Before revision: Protactinium is naturally present in soil, rock, surface water, groundwater, plants and animals in very low concentrations (on the order of 1 ppt or 0.1 picocuries (pCi)/g).
After revision: per gramProtactinium is naturally present in soil, rock, surface water, groundwater, plants and animals in very low concentrations (on the order of 1 ppt or 0.1 picocuries (pCi)/g).