Just How Much is a Part Per Million?
In these days of heightened environmental and health consciousness, most people pay close attention when a report discusses dangerous – or even potentially dangerous – substances. The possible danger in any substance is, however, relative to the amount and intensity of exposure.
Worker exposure to certain chemicals is limited to a few parts per million, while regulations reduce an allowable industrial waste discharge to one part per billion, and pesticide residues are found in drinking water in the low parts per trillion.
But just how much is “one part per million” – or billion, or trillion? Most people probably have difficulty comprehending such infinitesimal amounts. The following table helps put the figures in perspective:
| Trace Concentration Units |
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| UNIT | 1 Part Per Million | 1 Part Per Billion | 1 Part Per Trillion |
| Length | 1 inch/16 miles | 1 inch/16,000 miles | 1 inch/16 million miles. 6 inch step on trip to the sun. |
| Time | 1 minute/2 years | 1 second/32 years | 1 sec/320 centuries |
| Money | 1 cent/$10,000 | 1 cent/$10 million | 1 cent/$10 billion |
| Weight | 1 oz salt/32 tons chips | 1 pinch salt/10 tons chips | 1 pinch salt/10,000 tons chips |
| Volume | 1 drop vermouth/ 80 fifths gin |
1 drop vermouth/ 500 barrels gin |
1 drop vermouth/ 500,000 barrels gin |
| Area | 1 sq ft/23 acres | 1 sq ft/36 sq miles | 1 sq inch/250 sq mi 1 sq ft in Indiana |
| Action | 1 bogey/3,500 golf tournaments | 1 bogey/3.5 million golf tournaments | 1 bogey/3.5 billion golf tournaments |
| Quality | 1 bad apple/ 2,000 barrels |
1 bad apple/ 2 million barrels |
1 bad apple/ 2 billion barrels |
| Rate | 1 dented fender/ 10 car lifetimes |
1 dented fender/ 10,000 car lifetimes | 1 dented fender/ 10 million car lifetimes |