Investigations into the Role of Herbicides and Other Chemicals in Causing Male-mediated Development Toxicity

This synopsis courtesy of Assoc Prof Bill Webster, University of Sydney
incorporating an update of 16 December 1998 from Diana Oaks

The three-year project (funded by the Department of Veterans' Affairs) commenced in July 1997 and is designed to investigate whether paternal exposure to herbicides, such as those used in the Vietnam war, can result in the an increased incidence of spina bifida or other birth defects.

Australian soldiers who served in Vietnam were exposed to a number of herbicide chemical mixtures that may have damaged their health or reproductive ability.  The most frequently used of these was Agent Orange (11 million gallons sprayed) and this chemical mixture has been extensively studied to identify and classify its various toxic properties.  The second most used herbicide mixture was code-name Agent White (5 million gallons sprayed).  Unlike agent orange, there have been very few studies to examine the toxic properties of Agent White.

Epidemiological studies, in which the incidence of birth defects is determined in the offspring of Vietnam Veterans and in control populations, has not resolved the issue and it was decided to perform studies with experimental animals in an attempt to get some useful answers. Animal studies have the advantage that chemical exposure can be precisely measured and controlled and the effects on the offspring can be examined in detail.

Briefly, male rats will be exposed to high doses of herbicides containing 2,4-D and picloram and their offspring will be examined for birth defects and chromosomal (genetic) abnormalities. Tissues from the treated rats will also be examined for evidence of DNA damage. It was decided not to use dioxin in these initial experiments because although it is a highly toxic compound found in some herbicides it does not appear to damage genetic material (DNA).

This study is almost half-way to completion.  The current, incomplete results, do not show any evidence of an increased incidence of abnormalities.  The offspring (fetuses) will be further examined for genetic abnormalities by examination of their chromosomes.  The work is still in progress.

Other experiments will be performed using a larger range of chemicals found in herbicides used in Vietnam. In these experiments particles (mitochondria) derived from rat liver will be exposed to various combinations of these chemicals and the effect on mitochondrial function (energy production) will be measured. These studies will indicate whether certain mixtures of chemicals lead to enhanced and unexpected toxicity that might not be predicted from examination of individual chemicals.

An interesting finding has been that the active components of the formulation (2,4-D) and picloram) showed little or no toxicity compared with the toxicity of the surfactant present in the mixture.  Surfactants are added to herbicides to aid penetration and spreading of the active components.  It is unknown what relevance this has to human exposure since the behaviour of the surfactant in humans has not been studied.  It is possible that ingested surfactants are not absorbed or are inactivated before they reach important structures.

Using similar techniques, the team is also examining the formulations known as Agent Orange and Agent Blue.  The results of these experiments are currently being prepared for publication in a scientific journal.

The people involved in this project are listed below:

At the Dept Anatomy and Histology, University of Sydney:

Assoc Professor Bill Webster,
Dr John Pollak, Hon Research Associate
Ms Diana Oakes (enrolled PhD)

At the Dept of Biomedical Sciences, Cumberland College Campus, University of Sydney:

Dr Patricia Brown-Woodman
Dr. Helen Ritchie


Copyright reserved by Vietnam Veterans Association of Australia Inc
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