T-4- 93 - Standards for Metals in Fertilizers and Supplements

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September 1997

There is increasing interest in the recycling of by-products and waste materials for land application as fertilizers and supplements (example; soil amendments). The obvious benefits from this practice include the return of a number of nutrients to soil and the improvement of soil physical conditions.

The benefits associated with the recycling of these materials must be balanced, however, against the potential hazards which the materials may also present. For instance, they may contain significant levels of metals which can, at high exposure levels, adversely affect plants, animals or humans. In response to this concern, numerous regulatory agencies have enacted policies for by-product utilisation.

In 1979, under the authority of the Fertilizers Act and Regulations, Agriculture and Agri-Food Canada (AAFC) introduced a series of standards for metals in fertilizers and supplements. They were developed to help to ensure that fertilizers and supplements continue to pose only a minimum risk of adverse effects due to metal contamination. This was a time of particular interest in the use of processed sewage as fertilizer.

These metal standards are based on generic principles and are generally applicable to fertilizers or supplements applied to land or in crop production. These standards have been used to evaluate and manage all products regulated under the Fertilizers Act and for which metal concerns have been raised (example; organic fertilizers, processed sewage, compost, phosphate rich fertilizers such as monoammonium phosphate and diammonium phosphate, and recycled inorganic materials). The standards tend to be conservative. This is partly because metals in excess amounts can adversely affect plants, animals and/or humans, and some long term cumulative effects of metals may not be fully understood. As well, significant metal concentrations are already present in soils of some areas, and the degree of plant uptake of metals is affected by factors such as soil acidity, soil cation exchange capacity and plant species.

Between 1993 and 1995, the AAFC metal standards were re-evaluated in response to standard development activities elsewhere (example; the United States Environmental Protection Agency (USEPA), the variety of by-products being proposed for re-use as fertilizers and supplements, and the progressive depletion of phosphate rock deposits worldwide. It was concluded that the AAFC metal standards remain valid. This fact is perhaps best reflected by their recent adoption into the Canadian Council of Ministers of the Environment (CCME) Guidelines for Compost Quality, and into the National Standard of Canada on Compost.

These standards for metals in fertilizers and supplements are described in this Trade Memorandum. They are required under provisions of Section 11 of the Fertilizers Regulations, and include maximum acceptable cumulative metal additions to soils (Table I) as well as maximum acceptable metal concentrations in products (Table II).

Note: Many provinces also have guidelines for metals in soils, or in sludge, compost, and other products that are land applied. We recommend that you contact your provincial government to obtain additional information.

Maximum Acceptable Cumulative Metal Additions to Soil
Arsenic 15
Cadmium 4
Cobalt 30
Mercury 1
Molybdenum 4
Nickel 36
Lead 100
Selenium 2.8
Zinc 370

Note: Please note that the standards in Table I pertain to total cumulative additions to soil over the long term, and that for the purpose of evaluating individual products long term is taken to mean 45 years.

Processed sewage, compost and other by-products

The following (Table II) are the maximum acceptable metal concentrations in processed sewage, sewage-based products, compost, compost-based products, and other by-products represented for sale as fertilizers or supplements. (These products include but are not limited to composted manure, municipal waste tankage, garbage tankage, leather tankage, and industrial sewage.)

Maximum Acceptable Metal Concentrations
(mg/kg dry weight)
Arsenic 75
Cadmium 20
Cobalt 150
Mercury 5
Molybdenum 20
Nickel 180
Lead 500
Selenium 14
Zinc 1,850

Note: The maximum acceptable metal concentrations in Table II are based on the assumption of a cumulative total application to soil of 200 dry tonnes per hectare of a product that contains 50% moisture and a total nitrogen guarantee of 2.5% (example; 5% nitrogen on a dry weight basis). Such a product, applied annually at a rate of 220 kilograms of nitrogen per hectare (or 4,400 kilograms dry product per hectare) would reach the standards for maximum acceptable cumulative metal additions to soil (Table I) within 45 years.

Table Notes

Table Note 1

Acceptable metal concentrations increase as the rate of application decreases relative to 4400 kilograms dry product per hectare (example; if the rate of application is 2200 kilograms dry product per hectare, this is half of 4400 kilograms therefore the metal concentrations can be double the values in Table II). Or, when products are applied on the basis of their nitrogen content, acceptable metal concentrations increase proportionally with total % nitrogen on a dry weight basis and can be calculated using the following equation:

Acceptable metal concentration
(mg/kg dry weight) =

Concentration in Table II (Part 1) X % N as is 5% (Part 2) X 1 (1 - moisture) (Part 3)

Return to table note 1 referrer

(Tip: If the product meets Table II concentrations, STOP. If not, include Part 2 of the equation, example, the nitrogen component. If the concentration fails to meet the calculated level, then add Part 3 of the equation example; the moisture component. If the concentration still fails to meet the final calculated level, then it definitely exceeds our standards.)

All fertilizers and supplements

All fertilizers and supplements, including processed sewage, composts and other by-products must meet the standards for maximum acceptable cumulative metal additions to soil which are shown in Table I. In this regard, the metal concentrations of products are evaluated as follows:

The annual application rate x the metal concentration must be less than the Table I value per 45 years.

Note: The application rate and the metal concentration must be presented on the same basis, example; both dry weight or both as is.

Second Note: If the product is to be applied every 5 years, for example, then the 5 year application rate x metal concentration must be less than the Table I value per 9 years. (Tip: the numbers in bold must multiply to give 45.)

The two metals, molybdenum (Mo) and zinc (Zn) are also plant nutrients. For this reason, higher concentrations than those presented herein may be permitted. Products which contain higher Mo and Zn concentrations may be allowed if they meet all applicable minimum concentration, tolerance, and labelling criteria of the Fertilizers Act and Regulations. This includes representation of the element as a plant nutrient and the associated guaranteed analysis. If you are considering this alternative, we recommend that you contact the Fertilizer Section to discuss the details.

Should you have any questions in the matter, please contact the Canadian Food Inspection Agency at:

Fertilizer Safety Section
c/o Pre-market Application Submissions Office (PASO)
Canadian Food Inspection Agency
59 Camelot Drive
Ottawa, ON K1A 0Y9
Phone: 1-855-212-7695
Fax: 613-773-7115
Email: paso-bpdpm@inspection.gc.ca

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