A comparison of the transition metal concentrations in the faeces, urine, and manure slurry from different livestock animals related to environmentally relevant microbial processes

Abstract

Abstract The microbiological communities in livestock manure slurries produce gases of environmental concern such as ammonia, methane and nitrous oxide and require trace metals such as nickel, iron, and copper to synthesize active metalloenzymes that catalyse key biochemical reactions. Additionally, large quantities of trace metals are supplied to the soil when animal manure/manure slurry is used as a fertilizer, which has led to more strict legislation regarding metal contents in manure slurry. In this study, the concentrations of the environmentally relevant transition metals nickel (Ni), copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) in faeces and urine from pigs, cattle and horses were determined using graphite furnace and flame atomic absorption spectroscopy. We show that for all three animal species 97–100% of the metal contents in manure slurry originate from faeces. The analyses show that uncontaminated manure slurry from pigs has higher metal contents than the manure slurries from cattle and horses. Specifically, on a dry matter (dm) basis, pig manure slurry contains approximately 8 mg Ni/kg dm, 104 mg Cu/kg dm, 185 mg Zn/kg dm, 1134 mg Fe/kg dm, and 356 mg Mn/kg dm. Comparing the determined transition metal contents with published values for manure/manure slurry reveals that especially Cu, Zn and Fe concentrations in manure slurry have decreased in recent years. Comparing our results with other observations suggest that the levels of Ni, Cu, Zn, Fe, and Mn in manure slurries do not limit the microbial processes involved in the production or assimilation of environmentally relevant biogenic gasses.