Hopkins dioxin model

[Dave Pettingill <isobar@igc.apc.org>]

Topic 837       Risk Model Identifies Safe Exposure
ewire	EWire	10:21 PM  Feb 27, 1996

TO NATIONAL, ENVIRONMENTAL AND HEALTH/MEDICAL EDITORS:

RISK MODEL IDENTIFIES SAFE LEVEL OF CHEMICAL EXPOSURE

      BALTIMORE, Feb. 27 -/E-Wire/-- Using a new model of risk 
assessment, researchers at the Johns Hopkins School of Public Health 
have identified a safe level of exposure to the nongenotoxic 
carcinogen dioxin.  This knowledge could help scientists determine 
whether people are being exposed to an unsafe, or potentially 
carcinogenic, level of the toxin.  The study is reported in the 
December 1995 issue of "Regulatory Toxicology and Pharmacology," 
released today.

     Nongenotoxic carcinogens stimulate cell receptors that cause 
enzymatic changes in the cell.  These changes, in turn, may cause a 
series of other cellular events, eventually resulting in cancer.  
Lead author Thomas Sutter, Ph.D., assistant professor of 
environmental health sciences at the School, said that in the United 
States, other commonly used models of risk assessment for these types 
of carcinogens are inappropriate because they presume that cancer 
occurs as a domino effect:  a direct result of chemical activation of 
cell receptors.  This implies that health hazards exist at any amount 
of exposure.

     "Our model is unique because it embodies an understanding of the 
receptor process.  As a result, it shows that below a certain level, 
dioxin does not cause harm," said Dr. Sutter.

     According to this new model, tissue concentrations of dioxin 
below 2.5 parts per trillion are unlikely to harm people.  Current 
human exposure levels for dioxin and dioxin-like chemicals are about 
1 and 10 parts per trillion, respectively.  Humans may be close to a 
level of dioxin exposure at which biological changes are likely to 
occur.  This model offers hope that scientists could find out for 
sure.

     "We now know that people are safe below a certain amount of 
exposure," Dr. Sutter explained.  "We also know that enzymatic 
changes occur above these levels.  We currently have the tools to 
measure those changes, so we should be able to determine whether 
current levels are truly dangerous."

     -0-
     /CONTACT:  Lisbeth Pettengill or Sharon 
Rippey of the Johns Hopkins School of Public 
Health, 410-955-6878/

Conf?