Well, you have to put things in perspective. This was a very large individual, I think he was about 300 pounds. So for concentration of 12 nanograms in a large person, that shows it was a large dose.
In a small person, say like 100 pounds to get to 12 nanograms wouldn't take a lot. A single joint could easily do that. But when you talk about a larger body mass, just like drinking alcohol, larger persons can drink more alcohol because they have the receptacle to hold it.