11.   Olson said the standard should be three parts per billion, which is probably the lowest concentration that towns and cities can realistically achieve.

12.   Rieders had cited an EPA study that concluded that EDTA, when consumed in foods, would show up in the body as only a few parts per billion.

13.   Since ozone is so diffuse -- it is measured in parts per billion -- it is hard to find before it can be destroyed.

14.   Some faucets had been shown to add hundreds of parts per billion to water, and consumers had no way to know.

15.   The antennas detected combustion derivatives in concentrations as low as a few parts per billion, the researchers reported.

16.   The analysis showed two to five parts per billion of HMX.

17.   The EPA has a regulatory limit of five parts per billion for TCE.

18.   The practice is not outlawed in Houston on the theory that treatment plants bring perc concentration below five parts per billion, or the accepted level.

19.   The residents here do not think in terms of excess cancer risks, or parts per billion.

20.   The safety limit for drinking water is five parts per billion.