United States Environmental Protection Agency

About: United States Environmental Protection Agency is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Population & Environmental exposure. The organization has 13873 authors who have published 26902 publications receiving 1191729 citations. The organization is also known as: EPA & Environmental Protection Agency.

Consensus on the key characteristics of endocrine-disrupting chemicals as a basis for hazard identification.

Abstract: Endocrine-disrupting chemicals (EDCs) are exogenous chemicals that interfere with hormone action, thereby increasing the risk of adverse health outcomes, including cancer, reproductive impairment, cognitive deficits and obesity. A complex literature of mechanistic studies provides evidence on the hazards of EDC exposure, yet there is no widely accepted systematic method to integrate these data to help identify EDC hazards. Inspired by work to improve hazard identification of carcinogens using key characteristics (KCs), we have developed ten KCs of EDCs based on our knowledge of hormone actions and EDC effects. In this Expert Consensus Statement, we describe the logic by which these KCs are identified and the assays that could be used to assess several of these KCs. We reflect on how these ten KCs can be used to identify, organize and utilize mechanistic data when evaluating chemicals as EDCs, and we use diethylstilbestrol, bisphenol A and perchlorate as examples to illustrate this approach.

Effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of select crop species.

Abstract: Single-walled carbon nanotubes have many potential beneficial uses, with additional applications constantly being investigated Their unique properties, however, create a potential concern regarding toxicity, not only in humans and animals but also in plants To help develop protocols to determine the effects of nanotubes on plants, we conducted a pilot study on the effects of functionalized and nonfunctionalized single-walled carbon nanotubes on root elongation of six crop species (cabbage, carrot, cucumber, lettuce, onion, and tomato) routinely used in phytotoxicity testing Nanotubes were functionalized with poly-3-aminobenzenesulfonic acid Root growth was measured at 0, 24, and 48 h following exposure Scanning-electron microscopy was used to evaluate potential uptake of carbon nanotubes and to observe the interaction of nanotubes with the root surface In general, nonfunctionalized carbon nanotubes affected root length more than functionalized nanotubes Nonfunctionalized nanotubes inhibited root elongation in tomato and enhanced root elongation in onion and cucumber Functionalized nanotubes inhibited root elongation in lettuce Cabbage and carrots were not affected by either form of nanotubes Effects observed following exposure to carbon nanotubes tended to be more pronounced at 24 h than at 48 h Microscopy images showed the presence of nanotube sheets on the root surfaces, but no visible uptake of nanotubes was observed

Travel-time uncertainty, departure time choice, and the cost of morning commutes

Abstract: Existing models of the commuting time-of-day choice are extended in order to analyze the effect of uncertain travel times. Travel time includes a time-varying congestion component and a random element specified by a probability distribution. Results from the uniform and exponential probability distributions are compared and the optimal "head start" time that the commuter chooses to account for travel time variability, i.e., a safety margin that determines the probability of arriving late for work, is derived. The model includes a one-time lateness penalty for arriving late as well as the per minute penalties for early and late arrival that other investigators have included. It also generalizes earlier work by accounting for the time variation in the predictable component of congestion, which interacts with uncertainty in interesting ways. A brief numerical analysis of the model reveals that uncertainty can account for a large proportion of the costs of the morning commute.