Mercury is Now Traceable

The heavy metal can be fingerprinted to find its source

The global emission of mercury—a heavy metal notorious for its toxicity—is on the rise. Although the metal occurs naturally in stable form, some 2000 tonnes of it is released annually into the atmosphere from coal-based power plants, incinerators and chloro-alkali plants. Various options such as a global mercury convention, inclusion in the Stockholm Convention on Persistent Organic Pollutants and voluntary partnerships, are being discussed to phase it out, but for that the source of the pollution needs to be pinpointed first. Researchers from the department of Geological Sciences and Air Quality Laboratory at the University of Michigan have developed a fingerprint technique to find out how much mercury is released by different sources.

The researchers relied on a separation process called isotopic fractionation for the fingerprint method, which took eight years to develop. Isotopes are atoms of the same element having same number of protons but different number of neutrons which gives each isotope a different mass number.

Fractionation is of two kinds—mass dependent and mass independent. Mass dependent fractionation depends on the difference in the isotopic masses. In mass independent fractionation, isotopes react to form new compounds, not on the basis of their mass, but on whether their mass numbers are odd or even. The researchers combined both mass dependent and mass independent fractionation using the seven isotopes of mercury to make the fingerprint.

The group tested the technique on 30 coal deposits from the US, China and Russia-Kazakhstan. They studied the isotopic composition of mercury in soil from different parts of North America. "The results show significant differences not only between mercury from coal and, say, metallic forms of mercury used in industries, but also between different coal deposits," Joel Blum, one of the authors of the study published online in the journal Environmental Science and Technology on October 8, 2008, said.

A UN report found that mercury travels through earth at a far greater rate than was previously known. Once deposited on land and water, micro-organisms convert it into methyl-mercury. A highly toxic compound, it enters the food chain via fish eaten by animals which are then eaten by humans. In animals, methyl-mercury can hamper reproduction, overall development and may even lead to death.

In humans, methyl-mercury interferes with the working of the central nervous system, the heart and the immune system. The development of mental faculties in young children can also be jeopardized.


Down to Earth December, 2008