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Abstract Band 62

Bradel, P.L., Prost, K., Lehndorff, E. & Amelung, W. (2015): Steroid composition of different farmyard manures (horse and cattle) in the course of composting. Bonner Bodenkundliche Abhandlungen 62, 93 S.



Steroid biomarkers are used for the detection of faecal inputs in the environment as well as for their source identification. For this purpose, ratios between different, specific steroid groups (i.e. sterols, a-stanols, ß-stanols, epi-ß-stanols, stanones and bile acids) are utilized. However, there is evidence that bile acids comprise a greater stability than at least two other steroid groups (the a- and ß-stanols). The stability of all other groups has not yet been investigated by degradation experiments. Hence, the question arises if steroid profiles remain reliable over time.

To create a dissipation environment with high microbial activity and enhanced temperatures, two 168 days lasting compost trials were conducted, one with horse and one with cattle farmyard manure. According to previous studies, bile acids were expected to show the highest persistence, followed by a-stanols and the faecal markers (coprostanol and ß–stigmastanol).

In the course of composting, all steroid groups were subjected to dissipation with losses of 45-100% for the horse and 87-99.8% for the cattle farmyard manure, although composting parameters indicated a slightly inhibited dissipation process for the horse compared to the cattle farmyard manure. Regression curves and calculated dissipation half-lives (of 4.6–17.8 days) revealed for the cattle farmyard manure, a main dissipation of all steroids within the first 28 days. Especially bile acids and faecal markers were primarily affected by dissipation processes comprising the fastest dissipation rates and the largest content decreases (98.5-99.8%). Due to a release of plant sterols (stigmasterol and ß-sitosterol) and cholesterol in the course of straw degradation on day 14, temporary content increases of these sterols and a slower dissipation of their transformation products occurred. Plant sterols were further on mainly degraded. In contrast cholesterol as well as its transformation products a-cholestanol and coprostanone showed slight content increases to the end of composting, probably due to the release of cholesterol from the increasing fungal biomass.

One substance (6-ketocholestanol), originally not present in the initial faecal matter, was produced in the course of composting (days 7-56), but later on completely degraded. At the end of composting, different dissipation behaviours of single steroids resulted in changed steroid profiles compared to those of the initial farmyard manure. Therefore, it was neither possible to detect composted farmyard manure as faecal material nor to identify its sources with the commonly used ratios anymore. Apart from that, based on these specific changes in steroid profiles a ratio for the identification of composted faecal material could be developed and applied on both manure types:

(coprostanol + epi-coprostanol) + (ß-stigmastanol + epi-ß-stigmastanol)

coprostanol ß-stigmastanol