Dead Sea generates deadly toxin

Scientists have discovered that the air above the Dead Sea in Israel is laden with oxidized mercury, showing some of the highest levels of the oxidized form of the dangerous neurotoxin ever observed outside the polar regions, according to the United States National Science Foundation.

The results throw light on how mercury may get into the global fish supply.

The foundation's report, compiled by researchers from the Desert Research Institute in Nevada and Hebrew University in Israel, appears in the Nov. 28 online publication of Nature Geoscience.

The Hebrew name for the Dead Sea translates Sea of Salt. It is one of the world's saltiest bodies of water, registering over 33 percent salinity. That heavy concentration of salt, scientists say, is the key to the oxidized mercury above the water.

Mercury is highly toxic and can severely sicken, even kill, people who are exposed to it in certain concentrations.

Mercury exists in the atmosphere in both an elemental and an oxidized form, and can be converted from the elemental to the oxidized form in the atmosphere in a process called atmospheric mercury depletion. Until the Dead Sea discoveries, mercury depletion was believed to occur only in polar atmospheres.

Low temperatures were thought to assist the depletion process and high temperatures to impede it. But scientists are now saying that the bromine in the salt of the Dead Sea is apparently also a driver of the atmospheric mercury depletion process.

We've found near-complete depletion of elemental mercury--and formation of some of the highest oxidized mercury levels ever seen--above the Dead Sea, a place where temperatures reach 45 degrees Celsius, said David Obrist, a scientist on the Dead Sea project.

Obrist said high levels of oxidized mercury are a concern because, in that form, mercury is quickly deposited in the environment - that is, into ecosystems and food chains.

These levels are of major concern to humans, especially in the consumption of mercury-laden fish, he said.

The Dead Sea research indicates that bromine levels observed above oceans may also be high enough to initiate mercury oxidation.

We discovered that bromine can oxidize mercury in the mid-latitude atmosphere, far from the poles, Obrist said. That points to an important role of bromine-induced mercury oxidation in mercury deposition over the world's oceans.

Fish caught in oceans are the main source of mercury intake in the U.S. population, the NSF said.