Asian Scientist (May 25, 2022)– In the early 1950s, some residents in Japan’s Minamata city noticed that their domestic cats were behaving weirdly— they would shake their body violently while producing annoying noises, and then die. A couple of years later, even local residents began to experience something similar with additional symptoms such as numbness in their hands and loss of vision and hearing. In 1959, scientists would discover the culprit: methylmercury.
The compound is one of the poisonous forms of mercury, which retains its toxicity in the environment for years even after its first release. In recent research, South Korean scientists at the Gwangju Institute of Science and Technology (GIST) have identified two main sources contributing to the accumulation of methylmercury in the country’s river bodies: surface runoff and sediment residue. The researchers also suggest that understanding methylmercury’s physiology and pattern of accumulation is critical to maintaining a healthy ecosystem. The study was published in the journal of Chemosphere.
In addition to many natural sources like volcanoes and geothermal springs, anthropogenic activities such as coal burning, gold mining, and chlor-alkali manufacturing plants significantly add to the amount of mercury released in the environment. Asia holds the second record after North America for causing highest mercury poisoning in the world.
When Eunji Jung, a Ph.D. researcher at GIST, learnt about the dangers of methylmercury to unborn children, she couldn’t stop herself from investigating the problem further. “I felt a strong sense of responsibility as a female scientist to [carry out] this research,” said Jung, the first author of the study.
Jung and her team investigated mercury levels in five artificial lakes in South Korea between 2016 and 2020. “We looked at total mercury and methylmercury concentrations in water, sediment, as well as common fish species,” explains Seunghee Han, an environmental scientist at the GIST, and senior author of the study. Han explained that they also used data from the national water quality monitoring network to figure out for how long the water stays in the reservoir lakes and the changes in water level in the reservoir, which in turn affect the transport and concentration of mercury in these lakes.
The analysis revealed two key conclusions. First, soil in the catchment areas and its runoff was the fundamental cause of the accumulation of methylmercury in the reservoirs. Second, the reservoirs where water was stored for longer, the silt and sediments contributed to methylmercury accumulation. Fish living in these reservoirs also had high mercury concentrations in their body. Eating contaminated fish and shellfish is the biggest source of methylmercury buildup in the human body.
Source: Gwangju Institute of Science and Technology; Image: Unsplash