“Otter Found Dead Due to Mercury Poisoning in Bukhangang River: Implications for Heavy Metal Pollution and Ecosystem Health”

A study has found that the cause of death of an otter who died four days after being rescued from the upper reaches of the Bukhangang River was mercury poisoning. It is pointed out that it is necessary to investigate the surrounding environment as otters, which are at the top of the river ecosystem food chain, are exposed to heavy metal damage.

According to a paper titled ‘Mercury Poisoning in Eurasian Otters’ published in the latest issue of the Journal of Ecology and Environment on the 29th, an otter was rescued from the upper reaches of the Bukhangang River in Hwacheon-gun, Gangwon-do in February of last year. It was a young individual with a body length of 41 cm. At the time of rescue, the otter showed symptoms of dehydration, exhaustion, and severe lethargy. It also exhibited abnormal behavior of spinning on one side only. Despite subsequent treatment, the condition of the otter did not recover, and eventually died 4 days after being rescued.

Researchers performed an autopsy on the otter’s body to determine the cause of death. As a result, extensive vascular damage and hepatocellular necrosis due to mercury toxicity were found in several organs. High levels of mercury were also detected in kidneys and hair. The research team concluded, “As a result of a comprehensive review of symptoms and diagnostic results, the deaths of otters were found to be caused by mercury poisoning.” In addition, “the concentration of mercury in the liver did not exceed the minimum effect level,” he said, “even at low concentrations, if accumulated for a long time, symptoms such as neuropathy may appear.”

The otter is a natural monument number 330 and a first-class endangered species. Despite their cute appearance, they are the top predators of river ecosystems. It hunts not only fish, but also birds such as ducks. Because of this, they are most vulnerable to heavy metal contamination, which accumulates in higher concentrations toward higher predators. Han Seong-yong, director of the Korea Otter Research Center, said, “Since mercury has a long half-life, concentration occurs along the food chain from small organisms to top predators.” said.

The dead otter was found in the upper reaches of the Bukhangang River leading to the Han River. Going further up the river leads to Lake Paro. Lake Paro is known for its rich and clean fishing grounds, but in reality, it is considered to be the most severely mercury-polluted among domestic lakes and rivers.

According to the Ministry of Environment’s ‘National Mercury Integrated Measurement Network Pilot Project Final Report’, the total mercury concentration in the sediments of Lake Paro in 2020 was an average of 212 μg (microgram, 1 μg = 1/1 millionth of a gram) per kg. It was more than 5 times higher than the average value (36 μg/kg) of the Paldang Lake downstream. The National Institute of Environmental Research believes that if the mercury concentration in the sediment exceeds 100 μg/kg, organisms living on the bottom of the lake may be harmed.

In particular, mercury contamination was the most serious in the north of the Peace Dam. Accordingly, the investigation team believes that there is a potential source of contamination in the upper reaches of the Peace Dam, that is, in North Korea, and that mercury discharged from it continues to flow into Lake Paro. Lee Jong-hyeon, head of the Environment, Health and Safety Research Institute at EH R&C, who was in charge of the research service, said, “It is estimated that pollutants have flowed south along the river from the abandoned mine area in North Korea upstream for a long time.”

Mercury contamination in Faro Lake also affected other areas along the river. The report said, “It is judged that the contaminated sediments of Lake Paro affect Lake Chuncheon.”

As the otter’s habitat is developed, the possibility of exposure to heavy metal contamination is also raised. The research team said, “Recent developments in the surrounding environment, such as the construction of a waste disposal site and a golf course, have raised questions about the ecological integrity of the area.” Therefore, it seems that continuous monitoring is necessary.”

Reporter Cheon Kwon-pil [email protected]