Combined analysis of bile acids and sterols/stanols from riverine particulates to assess sewage discharges and other fecal sources

This investigation aimed to demonstrate the combined use of bile acids, stanols, and sterols to assess fecal matter inputs into aquatic environments. Bile acids, stanols, and sterols were determined in suspended particulates in water samples collected from sites in the vicinity of discharges from sewage treatment works along the course of the Avon River, Bristol, U.K. The concentrations of the major fecal bile acids [lithocholic (LCA) and deoxycholic (DOCA)] were determined using GC and GC/MS and found to increase along the course of the river. These results agreed with those obtained for coprostanol, the traditional indicator of fecal pollution and other related sterols and stanols. In contrast, sterols and stanols not originating from feces, i.e., 24-ethylcholesterol and 24-ethylcholestanol, tended to decrease in concentration as compared to coprostanol and other fecal markers in the lower reaches of the river. The increasing concentration of bile acids downstream of sewage discharges correlates with the coprostanol/(coprostanol + 5 alpha-cholestanol) ratio of >0.7, thus supporting the use of bile acids as sewage pollution markers. Overall, it is demonstrated that a combined multimolecular approach involving bile acids, stanols, and sterols provides an enhanced means of assessing fecal matter inputs into aquatic environments.