The Dutch authorities' independent study of 26 samples of rice imported from Asian nations found average levels of seven parts per billion - a thousandth of those found in the original study - and with no samples above the EU limit of 200 parts per billion.

BBC: Study of lead levels in rice under scrutiny

Nitrous oxide, emitted into the atmosphere from natural and man-made sources, including biomass burning and fertiliser use, was 323.2 parts per billion in 2010 - 20%higher than in the pre-industrial era.

BBC: No let up in greenhouse gas rise

Levels of methane, a more potent greenhouse gas, hit a new record at 1, 813 parts per billion - more than two-and-a-half times the pre-industrial level.

BBC: Greenhouse gases hit record high

My favorite example of this environmental excess is the ground water cleanup efforts around Sacramento, California, where one aerospace company has managed to reduce the incidence of rocket-fuel ingredient perchlorate to four parts per billion.

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On the horizontal axis of each graph, we have total traffic-related air pollution exposure, increasing in parts per billion (a part here would be a drop in a billion drops) from left to right.

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In 2011, concentrations reached a new high of 1813 parts per billion (ppb), 259% higher than pre-industrial levels.

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