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PubMed2000

Risk metrics and cumulative risk assessment methodology for the FQPA.

The Food Quality Protection Act (FQPA) of 1996 mandates that the U.S. Environmental Protection Agency consider both aggregate and cumulative risks. Aggregate assessments account for multiple sources and routes of exposure for a single chemical. Cumulative assessments combine exposures to two or more chemicals that share a common mechanism of toxicity. Probabilistic risk assessment methods are described for determining a population's distribution of the dose from exposure and the combination of that exposure characterization with appropriate toxicological information to form a risk assessment. An individual's dose from exposure is characterized as a set of chemical- and route-specific dose profiles over time. For each individual and each chemical and route, a margin of exposure (MOE) is calculated by dividing a toxicologically relevant benchmark dose (e.g., an ED(10)) by the individual's dose from exposure. The set of these MOEs for an individual is combined into the individual's Total MOE. The distribution of the Total MOEs in a population is compared to an Acceptable MOE. Advantages of the Total MOE approach over approaches based on reference doses are discussed. Some general comments on risk metrics are made, and some general guidance for cumulative risk assessments is provided.

Dose-Response Relationship, Drug↗
PubMed2006

Animal carcinogenicity studies: 1. Poor human predictivity.

The regulation of human exposure to potentially carcinogenic chemicals constitutes society's most important use of animal carcinogenicity data. Environmental contaminants of greatest concern within the USA are listed in the Environmental Protection Agency's (EPA's) Integrated Risk Information System (IRIS) chemicals database. However, of the 160 IRIS chemicals lacking even limited human exposure data but possessing animal data that had received a human carcinogenicity assessment by 1 January 2004, we found that in most cases (58.1%; 93/160), the EPA considered animal carcinogenicity data inadequate to support a classification of probable human carcinogen or non-carcinogen. For the 128 chemicals with human or animal data also assessed by the World Health Organisation's International Agency for Research on Cancer (IARC), human carcinogenicity classifications were compatible with EPA classifications only for those 17 having at least limited human data (p = 0.5896). For those 111 primarily reliant on animal data, the EPA was much more likely than the IARC to assign carcinogenicity classifications indicative of greater human risk (p < 0.0001). The IARC is a leading international authority on carcinogenicity assessments, and its significantly different human carcinogenicity classifications of identical chemicals indicate that: 1) in the absence of significant human data, the EPA is over-reliant on animal carcinogenicity data; 2) as a result, the EPA tends to over-predict carcinogenic risk; and 3) the true predictivity for human carcinogenicity of animal data is even poorer than is indicated by EPA figures alone. The EPA policy of erroneously assuming that tumours in animals are indicative of human carcinogenicity is implicated as a primary cause of these errors.

Animals↗
PubMedDate not supplied

Hormesis: policy implications.

Protecting workers and the public from toxic chemicals, particularly carcinogens, has been a principal focus of public policy. Uncertainty regarding the toxicity of particular chemicals and their dose-response relationship has led to the use of the 'precautionary principle' in which regulators are willing to accept more costly regulation than necessary in order to prevent exposure and disease from these toxic chemicals. The Environmental Protection Agency's (EPA's) current policy of using 'mechanism of action' to set regulations means that hormesis could be used by the EPA without any change in policy if hormesis is accepted as scientifically valid. Hormesis could result in a qualitative change in regulatory policy. Because exposure to toxic chemicals conveys no health benefit in the current dose-response model, public risk aversion leads to a Delaney Clause-like 'no-risk' model for policy: ban toxic chemicals or lower exposure to trivial levels. Hormesis implies that individuals benefit from low exposure to toxicants. Although hormesis may not be relevant for individuals with compromised immune systems, it would be expected to help the vast majority of people. If so, permitting exposure levels that provided the greatest health benefit to most people would be balanced against these same levels hurting the most immune-compromised individuals. Public health routinely makes these trade-offs using a 'risk-risk' model. Thus, hormesis could transform the 'no-risk' approach into a 'risk-risk' approach that could tolerate much higher exposures to toxic chemicals than the current policy.

