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

Contamination of soils with trace metals or semi-metals has become a m ajor public concern in recent years. Potential sources of these contam inants include commercial phosphorus (P) fertilizers and the phosphate rocks used in production of the P fertilizers. Solid commercial P fer tilizers marketed in Iowa and phosphate rock samples (PRs) obtained fr om deposits around the world were analyzed for arsenic (As), molybdenu m (Mo), selenium (Se), and tungsten (W). The fertilizer materials incl uded 24 samples of triple superphosphate (TSP), 23 samples of monoammo nium phosphate (MAP), and 25 samples of diammonium phosphate (DAP). Tw elve 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 ra nges 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, an d PR were: 8-17, 13; 12-17, 15; 10-21, 14; and 2-21, 6, mg/kg, respect ively. 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 tha n the other samples analyzed. The concentrations of As, Mo, Se, and W in the fertilizer materials and PRs analyzed were generally greater th an those found in Iowa surface soils.