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PubMed2001

Statistical issues in the analysis of low-dose endocrine disruptor data.

UNLABELLED: The National Institute of Environmental Health Sciences (NIEHS) and the U.S. Environmental Protection Agency (U.S. EPA) recently cosponsored the Endocrine Disruptors Low-Dose Peer REVIEW: The purpose of this meeting was to examine data supporting the presence or absence of low-dose effects of endocrine disruptors in specific studies and then to evaluate the likelihood and significance of these and/or other potential low-dose effects for humans. All invited speakers agreed to provide their raw data in advance of the meeting to a Statistics Subpanel, which was asked to reevaluate the authors' experimental design, data analysis, and interpretation of experimental results. The purpose of this statistical reevaluation was to provide an independent assessment of the experimental design and data analysis used in each of the studies and to identify key statistical issues relevant to the evaluation and interpretation of the data. This paper presents a summary of the Statistics Subpanel's evaluation. Specific examples are presented to illustrate problems that arose in the experimental design and data analysis of certain studies. The statistical principles and issues that are discussed in this paper are not unique to endocrine disruptor studies and should provide important guidelines regarding appropriate experimental design and statistical analysis for other types of laboratory investigations.

Analysis of Variance↗
PubMed1994

Pesticide registration in the United States: overview and new directions.

This paper provides an overview of EPA's pesticide registration program and a discussion of recent activities. The registration of pesticides is the responsibility of the Office of Pesticide Programs, an office of the U.S. Environmental Protection Agency (EPA). EPA's pesticide regulatory authority derives from the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) and the Federal Food, Drug and Cosmetic Act (FFDCA). FIFRA governs the registration or licensing of pesticide products including insecticides, herbicides, fungicides, rodenticides, disinfectants, plant growth regulators, and biological agents. FFDCA governs pesticide residue levels in food and feed crops. FIFRA gives EPA authority for registering pesticides to ensure that when used according to label directions, they will not pose unreasonable adverse effects to the environment. FIFRA requires EPA to balance the risks and benefits of a pesticide in deciding whether or not to grant a pesticide registration. In a typical year EPA reviews over 5000 registration submissions that vary from routine label amendments to the review of a new active ingredient. About 20 applications for registration of a new active ingredient are received each year. Registration for a new active ingredient requires a significant investment in time and money by the registrant. Data development for a major agricultural chemical can cost 10 million dollars or more and take several years to complete. EPA is embarking on a number of new initiatives in the registration program designed to reduce the use of chemical pesticides, limit the regulatory burden on lower risk and reduced risk products, and streamline the review process generally.

Agriculture↗
PubMed2006

Measurement of total polycyclic aromatic hydrocarbon concentrations in sediments and toxic units used for estimating risk to benthic invertebrates at manufactured gas plant sites.

The U.S. Environmental Protection Agency's (U.S. EPA) narcosis model requires the measurement of 18 parent and 16 groups of alkyl polycyclic aromatic hydrocarbons (PAHs) (so-called 34 PAHs) in sediments to calculate the number of PAH toxic units (TU) available to benthic organisms. If data for the 34 PAHs are not available, the U.S. EPA proposes estimating the risk by multiplying the TU for 13 parent PAHs by 11.5 (95% confidence interval) based on data from 488 sediments. This estimate is overly conservative for PAHs from pyrogenic manufactured gas plant (MGP) processes based on the analysis of 45 sediments from six sites. Parent PAHs contributed approximately 40% of the total concentrations and TU for MGP sediments. In contrast, parent PAHs from diesel fuel and petroleum crude oil contributed only 2 and 1%, respectively, of the PAH concentrations and TU, compared to approximately 98 to 99% contributed by the alkyl PAHs. Statistical comparison of the TU based on the measured 34 alkyl and parent PAHs and those based on only 13 parent PAHs demonstrated that a factor of 4.2 (rather than 11.5) is sufficient to estimate total TU within a 95% confidence level for MGP sites. Similarly, measurement of parent PAHs is sufficient to accurately estimate the total 34 alkyl and parent PAH concentrations for MGP-impacted sediments.

Animals↗
PubMed2006

Recent exposure to particulate matter and C-reactive protein concentration in the multi-ethnic study of atherosclerosis.

