This is pointed out in the article: "“The widespread distribution of cadmium contamination comes from both natural and anthropogenic sources,”" "“Geochemicall

This is pointed out in the article: "“The widespread distribution of cadmium contamination comes from both natural and anthropogenic sources,”" "“Geochemically, certain parent rock materials [substrate below the ground], such as black shales, contain high levels of cadmium, leading to elevated concentrations in the soil due to weathering.”" "However, the study does not assign blame to either natural or human causes."