Fertilizer containing cadmium

Cyanuric Acid. Organic cyanurates and isocyanurates have been prepared as pure materials and their use as metal precipitants has been reported in the literature (25-25). Diallylisocyanurate salts of cadmium, copper, and lead have been described and polyisocyanurates have been cited as precipitants for monovalent and divalent metal ions — including Cd, Hg and Pb —from waste streams (26). Initial tests with 10-34-0 (pH 6.8) indicated that ammonium cyanurate was soluble in the media however, no measurement of the solubility was made and no precipitate was observed. Addition of ammonium cyanurate to a 10-30-0 (pH 6.0) grade phosphate fluid fertilizer containing 40 ppm cadmium indicated low solubility of the reactant in the media and resulted in no cadmium removal at stoichiometries ranging from 25 to 480%. Confirmatory tests... 

Industrial uses of cadmium include electroplating and the manufacture of batteries, metal coatings, and alloys. Cadmium is also used as a pigment in paints and plastics. Some fertilizers also contain cadmium. 

Another source of cadmium is fertilizers containing phosphate. Moroccan phosphate rock contains more than 50 g/tonne of cadmium and is no longer used as a fertilizer within the European Union. Industries for the production of zinc are a third source. Even here the situation is improved, as is exemplified by the following figures. In 1970 the total cadmium emissions to the atmosphere in Sweden were estimated to be 25 tonne/year. A large metal producer, Boliden, accounted for half this... 

Fluorides and dust are emitted to the air from the fertilizer plant. All aspects of phosphate rock processing and finished product handling generate dust, from grinders and pulverizers, pneumatic conveyors, and screens. The mixer/reactors and dens produce fumes that contain silicon tetrafluoride and hydrogen fluoride. A sulfuric acid plant has two principal air emissions sulfur dioxide and acid mist. If pyrite ore is roasted, there will also be particulates in air emissions that may contain heavy metals such as cadmium, mercury, and lead. 

Small amounts of cadmium enter the environment from the natural weathering of minerals, but most is released as a result of human activities such as mining, smelting, fuel combustion, disposal of metal-containing products, and application of phosphate fertilizers or sewage sludges (USPHS 1993). In 1988, an estimated 306,000 kg of cadmium entered the domestic environment as a result... 

Due to the wide use of cadmium-based products, cadmium is widely distributed in the environment. The cadmium content in soil and water has been increasing as a result of disposal of cadmium-contaminated waste and the use of cadmium-containing fertilizers (particularly on cereal crops). Commercial sludge, contaminated with cadmium, has been used to fertilize agricultural fields. Cadmium concentrations in urban air are quite low, because of regulation of industrial air emissions. Lead and zinc smelters and waste incineration account for the majority of cadmium present in ambient air. 

Fertile soils supply plants with all of the trace elements essential for growth, believed at the present time to be Fe, Mn, Zn, B, Cu, Mo, and CL These seven elements are called the micronutrients, a term that indicates the small quantities needed by plants but not necessarily the concentrations found in soils. Deficiencies can occur in soils either because they contain extremely low concentrations of these elements or because the elements are present in very unavailable (insoluble) forms. Conversely, many trace elements, including ail of the micronutrients, can reach concentrations in soils that are toxic to plants and microoiganisms. Some of the most toxic are mercury (Hg), lead (Pb), cadmium (Cd), copper (Cu), nickel (Ni), and cobalt (Co). The first three are particularly toxic to higher animals. The last three are more toxic to plants than animals and are termed phytotoxic. From the standpoint of potential hazard to human health, an extended Ust of priority metals has been established. This list presently consists of ... 

The long-term application of mineral fertilizers such as phosphates - which may contain high concentrations of cadmium -contributes to increase the soil background levels of cadmium. On the whole, the use of fertilizer in many countries has been reduced in connection with the Good Farm Practice realized by the farmers. 

The increased use of fertilizers makes a large contribution to the penetration of elements into the nutritional chain. The fertilizers can contain, depending on their production and origin, high amounts of particular elements, including toxic ones. By the application of such fertilizers, the content of these elements in the soil is increased and they enter plants via their root system. Certain types of fertilizers, particularly natural superphosphates, contain more than 30 mg kg of cadmium and lead. Depending on the soil pH, absorption of these metals and their accumulation in particular parts of plants is encountered. The increased global use of fertilizers fortified by certain microelements has considerably increased their contents in the soil and foodstuffs. 

Phosphorus fertilizers may contain impurities among those are some heavy metals that are of concern. In particular, cadmium (Cd) has received attention during the past few years. The level of cadmium content in fertilizers has been more or less arbitrarily limited to the concentration of 50 mg Cd/kg of P2O5 [7]. WHO has limited the daily intake of Cd to 1 microgram Ag of body weight per day [7]. The current average intake in Europe is lower than this limit [8]. 

The cadmium level in fertilizers made from phosphoric acid is increasingly causing concern, and this may influence the choice of raw materials. Igneous phosphate rock typically contains very little cadmium (<1 mg Cd/ kg P), whereas sedimentary sources contain much higher but widely varying amounts (from 43 mg Cd/kg P to... 

Hazardous Waste - There are no hazardous wastes in fertilizer production other than the cadmium contained in certain fertilizers. 

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