Since the cannabis plant is known to scavenge cadmium and lead from the soil. Is there a way to avoid our risk of accumulating these poisons in our blood.
With how prevalent heavy metals and other toxins are in our food supply, I think your best off focusing on improving your nutrition, and bolstering your detoxification system. There are a number of good herbs and supplements to take in that regard. Still probably a good idea not to use amendments or nutrients with higher levels of these toxins, or to harvest leaves from around a shooting range.
Testing the soil one uses to cultivate cannabis would be the best way. No lead/cadmium in the grow medium or nutrients = none in the finished product.
The only way to be sure that there isn't a bunch of crap and it is to grow in oneself and test it regularly. Unfortunately, not everybody has the capacity to do that.