Adaptation, Physiological↗
PubMed1997

Methylmercury in fish from Owyhee Reservoir in southeast Oregon: scientific uncertainty and fish advisories.

Data collected during 1987-1994 showed elevated levels of mercury (Hg) in fish tissue from the Owyhee Reservoir in southeastern Oregon. Sixty-five percent of the samples analyzed had total Hg levels exceeding the US Environmental Protection Agency's (EPA) health screening value of 0.6 mg/kg. Eighteen out of 89 (20%) fish tissue samples also had total Hg levels greater than the US Food and Drug Administration's (FDA) mercury action level of 1.0 mg/kg. The overall mean Hg content for all fish collected from the reservoir was 0.75 mg/kg wet weight (wet wt.). Fish muscle taken from largemouth bass (Micropterus salmoides), smallmouth bass (Micropterus dolomieu) and channel catfish (Ictalurus punctatus) had the highest mean Hg levels of 0.92, 0.87 and 0.82 mg/kg, respectively. In contrast, rainbow trout (Salmo gairdneri) had the lowest mean Hg content of 0.37 mg/kg. Increases in total Hg concentrations were found to be positively correlated with size for rainbow trout and yellow perch. A weak but significant correlation was also observed between total mercury content and age for smallmouth bass. Based on these data, in 1994 the Oregon Health Division (OHD) issued a fish consumption advisory for the Owyhee Reservoir using a conservative risk-based approach. The process of defining and communicating these consumption limits is the subject of this paper.

Animals↗
PubMed2005

Estimated risks of radon-induced lung cancer for different exposure profiles based on the new EPA model.

Radon is a naturally occurring radioactive gas. When inhaled, radon can cause mutations that lead to lung cancer. Some new epidemiologic studies indicate that indoor radon is a public health problem. The BEIR VI report outlined its preferred two risk models for the combined effects of smoking and exposure to radon progeny, and listed the estimated risk to ever-smokers and never-smokers of both sexes due to lifetime exposure. However, exposures for shorter periods of time are of practical interest since exposure to elevated levels of radon may occur and end at any age. This study aims to produce practical tables of lifetime relative risks for exposures between any two age intervals from 0 to 110, and for various radon concentrations found in homes from 100 to 1,000 Bq m(-3). The calculations are based on the risk model developed recently by U.S. Environmental Protection Agency. The EPA's risk model is a single model that gives risk values midway between those obtained from the two BEIR VI preferred models. The detailed tables provide a clearer view of the age groups at higher risk and the effect of exposure duration. The results will help radiation protection practitioners to better communicate indoor radon risk to members of the public.

Adolescent↗
PubMed1997

Reassessment of the carcinogenicity of polychlorinated biphenyls (PCBs).

The current policy for regulating polychlorinated biphenyls (PCBs) is based on one chronic bioassay that examined the carcinogenicity of a 60% chlorinated PCB (Norback & Weltman, 1985). All studies originally considered by the U.S. Environmental Protection Agency (EPA) for use in calculating a cancer slope factor (CSF) for PCBs were reevaluated and new CSFs calculated based on the results of a pathology reassessment (Moore et al., 1994). When studies of 60% chlorine PCBs from 3 different laboratories were compared, there was no scientific basis for selecting only 1 data set for deriving CSF estimates. Using a geometric mean to calculate a CSF based on all studies of PCBs with 60% chlorine replaces the current value of 7.7 (mg/kg/d)(-1) with a value of 1.9 (mg/kg/d)(-1). CSFs for PCBs containing less than 60% chlorine (54% and 42%) were less than 1.0 (mg/kg/d)(-1). Using a toxic equivalency factor (TEF) approach similar to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin shows no correlation between toxic equivalent dose and CSFs, indicating that use of TEFs is not predictive of cancer potency for PCBs. Based on these findings, PCB cancer risk assessment policy would more closely reflect scientific data if (1) separate risk assessments were developed for each major PCB formulation and (2) all appropriate data were used when calculating cancer potency for PCB mixtures of 60% chlorine.

