One in five senior IT managers are unsure whether some of their company's PCs end up in landfill after they dispose of them, according to a survey by charity Computer Aid.

The 100 respondents to the poll disposed of an average 542 computers per year, but only 65 were "confident" or "very confident" that all their unwanted IT avoided being sent to landfill. Moreover, 13 were wholly unaware of the Waste Electrical and Electronic Equipment (WEEE) directive, which outlaws dumping e-waste.

"It is extremely worrying that many of the U.K.'s largest companies are not able to guarantee that their equipment is not illegally dumped in landfill," said Anja ffrench, director of communications at Computer Aid, in a statement. "Companies must use disposal providers that can track exactly where their equipment is sent so as to avoid the devastating impact on health and the environment that e-waste can cause."

Companies typically replace their base units every 3.7 years and their monitors every four years, and Computer Aid wants more of these businesses to donate computers it can refurbish and send to developing countries.

However, recycling IT remains the most popular disposal option, with 28 percent of businesses recycling all their IT and 41 percent recycling more than half.

Just 14 percent sent followed what the charity called "best practice in IT disposal" by sending all their working computers for reuse and recycling the remainder.

Cost, fears over data protection and contractual obligations to a leasing company were cited as the main reasons why companies did not reuse more computers, although 83 percent said they would reuse working equipment if these factors were addressed.

"Policies need to be in place to ensure more reuse of working equipment," ffrench added. "Disposing of PCs after four years is a huge waste of resources since most computers will last at least double that."

This article originally appeared on BusinessGreen.