What little reliable information can be gleaned from the mass of estimates, best guesses and informed speculation paints a troubling picture. According to a pioneering 2007 study by James J. Corbett and others published in Environmental Science & Technology, shipping-related emissions of particulate matter contribute to approximately 60,000 premature cardiopulmonary and lung cancer deaths each year, mostly in coastal regions along major trade routes. In a 2007 rulemaking announcement, the EPA published estimates that worldwide shipping in 2001 emitted more than 54,000 tons of PM2.5, as much as 117 power plants, and approximately 745,000 tons of NOx, equivalent to about 800 million modern automobiles. That number is not a typo ─ the global fleet of approximately 90,000 ships really is that dirty.

http://www.dcbureau.org/20090831252/NRNS-Stories/no-safe-harbor-the-shipping-industrys-pollution-problem-part-i-low-hanging-fruit.html