Characteristics of Heavy Metals Pollution in Pig Manures and Environmental Risks Evaluation in Intensive Pig Farming Areas in China

Abstract:

Information about the concentrations of heavy metals in pig manure from large-scale pig farms was collected from 21 provinces and cities in China, and information about the concentrations of heavy metals in pig feeds was collected from 11 provinces and cities. The data were analyzed systematically to evaluate the total amount of pig manure and heavy metals produced in each province. The period over which the pig manure could safely be applied to agricultural land was assessed by calculating the total amount of heavy metals found in the manure produced and the total land available for application in each province and city. The results indicated that in the 21 provinces and cities, 20 of them had pig manure samples that were over the recommended concentration limit for Cu, 18 of them were over the limit for Zn, six of them were over the limit for As, four of them were over the limit for Cd and one of them was over the limit for Cr. Moreover, in 10 provinces 100% of the pig feed samples were over the national standard for Cu (13.2~49.0 times of the standard) and in one province 75% were over the standard. On average, for Zn concentrations the pig feeds were 1.3~9.5 times of the national standard. There were significant positive correlations for Cu and Zn between pig manures and feeds (p<0.01). The main limitations to the land application of the pig manure were due to the amounts of Cu, Zn and Cd. For example, in Jilin, Liaoning and Shandong Provinces, the concentrations of Cd in soils would exceed the environmental quality standards for soils after 16, 23 and 91 years, respectively, if the manure was applied to land in these provinces at the current rate. Additionally, the concentrations of Cu and Zn in soils in Beijing would exceed the standards in 65 and 51 years, respectively, while in Tianjin the soil standards for Cu and Zn would be exceeded in 53 and 91 years, respectively. This analysis suggested that it was important to control the rates of pig manure application in agriculture and reduce the amounts of Cu and Zn in pig feeds.