It’s probably either “normal” (for the locale where the primary ingredients are sourced) background levels of lead or elevated to some extent being near/downwind from a local freeway with a decent traffic load dating back to the era of Tetra Ethyl Lead (TEL) in gasoline. Once the amount in a plant or animal begins to bioaccumulate at a rate higher than the rate it is flushed from the given system it begins to increase.
The key take would be does a given source provide enough ingestible and bioavailable lead to begin accumulating? If you ingest a pellet from that shot infested turkey you’re probably not going to notice it in a subsequent blood test from that one time occurance because the bioavailability of it is going to be predominantly associated with the oxidized surface of the pellet and a very small amount amenable to dissolving during it’s brief exposure to stomach acid. The bulk of it (say ~99.9XX%) is just going to get pooped out.
A large percentage of my geo-career has been spent sampling for hazardous materials in stuff (mostly soils and water) and a LOT of that was for lead as aerially deposited lead alongside roadways. I have worked with soil that has had thousands of parts per million (ppm) lead in it and never “popped” high on my annual physical blood tests.
There is a rate at which you process it out, and you have to ingest at a higher rate to begin the process of accumulating it. I knew a couple guys back in my early days who related to me their transporting of “bad batch” TEL for dumping (thank god it reacts relatively fast to insoluble) and they would exceed the limits fairly quickly and be “pulled off that detail” for several months to get their levels back below limits and they wore hefty protective gear (suit and full face respirator). TEL is horrid stuff, there was a big stink over it’s original creation and use that got mostly relegated to the memory hole, but it killed the hell out of the original workers with it, and a large number of competent people raised hell that it would cause lead poisoning everywhere (and they were right). Industry and politicians you know... TEL is hatefully mobile too, if you spilled it on yourself you had instant lead poisoning. I have called BS on samples I have submitted coming back unusually high for lead and the laboratory upon investigation discovered that my samples had (along with others) been stored in a refrigerator along with samples submitted that contained TEL which cross contaminated everything.
Oh, and lead “fouled” engines too, leading to Ethylene Dibromide and 1,2 Dichloroethane (EDB, DCA) being added to gas to get the lead to form halides on combustion and be exhausted out instead of dropping out as oxides on components. They weren’t happy chemicals either...
Good to hear from someone with direct experience in testing/monitoring/etc for nasty stuff. I got into the generals area a long time ago making sure submariners had clean air inside the hull. It was entertaining to hear the sailors grump about how the Outside air stunk after a months-long tour inside.
But my main peeve is food makers that pass junk along to us. If they want to claim the krap in their food comes from the cars driving by their mill they ought to say so.