United States — AAPFCO (Model Guidance)

Maximum Allowable Metal Concentrations

Metals in Fertilizers

Federal, state, and industry-sponsored risk-based assessments have determined that metals present in fertilizers generally do not pose a risk to human health or the environment when they remain below established thresholds. Under Section 13(a) of the Uniform State Fertilizer Bill, fertilizers that contain guaranteed phosphate and/or micronutrients are considered adulterated if metal concentrations exceed the limits outlined below.

Maximum Allowable Metal Concentrations

Metal limits are expressed in parts per million (ppm) and are calculated based on either:

• percent guaranteed P₂O₅, or
• percent guaranteed micronutrients, depending on the product type.

The metals regulated under this framework include:
Arsenic, Cadmium, Cobalt, Lead, Mercury, Molybdenum, Nickel, Selenium, and Zinc.

Metals Concentration Limits

How to Apply the Metal Limits

To determine compliance, one of the following scenarios applies:

1. Fertilizers with a phosphate guarantee only (no micronutrient guarantee)

Multiply the guaranteed percent P₂O₅ by the metal limits listed for phosphate fertilizers to determine the maximum allowable concentration for each metal.
A minimum multiplier of 6.0% P₂O₅ must be used, even if the actual guarantee is lower.

2. Fertilizers with one or more micronutrient guarantees (no phosphate guarantee)

Multiply the sum of all guaranteed micronutrient percentages by the metal limits listed for micronutrients to determine the maximum allowable concentration for each metal.
A minimum multiplier of 1.0% micronutrients must be used.

3. Fertilizers with both phosphate and micronutrient guarantees

• First, calculate metal limits based on the guaranteed percent P₂O₅ using a minimum multiplier of 6.0%.
• Next, calculate metal limits based on the sum of guaranteed micronutrient percentages using a minimum multiplier of 1.0%.
• The higher of the two calculated values is used as the maximum allowable concentration for each metal.

Biosolids and Compost Products

Biosolids and compost products are considered adulterated if they exceed the metal concentration limits established by the U.S. Environmental Protection Agency under 40 CFR Part 503. This applies to:

• dried biosolids,
• manure,
• processed manure products, and
• mixtures of these materials.

Hazardous waste-derived fertilizers, as defined by EPA regulations, are also deemed adulterated if they exceed EPA contaminant limits outlined in 40 CFR Parts 261, 266, and 268.

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