The US has thresholds at the federal and state levels for domestic food contamination. The federal limits tend to be lower to allow states to decide what they consider safe, not because they're goals, which also implies they're regularly sampled.

FDA and USDA are occasionally the testers (like for PFAS) and always the arbiters, but it's the individual members of the self-regulated farming and import organizations who are responsible for getting the testing, and only the high level aggregate reports are published, I believe. Look up lab testing services - it's a big business, and they're required.

You're also asking a question that you probably aren't aware of the scale of. US ag is huge and time sensitive. It's a miracle it works, and its systems run on the labor of millions. By the time that processed seasonal Starbucks muffin gets sold, the various parts of it have travelled farther than most Americans will in their entire lives.