Coprostanol in Siak River sediments, E Sumatra, Indonesia

To follow faecal pollution steroid compounds have been analysed in 106 sediment samples from the Siak River, E Sumatra, Indonesia. Coprostanol was detected in 40 of these. Contents ranged from 50 to 10,530 ng/g d.w. with a mean of 878 (TOC-normalised: range 7.4-393.0, mean 44.1 μg/g TOC). Total contents and the coprostanol/cholesterol ratio argue for a major contribution from untreated sewage which is also evident from field observations. The distribution along the river indicates the quantitatively dominant source to be the city of Pekanbaru with an estimated population of 1.5 million. Coprostanol contents decrease downstream indicating ongoing degradation either during transport or in the surface sediment. However, additional sources of coprostanol become evident further downstream. On the other hand, the 5β/(5β + 5α)-cholestan-3β-ol ratio versus cholesterol and a ternary plot using C27 sterols suggest that plant sources also contribute to the sedimentary coprostanol due to its formation by bacteria in suboxic/anoxic sediments.