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De-icing agent in deer debate

Chunichi Shimbun

Nagano Prefecture applies a de-icing compound to its roads to prevent them from freezing over in winter, but the substance may be endangering wild deer by luring them to busy routes to feed on the salt it contains.

“The compound is an easily accessible source of salt for deer, and more of them are wandering onto roads to lap it up,” said Manabu Miyazaki, 62, who has photographed such behavior.

The de-icing compound, which is made from sodium chloride or calcium chloride and other chemicals, has been in use nationwide since the 1980s.

It was introduced to stop drivers with studded snow tires from kicking up asphalt dust on dry roads in winter, causing air pollution.

Nagano sprayed its prefectural and national roads with 21,000 tons of the compound in fiscal 2010, while Gifu Prefecture used around 6,500 tons the same year.

Herbivores, such as deer, usually search for mineral nutrients, including salt, in natural deposits on mountainsides, but mineral licks are limited in some of the areas they populate. Hunters use salt to lure deer within range.

Last year, it occurred to Miyazaki that water containing the de-icing compound might be accumulating under elevated sections of the Chuo Expressway and that deer may be feeding off it. To test his theory, he set up a sensor-equipped camera under a stretch of the expressway in Iijimamachi, Nagano Prefecture, in December.

The first two months were fruitless, but in February the camera captured images of a group of deer lapping up the crystallized salt.

“The experiment confirms that deer gather to feed on the compound’s salt,” said Akihiko Naniwa, an official at Hokkaido University’s Field Science Center for Northern Biosphere.

“So it is possible that it can lure wild animals to roads closer to towns,” where they are at greater risk from busier traffic, he warned.

Miyazaki also voiced concerns about the standard de-icing method, and called on local governments to scale down their application of the compound.

But a prefectural official in Nagano dismissed his claims.

“We believe the compound’s influence on the environment is minimal, and as we don’t have any substitute we will continue to use it in future,” the official said.

This section, appearing Saturdays, features topics and issues from the Chubu region covered by the Chunichi Shimbun. The original article was published April 7.