I think it was the cleric and economist Robert Malthus who developed a theory that large populations of organisms would slowly make their own environment more “toxic” and no longer sustain themselves. In some ways what he observed is true. We are living in an environment that is becoming more “toxic” as we grow our own food. Some of these “toxicities” come from industrial processes and some of them from our own efforts.
Fertilizers and Toxicity
Our worlds are becoming more and more toxic. A few states in the US have posted the level of toxicity in fertilizers for home gardens. There has been lots of research on this topic. Brochures exist on heavy metals and gardens. And here. These toxicities are below what the US EPA considers “safe” for human health but they do exist.
Another problem with additions to garden soils are the levels of pharmaceuticals used when producing gardens soils and compost.
This is from the Washington State Department of Agriculture website