Last month, The Washington Post reported that President George W. Bush had personally intervened to weaken new regulations to control smog just as they were about to be announced by the Environmental Protection Agency (EPA). In response, advocates of tighter standards predictably charged that the president had overturned a scientific judgement. Carol Browner, who headed the EPA under President Bill Clinton, put the matter starkly, telling the Post that the Clean Air Act creates "a moral and ethical commitment that we're going to let the science tell us what to do'.

The introduction of chlorine at the end of the treatment line for residual protection purposes, widespread use of ozone at various stages of treatment and the development of new ozone generators are the latest technical trends that have led to numerous changes in the water disinfection processes.

Destruction of the Earth's ozone shield due to the release of hydrogen sulphide and methane has been suggested as a cause of mass extinctions during periods of ocean anoxia over the past two billion years. This mechanism does not explain the end-Permian mass extinction, according to simulations with a two-dimensional atmospheric chemistry-transport model, which show that the ozone shield remains intact even with massive releases of hydrogen sulphide and methane.