Grape growers will have to certify starting Jan. 1 that their fruit is free from sulfites, a substance that can cause deadly allergic reactions in some people, the Environmental Protection Agency said yesterday.

The new rule requires growers to test their grapes and certify that the amount of sulfites on the fruit is less than 10 parts per million. The sulphur compound helps to prevent spoilage in stored grapes.

Under the old rule, growers were allowed to have higher levels of the sulfites on their grapes provided they tagged 40 percent of the bunches with labels saying that the fruit had been treated. An EPA spokesman said that later next year the EPA may revise its rule to allow uncertified grapes, provided growers tag all the bunches to show they have been treated.

Grapes in storage are gassed every seven to 10 days with sulfur compounds that prevent mold and other spoilage organisms from growing on the fruit.

The EPA announcement is "a very positive step to protect consumers," said Mitchell Zeller, assistant director for legal affairs at the Center for Science in the Public Interest, a consumer group that has fought the EPA for 18 months over the sulfite rules for grapes.

The 10-parts-per-million level is considered the level of detectability for sulfites, but Zeller said that no safe level has been found for the sulfites.

He said as many as 1 million Americans, especially those with asthma, may be sensitive to sulfites. Severe reactions can cause death, with milder symptoms including breathing difficulties, headaches, skin rashes, nausea and diarrhea.