Cd content in phosphate fertilizer: which potential risk for the environment and human health?
2022
Suciu, Nicoleta Alina | Devivo, Romano | Rizzati, Niccolò | Capri, Ettore
Cadmium (Cd) is a heavy metal that accumulates in soil and in living organisms and causes severe and permanent damage. Its presence in the soil depends largely on the use of phosphate fertilizers. Phosphorite and apatite rocks used in phosphate fertilizers production contain several other minerals, including Cd.. The amount of Cd incorporated in phosphate fertilizers depends on the type of phosphorite and apatite rocks (with low or high Cd content). Cd is present in soil mainly in insoluble form and has no bioavailability for plants. However, plants can increase Cd solubility by releasing root exudates that change the pH of the rhizosphere, therefore increasing Cd accumulation. Once crops absorb Cd, it enters the food chain. Food is the primary source of Cd exposure (for the non-smoking population), with cereals, nuts and legumes, fish and shellfish being the major contributors. Progressive accumulation of Cd in humans impairs kidney function, affects the liver, and causes bone demineralization. Cd classification as a human carcinogen goes back to the 1990s. The European Union adopted Regulation (EU) 2019/1009, limiting Cd content in organo-mineral fertilizer having total phosphorus (P) content of 5 % P₂O₅ equivalent at 60 mg kg⁻¹ P₂O₅. This threshold seems inadequate compared to the threshold values for Cd currently in place in some EU countries: 12 member states have a Cd threshold between 20 and 50 mg kg⁻¹ P₂O₅, 8 have the same threshold as that proposed in the regulation, and 2 have a higher threshold. Meanwhile, the new EU Regulation on CAP Strategic Plans explicitly references soil health and fertility protection and the limitation of contaminants in fertilizers. Fertilizers with low Cd content, with thresholds no higher than 20 mg kg⁻¹ P₂O₅, would effectively limit bioaccumulation. As stopping P fertilizer application cannot be an option, strategies such as the use of P fertilizers with low Cd content, the use of cultivars that accumulate less Cd in their consumed parts, production of mineral P fertilizers with higher nutrient use efficiency than those actually produced, the decadmiation of P rocks from the raw materials, soil phytoremediation before crops cultivation, and an increased use of recovered nutrients, should be adopted.
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