Fertilizers and Tree Planting: draft info sheet

Adequate nutrient availability is a key to maximizing tree growth and ensuring an adequate timber supply. Consequently, fertilization has become an integral part of stand management.

Fertilizers are applied in two situations: (1) by hand at the time of planting or (2) aerially applied later in stand development, often in conjunction with thinning. Most aerial fertilization programs in coastal BC apply only nitrogen, that as urea (46-0-0). On northern Vancouver Island, nitrogen and phosphorus may be aerially applied. In interior BC, nitrogen and sulphur are aerially applied. Fertilizers applied at planting typically contain a greater variety of elements and often include micronutrients (Fe, B, Cu, Mn, Zn).

In recent months, some tree planters in British Columbia have expressed concerns about the levels of non-fertilizer metals in fertilizers applied at planting, the health effects of exposure to those fertilizers, and the impacts of fertilizer additions on forest ecosystems. This followed an investigation by the Seattle Times indicating that some materials otherwise classified as hazardous waste were being recycled into some fertilizers. Following this investigation, the state of Washington passed regulations mandating maximum levels of metal contaminants in fertilizers sold in the state, with standards for maximum metal contents adopted from Canadian regulations. Similar legislation has been passed or is being considered in other states.

The purpose of this note is to address key questions relating to fertilizer composition and its regulation in Canada, effects of exposure, and possible rates of addition of non-fertilizer metals during forest fertilization.

What elements in fertilizers have raised concern ?

The components of fertilizer raising the most concern are metal contaminants, in other words, heavy metals which may be present in the fertilizer, but are not essential plant nutrients. These include cadmium, lead, arsenic, chromium, and strontium, all of which are found in native soils. Concerns have also been raised about other metals, which are essential elements for plant growth at low doses, but which may result in health problems if ingested in high doses. These include zinc, copper, boron, nickel and iron.

What are the fertilizers most likely to contain undesirable components ?

Phosphate rock, from which other phosphate fertilizers (e.g., triple super phosphate and ammonium phosphates) are derived, contain varying concentrations of cadmium. Cadmium concentrations tend to be higher in phosphate rock mined in Idaho and Wyoming than in rock mined in North Carolina and Florida. Phosphate rock of igneous origin generally has lower concentrations of cadmium than does rock occurring in the more commonly-mined sedimentary deposits. Phosphate fertilizers may be applied as a component of fertilizers added at the time of tree planting or aerially in conjunction with nitrogen (N. Vancouver Island).

Fertilizers designed to supply micronutrients, particularly zinc, may incorporate industrial wastes or by-products. These include electric arc furnace dust (collected from emission control devices in steel manufacturing), which may be high in lead and cadmium, tire ash (from burning of tires for energy recovery), which may be high in cadmium, and mine tailings. Arsenic, chromium, and mercury may also occur in high concentrations. Micronutrients are typically added as part of fertilization at the time of tree planting, but not thereafter.

Liming agents, particularly cement kiln dust, may contain significant amounts of lead, arsenic, and chromium. However, liming agents are generally not applied in forestry operations in British Columbia.

Who regulates fertilizer composition in Canada ?

The Canadian Food Inspection Agency (CFIA) regulates fertilizer contents under the authority of the federal Fertilizers Act. Key requirements of the regulations as they pertain to forest fertilization are:

registration requirements: micronutrient fertilizers must be registered by the manufacturer; metal analyses must be submitted by the manufacturer, and concentrations must be below the Canadian limits. labelling requirements: the guaranteed amounts of N, P, and K ( all fertilizers) and micronutrients (e.g. Fe, Cu, B, Mn, Zn, Mo in fertilizers designated as micronutrient fertilizers), must be provided on the label. maximum allowable concentrations: the regulations define maximum allowable concentrations of metals in fertilizers.

Phosphate fertilizers are not required to be registered; the CFIA randomly selects samples of available products for analysis and can sieze products exceeding metal concentration limits. Concentrations of metal contaminants (those elements present, but not intentionally incorporated as plant nutrients, are not required to be shown on the label.

What are the allowable concentrations of metal contaminants in fertilizers sold in Canada?

