Degradation of faecal sterols in urine for assessment of faecal cross-contamination in source-separated human urine and urine storage tank sediment

The degradation of the faecal sterol coprostanol and its precursor cholesterol, were determined in source-separated human urine and urine tank sediment. The aim was to assess their potential as biomarkers of faecal cross-contamination in source-separated waste systems since traditional microbial indicators have been shown not to be reliable in this context. Investigations were performed at 4 and 20°C in collected human urine and urine tank sediment to which human faeces and synthetic cholesterol and coprostanol were added. The individual degradation experiments were performed over periods of up to 118 days and represented a wide concentration range both for the urine and the urine tank sediment. Coprostanol showed no significant degradation in either the urine or urine tank sediment when faeces or synthetic coprostanol were added. Neither the normalised variance for the individual slopes, nor the combined regression analysis showed any significant difference from the common slope of zero. For cholesterol no significant degradation was found in the urine tank sediment, but based on pooled data, a moderate decrease occurred in the urine. This was most evident for endogenous cholesterol in the urine at low concentrations where 38 and 55% of the original amounts were lost at 4 and 20°C, respectively. The daily rate of loss of cholesterol based on the regression analysis was 0.73 μg l−1 per day. It is concluded that amounts of coprostanol in urine collection tanks can be used as an indicator of faecal cross-contamination cumulatively occurring over the collection period. Together with die-off data of indicator organisms and pathogens, establishment of a baseline risk assessment would now be possible in relation to storage, handling and reuse of the urine.