While some levels of mercury are naturally present in the atmosphere, human activity has increased the number of mercury atoms in the atmosphere by a factor of five over the last century, according to research presented this week at the fall meeting of the American Geophysical Union.
Many human activities have raised concentrations of the pollutant, including coal-fired power plants, mining operations and agriculture, among others.
The concentrations of mercury in fog are 20 times higher than they are in rain, and the researchers estimate that plants and animals from foggy regions may have 10 times more mercury than those from other areas.
The concentrations of mercury in fog — on the order of 10 parts per trillion — are not an immediate health risk to organisms — including humans, said Peter Weiss-Penzias, a researcher of microbiology and environmental toxicology at the University of California, Santa Cruz, and one of the scientists involved with the research.
But mercury can accumulate in tissue over time, and marine fog can provide a constant source of the pollutant. That means there could be long-term ecological effects, or effects on food supplies. Large fish, such as tuna and tilefish, have long been known to have perilously high levels of mercury, for example.