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

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.

Keywords:

• agriculture
• pig
• cattle
• horse
• transition metals
• metalloenzymes

PUBLIC INTEREST STATEMENT

Intensive animal production influences the environment in a number of ways. The large amounts of manure slurry produced contain many different microorganisms which through metabolic processes produce and emit considerable quantities of ammonia and greenhouse gasses, which can affect both the environment and climate, and cause economic losses to the farmers. Common to these biogenic gasses is the metals needed by the microbial enzymes to produce the volatile substances. Generally, animal feed is rich in certain metals and, therefore, livestock manure slurries contain plenty of zinc, copper, nickel, iron and manganese. This means that large quantities of metals, especially copper and zinc, are supplied to the soil and affect the surrounding environment when animal manure slurry is used as a fertilizer. Therefore, it is important to measure and compare the metal contents in waste from different livestock animals to create responsible policies and regulations in agriculture.

Competing Interests

The authors declare no competing interests.

Acknowledgements

This work was supported by a grant (ManUREA Technology; File Number 34009-15-0934) from the Green Development Programme, GUDP, under The Danish Ministry of Environment and Food. The authors would like to thank the staff at Dalum Landbrugsskole (5260 Odense and 5600 Spanget, Denmark), Højgård Hestehospital (5462 Morud, Denmark) and Grønhøj research station (7470 Krarup, Denmark) for their kind assistance in collecting animal faeces, urine and feed samples.

Declaration of interest statement

None of the authors has any affiliations with or involvement in any companies, trade associations, unions, or other groups with a direct financial interest in the subject matter discussed in the manuscript and/or their immediate family.

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Funding

This work was supported by a grant (ManUREA Technology; File Number 34009-15-0934) from the Green Development Programme, GUDP, under The Danish Ministry of Environment and Food.

Notes on contributors

Henrik Karring

The research group has expertise in the fields of microbiology, biochemistry, and analytical chemistry, and in characterization and study of the chemical and microbiological processes in livestock manure slurry. The group has investigated the degradation of urea by ureolytic bacteria and is working on different strategies to modulate specific biochemical and microbiological activities in manure slurry. The determination and comparison of transition metal concentrations in faeces, urine, and manure slurry from livestock animals is part of the overall characterization of livestock waste. Currently, the group’s research is focused on developing new technologies to mitigate ammonia and greenhouse gas emissions from manure slurry.