposure measurements are subject to left censoring due to values falling below assay detection limits. A zero-inflated log-normal mixture model is suggested in this situation since unexposed zeros are not distinguishable from those exposed with values below detection limits. In the context of this mixture distribution, the information contributed by values falling below a fixed detection limit is used only to estimate the probability of unexposed. We consider sample size and statistical power calculation when comparing the median of exposed measurements to a regulatory limit. We calculate the required sample size for the data presented in a recent paper comparing the benzene TWA exposure data to a regulatory occupational exposure limit. A simulation study is conducted to investigate the performance of the proposed sample size calculation methods. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Voltammetric Detection of Lead(II) Using Amide-Cyclam- Functionalized Silica-Modified Carbon Paste Electrodes

ELECTROANALYSIS, Issue 15 2009
Stéphanie Goubert-Renaudin
Abstract 2-(4,8,11-Triscarbamoylmethyl-1,4,8,11-tetraazacyclotetradec-1-yl)acetamide (TETAM) derivatives bearing 1, 2, or 4 silylated arms have been synthesized and grafted to the surface of silica gel and ordered mesoporous silica samples. The resulting organic-inorganic hybrids have been incorporated into carbon paste electrodes and applied to the preconcentration electroanalysis of Pb(II). The attractive recognition properties of these cyclam derivatives functionalized with amide pendent groups toward Pb(II) species and the highly porous structure of the adsorbents can be exploited for the selective and sensitive detection of the target analyte. Various parameters affecting the preconcentration and detection steps have been discussed with respect to the composition and pH of both accumulation and detection media, the nature of the adsorbent (number of silylated groups linking the macrocycle to silica, texture of materials), the accumulation time, and the presence of interfering cations. Under optimal conditions and for 2,min accumulation at open-circuit, the voltammetric response increased linearly with the Pb(II) concentration in a range extending from 2×10,7 to 10,5,M, while a longer accumulation time of 15,min afforded a linear calibration curve between 10,8 and 10,7,M with a detection limit of 2.7×10,9,M which is well below the European regulatory limit of lead in consumption water. [source]

Treatment of a Chromate-Contaminated Soil Site by in situ Gaseous Reduction

GROUND WATER MONITORING & REMEDIATION, Issue 1 2007
E.C Thornton
A proof-of-concept field test for the treatment of hexavalent chromium in the vadose zone using in situ gaseous reduction was successfully completed by the U.S. Department of Energy and U.S. Department of Defense in a joint demonstration conducted at White Sands Missile Range, New Mexico. The test involved injecting hydrogen sulfide, diluted in air, into contaminated vadose zone sediment to reduce Cr(VI) to Cr(III). The gaseous mixture was injected directly into the contaminated sediment through a central injection well and vacuum extracted through the flow field with six boreholes at the site periphery over a 76-d period. Comparison of soil samples taken before and after the test indicated 70% of the total mass of hexavalent chromium originally present at the site was reduced and immobilized. The zone of highest contamination was nearly completely treated, with average Cr(VI) concentrations decreasing in this interval from an average of 8.1 mg/kg before treatment to 1.1 mg/kg after treatment. Treatment was best in higher permeability clean gypsum sands and less effective in zones containing greater amounts of silt and clay and a slightly higher iron content. All hexavalent chromium concentrations measured in the posttest samples, however, were well below the remedial goal and regulatory limit of 30 mg/kg. In addition, the field test demonstrated that vadose zone treatment of contamination can be safely conducted using diluted hydrogen sulfide gas mixtures. Ongoing development of the technology is being directed toward addressing the limitations of gaseous treatment arising from variations in sediment permeability and iron content and assessing the relationship between hydrogen sulfide consumption and reaction kinetics. [source]

Why do Underwriters Charge Low Underwriting Fees for Initial Public Offerings in Taiwan?

JOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 7-8 2006
Hsuan-Chi Chen
Abstract:, In Taiwan, underwriting fees for initial public offerings (IPOs) are extremely low compared to fees in other countries. From 1989 to 1999, the average underwriting fee for IPOs in Taiwan is 0.99%,far below the regulatory limit. Although the Taiwanese underwriting industry is highly concentrated, underwriting fees do not cluster at any particular level. We examine the underwriting fee and income structure in Taiwan and find support for an incentive hypothesis. Underwriters have an incentive to charge lower underwriting fees when market demand for IPO shares increases and capital gains account for a larger portion of their total income. [source]

A Note on Comparing Exposure Data to a Regulatory Limit in the Presence of Unexposed and a Limit of Detection

Combining evidence on air pollution and daily mortality from the 20 largest US cities: a hierarchical modelling strategy

JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 3 2000
Francesca Dominici
Reports over the last decade of association between levels of particles in outdoor air and daily mortality counts have raised concern that air pollution shortens life, even at concentrations within current regulatory limits. Criticisms of these reports have focused on the statistical techniques that are used to estimate the pollution,mortality relationship and the inconsistency in findings between cities. We have developed analytical methods that address these concerns and combine evidence from multiple locations to gain a unified analysis of the data. The paper presents log-linear regression analyses of daily time series data from the largest 20 US cities and introduces hierarchical regression models for combining estimates of the pollution,mortality relationship across cities. We illustrate this method by focusing on mortality effects of PM10 (particulate matter less than 10 ,m in aerodynamic diameter) and by performing univariate and bivariate analyses with PM10 and ozone (O3) level. In the first stage of the hierarchical model, we estimate the relative mortality rate associated with PM10 for each of the 20 cities by using semiparametric log-linear models. The second stage of the model describes between-city variation in the true relative rates as a function of selected city-specific covariates. We also fit two variations of a spatial model with the goal of exploring the spatial correlation of the pollutant-specific coefficients among cities. Finally, to explore the results of considering the two pollutants jointly, we fit and compare univariate and bivariate models. All posterior distributions from the second stage are estimated by using Markov chain Monte Carlo techniques. In univariate analyses using concurrent day pollution values to predict mortality, we find that an increase of 10 ,g m -3 in PM10 on average in the USA is associated with a 0.48% increase in mortality (95% interval: 0.05, 0.92). With adjustment for the O3 level the PM10 -coefficient is slightly higher. The results are largely insensitive to the specific choice of vague but proper prior distribution. The models and estimation methods are general and can be used for any number of locations and pollutant measurements and have potential applications to other environmental agents. [source]

Arsenic and thallium data in environmental samples: Fact or fiction?

REMEDIATION, Issue 4 2010
Susan D. Chapnick
Matrix effects may increasingly lead to erroneous environmental decisions as regulatory limits or risk-based concentrations of concern for trace metals move lower toward the limits of analytical detection. A U.S. Environmental Protection Agency Office of Technical Standards Alert estimated that environmental data reported using inductively coupled plasma spectrometry (ICP-AES) has a false-positive rate for thallium of 99.9 percent and for arsenic of 25 to 50 percent. Although this does not seem to be widely known in the environmental community, using three case studies, this article presents data in environmental samples that demonstrate severe matrix effects on the accuracy of arsenic and thallium results. Case Study 1 involves soil results with concentrations that approached or exceeded the applicable regulatory soil cleanup objectives of 13 mg/kg for arsenic and 2 mg/kg for thallium. Reanalysis using ICP coupled with a mass spectrometer (ICP-MS) confirmed all thallium results were false positives and all arsenic results were biased high, concluding no action was required for soil remediation. Case Study 2 involves groundwater results for thallium at a Superfund site, where thallium was detected in groundwater up to 21.6 , g/L using ICP-AES. Reanalysis by ICP-MS reported thallium as nondetect below the applicable regulatory level in all samples. ICP-MS is usually a more definitive and accurate method of analysis compared to ICP-AES; however, this is not always the case, as we demonstrate in Case Study 3, using data from groundwater samples at an industrial site. Through a weight-of-evidence approach, it is demonstrated that although method quality control results were acceptable, interferences in some groundwater samples caused biased high results for arsenic using ICP-MS, which were significantly lower when reanalyzed using hydride generation atomic fluorescence spectrometry. Causes of these interference effects and conclusions from the three case studies to obtain accurate metal data for site assessment, risk characterization, and remedy selection are discussed. © 2010 Wiley Periodicals, Inc. [source]

Mineralogical Characteristics and Cationic Exchange Properties of a Zeolite Mineral from Romana, NW Sardinia, Italy

RESOURCE GEOLOGY, Issue 1 2009
Maria L. Fercia
Abstract An investigation was conducted into the Tertiary ignimbrite formations in the Romana area in NW Sardinia. Scanning electron microscopy,energy-dispersive spectrometry indicated the presence of clinoptilolite and subordinate smectite, quartz, mordenite and calcite. Laboratory analyses of representative samples collected from the deposit indicated a cation exchange capacity ranging from 85 to 135 mEq per 100 g. Ion exchange experiments conducted in flasks containing different initial cation concentrations and in columns supplied with solution having constant cation concentration, showed different selectivity towards the cations examined, in the order: NH4+> Pb2+> Cd2+> Cu2+> Zn2+> Mn2+> Ni2+. Compared to the untreated material, under the experimental conditions used and considering the eluate, and the Italian regulatory limits for discharge into surface waters, the zeolite treated with a 1-N NaCl solution yielded a 1.3,5-fold increase in the volume of treated water, depending on the cation examined. The experimental results obtained show that the cationic exchange properties of the zeolite rock from the Romana deposit are comparable with the average quality of zeolites currently imported into Italy from non-European countries. [source]