Analysis of heavy metal contents and source tracing in organic fertilizer from livestock manure in North China

Abstract: At present, commercial organic fertilizer in China generally exists a problem that heavy metal content exceeds standard limitation. In this study, we took the main field for agricultural products in North China as the research scope. In order to get the situation of heavy metal pollution of commercial organic fertilizer in North China, we investigated and analyzed the commercial organic fertilizer samplings. By using method of principal component analysis, we present a preliminary discussion of the heavy metal sources. We are also clear about an important factor affecting the heavy metal contamination of organic fertilizer products in North China. The results showed that the average content of heavy metal Cd, Cr, Cu, Pb, Zn, Ni, As, Hg in commercial organic fertilizer used by agricultural products producing area in North China were 0.21、45.42、69.22、87.40、274.58、16.50、3.21、0.33 mg/kg. According to the China's organic fertilizer industry standard, the content of Pb exceeded the rate of up to 80.56%, the rest of the heavy metal content is not ovenproof. However, according to the German rotten compost standards, most of the heavy metal content exceeds standard limitation, the content of Cr, Cu, Pb, Zn, Ni, Hg exceeds the rate of 8.33%, 13.89%, 16.67%, 19.44%, 2.78% and 11.11% respectively, yet the content of Cd is not ovenproof. The results of principal component analysis showed that the contribution rates of the first three principal components were 34.7%, 16.6%, 13.0%, which can explain 64.3% of total variables and reflected most of the original data information. Combining with the characteristics of raw materials of commercial organic fertilizer and process analysis, we find that the major source of heavy metal pollution in commercial organic fertilizer in the agricultural regions of North China can be feed additives with high content of Pb, Hg, additives with phosphate fertilizer, and feed additives with high content of Cu, Zn. Meanwhile, the average content of heavy metal Cd, Cr, Cu, Pb, Zn, Ni, As, Hg in farm feed used by agricultural products producing area in North China were 0.02, 13.89, 87.027, 6.32, 297.90, 23.00, 0.65, 0.01mg kg-1. Furthermore, correlation analysis of heavy metal content in the feed and organic fertilizer results showed that, the contents of most of heavy metal in the fertilizer had significant positive correlation with their contents in the feed except Ni and As. This determination results confirmed the above view of the main sources of heavy metals. However, from the result of principal component analysis, other components can still explain 35.7% of the total variable, which indicated that there were other sources of heavy metals in organic fertilizer. Binder is a necessary add material in commercial organic fertilizer production which conclude attapulgite, bentonite, and phosphogypsum. Studies have shown that the common binder contained higher heavy metal. Therefore, binder may be one of the sources of heavy metal in organic fertilizer. In addition, the environmental factors such as atmospheric dust fall and traffic pollution related to the organic fertilizer production process and the background values of heavy metals in the soil may affect the heavy metal contents of organic fertilizer, which needs to be further studied.