Measuring change in sterol input to estuarine sediments

Abstract

In complex estuarine environments suites of sterols can be used to define autochtonous and allochtonous sources of organic matter and to identify biological processes occurring in situ. Coprostanol is a major faecal sterol present in human waste (40%–60% of total faecal sterols excreted). As raw sewage is the primary source of this sterol, its determination is an effective measure of the degree of untreated sewage contamination. Mean concentrations of sterols in μg.g⁻¹ dry sediment are reported for the Tay Estuary. Ratios of coprostanol/cholesterol, coprostanol/epicoprostanol and the 5β/(5β + 5α) stanol index were used to assess and cross-validate sterol sources. These results have a special significance in that the disposal of raw sewage is being phased-out in north-east Scotland. Our study will therefore act as a record, showing the degree of contamination during discharge of raw sewage. Adherence to the EC Urban Waste Water Directive 1991 (91/271/EEC) by the Scottish Environmental Protection Agency and the North of Scotland Water Authority, means that all sewage sludge should receive primary treatment. This work establishes a baseline against which reduction in sedimentary sterol concentrations can be measured.