BACKGROUND: Risk assessment of human environmental exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) and other dioxin-like compounds is complicated by several factors, including limitations in measuring intakes because of the low concentrations of these compounds in foods and the environment and interspecies differences in pharmacokinetics and responses. OBJECTIVES: We examined the feasibility of relying directly on human studies of exposure and potential responses to PCDD/PCDFs and related compounds in terms of measured lipid-adjusted concentrations to assess margin of exposure (MOE) in a quantitative, benchmark dose (BMD)-based framework using representative exposure and selected response data sets. METHODS: We characterize estimated central tendency and upper-bound general U.S. population lipid-adjusted concentrations of PCDD/PCDFs from the 1970s and early 2000s based on available data sets. Estimates of benchmark concentrations for three example responses of interest (induction of cytochrome P4501A2 activity, dental anomalies, and neonatal thyroid hormone alterations) were derived based on selected human studies. RESULTS: The exposure data sets indicate that current serum lipid concentrations in young adults are approximately 6- to 7-fold lower than 1970s-era concentrations. Estimated MOEs for each end point based on current serum lipid concentrations range from < 10 for neonatal thyroid hormone concentrations to > 100 for dental anomalies-approximately 6-fold greater than would have existed during the 1970s. CONCLUSIONS: Human studies of dioxin exposure and outcomes can be used in a BMD framework for quantitative assessments of MOE. Incomplete exposure characterization can complicate the use of such studies in a BMD framework.

Studies of children indicate that exposure of the general population to low levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) does not result in any clinical evidence of disease, although accidental exposure to high levels either before or after birth have led to a number of developmental deficits. Breast-fed infants have higher exposures than formula-fed infants, but studies consistently find that breast-fed infants perform better on developmental neurologic tests than their formula-fed counterparts, supporting the well-recognized benefits of breast feeding. Children receive higher exposures to PCDD/Fs from food than adults on a body-weight basis but those exposures are below the World Health Organization's tolerable daily intake. Laboratory rodents appear to be at least an order of magnitude more sensitive than humans to the aryl hydrocarbon receptor-mediated effects of these substances, which makes them poor surrogates for predicting quantitative risks but makes them good models for establishing safe levels of human exposure by organizations mandated to protect public health. Any exposure limit for PCDD/Fs based on developmental toxicity in sensitive laboratory animals can be expected to be especially protective of human health, including the health of infants and children. Because body burdens and environmental levels continue to decline, it is unlikely that children alive today in the USA will experience exposures to PCDD/Fs that are injurious to their health.

In recent years, there has been increasing regulatory pressure to protect the health of children, with the basic tenet being that children differ significantly from adults in their biological or physiological responses to chemical exposures. In a regulatory context, this has been translated to mean a requirement for an additional 10-fold safety factor for environmental contaminants, specialized tests, or both. Much of the initial focus has been on the developing endocrine and nervous systems; but increasingly, the developing immune system has been identified as a potential target organ for chemically mediated toxicity. More recently, the question has been raised regarding whether the current state of science supports the creation of developmental immunotoxicology (DIT) test guidelines. What is needed is a risk-based evaluation of the biology associated with the proposed differential sensitivity between children and adults and the impact of that assessment on additional regulatory measures to protect children in risk assessment analyses. Additionally, an understanding of whether the developing immune system shows greater susceptibility, either qualitatively or quantitatively, to chemical perturbation is critical. To address the question "What's so special about the developing immune system?" a symposium was organized for the 2003 Society of Toxicology annual meeting that brought together risk assessors, clinicians, immunologists, and toxicologists.

In their letter, Sass and Needleman argue against the regulatory use of data from human subjects on both scientific and ethical grounds. The studies they evaluated were conducted in accordance with the same ethical standards that guide all studies involving human volunteers that are conducted by the federal government. Sass and Needleman claim, however, that these studies were not ethical and should not be used. We would like to address a common concern regarding the ethical conduct of these types of studies.

Arguments have been made for and against the regulatory use of data from human subjects on both scientific and ethical grounds. One argument against the use of data from human clinical studies involving pesticides asserts that such data are obtained from studies that do not follow the Common Rule (40 CFR 26), which provides procedures for protecting human subjects in studies funded by federal agencies, including the U.S. Environmental Protection Agency (U.S. EPA). Although privately conducted studies using human subjects are not legally subject to or required to comply with the Common Rule, the protections of the Declaration of Helsinki and the International Conference on Harmonisation (ICH) Good Clinical Practice are commonly followed. We sought to answer the question of whether recent human clinical studies with insecticides performed according to Good Clinical Practice provided volunteers with the same protections as the Common Rule. All three sets of guidance have in common the intent to protect volunteer human subjects by providing standards for the conduct of studies in which they participate. This analysis compares the elements of the Common Rule with comparable elements from the Declaration of Helsinki and Good Clinical Practice to evaluate similarities and differences in procedural requirements. It then evaluates the documentation from 15 recent human studies of twelve insecticides conducted at four clinical laboratories in order to determine whether the conduct of those studies is consistent with the protections of the Common Rule. There were some cases for which we could not verify compliance with certain Common Rule elements; however, based on our evaluation it is apparent that the studies we reviewed were conducted in a manner substantially consistent with the fundamental protections of the Common Rule-voluntary participation, informed consent, and review by an ethical committee or institutional review board.