Animals↗
PubMed2002

Runoff of trifluralin, metolachlor, and metribuzin from a clay loam soil of Louisiana.

Trifluralin[2,6-dinitro-N,N-dipropyl-4-(trifluormethyl)benzenamine], metolachlor[2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] and metribuzin[4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)one] were applied as pre-emergent herbicides to soybean plots in Louisiana (LA) at the rate of 1683 g/ha, 2759 g/ha and 609 g/ha, respectively. The concentrations of trifluralin in the runoff water ranged between 0.09 ng/mL and 0.02 ng/mL, which is lower than the 2 ng/mL US Environmental Protection Agency (EPA) advisory level for trifuralin in drinking water. Metolachlor concentrations in the runoff water ranged from 9.0 ng/mL to 221.5 ng/mL, which is both lower and higher than the 175 ng/mL EPA advisory level for metolachlor. Similarly, metribuzin concentrations in the runoff water ranged between 1.5 ng/mL and 56.2 ng/mL, which is also lower and higher than the 10 ng/mL EPA advisory level for metribuzin. Accordingly, from the field plots located on a Commerce clay loam soil in LA, although the concentration of trifluralin in runoff water were substantially lower than the EPA advisory level, metolachlor and metribuzin concentrations are likely to exceed the EPA advisory levels early on in the application season with a subsequent rapid decrease to safe levels. The total loss of trifluralin in runoff water was 0.005% of the applied amount over an 89 day period after application. The total loss of metolachlor and metribuzin in the runoff water was 4.67% and 5.36% of the applied amount, respectively, over a 22 day period after application. As such, there was almost no movement of trifluralin in the runoff water, whereas metolachlor and metribuzin were much more easily moved.

Acetamides↗
PubMed2003

An environmental decision-making tool for evaluating ground-level ozone-related health effects.

A computer model called the Ozone Risk Assessment Model (ORAM) was developed to evaluate the health effects caused by ground-level ozone (O3) exposure. ORAM was coupled with the U.S. Environmental Protection Agency's (EPA) Third-Generation Community Multiscale Air Quality model (Models-3/CMAQ), the state-of-the-art air quality model that predicts O3 concentration and allows the examination of various scenarios in which emission rates of O3 precursors (basically, oxides of nitrogen [NOx] and volatile organic compounds) are varied. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, and sensitivity and uncertainty analysis through a Monte Carlo simulation. As a demonstration of the system, ORAM was applied to the eastern Tennessee region, and the entire O3 season was simulated for a base case (typical emissions) and three different emission scenarios. The results indicated that a synergism occurs when reductions in NOx emissions from mobile and point sources were applied simultaneously. A 12.9% reduction in asthma hospital admissions is expected when both mobile and point source NOx emissions are reduced (50 and 70%, respectively) versus a 5.8% reduction caused by mobile source and a 3.5% reduction caused by point sources when these emission sources are reduced individually.

Air Pollution↗
PubMed1991

Characteristics of the U.S. EPA's Office of Pesticide Programs' toxicity information databases.

The United States Environmental Protection Agency's Office of Pesticide Programs (OPP) requires that data from toxicity testing be submitted to the OPP to support the registration of pesticide chemicals. Once the toxicity data are submitted, they are entered into various toxicity databases. The studies are listed in an archival database to catalog and allow retrieval of the study for review. Reviews of toxicity studies are then placed into a separate database that can be retrieved to support a regulatory position. Toxicity information for health effects other than cancer and gene mutations from chronic exposure is reviewed through a reference dose (RfD) approach, and these decisions and supporting data are entered into an RfD database. Carcinogenicity data are reviewed by a peer review process, and these decisions are entered into a newly developed database to show the regulatory decision with supporting data. The mutagenicity data are reviewed and acceptable data are entered into the Genetic Activity Profile system to catalog and display the submitted information. These databases contain the information used for hazard evaluations as part of the OPP review of pesticide chemicals.

Animals↗
PubMed2004

Development of the IM147: an alternative inspection/maintenance mass-emission transient test to address vehicle preconditioning concerns.

