METAL CONTENTS OF FERTILIZERS MARKETED IN IOWA

Contamination of soils with trace metals has become an issue of major concern in recent years. One potential source of metals is commercial fertilizers. In this work, we analyzed 97 samples of solid commercial fertilizers sold in Iowa for 13 trace metals (Ba, Cd, Co, Cr, Cs, Cu, Li, Mn, Ni, Pb, Rb, Sr, and Zn) and six non-trace metals (Al, Ca, Fe, K, Mg, and Na). Fertilizers included 24 samples of triple superphospha te (TSP), 23 of monoammonium phosphate (MAP), 25 of diammonium phospha te (DAP), and 25 samples of muriate of potash (MP) . The concentration s of Cd, Cr, Mn, Sr, and Zn were greater and more variable than those of Co, Cu, and Ni in all the materials analyzed. The concentrations of Cd in the TSP samples ranged from 6.8 to 47 mg/kg, with a median of 8 .1 mg/kg, but they were more uniform in the other fertilizer materials analyzed, with median values of 7.0, 6.7, and 1.6 mg/kg for MAP, DAP, and MP, respectively. The median values of Mn, Sr, and Zn in TSP samp les were 288, 554, and 97 mg/kg, respectively. The corresponding media n values of these elements in the MAP samples were 358, 95, and 73 mg/ kg and, in the DAP samples, were 295, 70, and 86 mg/kg. The concentrat ions of Al, Ca, K, Mg, and Na were, in general, uniform, but the conce ntrations of Fe varied considerably among the TSP samples analyzed. Th e levels of the nontrace metals in the fertilizer materials analyzed a re not significant relative to those naturally present in soils. No Rb could be detected in any of the TSP, MAP, or DAP samples, but Rb was found in four of the MP samples analyzed.