Ambient levels of particulate matter have been linked to cardiovascular disease. The mechanisms mediating these associations are poorly understood. One candidate mechanism is inflammation. Using data from the Multi-Ethnic Study of Atherosclerosis (2000-2002), the authors investigated the relation between exposure to particulate matter of less than or equal to 2.5 microm in diameter (PM2.5) and C-reactive protein concentration in 5,634 persons aged 45-84 years who were free of cardiovascular disease. Data from US Environmental Protection Agency monitors were used to estimate PM2.5 exposures for the prior day, prior 2 days, prior week, prior 30 days, and prior 60 days. Only the 30-day and 60-day mean exposures showed a weak positive association with C-reactive protein, and confidence intervals were wide: relative increases in C-reactive protein per 10 microg/m3 of PM2.5 adjusted for person-level covariates were 3% (95% confidence interval (CI): -2, 10) for a 30-day mean and 4% (95% CI: -3, 11.0) for a 60-day mean. The means of 7-day, 30-day, and 60-day exposures were weakly, positively, and nonsignificantly associated with the odds of C-reactive protein of greater than or equal to 3 mg/liter: adjusted odds ratios were 1.05 (95% CI: 0.96, 1.15), 1.12 (95% CI: 0.98, 1.29), and 1.12 (95% CI: 0.96, 1.32), respectively. Slightly stronger associations were observed in persons without other risk factors for elevated C-reactive protein, but this heterogeneity was not statistically significant. The authors' results are not compatible with strong effects of particulate matter exposures on population levels of C-reactive protein.

Aged↗
PubMed1999

Estimating risk assessment exposure point concentrations when the data are not normal or lognormal.

The U.S. Environmental Protection Agency (EPA) recommends the use of the one-sided 95% upper confidence limit of the arithmetic mean based on either a normal or lognormal distribution for the contaminant (or exposure point) concentration term in the Superfund risk assessment process. When the data are not normal or lognormal this recommended approach may overestimate the exposure point concentration (EPC) and may lead to unecessary cleanup at a hazardous waste site. The EPA concentration term only seems to perform like alternative EPC methods when the data are well fit by a lognormal distribution. Several alternative methods for calculating the EPC are investigated and compared using soil data collected from three hazardous waste sites in Montana, Utah, and Colorado. For data sets that are well fit by a lognormal distribution, values for the Chebychev inequality or the EPA concentration term may be appropriate EPCs. For data sets where the soil concentration data are well fit by gamma distributions, Wong's method may be used for calculating EPCs. The studentized bootstrap-t and Hall's bootstrap-t transformation are recommended for EPC calculation when all distribution fits are poor. If a data set is well fit by a distribution, parametric bootstrap may provide a suitable EPC.

Evaluation Studies as Topic↗
PubMed2006

Trichloroethylene cancer epidemiology: a consideration of select issues.

A large body of epidemiologic evidence exists for exploring causal associations between cancer and trichloroethylene (TCE) exposure. The U.S. Environmental Protection Agency 2001 draft TCE health risk assessment concluded that epidemiologic studies, on the whole, support associations between TCE exposure and excess risk of kidney cancer, liver cancer, and lymphomas, and, to a lesser extent, cervical cancer and prostate cancer. As part of a mini-monograph on key issues in the health risk assessment of TCE, this article reviews recently published scientific literature examining cancer and TCE exposure and identifies four issues that are key to interpreting the larger body of epidemiologic evidence: a) relative sensitivity of cancer incidence and mortality data ; b) different classifications of lymphomas, including non-Hodgkin lymphoma ; c) differences in data and methods for assigning TCE exposure status ; and d) different methods employed for causal inferences, including statistical or meta-analysis approaches. The recent epidemiologic studies substantially expand the epidemiologic database, with seven new studies available on kidney cancer and somewhat fewer studies available that examine possible associations at other sites. Overall, recently published studies appear to provide further support for the kidney, liver, and lymphatic systems as targets of TCE toxicity, suggesting, as do previous studies, modestly elevated (typically 1.5-2.0) site-specific relative risks, given exposure conditions in these studies. However, a number of challenging issues need to be considered before drawing causal conclusions about TCE exposure and cancer from these data.

Animals↗
PubMed2001

The cost of developing site-specific environmental regulations: evidence from EPA's project XL.

