Benchmark dose (BMD) modeling has been touted as a more accu­ rate method for conducting chemical risk assessments. In this issue of EHP, a team of researchers applied BMD modeling to hundreds of chemicals whose health effects are already known in an effort to optimize the approach. To calculate the highest safe oral dose of a noncarcinogenic chem­ ical, regulators must first estimate the point...

The determination of the value of the no-observed-adverse-effect level (NOAEL) when observed responses can be categorized by severity (categorical data) and sample sizes are small is discussed. The common situation of only two categories, where only the presence or absence of an effect is observed, is addressed first (dichotomous data). Three tests for dichotomous data are critically examined, ...

Hormesis, a dose-response relationship phenomenon characterized by low-dose stimulation and high-dose inhibition, has been frequently observed in properly designed studies and is broadly generalizable as being independent of chemical/physical agent, biological model, and endpoint measured. This under-recognized and -appreciated concept has the potential to profoundly change toxicology and its r...

BACKGROUND The U.S. National Toxicology Program (NTP) cancer bioassay database provides an opportunity to compare both existing and new approaches to determining points of departure (PoDs) for establishing reference doses (RfDs). OBJECTIVES The aims of this study were a) to investigate the risk associated with the traditional PoD used in human health risk assessment [the no observed adverse e...

in the management of river basins, prediction of river water quality is essential to maintain water quality within standard limits. this study performed a time-series analysis of the prediction of chlorine concentration and electrical conductivity time series data for the period of 1991-2005 from sefidrood river in northern iran. the seasonal prediction of chlorine and electrical conductivity t...