A series of studies was performed to develop an alternative to the U.S. Environmental Protection Agency's gold standard IM240 mass-based emission test. The new IM147 test was based on the second phase of the IM240 that consists of 147 sec of transient vehicle operation. Paired IM240/IM147 tests were conducted on vehicles ranging from 1981 to 1996 to determine IM147 cutpoints and excess emissions were identified. Additionally, an optimized test procedure was developed that combined possible triplicate IM147s with improved drive trace quality control, fast-pass, and retest methods. The optimized procedure was found to provide improved vehicle preconditioning with a relatively minor decrease in excess emissions identification. Resulting identification rates ranged from 96 to 100% for hydrocarbons (HC), 93-100% for CO, and 93-100% for NOx, depending on cutpoint selection, while false failures caused by lack of vehicle preconditioning were reduced to essentially zero. Significant vehicle throughput improvements were achieved through the development of software algorithms involving modal fast-pass and retest procedures. Modal drive trace variation limits also were developed to improve test accuracy. The combination of the algorithms reduced average IM147 test times by nearly 60%.

Air Pollutants↗
PubMed1990

Air toxics in the U.S.: magnitude of the problem and strategy for control.

Over the past several years, substantial concern has been expressed by some in Congress, environmental groups, and members of the public concerning the lack of progress in regulating toxic air pollutants by the U.S. Environmental Protection Agency (EPA). As a result, a number of amendments to the Federal Clean Air Act have been introduced to require EPA to regulate in a relatively rapid timeframe, a large number of potentially toxic pollutants that are released to the ambient air. This paper discusses EPA's current understanding of the magnitude and nature of the air toxics problem in the U.S., and the pollutants and source categories that pose the most significant risk to the public. The focus of the discussion is on routine releases, as opposed to catastrophic, accidental releases such as the one in Bhopal, India. The paper then discusses the strategy that EPA has put in place to deal with the problem and presents the status of a number of regulatory and non-regulatory activities under way to better understand the problem and to mitigate it. The strategy involves important roles for: (1) EPA to regulate national problems using a variety of Federal authorities in addition to the Clean Air Act, and (2) States to develop their own air toxic control programs to deal with unique local problems involving high risk point sources and multipollutant, multisource problems in large urban or industrialized areas.

Air Pollutants↗
PubMed1997

Risk assessment as a management tool used to assess the effect of pesticide use in an irrigation system, situated in a semi-desert region.

A preliminary study undertaken by the CSIR in July 1993 on the health effects of aerial crop spraying of pesticides in the Vaalharts irrigation area in South Africa indicated that potential health risks could exist for the inhabitants of this area. An extensive scientific health risk assessment and epidemiological study to determine the actual health risks, is very expensive and requires medical and financial justification. The aim of this study was to develop a theoretical health risk model, which could be used as a predictive tool to determine as accurately as possible from the data available if a complete scientific health risk assessment study is justified. The actual amounts of pesticides sold in the Vaalharts area by two major pesticide manufacturers were used to perform a theoretical health risk assessment. The risks were assessed by making use of RISK*ASSISTANT, a computer modeling system and chemical database. The United States Environmental Protection Agency's (EPA) health risk model was applied to the data to identify the hazards, assess the exposures and dose response, and characterize the risks. Three exposure scenarios, namely, the ingestion of food and water and the inhalation of air were evaluated. The method used to calculate the risks varied according to the type of health hazard and the results were characterized accordingly. The acute health effects due to exposure to pesticides are well known and the risks are easy to determine. However, the risks associated with chronic health hazards were more difficult to calculate. For this reason a ranking model was developed which made use ofa point scoring system. This model highlights those pesticides which have the greatest possibility of causing chronic health effects. From the results it can be concluded that very large amounts of pesticides are used in the Vaalharts area and that the community might be at risk to chronic health effects. Although the theoretical health risk assessment model was successfully used in this study, its effectiveness as a predictive tool still has to be proven by a complete scientific study.

Air Pollution↗
PubMedDate not supplied

Workshop on the qualitative and quantitative comparability of human and animal developmental neurotoxicity, Work Group IV report: triggers for developmental neurotoxicity testing.

