yes, 10µM is definatly more than a human is going to get. Though its hard to tell exactly. Follow the pharmacokinetics:
Its been shown that if you smoke a joint with 35mg of THC, you get a peak blood concentration of 150µg/L. Now mind, those are weak (~3%), 1gram joints. (
1)
150µg/L is about 0.5µM. Now I think its reasonable that recreational users often take total dose of well more than that. If we say they smoked 2 of those aformentioned joints, they would get 1µM.
Now you can get a reasonable level of cell death (75%) with an hour of THC at 5µM. If you leave 1µM of THC on cells for 2 days, you get 75% cell death.(
2)
The is obviously a concentration and time dependent effect. Now while I'm NOT suggesting that if you have a brain concentration of 1µM of THC for 2 days, 75% of your brain cells would die, it does show that these doses aren't stupidly high, and they are a reason to be cautious before you say "There is no evidence that cannabinoids are neurotoxic".
As the article linked to above showed, that doses of 10mg/kg THC in rats probably causes a change in neuronal structure. Now 10mg/kg is a preety big dose. Recreational users probably get around 0.5mg/kg on a big night, and I wouldn't be surprised if I've gotten up to 1mg/kg on the odd stupid occasion. So again, these doses aren't stupidly high.
I also might add, its possible that THC accumulates in the brain to a much higher extent than plasma concentrations would indicate(
3), but then there also evidence that it doesn't (
4). Theres also evidence that THC doesn't have the same pharmacokinetics as THC/CBD mixes, where CBD allows THC to permiate into the brain to reach concentrations 3x higher than THC alone (
5). So we can't be that sure about what kinda brain concentrations people get when the smoke bud just from their plasma.