The world has to face the fact that dirt costs, and dirty cities cost big time. Today over half the world lives in urban as opposed to rural environments. This means ever more concentrated dirt.

Urban environments create their own ambiance. The dirty cities are where air pollution, water pollution, ground pollution and open landfill problems are out of control. To these less-than-glorious conditions there may be added in some cities mercury or lead poisoning, radiation poisoning or other severe risks.

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Part of dirt is garbage. In the state of New Jersey, every person throws away their own body weight every seven weeks. But garbage is complex dirt, since it may be recycled and act as a source for materials and money for the recycler. Garbage out of control is either uncollected rubbish or badly disseminated landfill. Garbage out of control leads to ground pollution, air pollution and water pollution.

The relationship between traffic pollution and garbage pollution could use some intense study worldwide since these two sources, combined with industrial waste and energy generation, comprise the core of urban dirt.

Take batteries--which the world uses in ever greater numbers. Each contains heavy metals, and their incineration can cause toxic air pollution. Coal, the mainstay of China's Great Leap Forward, is the nastiest energy source when it comes to air pollution. Choices have to be made in tradeoffs of economics and health since not every energy source can be clean and cheap.

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Despite dirt's economic and environmental costs, governments have been slow in keeping track of just how dirty the world is. The US and some European cities and countries have more data than dozens of other countries and hundreds of cities that don't really know how dirty they are at all.

To clean up, the first order of business will be to find the dirt and record it. Such agencies as the United Nations statistics division are overtaxed and, as a result, often out of date. Others, like the Blacksmith Institute, an organization that does global studies of city pollution, and the American Lung Association, appear to be making some headway.

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"The good news is we have known technologies for eliminating a lot of this pollution," says Richard Fuller, founder and director of the Blacksmith Institute, which in addition to its global studies of the most polluted cities also makes recommendations for their cleanup.

The Blacksmith Institute's 2006 report states that, "living in a town with serious pollution is like living under a death sentence. If the damage does not come from the immediate poisoning, then cancers, lung infections, mental retardation are likely the outcomes."

Of the 10 most polluted cities according to the Blacksmith Institute report, three are in the Russian Federation. The Ukraine's Chernobyl remains at the top of the list 20 years after the horrendous nuclear accident there.

When the focus is US cities, the American Lung Association's latest report for 2005 states that 55per cent of Americans live in areas with unhealthy levels of ozone or particle pollution. It appears that US citizens do not have to visit Russia or China to get a lungful of bad air.

Some hope that the EPA's new, stricter emissions standards--put in place in December 2006 as outlined in the Clean Air Interstate Rule--will make a difference, at least in the US.