A Work Group was formed to evaluate the criteria considered important in determining when to require developmental neurotoxicity testing in animal studies (i.e., triggers for testing). The primary objective of the Work Group was to determine whether there is sufficient scientific evidence to support the triggers identified by the Environmental Protection Agency and determine whether there is sufficient evidence to use structure activity relationships (SAR) to trigger automatic testing of certain classes of chemicals. A weight of evidence (WOE) approach was recommended by the Work Group in order to assist in determining which agents should undergo developmental neurotoxicity testing and to what level of testing. Evaluation of biological effects, length and duration of exposure, and quality and quantity of data available on an agent should be used in the WOE approach. Agents that are teratogenic to the central nervous system (CNS) were considered of highest priority for developmental neurotoxicity testing, especially if there is the potential for a high degree of exposure. Neuropathic and neuroactive compounds, chemicals with hormone-like activity, and developmental toxicants (with effects other than structural abnormalities of the CNS) were also considered likely candidates for such testing. Although reluctant to recommend testing based solely on SAR or chemical class, the Work Group recognized the importance of considering SAR along with other toxicity data, pharmacokinetic data and potential human exposure in making final requirements or recommendations for further testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Evaluation and recommendation of sensitivity analysis methods for application to Stochastic Human Exposure and Dose Simulation models.

Sensitivity analyses of exposure or risk models can help identify the most significant factors to aid in risk management or to prioritize additional research to reduce uncertainty in the estimates. However, sensitivity analysis is challenged by non-linearity, interactions between inputs, and multiple days or time scales. Selected sensitivity analysis methods are evaluated with respect to their applicability to human exposure models with such features using a testbed. The testbed is a simplified version of a US Environmental Protection Agency's Stochastic Human Exposure and Dose Simulation (SHEDS) model. The methods evaluated include the Pearson and Spearman correlation, sample and rank regression, analysis of variance, Fourier amplitude sensitivity test (FAST), and Sobol's method. The first five methods are known as "sampling-based" techniques, wheras the latter two methods are known as "variance-based" techniques. The main objective of the test cases was to identify the main and total contributions of individual inputs to the output variance. Sobol's method and FAST directly quantified these measures of sensitivity. Results show that sensitivity of an input typically changed when evaluated under different time scales (e.g., daily versus monthly). All methods provided similar insights regarding less important inputs; however, Sobol's method and FAST provided more robust insights with respect to sensitivity of important inputs compared to the sampling-based techniques. Thus, the sampling-based methods can be used in a screening step to identify unimportant inputs, followed by application of more computationally intensive refined methods to a smaller set of inputs. The implications of time variation in sensitivity results for risk management are briefly discussed.

Analysis of Variance↗
PubMed2001

The importance of considering biological processes when setting total maximum daily loads (TMDL) for phosphorus in shallow lakes and reservoirs.

Total maximum daily loads (TMDL) are required by the US Environmental Protection Agency for pollutants that have impaired the designated uses of surface waters in the nation. Setting an appropriate TMDL requires quantitative information on both the external pollutant inputs and the processes affecting pollutant dynamics within the ecosystem. Here we focus on phosphorus (P), a globally important pollutant of freshwater lakes. We consider how biological processes (including those related to algae, plants, invertebrates and fish) can influence the ability of lakes to assimilate P, and in turn the ability of managers to select appropriate TMDLs. The primary focus is on shallow eutrophic lakes, with Lake Okeechobee (Florida, USA) serving as a case study. The paper deals only with in-lake processes as they relate to setting the TMDL and not the subsequent issue of load allocation among pollution sources. The results indicate that the ability of a shallow lake to assimilate P is substantially reduced when surplus levels of P occur in the water column, the phytoplankton becomes dominated by cyanobacteria, the benthic invertebrate community becomes dominated by oligochaetes, and submerged plant biomass is low. If some of these biological changes can be reversed in a rehabilitation program then the lake may be able to support a higher TMDL.

Biomass↗
PubMed2006

Validation and update of a model used to predict copper toxicity to the marine bivalve Mytilus sp.

