Development of Risk-Based Concentrations of Heavy Metals in Inorganic Fertilizers. M. K. Jones, L. R. Shull, M. A. Bowland, S. A. Klasing, and S. D. Wong, NewFields, Inc., West Sacramento, CA; and California Department of Food and Agriculture, Sacramento, CA
The presence of lead, cadmium, and arsenic in inorganic fertilizers has been well established. The purpose of the health risk assessment (HRA) was to establish risk-based concentrations (RBCs) of these metals that could be used as benchmarks by the industry for evaluating the safe use of inorganic fertilizers distributed commercially in California. The work was also necessitated by the lack of available risk-based standards for these metals in commercial inorganic fertilizers. A screening HRA defined the magnitude and probability of theoretical cancer and non-cancer threats to human health posed by the three metals in 44 fertilizers known to contain the metals and to be available for application to agricultural croplands in California. The screening HRA focused the scope of the subsequent RBC HRA, which used a probabilistic approach. Probability density functions were used or developed, where available. Because of the wide range of fertilizer products, RBCs for individual products were not derived. Instead, unit factors (i.e., mg of metal per kg of nutrient) were derived that can be used to calculate RBCs for individual fertilizers. The basis for these factors is that the metals co-exist with specific fractions (e.g., P2O5 in phosphate fertilizers) and that application rates depend on plant nutrient requirements. Therefore, product-specific RBCs can be readily calculated from the unit factors and the percentage of the nutrient (e.g., P2O5 or zinc) in the fertilizer product.
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