Contents, source and safety status of major heavy metals in water-soluble fertilizers in China

【Objectives】 In this paper, the contents and sources of toxic heavy metals As, Pb, Cd, Cr and Hg in water-soluble fertilizers were studied and their maximal limits in fertilizer standards are discussed, aiming to understand the safety situation of water-soluble fertilizers,reduce environmental risk of heavy metals and ensure the quality safety of agricultural products.【Methods】 Samples were collected from all the fertilizer products registered in the National Center for Quality Supervision and Testing of Chemical Fertilizers (Beijing). Heavy metal contents were measured using method of agriculture standard NY/T 1978-2010(Determination of mercury, arsenic, cadmium, lead and chromium content for fertilizers). The heavy metal source adopted an empirical investigation method. The data about the contents of heavy metals in raw materials were from openly published documents at home and abroad.【Results】 The contents of As, Pb, Cd, Cr and Hg in five types of water-soluble fertilizers are all in the safe levels according to the agricultural standard (NY/T 1110-2010: Water-soluble fertilizers content limits of mercury, arsenic, cadmium, lead and chromium), and are far below the maximal limits. There are some fertilizer samples in which heavy metal contents exceed the maximal limits, but the proportion is very low and mainly occurred in As and Cd with exceeding percentage of 3.50% and 1.27% separately. The proportion for Pb, Cr and Hg are all less than 1%. The Cd contents in the samples above the limit is often several to several hundred times of the up limit, while the contents of As, Pb and Cr are just one to several times higher. The survey results of 127 samples show that heavy metals mainly come from raw materials, and more than half of the raw materials are used for phosphate and micronutrients fertilizer production. The heavy metals in water-soluble fertilizers containing nitrogen, phosphorus and potassium are mainly from phosphate fertilizers including monopotassium phosphate and monoammonium phosphate, followed by zinc sulfate and other micronutrients fertilizers. In water-soluble fertilizers containing micronutrients, the heavy metals mainly come from zinc sulfate and ferrous sulfate. Most As and Cd in water-soluble fertilizers containing amino-acids derive from zinc sulfate, ferrous sulfate and amino-acids, And the heavy metals, especially As, in water-soluble fertilizers containing humic-acids,mainly come from sodium humate, potassium humate and phosphate fertilizers. The researches at home and aboard all reported the extremely low heavy metal contents in nitrogen and potash fertilizers, but relatively high in phosphate and micronutrient fertilizers. Therefore, nitrogen and potash fertilizers are environmentally safe as raw materials of water-soluble fertilizers, phosphate and micronutrient fertilizers should be monitored for the heavy metal contents before used as raw materials of water-soluble fertilizers. Considering the fertilizer standards,the maximal limits of As, Pb, Cd, Cr and Hg are absent or too broad, lack of pertinence. 【Conclusions】 On the whole, the quality of water-soluble fertilizers is satisfactory, occasionally the contents of As, Pb, Cd, Cr and Hg exceed the up limit in the relative standards in China. So they are generally safe to farmland. However, attention still should be paid to the As and Cd contents in water-soluble fertilizers. The fertilizer standardization system should be strengthen the construction for suitable fertilizer environmental evaluation and fertilizer quality consciousness.