Photo/Illutration A Tsushima leopard cat on Tsushima island in Nagasaki Prefecture (Provided by Tsushima Yamaneko wo Mamoru Kai)

MATSUYAMA—High concentrations of synthetic chemicals have been detected in Tsushima leopard cats, an endangered species found only on one island between Kyushu and South Korea, a research team said.

The pollutants are polyfluoroalkyl substances (PFAS), known for their ability to repel oil and water. They are nearly non-degradable in nature and pose significant environmental and health risks.

The Tsushima leopard cat is listed in the “Endangered Class 1A” category on the Environment Ministry’s red list and is also designated by the central government as a natural monument.

About 100 of them live on Tsushima island, Nagasaki Prefecture, according to the ministry.

It remains unclear how PFAS and other chemical substances got into their bodies.

“It is necessary to conduct research on water, soil, creatures and other factors on the island to find out the source of pollution,” a member of the research team said.

The study was conducted by Ehime University’s Center for Marine Environmental Studies (CMES) in Matsuyama and the Faculty of Veterinary Medicine at the Okayama University of Science (OUS) in Imabari, Ehime Prefecture.

The team obtained approval to examine Tsushima leopard cats killed by traffic accidents and other causes that are kept by the ministry.

The OUS anatomized 20 of them that died between 2022 and 2024. The CMES then found and analyzed chemical substances accumulated in their livers and kidneys.

PFAS and other organic pollutants were detected in all of the cats.

The highest concentration in the kidneys was about 210 nanograms of PFAS per gram. One nanogram equals one-billionth of a gram.

It is a level that could cause lipid metabolic abnormalities and lead to kidney diseases, the team said.

Kei Nomiyama, an associate professor at the CMES, has visited Tsushima island many times to study the wildcats.

He said he is worried about the debris washing up on beaches and serious feeding damage caused by deer in mountain forests.

“I think it is important to restore ‘satoyama’ (mountain foothills near rural communities) and mountain forests with no undergrowth to maintain the living environment for Tsushima leopard cats,” Nomiyama said.

Volunteers have set up a nonprofit organization called “Tsushima Yamaneko wo Mamoru Kai” (Tsushima leopard cat guardians).

Tsushima leopard cats living in satoyama areas enter agricultural fields to eat mice, insects and other small creatures.

But the aging population on the island has led to an increase in abandoned farmland and a decrease in feeding grounds for the wildcats.

To help the leopard cats, the NPO is developing “soba” buckwheat fields on about 4,000 square meters of abandoned terraced fields near a beach on the west side of the island.

It started a crowdfunding campaign to rent agricultural equipment and buy mesh fences to prevent damage from animals.

“It is a place that offers a great view, and we think it will provide a stage for visitors to think about the Tsushima leopard cat and the island’s environment,” a representative said.

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