Anti-pesticide and community activists celebrated the new requirements, saying they would help protect rural residents from being sickened by the chemicals' gaseous byproducts.
A prominent national grower's organization said their members may challenge the agency's call for buffer zones up to a half-mile wide, which could force farmers to forgo planting thousands of acres.
"Our policy is not in favor of buffer zones that are politically motivated," said Paul Schlegel, director of public policy for the American Farm Bureau. "We don't think there should be buffer zones if they're not related to a clear risk."
The agency considers Thursday's decisions final but may make some modifications after a 60-day comment period, said Steven Bradbury, who directs the EPA's pesticide reviews.
The restrictions apply to five toxic fumigants: methyl bromide, metam sodium, metam potassium, dazomet and chloropicrin.
As part of their lengthy evaluation process, EPA scientists traveled to California's San Joaquin Valley to meet with farmers who sterilize their soil before planting season by injecting it with metam sodium in hopes of yielding better strawberries, potatoes and carrots.
In 1999, that chemical also caused the state's largest known pesticide drift, when 250 people fell violently ill after a cloud wafted over the farm worker town of Earlimart.
State regulators have since restricted the use of fumigants in three growing regions on the grounds that they cause smog.
California is in the process of improving its regulation of fumigants and expects to implement measures that will meet or exceed federal rules before 2010, a Department of Pesticide Regulation spokesman said.
In addition to the buffer zones of between 25 feet and a half-mile, the new federal instructions also require that growers post warning signs around their fields, monitor gas levels and provide workers with protective breathing masks.
Environmental and community groups called the decision a good first step but said they fell short of their petition to ban fumigants altogether.
"The combination of posting, advance notification of state agencies, and buffer zones around fields will substantially reduce the number of fumigant poisonings," said Dr. Brian Hill, science department director at the San Francisco-based Pesticide Action Network. "And when something does go wrong, communities and emergency personnel will be much better prepared to respond."