Evidence that one in five Washington farmworkers handling pesticides suffered excessive exposure to the chemicals has farmworker advocates pushing for stricter safety regulations and a ban on pesticides widely used by fruit growers.

They've persuaded state Rep. Steve Conway, D-Tacoma, to sponsor legislation that would phase out the use of the pesticides by 2012, with limited exceptions.

"We cannot ignore the workers and their families. It's not a question of whether to stop this from happening further, it's a question of how to," said Carol Dansereau, director of the Farm Worker Pesticide Project, a nonprofit working to reduce pesticide exposure for Washington farmworkers.

State regulators, however, say evidence of the problem is not clear-cut. And they are leery of restrictions that could place additional costs on farmers.

"I would be hesitant to say we have firm enough data to reach any policy conclusions," said Michael Wood, head of the Occupation Safety and Health Program at the state Department of Labor and Industries.

And a farm industry representative denounced the Labor and Industries study at the center of the debate, charging the results aren't reliable and that stiff regulations proposed by Conway would threaten state agriculture.

"There was no evidence of any serious widespread problems of exposure to pesticides that would call for any draconian measures," said Dean Boyer, spokesman for the Washington Farm Bureau.

Last year, Labor and Industries tested the blood of 580 farmworkers who regularly work around pesticides known as organophosphates or carbamates, chiefly used in fruit orchards but also on other crops. The study found 21 percent of them with sizable decreases in the enzyme cholinesterase, vital to the functioning of the nervous system.

The pesticides can cause drops in cholinesterase. Nearly 17 percent of the farmworkers had a drop greater than 20 percent in enzyme levels after working around the chemicals for more than 50 hours during a 30-day period. Another 4 percent of workers showed a 30 percent drop or greater, triggering their immediate removal from the work site.

Symptoms can range from flu-like in mild cases to tremors, breathing problems and even death in severe cases.

Heather Hansen, a representative for growers and pesticide applicators, said that while the study found lower enzyme levels, only one of the workers reported symptoms that could be traced to the pesticides. She criticized the rhetoric of farmworker groups.

"It implies that we have a lot of really ill and injured people out there. And I want folks to understand that that is not the case," said Hansen, of Washington Friends of Farms and Forests.

Wood said the findings convinced him the pesticides were affecting workers. But he said the best way to address exposure is not clear. The results suggest it may be linked to the use of air-blast sprayers, which blow pesticide onto trees, he said.

Interviews with workers and farmers also showed they were generally following safety regulations, he said.

Another batch of results to be taken this year should give a clearer picture about the chief source of exposure problems, providing a better basis for any additional restrictions, Wood said.

Farmworker representatives argue the evidence is clear enough to warrant basic protective measures. Regulators should require employers to use systems that isolate pesticides from the surrounding air during mixing, provide full respirators and encase the cabs of vehicles used to apply pesticide, Dansereau said.

There should also be a broader effort to replace pesticides with agricultural techniques that have less impact on workers, she said.

Conway said he was sponsoring legislation as a courtesy to farmworkers and that he would be open to possible changes. "This is just the beginning of a dialogue."

Such restrictions could take a toll on an industry that relies on pesticides to meet strict rules of other countries on the export of fruit containing insects like the apple coddling moth, said Ann Wick, a program manager at the state Department of Agriculture. Other measures haven't proved as effective, she said.

Warren Cornwall: 206-464-2311 or wcornwall@seattletimes.com