Objectives Intensive swine industry in large scale is developed in Zhejiang Province. Over 96% of the livestock and poultry waste produced have been recycled through making compost and organic fertilizer for agricultural production, one of the main way-outs. The heavy metals added in the feeds could find their ways through wastes into soil, affecting the soil safety and the growth of crops. In this study, we monitored the total content of heavy metals in swine feed and waste from pig farms in Zhejiang Province and evaluated the safety of feed use from the aspect of environment protection.
Methods We collected 566 samples of swine feed and swine waste from three stages of pigs in 35 different scale farms, using high-pressure digestion, AAS, AFS, ICP-MS method to analyze the contents of nine metals including iron (Fe), copper(Cu), manganese (Mn), zinc (Zn), arsenic (As), lead (Pb), chromium (Cr), cadmium (Cd) and mercury (Hg).
Results 1) The average contents in the swine feces were in order of Zn > Cu > Mn > As > Cr > Pb > Cd > Hg. The main residual elements were Zn, Cu, Mn, and As, and their average levels were 2405, 1288, 528 and 28.2 mg/kg (dry base), with CV of 83%, 34%, 6% and 15%, respectively. The levels of Cr, Pb, Cd were relatively low in swine wastes, ranging from 0.29 to 3.52 mg/kg, the Hg content was only 3.97 μg/kg. The metal contents in piglet stage were relatively high, and showed decreasing in big pig stage, the variations at all the three stages were large, with the CV 21%–112%, indicating that the addition of trace elements in pig breeding was chaotic. 2) 54.9% of swine feces samples contained more than 15 mg/kg of As, and 16.9% of samples contained more than 50 mg/kg of As, and 2.8% samples contained more than 70 mg/kg of As. The monitoring data showed that there were obvious regional differences in the use of organic As, which had been forbidden in large feed companies. In Xiaoshan and Quzhou, about 72.7% and 33.3% of the samples added organic As in pig feed in different stages, however, both the regions had one pig farm in which organic was not used, indicating the possibility of banning organic As in feeds. 3) According to the “safety regulation for using livestock and poultry manure”, 69.9% and 16.9% of swine feces samples were over limit in Cu and As levels. According to the “standard of organic fertilizer”, 54.9% of pig manure was found to be above the standards in As. 4) Generally, the contents of Fe, Zn, Cu in swine feces were concentrated in 7.0 to 10 times and Mn in 3 times. According to the current feeding monitoring, the contents of Zn, Cu and Fe were over added. 5) According to the estimation of dry land bearing capacity per unit area, Zhejiang Province is still capable of bearing the Zn, Cu load through swine wastes, but is not if the application of pig waste is more than 2.27 t per hectares (dry).
Conclusions The addition of metal elements in the swine feed should be reduced, and organic arsenic should be forbidden in the feed production. According to the present monitored levels, the waste-produced compost should be applied in less than 2.27 t per hectare (dry) to prevent soil from heavy metal contamination.
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