Heavy Metals Content of Commercial Inorganic Fertilizers Used in the Kingdom of Saudi Arabia

In recent years much concern has been given to toxic heavy metals, which enter the human food chain. Application of inorganic fertilizers is considered one of the potential routes of such entry, in this work 74 samples of commercial fertilizers marketed in the Kingdom of Saudi Arabia were analyzed for their heavy metal concentrations. Fertilizer samples included 20 samples of phosphatic fertilizers [monoammonium phosphate (MAP), diammonium phosphate (DAP) and triple superphosphate (TSP)], 11 samples of liquid fertilizers. 31 samples of water-soluble multiple nutrient fertilizers (WSMF) and 12 samples of solid multiple nutrient fertilizers (SMNF). Concentrations of heavy metals varied according to the type of fertilizer and the tested metal; Cr levels were the highest and Co was the lowest. Results revealed that Cd ranged from < l to 36.8 mg.kg-1, with a median of 33.2 mg.kg-1 for the phosphatic fertilizers, 9.5 mg.kg-1 for the liquid fertilizers, 19.7 for the SMNF, and 2.9 mg.kg-1 for the WSMF. The median values of Pb, Ni, Co and Cr in the phosphatic fertilizers were 14.3, 72.1, 1 1.8 and 249.3 mg.kg-1, respectively. However, the corresponding median values of these elements, in the liquid fertilizers, were 9.9, 15.6, 11.2 and 64.0 mg.kg-1 and 15.3, 43.0, 12.5 and 170.7 mg.kg-1 in the SMNF. The median contents of three heavy metals in the WSMF samples were 9.8 mg.kg-1 for Pb, 5.6 mg.kg-1 for Co. and 7.4 mg.kg-1 for Ni. The Cd. Co. Cr and Ni concentrations were lower than the tolerance limits for heavy metal addition (Cd 100 mg.kg-1, Cr, 100 mg.kg-1 and Ni, 50 mg.kg-1), and they were in a range similar to those found internationally. It is estimated that the application of an average dose of 80 kg P ha-1 annually in Saudi Arabia, contributes 13 g of Cd ha-1 to the soil.