Abstract  This document provides technical support concerning cancer and noncancer risk assessment methods used in the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) (USEPA, 2000a; hereafter the 2000 Human Health Methodology). Ambient water quality criteria (AWQC) developed under Section 304(a) of the Clean Water Act (hereafter the CWA or the Act) are based solely on data and scientific judgments on the relationship between pollutant concentrations and environmental and human health effects. The 304(a) criteria do not reflect consideration of economic impacts or the technological feasibility of meeting the chemical concentrations in ambient water. As discussed below, 304(a) criteria are used by States and authorized Tribes to establish water quality standards, and ultimately provide a basis for controlling discharges or releases of pollutants.

Abstract  Hexabromocyclododecanes (HBCDs) are high production volume chemicals (16700 t worldwide in 2001) used as flame-retardants for plastics and textiles. HBCDs exhibit typical properties of persistent organic pollutants (POPs). They are highly lipophilic and accumulate in biota. Increasing environmental concentrations of HBCDs, mostly reported as sum values, have been observed. As such, HBCDs have to be considered as potential emerging POPs, but their occurrence and environmental fate have not yet been addressed at the level of individual HBCD stereoisomers. Considering the six stereogenic centers of HBCDs, 16 stereoisomers, six diastereomeric pairs of enantiomers as well as four meso forms, can be deduced. Herein, we report spectroscopic and chromatographic data for eight out of 16 possible HBCD stereoisomers, which were isolated from a technical product. Six stereoisomers were identified as three pairs of enantiomers ((+/-) alpha-, beta-, and gamma-HBCDs), differing in optical rotation and chromatographic retention on a chiral phase. The crystal structures of these pairs of enantiomers were determined. Another two of these eight HBCD stereoisomers, not yet described in the literature, showed no optical rotation and are tentatively assigned as meso forms (delta- and epsilon-HBCD). The given spectroscopic and chromatographic information allows the unambiguous identification of eight HBCD stereoisomers and the occurrence, fate, and toxicology of these individual stereoisomers can now be studied.

Abstract  Bromine has been added to cis,trans,trans-1,5,9-cyclododecatriene under various reaction conditions. All expected direct addition products have been isolated, and their structures have been determined by microanalysis, NMR and X-ray crystallography. Advanced NMR techniques were used to determine solution conformations of several of the compounds, enabling comparison with the solid-state conformations obtained by crystallography.

Abstract  This article is concerned with the general theory of expansion, manufacturing processes, properties, and applications of foamed (cellular) plastics. The high strength-to-weight ratio, excellent insulating properties, and cushioning properties of cellular plastics have contributed to the development and growth of the broad range of cellular plastics in use. The total usage of foamed plastics in the United States has risen from 441 thousand metric tons in 1967 to 1.6 million metric tons in 1982 and has been projected to rise to about 2.8 million metric tons in 1995. The manufacturing processes for cellular polymers are described in terms of three classified methods based on the cell growth and stabilization processes. The properties of cellular plastics including mechanical, thermal, electrical, and environmental aging properties, are summarized. A general discussion is given on the properties of cellular plastic necessary in many applications such as the comfort cushioning, thermal insulation, packaging, structural components, buoyancy, electrical insulation, and space-filling markets. A brief discussion is also given on the process economics, raw materials, and energy considerations for the commercial products of primary importance.

Abstract  This problem formulation document refines the conditions of use, exposures and hazards presented in the scope of the risk evaluation for HBCD and presents refined conceptual models and analysis plans that describe how EPA expects to analyze the risk associated with the conditions of use of HBCD.

Abstract  To evaluate the process of trophic transfer of microplastics, it is important to consider various abiotic and biotic factors involved in their ingestion, egestion, bioaccumulation, and biomagnification. Toward this end, a review of the literature on microplastics has been conducted to identify factors influencing their uptake and absorption; their residence times in organisms and bioaccumulation; the physical effects of their aggregation in gastrointestinal tracts; and their potential to act as vectors for the transfer of other contaminants. Limited field evidence from higher trophic level organisms in a variety of habitats suggests that trophic transfer of microplastics may be a common phenomenon and occurs concurrently with direct ingestion. Critical research needs include standardizing methods of field characterization of microplastics, quantifying uptake and depuration rates in organisms at different trophic levels, quantifying the influence that microplastics have on the uptake and/or depuration of environmental contaminants among different trophic levels, and investigating the potential for biomagnification of microplastic-associated chemicals. More integrated approaches involving computational modeling are required to fully assess trophic transfer of microplastics. Integr Environ Assess Manag 2017;13:505-509. © 2017 SETAC.

