"The Dosage is the Poison".
And no, the dosage is unlikely to matter over the lifespan of your chickens. Not sure what, or where, you read - but EVERYTHING is dangerous. EVERY SINGLE THING.
If dosing information isn't being provided (exposure, timeframe), then its most likely alarmism intended to advance a political aim - such as reducing reliance on fossil fuels/petroleum products.
However laudible those goals may (or may not) be, I don't find them well served by misrepresentations, "errors" of ommision, and emotional appeals. Understanding that none of us are getting out alive, the only way to *effectively* manage risks are to discuss them honestly, in ways that they can be compared and weighed agaisnt one another.