LONDON — More than three decades after the Chernobyl nuclear disaster in Ukraine, cows far from the accident site still produce milk with dangerous levels of radiation, children still drink it and the problem could persist for decades to come, researchers reported on Friday.

In villages as much as 140 miles from the Chernobyl nuclear plant, radioactivity readings in milk are up to five times the Ukranian government’s official limit for adults, and more than 12 times the limit for children, according to scientists from the Greenpeace Research Laboratories at the University of Exeter, in Britain, and the Ukrainian Institute of Agricultural Radiology.

Without large-scale intervention, the radiation will remain above the adult level until at least 2040 and above the child threshold even longer, they predicted. They reported their findings in the journal Environment International.

The researchers examined samples from 14 villages in the Rivne region, in northwest Ukraine, where the milk is consumed by the farmers and their neighbors. They found wide variations in radiation levels, depending on soil conditions and other factors, and it is not clear that the same results would hold true for large-scale commercial farms.