The metal osmium is increasingly prevalent in rain and snow around the world, according to a study led by earth sciences professor Mukul Sharma. Sharma and his team found that the increased osmium levels are likely due to the use of platinum in industrial applications and automobile catalytic converters, which release the metal as a by-product as the platinum is processed. The findings were published in the April 20 issue of the Proceedings of the National Academy of Sciences.
The researchers discovered trace levels of osmium in samples they collected from rain and snow in North America, Europe, Asia and Antarctica, as well as from the waters of the North Atlantic, Pacific, Indian and Antarctic Oceans. The team discovered 0.25 to 23 femtograms of the metal in every gram of water, he said.
Osmium is released naturally by "black smokers," volcanic vents found on the sea floor, as well as some meteorites, Sharma said. The team determined that the osmium found in the water sources, however, is man made, since cosmic dust produces an insignificant amount of osmium and volcanoes produce a different isotope of the element than that identified, Sharma said.
Sharma suggested that "scrubbers" could be installed at production facilities that generate osmium to extract waste like sulphur dioxide and metal oxides in order to minimize environmental effects, but explained that these devices are not required by law in South Africa or Russia, where 95 percent of all the world's platinum is refined. Because these "scrubbers" are expensive, Sharma said that without government regulation it is unlikely they will be installed.
"Neither South Africa nor Russia has implemented environmental laws regulating this, but if steps are taken to minimize these emissions, the incidence of osmium will certainly subside," Sharma said in a College press release. "It's surprising that we are seeing this measurable increase in osmium on a global scale, and we can virtually blame it on one thing -- our insatiable demand for platinum-based catalytic converters."
Sharma said it was unclear whether increased levels of osmium will have any effect on humans or other organisms. If there are effects, the low levels of osmium compared to other more prevalent toxins in the environment makes it difficult to identify them, he added.
"You don't want to be scared of this problem, it is just an interesting problem affecting the osmium chemistry in the rivers and oceans," he said.
Sharma said he had been researching osmium isotopes in the environment for a number of years, but chose to look at osmium levels in rain and snow after teaching a geochemistry class at Dartmouth.
"I took the class to the Connecticut River to collect and analyze samples of the water for osmium," he said. "And the results didn't jive with what I thought they should be, and my [teaching assistant] for that class was Cynthia Chen [Gr '08] who proposed that maybe the osmium levels were due to precipitation. It had rained extensively for two or three days."
Sharma worked with Chen and Peter Sedwick, a research scientist at Old Dominion University.
Sharma said he will continue to research osmium pollution in precipitation. He has obtained a 200-year-old piece of ice core, and plans to determine how osmium levels have changed over time, focusing on any potential increase in osmium after the introduction of catalytic converters.