Under Canadian standards, acceptable concentrations of metal contaminants in fertilizers are based on maximum acceptable cumulative additions of the fertilizer elements to the soil over a 45 year growing period. Standards were not based on quantitative risk assessments, but on best estimates of leading scientists as levels associated with no adverse effects on plants, animals, or land over the long term.

Cumulative additions allowed over a 45 year period and the associated annual rate (shown in brackets) are (in kg ha-1): arsenic, 15 (15/45); cadmium 4 (4/45); lead 100 (100/45). The allowable concentrations of non-fertilizer metals varies with the recommended rate of fertilizer application. As an example, allowable concentrations of cadmium in a triple super phosphate fertilizer applied annually to supply 100kgP ha-1, would be 174ppm.

Mean soil concentrations(ppm) of some different non-fertilizer metals are as follows: arsenic (5/0.01-97/2-50/8) cadmium (0.25, 0.01-2.5/0.1-1.0/1) lead (15,<1-100/2-25/17). Potential rates of addition vary with the fertilizer used. As an example of a “worst-case” scenario: if 1600 trees are planted per hectare, each is fertilized with sufficient monammomium phosphate to supply 20g P per tree, and the MAP is high in cadmium (e.g. 200ppm), the amount of cadmium added at planting is 0.028kg per hectare, less than half of the allowable annual loading under Canadian standards. Since fertilization at planting typically would occur at intervals greater than 45 years, the rate of application is far less than that legally allowed.

Thus, the rates of addition from fertilization at planting are far less than those allowed for agriculture.

How do potential rates of metal additions from aerial fertilization compare with additions at tree planting ?

Most aerial forest fertilization in British Columbia consists of urea alone or urea and sulphur, each of which contains negligible amounts of metal contaminants. However, forests on northern Vancouver Island may be fertilized with nitrogen and phosphorus. Assuming 100kg P per hectare are applied as triple super phosphate every 10 years, and further assuming the cadmium content is high (200ppm), this would correspond to applying 0.1kg cadmium per hectare every 10 years, in other words, 0.01kg per year. Again, the rate is far beneath that of allowable rates.

Is handling fertilizers at the time of planting safe for tree planters ?

Compared with other fertilizer applicators, tree planters may receive considerable continuous direct exposure to fertilizers, especially if the added fertilizers are scooped from bulk supplies on a per tree basis. There may be ingestion of fertilizer dust and caked fertilizer may come into contact with skin, mouth or eyes during the course of planting. There is little opportunity to regularly wash off fertilizer dust and it is difficult to maintaining recommended skin and breathing protection while planting trees in difficult terrain.

The Fertilizer Institute commissioned a study to assess the health risk evaluation for fertilizer applicators exposed to non-fertilizer elements. The scenarios used were for a lawn care professional (high rate of exposure) and for a farm worker (lower rate of application), assumed exposure through incidental ingestion, dermal contact, and inhalation and assumed a low acceptable target cancer risk. Risk-based concentrations of arsenic, cadmium, lead and mercury were not exceeded in approximately 2600 phosphate fertilizer samples and were marginally exceeded in 15 of 600 samples of micronutrient fertilizers. Because calculations were considered to be conservative, the report concluded that there were no risks for the studied applicator groups. Whether this also applies to tree planters and the tree planting environment is unknown.

How can exposure of planters to fertilizers be minimized ?

Selection of fertilizer: (Brinkman data, Cavendish Labs).

Use of coated, packaged fertilizers

How does exposure to non-fertilizer elements from fertilizers compare with other sources ?

Cadmium

Lead

Arsenic

If concentrations of non-fertilizer metals are not listed on the fertilizer label, how does the fertilizer purchaser know what those concentrations are?

reference the Washington State Dept. of Agriculture database. The problem with do so is that fertilizers sold in Canada may not be registered in Washington. Also, fertilizers which are blends may not be listed under the retail name. The purchaser may need to know the names of the manufacturers whose products were used in the blend and the proportions used of each.

Contact the Canadian Food Inspection Agency

Contact the retailer and, in turn, the manufacturer. Concentrations of non-fertilizer metals may be posted on the manufacturer’s web site. Have the fertilizer tested by a reputable lab. If doing so, it is important to ensure that proper sampling procedures are followed and that the laboratory follows recognized analytical procedures.