Cadmium in inorganic fertilizers

Resumen

The addition of Cadmium to cultivated land is due to rainfall and aerial depositions, inorganic fertilizers, livestock waste and urban waste. The mean cadmium content in the earth's crust is about 0.11 mg kg-1, and it can be found in raw materials used for phosphatic fertilizers and liming materials production. The Cadmium content in phosphate rocks used as raw materials for phosphatic fertilizer production varies with the geographic origin and the type of rock: 0.15-5 mg Cd kg rock-1 in rocks of volcanic origin and 5-300 mg Cd kg rock-1, in sedimentary rocks. The amount of Cd can vary considerably in a deposit. The phosphate rocks used in the European Community and Spain are either of volcanic or sedimentary origin. The European Community imports 18.1 x 106 t of phosphate rock; this amount is equivalent to 470 t of cadmium. In fertilizer industrial processes, some 60-80% of the cadmium in phosphate rocks becomes part of the fertilizer; the amount depends on the type of rock and the P2O5 content of the fertilizer. Typical values for the cadmium content in phosphatic fertilizers are between 3 and 110 mg Cd kg P2O5-1. The application of a mean dose of 50 kg P2O5 ha-1 year-1 contributes from 0.15 to 5.5 g of Cd ha-1 year-1 to the soil. The consumption of phosphatic fertilizers in Spain was 531.7 1 × 103 t P2O5 year-1 in 1989 and 343.3 1 x 103 t P2O5 year-1 in 1993.