An integrated evaluation of molecular marker indices and linear alkylbenzenes (LABs) to measure sewage input in a subtropical estuary (Babitonga Bay, Brazil)

Babitonga Bay is a South Atlantic estuary with significant ecological function; it is part of the last remaining areas of mangrove communities in the Southern Hemisphere. The aim of this study was to determine the spatial distribution of the faecal sterols and linear alkylbenzenes (LABs) in surface sediments and to perform an integrated evaluation of several molecular marker indices to assess the sewage contamination status in the study area. The highest observed concentrations of faecal sterols (coprostanol + epicoprostanol) and LABs were 6.65 μg g−1 and 413.3 ng g−1, respectively. Several faecal sterol indices were calculated and correlated with coprostanol levels; these analyses showed that the index limits presented in the current literature could underestimate the sewage contamination in this study area. For the overall estuarine system, a low sewage impact may be assumed based on the low total mass inventories calculated for coprostanol (between 1.4% and 4.8%). •Sewage contamination in a South Atlantic estuary was confirmed by molecular markers.•Faecal sterol indices were established as indicators of sewage contamination.•Estimates of the total mass inventory of coprostanol and LABs are presented.•Faecal sterols are preferable to LABs for the evaluation of sewage inputs in this study area. Faecal sterols index limits has been established to a subtropical environment as way to ensure reliability for a more precise assessment of sewage contamination.