Geochemistry of fecal sterols in a contaminated estuary in southeastern Brazil

Domestic sewage contamination in the Iguaçu River, located in the northwestern sector of Guanabara Bay (Rio de Janeiro, Brazil) was investigated by using sterols extracted from suspended particles and sediments. Coprostanone (5β-cholestan-3-one), epicholestanol (5α-cholestan-3α-ol) and coprostanol (5β-cholestan-3β-ol) occurred in high concentration (up to 12.3 μg L−1 and 70.6 μg g−1 in suspended particles and sediments, respectively). In general, fecal sterol concentrations decreased from the river to the bay, associated with increasing distance from the diffuse sewage sources. Seasonal variation also influenced the sterol distribution. The distribution of fecal sterols suggests that system dynamics, as well as pre- and post-depositional processes, must be carefully taken into consideration if sterols are to be used in the evaluation of sewage derived contamination.