The 1996 Food Quality Protection Act (FQPA) requires the evaluation of both aggregate and cumulative health risks from pesticides (FFDCA 408(b)(2)(D)(v) and (vi).) Organophosphate (OP) pesticides are the first class of chemicals to undergo FQPA mandated aggregate and cumulative assessments. In this report, summary data on biomonitoring for urinary levels of six alkyl phosphate (AP) metabolites of OPs, as reported in the initial, March 2001, U.S. Centers for Disease Control and Prevention's (CDC)"National Report on Human Exposure to Environmental Chemicals," are compared to EPA modeled estimates of OP exposure reported in Registration Eligibility Decision documents (REDs), Interim REDs and to currently reported cumulative exposure estimates in the EPA's Cumulative Risk Assessment of the Organophosphate Pesticides. This comparison indicates that EPA's aggregate exposure estimates (dietary, drinking water, and non-dietary residential exposures) for many individual OPs were greater than the cumulative estimate for all OPs combined based on the CDC AP biomonitoring data. The results also suggest that EPA's screening level assessments of OPs, while being qualitative indicators of the relative importance of various exposure sources, are not good quantitative indicators of actual exposures. However, the mean biomonitoring estimate of cumulative OP exposure appears to exceed the EPA's subsequent preliminary estimate of cumulative OP exposure by as much as the REDs appear to overestimate the biomonitoring results. While the conservatism, tendency to overestimate exposure, in the individual REDs is readily acknowledged, the conservatism and limitations of applying currently available CDC AP biomonitoring data to evaluate human exposure to OPs are not as readily apparent. We postulate that oral absorption of non-anti cholinergic, pre-hydrolyzed OPs, sources of APs other than pesticides, and the conservative result of summing exposure from each AP at the geometric mean contribute to non-quantified overestimates of absorbed dosage from the CDC biomonitoring data reported in March 2001. CDC AP biomonitoring data may serve a useful purpose in providing an upper bound estimate of absorbed dosage for "ground truthing" aggregate exposure estimated from first tier models used in REDs, but at best may provide only a credible "target" for the complex cumulative exposure assessment models currently under development. The reliability of quantitative estimates of OP exposure levels will improve as cumulative risk exposure models are validated over time and under use conditions prevalent at the time the AP biomonitoring samples are collected. Analyses contained herein should be revisited and compared to the CDC Second National Report on Human Exposure to Environmental Chemicals ( http://www.cdc.gov/exposurereport), released to the public on January 31, 2003, and the final EPA OP Cumulative Risk Assessment.

Background: Recent policies attempting to reduce adverse effects of methylmercury exposure from fish consumption in the United States have targeted reductions in anthropogenic emissions from U.S. sources.Objectives: To analyze the prospects for future North American and international emissions controls, we assessed the potential contributions of anthropogenic, historical, and natural mercury to exposure trajectories in the U.S. population over a 40-year time horizon.Methods: We used models that simulate global atmospheric chemistry (GEOS-Chem); the fate, transport, and bioaccumulation of mercury in four types of freshwater ecosystems; and mercury cycling among different ocean basins. We considered effects on mercury exposures in the U.S. population based on dietary survey information and consumption data from the sale of commercial market fish.Results: Although North American emissions controls may reduce mercury exposure by up to 50% for certain highly exposed groups such as indigenous peoples in the Northeast, the potential effects of emissions controls on populations consuming marine fish from the commercial market are less certain because of limited measurements.Conclusions: Despite uncertainties in the exposure pathway, results indicate that a combination of North American and international emissions controls with adaptation strategies is necessary to manage methylmercury risks across various demographic groups in the United States. Editor's SummaryEfforts to reduce human exposure to methylmercury have focused on dietary recommendations and policies to reduce emissions from anthropogenic sources. Selin et al.(p. 137) note that current and future exposures are also a function of historical anthropogenic emissions and argue that a comprehensive evaluation of mercury dynamics in aquatic and atmospheric systems, bioaccumulation in food webs, and patterns of human food consumption is needed to predict the potential impact of emissions reductions on human exposure over time. In addition to dietary consumption data, the authors used models that simulate global atmospheric chemistry (GEOS-Chem); the fate, transport, and bioaccumulation of mercury in four freshwater ecosystems; and mercury cycling among different ocean basins to assess potential contributions of anthropogenic, historical, and natural mercury sources to exposure trajectories in U.S. populations. They estimate that North American emissions controls may reduce mercury exposure by up to 50% in certain highly exposed groups but note that potential effects on populations consuming marine fish are uncertain. The authors conclude that a combination of North American and international emissions controls and dietary adaptation strategies are needed to manage methylmercury risks across population subgroups.

