Personally, I share your concern for wildlife, but in my totally uneducated opinion, I can't see how fishing tackle could make that big of an impact. I mean, how many fish swallow split-shot? If it's a lost lure with lead in it, I'd think ingesting the lure would be the least of a raptor's worries.

I know raptors WILL eat carrion if available, but don't they prefer to catch their prey alive? (I'm talking eagles, hawks, owls, etc) I believe a Vulture is also considered a raptor, but all they eat is carrion. Why aren't they dying off from shot/injured/lost prey?

I'm probably much too ignorant of the subject to comment, but with my limited knowledge and trying to think it through using common sense, I'd have to lean more toward chemicals than lead. Who knows?