ARSENIC, MOLYBDENUM, SELENIUM, AND TUNGSTEN CONTENTS OF FERTILIZERS AND PHOSPHATE ROCKS

Contamination of soils with trace metals or semi-metals has become a major public concern in recent years. Potential sources of these contaminants include commercial phosphorus (P) fertilizers and the phosphate rocks used in production of the P fertilizers. Solid commercial P fertilizers marketed in Iowa and phosphate rock samples (PRs) obtained from deposits around the world were analyzed for arsenic (As), molybdenum (Mo), selenium (Se), and tungsten (W). The fertilizer materials included 24 samples of triple superphosphate (TSP), 23 samples of monoammonium phosphate (MAP), and 25 samples of diammonium phosphate (DAP). Twelve PRs from different PR deposits in Africa, United States, and Peru were also analyzed. The concentrations of As and Mo were greater and more variable than those of Se and W in TSP, MAP, DAP, and PRs. The ranges and median values of As, expressed in mg/kg, were: TSP (2.4-18.5, 10.1), MAP (8.1-17.8, 12.4), DAP (6.8-15.6, 12.4), and PR (3.2-32.1, 9.6). The range and median values for Mo contents of TSP, MAP, DAP, and PR were: 8-17, 13; 12-17, 15; 10-21, 14; and 2-21, 6, mg/kg, respectively. The median values for the Se and W contents were: TSP (1.1 and 2.7), MAP (0.3 and 2.1), DAP (0.1 and 2.4), and PR (1.0 and 1.9). One each of the TSP and PRs contained much higher concentrations of Se than the other samples analyzed. The concentrations of As, Mo, Se, and W in the fertilizer materials and PRs analyzed were generally greater than those found in Iowa surface soils.