Italian legislation requires companies undertaking certain work activities involving naturally occurring radioactive materials (NORM) to check compliance with action levels (1 mSv y(-1) for workers, 0.3 mSv y(-1) for the public). A project is being carried out by ARPAV and other Environmental Agencies to estimate doses to members of the public from NORM from several activities (refractory and tile industry, integrated steelworks, phosphate industry, aluminium production, coal-fired power plants). Activity concentration values of residues have been compared with general clearance levels given in Radiation Protection 122 part 2 and, in several cases, these levels appeared to be exceeded. Doses due to air emissions from stacks, from wastes in disposal sites and from the use of fertilisers in agriculture have been calculated through simulation models (PC-Cream, Resrad, Unscear algorithms), which produce fairly low dose estimates. A major problem for NORM control in Italy at the moment is the lack of official technical and legislative rules (concerning, for instance, residues and effluents management).

The Lake Wabamun area, in Alberta, is unique within Canada as there are four coal-fired power plants within a 500km(2) area. Continuous monitoring of ambient total gaseous mercury (TGM) concentrations in the Lake Wabamun area was undertaken at two sites, Genesee and Meadows. The data were analyzed in order to characterise the effect of the coal-fired power plants on the regional TGM. Mean concentrations of 1.57ng/m(3) for Genesee and 1.50ng/m(3) for Meadows were comparable to other Canadian sites. Maximum concentrations of 9.50ng/m(3) and 4.43ng/m(3) were comparable to maxima recorded at Canadian sites influenced by anthropogenic sources. The Genesee site was directly affected by the coal-fired power plants with the occurrence of northwest winds, and this was evident by episodes of elevated TGM, NO(x) and SO(2) concentrations. NO(x)/TGM and SO(2)/TGM ratios of 21.71 and 19.98microg/ng, respectively, were characteristic of the episodic events from the northwest wind direction. AERMOD modeling predicted that coal-fired power plant TGM emissions under normal operating conditions can influence hourly ground-level concentrations by 0.46-1.19ng/m(3)(.) The effect of changes in coal-fired power plant electricity production on the ambient TGM concentrations was also investigated, and was useful in describing some of the episodes.

In this paper measurements, results and model estimates, with reference to hydroelectric power plant noise emissions in the Aosta Valley territory, are compared in different contexts. The analysis was performed to evaluate and point out the influence of the noise source context on the accuracy of the model results. The estimates were implemented considering power plants as: point sources and area sources taking (or not) into account the building elements of the plant. This method allowed evaluating the detail that is suitable to achieve in an estimate and to justify possible simplifications in this kind of noise source description. Noise measurements were carried out simultaneously, at different distances from the power plants that were taken into account. The measurement results at the closest points to the sources were used as the model input data, while the levels found at the other points were used for comparison with the estimate results.

Clean energy production has become one of the most prominent global issues of the early 21st century, prompting social, economic, and scientific debates regarding energy usage, energy sources, and sustainable energy strategies. The reduction of greenhouse gas emissions, specifically carbon dioxide (CO(2)), figures prominently in the discussions on the future of global energy policy. Billions of tons of annual CO(2) emissions are the direct result of fossil fuel combustion to generate electricity. Producing clean energy from abundant sources such as coal will require a massive infrastructure and highly efficient capture technologies to curb CO(2) emissions. Current technologies for CO(2) removal from other gases, such as those used in natural gas sweetening, are also capable of capturing CO(2) from power plant emissions. Aqueous amine processes are found in the vast majority of natural gas sweetening operations in the United States. However, conventional aqueous amine processes are highly energy intensive; their implementation for postcombustion CO(2) capture from power plant emissions would drastically cut plant output and efficiency. Membranes, another technology used in natural gas sweetening, have been proposed as an alternative mechanism for CO(2) capture from flue gas. Although membranes offer a potentially less energy-intensive approach, their development and industrial implementation lags far behind that of amine processes. Thus, to minimize the impact of postcombustion CO(2) capture on the economics of energy production, advances are needed in both of these areas. In this Account, we review our recent research devoted to absorptive processes and membranes. Specifically, we have explored the use of room-temperature ionic liquids (RTILs) in absorptive and membrane technologies for CO(2) capture. RTILs present a highly versatile and tunable platform for the development of new processes and materials aimed at the capture of CO(2) from power plant flue gas and in natural gas sweetening. The desirable properties of RTIL solvents, such as negligible vapor pressures, thermal stability, and a large liquid range, make them interesting candidates as new materials in well-known CO(2) capture processes. Here, we focus on the use of RTILs (1) as absorbents, including in combination with amines, and (2) in the design of polymer membranes. RTIL amine solvents have many potential advantages over aqueous amines, and the versatile chemistry of imidazolium-based RTILs also allows for the generation of new types of CO(2)-selective polymer membranes. RTIL and RTIL-based composites can compete with, or improve upon, current technologies. Moreover, owing to our experience in this area, we are developing new imidazolium-based polymer architectures and thermotropic and lyotropic liquid crystals as highly tailorable materials based on and capable of interacting with RTILs.

