I have cleared woodland by apiary and exposed Alder Buckthorn which reveals itself online as toxic. It was smothered in honey bees in April and May , now small glossy black berries. Wanted to take honey to village show; how do I know whether the honey is safe ?
They forage over a wide range of plants many are regarded toxic( e.g. laurel contains cyanide)plus whatever nasty chemicals humans leave exposed.
Unless you think they have foraged exclusively on a particular plant (highly unlikely unless you move your hives to plantation or moorland) then don't give it any more thought