As San Franciscans load up on potassium iodide pills against drifting fallout from the Japanese nuclear reactor catastrophe -- unnecessarily, health authorities insist -- the April issue of Discover calls attention to a more serious menace: mercury and other pollutants from Chinese manufacturing and power generation:

Prevailing winds across the Pacific are pushing thousands of tons of other contaminants--including mercury, sulfates, ozone, black carbon, and desert dust--over the ocean each year. Some of this atmospheric junk settles into the cold waters of the North Pacific, but much of it eventually merges 
with the global air pollution pool that circumnavigates the planet.

These contaminants are implicated in a long list of health problems, including neurodegenerative disease, cancer, emphysema, and perhaps even pandemics like avian flu. And when wind and weather conditions are right, they reach North America within days. Dust, ozone, and carbon can accumulate in valleys and basins, and mercury can be pulled to earth through atmospheric sinks that deposit it across large swaths of land.

Citing the University of Washington atmospheric scientist Dan Jaffe and the Woodrow Wilson Center program director Jennifer Turner, the author, David Kirby, points to two worrying trends. First, while China is taking positive environmental steps, the momentum of its growth threatens to swamp them:

350 million people, equivalent to the entire U.S. population, will be moving to its cities over the next 10 years. China now emits more mercury than the United States, India, and Europe combined. "What's different about China is the scale and speed of pollution and environmental degradation," Turner says. "It's like nothing the world has ever seen."

Second, America contributes to and receives a global pool of mercury and other pollutants:

The EPA has estimated that just one-quarter of U.S. mercury emissions from coal-burning power plants are deposited within the contiguous U.S. The remainder enters the global cycle. Conversely, current estimates are that less than half of all mercury deposition within the United States comes from American sources.

We naturally focus on catastrophic risks like nuclear meltdowns. But we should also be aware that chronic ones, not the fault of a single nation but the consequences of the global economy, may in the long run be even more serious.