Chlormequat in food and urine from adults in the United States from 2017 to 2023 (opens in new tab)

They funded a state-of-the-art ecotoxicology research lab next to where I live, that was going to do pioneering work in the field, within a university-industry cooperation framework. As coincidence would have it, once the first results started coming in, there was a lot less interest from the industry in cooperation. The lab now runs at a fraction of its capacity.

But in the case of interaction between substance A and B from different vendors, who's responsible?

Here’s a source that doesn’t fit your buddy’s description…

Along the central coast of California, conventional strawberry growers apply chemicals like methyl bromide, an internationally banned substance that is no longer being manufactured, but is stockpiled for exemptions to the ban, which these growers exploit. Alternatively they have been experimenting with methyl iodide and other hardcore synthetic chemicals. They hire undocumented laborers to apply them.

Organic strawberry growers, on the other hand, use crop rotation of a brassica crop as a bio-fumigant, and they grow rows of alfalfa as a trap crop where pest infestations can be literally vacuumed up with a tractor implement.

In this case, there is a huge difference.

It is true that the National Organic Program is a joke, since they let the board get taken over by corporate big ag long ago. That doesn’t mean “it just makes people feel good and there is virtually zero difference”. In some cases it does, but to paint the whole thing as such is denying the larger reality.

But at least naively, these all seem like the least concern: Fairly well behaved nutrient stuff like phosphate rock, nitrates, sulfur, etc.; while all the concerning compounds are synthetic or semisynthetic (besides arsenic lead etc. which have been out of use for a long time right?!)

AFAIK there is no natural source for most of the concerning pesticides/herbicides like glyphosate, chlormequat, paraquat, aminopyralid, maybe synthetic/semisynthetic pyrethrenoids etc. while the much smaller list of "natural" pestidides (pyrethrum, any others?) aren't concerning because they degrade quickly etc.

But I'm also assuming here that "approved for organic use" means "the substance can be trivially extracted from natural sources" which might not be true

But locally I've visited some of the small farms we buy produce from, and they use very minimal sprays, or none at all and instead plant companion plants that attract the pests to them instead of the main crop.