Pollution can take many forms.
Air, water, solid waste - most agree that pollution is harmful for people and other life on Earth. But more controversial is how to best prevent it - and clean it up.
The Greek opposition and Athens' local mayors have accused the government of allowing an oil spill to spread unchecked. But the government says everything is under control and all will be "forgotten in a few days."
Mongolia's huge deposits of copper, ore, uranium and gold, has made mining one of the biggest contributors to the country's economy today. While some Mongolians welcome the additional jobs, others fear that the growth of the mining sector could destroy their health and their environment. Now, small-scale gold miners are trying to strike a balance.
California's Silicon Valley is a mecca for young entrepreneurs turning cutting-edge lifestyle concepts into big money. At least, that's the cliché. In reality, San Francisco's techies are also working on more serious issues. Young entrepreneurs Vivian Qu and Felix Fischer have developed a nanofilter to clean water and air, which they say could improve the lives of millions.
Discarded car tires littering the streets of Senegal's capital Dakar often become breeding grounds for disease-spreading mosquitoes. If they end up in landfills, their toxic components can break down and seep into waterways. One young entrepreneur, sick of seeing the black tubes polluting her country, decided to give them new life as shoe soles or synthetic turf in playgrounds and courtyards.
Paris is carving out a reputation for itself as the most anti-car city in the world. Its mayor has banned the most polluting private cars from the city, turned a riverside highway into a leisure zone, and begun an ambitious program of motor-traffic limitation.