Traces of a banned and highly toxic insecticide that has never been used or manufactured in Japan have been found in animals such as crows and monkeys in the eastern part of the country, the Environment Ministry said Friday.
The detected amounts of the organochlorine insecticide, called mirex, were extremely small and posed no direct threat to human beings, ministry officials said.
The officials said they believe the chemical may have come to Japan in the atmosphere or via sea currents and are investigating possible routes.
Mirex was found in monkeys, raccoon dogs, dolphins and three kinds of wild bird inhabiting the Kanto region, including Tokyo. This is the first time that land animals in Japan have tested positive for mirex, which is banned in developed countries due to its toxicity and persistent residue.
The densities were below 6 nanograms per gram of tissue, the officials said. A nanogram is one-billionth of a gram.
"It is possible for mirex pollution to spread to countries that have no record of using it," said Shinsuke Tanabe, an environment chemistry professor at Ehime University's Center for Marine Environmental Studies. Tanabe was the first to detect mirex and other substances in dolphins and whales in seas near Japan in June.
The ministry said the insecticide had been used in the United States until the 1970s but Japan has never manufactured nor imported it. It is used overseas, especially against ants, but was found to be carcinogenic in experiments on laboratory rats.
Mirex, like dioxin and polychlorinated biphenyl, is a persistent organic pollutant (POP) that is highly toxic and does not easily break down in nature.