The Carcinogen Assessment Group has added its voice, saying there is substantial evidence that the dioxyn TCDD is likely to cause cancer in humans.
Dow Chemical Company, which manufactures the herbicides, has since tried to suppress the publication of the results of tests carried out in its own laboratories that show damage to animals exposed to TCDD. The tests demonstrate a large number of problems suffered during reproduction, including miscarriages, stillbirths, and ill-health and death among the young that survive. Even at the lowest dosage there were significant increases in the number of stillbirths, and deaths before the young were three weeks old.
Dow Chemical Company claimed that the results of the studies are "trade secrets" or "confidential" and won a court injunction against the EPA's disclosing the data at this time.
But it wasn't the animal research, which the EPA describes as almost unprecedented in its conclusiveness, that finally led to the emergency ban on 2,4,5-T and the related herbicide Silvex. It was the careful and dispassionate gathering of evidence and documentation by one woman - 33-year-old Bonnie Hill, a school teacher at a small country school in the tiny settlement of Alsea in southwest Oregon.
It was her work, carried out for more than two years in her own time and expense, that sparked further investigations by the EPA. What it discovered was sufficient to justify an emergency ban on the herbicides while fullscale hearings took place on whether the ban should become permanent.
Bonnie Hill's work had tipped the balance. It was the first time any substantial link between the use of chemicals herbicides and damage to human health had been established.
Bonnie had two children before her miscarriage in the spring of 1975. Her doctor had no explanation for it and no one thought of herbicides as a possible cause. No one was aware that they were used that much.
A few months later Bonnie came across an article referring to the studies of Dr James Allen at the University of Wisconsin. His studies indicated that exposure to 2,4,5-T caused adverse effects, including miscarriages, upon the reproductive systems of rhesus monkeys.
She immediately realized the possible connection.
She phoned the Bureau of Land Management, which manages the land all around her, and discovered that Silvex and 2,4,5-T had been sprayed in her area a month before her miscarriage.
She thought that could just be coincidental. Then she started to remember former students of hers from the Alsea school having miscarriages and wondered whether their doctors had any explanations. She was careful not to alarm them nor to suggest that herbicides could be responsible. Eventually she found out about other miscarriages.
"I was not inquiring about spring miscarriages exclusively, but about all miscarriages in the area," says Bonnie. "Every time we heard about a miscarriage it was in the spring. One was in October (autumn) - but that year they sprayed in September, so it seemed to fit into the pattern as well."