The containers, shipped to Indonesia by CRT Recycling Inc., were seized by port officials there after an environmental organization staked out the company’s Massachusetts operations and alerted the Indonesian government about a possibly illegal shipment of e-waste.

The cathode-ray tubes in televisions and computer monitors contain more than four pounds of lead, as well as mercury and other toxins, that, if not disposed of properly, can seep into groundwater or soil. An international treaty restricts shipments of these tubes for disposal in developing countries.

But CRT Recycling says the TV tubes were being sent to the country to be reused - not thrown away. “We send good [material] overseas," said Peter Kopcych, general manager of CRT, which takes thousands of tons of old computers and televisions every year from close to 200 municipalities, including some in Massachusetts.

Indonesia sent the containers back to Boston, and yesterday, the US Environmental Protection Agency released the shipment to the company, suggesting it found no clear violations of US law. The Indonesian government did not return e-mails and phone calls.

It can be difficult for the public to know where its old computers and televisions wind up. The United States has not ratified the Basel Convention treaty, a 172-nation pact to prevent the transfer of hazardous waste from developed countries to less-developed ones.

The Basel Convention considers cathode ray, or CRT tubes, hazardous waste, and it prohibits them from being sent to developing countries to be thrown away or recycled, according to the Basel Action Network, the group that alerted Indonesia to the shipment. To gain entry to those nations, many companies say the tubes are going to be reused or resold, the group said. Instead, it says, the majority of the tubes are burned, dumped, or, disassembled to extract reusable material by workers with little protection against toxins.

A 2008 Government Accountability Office report said US companies send broken CRTs overseas. Investigators posed as foreign buyers of broken CRTs in Hong Kong, India, Pakistan, and other countries - and 43 US companies told the investigators they would export those items. The report was critical of EPA’s oversight and enforcement.

“There is enough documented evidence indicating that monitors and other types of electronics shipped under the guise of resale or reuse winds up being disassembled in dangerous conditions,’’ said Allen Hershkowitz, senior scientist with the Natural Resources Defense Council. “There is so much documentation consumers should assume that unless the material is going abroad [to be repaired under warranty] it will be disassembled."

Basel Action Network, a Seattle-based nonprofit, staked out CRT Recycling and took photographs of a container it says was being filled with computer monitors. Using container numbers and online shipping company databases, the group tracked the container and its ship to the port of Semarang, in Indonesia, in November. The group alerted the Indonesian government, which sent it back to the United States on Dec. 13, according to a letter from the Indonesian company slated to receive the material.

“We can explain that the green organization ... known as ‘BASEL’ took photos of the cargo while being loaded in U.S.A. and then asked the Indonesian Environmental authorities to ship these containers back to the U.S.A. because BASEL CONVENTION description of CRT is ‘hazardous material,’" according to the letter from Intech Anugrah Indonesia.

Kopcych said Basel Action got its information wrong. The company sent televisions - not computer monitors - in the containers. And he said the Indonesian government never opened them to see what was inside. A Basel Action Network official said the Indonesian government did open the containers.

Kopcych said company representatives asked people whether their televisions worked when they picked them up, and the machines were separated based on the answer. In cases where there was no one to ask, the company workers separated the TVs themselves. He said it ships only 3 percent of all the televisions they collect, and of those, about 97 percent can be reused.

But Jim Puckett of Basel Action Network said those assertions defy belief. Research his group has done shows that 75 percent of CRT tubes sent overseas do not work. Testing should be done on each one, he said.

The United States needs to ban the export of e-waste, he said.

“Even though our own government knows that the importation of toxic waste from the US is a violation of the laws of most countries of the world, our own EPA shamefully allows the global dumping to continue."