We wrote down a list of house rules and one of them we invented (in the being polite and respectful of others category) is that people get to express their feelings twice and then if no one else wants to talk about it the issue needs to be dropped for the moment. Us adults try to remember to ask him later or the next day if he wants to talk about X that he was upset about earlier, bring it back up once he's well fed and exercised and all that. We don't always remind DS of the rule but when he has said a couple times in a row "are you sure this apple doesn't have chemicals on it?" we remind him of the two times rule and ask him to move on to something else. If he doesn't he gets a time out.
I hope this response happened after someone had already addressed the question, because it's a good one. What with all the talk about organics these days, it's very likely he has been exposed to information about the pesticides and other treatments our produce is subjected to.
If the child is already worried about something, legitimately or otherwise, it can only increase their anxiety if nobody in a position of power is even listening. The internal dialog starts leading to questions like these: "Does Mommy know about pesticides? What other dangers doesn't Mommy know about? Where can I turn to learn about them if Mommy doesn't?"
All of which can be headed off with, "Yes, I washed it."
