Monday, April 2, 2012

Environmental Health Perspectives Editorial on Evaluating Low Dose Effects of Chemicals (with Implications for Ionizing Radiation)


Environmental Chemicals: Evaluating Low-Dose Effects. In Environmental Health Perspectives.

By Linda S. Birnbaum, Director, NIEHS and NTP, National Institutes of Health, Department of Health and Human Services,
 http://ehp03.niehs.nih.gov/article/fetchArticle.action;jsessionid=A5B54007B66F7D4DC1388B53848478B9?articleURI=info%3Adoi%2F10.1289%2Fehp.1205179

 [excerpt] "Making connections between the exposome and risk assessment is a difficult but important venture (Paustenbach and Galbraith 2006; Rappaport and Smith 2010). 

Risk assessments typically examine the effects of high doses of administered chemicals to determine the lowest observed adverse effect levels (LOAELs) and no observed adverse effect levels (NOAELs); reference doses, which are assumed safe for human exposure, are then calculated from these doses using a number of safety factors. 

Thus, human exposures to thousands of environmental chemicals fall in the range of nonnegligible doses that are thought to be safe from a risk assessment perspective. 

Yet the ever-increasing data from human biomonitoring and epidemiological studies suggests otherwise: Low internal doses of endocrine disruptors found in typical human populations have been linked to obesity (Carwile and Michels 2011), infertility (Meeker and Stapleton 2010), neurobehavioral disorders (Swan et al. 2010), and immune dysfunction (Miyashita et al. 2011), among others.

For several decades, environmental health scientists have been dedicated to addressing the “low-dose hypothesis,” which postulates that low doses of chemicals can have effects that would not necessarily be predicted from their effects at high doses. More than 10 years ago, a National Toxicology Program expert panel concluded that there was evidence for low-dose effects for a select number of well-studied endocrine disruptors (Melnick et al. 2002).

Now, a diverse group of scientists has reexamined this large body of literature, finding examples of low-dose effects for dozens of chemicals across a range of chemical classes, including industrial chemicals, plastic components and plasticizers, pesticides, phytoestrogens, preservatives, surfactants and detergents, flame retardants, and sunblock, among others (Vandenberg et al. 2012)...."

[end excerpt] 
 
I RECOMMEND READING ENTIRE EDITORIAL...

The editorial is important because it explains how the methods used in the past to study chemicals' effects shaped the determination of risks.

Risk models extrapolated 'no' or 'few' effects based on research on high doses.

However, new research and re-evaluation of older studies is demonstrating that low-levels of exposure of chemicals can produce effects not predicted by the higher-dose studies.

One can imagine that the synergy of chemicals in living bodies also has effects that have not been adequately measured.

This research is particularly relevant for ionizing radiation.

New research has found that the risk models for the health effects of ionizing radiation that were based on high-dose exposures (e.g., Hiroshima and Nagasaki) grossly under-estimate the effects of low levels of ionizing radiation on living cells and disease in populations.

For instance, the research published in Deadly Deceit: Low-level Radiation, High-level Cover-up by Dr. Jay M. Gould (Author), Benjamin A. Goldman found after Chernobyl that for human infants the dose-response is “supralinear” rather than linear, “which means that infant mortality rises more rapidly at low doses.”

In June of 2011, the online journal Counterpunch published an article by Dr. Janet Sherman and epidemiologist Joseph Mangano reporting a 35 percent spike in infant mortality rates for the 10 weeks following Fukushima’s March releases in 8 US cities (Boise ID, Seattle WA, Portland OR, plus the northern California cities of Santa Cruz, Sacramento, San Francisco, San Jose, and Berkeley).

The report, using CDC data, was challenged for allegedly cherry picking data to support conclusions. Counterpunch subsequently had their statistical consultant, Pierre Sprey, evaluate and confirm the analysis. Sprey found the analysis to be robust.

Janette D. Sherman and Joseph Mangano “Is the Increase in Baby Deaths in the US a Result of Fukushima Fallout?” Counterpunch (2011, June 11-12): http://www.counterpunch.org/2011/06/10/is-the-increase-in-baby-deaths-in-the-us-a-result-of-fukushima-fallout/.

Cited in Alexander Cockburn “Post-Fukushima Infant Deaths in the Pacific Northwest,” Counterpunch (2011, June 17): http://www.counterpunch.org/cockburn06172011.html.


For background on how radiation dose has been measured see
http://majiasblog.blogspot.com/2012/03/estimating-dose-and-history-of.html




Implications: We must be wary of risk studies that do not model accurately how people are actually exposed to chemicals. 

We must demand that our risk models be based on studies that examine:
a. Actual exposure levels, including very low-levels of exposure
b. Examine synergies in exposures
C. Examine exposure across time

Anything else to add?
 

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