Objectives Organic fertilizer is an important nutrient sources in agricultural production. Studying the safety quality of organic fertilizer could provide reference for its rational and safe application.
Methods A total of 99 commercial organic fertilizer samples were collected from 96 organic fertilizer manufacturers in Zhejiang Province in 2017. The contents of Hg, As, Cd, Pb, Cr, Cu, Zn and Ni were determined. The heavy metal sources were discussed and the application risks were proposed. And the heavy metal content variation was compared with that in literature of 2013.
Results 1) The average contents of Hg, As, Cd, Pb, Cr, Cu, Zn and Ni in the 99 organic fertilizer samples varied greatly, averaging 0.17, 5.5, 0.63, 17.3, 33.2, 213.8, 660.5 and 17.7 mg/kg, respectively, with coefficients of variation ranging from 54.9% to 151.3%. The contents of Cd, Pb, Cr, Hg and As had declined significantly by 23.0%–72.7% in 2017, compared with those in 2013. Among them, the contents of Hg and As declined year by year. In 2017, the average contents of Hg and As declined by 74.2% and 51.8% compared with 2009, Cr and Pb contents declined by 74.9% and 54.4% compared with 2010, and Cd contents declined significantly in recent four years, with a decline of 72.7% compared with 2013. Even so, the content of As in 8.1% of organic fertilizer samples still exceeded the standard. The contents of Cu and Zn were relatively high, and Ni content tended to increase, which were the main risk factors for commercial organic fertilizers in Zhejiang Province. 2) The results of principal component analysis (PCA) and correlation analysis showed that the pollution sources of Cu-Zn, Cr-Ni-Hg and Cd-Pb were homologous. The main source of Cu, Zn and As pollution was feed addition. Cr, Hg and Ni might mainly come from feed raw materials, while Cd and Pb might mainly come from feed raw materials or from the production of binders or environment. 3) The components of commercial organic fertilizer were various, and the pig manure were the main raw material, which followed by chicken manure and cow manure. According to organic fertilizer standard of NY 525—2012, the As contents in 9.6% of pig manure exceeded the standard, but all heavy metal contents in chicken manure and sheep manure were below the standard. According to the standard of German mature compost, there were more organic fertilizer samples of pig manure and chicken manure with Cu and Zn contents exceeding the standard, but excessive Ni was found only in organic manure with the main raw material of pig manure and chicken manure. 4) Long-term unreasonable application of commercial organic fertilizers caused the risk of heavy metal accumulation in soil, according to the annual fertilization amount of organic fertilizer at 30 t/hm2, the risk of Cu, Zn and Cd was relatively higher, with safe application period of 14 years, 18 years and 34 years, respectively.
Conclusions The overall quality and safety are relatively high in the commercial organic fertilizer in Zhejiang Province. In recent years, the contents of Cr, Pb, Hg, As and Cd have been well controlled. Nevertheless, there are still some samples in which the Cu, Zn and Ni, and As contents exceeded the up limit of national standard. Long-term and large amount application of such organic fertilizers might bring accumulation of heavy metals in soils. Therefore, in order to ensure the long-term sustainable development, it is necessary to strengthen the control of heavy metals in organic fertilizers and formulate the limit standards of Cu, Zn and Ni in commercial organic fertilizers.
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