The flagship of the Environmental Protection Agency's regulatory reinvention initiative, Project XL has been touted as a regulatory blueprint for a site-specific, performance-based pollution-control system, but widespread complaints about the costs of the program beg the question of whether the costs of tailoring regulations to individual facilities are manageable. To address this question, this paper presents original survey data on a sample of 11 XL projects. We find that the fixed costs of putting in place XL agreements are substantial, averaging over $450,000 per firm. While stakeholder negotiations are widely cited as the principal source for these costs, we find that they actually arise mainly from interaction between participating facilities and the EPA. Moreover, EPA management problems are perceived by our survey respondents as having inflated project development costs. Finally, we find that the key factors that explains differences in costs across XL projects are the scope and complexity of the project proposal. These findings suggest that Project XL favors large firms that can afford to pay significant project development costs, that EPA management problems must be resolved to reduce costs, and that there may be a significant economic bias against complex and innovative proposals--precisely the type of proposals that Project XL was designed to foster in order to improve the efficiency of the regulatory system.

Commerce↗
PubMedDate not supplied

Development of chronic aquatic water quality criteria and standards for silver.

U.S. Environmental Protection Agency (EPA) is updating its aquatic life ambient water quality criteria (aqAWQC) for a number of parameters, including silver. The silver aqAWQC was last issued in 1980. At that time only an acute aqAWQC was established. With the increased reliance on water quality criteria to drive and prioritize the United State's efforts to improve water quality, the scientific basis of new and modified water quality criteria must be both strong and transparent. Although few, if any, natural waters in the United States have suffered water quality impairments because of silver, the lack of valid silver chronic toxicity data in combination with the misapplication of the current U.S. EPA guidelines on deriving chronic aqAWQC could lead to derivation of chronic criteria (by U.S. EPA) and chronic standards (by states, tribes, etc.) that are not supported by scientific data. This misapplication could result in U.S. EPA and the states listing many waters as impaired by silver where, in fact, no silver-related water quality problem exists. This Research Note reviews available information on studies of both acute and chronic silver toxicity to aquatic organisms, as well as U.S. EPA's 1985 procedure for adopting chronic water quality criteria. It identifies existing gaps in the underlying research data base and identifies additional work necessary to derive valid chronic water quality criteria and standards for silver.

Animals↗
PubMed1999

A survey of EPA/OPP and open literature on selected pesticide chemicals. II. Mutagenicity and carcinogenicity of selected chloroacetanilides and related compounds.

With this effort, we continue our examination of data on selected pesticide chemicals and their related analogues that have been presented to the U.S. Environmental Protection Agency's (USEPA's) Office of Pesticide Programs (OPP). This report focuses on a group of selected chloroacetanilides and a few related compounds. As part of the registration process for pesticidal chemicals, interested parties (registrants) must submit toxicity information to support the registration including both mutagenicity and carcinogenicity data. Although this information is available to the public via Freedom of Information (FOI) requests to the OPP, publication in the scientific literature allows greater dissemination and examination of the data. For this Special Issue, graphic profiles have been prepared of the mutagenicity and carcinogenicity data available in the submissions to OPP. Also, a discussion is presented about how toxicity data are used to help establish tolerances (limits of pesticide residues in foods). The mutagenicity results submitted by registrants are supplemented by data on these chemicals from the open literature to provide a full perspective of their genetic toxicology. The group of chloroacetanilides reviewed here display a consistent pattern of mutagenic activity, probably mediated via metabolites. This mutagenic activity is a mechanistically plausible factor in the development of tumors seen in experimental animals exposed to this class of chemicals.

Acetamides↗
PubMed2005

Development of U.S. EPA method 527 for the analysis of selected pesticides and flame retardants in the UCMR survey.

