Moving the black market in marijuana into the light has been a boon for state tax coffers, entrepreneurs and cannabis users, but an inconvenient fact went unaddressed in the process: Potentially dangerous chemicals are used to grow it.

That changed last fall, when a Colorado newspaper’s investigation found shelves stocked with products grown using pesticides that hadn’t been approved for cannabis farming, spurring a rush of legal, regulatory and business activity.

Since then, states have quickly drawn up regulations, companies have seen their products and methods put under the microscope — sometimes taking big hits to their businesses — and cannabis product and pesticide buyers have filed lawsuits against their manufacturers.

There is even concern that the Federal government could intervene out of concern for public health, stalling the spread of cannabis legalization and the growth it has fostered.

“If the feds wanted to crack down, we’ve given them all...