This will depend on your jurisdiction. For example, in Arizona, any measurable amount of a drug or it metabolites is sufficient evidence. Here in Washington, where I practice, we do not have "per se" limits for drugs other than alcohol. In general, the relevant scientific community believes that impairment by THC occurs somewhere between 5 and 10 ng. What your son's test is showing is that there was only 1 ng of active THC in his blood at the time of the draw. The 9 ng of Carboxy THC, which is metabolized THC will not affect his ability to drive a car. As a mom, it should also put you at least a little at ease, that having only 9 ng of Carboxy in his blood shows that he is not a fairly frequent user of marijuana. The best advice I can give you is to get a competent DUI lawyer from your jurisdiction on board ASAP.
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