Evan Mascagni '11, a Research Assistant at the California Anti-SLAPP Project (CASP), published an article at PolicyMic on pesticide contamination of cannabis.
Mascagni writes, "While it is possible to at the least wash off non-organic fruits and
vegetables to remove some pesticide residue before consumption, there is
no way to wash the pesticides off a cannabis flower or bud. As a
result, when marijuana is inhaled or ingested for the effects of its
natural chemical compound, tetrahydrocannabinol (THC), additional
unknown chemical residues enter one’s system as well."