There have been contradictory reports of the relative proportion of mercury from coal-fired power plants that deposits locally. Our objective was to determine any local effect of coal-fired power plants on total mercury concentrations in wetland sediment and tadpole samples. Four power plants and 45 wetlands were selected for study. Total mercury concentrations were determined in 75 sediment samples (range: 8-82 ng/g dry weight) and 100 bullfrog (Lithobates catesbeiana) and green frog (Lithobates clamitans) tadpoles (range: 5-318 ng/g wet weight). Tadpole and sediment total mercury did not significantly vary by power plant or distance from the plant. Only one power plant had a significantly greater concentration of total mercury in sediment downwind compared to upwind wetlands. A similar (but non-significant) trend was found for tadpole total mercury surrounding the same plant. Tadpole total mercury was negatively correlated with both tadpole weight and total length. Tadpole and sediment total mercury concentrations were not significantly correlated with one another. The results of the current study suggest that coal-fired power plants are not significantly affecting mercury concentrations in surrounding wetlands.

Climate change mitigation requires a rapid decrease of global emissions of greenhouse gases (GHGs) from their present value of 8.4 Gt/C/year to, as of current knowledge, approximately 1 GtC/year by the end of the century. The necessary decrease of GHG emissions will have large impacts on existing and new investments with long lifetimes, such coal-fired power plants or buildings. Strategic decision making for major investments can be facilitated by indicators that express the likelihood of costly retrofitting or shut-down of carbon intensive equipment over time. We provide a set of simple indicators that support assessment and decision making in this field. Given a certain emissions target, carbon allowance prices in a cap-and-trade plan will depend on the development of the global economy and the degree to which the target is approached on the global and national levels. The indicators measure the degree to which a given emissions target is approached nationally and assess risks for long-lived investments subject to a range of emissions targets. A comparative case study on existing coal-fired power plants with planned plants and utility-scale photovoltaic power-plants confirms that high risk for coal-fired power plants is emerging. New legislation further confirms this result.

An investigation of the potential environmental and health impacts in the immediate aftermath of one of the largest coal ash spills in U.S. history at the Tennessee Valley Authority (TVA) Kingston coal-burning power plant has revealed three major findings. First the surface release of coal ash with high levels of toxic elements (As = 75 mg/kg; Hg = 150 microg/kg) and radioactivity (226Ra + 228Ra = 8 pCi/g) to the environment has the potential to generate resuspended ambient fine particles (< 10 microm) containing these toxics into the atmosphere that may pose a health risk to local communities. Second, leaching of contaminants from the coal ash caused contamination of surface waters in areas of restricted water exchange, but only trace levels were found in the downstream Emory and Clinch Rivers due to river dilution. Third, the accumulation of Hg- and As-rich coal ash in river sediments has the potential to have an impact on the ecological system in the downstream rivers by fish poisoning and methylmercury formation in anaerobic river sediments.

Large numbers of proposed new coal power generators in the United States have been canceled, and some states have prohibited new coal power generators. We examine the effects on the U.S. electric power system of banning the construction of coal-fired electricity generators, which has been proposed as a means to reduce U.S. CO2 emissions. The model simulates load growth, resource planning, and economic dispatch of the Midwest Independent Transmission System Operator (ISO), Inc., Electric Reliability Council of Texas (ERCOT), and PJM under a ban on new coal generation and uses an economic dispatch model to calculate the resulting changes in dispatch order, CO2 emissions, and fuel use under three near-term (until 2030) future electric power sector scenarios. A national ban on new coal-fired power plants does not lead to CO2 reductions of the scale required under proposed federal legislation such as Lieberman-Warner but would greatly increase the fraction of time when natural gas sets the price of electricity, even with aggressive wind and demand response policies.