Abstract  The highly conserved nature of the thyroid gland and the thyroid system among mammalian species suggests it is critical to species survival. Studies show the thyroid system plays a critical role in the development of several organ systems, including the reproductive tract. Despite its highly conserved nature, the thyroid system can have widely different effects on reproduction and reproductive tract development in different species. The present review focuses on assessing the role of thyroid hormones in human reproduction and reproductive tract development and comparing it to the role of thyroid hormones in laboratory animal reproduction and reproductive tract development. The review also assesses the effects of thyroid dysfunction on reproductive tract development and function in humans and laboratory animals. Consideration of such information is important in designing, conducting, and interpreting studies to assess the potential effects of thyroid toxicants on reproduction and development.

Abstract  The estimation and assessment of substance exposure (EASE) model has been under development and in use since the early 1990s. It is a general model that can be used to predict workplace exposure to any substance hazardous to health. The current EASE model (version 2.0) has been used widely in the risk assessment of new and existing chemicals by the UK Health and Safety Executive (HSE) and other regulatory agencies. EASE has also been distributed globally to over 200 users and therefore may have been used for many other purposes. Despite widespread use of the model, neither the development of its structure nor its underlying concepts and principles have been published in the open literature. Using surviving documentary evidence and discussions with key personnel, the creation and development of the model from 1992 to 2002 is described. The role of the HSE's National Exposure Database (NEDB) as the principal data source for the development of the model output exposure ranges is described. A number of problems and limitations of the model have been identified and the description of the model's development provides some explanation of their presence.

Abstract  This chapter illustrates the thermal rearrangement of Hexabromocyclododecane (HBCD) and pure isomers. It was found that all isomers thermally rearrange to give the same final isomer distribution. During this rearrangement no evidence was found for “bromine dancing” on the ring. No side reaction was detected. The longer the time and the higher the temperature the greater thermal degradation of the HBCD occurred. Thermal equilibrium consists of 78 % isomer 3, 13 % isomer 2 and 9 % isomer 1.

Abstract  A common dermal exposure assessment strategy estimates the systemic uptake of chemical in contact with skin using the fixed fractional absorption approach: the dermal absorbed dose is estimated as the product of exposure and the fraction of applied chemical that is absorbed, assumed constant for a given chemical. Despite the prominence of this approach there is little guidance regarding the evaluation of experiments from which fractional absorption data are measured. An analysis of these experiments is presented herein, and limitations to the fixed fractional absorption approach are discussed. The analysis provides a set of simple algebraic expressions that may be used in the evaluation of finite dose dermal absorption experiments, affording a more data-driven approach to dermal exposure assessment. Case studies are presented that demonstrate the application of these tools to the assessment of dermal absorption data.

Abstract  The results of dermal absorption experiments are routinely and often exclusively reported in terms of fractional absorption. However, fractional absorption is not generally independent of skin loading conditions. As a consequence, experimental outcomes are commonly misinterpreted. This can lead in turn to poor estimation of exposures under field conditions and inadequate threat assessment. To aid interpretation of dermal absorption-related phenomena, a dimensionless group representing the ratio of mass delivery to plausible absorptive flux under experimental or environmental conditions is proposed. High values of the dimensionless dermal number (N(DERM)) connote surplus supply (i.e., flux-limited) conditions. Under such conditions, fractional absorption will generally depend on load and should not be assumed transferable to other conditions. At low values of N(DERM), dermal absorption will be delivery-limited. Under those conditions, high fractional absorption is feasible barring maldistribution or depletion due to volatilization, washing, mechanical abrasion or other means. Similar logic also applies to skin sampling and dermal toxicity testing. Skin surface sampling at low N(DERM) is unlikely to provide an appropriate measure of potential dermal dose due to depletion, whereas dermal toxicity testing at high N(DERM) is unlikely to show dose dependence due to saturation.