A model was recently published that relates the toxicity of copper to the most sensitive taxa in the U.S. Environmental Protection Agency's criteria database (Mytilus sp.) with dissolved organic carbon concentrations in saltwater. This model was developed for potential use in risk assessment and in the development of site-specific criteria (SSC) for copper in saltwater environments where Mytilus sp. is considered an appropriate indicator species. This manuscript presents the results of a field validation study of that model. Effective concentration 50% (EC(50)) values (n = 21) for seven sites were all predicted by the model within the previously established range of acceptability. Slopes and intercepts of the two data sets were not significantly different. Consequently, the data were pooled, and new equations were developed. Dissolved copper EC(50) values were highly correlated (r(2) = 0.76, n = 75, P < 0.0001) across a wide range of sample dissolved organic carbon (DOC) concentrations (0.3-12 mg C/L) and were explained by the equation EC(50) = 11.22 DOC(0.60). Two updated equations are proposed for consideration as a means of estimating site-specific final chronic criteria (FCC) and final acute criteria (FAC) for copper in marine and estuarine environments (copper FCC(DOC) = 3.59 DOC(0.60); copper FAC(DOC) = 5.61 DOC(0.60)).

Animals↗
PubMed2000

Evaluation of biologically based dose-response modeling for developmental toxicity: a workshop report.

Biologically based dose-response (BBDR) modeling represents a novel approach for quantitative assessment of health risk by incorporating pharmacokinetic and pharmacodynamic characteristics of a chemical and by relating the immediate cellular responses to a cascade of aberrant biological actions that leads to detectable adverse outcomes. The quantitative relationship of each of the intervening events can be described in mathematical forms that are amenable for adjustment and extrapolation over a range of doses and across species. A team of investigators at the Reproductive Toxicology Division of the U.S. Environmental Protection Agency has explored the feasibility of BBDR modeling by examining the developmental toxicity of a known teratogen, 5-fluorouracil. A panel of researchers from academic and industrial laboratories, biomathematical modelers, and risk assessment scientists was convened in a workshop to evaluate the approaches undertaken by the EPA team and to discuss the future prospects of BBDR modeling. This report summarizes the lessons learned from one approach to BBDR modeling and comments from the panelists: while it is possible to incorporate mechanistic information into quantitative dose-response models for the assessment of health risks, the process is enormously data-intensive and costly; in addition, the confidence of the model is directly proportional to our current understanding of basic biology and can be enhanced only through the ongoing novel discoveries. More importantly, the extent of "uncertainty" (inherent with the default assumptions associated with the NOAEL or benchmark approach) reducible by BBDR modeling requires further scrutiny and comparison.

Abnormalities, Drug-Induced↗
PubMed2003

Using human activity data in exposure models: analysis of discriminating factors.

This paper tests factors thought to be important in explaining the choices people make in where they spend time. Three aggregate locations are analyzed: outdoors, indoors, and in-vehicles for two different sample groups: a year-long (longitudinal) sample of one individual and a cross-sectional sample of 169 individuals from the US Environmental Protection Agency's Consolidated Human Activity Database (CHAD). The cross-sectional sample consists of persons similar to the longitudinal subject in terms of age, work status, education, and residential type. The sample groups are remarkably similar in the time spent per day in the tested locations, although there are differences in participation rates: the percentage of days frequenting a particular location. Time spent outdoors exhibits the most relative variability of any location tested, with in-vehicle time being the next. The factors found to be most important in explaining daily time usage in both sample groups are: season of the year, season/temperature combinations, precipitation levels, and day-type (work/nonwork is the most distinct, but weekday/weekend is also significant). Season, season/temperature, and day-type are also important for explaining time spent indoors. None of the variables tested are consistent in explaining in-vehicle time in either the cross-sectional or longitudinal samples. Given these findings, we recommend that exposure modelers subdivide their population activity data into at least season/temperature, precipitation, and day-type "cohorts" as these factors are important discriminating variables affecting where people spend their time.

Cross-Sectional Studies↗