Fertilizers can be viewed as any combination of nutrients, facilitating plant growth and fertility. As pressure mounts to meet the needs of a growing population, fertilizers are seen as key to food security. Just as important, is the way that they are manufactured and used. Fertilizers contaminated with excess impurities, such as heavy metals, could pose environmental and health risks.
Phosphate containing rocks are today the main feedstock used in the production of phosphate fertilizers. These contain a number of impurities, depending on the formation and location of the deposit.
The existence of impurities in phosphate rock concentrates affects the cost of producing fertilizers, and also the price at which phosphate rock is sold. For example, traded rock can contain as little as 20% P2O5 and as much as 40% P2O5. Low grade concentrates (<29% P2O5) contain less nutrient, therefore requiring greater quantities to produce a tonne of fertilizer. Their use incurs higher logistics costs (as one moves more waste) and in many instances has not been adequately beneficiated (processed). This places an extra burden on the buyer.
Besides the nutrient grade, other factors also come into play when producing ammonium phosphates. For example, the ratio between calcium oxide and phosphate affects the amount of sulphuric acid that is consumed during acidulation. Similarly, metal oxides (including iron, aluminium and magnesium oxides), silica, and organics all impact raw material usage and/or the efficiency of the process.
Heavy metals are among the impurities found in phosphate rock concentrates. These are generally found in such small quantities, relative to other elements, that they do not impact processing costs. However, some concentrates do have high enough concentrations of cadmium, lead, arsenic and other heavy metals to pose a long term risk to the environment and possibly also to human and animal health.
Research undertaken by the International Fertilizer Development Centre (IFDC) has assessed the concentrations of cadmium and other trace elements across different phosphate deposits around the globe.
The highest concentrations of cadmium have been found in sedimentary and guano rock deposits, located in North and West Africa, parts of the Americas and on Pacific and Indian Ocean islands. Phosphate rock concentrates (and fertilizers) in these areas can reach concentrations close to 300 mg Cd/Kg P2O5, which is in excess of what is considered to be safe by the European Commission.
The highest concentrations of lead within phosphate rock concentrates were recorded in Brazil, Australia and Morocco. Arsenic concentrations, meanwhile, were highest in Egypt, China, Jordan and Peru. Unlike cadmium, even the highest among these are thought to be within the limits proposed by the European Commission.
Although the research undertaken by the IFDC shows most safer phosphate rock concentrates to be of an igneous nature, various sedimentary rocks meet even the strictest heavy metals standard proposed. When the results of IFDC’s research into cadmium is overlaid against current rock production volumes, around half is thought to contain less than 20 mg Cd/Kg P2O5 (presuming that they are eventually fed through a phosphoric acid unit). This includes product from Russia, Brazil and South Africa (currently all of an igneous origin), as well as that from Jordan, Saudi Arabia, Australia, Kazakhstan and some Egyptian material (all of a sedimentary background).
There are numerous projects currently being developed across North America (Canada), Africa (South Africa) and Oceania (Australia) which are similarly low in heavy metal contents. Many of these could be brought into production, providing a market and funding can be found.
Cadmium limits, of varying degrees, already exist in various jurisdictions. Among them are Australia, New Zealand, Kenya, Japan and the state of California. The global leader in fertilizer Cd content governance is Switzerland. A legal limit for Cd has been in place since 1986 and is set at 22 mg Cd/kg P2O5 in products that contain more than 1% P. For P fertilizer products from waste, a new limit of 11 mg/kg P2O5 has been established. Although Europe does not have region-wide limits in place, several member states apply a limit to product consumed within their borders. These range from 90 mg/kg P2O5 in Belgium to as low as 20 mg Cd/kg P2O5 in Hungary and Slovakia.
As part of the efforts to introduce a new fertilizer legislation, the European Commission proposed introducing limits to cadmium and other heavy metals. Cadmium limits would be introduced on a progressive basis, initially set at 60 mg/kg P2O5 and gradually tightened 20 mg/kg P2O5, thereby giving industry (and consumers) sufficient time to implement changes and adjust to the changes. Since being proposed, heavy metals limits have been backed by the European Parliament Committee on the Environment, Public Health and Safety (ENVI) and the wider European Parliament.
Even with regulation, there remains a considerable lack of information to make good fertilization choices. Buyers have little or no information over the origin of products they purchase or impurities that they contain. Safer PhosphatesTM advocates for clear labelling for products, listing the content of any potentially harmful heavy metals. Although this is not part of the initial proposal made by the European Commission, the idea of clearer labelling for heavy metal contents has gained traction. Currently, there is support for a green label for products containing less than 5 parts per million (PPM) of CD, AS, PB, CR (VI) and MG.
Since the mid-1970s several processes have been developed that could be used to remove cadmium from either phosphate rock or phosphoric acid (so far no processes exist that can remove cadmium from the final product - fertilizer). As the removal of cadmium (or decadmiation) does represent an extra cost, it is viewed as a burden which producers prefer to avoid. It is, however, not insurmountable. Most decadmiation technologies incur up to US$15 more per tonne DAP equivalent. Meanwhile, across the EU, most foreign fertilizer suppliers are subject to a US$25-30/tonne import tariff, which could be removed to counteract any additional cost. Additionally, some of the key raw materials suppliers to the EU, enjoy good margins on the sales of rock, estimated between US$40-70/tonne, and therefore could absorb the additional cost.
Looking at the phosphate value chain, from mine to table, around 4-5 million tonnes of P2O5 is made available in Europe annually. Less than 10% of the product – whether it be phosphate rock, phosphoric acid or finished product – is originally sourced from within the EU-borders. The remainder is supplied from Morocco, Russia, Israel, Tunisia, Algeria and a selection of other countries.
Considering the original source of raw material, the manufacturing process and available RESEARCH INTO CONTAMINANTS, the weighted average content of fertilizer available across the EU-28 is estimated at 31 mg Cd/Kg P2O5. Around half of the total product falls within the 20 mg Cd/Kg P2O5 limit, while only 12% breaches the 6o mg Cd/Kg P2O5 limit.
Product stemming from parts of North and West Africa tend to have the highest cadmium concentrations. Some of these operations are believed to be enjoying a good profit margin over their cost. For example, the phosphate rock cost in Morocco has been estimated between US$20-30/tonne (free on board, 68-72% BPL), and may fall in the coming years, due to operational improvement/modernization efforts. Meanwhile, corresponding prices have averaged between 90-150/tonne over the past five years. With such good margins on raw materials supplies, it seems that the extra cost of decadmiation could be absorbed by manufacturers without having to raise final product prices.
Alternatively, the EU could also choose to review its phosphate fertilizer import tariff position. Currently Chinese, US, Russian and Saudi Arabian suppliers are all subject to a 6.5% import tariff on ammoniated phosphate supplies into Europe. Depending on prices, this could add US$15-30/tonne of extra cost to the final product. Removing this would make Europe more accessible for a number of low-cost, low-cadmium suppliers, benefitting farmers in the long term.
While introducing maximum limits on contaminants in fertilizers is a comparatively new proposition, Codex Alimentarius has been implementing and managing international standards/guidelines for food since the early 1960s. Although enforcement is voluntary, in many instances they serve as the basis for national standards. To date, Codex has outlined more than sixty maximum limits in relation to heavy metals, of which thirty-seven are related to lead, fifteen for cadmium, six for arsenic and two for mercury.
As Codex increasingly looks to implement maximum limits for contaminants in food, change will be forced onto agriculture. One of these areas is fertilizer, which through soil, is thought to be one of the key sources of heavy metal accumulation in food.