Our local water department sent out a big full color brochure this week talking about what they were doing and what all was involved in delivering water.
One of the things they are looking at is detecting chemicals with a presence in the range of parts per trillion.
Seems like I heard something once that said there were about a trillion atoms in a cell in a human body, a trillion cells in a human body, and a trillion stars in the galaxy. It may not have been a trillion, it may have been more or less, but the idea was these numbers were all on the same order of magnitude.
The brochure gave some examples of what one part per trillion would look like, but I didn't particularly like any of them, so I worked up a little spreadsheet to try and generate my own example. One part per trillion is like one teaspoon of your mystery substance in square field two and a half miles on a side flooded with water to a depth of one foot. I suppose the question now is how many molecules are in that teaspoon?
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We just got the city's water report card for 2007, and everything is within spec - though the tightest spec seems to be for arsenic, which is supposed to be less than 10 parts per billion. (Of the three water supplies, the one with the highest arsenic level pulled a 1.06.)
If there are trillions being talked about, I didn't hear about them.
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