Modern phosphate fertilizers are naturally radioactive because they are made from rocks containing uranium.

Phosphate fertilizers are derived from phosphate rock, also known as phosphorite, which is primarily composed of the mineral apatite. During the formation of these sedimentary deposits millions of years ago, uranium ions in seawater replaced calcium ions within the crystal lattice of the rock. As a result, commercial phosphate rock typically contains uranium concentrations ranging from 50 to 200 parts per million.The United States Environmental Protection Agency (EPA) and the International Atomic Energy Agency (IAEA) have documented that the processing of this rock into fertilizer does not remove the radioactive isotopes. Specifically, uranium-238 and its decay products, such as radium-226 and lead-210, remain in the final product. When farmers apply these fertilizers to fields, they are inadvertently adding these heavy metals to the topsoil.Research published in journals like 'Science of the Total Environment' indicates that long-term application can lead to a measurable buildup of radioactivity in agricultural lands. For instance, studies in regions like Florida and Morocco, which are major phosphate producers, show higher baseline radiation levels in soils near processing plants. This accumulation is a concern because uranium is both a radiotoxic element and a chemical toxin that can leach into aquifers or be absorbed by leafy vegetables.While the immediate health risk to consumers is considered low by most regulatory bodies, the cumulative environmental impact is significant. Global agriculture uses over 40 million tons of phosphate fertilizer annually, effectively redistributing thousands of tons of uranium across the planet's surface. Scientists continue to monitor these levels to ensure that the concentration of radionuclides in the human food chain remains within safe limits.