The problem with lead is, its in everything that comes from the ocean. even Azomite, which is another soil amendment for minerals, has all those nasty guys.
what you need to consider is how much is there? micro doses of lead and arsenic may already be in your soil, or even in natural fertilizers. whats important is how much is there already.
plants do not absorb or accumulate lead. However, in soils testing high in lead, it is possible for some lead to be taken up. Studies have shown that lead does not readily accumulate in the fruiting parts of vegetable and fruit crops (e.g., corn, beans, squash, tomatoes, strawberries, apples). Higher concentrations are more likely to be found in leafy vegetables (e.g., lettuce) and on the surface of root crops (e.g., carrots)
http://www.extension.umn.edu/garden/yard-garden/soils/lead-in-home-garden/There are many sources of natural fertilizers, one you may consider is worm compost, and teas made from them. instead of Kelp. you can usually buy the stuff from those that make it, or make your own.
Not sure of your set up, just a few trees, or an orchard. but plain old mulching with leaves and chopped up branches and stuff. after all that's how it works in forests. .
Personally I will use regular fertilizers if one is marked Organic, then I will get that one, what I stay away from completely is herbicides, and pesticides. I may use Neem or some other natural stuff. and bugs have really not been a problem for me.
As for previous comment that "Organic and Natural is a Racket" this is what some people
choose to believe due to corporate misinformation on channels like Fox News. If you think its easy to put out a product and label it Organic you will see how difficult it is, and how many inspections and requirements are needed. this is the main reason organic stuff cost more.
As for stuff that is not Organic, there is NO TESTING whatsoever, this is where you can really say that you do not know whats in it. remember DDT? they said that was safe also. Organic and Natural are cutting into corporate profits, so you can expect them to say Organic is a racket.
We have the power to decide what we put in our bodies. and if your growing your own food, you have the best way to insure eating stuff that is safe.
What I do not like about the "Organic" label is that its a business, they make it too expensive for mom and pop operations to use it, you cannot just stick the "Organic" label on you package, no matter how safe or natural it is.
This is why a new movement to label "Natural Grown" is going forward. this works on a different system, and is even more strict in what can and cannot be used. this is specifically for small farms and Mom and Pop operations.
https://www.naturallygrown.org/