Method 527 was developed to address the occurrence monitoring needs of the U.S. Environmental Protection Agency (EPA) under its second unregulated contaminant monitoring rule (UCMR 2). This method includes a wide range of semivolatile organic contaminants, including pesticides that were deferred during the first UCMR, flame retardants, and pyrethroid pesticides. This paper discusses the rationale for selection and inclusion of the various contaminants included in Method 527 and describes the challenges associated with developing analytical methods that will be used for the occurrence monitoring of such a diverse group of organic molecules. Method 527 employs solid-phase extraction with analysis by gas chromatography/ mass spectrometry (GC/MS). The final method preservation scheme requires the storage of samples in amber bottles buffered at pH 3.8 using citric acid to prevent degradation from acid-catalyzed hydrolysis and from UV light. Citric acid is also an effective antimicrobial reagent, preventing this mode of loss during storage. Ethylenediaminetetraacetic acid (EDTA) is added to remove transition metals such as copper, which was determined to degrade target analytes upon storage. Finally, free available chlorine (FAC), which is present in many finished waters and found to degrade a number of the targets, is removed using ascorbic acid. The final method meets all of the EPA UCMR survey requirements for sample storage, precision, accuracy, and sensitivity and will be proposed for use under the UCMR 2.

Data Collection↗
PubMed2002

Combined application of simulated reuse and quantitative carrier tests to assess high-level disinfection: experiments with an accelerated hydrogen peroxide-based formulation.

BACKGROUND: Heat-sensitive medical devices require chemical disinfection between patients, and certain formulations for this purpose can be reused for several days. Because dilution, evaporation, and breakdown or neutralization of active ingredients can occur during reuse, it is vital to ensure that the solution retains its broad-spectrum germicidal activity even at the end of the recommended reuse period. OBJECTIVE: The purpose of this study was to combine the US Environmental Protection Agency's and the Food and Drug Administration's recommended simulated reuse method with recently developed quantitative carrier tests (QCT) to assess the broad-spectrum germicidal activity of a 7% solution of accelerated hydrogen peroxide (pH 2.9) stressed for 14 days. MATERIALS AND METHODS: On alternate days baths with 3 lots of the test formulation were stressed by the addition of bacteria (Salmonella choleraesuis, Staphylococcus aureus, and Pseudomonas aeruginosa ) on glass beads and spores (Bacillus subtilis and Clostridium sporogenes ) on metallic penicylinders. In addition, one set of respiratory therapy equipment was subjected to 3 daily cycles of disinfection in each bath. The pH and H(2)O(2) levels in the test samples were measured, and they were also subjected to QCTs for their sporicidal, bactericidal, virucidal, fungicidal, and mycobactericidal activities. RESULTS: After 14 days of reuse, the pH of the test solutions remained essentially unchanged. Although the level of H(2)O(2) dropped from a high of 7.66% to as low as 6.40%, all lots showed the required level of broad-spectrum germicidal activity after 14 days of stress. CONCLUSIONS: The stress test and QCT were successfully combined in demonstrating the broad-spectrum germicidal activity of a high-level disinfectant subjected to 14 days of simulated reuse.

Chemistry, Pharmaceutical↗
PubMed2001

The mammalian safety of Bacillus thuringiensis-based insecticides.

The United States Environmental Protection Agency between the years 1961 and 1995 registered 177 products containing viable Bacillus thuringiensis (Bt). Numerous laboratory studies have demonstrated that Bt and Bt products are noninfectious and are toxic to mammals only at a dose > or =10(8) colony forming units (cfu) per mouse (a human equivalent based on the weight of >10(11) cfu). In contrast, as few as three vegetative cells of Bacillus anthracis can kill mice (a human equivalent of >10(3) cfu). There are only two literature reports of Bt infection in man between the year 1997 and the present, and all infected individuals had experienced either extensive burns or a blast injury, which predisposed them to infection. Two epidemiology studies conducted during large-scale aerial Bt serovar kurstaki spray campaigns reported no increased incidence of illness. Some recent papers have expressed concern about the production of Bacillus cereus enterotoxins by Bt isolates. Laboratory studies found no evidence of illness in rats and sheep fed Bt products, nor have epidemiology studies found increased incidence of diarrhea during Bt aerial spray campaigns. Increases in human antibody levels following exposure to Bt products have been reported but there was no increased incidence in asthma or other illness. Based on laboratory studies and field experience, Bt insecticides have an excellent safety record.

Animals↗
PubMed2005

Diazinon in surface waters before and after a federally-mandated ban.

