SAN FRANCISCO — Most Americans think they're helping the Earth when they recycle their old computers, televisions and cell phones. But chances are they're contributing to a global trade in electronic trash that endangers workers and pollutes the environment overseas.

While there are no precise figures, activists estimate that 50 percent to 80 percent of the 300,000 to 400,000 tons of electronics collected for recycling in the U.S. each year ends up overseas. Workers in countries such as China, India and Nigeria then may use hammers, gas burners and their bare hands to extract metals, glass and other recyclables, exposing themselves and the environment to a cocktail of toxic chemicals.

"It is being recycled, but it's being recycled in the most horrific way you can imagine," said Jim Puckett of the Basel Action Network, a Seattle-based environmental group. "We're preserving our own environment, but contaminating the rest of the world."

The gear most likely to be shipped abroad is collected at free recycling drives, often held each April around Earth Day, recycling industry officials say. The sponsors — chiefly companies, schools, cities and counties — often hire the cheapest firms and do not ask enough questions about what becomes of the discarded equipment, the officials say.

Many so-called recyclers simply sell the working units and components, then give or sell the remaining scrap to export brokers.

The problem could get worse. Most of the 2 million tons of old electronics discarded annually by Americans goes to U.S. landfills, according to U.S. Environmental Protection Agency data. But a growing number of states are banning such waste from landfills, which could drive more e-waste into the recycling stream and fuel exports, activists say.

Many brokers claim they are simply exporting used equipment for reuse in poor countries.

But activists complain that most exporters don't test units to make sure they work before sending them overseas.

"Reuse is the new excuse. It's the new passport to export," said Puckett of the Basel Action Network. "Other countries are facing this glut of exported used equipment under the pretext that it's all going to be reused."

Exporting most electronic waste isn't illegal in the United States. The U.S. does bar the export of monitors and televisions with cathode-ray tubes without permission from the importing country, but federal authorities don't have the resources to check most containers.

The EPA recognizes the problem but doesn't believe that stopping exports is the solution, said Matt Hale, who heads the agency's office of solid waste. Since most electronics are manufactured abroad, it makes sense to recycle them abroad, Hale said.

"What we need to do is work internationally to upgrade the standards (for recycling) wherever it takes place," he said.

The EPA is working with environmental groups, recyclers and electronics manufacturers to develop a system to certify companies that recycle electronics responsibly. But so far the various players have not agreed on standards and enforcement.

Many activists believe the answer lies in requiring electronics makers to take back and recycle their own products. Such laws would encourage manufacturers to make products that are easier to recycle and contain fewer dangerous chemicals, they say.

Eight states, including five this year, have passed such laws, and companies such as Apple, Dell, Hewlett-Packard and Sony now take back their products at no charge.

Some require consumers to mail in their old gear, while others have drop-off centers.