Declaring that endosulfan is unsafe, the Environmental Protection Agency announced Wednesday that it is about to ban one of the last organochlorine pesticides still used in the United States.

Endosulfan—used largely on vegetables, apples, melons and cotton—"poses unacceptable risks" to farm workers and wildlife, EPA officials said. In response, the agency is moving to cancel the pesticide's registration.

Endosulfan is a chlorinated insecticide that is chemically similar to DDT, which was banned nearly 40 years ago. Like DDT, endosulfan builds up in the environment and in the bodies of people and wildlife, and it is transported around the world via winds and currents. Nearly all other organochlorine pesticides already have been banned.

Because of the risks to human health and the environment, "pesticide products containing endosulfan do not meet the standard for registration" under a federal law governing pesticides, EPA officials announced. The agency is now working with endosulfan's sole manufacturer, Makhteshim Agan of North America, a North Carolina subsidiary of an Israeli company, to terminate all uses yet give growers time to shift to alternatives.

The agency's move reverses a decision made in 2002 under the Bush Administration that allowed continued use of endosulfan with some restrictions. That decision triggered a lawsuit two years ago filed by farm labor unions and environmental groups.

EPA officials said new research shows that the health risks to workers who apply endosulfan to crops "are greater than previously known, in many instances exceeding the agency's levels of concern." The agency also found the risks for wildlife, particularly fish and birds, were greater than estimated in 2002.

The human effects are largely unknown but tests on lab animals have shown that endosulfan is toxic to the nervous system and can damage the kidney, liver and male reproductive organs.

The coalition of environmental and farm worker advocates that sued the EPA welcomed the decision to ban all uses of endosulfan.

"Finally," said Kristen Boyles, who handled the lawsuit for the groups, which included United Farm Workers, Pesticide Action Network North America and the Natural Resources Defense Council. "Endosulfan should have been banned years ago. As this growing season enters full swing, we sincerely hope it's the last one where this dangerous poison is let loose in our communities and our environment."

In late 2007, the EPA updated its assessment of endosulfan's risks based largely on new research showing effects on the developing brains of lab animals and studies of farm workers that showed their exposure was greater than previously believed despite use of protective equipment. Two months later, California officials—who also were reviewing the risks of endosulfan—reported an even higher risk to workers than the EPA reported.

In addition, California officials determined that the amounts found in the air near some fields and orchards posed a public health risk to bystanders. The state declared endosulfan a toxic air contaminant in 2008, which triggered efforts to reduce people's exposure.

Last year, the EPA launched a review of the economic benefits of endosulfan, which is required before banning a substance under federal pesticides law. Its conclusion: "While a few crop uses have relatively high benefits for growers, the nationwide benefits to society as a whole are low for all uses of endosulfan and do not exceed the risks," says an EPA document released online Wednesday.

The top crops that use endosulfan are tomatoes, cucurbits (which include melons, cucumbers and squashes), potatoes, apples and cotton. Usage has been decreasing since 2002, when new restrictions were added. In California, about 60,000 pounds were applied to crops in 2008, compared with 151,000 pounds in 2002, according to the California Dept. of Pesticide Regulation.

First registered for use in the United States in the 1950s, endosulfan is one of the most abundant pesticides found in the global atmosphere. And unlike most other organochlorines, which were banned in the 1970s, its concentrations have been increasing since the 1980s in the Arctic and in other remote ecosystems, according to a 2009 study by British and Canadian researchers.

Traces of endosulfan are found on food crops, but EPA officials say the risks from consuming the residue are low. Because organochlorines accumulate in fatty tissue, those who eat high on food chains—such as the Inuit who eat marine mammals —are the most highly exposed.

United Nations countries are evaluating endosulfan for inclusion in the Stockholm Convention, an international treaty which bans or restricts persistent organic pollutants—chemicals that can build up in the environment. A decision by the UN's review committee is expected next year.

The ban on endosulfan will leave dicofol as the last major chlorinated pesticide allowed today in the United States, where it is used to kill mites, mostly on cotton and citrus. Pentachlorphenol is also used as a pesticide, although its use is restricted to treatment of railroad ties and utility poles, not food crops. Lindane is banned from crops but continues to be used in prescription shampoos for treating lice.