Microbiologist rejects birth defect claims

Press, 13 June 1984, Page 35

Microbiologist rejects birth defect claims

NZPA-AAP Canberra Vietnam veterans' claims of increased birth defects in their ranks could be confidently rejected, a Melbourne microbiologist told the Australia and New Zealand Association for the Advancement of Science (A.N.Z.A.A.S.) Congress.

Dr Donald MacPhee, of La Trobe University, also suggested that veterans should cast their net wider than Agent Orange to malaria drugs when looking for possible carcinogens in their war environment.

But he said it was impossible to prove that any of these chemicals might have caused cancer in Vietnam veterans.

Another paper, presented by a Western Australian psychiatrist, Dr Wayne Hall, said psychiatric disorders of veterans were probably ser-vice-related but unlikely to be the result of chemical exposure. Dr MacPhee said the types of birth defects which had figured in public debate had shown identifiable patterns. These types of defects were produced by toxic exposure of a foetus while developing in the mother's

uterus, a process known as teratogenesis.

Exposure of the father to a chemical could result in mutagenic changes to his reproductive cells.

Dr MacPhee said this type of damage would not show a consistent pattern of abnormality because interaction between the reproductive cell’s genetic material and the chemical would be random. The most likely effect of a potent mutagenic chemical on birth defects in a population would be a small increase in the variety of mutations in individuals rather than a pattern of defects. Studies of the atomic bombings of Hiroshima and Nagasaki had shown no heritable mutations in a population subject to the most massive exposure to a mutagenic agent in human history.

“Most of the defects reported by the Vietnam Veterans’ Association of Australia (V.V.A.A.) appear to be of teratogenic origin.” Dr MacPhee said.

“It is extremely unlikely that exposure of the father some five years before the

birth of affected children could produce teratogenic birth defects."

To do so. a highly implausible situation had to be imagined where the chemical would have to be stored in the father's body and transported to the foetus at the right moment to produce a birth defect rather than spontaneous abortion. Dr .MacPhee said that if the chemical was stored in the father he would more likely be sterile and therefore incapable of producing the child he was meant to have in some way deformed.

It was important to seperately consider the toxicity, mutagenicity and carcinogenicity of a chemical as one of these properties did not infer the other. A chemical of low toxicity which was highly mutagenic or carcinogenic could cause severe long-term problems without attracting attention.

Dr MacPhee said the V.V.A.A. had made claims about an increase in the rate of cancer among veterans but he thought the

preoccupation with herbicides should end. All men who served in Vietnam had been treated with the anti-malarial drugs. Dapsone and Chloroquine. a mutagen.

“If there is any increase in the rate of cancers among Vietnam veterans it is more likely to be due to exposure to these chemicals than to herbicides." Dr MacPhee said. Whatever chemicals might have caused an increase in cancer, it would not be easy to show, because of the long lead times between exposure and development.

Veterans had been exposed to a variety of potentially harmful substances before and after their war experiences which would make conclusive epidemiological study impossible with today’s methods. Dr MacPhee said anycompensation for cancer should not be delayed for conclusive results but be based on the best available scientific knowledge of the chemical’s potential to cause harm.