Thousands of tons of flat-screen TVs, personal computers, refrigerators, and sundry used electronic equipment is being dumped illegally in Nigeria every year.

That is the broad upshot of a two-year study put together by researchers at United Nations University, an academic research arm of the U.N.

According to the report, the majority of 66,000 tons of the used equipment came from EU countries, 17,000 tons of which was inoperable and was therefore classified as e-waste.

“It’s clearly illegal to export stuff that does not function,” said Otmar Deubzer, a scientific adviser for United Nations University in...