DUpont insists that its product - when used as directed - harms neither plants nor humans.

While Benlate DF's active ingredient, breakdown products and contaminants do have the potential to create adverse effects in both, no single known factor seems to explain the diverse symptoms in either.

"I have likened it to trying to put together a six-foot picture puzzle with pieces the size of a penny. Don't underestimate the complexity of it," said Carl Whitcomb, a crop consultant who believes that sulfonylureas (SUS), a class of potent weedkillers that have been named as a Benlate DF contaminant, most likely are responsible for the widespread plant damage.

The powerful plant-killers target one enzyme system specific to bacteria, yeast, fungi and plants, he said, citing the basis for the assumption that the chemicals are nontoxic to humans and animals.

"Where it gets unclear is the question of breakdown products of these herbicides," said Whitcomb. As these things break down in the environment, they may or may not affect people."

More is known about the breakdown products of benomyl - Benlate's active ingredient - which converts to carbendazim, n-butyl isocyanate (BIC) and dibutylurea in the environment.

According to tests performed by regulatory agencies and independent laboratories, all have been found to persist in air and soil samples after they should have dissipated. And some can be harmful to human health.

Of the three, BIC - a form of cyanide gas - is rated high on the list of suspects related to respiratory complaints from people who say they've been exposed to the fungicide. "The isocyanates are known for their ability to sensitize people," said Roger Inman, the state's chief toxicologist. "You could get tearing, nosebleeds and allergic-type reactions right down to pulmonary symptoms like asthma."

The presence of BIC and other breakdown products after they should be gone indicates an imbalance in the number and kind of microorganisms in the soil, say some scientists working on the puzzle. These organisms are responsible for breaking the compounds down in the environment.

In essence, the chemicals may be killing the organisms, said Whitcomb. Its supposed to work the other way.

SUs, which can affect bacteria, yeast and fungi, as well as plants, could be one factor in upsetting the microbial world, he said. DUpont says SUs were not present in any of the recalled Benlate DF.

Benomyl, itself, could also affect microorganisms. Benlate's active ingredient is known to cause mutations in some microorganisms.

It has been suggested that microbes could even be the source of some symptoms. At least one Benlate-related human health complaint involves a man infected with fusarium, a fungus known to mutate when exposed to Benlate.

There are other factors as well.

Chlorothalonil and flusilazole - two other fungicides discovered in some batches of Benlate - are contaminants that recently have become the focus of more intense scrutiny by regulatory agencies.

Chlorothalonil, a chemical whose residue is supposed to be washed from stems and leaves, was found inside some Benlate DF treated plant tissues - a place it was not expected to be.

Flusilazole is not registered for use in the United States.

Both compounds are not supposed to be applied to soil, which they were as part of Benlate DF soil drench treatments by growers who didn't know they were in the fungicide.

According to some scientists,. either of these compounds by themselves, or in concert with other chemicals in Benlate DF - known and unknown - may have created microbial mayhem toxic to all living things.

Only this year has anyone even agreed to explore the synergy - the combined action of these compounds - upon each other, the environment and human health.

"This is a problem of monumental proportions. where are the scientists that are supposed to be working on this?" said whitcomb.

University of Florida researcher R. Hilton Biggs, who for a time led the state's investigation into plant damage, believes that the contaminants and breakdown products in Benlate, combined with certain environmental factors, creates both chemical buildup and an imbalance in microorganisms. Both have toxic implications, he said.

He believes the phenomenon is not limited to the recalled dry flowable formulation, but includes all forms of Benlate, which was introduced in 1970. Biggs' theory is that Benlate has been accumulating in the environment ever since. The process was more rapid and dramatic when certain batches of the DF formula - containing contaminants - was applied as a root drench he said.
"In my opinion, Benlate is the second worst chemical disaster in the history of the world," said the retired biochemist. Second only to the "Silent Spring" of DDT.

"And its still out there," he said.

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