Rockphosphates and Phosphate fertilizers manufactured from the former are applied to soil to meet the P requirement of crops.Cadmium present in those P sources may accumulate in soil over time because of their continuous use.The accumulated Cd may enter into soil-plant-animal/human system.So for safe use of P sources in agriculture, what are the permissible limits for Cd in rockphosphates and Phosphatic fertilizers?
Dr. Rao, it is a very good question. But unfortunately the limit varies from country to country. For example, EU proposed the limit 20mg Cd/Kg P2O5. But the limit is rarely followed. Please find the attached pdf for every details.
Dr.Tarafdar,Thank you for your comments.Is there any published information from India in this line?
Dear Sir,
As per the FAO fertilizer specifications, Cadmium (as Cd) content by weight: maximum 27 mg/kg of Rock Phosphate. Similarly for micronutrients and organic manures limit is available, However no limits are available for SSP or other P fertilizers. Link to FAO is as below
http://www.fao.org/agriculture/crops/thematic-sitemap/theme/spi/plantnutrition/fertspecs/en/#c29988
which shows as below
Rock Phosphate (RP)/Phosphate Rock (PR) for Direct Application
· Total phosphates (as P2O5) content by weight: between 15-35% depending on source
· Cadmium (as Cd) content by weight: maximum 27 mg/kg of RP
· Particle size: Not less than 90% of the material shall pass through 0.15 mm IS sieve and the balance shall pass through 0.25 mm IS sieve
Besides, I am enclosing Indian Fertilizer Control Order, which has Cadmium limit for micronutrients and organic manures
Dr. Rao, In Indian phosphatic fertilizer the Cadmium concentration generally varies between 18.2 and 28.5 mg/Kg. Please find an Indian work on the aspect in below mentioned reference.
Srikant et al (1994). Environmental Monitoring and Assessment 33(1), 71-74.
Dr.Tarafdar and Dr.Surendran, thanks for your good inputs.As mentioned by me earlier, continuous application of Cd containing P sources may result in accumulation of Cd in soil.If soil conditions favour, the soluble Cd may be taken up by crop plants which under specific situations may attain toxic proportions.Are there some published papers/documents on this aspect?.What are the permissible/toxic limits for Cd in soil and plants.The limits may also differ in sensitive crops and tolerant crops.Is such information available?.
In Australia, Food Standards Australia New Zealand sets maximum permitted concentrations for contaminants, such as Cd in foods. The standards cannot be enforced on imports under international trade guidelines unless Australian produce complies . This is the direction I suggest you explore for individual countries and groups e.g. like the EU
Australia had a Cd minimisation strategy and fertiliser suppliers consequently now abide by an agreed maximum concentration expressed us mg Cd/kg P.
Dr.Milham, thanks for your comments.Can you provide any additional information /references on this pertaining to Australia?
Please find enclosed a paper on permissible/toxic limits for Cd in soil and plants
The limits on Cd Cadmium in soil can be misguided. The most important concept is the Cd availability which is a function of the absorption in the crop tissues. A better strategy is the concentration on ensuring the proper pH and then monitoring and confirming that excessive levels do not occur in the crops themselves. Cadmium solubility and availability is largely influenced by pH. Assuring that acidity does not develop below the pH level of 6.0 would suffice in most areas to prevent issues developing from Cd. This reminds me in some aspect of the embargo on elm seedlings while permitting the dumping of wood products when the source of dutch elm disease was vectored in the wood by beetles and not on the seedlings. Regulatory efforts are not always directed on the system to prevent issues because of poor application of our knowledge base. For heavy metals the concentration on crop concentration and underlying soil factors may more sense than focusing on soil concentrations which can be largely unavailable under the proper soil conditions. While the soil pH has been under appreciated and applied monitoring of tissue concentrations and assure soil pH values is a good way to approach these issues.
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