|Mineral Fertilizer Use and the Environment (IFA - UNEP, 1998, 52 p.)|
Phosphate fertilizers often contain small amounts of elements which occur naturally in phosphate rock and are earned through, in the manufacturing process, to the finished product. When the final product is a relatively high-value material destined for use, for example, in the food industry the potentially harmful elements are removed, but to date economic processes for removing these elements economically in fertilizer production have not been found. Among these elements, most attention has been paid to cadmium (Cd).
There is evidence that Cd is slowly building up in some soils. This is of concern because Cd is not essential to plants or animals, and at high levels can be toxic. Sources include atmospheric deposition from industrial processes, sewage sludges, animal manures and phosphate fertilizers. In many European countries about 50% of total Cd input to agricultural soils is from airborne sources. Sewage sludges contain amounts of Cd which can vary from a few p.p.m. to several thousand p.p.m. The use in the manufacture of phosphate fertilizers of phosphate rock with a low cadmium content is one solution, but the total supply is limited. This places the emphasis on developing effective and viable cadmium removal processes and research with this objective continues.
Ultimately the solution could be a combination of the removal of Cd in the manufacturing process and farm management strategies which minimize its potential entrance into the food chain. The uptake of Cd by plants can in fact be affected by many factors, such as soil pH, moisture content, variety etc, which can be controlled by the farmer.
There is no immediate urgency because, apart from a few sites heavily polluted by industry, soil cadmium levels are generally well below critical levels. However, the existence of a medium and long-term problem is recognized by the fertilizer industry and studies and research on the subject continue.