Samples collected from rural and urban streams in the City of Denton, Texas, USA were analyzed for the organophosphorus pesticide diazinon during the years preceding and following a United States Environmental Protection Agency ban on many diazinon uses. A network of 70 monitoring stations, based mainly on topography and hydrological considerations, were established within the three main watersheds of Denton. Monitoring stations were sampled monthly from March through August during periods of normal flow (baseflow), resulting in a total of 1243 samples collected during the years of 2001-2004. Pesticide concentrations were determined using commercially available enzyme-linked immunosorbent assays (ELISAs) specific for diazinon. Results from this temporally and spatially dense monitoring effort illustrated the impacts of a decrease in diazinon production during 2002, followed by a ban on most outdoor, non-agricultural diazinon retail sales imposed during 2003. The total number of samples exhibiting diazinon concentrations above the lower limits of detection (LLD) significantly decreased between 2001 through 2004 (Mantel-Haenszel Chi-Square test, p<0.0001, n=1243) and decreased significantly during the four monitoring years (Cochran-Armitage Trend test, z=-17.94, p<0.0001, n=1243). The total number of stations exhibiting at least one sample above the LLD during the four monitoring years showed similar patterns (Mantel-Haenszel Chi-Square test, p<0.0001; Cochran-Armitage Trend test, z=-3.21, p=0.0007; n=276). Results indicate that the phased reduction of outdoor, non-agricultural diazinon uses led to a highly significant decrease in surface water occurrences of this pesticide.

Diazinon↗
PubMed1996

Quantitative risk assessment and the limitations of the linearized multistage model.

1. Quantifying carcinogenic risk is an important objective for assisting in the assessment and management of risks from chemical exposure. The most widely used of the many mathematical models proposed for extrapolation of carcinogenicity data from animal studies to low dose human exposures is the linearized multistage (LMS) model. This has, in effect, become the default approach for much of Quantitative Risk Assessment (QRA). The practical properties of this model have been investigated. 2. Analysis of stimulated data using the LMS model showed (i) that the Maximum Likelihood Estimate (MLE) of the low dose slope, q1, was unstable and extremely sensitive to small changes in the data; (ii) the 95% Upper Confidence Limit (UCL) estimate, q1*, preferred by the US Environmental Protection Agency (EPA) was insensitive with only small changes in values being obtained for large changes in the data; (iii) data sets where there was no statistical significance could give risk estimates similar to those obtained from data sets with clear dose-related effects; (iv) the size of the values of the Virtually Safe Dose (VSD) obtained did not necessarily relate to the biological interpretation of the data sets; (v) the value of q1* obtained was closely related to the top dose used in the study. 3. Limitations of the LMS model were illustrated by examples of its use in assessing the carcinogenicity of 2, 3, 7, 8-TCDD leading to the conclusion that the existing models are not suitable for routine use in the estimation of the risk from chemical carcinogens. The use of the LMS model has been justified in part by its original derivation from a mathematical model based upon a multistage model of carcinogenesis. However, estimates of the parameters of the model used to provide estimates of low dose risk to humans have no direct relationship to specific biological event in carcinogenesis. Further developments in mathematical models and increased understanding of the biological events underlying the carcinogenesis will lead to more biologically plausible QRA methods which would then justify serious consideration of QRA by regulatory authorities throughout the world.

Animals↗
PubMed2002

The U.S. EPA Science Advisory Board Evaluation (2001) of the EPA dioxin reassessment.

The U.S. Environmental Protection Agency (EPA) began a "reassessment" of the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) and related chemicals in 1991 and issued an interim report in 1994. In 1995, the Science Advisory Board (SAB) reviewed this document and requested revisions. After considerable additional work, EPA issued its final draft report in September 2000. A new EPA SAB reviewed this draft and issued its recommendations in June 2001. This group of scientists offered suggestions to EPA on the following topics, which are discussed in some detail in this article: classification as a "known" human carcinogen, how to estimate the carcinogenic potency, the possible significance of the noncancer hazard, the proper dose metric for cancer and noncancer effects, the uncertainties inherent in the toxicity equivalency factor approach, use of the margin of exposure approach, adequacy of the exposure assessment, body burden calculations, risks to breast feeding children, nonmonotonic responses (U- or J-shaped dose-response curves, or hormetic effect), the possible significance of naturally occurring dioxin-like chemicals, and risks to special populations. The basis for the recommendations, as generally presented in the SAB report, is described here. A discussion of some of the recently published work within the regulatory and scientific communities that has been issued since the SAB report is also presented.

