The US government agency has published the first of two volumes of its response to the National Academy of Sciences 2006 report on the EPA's original dioxin reassessment.
The US Environmental Protection Agency (EPA) has released
the first part of its long-awaited dioxin reassessment.
The document is the first of two EPA reports that, together, will respond to the recommendations and comments on 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) dose-response assessment included in the 2006 NAS report, Health Risks from Dioxin and Related Compounds: Evaluation of the EPA Reassessment.
The released document, Reanalysis Volume 1, includes (1) a systematic evaluation of the peer-reviewed epidemiologic studies and rodent bioassays relevant to TCDD dose-response analysis; (2) dose-response analyses using a TCDD physiologically based pharmacokinetic model that simulates TCDD blood concentrations following oral intake; and (3) an oral reference dose (RfD) for TCDD.
An RfD of 7 × 10−10 mg/kg-day is derived based on two epidemiologic studies: (a) a study that associated TCDD exposures with decreased sperm concentration and sperm motility in men who were exposed during childhood and (b) a study that associated increased thyroid-stimulating hormone levels in newborn infants born to mothers who were exposed to TCDD.
A qualitative discussion of uncertainties in the RfD and a focused quantitative uncertainty analysis of the choices made in the development of points of departure for RfD derivation are also provided.