45 nanograms per liter means about 1 cup of coffee every 6000 liters of water. This doesn't sound like a lot, but 6000 liters fit in a cube of ~1.8m - and there is a lot of water out there.

The biological half-life of caffeine (how long it takes the human body to eliminate it) is not important here; it's not about humans but the sea life; nobody knows what happens to marine life in a continuous exposure to traces of caffeine and other substances.

Wait, what?

If we assume 100 mg in a cup of coffee, we can do the math by: 1.010E^(-1)/4.510E^(-8)

which is equal to 2.22*10E^(6) or 2.22M liters of water. You're only off by a factor of 370!

Since one cubic meter is 1000 liters, you're looking at a cubic body of water that is 13 meters or ~40ft on each side.

What does "x * 10E^(y)" mean?

You'll notice that the link you provided does not actually include an example of the usage you intended it to serve as a reference for. This is probably because the usage is nonstandard, which is probably why GP asked their question.

It's reasonable to assume that "x * 10E^(y)" was meant as a notation for "x * 10^(y)" = "xEy", but many mathematical notations are overloaded. I have no way of knowing whether GP was genuinely confused, or merely trying to point out the nonstandard usage, but I prefer to believe the former.

Judging from personal experience, they'll probably get a lot more work done, but make more frequent trips to the restroom.

If 1 cup of coffee contains 150 milligrams of caffeine (http://www.wolframalpha.com/input/?i=how+much+caffeine+in+1+...) that would take 3.3 million liters (not 6000).

Slight miscalculation: 6,000 litres fits in 6m3 not 1.8m3 (ref: http://www.wolframalpha.com/input/?i=6000+litres+in+meters+c...)

No, the grandparent was right. He's talking about how big a cube could contain 6000L, but you're calculating the volume of 6000L.

Simple way to visualize this: Think about the difference between a 4-foot square and 4 square feet. The former is a much bigger area.

Of course! Thanks :)

He said a cube of 1.8m, not 1.8m3 - he means 1.8m x 1.8m x 1.8m, making it easier to visualise :)

> considering the short half life of caffeine

But the thing is - it's 45 ng/l in the whole environment around sea organisms.

I don't know if that's a large dose or not, I'm just saying the half-life comment doesn't seem to apply in this case.

Right, we should presume that it's being replenished at the same rate it's decaying unless the measurement happened to be taken right after a big dump or something.

It is not unreasonable to claim that the fish actively pump the caffeine out of their system. In many ways fish are hermetically sealed.

So is caffeine actually easier to measure than coliform bacteria detection? It'd be cool if this resulted in better ocean water safety reports.

Can you give a value for the half-life of caffeine? I think you might be confusing its biological half-life with its half-life as it decomposes in water. From what I can gather, the latter isn't particularly short.

According to the linked-to article: "Caffeine ... might persist for up to 30 days in marine waters, study co-author Granek noted."

Ah. Serves me right for skimming.