Advisory Committees↗
PubMed1999

Statistical considerations in determining the health significance of constituents of airborne particulate matter.

Because of the U.S. Environmental Protection Agency's (EPA) new ambient air quality standard for fine particles, the need is likely to continue for more detailed scientific investigation of various types of particles and their effects on human health. Epidemiology studies have become the method of choice for investigating health responses to such particles and to other air pollutants in community settings. Health effects have been associated with virtually all of the gaseous criteria pollutants and with the major constituents of airborne particulate matter (PM), including all size fractions less than about 20 microns, inorganic ions, carbonaceous particles, metals, crustal material, and biological aerosols. In many of the more recent studies, multiple pollutants or agents (including weather variables) have been significantly associated with health responses, and various methods have been used to suggest which ones might be the most important. In an ideal situation, classical least-squares regression methods are capable of performing this task. However, in the real world, where most of the pollutants are correlated with one another and have varying degrees of measurement precision and accuracy, such regression results can be misleading. This paper presents some guidelines for dealing with such collinearity and model comparison problems in both single- and multiple-pollutant regressions. These techniques rely on mean effect (attributable risk) rather than statistical significance per se as the preferred indicator of importance for the pollution variables.

Air Pollution↗
PubMedDate not supplied

Comparison of five extraction methods for determination of incurred and added pesticides in dietary composites.

The National Exposure Research Laboratory of the U.S. Environmental Protection Agency conducts research to measure exposure of individuals to chemical pollutants through the diet. In support of this research, methods are being evaluated for the determination of pesticides in dietary composite samples. In the present study, Soxhlet, blender, microwave-assisted, pressurized fluid, and supercritical fluid extraction methods were compared for the determination of incurred and added pesticides in 4 dietary composites, which varied in fat and water content. Incurred pesticides were chlorothalonil, chlorpyrifos, DDE, dicloran, dieldrin, endosulfan I, malathion, cis- and trans-permethrin, and trifluralin. Added pesticides were alpha- and gamma-chlordane, hexachlorobenzene, and fonofos. Concentrations of the individual pesticides were between 0.2 and 20 ng/g composite. All 5 methods tested could extract pesticides from dietary composites. Most incurred pesticides were recovered from the dietary composites within the range of 59-140% of expected values. Recoveries of added pesticides were between 60 and 130%. Microwave-assisted extraction led to significantly higher concentrations of 7 pesticides. Blender extraction yielded significantly higher concentrations of chlorothalonil and fonofos. Water content was a significant factor in the recovery of chlorothalonil, and fat content was a significant factor in the recovery of fonofos. In designing an exposure study, the selection of the extraction method would be determined by number of samples to be extracted, analyte stability, and cost.

Diet↗
PubMed2002

Toxicity of methyl tert-butyl ether to marine organisms: ambient water quality criteria calculation.

In response to increasing concerns over the detection of methyl tert-butyl ether (MTBE) in groundwater and surface water and its potential effects in aquatic ecosystems, industry and the United States Environmental Protection Agency (USEPA) began to collaborate in 1997 to develop aquatic toxicity databases sufficient to derive ambient water quality criteria for MTBE consistent with USEPA requirements. Acute toxicity data for seven marine species, chronic toxicity data for an invertebrate, and plant toxicity data were developed to complete the saltwater database. The species tested were Cyprinodon variegatus, Gasterosteus aculeatus, Callinectes sapidus, Mytilus galloprovincialis, Palaemonetes pugio, Rhepoxynius abronius, Americamysis bahia, and Skeletonema costatum. The toxicity tests were conducted in accordance with USEPA and American Society for Testing and Materials testing procedures and Good Laboratory Practice guidelines. Data developed from this study were consistent with existing data and showed that MTBE has low acute and chronic toxicity to the marine species tested. Based upon measured MTBE concentrations, acute effects were found to range from 166 mg MTBE/l for the grass shrimp to 1950 mg MTBE/l for marine mussel. The no-observed effect concentration for the reproduction and growth of mysids was 26 mg MTBE/l during the life cycle test. The toxicity of MTBE to saltwater organisms is comparable to its toxicity to the freshwater species tested. Reported MTBE concentrations in coastal waters are several orders of magnitude lower than concentrations observed to cause effects in marine organisms.

Animals↗